Isolation of Synaptosomes, Synaptic Plasma Membranes, and Synaptic Junctional Complexes.

PubMed

Michaelis, Mary L; Jiang, Lei; Michaelis, Elias K

2017-01-01

Isolation of synaptic nerve terminals or synaptosomes provides an opportunity to study the process of neurotransmission at many levels and with a variety of approaches. For example, structural features of the synaptic terminals and the organelles within them, such as synaptic vesicles and mitochondria, have been elucidated with electron microscopy. The postsynaptic membranes are joined to the presynaptic "active zone" of transmitter release through cell adhesion molecules and remain attached throughout the isolation of synaptosomes. These "post synaptic densities" or "PSDs" contain the receptors for the transmitters released from the nerve terminals and can easily be seen with electron microscopy. Biochemical and cell biological studies with synaptosomes have revealed which proteins and lipids are most actively involved in synaptic release of neurotransmitters. The functional properties of the nerve terminals, such as responses to depolarization and the uptake or release of signaling molecules, have also been characterized through the use of fluorescent dyes, tagged transmitters, and transporter substrates. In addition, isolated synaptosomes can serve as the starting material for the isolation of relatively pure synaptic plasma membranes (SPMs) that are devoid of organelles from the internal environment of the nerve terminal, such as mitochondria and synaptic vesicles. The isolated SPMs can reseal and form vesicular structures in which transport of ions such as sodium and calcium, as well as solutes such as neurotransmitters can be studied. The PSDs also remain associated with the presynaptic membranes during isolation of SPM fractions, making it possible to isolate the synaptic junctional complexes (SJCs) devoid of the rest of the plasma membranes of the nerve terminals and postsynaptic membrane components. Isolated SJCs can be used to identify the proteins that constitute this highly specialized region of neurons. In this chapter, we describe the steps involved in isolating synaptosomes, SPMs, and SJCs from brain so that these preparations can be used with new technological advances to address many as yet unanswered questions about the synapse and its remarkable activities in neuronal cell communication.

P-type voltage-dependent calcium channel mediates presynaptic calcium influx and transmitter release in mammalian synapses.

PubMed Central

Uchitel, O D; Protti, D A; Sanchez, V; Cherksey, B D; Sugimori, M; Llinás, R

1992-01-01

We have studied the effect of the purified toxin from the funnel-web spider venom (FTX) and its synthetic analog (sFTX) on transmitter release and presynaptic currents at the mouse neuromuscular junction. FTX specifically blocks the omega-conotoxin- and dihydropyridine-insensitive P-type voltage-dependent Ca2+ channel (VDCC) in cerebellar Purkinje cells. Mammalian neuromuscular transmission, which is insensitive to N- or L-type Ca2+ channel blockers, was effectively abolished by FTX and sFTX. These substances blocked the muscle contraction and the neurotransmitter release evoked by nerve stimulation. Moreover, presynaptic Ca2+ currents recorded extracellularly from the interior of the perineural sheaths of nerves innervating the mouse levator auris muscle were specifically blocked by both natural toxin and synthetic analogue. In a parallel set of experiments, K(+)-induced Ca45 uptake by brain synaptosomes was also shown to be blocked or greatly diminished by FTX and sFTX. These results indicate that the predominant VDCC in the motor nerve terminals, and possibly in a significant percentage of brain synapses, is the P-type channel. Images PMID:1348859

P-type voltage-dependent calcium channel mediates presynaptic calcium influx and transmitter release in mammalian synapses.

PubMed

Uchitel, O D; Protti, D A; Sanchez, V; Cherksey, B D; Sugimori, M; Llinás, R

1992-04-15

We have studied the effect of the purified toxin from the funnel-web spider venom (FTX) and its synthetic analog (sFTX) on transmitter release and presynaptic currents at the mouse neuromuscular junction. FTX specifically blocks the omega-conotoxin- and dihydropyridine-insensitive P-type voltage-dependent Ca2+ channel (VDCC) in cerebellar Purkinje cells. Mammalian neuromuscular transmission, which is insensitive to N- or L-type Ca2+ channel blockers, was effectively abolished by FTX and sFTX. These substances blocked the muscle contraction and the neurotransmitter release evoked by nerve stimulation. Moreover, presynaptic Ca2+ currents recorded extracellularly from the interior of the perineural sheaths of nerves innervating the mouse levator auris muscle were specifically blocked by both natural toxin and synthetic analogue. In a parallel set of experiments, K(+)-induced Ca45 uptake by brain synaptosomes was also shown to be blocked or greatly diminished by FTX and sFTX. These results indicate that the predominant VDCC in the motor nerve terminals, and possibly in a significant percentage of brain synapses, is the P-type channel.

Neuromodulation of activity-dependent synaptic enhancement at crayfish neuromuscular junction.

PubMed

Qian, S M; Delaney, K R

1997-10-17

Action potential-evoked transmitter release is enhanced for many seconds after moderate-frequency stimulation (e.g. 15 Hz for 30 s) at the excitor motorneuron synapse of the crayfish dactyl opener muscle. Beginning about 1.5 s after a train, activity-dependent synaptic enhancement (ADSE) is dominated by a process termed augmentation (G.D. Bittner, D.A. Baxter, Synaptic plasticity at crayfish neuromuscular junctions: facilitation and augmentation, Synapse 7 (1991) 235-243'[4]; K.L. Magleby, Short-term changes in synaptic efficacy, in: G.M. Edelman, L.E. Gall, C.W. Maxwell (Eds.), Synaptic Function, John Wiley and Sons, New York, 1987, pp. 21-56; K.L. Magleby; J.E. Zengel, Augmentation: a process that acts to increase transmitter release at the frog neuromuscular junction, J. Physiol. (Lond.) 257 (1976) 449-470) which decays approximately exponentially with a time constant of about 10 s at 16 degrees C, reflecting the removal of Ca2+ which accumulates during the train in presynaptic terminals (K.R. Delaney, D.W. Tank, R.S. Zucker, Serotonin-mediated enhancement of transmission at crayfish neuromuscular junction is independent of changes in calcium, J. Neurosci. 11 (1991) 2631-2643). Serotonin (5-HT, 1 microM) increases evoked and spontaneous transmitter release several-fold (D. Dixon, H.L. Atwood, Crayfish motor nerve terminal's response to serotonin examined by intracellular microelectrode, J. Neurobiol. 16 (1985) 409-424; J. Dudel, Modulation of quantal synaptic release by serotonin and forskolin in crayfish motor nerve terminals, in: Modulation of Synaptic Transmission and Plasticity in Nervous Systems, G. Hertting, H.-C. Spatz (Eds.), Springer-Verlag, Berlin, 1988; S. Glusman, E.A. Kravitz. The action of serotonin on excitatory nerve terminals in lobster nerve-muscle preparations, J. Physiol. (Lond.) 325 (1982) 223-241). We found that ADSE persists about 2-3 times longer after moderate-frequency presynaptic stimulation in the presence of 5-HT. This slowing of the decay of ADSE by 5-HT was not accompanied by significant changes in the initial amplitude of activity-dependent components of enhancement 1.5 s after the train. Measurements of presynaptic [Ca2+] indicated that the time course of Ca2+ removal from the presynaptic terminals after trains was not altered by 5-HT. Changes in presynaptic action potential shape, resting membrane potential or postsynaptic impedance after trains cannot account for slower recovery of ADSE. Axonal injection of EDTA slows the removal of residual Ca2+ and the decay of synaptic augmentation after trains of action potentials (K.R. Delaney, D.W. Tank, A quantitative measure of the dependence of short-term synaptic enhancement on presynaptic residual calcium, J. Neurosci. 14 (1994) 5885-5902), but has little or no effect on the 5-HT-induced persistence of ADSE. This also suggests that the time course of ADSE in the presence of 5-HT is not determined primarily by residual Ca2+ removal kinetics. The slowing of ADSE recovery after trains by 5-HT reverses with washing in 5-HT-free saline along with the 5-HT-mediated enhancement of release.

Huntingtin-interacting protein 1 influences worm and mouse presynaptic function and protects Caenorhabditis elegans neurons against mutant polyglutamine toxicity.

PubMed

Parker, J Alex; Metzler, Martina; Georgiou, John; Mage, Marilyne; Roder, John C; Rose, Ann M; Hayden, Michael R; Néri, Christian

2007-10-10

Huntingtin-interacting protein 1 (HIP1) was identified through its interaction with htt (huntingtin), the Huntington's disease (HD) protein. HIP1 is an endocytic protein that influences transport and function of AMPA and NMDA receptors in the brain. However, little is known about its contribution to neuronal dysfunction in HD. We report that the Caenorhabditis elegans HIP1 homolog hipr-1 modulates presynaptic activity and the abundance of synaptobrevin, a protein involved in synaptic vesicle fusion. Presynaptic function was also altered in hippocampal brain slices of HIP1-/- mice demonstrating delayed recovery from synaptic depression and a reduction in paired-pulse facilitation, a form of presynaptic plasticity. Interestingly, neuronal dysfunction in transgenic nematodes expressing mutant N-terminal huntingtin was specifically enhanced by hipr-1 loss of function. A similar effect was observed with several other mutant proteins that are expressed at the synapse and involved in endocytosis, such as unc-11/AP180, unc-26/synaptojanin, and unc-57/endophilin. Thus, HIP1 is involved in presynaptic nerve terminal activity and modulation of mutant polyglutamine-induced neuronal dysfunction. Moreover, synaptic proteins involved in endocytosis may protect neurons against amino acid homopolymer expansion.

Presynaptic facilitatory adenosine A2A receptors mediate fade induced by neuromuscular relaxants that exhibit anticholinesterase activity.

PubMed

Bornia, Elaine Cs; Correia-de-Sá, Paulo; Alves-Do-Prado, Wilson

2011-03-01

1. Pancuronium, cisatracurium and vecuronium are antinicotinic agents that, in contrast with d-tubocurarine and hexamethonium, exhibit anticholinesterase activity. Pancuronium-, cisatracurium- and vecuronium-induced fade results from blockade of facilitatory nicotinic receptors on motor nerves, but fade produced by such agents also depends on the presynaptic activation of inhibitory muscarinic M2 receptors by acetylcholine released from motor nerve terminals and activation of inhibitory adenosine A1 receptors by adenosine released from motor nerves and muscles. The participation of presynaptic facilitatory A2A receptors in fade caused by pancuronium, cisatracurium and vecuronium has not yet been investigated. In the present study, we determined the effects of ZM241385, an antagonist of presynaptic facilitatory A2A receptors, on fade produced by these neuromuscular relaxants in the rat phrenic nerve-diaphragm (PND) preparation. 2. The muscles were stimulated indirectly at 75±3Hz to induce a sustained tetanizing muscular contraction. The lowest concentration at which each antinicotinic agent produced fade without modifying initial tetanic tension (presynaptic action) was determined. 3. d-Tubocurarine-induced fade occurred only at 55 nmol/L, a concentration that also reduced maximal tetanic tension (post-synaptic action). At 10 nmol/L, ZM 241385 alone did not produce fade, but it did attenuate pancuronium (0.32 μmol/L)-, cisatracurium (0.32 μmol/L)- and vecuronium (0.36 μmol/L)-induced fade. 4. The fade induced by the 'pure' antinicotinic agents d-tubocurarine (55 nmol/L) and hexamethonium (413 μmol/L) was not altered by 10 nmol/L ZM 241385, indicating that presynaptic adenosine A2A receptors play a significant role in the fade produced by antinicotinic agents when such agents have anticholinesterase activity. © 2011 The Authors. Clinical and Experimental Pharmacology and Physiology © 2011 Blackwell Publishing Asia Pty Ltd.

Muscle Contraction Regulates BDNF/TrkB Signaling to Modulate Synaptic Function through Presynaptic cPKCα and cPKCβI.

PubMed

Hurtado, Erica; Cilleros, Víctor; Nadal, Laura; Simó, Anna; Obis, Teresa; Garcia, Neus; Santafé, Manel M; Tomàs, Marta; Halievski, Katherine; Jordan, Cynthia L; Lanuza, Maria A; Tomàs, Josep

2017-01-01

The neurotrophin brain-derived neurotrophic factor (BDNF) acts via tropomyosin-related kinase B receptor (TrkB) to regulate synapse maintenance and function in the neuromuscular system. The potentiation of acetylcholine (ACh) release by BDNF requires TrkB phosphorylation and Protein Kinase C (PKC) activation. BDNF is secreted in an activity-dependent manner but it is not known if pre- and/or postsynaptic activities enhance BDNF expression in vivo at the neuromuscular junction (NMJ). Here, we investigated whether nerve and muscle cell activities regulate presynaptic conventional PKC (cPKCα and βI) via BDNF/TrkB signaling to modulate synaptic strength at the NMJ. To differentiate the effects of presynaptic activity from that of muscle contraction, we stimulated the phrenic nerve of rat diaphragms (1 Hz, 30 min) with or without contraction (abolished by μ-conotoxin GIIIB). Then, we performed ELISA, Western blotting, qRT-PCR, immunofluorescence and electrophysiological techniques. We found that nerve-induced muscle contraction: (1) increases the levels of mature BDNF protein without affecting pro-BDNF protein or BDNF mRNA levels; (2) downregulates TrkB.T1 without affecting TrkB.FL or p75 neurotrophin receptor (p75) levels; (3) increases presynaptic cPKCα and cPKCβI protein level through TrkB signaling; and (4) enhances phosphorylation of cPKCα and cPKCβI. Furthermore, we demonstrate that cPKCβI, which is exclusively located in the motor nerve terminals, increases activity-induced acetylcholine release. Together, these results show that nerve-induced muscle contraction is a key regulator of BDNF/TrkB signaling pathway, retrogradely activating presynaptic cPKC isoforms (in particular cPKCβI) to modulate synaptic function. These results indicate that a decrease in neuromuscular activity, as occurs in several neuromuscular disorders, could affect the BDNF/TrkB/PKC pathway that links pre- and postsynaptic activity to maintain neuromuscular function.

Muscle Contraction Regulates BDNF/TrkB Signaling to Modulate Synaptic Function through Presynaptic cPKCα and cPKCβI

PubMed Central

Hurtado, Erica; Cilleros, Víctor; Nadal, Laura; Simó, Anna; Obis, Teresa; Garcia, Neus; Santafé, Manel M.; Tomàs, Marta; Halievski, Katherine; Jordan, Cynthia L.; Lanuza, Maria A.; Tomàs, Josep

2017-01-01

The neurotrophin brain-derived neurotrophic factor (BDNF) acts via tropomyosin-related kinase B receptor (TrkB) to regulate synapse maintenance and function in the neuromuscular system. The potentiation of acetylcholine (ACh) release by BDNF requires TrkB phosphorylation and Protein Kinase C (PKC) activation. BDNF is secreted in an activity-dependent manner but it is not known if pre- and/or postsynaptic activities enhance BDNF expression in vivo at the neuromuscular junction (NMJ). Here, we investigated whether nerve and muscle cell activities regulate presynaptic conventional PKC (cPKCα and βI) via BDNF/TrkB signaling to modulate synaptic strength at the NMJ. To differentiate the effects of presynaptic activity from that of muscle contraction, we stimulated the phrenic nerve of rat diaphragms (1 Hz, 30 min) with or without contraction (abolished by μ-conotoxin GIIIB). Then, we performed ELISA, Western blotting, qRT-PCR, immunofluorescence and electrophysiological techniques. We found that nerve-induced muscle contraction: (1) increases the levels of mature BDNF protein without affecting pro-BDNF protein or BDNF mRNA levels; (2) downregulates TrkB.T1 without affecting TrkB.FL or p75 neurotrophin receptor (p75) levels; (3) increases presynaptic cPKCα and cPKCβI protein level through TrkB signaling; and (4) enhances phosphorylation of cPKCα and cPKCβI. Furthermore, we demonstrate that cPKCβI, which is exclusively located in the motor nerve terminals, increases activity-induced acetylcholine release. Together, these results show that nerve-induced muscle contraction is a key regulator of BDNF/TrkB signaling pathway, retrogradely activating presynaptic cPKC isoforms (in particular cPKCβI) to modulate synaptic function. These results indicate that a decrease in neuromuscular activity, as occurs in several neuromuscular disorders, could affect the BDNF/TrkB/PKC pathway that links pre- and postsynaptic activity to maintain neuromuscular function. PMID:28572757

Presynaptic LRP4 promotes synapse number and function of excitatory CNS neurons

PubMed Central

Mosca, Timothy J; Luginbuhl, David J; Wang, Irving E; Luo, Liqun

2017-01-01

Precise coordination of synaptic connections ensures proper information flow within circuits. The activity of presynaptic organizing molecules signaling to downstream pathways is essential for such coordination, though such entities remain incompletely known. We show that LRP4, a conserved transmembrane protein known for its postsynaptic roles, functions presynaptically as an organizing molecule. In the Drosophila brain, LRP4 localizes to the nerve terminals at or near active zones. Loss of presynaptic LRP4 reduces excitatory (not inhibitory) synapse number, impairs active zone architecture, and abolishes olfactory attraction - the latter of which can be suppressed by reducing presynaptic GABAB receptors. LRP4 overexpression increases synapse number in excitatory and inhibitory neurons, suggesting an instructive role and a common downstream synapse addition pathway. Mechanistically, LRP4 functions via the conserved kinase SRPK79D to ensure normal synapse number and behavior. This highlights a presynaptic function for LRP4, enabling deeper understanding of how synapse organization is coordinated. DOI: http://dx.doi.org/10.7554/eLife.27347.001 PMID:28606304

Synaptic Vesicle Mobility and Presynaptic F-Actin Are Disrupted in a N-ethylmaleimide–sensitive Factor Allele of Drosophila

PubMed Central

Nunes, Paula; Haines, Nicola; Kuppuswamy, Venkat; Fleet, David J.

2006-01-01

N-ethylmaleimide sensitive factor (NSF) can dissociate the soluble NSF attachment receptor (SNARE) complex, but NSF also participates in other intracellular trafficking functions by virtue of SNARE-independent activity. Drosophila that express a neural transgene encoding a dominant-negative form of NSF2 show an 80% reduction in the size of releasable synaptic vesicle pool, but no change in the number of vesicles in nerve terminal boutons. Here we tested the hypothesis that vesicles in the NSF2 mutant terminal are less mobile. Using a combination of genetics, pharmacology, and imaging we find a substantial reduction in vesicle mobility within the nerve terminal boutons of Drosophila NSF2 mutant larvae. Subsequent analysis revealed a decrease of filamentous actin in both NSF2 dominant-negative and loss-of-function mutants. Lastly, actin-filament disrupting drugs also decrease vesicle movement. We conclude that a factor contributing to the NSF mutant phenotype is a reduction in vesicle mobility, which is associated with decreased presynaptic F-actin. Our data are consistent with a model in which actin filaments promote vesicle mobility and suggest that NSF participates in establishing or maintaining this population of actin. PMID:16914524

Presynaptic Disorders: Lambert-Eaton Myasthenic Syndrome and Botulism.

PubMed

Gable, Karissa L; Massey, Janice M

2015-08-01

Lambert-Eaton myasthenic syndrome (LEMS) and botulism are acquired presynaptic nerve terminal disorders of the neuromuscular junction. Lambert-Eaton myasthenic syndrome is an idiopathic or paraneoplastic autoimmune syndrome in which autoantibodies of the P/Q-type voltage-gated calcium channel play a role in decreasing the release of acetylcholine, resulting in clinical symptoms of skeletal muscle weakness, diminished reflexes, and autonomic symptoms. Paraneoplastic LEMS is most often associated with small cell lung cancer. Diagnosis is confirmed by positive serologic testing and electrophysiological studies, which display characteristic features of low compound muscle action potentials, a decrement at 3Hz repetitive nerve stimulation, and facilitation with exercise or high-frequency repetitive stimulation. Treatment involves cancer monitoring and treatment, 3,4-diaminopyridine, immunosuppressive medications, and acetylcholinesterase inhibitors. Botulism is another presynaptic disorder of neuromuscular transmission. Clinical features classically involve cranial and bulbar palsies followed by descending weakness of the limbs, respiratory failure, and autonomic dysfunction. Electrodiagnostic testing is important in the evaluation and diagnosis. Treatment is supportive, and administration of antitoxin is beneficial in selected cases. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

Presynaptic and postsynaptic effects of the venom of the Australian tiger snake at the neuromuscular junction

PubMed Central

Datyner, M. E.; Gage, P. W.

1973-01-01

1. Crude venom (TSV) from the Australian tiger snake (Notechis scutatus scutatus) has both presynaptic and postsynaptic effects at the neuromuscular junctions of toads. 2. TSV (50 μg/ml) rapidly blocked indirectly elicited muscle twitches without affecting the compound action potential in the sciatic nerve or twitches elicited by direct stimulation. 3. Low concentrations of the venom (1-10 μg/ml) reduced the amplitude of miniature endplate potentials (m.e.p.ps) and inhibited the depolarization of muscle fibres normally caused by carbachol. It was concluded that a fraction of the venom binds to acetylcholine receptors. 4. The frequency of m.e.p.ps was at first increased by TSV at a concentration of 1 μg/ml. Occasional, high frequency `bursts' of m.e.p.ps were recorded in some preparations. The mean frequency of m.e.p.ps appeared to fall after several hours in the venom. 5. The quantal content of endplate potentials (e.p.ps) was reduced by the venom. With low concentrations (1 μg/ml), an initial increase in quantal content was often seen. When the quantal content was markedly depressed there was no parallel reduction in the amplitude of nerve terminal spikes recorded extracellularly, though a later fall in size and slowing of time course was often seen. 6. There was evidence that TSV eventually changed the normal Poisson characteristics of the spontaneous release of quanta and this may be correlated with electronmicroscopic changes in nerve terminals. 7. Tiger snake antivenene counteracted the postsynaptic, but not the presynaptic effects of TSV when they had developed. PMID:4367126

Synaptic Activity and Muscle Contraction Increases PDK1 and PKCβI Phosphorylation in the Presynaptic Membrane of the Neuromuscular Junction.

PubMed

Hurtado, Erica; Cilleros, Víctor; Just, Laia; Simó, Anna; Nadal, Laura; Tomàs, Marta; Garcia, Neus; Lanuza, Maria A; Tomàs, Josep

2017-01-01

Conventional protein kinase C βI (cPKCβI) is a conventional protein kinase C (PKC) isoform directly involved in the regulation of neurotransmitter release in the neuromuscular junction (NMJ). It is located exclusively at the nerve terminal and both synaptic activity and muscle contraction modulate its protein levels and phosphorylation. cPKCβI molecular maturation includes a series of phosphorylation steps, the first of which is mediated by phosphoinositide-dependent kinase 1 (PDK1). Here, we sought to localize PDK1 in the NMJ and investigate the hypothesis that synaptic activity and muscle contraction regulate in parallel PDK1 and cPKCβI phosphorylation in the membrane fraction. To differentiate the presynaptic and postsynaptic activities, we abolished muscle contraction with μ-conotoxin GIIIB (μ-CgTx-GIIIB) in some experiments before stimulation of the phrenic nerve (1 Hz, 30 min). Then, we analyzed total and membrane/cytosol fractions of skeletal muscle by Western blotting. Results showed that PDK1 is located exclusively in the nerve terminal of the NMJ. After nerve stimulation with and without coincident muscle contraction, total PDK1 and phosphorylated PDK1 (pPDK1) protein levels remained unaltered. However, synaptic activity specifically enhanced phosphorylation of PDK1 in the membrane, an important subcellular location for PDK1 function. This increase in pPDK1 coincides with a significant increase in the phosphorylation of its substrate cPKCβI also in the membrane fraction. Moreover, muscle contraction maintains PDK1 and pPDK1 but increases cPKCβI protein levels and its phosphorylation. Thus, even though PDK1 activity is maintained, pcPKCβI levels increase in concordance with total cPKCβI. Together, these results indicate that neuromuscular activity could induce the membrane targeting of pPDK1 in the nerve terminal of the NMJ to promote the phosphorylation of the cPKCβI, which is involved in ACh release.

Synaptic Activity and Muscle Contraction Increases PDK1 and PKCβI Phosphorylation in the Presynaptic Membrane of the Neuromuscular Junction

PubMed Central

Hurtado, Erica; Cilleros, Víctor; Just, Laia; Simó, Anna; Nadal, Laura; Tomàs, Marta; Garcia, Neus; Lanuza, Maria A.; Tomàs, Josep

2017-01-01

Conventional protein kinase C βI (cPKCβI) is a conventional protein kinase C (PKC) isoform directly involved in the regulation of neurotransmitter release in the neuromuscular junction (NMJ). It is located exclusively at the nerve terminal and both synaptic activity and muscle contraction modulate its protein levels and phosphorylation. cPKCβI molecular maturation includes a series of phosphorylation steps, the first of which is mediated by phosphoinositide-dependent kinase 1 (PDK1). Here, we sought to localize PDK1 in the NMJ and investigate the hypothesis that synaptic activity and muscle contraction regulate in parallel PDK1 and cPKCβI phosphorylation in the membrane fraction. To differentiate the presynaptic and postsynaptic activities, we abolished muscle contraction with μ-conotoxin GIIIB (μ-CgTx-GIIIB) in some experiments before stimulation of the phrenic nerve (1 Hz, 30 min). Then, we analyzed total and membrane/cytosol fractions of skeletal muscle by Western blotting. Results showed that PDK1 is located exclusively in the nerve terminal of the NMJ. After nerve stimulation with and without coincident muscle contraction, total PDK1 and phosphorylated PDK1 (pPDK1) protein levels remained unaltered. However, synaptic activity specifically enhanced phosphorylation of PDK1 in the membrane, an important subcellular location for PDK1 function. This increase in pPDK1 coincides with a significant increase in the phosphorylation of its substrate cPKCβI also in the membrane fraction. Moreover, muscle contraction maintains PDK1 and pPDK1 but increases cPKCβI protein levels and its phosphorylation. Thus, even though PDK1 activity is maintained, pcPKCβI levels increase in concordance with total cPKCβI. Together, these results indicate that neuromuscular activity could induce the membrane targeting of pPDK1 in the nerve terminal of the NMJ to promote the phosphorylation of the cPKCβI, which is involved in ACh release. PMID:28890686

Cellular projections from sensory hair cells form polarity-specific scaffolds during synaptogenesis

PubMed Central

Dow, Eliot; Siletti, Kimberly

2015-01-01

The assembly of a nervous system requires the extension of axons and dendrites to specific regions where they are matched with appropriate synaptic targets. Although the cues that guide long-range outgrowth have been characterized extensively, additional mechanisms are required to explain short-range guidance in neural development. Using a complementary combination of time-lapse imaging by fluorescence confocal microscopy and serial block-face electron microscopy, we identified a novel type of presynaptic projection that participates in the assembly of the vertebrate nervous system. Synapse formation by each hair cell of the zebrafish's lateral line occurs during a particular interval after the cell's birth. During the same period, projections emerge from the cellular soma, extending toward a specific subpopulation of mature hair cells and interacting with polarity-specific afferent nerve terminals. The terminals then extend along the projections to reach appropriately matched presynaptic sites, after which the projections recede. Our results suggest that presynaptic projections act as transient scaffolds for short-range partner matching, a mechanism that may occur elsewhere in the nervous system. PMID:25995190

Strontium, barium, and manganese metabolism in isolated presynaptic nerve terminals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rasgado-Flores, H.; Sanchez-Armass, S.; Blaustein, M.P.

1987-06-01

To gain insight into the mechanisms by which the divalent cations Sr, Ba, and Mn affect neurotransmitter release from presynaptic nerve terminals, the authors examined the sequestration of these cations, ion comparison to Ca, by mitochondrial and nonmitochondrial organelles and the extrusion of these cations from isolated nerve terminals. Sequestration was studied in synaptosomes made leaky to small ions by treatment with saponin; efflux was examined in intact synaptosomes that were preloaded with the divalent cations by incubation in depolarizing (K rich) media. The selectivity sequence for ATP-dependent mitochondrial uptake that they observed was Mn>>Ca>Sr>>Ba, whereas that for the SERmore » was Ca greater than or equal to Mn>Sr>>Ba. When synaptosomes that were preloaded with divalent cations were incubated in Na- and Ca-free media, there was little efflux of /sup 45/Ca, /sup 133/Ba, /sup 85/Sr, or /sup 54/Mn. When the incubation was carried out in media containing Na without Ca, there was substantial stimulation of Ca and Sr efflux, but only slight stimulation of Ba or Mn efflux. In Na-free media, the addition of 1 mM Ca promoted the efflux of all four divalent cations, probably via Ca-divalent cation exchange. In summary, the sequestration and extrusion data suggest that, with equal loads, Mn will be buffered to the greatest extent, whereas Ba will be least well buffered. These results may help to explain why Mn has a very long-lasting effect on transmitter release, while the effect of Sr is much briefer.« less

Flow Cytometric Analysis of Presynaptic Nerve Terminals Isolated from Rats Subjected to Hypergravity

NASA Astrophysics Data System (ADS)

Borisova, Tatiana

2008-06-01

Flow cytometric studies revealed an insignificant decrease in cell size heterogeneity and cytoplasmic granularity of rat brain nerve terminals (synaptosomes) isolated from animals subjected to centrifuge-induced hypergravity as compared to control ones. The analysis of plasma membrane potential using the potentiometric optical dye rhodamine 6G showed a decrease in fluorescence intensity by 10 % at steady state level in hypergravity synaptosomes. To monitor synaptic vesicle acidification we used pH-sensitive fluorescent dye acridine orange and demonstrated a lower fluorescence intensity level at steady state (10%) after hypergravity as compared to controls. Thus, exposure to hypergravity resulted in depolarization of the synaptosomal plasma membrane and diminution in synaptic vesicle acidification that may be a cause leading to altered synaptic neurotransmission.

Fibroblast Growth Factor 22 Contributes to the Development of Retinal Nerve Terminals in the Dorsal Lateral Geniculate Nucleus

PubMed Central

Singh, Rishabh; Su, Jianmin; Brooks, Justin; Terauchi, Akiko; Umemori, Hisashi; Fox, Michael A.

2012-01-01

At least three forms of signaling between pre- and postsynaptic partners are necessary during synapse formation. First, “targeting” signals instruct presynaptic axons to recognize and adhere to the correct portion of a postsynaptic target cell. Second, trans-synaptic “organizing” signals induce differentiation in their synaptic partner so that each side of the synapse is specialized for synaptic transmission. Finally, in many regions of the nervous system an excess of synapses are initially formed, therefore “refinement” signals must either stabilize or destabilize the synapse to reinforce or eliminate connections, respectively. Because of both their importance in processing visual information and their accessibility, retinogeniculate synapses have served as a model for studying synaptic development. Molecular signals that drive retinogeniculate “targeting” and “refinement” have been identified, however, little is known about what “organizing” cues are necessary for the differentiation of retinal axons into presynaptic terminals. To identify such “organizing” cues, we used microarray analysis to assess whether any target-derived “synaptic organizers” were enriched in the mouse dorsal lateral geniculate nucleus (dLGN) during retinogeniculate synapse formation. One candidate “organizing” molecule enriched in perinatal dLGN was FGF22, a secreted cue that induces the formation of excitatory nerve terminals in muscle, hippocampus, and cerebellum. In FGF22 knockout mice, the development of retinal terminals in dLGN was impaired. Thus, FGF22 is an important “organizing” cue for the timely development of retinogeniculate synapses. PMID:22363257

Structure activity relationship of synaptic and junctional neurotransmission.

PubMed

Goyal, Raj K; Chaudhury, Arun

2013-06-01

Chemical neurotransmission may include transmission to local or remote sites. Locally, contact between 'bare' portions of the bulbous nerve terminal termed a varicosity and the effector cell may be in the form of either synapse or non-synaptic contact. Traditionally, all local transmissions between nerves and effector cells are considered synaptic in nature. This is particularly true for communication between neurons. However, communication between nerves and other effectors such as smooth muscles has been described as nonsynaptic or junctional in nature. Nonsynaptic neurotransmission is now also increasingly recognized in the CNS. This review focuses on the relationship between structure and function that orchestrate synaptic and junctional neurotransmissions. A synapse is a specialized focal contact between the presynaptic active zone capable of ultrafast release of soluble transmitters and the postsynaptic density that cluster ionotropic receptors. The presynaptic and the postsynaptic areas are separated by the 'closed' synaptic cavity. The physiological hallmark of the synapse is ultrafast postsynaptic potentials lasting milliseconds. In contrast, junctions are juxtapositions of nerve terminals and the effector cells without clear synaptic specializations and the junctional space is 'open' to the extracellular space. Based on the nature of the transmitters, postjunctional receptors and their separation from the release sites, the junctions can be divided into 'close' and 'wide' junctions. Functionally, the 'close' and the 'wide' junctions can be distinguished by postjunctional potentials lasting ~1s and tens of seconds, respectively. Both synaptic and junctional communications are common between neurons; however, junctional transmission is the rule at many neuro-non-neural effectors. Published by Elsevier B.V.

Structure activity relationship of synaptic and junctional neurotransmission

PubMed Central

Goyal, Raj K; Chaudhury, Arun

2013-01-01

Chemical neurotransmission may include transmission to local or remote sites. Locally, contact between ‘bare’ portions of the bulbous nerve terminal termed a varicosity and the effector cell may be in the form of either synapse or non-synaptic contact. Traditionally, all local transmissions between nerves and effector cells are considered synaptic in nature. This is particularly true for communication between neurons. However, communication between nerves and other effectors such as smooth muscles has been described as nonsynaptic or junctional in nature. Nonsynaptic neurotransmission is now also increasing recognized in the CNS. This review focuses on the relationship between structure and function that orchestrate synaptic and junctional neurotransmissions. A synapse is a specialized focal contact between the presynaptic active zone capable for ultrafast release of soluble transmitters and the postsynaptic density that cluster ionotropic receptors. The presynaptic and the postsynaptic areas are separated by the ‘closed’ synaptic cavity. The physiological hallmark of the synapse is ultrafast postsynaptic potentials lasting in milliseconds. In contrast, junctions are juxtapositions of nerve terminals and the effector cells without clear synaptic specializations and the junctional space is ‘open’ to the extracellular space. Based on the nature of the transmitters, postjunctional receptors and their separation from the release sites, the junctions can be divided into ‘close’ and ‘wide’ junctions. Functionally, the ‘close’ and the ‘wide’ junctions can be distinguished by postjunctional potentials lasting ~1 second and 10s of seconds, respectively. Both synaptic and junctional communications are common between neurons; however, junctional transmission is the rule at many neuro-non-neural effectors. PMID:23535140

Effect of O-methyl-β-cyclodextrin-modified magnetic nanoparticles on the uptake and extracellular level of l-glutamate in brain nerve terminals.

PubMed

Horák, Daniel; Beneš, Milan; Procházková, Zuzana; Trchová, Miroslava; Borysov, Arsenii; Pastukhov, Artem; Paliienko, Konstantin; Borisova, Tatiana

2017-01-01

Changes in cholesterol concentration in the plasma membrane of presynaptic nerve terminals nonspecifically modulate glutamate transport and homeostasis in the central nervous system. Reduction of the cholesterol content in isolated rat brain nerve terminals (synaptosomes) using cholesterol-depleting agents decreases the glutamate uptake and increases the extracellular level of glutamate in nerve terminals. Extraction of cholesterol from the plasma membrane and its further removal from the synaptosomes by external magnetic field can be achieved by means of magnetic nanoparticles with immobilized cholesterol-depleting agent such as O-methyl-β-cyclodextrin (MCD). A simple approach is developed for preparation of maghemite (γ-Fe 2 O 3 ) nanoparticles containing chemically bonded MCD. The method is based on preparation of a silanization agent containing MCD. It is synthesized by the reaction of triethoxy(3-isocyanatopropyl)silane with MCD. Base-catalyzed silanization of superparamagnetic γ-Fe 2 O 3 provides a relatively stable colloid product containing 48μmol of MCDg -1 . MCD-modified γ-Fe 2 O 3 nanoparticles decrease the initial rate of the uptake and accumulation of l-[ 14 C]glutamate and increase the extracellular l-[ 14 C]glutamate level in the preparation of nerve terminals. The effect of MCD-immobilized nanoparticles is the same as that of MCD solution; moreover, magnetic manipulation of the nanoparticles enables removal of bonded cholesterol. Copyright © 2016 Elsevier B.V. All rights reserved.

Regulation of presynaptic Ca2+, synaptic plasticity and contextual fear conditioning by a N-terminal β-amyloid fragment.

PubMed

Lawrence, James L M; Tong, Mei; Alfulaij, Naghum; Sherrin, Tessi; Contarino, Mark; White, Michael M; Bellinger, Frederick P; Todorovic, Cedomir; Nichols, Robert A

2014-10-22

Soluble β-amyloid has been shown to regulate presynaptic Ca(2+) and synaptic plasticity. In particular, picomolar β-amyloid was found to have an agonist-like action on presynaptic nicotinic receptors and to augment long-term potentiation (LTP) in a manner dependent upon nicotinic receptors. Here, we report that a functional N-terminal domain exists within β-amyloid for its agonist-like activity. This sequence corresponds to a N-terminal fragment generated by the combined action of α- and β-secretases, and resident carboxypeptidase. The N-terminal β-amyloid fragment is present in the brains and CSF of healthy adults as well as in Alzheimer's patients. Unlike full-length β-amyloid, the N-terminal β-amyloid fragment is monomeric and nontoxic. In Ca(2+) imaging studies using a model reconstituted rodent neuroblastoma cell line and isolated mouse nerve terminals, the N-terminal β-amyloid fragment proved to be highly potent and more effective than full-length β-amyloid in its agonist-like action on nicotinic receptors. In addition, the N-terminal β-amyloid fragment augmented theta burst-induced post-tetanic potentiation and LTP in mouse hippocampal slices. The N-terminal fragment also rescued LTP inhibited by elevated levels of full-length β-amyloid. Contextual fear conditioning was also strongly augmented following bilateral injection of N-terminal β-amyloid fragment into the dorsal hippocampi of intact mice. The fragment-induced augmentation of fear conditioning was attenuated by coadministration of nicotinic antagonist. The activity of the N-terminal β-amyloid fragment appears to reside largely in a sequence surrounding a putative metal binding site, YEVHHQ. These findings suggest that the N-terminal β-amyloid fragment may serve as a potent and effective endogenous neuromodulator. Copyright © 2014 the authors 0270-6474/14/3414210-09$15.00/0.

Wild-Type Monomeric α-Synuclein Can Impair Vesicle Endocytosis and Synaptic Fidelity via Tubulin Polymerization at the Calyx of Held.

PubMed

Eguchi, Kohgaku; Taoufiq, Zacharie; Thorn-Seshold, Oliver; Trauner, Dirk; Hasegawa, Masato; Takahashi, Tomoyuki

2017-06-21

α-Synuclein is a presynaptic protein the function of which has yet to be identified, but its neuronal content increases in patients of synucleinopathies including Parkinson's disease. Chronic overexpression of α-synuclein reportedly expresses various phenotypes of synaptic dysfunction, but the primary target of its toxicity has not been determined. To investigate this, we acutely loaded human recombinant α-synuclein or its pathological mutants in their monomeric forms into the calyces of Held presynaptic terminals in slices from auditorily mature and immature rats of either sex. Membrane capacitance measurements revealed significant and specific inhibitory effects of WT monomeric α-synuclein on vesicle endocytosis throughout development. However, the α-synuclein A53T mutant affected vesicle endocytosis only at immature calyces, whereas the A30P mutant had no effect throughout. The endocytic impairment by WT α-synuclein was rescued by intraterminal coloading of the microtubule (MT) polymerization blocker nocodazole. Furthermore, it was reversibly rescued by presynaptically loaded photostatin-1, a photoswitcheable inhibitor of MT polymerization, in a light-wavelength-dependent manner. In contrast, endocytic inhibition by the A53T mutant at immature calyces was not rescued by nocodazole. Functionally, presynaptically loaded WT α-synuclein had no effect on basal synaptic transmission evoked at a low frequency, but significantly attenuated exocytosis and impaired the fidelity of neurotransmission during prolonged high-frequency stimulation. We conclude that monomeric WT α-synuclein primarily inhibits vesicle endocytosis via MT overassembly, thereby impairing high-frequency neurotransmission. SIGNIFICANCE STATEMENT Abnormal α-synuclein abundance is associated with synucleinopathies including Parkinson's disease, but neither the primary target of α-synuclein toxicity nor its mechanism is identified. Here, we loaded monomeric α-synuclein directly into mammalian glutamatergic nerve terminals and found that it primarily inhibits vesicle endocytosis and subsequently impairs exocytosis and neurotransmission fidelity during prolonged high-frequency stimulation. Such α-synuclein toxicity could be rescued by blocking microtubule polymerization, suggesting that microtubule overassembly underlies the toxicity of acutely elevated α-synuclein in the nerve terminal. Copyright © 2017 the authors 0270-6474/17/376043-10$15.00/0.

Presynaptic GABAergic inhibition regulated by BDNF contributes to neuropathic pain induction

PubMed Central

Chen, Jeremy Tsung-chieh; Guo, Da; Campanelli, Dario; Frattini, Flavia; Mayer, Florian; Zhou, Luming; Kuner, Rohini; Heppenstall, Paul A.; Knipper, Marlies; Hu, Jing

2014-01-01

The gate control theory proposes the importance of both pre- and post-synaptic inhibition in processing pain signal in the spinal cord. However, although postsynaptic disinhibition caused by brain-derived neurotrophic factor (BDNF) has been proved as a crucial mechanism underlying neuropathic pain, the function of presynaptic inhibition in acute and neuropathic pain remains elusive. Here we show that a transient shift in the reversal potential (EGABA) together with a decline in the conductance of presynaptic GABAA receptor result in a reduction of presynaptic inhibition after nerve injury. BDNF mimics, whereas blockade of BDNF signalling reverses, the alteration in GABAA receptor function and the neuropathic pain syndrome. Finally, genetic disruption of presynaptic inhibition leads to spontaneous development of behavioural hypersensitivity, which cannot be further sensitized by nerve lesions or BDNF. Our results reveal a novel effect of BDNF on presynaptic GABAergic inhibition after nerve injury and may represent new strategy for treating neuropathic pain. PMID:25354791

Stimulation Induced Changes in Frog Neuromuscular Junctions: A Quantitative Ultrastructural Comparison of Rapid-Frozen and Chemically Fixed Nerve Terminals

DTIC Science & Technology

1984-03-06

study was conducted to determine the presynaptic morphological changes due to neural activity in rapidly stimulated neuromuscular junctions...Control preparations were unstimulated and preserved either by chemical fixation or rapid-freezing. This study provides evidence that most of the...tissue. The rapid-frozen preparations in the present study showed, in addition, that rapid stimulation produces an increase in synaptic vesicle

Coenzyme Q10 inhibits the release of glutamate in rat cerebrocortical nerve terminals by suppression of voltage-dependent calcium influx and mitogen-activated protein kinase signaling pathway.

PubMed

Chang, Yi; Huang, Shu-Kuei; Wang, Su-Jane

2012-12-05

This study investigates the effects and possible mechanism of coenzyme Q10 (CoQ10) on endogenous glutamate release in the cerebral cortex nerve terminals of rats. CoQ10 inhibited the release of glutamate evoked by the K+ channel blocker 4-aminopyridine (4-AP). CoQ10 reduced the depolarization-induced increase in cytosolic [Ca2+]c but did not alter the 4-AP-mediated depolarization. The effect of CoQ10 on evoked glutamate release was abolished by blocking the Cav2.2 (N-type) and Cav2.1 (P/Q-type) Ca2+ channels and mitogen-activated protein kinase kinase (MEK). In addition, CoQ10 decreased the 4-AP-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and synaptic vesicle-associated protein synapsin I, a major presynaptic substrate for ERK. Moreover, the inhibition of glutamate release by CoQ10 was strongly attenuated in mice without synapsin I. These results suggest that CoQ10 inhibits glutamate release from cortical synaptosomes in rats through the suppression of the presynaptic voltage-dependent Ca2+ entry and ERK/synapsin I signaling pathway.

Receptor-mediated internalization of [3H]-neurotensin in synaptosomal preparations from rat neostriatum.

PubMed

Nguyen, Ha Minh Ky; Cahill, Catherine M; McPherson, Peter S; Beaudet, Alain

2002-06-01

Following its binding to somatodendritic receptors, the neuropeptide neurotensin (NT) internalizes via a clathrin-mediated process. In the present study, we investigated whether NT also internalizes presynaptically using synaptosomes from rat neostriatum, a region in which NT1 receptors are virtually all presynaptic. Binding of [(3)H]-NT to striatal synaptosomes in the presence of levocabastine to block NT2 receptors is specific, saturable, and has NT1 binding properties. A significant fraction of the bound radioactivity is resistant to hypertonic acid wash indicating that it is internalized. Internalization of [(3)H]-NT, like that of [(125)I]-transferrin, is blocked by sucrose and low temperature, consistent with endocytosis occurring via a clathrin-dependent pathway. However, contrary to what was reported at the somatodendritic level, neither [(3)H]-NT nor [(125)I]-transferrin internalization in synaptosomes is sensitive to the endocytosis inhibitor phenylarsine oxide. Moreover, treatment of synaptosomes with monensin, which prevents internalized receptors from recycling to the plasma membrane, reduces [(3)H]-NT binding and internalization, suggesting that presynaptic NT1 receptors, in contrast to somatodendritic ones, are recycled back to the plasma membrane. Taken together, these results suggest that NT internalizes in nerve terminals via an endocytic pathway that is related to, but is mechanistically distinct from that responsible for NT internalization in nerve cell bodies.

Genetically encoded pH-indicators reveal activity-dependent cytosolic acidification of Drosophila motor nerve termini in vivo

PubMed Central

Rossano, Adam J; Chouhan, Amit K; Macleod, Gregory T

2013-01-01

All biochemical processes, including those underlying synaptic function and plasticity, are pH sensitive. Cytosolic pH (pHcyto) shifts are known to accompany nerve activity in situ, but technological limitations have prevented characterization of such shifts in vivo. Genetically encoded pH-indicators (GEpHIs) allow for tissue-specific in vivo measurement of pH. We expressed three different GEpHIs in the cytosol of Drosophila larval motor neurons and observed substantial presynaptic acidification in nerve termini during nerve stimulation in situ. SuperEcliptic pHluorin was the most useful GEpHI for studying pHcyto shifts in this model system. We determined the resting pH of the nerve terminal cytosol to be 7.30 ± 0.02, and observed a decrease of 0.16 ± 0.01 pH units when the axon was stimulated at 40 Hz for 4 s. Realkalinization occurred upon cessation of stimulation with a time course of 20.54 ± 1.05 s (τ). The chemical pH-indicator 2′,7′-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein corroborated these changes in pHcyto. Bicarbonate-derived buffering did not contribute to buffering of acid loads from short (≤4 s) trains of action potentials but did buffer slow (∼60 s) acid loads. The magnitude of cytosolic acid transients correlated with cytosolic Ca2+ increase upon stimulation, and partial inhibition of the plasma membrane Ca2+-ATPase, a Ca2+/H+ exchanger, attenuated pHcyto shifts. Repeated stimulus trains mimicking motor patterns generated greater cytosolic acidification (∼0.30 pH units). Imaging through the cuticle of intact larvae revealed spontaneous pHcyto shifts in presynaptic termini in vivo, similar to those seen in situ during fictive locomotion, indicating that presynaptic pHcyto shifts cannot be dismissed as artifacts of ex vivo preparations. PMID:23401611

Analysis of slow depolarizing potential in frog taste cell induced by parasympathetic efferent stimulation under hypoxia.

PubMed

Sato, Toshihide; Nishishita, Kazushisa; Okada, Yukio; Toda, Kazuo

2007-05-01

Strong electrical stimulation (ES) of the frog glossopharyngeal (GP) efferent nerve induced slow depolarizing potentials (DPs) in taste cells under hypoxia. This study aimed to elucidate whether the slow DPs were postsynaptically induced in taste cells. After a block of parasympathetic nerve (PSN) ganglia by tubocurarine, ES of GP nerve never induced slow DPs in the taste cells, so slow DPs were induced by PSN. When Ca(2+) in the blood plasma under hypoxia was decreased to approximately 0.5 mM, the slow DPs reduced in amplitude and lengthened in latency. Increasing the normal Ca(2+) to approximately 20 mM increased the amplitude of slow DPs and shortened the latency. Addition of Cd(2+) to the plasma greatly reduced the amplitude of slow DPs and lengthened the latency. These data suggest that the slow DPs depend on Ca(2+) and Cd(2+) concentration at the presynaptic PSN terminals of taste disk. Antagonists, [D-Arg(1), D-Trp(7,9), Leu(11)]-substance P and L-703 606, of neurotransmitter substance P neurokinin(1) receptor completely blocked the slow DPs. Intravenous application of substance P induced a DP of approximately 7 mV and a reduction of membrane resistance of approximately 48% in taste cells. A nonselective cation channel antagonist, flufenamic acid, completely blocked the slow DPs. These findings suggest that the slow DPs are postsynaptically initiated in frog taste cells under hypoxia by opening nonselective cation channels on the postsynaptic membrane after substance P is probably released from the presynaptic PSN axon terminals.

Developmental up-regulation of vesicular glutamate transporter-1 promotes neocortical presynaptic terminal development.

PubMed

Berry, Corbett T; Sceniak, Michael P; Zhou, Louie; Sabo, Shasta L

2012-01-01

Presynaptic terminal formation is a complex process that requires assembly of proteins responsible for synaptic transmission at sites of axo-dendritic contact. Accumulation of presynaptic proteins at developing terminals is facilitated by glutamate receptor activation. Glutamate is loaded into synaptic vesicles for release via the vesicular glutamate transporters VGLUT1 and VGLUT2. During postnatal development there is a switch from predominantly VGLUT2 expression to high VGLUT1 and low VGLUT2, raising the question of whether the developmental increase in VGLUT1 is important for presynaptic development. Here, we addressed this question using confocal microscopy and quantitative immunocytochemistry in primary cultures of rat neocortical neurons. First, in order to understand the extent to which the developmental switch from VGLUT2 to VGLUT1 occurs through an increase in VGLUT1 at individual presynaptic terminals or through addition of VGLUT1-positive presynaptic terminals, we examined the spatio-temporal dynamics of VGLUT1 and VGLUT2 expression. Between 5 and 12 days in culture, the percentage of presynaptic terminals that expressed VGLUT1 increased during synapse formation, as did expression of VGLUT1 at individual terminals. A subset of VGLUT1-positive terminals also expressed VGLUT2, which decreased at these terminals. At individual terminals, the increase in VGLUT1 correlated with greater accumulation of other synaptic vesicle proteins, such as synapsin and synaptophysin. When the developmental increase in VGLUT1 was prevented using VGLUT1-shRNA, the density of presynaptic terminals and accumulation of synapsin and synaptophysin at terminals were decreased. Since VGLUT1 knock-down was limited to a small number of neurons, the observed effects were cell-autonomous and independent of changes in overall network activity. These results demonstrate that up-regulation of VGLUT1 is important for development of presynaptic terminals in the cortex.

Developmental Up-Regulation of Vesicular Glutamate Transporter-1 Promotes Neocortical Presynaptic Terminal Development

PubMed Central

Berry, Corbett T.; Sceniak, Michael P.; Zhou, Louie; Sabo, Shasta L.

2012-01-01

Presynaptic terminal formation is a complex process that requires assembly of proteins responsible for synaptic transmission at sites of axo-dendritic contact. Accumulation of presynaptic proteins at developing terminals is facilitated by glutamate receptor activation. Glutamate is loaded into synaptic vesicles for release via the vesicular glutamate transporters VGLUT1 and VGLUT2. During postnatal development there is a switch from predominantly VGLUT2 expression to high VGLUT1 and low VGLUT2, raising the question of whether the developmental increase in VGLUT1 is important for presynaptic development. Here, we addressed this question using confocal microscopy and quantitative immunocytochemistry in primary cultures of rat neocortical neurons. First, in order to understand the extent to which the developmental switch from VGLUT2 to VGLUT1 occurs through an increase in VGLUT1 at individual presynaptic terminals or through addition of VGLUT1-positive presynaptic terminals, we examined the spatio-temporal dynamics of VGLUT1 and VGLUT2 expression. Between 5 and 12 days in culture, the percentage of presynaptic terminals that expressed VGLUT1 increased during synapse formation, as did expression of VGLUT1 at individual terminals. A subset of VGLUT1-positive terminals also expressed VGLUT2, which decreased at these terminals. At individual terminals, the increase in VGLUT1 correlated with greater accumulation of other synaptic vesicle proteins, such as synapsin and synaptophysin. When the developmental increase in VGLUT1 was prevented using VGLUT1-shRNA, the density of presynaptic terminals and accumulation of synapsin and synaptophysin at terminals were decreased. Since VGLUT1 knock-down was limited to a small number of neurons, the observed effects were cell-autonomous and independent of changes in overall network activity. These results demonstrate that up-regulation of VGLUT1 is important for development of presynaptic terminals in the cortex. PMID:23226425

Transmitter release modulation in nerve terminals of rat neocortical pyramidal cells by intracellular calcium buffers

PubMed Central

Ohana, Ora; Sakmann, Bert

1998-01-01

Dual whole-cell voltage recordings were made from synaptically connected layer 5 (L5) pyramidal neurones in slices of the young (P14-P16) rat neocortex. The Ca2+ buffers BAPTA or EGTA were loaded into the presynaptic neurone via the pipette recording from the presynaptic neurone to examine their effect on the mean and the coefficient of variation (c.v.) of single fibre EPSP amplitudes, referred to as unitary EPSPs. The fast Ca2+ buffer BAPTA reduced unitary EPSP amplitudes in a concentration dependent way. With 0.1 mm BAPTA in the pipette, the mean EPSP amplitude was reduced by 14 ± 2.8% (mean ±s.e.m., n = 7) compared with control pipette solution, whereas with 1.5 mm BAPTA, the mean EPSP amplitude was reduced by 72 ± 1.5% (n = 5). The concentration of BAPTA that reduced mean EPSP amplitudes to one-half of control was close to 0.7 mm. Saturation of BAPTA during evoked release was tested by comparing the effect of loading the presynaptic neurone with 0.1 mm BAPTA at 2 and 1 mm[Ca2+]o. Reducing [Ca2+]o from 2 to 1 mm, thereby reducing Ca2+ influx into the terminals, decreased the mean EPSP amplitude by 60 ± 2.2% with control pipette solution and by 62 ± 1.9% after loading with 0.1 mm BAPTA (n = 7). The slow Ca2+ buffer EGTA at 1 mm reduced mean EPSP amplitudes by 15 ± 2.5% (n = 5). With 10 mm EGTA mean EPSP amplitudes were reduced by 56 ± 2.3% (n = 4). With both Ca2+ buffers, the reduction in mean EPSP amplitudes was associated with an increase in the c.v. of peak EPSP amplitudes, consistent with a reduction of the transmitter release probability as the major mechanism underlying the reduction of the EPSP amplitude. The results suggest that in nerve terminals of thick tufted L5 pyramidal cells the endogenous mobile Ca2+ buffer is equivalent to less than 0.1 mm BAPTA and that at many release sites of pyramidal cell terminals the Ca2+ channel domains overlap, a situation comparable with that at large calyx-type terminals in the brainstem. PMID:9782165

Transfer characteristics of the hair cell's afferent synapse

NASA Astrophysics Data System (ADS)

Keen, Erica C.; Hudspeth, A. J.

2006-04-01

The sense of hearing depends on fast, finely graded neurotransmission at the ribbon synapses connecting hair cells to afferent nerve fibers. The processing that occurs at this first chemical synapse in the auditory pathway determines the quality and extent of the information conveyed to the central nervous system. Knowledge of the synapse's input-output function is therefore essential for understanding how auditory stimuli are encoded. To investigate the transfer function at the hair cell's synapse, we developed a preparation of the bullfrog's amphibian papilla. In the portion of this receptor organ representing stimuli of 400-800 Hz, each afferent nerve fiber forms several synaptic terminals onto one to three hair cells. By performing simultaneous voltage-clamp recordings from presynaptic hair cells and postsynaptic afferent fibers, we established that the rate of evoked vesicle release, as determined from the average postsynaptic current, depends linearly on the amplitude of the presynaptic Ca2+ current. This result implies that, for receptor potentials in the physiological range, the hair cell's synapse transmits information with high fidelity. auditory system | exocytosis | glutamate | ribbon synapse | synaptic vesicle

Calcium transient in presynaptic terminal of squid giant synapse: detection with aequorin.

PubMed

Llinás, R; Blinks, J R; Nicholson, C

1972-06-09

Microinjection of aequorin, a bioluminescent protein sensitive tocalcium, into the presynaptic terminal of the squid giant synapse demnonstrated an increase in intracellular calcium ion concentration during repetitive synaptic transmission. Although no light flashes synchronous with individual presynaptic : tion potentials were detected, the results are considered consistent with the hypothesis that entry of calcium into the presynaptic terminal triggers release of e synaptic transmitter substance.

Substance P immunoreactive nerve terminals in the dorsolateral nucleus of the tractus solitarius: roles in the baroreceptor reflex.

PubMed

Massari, V J; Shirahata, M; Johnson, T A; Lauenstein, J M; Gatti, P J

1998-03-02

Physiological and light microscopic evidence suggest that substance P (SP) may be a neurotransmitter contained in first-order sensory baroreceptor afferents; however, ultrastructural support for this hypothesis is lacking. We have traced the central projections of the carotid sinus nerve (CSN) in the cat by utilizing the transganglionic transport of horseradish peroxidase (HRP). The dorsolateral subnucleus of the nucleus tractus solitarius (dlNTS) was processed for the histochemical visualization of transganglionically labeled CSN afferents and for the immunocytochemical visualization of SP by dual labeling light and electron microscopic methods. Either HRP or SP was readily identified in single-labeled unmyelinated axons, myelinated axons, and nerve terminals in the dlNTS. SP immunoreactivity was also identified in unmyelinated axons, myelinated axons, and nerve terminals in the dlNTS, which were simultaneously identified as CSN primary afferents. However, only 15% of CSN terminals in the dlNTS were immunoreactive for SP. Therefore, while the ultrastructural data support the hypothesis that SP immunoreactive first-order neurons are involved in the origination of the baroreceptor reflex, they suggest that only a modest part of the total sensory input conveyed from the carotid sinus baroreceptors to the dlNTS is mediated by SP immunoreactive CSN terminals. Five types of axo-axonic synapses were observed in the dlNTS. SP immunoreactive CSN afferents were very rarely involved in these synapses. Furthermore, SP terminals were never observed to form the presynaptic element in an axo-axonic synapse with a CSN afferent. Therefore, SP does not appear to be involved in the modulation of the baroreceptor reflex in the dlNTS. Copyright 1998 Elsevier Science B.V.

Invaginating Structures in Mammalian Synapses

PubMed Central

Petralia, Ronald S.; Wang, Ya-Xian; Mattson, Mark P.; Yao, Pamela J.

2018-01-01

Invaginating structures at chemical synapses in the mammalian nervous system exist in presynaptic axon terminals, postsynaptic spines or dendrites, and glial processes. These invaginating structures can be divided into three categories. The first category includes slender protrusions invaginating into axonal terminals, postsynaptic spines, or glial processes. Best known examples of this category are spinules extending from postsynaptic spines into presynaptic terminals in forebrain synapses. Another example of this category are protrusions from inhibitory presynaptic terminals invaginating into postsynaptic neuronal somas. Regardless of the direction and location, the invaginating structures of the first category do not have synaptic active zones within the invagination. The second category includes postsynaptic spines invaginating into presynaptic terminals, whereas the third category includes presynaptic terminals invaginating into postsynaptic spines or dendrites. Unlike the first category, the second and third categories have active zones within the invagination. An example of the second category are mossy terminal synapses of the hippocampal CA3 region, in which enlarged spine-like structures invaginate partly or entirely into mossy terminals. An example of the third category is the neuromuscular junction (NMJ) where substantial invaginations of the presynaptic terminals invaginate into the muscle fibers. In the retina, rod and cone synapses have invaginating processes from horizontal and bipolar cells. Because horizontal cells act both as post and presynaptic structures, their invaginating processes represent both the second and third category. These invaginating structures likely play broad yet specialized roles in modulating neuronal cell signaling. PMID:29674962

Human immunodeficiency virus-1 protein Tat induces excitotoxic loss of presynaptic terminals in hippocampal cultures.

PubMed

Shin, Angela H; Thayer, Stanley A

2013-05-01

Human immunodeficiency virus (HIV) infection of the CNS produces dendritic damage that correlates with cognitive decline in patients with HIV-associated neurocognitive disorders (HAND). HIV-induced neurotoxicity results in part from viral proteins shed from infected cells, including the HIV transactivator of transcription (Tat). We previously showed that Tat binds to the low density lipoprotein receptor-related protein (LRP), resulting in overactivation of NMDA receptors, activation of the ubiquitin-proteasome pathway, and subsequent loss of postsynaptic densities. Here, we show that Tat also induces a loss of presynaptic terminals. The number of presynaptic terminals was quantified using confocal imaging of synaptophysin fused to green fluorescent protein (Syn-GFP). Tat-induced loss of presynaptic terminals was secondary to excitatory postsynaptic mechanisms because treatment with an LRP antagonist or an NMDA receptor antagonist inhibited this loss. Treatment with nutlin-3, an E3 ligase inhibitor, prevented Tat-induced loss of presynaptic terminals. These data suggest that Tat-induced loss of presynaptic terminals is a consequence of excitotoxic postsynaptic activity. We previously found that ifenprodil, an NR2B subunit-selective NMDA receptor antagonist, induced recovery of postsynaptic densities. Here we show that Tat-induced loss of presynaptic terminals was reversed by ifenprodil treatment. Thus, Tat-induced loss of presynaptic terminals is reversible, and this recovery can be initiated by inhibiting a subset of postsynaptic NMDA receptors. Understanding the dynamics of synaptic changes in response to HIV infection of the CNS may lead to the design of improved pharmacotherapies for HAND patients. Copyright © 2012 Elsevier Inc. All rights reserved.

Trafficking of presynaptic AMPA receptors mediating neurotransmitter release: neuronal selectivity and relationships with sensitivity to cyclothiazide.

PubMed

Pittaluga, Anna; Feligioni, Marco; Longordo, Fabio; Luccini, Elisa; Raiteri, Maurizio

2006-03-01

Postsynaptic glutamate AMPA receptors (AMPARs) can recycle between plasma membrane and intracellular pools. In contrast, trafficking of presynaptic AMPARs has not been investigated. AMPAR surface expression involves interactions between the GluR2 carboxy tail and various proteins including glutamate receptor-interacting protein (GRIP), AMPA receptor-binding protein (ABP), protein interacting with C kinase 1 (PICK1), N-ethyl-maleimide-sensitive fusion protein (NSF). Here, peptides known to selectively block the above interactions were entrapped into synaptosomes to study the effects on the AMPA-evoked release of [3H]noradrenaline ([3H]NA) and [3H]acetylcholine ([3H]ACh) from rat hippocampal and cortical synaptosomes, respectively. Internalization of pep2-SVKI to prevent GluR2-GRIP/ABP/PICK1 interactions potentiated the AMPA-evoked release of [3H]NA but left unmodified that of [3H]ACh. Similar potentiation was caused by pep2-AVKI, the blocker of GluR2-PICK1 interaction. Conversely, a decrease in the AMPA-evoked release of [3H]NA, but not of [3H]ACh, was caused by pep2m, a selective blocker of the GluR2-NSF interaction. In the presence of pep2-SVKI the presynaptic AMPARs on noradrenergic terminals lost sensitivity to cyclothiazide. AMPARs releasing [3H]ACh, but not those releasing [3H]NA, were sensitive to spermine, suggesting that they are GluR2-lacking AMPARs. To conclude: (i) release-regulating presynaptic AMPARs constitutively cycle in isolated nerve terminals; (ii) the process exhibits neuronal selectivity; (iii) AMPAR trafficking and desensitization may be interrelated.

Spinal Cord Excitability and Sprint Performance Are Enhanced by Sensory Stimulation During Cycling

PubMed Central

Pearcey, Gregory E. P.; Noble, Steven A.; Munro, Bridget; Zehr, E. Paul

2017-01-01

Spinal cord excitability, as assessed by modulation of Hoffmann (H-) reflexes, is reduced with fatiguing isometric contractions. Furthermore, spinal cord excitability is reduced during non-fatiguing arm and leg cycling. Presynaptic inhibition of Ia terminals is believed to contribute to this suppression of spinal cord excitability. Electrical stimulation to cutaneous nerves reduces Ia presynaptic inhibition, which facilitates spinal cord excitability, and this facilitation is present during arm cycling. Although it has been suggested that reducing presynaptic inhibition may prolong fatiguing contractions, it is unknown whether sensory stimulation can alter the effects of fatiguing exercise on performance or spinal cord excitability. Thus, the aim of this experiment was to determine if sensory stimulation can interfere with fatigue-related suppression of spinal cord excitability, and alter fatigue rates during cycling sprints. Thirteen participants randomly performed three experimental sessions that included: unloaded cycling with sensory stimulation (CONTROL + STIM), sprints with sensory stimulation (SPRINT + STIM) and sprints without stimulation (SPRINT). Seven participants also performed a fourth session (CONTROL), which consisted of unloaded cycling. During SPRINT and SPRINT + STIM, participants performed seven, 10 s cycling sprints interleaved with 3 min rest. For CONTROL and CONTROL + STIM, participants performed unloaded cycling for ~30 min. During SPRINT + STIM and CONTROL + STIM, participants received patterned sensory stimulation to nerves of the right foot. H-reflexes and M-waves of the right soleus were evoked by stimulation of the tibial nerve at multiple time points throughout exercise. Sensory stimulation facilitated soleus H-reflexes during unloaded cycling, whereas sprints suppressed soleus H-reflexes. While receiving sensory stimulation, there was less suppression of soleus H-reflexes and slowed reduction in average power output, compared to sprints without stimulation. These results demonstrate that sensory stimulation can substantially mitigate the fatiguing effects of sprints. PMID:29326570

Spinal Cord Excitability and Sprint Performance Are Enhanced by Sensory Stimulation During Cycling.

PubMed

Pearcey, Gregory E P; Noble, Steven A; Munro, Bridget; Zehr, E Paul

2017-01-01

Spinal cord excitability, as assessed by modulation of Hoffmann (H-) reflexes, is reduced with fatiguing isometric contractions. Furthermore, spinal cord excitability is reduced during non-fatiguing arm and leg cycling. Presynaptic inhibition of Ia terminals is believed to contribute to this suppression of spinal cord excitability. Electrical stimulation to cutaneous nerves reduces Ia presynaptic inhibition, which facilitates spinal cord excitability, and this facilitation is present during arm cycling. Although it has been suggested that reducing presynaptic inhibition may prolong fatiguing contractions, it is unknown whether sensory stimulation can alter the effects of fatiguing exercise on performance or spinal cord excitability. Thus, the aim of this experiment was to determine if sensory stimulation can interfere with fatigue-related suppression of spinal cord excitability, and alter fatigue rates during cycling sprints. Thirteen participants randomly performed three experimental sessions that included: unloaded cycling with sensory stimulation ( CONTROL + STIM ), sprints with sensory stimulation ( SPRINT + STIM ) and sprints without stimulation ( SPRINT ). Seven participants also performed a fourth session ( CONTROL ), which consisted of unloaded cycling. During SPRINT and SPRINT + STIM, participants performed seven, 10 s cycling sprints interleaved with 3 min rest. For CONTROL and CONTROL + STIM , participants performed unloaded cycling for ~30 min. During SPRINT + STIM and CONTROL + STIM , participants received patterned sensory stimulation to nerves of the right foot. H-reflexes and M-waves of the right soleus were evoked by stimulation of the tibial nerve at multiple time points throughout exercise. Sensory stimulation facilitated soleus H-reflexes during unloaded cycling, whereas sprints suppressed soleus H-reflexes. While receiving sensory stimulation, there was less suppression of soleus H-reflexes and slowed reduction in average power output, compared to sprints without stimulation. These results demonstrate that sensory stimulation can substantially mitigate the fatiguing effects of sprints.

Vesicle capture, not delivery, scales up neuropeptide storage in neuroendocrine terminals.

PubMed

Bulgari, Dinara; Zhou, Chaoming; Hewes, Randall S; Deitcher, David L; Levitan, Edwin S

2014-03-04

Neurons vary in their capacity to produce, store, and release neuropeptides packaged in dense-core vesicles (DCVs). Specifically, neurons used for cotransmission have terminals that contain few DCVs and many small synaptic vesicles, whereas neuroendocrine neuron terminals contain many DCVs. Although the mechanistic basis for presynaptic variation is unknown, past research demonstrated transcriptional control of neuropeptide synthesis suggesting that supply from the soma limits presynaptic neuropeptide accumulation. Here neuropeptide release is shown to scale with presynaptic neuropeptide stores in identified Drosophila cotransmitting and neuroendocrine terminals. However, the dramatic difference in DCV number in these terminals occurs with similar anterograde axonal transport and DCV half-lives. Thus, differences in presynaptic neuropeptide stores are not explained by DCV delivery from the soma or turnover. Instead, greater neuropeptide accumulation in neuroendocrine terminals is promoted by dramatically more efficient presynaptic DCV capture. Greater capture comes with tradeoffs, however, as fewer uncaptured DCVs are available to populate distal boutons and replenish neuropeptide stores following release. Finally, expression of the Dimmed transcription factor in cotransmitting neurons increases presynaptic DCV capture. Therefore, DCV capture in the terminal is genetically controlled and determines neuron-specific variation in peptidergic function.

Vesicle capture, not delivery, scales up neuropeptide storage in neuroendocrine terminals

PubMed Central

Bulgari, Dinara; Zhou, Chaoming; Hewes, Randall S.; Deitcher, David L.; Levitan, Edwin S.

2014-01-01

Neurons vary in their capacity to produce, store, and release neuropeptides packaged in dense-core vesicles (DCVs). Specifically, neurons used for cotransmission have terminals that contain few DCVs and many small synaptic vesicles, whereas neuroendocrine neuron terminals contain many DCVs. Although the mechanistic basis for presynaptic variation is unknown, past research demonstrated transcriptional control of neuropeptide synthesis suggesting that supply from the soma limits presynaptic neuropeptide accumulation. Here neuropeptide release is shown to scale with presynaptic neuropeptide stores in identified Drosophila cotransmitting and neuroendocrine terminals. However, the dramatic difference in DCV number in these terminals occurs with similar anterograde axonal transport and DCV half-lives. Thus, differences in presynaptic neuropeptide stores are not explained by DCV delivery from the soma or turnover. Instead, greater neuropeptide accumulation in neuroendocrine terminals is promoted by dramatically more efficient presynaptic DCV capture. Greater capture comes with tradeoffs, however, as fewer uncaptured DCVs are available to populate distal boutons and replenish neuropeptide stores following release. Finally, expression of the Dimmed transcription factor in cotransmitting neurons increases presynaptic DCV capture. Therefore, DCV capture in the terminal is genetically controlled and determines neuron-specific variation in peptidergic function. PMID:24550480

CHRONIC HYPERTENSION ENHANCES PRE-SYNAPTIC INHIBITION BY BACLOFEN IN THE NUCLEUS OF THE SOLITARY TRACT

PubMed Central

Zhang, Weirong; Mifflin, Steve

2010-01-01

The selective γ-aminobutyric acid B-subtype receptor agonist baclofen activates both pre- and post-synaptic receptors in the brain. Microinjection of baclofen into the nucleus of the solitary tract increases arterial pressure, heart rate and sympathetic nerve discharge consistent with inhibition of the arterial baroreflex. The magnitude of these responses is enhanced in hypertension and is associated with increased post-synaptic GABAB receptor function. We tested whether a pre-synaptic mechanism contributes to the enhanced baclofen inhibition in hypertension. Whole-cell recordings of second-order baroreceptor neurons, identified by 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide labeling of aortic nerve, were obtained in brainstem slices from normotensive control and renal-wrap hypertensive rats. After 4 weeks, arterial blood pressure was 162±9 mmHg in hypertensive (n=6) and 107±3 mmHg in control rats (n=6/11, p<0.001). Baclofen reduced the amplitude of excitatory post-synaptic currents evoked by solitary tract stimulation and the EC50 of this inhibition was greater in control (1.5±0.5 µmol/L, n=6) than hypertensive cells (0.6±0.1 µmol/L, n=9, p<0.05). Baclofen (1 µmol/L) elicited greater inhibition on evoked response in hypertensive (58±6%, n=9) than control cells (40±6%, n=8, p<0.05). Another index of pre-synaptic inhibition, the paired-pulse ratio (ratio of second to first evoked response amplitudes at stimulus intervals of 40 ms), was greater in hypertensive (0.60±0.08, n=8) than control cells (0.48±0.06. n=5, p<0.05). The results suggest that in renal-wrap hypertensive rats, baclofen causes an enhanced pre-synaptic inhibition of glutamate release from baroreceptor afferent terminals to second-order neurons in the nucleus of the solitary tract. This enhanced pre-synaptic inhibition could contribute to altered baroreflex function in hypertension. PMID:20038748

[Development of the Human Olfactory Bulbs in the Prenatal Ontogenesis: an Immunochistochemical Study with Markers of Presynaptic Terminals (anti-SNAP-25, -Synapsin-I, -Synaptophysin)].

PubMed

Kharlamova, A S; Barabanov, V M; Saveliev, S V

2015-01-01

We provide the data of the olfactory bulbs (OB) development in the human fetuses on the stages from 8 week to birth. Immunochistochemical markers of presynaptic terminals (anti-SNAP-25, -synapsin-I, -synaptophysin) were used to evaluate the maturation of the OB. Differentiation of the OB layers begins from periphery, which implicitly evidences that growth of the olfactory nerves fibers induses not only anatomical differentiation of the OB, but also differentiation of its functional layers. The sites of the developing glomerulus are revealed using the immunochistochemical prosedure on the stage before distinct glomerulus can be identified with common histological procedure. OB conductive system demonstrates immunoreactivity with the antibodies to the presynaptic proteins on the all stages from 10-11 weeks of fetus development. Four stages of the OB development are described. All functional layers of the OB are mature at the 22-weeks stage. Further differentiation of the OB neuroblasts, including lamina formation of the internal granular leyer, glomerular layer development, OB growth continue after 20-22 weeks stage until 38-40 weeks of the fetus develoment. Patterns of the immunoreactivity with antibodies to SNAP-25, synapsin-I and synaptophysin are completely appropriate to those of adult's OB on the 38-40 weeks of the prenatal development. Complete maturity of the human OB is achived at 38-40 weeks of the prenatal development.

GLUT4 Mobilization Supports Energetic Demands of Active Synapses.

PubMed

Ashrafi, Ghazaleh; Wu, Zhuhao; Farrell, Ryan J; Ryan, Timothy A

2017-02-08

The brain is highly sensitive to proper fuel availability as evidenced by the rapid decline in neuronal function during ischemic attacks and acute severe hypoglycemia. We previously showed that sustained presynaptic function requires activity-driven glycolysis. Here, we provide strong evidence that during action potential (AP) firing, nerve terminals rely on the glucose transporter GLUT4 as a glycolytic regulatory system to meet the activity-driven increase in energy demands. Activity at synapses triggers insertion of GLUT4 into the axonal plasma membrane driven by activation of the metabolic sensor AMP kinase. Furthermore, we show that genetic ablation of GLUT4 leads to an arrest of synaptic vesicle recycling during sustained AP firing, similar to what is observed during acute glucose deprivation. The reliance on this biochemical regulatory system for "exercising" synapses is reminiscent of that occurring in exercising muscle to sustain cellular function and identifies nerve terminals as critical sites of proper metabolic control. Copyright © 2017 Elsevier Inc. All rights reserved.

Locomotor training improves premotoneuronal control after chronic spinal cord injury.

PubMed

Knikou, Maria; Mummidisetty, Chaithanya K

2014-06-01

Spinal inhibition is significantly reduced after spinal cord injury (SCI) in humans. In this work, we examined if locomotor training can improve spinal inhibition exerted at a presynaptic level. Sixteen people with chronic SCI received an average of 45 training sessions, 5 days/wk, 1 h/day. The soleus H-reflex depression in response to low-frequency stimulation, presynaptic inhibition of soleus Ia afferent terminals following stimulation of the common peroneal nerve, and bilateral EMG recovery patterns were assessed before and after locomotor training. The soleus H reflexes evoked at 1.0, 0.33, 0.20, 0.14, and 0.11 Hz were normalized to the H reflex evoked at 0.09 Hz. Conditioned H reflexes were normalized to the associated unconditioned H reflex evoked with subjects seated, while during stepping both H reflexes were normalized to the maximal M wave evoked after the test H reflex at each bin of the step cycle. Locomotor training potentiated homosynaptic depression in all participants regardless the type of the SCI. Presynaptic facilitation of soleus Ia afferents remained unaltered in motor complete SCI patients. In motor incomplete SCIs, locomotor training either reduced presynaptic facilitation or replaced presynaptic facilitation with presynaptic inhibition at rest. During stepping, presynaptic inhibition was modulated in a phase-dependent manner. Locomotor training changed the amplitude of locomotor EMG excitability, promoted intralimb and interlimb coordination, and altered cocontraction between knee and ankle antagonistic muscles differently in the more impaired leg compared with the less impaired leg. The results provide strong evidence that locomotor training improves premotoneuronal control after SCI in humans at rest and during walking. Copyright © 2014 the American Physiological Society.

Transmitter release modulation by intracellular Ca2+ buffers in facilitating and depressing nerve terminals of pyramidal cells in layer 2/3 of the rat neocortex indicates a target cell-specific difference in presynaptic calcium dynamics

PubMed Central

Rozov, A; Burnashev, N; Sakmann, B; Neher, E

2001-01-01

In connections formed by nerve terminals of layer 2/3 pyramidal cells onto bitufted interneurones in young (postnatal day (P)14–15) rat somatosensory cortex, the efficacy and reliability of synaptic transmission were low. At these connections release was facilitated by paired-pulse stimulation (at 10 Hz). In connections formed by terminals of layer 2/3 pyramids with multipolar interneurones efficacy and reliability were high and release was depressed by paired-pulse stimulation. In both types of terminal, however, the voltage-dependent Ca2+ channels that controlled transmitter release were predominantly of the P/Q- and N-subtypes. The relationship between unitary EPSP amplitude and extracellular calcium concentration ([Ca2+]o) was steeper for facilitating than for depressing terminals. Fits to a Hill equation with nH= 4 indicated that the apparent KD of the Ca2+ sensor for vesicle release was two- to threefold lower in depressing terminals than in facilitating ones. Intracellular loading of pyramidal neurones with the fast and slowly acting Ca2+ buffers BAPTA and EGTA differentially reduced transmitter release in these two types of terminal. Unitary EPSPs evoked by pyramidal cell stimulation in bitufted cells were reduced by presynaptic BAPTA and EGTA with half-effective concentrations of ∼0.1 and ∼1 mm, respectively. Unitary EPSPs evoked in multipolar cells were reduced to one-half of control at higher concentrations of presynaptic BAPTA and EGTA (∼0.5 and ∼7 mm, respectively). Frequency-dependent facilitation of EPSPs in bitufted cells was abolished by EGTA at concentrations of > 0.2 mm, suggesting that accumulation of free Ca2+ is essential for facilitation in the terminals contacting bitufted cells. In contrast, facilitation was unaffected or even slightly increased in the terminals loaded with BAPTA in the concentration range 0.02–0.5 mm. This is attributed to partial saturation of exogenously added BAPTA. However, BAPTA at concentrations > 1 mm also abolished facilitation. Frequency-dependent depression of EPSPs in multipolar cells was not significantly reduced by EGTA. With BAPTA, the depression decreased at concentrations > 0.5 mm, concomitant with a reduction in amplitude of the first EPSP in a train. An analysis is presented that interprets the effects of EGTA and BAPTA on synaptic efficacy and its short-term modification during paired-pulse stimulation in terms of changes in [Ca2+] at the release site ([Ca2+]RS) and that infers the affinity of the Ca2+ sensor from the dependence of unitary EPSPs on [Ca2+]o. The results suggest that the target cell-specific difference in release from the terminals on bitufted or multipolar cells can be explained by a longer diffusional distance between Ca2+ channels and release sites and/or lower Ca2+ channels density in the terminals that contact bitufted cells. This would lead to a lower [Ca2+] at release sites and would also explain the higher apparent KD of the Ca2+ sensor in facilitating terminals. PMID:11251060

Fusion competent synaptic vesicles persist upon active zone disruption and loss of vesicle docking

PubMed Central

Wang, Shan Shan H.; Held, Richard G.; Wong, Man Yan; Liu, Changliang; Karakhanyan, Aziz; Kaeser, Pascal S.

2016-01-01

In a nerve terminal, synaptic vesicle docking and release are restricted to an active zone. The active zone is a protein scaffold that is attached to the presynaptic plasma membrane and opposed to postsynaptic receptors. Here, we generated conditional knockout mice removing the active zone proteins RIM and ELKS, which additionally led to loss of Munc13, Bassoon, Piccolo, and RIM-BP, indicating disassembly of the active zone. We observed a near complete lack of synaptic vesicle docking and a strong reduction in vesicular release probability and the speed of exocytosis, but total vesicle numbers, SNARE protein levels, and postsynaptic densities remained unaffected. Despite loss of the priming proteins Munc13 and RIM and of docked vesicles, a pool of releasable vesicles remained. Thus, the active zone is necessary for synaptic vesicle docking and to enhance release probability, but releasable vesicles can be localized distant from the presynaptic plasma membrane. PMID:27537483

BDNF and its pro-peptide are stored in presynaptic dense core vesicles in brain neurons

PubMed Central

Dieni, Sandra; Matsumoto, Tomoya; Dekkers, Martijn; Rauskolb, Stefanie; Ionescu, Mihai S.; Deogracias, Ruben; Gundelfinger, Eckart D.; Kojima, Masami; Nestel, Sigrun; Frotscher, Michael

2012-01-01

Although brain-derived neurotrophic factor (BDNF) regulates numerous and complex biological processes including memory retention, its extremely low levels in the mature central nervous system have greatly complicated attempts to reliably localize it. Using rigorous specificity controls, we found that antibodies reacting either with BDNF or its pro-peptide both stained large dense core vesicles in excitatory presynaptic terminals of the adult mouse hippocampus. Both moieties were ∼10-fold more abundant than pro-BDNF. The lack of postsynaptic localization was confirmed in Bassoon mutants, a seizure-prone mouse line exhibiting markedly elevated levels of BDNF. These findings challenge previous conclusions based on work with cultured neurons, which suggested activity-dependent dendritic synthesis and release of BDNF. They instead provide an ultrastructural basis for an anterograde mode of action of BDNF, contrasting with the long-established retrograde model derived from experiments with nerve growth factor in the peripheral nervous system. PMID:22412021

Lateral presynaptic inhibition mediates gain control in an olfactory circuit.

PubMed

Olsen, Shawn R; Wilson, Rachel I

2008-04-24

Olfactory signals are transduced by a large family of odorant receptor proteins, each of which corresponds to a unique glomerulus in the first olfactory relay of the brain. Crosstalk between glomeruli has been proposed to be important in olfactory processing, but it is not clear how these interactions shape the odour responses of second-order neurons. In the Drosophila antennal lobe (a region analogous to the vertebrate olfactory bulb), we selectively removed most interglomerular input to genetically identified second-order olfactory neurons. Here we show that this broadens the odour tuning of these neurons, implying that interglomerular inhibition dominates over interglomerular excitation. The strength of this inhibitory signal scales with total feedforward input to the entire antennal lobe, and has similar tuning in different glomeruli. A substantial portion of this interglomerular inhibition acts at a presynaptic locus, and our results imply that this is mediated by both ionotropic and metabotropic receptors on the same nerve terminal.

Patterns of fast synaptic cholinergic activation of neurons in the celiac ganglia of cats.

PubMed

Niel, J P; Clerc, N; Jule, Y

1988-12-01

Fast nicotinic transmission was studied in vitro in neurons of isolated cat celiac ganglia. In the absence of nerve stimulation, neurons could be classified into three types: silent neurons, synaptically activated neurons, and spontaneously discharging neurons. In all three types, fast synaptic activation could be obtained in single neurons by stimulating with a single pulse both the splanchnic nerves or one of the peripheral nerves connected to the ganglia. During repetitive nerve stimulation, a gradual depression of the central and peripheral fast nicotinic activation occurred, which was not affected by phentolamine plus propranolol, domperidone, atropine, or naloxone. Repetitive nerve stimulation was followed by a long lasting discharge of excitatory postsynaptic potentials and action potentials that decreased gradually with time. This discharge, which was probably due to presynaptic or prejunctional facilitation of acetylcholine release from cholinergic terminals, was reduced by the application of phentolamine plus propranolol, domperidone, or atropine and increased with naloxone. The existence of the mechanisms described in this study reflects the complexity of the integrative processes at work in neurons of the cat celiac ganglia that involve fast synaptic cholinergic activation.

Berberine Inhibits the Release of Glutamate in Nerve Terminals from Rat Cerebral Cortex

PubMed Central

Lu, Cheng-Wei; Huang, Shu-Kuei; Wang, Su-Jane

2013-01-01

Berberine, an isoquinoline plant alkaloid, protects neurons against neurotoxicity. An excessive release of glutamate is considered to be one of the molecular mechanisms of neuronal damage in several neurological diseases. In this study, we investigated whether berberine could affect endogenous glutamate release in nerve terminals of rat cerebral cortex (synaptosomes) and explored the possible mechanism. Berberine inhibited the release of glutamate evoked by the K+ channel blocker 4-aminopyridine (4-AP), and this phenomenon was prevented by the chelating extracellular Ca2+ ions and the vesicular transporter inhibitor bafilomycin A1, but was insensitive to the glutamate transporter inhibitor DL-threo-beta-benzyl-oxyaspartate. Inhibition of glutamate release by berberine was not due to it decreasing synaptosomal excitability, because berberine did not alter 4-AP-mediated depolarization. The inhibitory effect of berberine on glutamate release was associated with a reduction in the depolarization-induced increase in cytosolic free Ca2+ concentration. Involvement of the Cav2.1 (P/Q-type) channels in the berberine action was confirmed by blockade of the berberine-mediated inhibition of glutamate release by the Cav2.1 (P/Q-type) channel blocker ω-agatoxin IVA. In addition, the inhibitory effect of berberine on evoked glutamate release was prevented by the mitogen-activated/extracellular signal-regulated kinase kinase (MEK) inhibitors. Berberine decreased the 4-AP-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and synapsin I, the main presynaptic target of ERK; this decrease was also blocked by the MEK inhibition. Moreover, the inhibitory effect of berberine on evoked glutamate release was prevented in nerve terminals from mice lacking synapsin I. Together, these results indicated that berberine inhibits glutamate release from rats cortical synaptosomes, through the suppression of presynaptic Cav2.1 channels and ERK/synapsin I signaling cascade. This finding may provide further understanding of the mode of berberine action in the brain and highlights the therapeutic potential of this compound in the treatment of a wide range of neurological disorders. PMID:23840629

Regulation of Synaptic Amyloid-β Generation through BACE1 Retrograde Transport in a Mouse Model of Alzheimer's Disease

PubMed Central

Ye, Xuan; Chang, Qing; Jeong, Yu Young; Cai, Huaibin; Kusnecov, Alexander

2017-01-01

Amyloid-β (Aβ) peptides play a key role in synaptic damage and memory deficits in the early pathogenesis of Alzheimer's disease (AD). Abnormal accumulation of Aβ at nerve terminals leads to synaptic pathology and ultimately to neurodegeneration. β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is the major neuronal β-secretase for Aβ generation. However, the mechanisms regulating BACE1 distribution in axons and β cleavage of APP at synapses remain largely unknown. Here, we reveal that dynein–Snapin-mediated retrograde transport regulates BACE1 trafficking in axons and APP processing at presynaptic terminals. BACE1 is predominantly accumulated within late endosomes at the synapses of AD-related mutant human APP (hAPP) transgenic (Tg) mice and patient brains. Defective retrograde transport by genetic ablation of snapin in mice recapitulates late endocytic retention of BACE1 and increased APP processing at presynaptic sites. Conversely, overexpressing Snapin facilitates BACE1 trafficking and reduces synaptic BACE1 accumulation by enhancing the removal of BACE1 from distal AD axons and presynaptic terminals. Moreover, elevated Snapin expression via stereotactic hippocampal injections of adeno-associated virus particles in mutant hAPP Tg mouse brains decreases synaptic Aβ levels and ameliorates synapse loss, thus rescuing cognitive impairments associated with hAPP mice. Altogether, our study provides new mechanistic insights into the complex regulation of BACE1 trafficking and presynaptic localization through Snapin-mediated dynein-driven retrograde axonal transport, thereby suggesting a potential approach of modulating Aβ levels and attenuating synaptic deficits in AD. SIGNIFICANCE STATEMENT β-Site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) trafficking and synaptic localization significantly influence its β secretase activity and amyloid-β (Aβ) production. In AD brains, BACE1 is accumulated within dystrophic neurites, which is thought to augment Aβ-induced synaptotoxicity by Aβ overproduction. However, it remains largely unknown whether axonal transport regulates synaptic APP processing. Here, we demonstrate that Snapin-mediated retrograde transport plays a critical role in removing BACE1 from presynaptic terminals toward the soma, thus reducing synaptic Aβ production. Adeno-associated virus–mediated Snapin overexpression in the hippocampus of mutant hAPP mice significantly decreases synaptic Aβ levels, attenuates synapse loss, and thus rescues cognitive deficits. Our study uncovers a new pathway that controls synaptic APP processing by enhancing axonal BACE1 trafficking, thereby advancing our fundamental knowledge critical for ameliorating Aβ-linked synaptic pathology. PMID:28159908

Neurotransmitter Release Can Be Stabilized by a Mechanism That Prevents Voltage Changes Near the End of Action Potentials from Affecting Calcium Currents

PubMed Central

Clarke, Stephen G.; Scarnati, Matthew S.

2016-01-01

At chemical synapses, presynaptic action potentials (APs) activate voltage-gated calcium channels, allowing calcium to enter and trigger neurotransmitter release. The duration, peak amplitude, and shape of the AP falling phase alter calcium entry, which can affect neurotransmitter release significantly. In many neurons, APs do not immediately return to the resting potential, but instead exhibit a period of depolarization or hyperpolarization referred to as an afterpotential. We hypothesized that presynaptic afterpotentials should alter neurotransmitter release by affecting the electrical driving force for calcium entry and calcium channel gating. In support of this, presynaptic calcium entry is affected by afterpotentials after standard instant voltage jumps. Here, we used the mouse calyx of Held synapse, which allows simultaneous presynaptic and postsynaptic patch-clamp recording, to show that the postsynaptic response is affected significantly by presynaptic afterpotentials after voltage jumps. We therefore tested the effects of presynaptic afterpotentials using simultaneous presynaptic and postsynaptic recordings and AP waveforms or real APs. Surprisingly, presynaptic afterpotentials after AP stimuli did not alter calcium channel responses or neurotransmitter release appreciably. We show that the AP repolarization time course causes afterpotential-induced changes in calcium driving force and changes in calcium channel gating to effectively cancel each other out. This mechanism, in which electrical driving force is balanced by channel gating, prevents changes in calcium influx from occurring at the end of the AP and therefore acts to stabilize synaptic transmission. In addition, this mechanism can act to stabilize neurotransmitter release when the presynaptic resting potential changes. SIGNIFICANCE STATEMENT The shape of presynaptic action potentials (APs), particularly the falling phase, affects calcium entry and small changes in calcium influx can produce large changes in postsynaptic responses. We hypothesized that afterpotentials, which often follow APs, affect calcium entry and neurotransmitter release. We tested this in calyx of Held nerve terminals, which allow simultaneous recording of presynaptic calcium currents and postsynaptic responses. Surprisingly, presynaptic afterpotentials did not alter calcium current or neurotransmitter release. We show that the AP falling phase causes afterpotential-induced changes in electrical driving force and calcium channel gating to cancel each other out. This mechanism regulates calcium entry at the end of APs and therefore stabilizes synaptic transmission. This also stabilizes responses when the presynaptic resting potential changes. PMID:27911759

Neurotransmitter Release Can Be Stabilized by a Mechanism That Prevents Voltage Changes Near the End of Action Potentials from Affecting Calcium Currents.

PubMed

Clarke, Stephen G; Scarnati, Matthew S; Paradiso, Kenneth G

2016-11-09

At chemical synapses, presynaptic action potentials (APs) activate voltage-gated calcium channels, allowing calcium to enter and trigger neurotransmitter release. The duration, peak amplitude, and shape of the AP falling phase alter calcium entry, which can affect neurotransmitter release significantly. In many neurons, APs do not immediately return to the resting potential, but instead exhibit a period of depolarization or hyperpolarization referred to as an afterpotential. We hypothesized that presynaptic afterpotentials should alter neurotransmitter release by affecting the electrical driving force for calcium entry and calcium channel gating. In support of this, presynaptic calcium entry is affected by afterpotentials after standard instant voltage jumps. Here, we used the mouse calyx of Held synapse, which allows simultaneous presynaptic and postsynaptic patch-clamp recording, to show that the postsynaptic response is affected significantly by presynaptic afterpotentials after voltage jumps. We therefore tested the effects of presynaptic afterpotentials using simultaneous presynaptic and postsynaptic recordings and AP waveforms or real APs. Surprisingly, presynaptic afterpotentials after AP stimuli did not alter calcium channel responses or neurotransmitter release appreciably. We show that the AP repolarization time course causes afterpotential-induced changes in calcium driving force and changes in calcium channel gating to effectively cancel each other out. This mechanism, in which electrical driving force is balanced by channel gating, prevents changes in calcium influx from occurring at the end of the AP and therefore acts to stabilize synaptic transmission. In addition, this mechanism can act to stabilize neurotransmitter release when the presynaptic resting potential changes. The shape of presynaptic action potentials (APs), particularly the falling phase, affects calcium entry and small changes in calcium influx can produce large changes in postsynaptic responses. We hypothesized that afterpotentials, which often follow APs, affect calcium entry and neurotransmitter release. We tested this in calyx of Held nerve terminals, which allow simultaneous recording of presynaptic calcium currents and postsynaptic responses. Surprisingly, presynaptic afterpotentials did not alter calcium current or neurotransmitter release. We show that the AP falling phase causes afterpotential-induced changes in electrical driving force and calcium channel gating to cancel each other out. This mechanism regulates calcium entry at the end of APs and therefore stabilizes synaptic transmission. This also stabilizes responses when the presynaptic resting potential changes. Copyright © 2016 the authors 0270-6474/16/3611559-14$15.00/0.

The effect of coniine on presynaptic nicotinic receptors.

PubMed

Erkent, Ulkem; Iskit, Alper B; Onur, Rustu; Ilhan, Mustafa

2016-01-01

Toxicity of coniine, an alkaloid of Conium maculatum (poison hemlock), is manifested by characteristic nicotinic clinical signs including excitement, depression, hypermetria, seizures, opisthotonos via postsynaptic nicotinic receptors. There is limited knowledge about the role of presynaptic nicotinic receptors on the pharmacological and toxicological effects of coniine in the literature. The present study was undertaken to evaluate the possible role of presynaptic nicotinic receptors on the pharmacological and toxicological effects of coniine. For this purpose, the rat anococcygeus muscle and guinea-pig atria were used in vitro. Nicotine (100 μM) elicited a biphasic response composed of a relaxation followed by contraction through the activation of nitrergic and noradrenergic nerve terminals in the phenylephrine-contracted rat anococcygeus muscle. Coniine inhibited both the nitrergic and noradrenergic response in the muscle (-logIC(50) = 3.79 ± 0.11 and -logIC(50) = 4.57 ± 0.12 M, respectively). The effect of coniine on nicotinic receptor-mediated noradrenergic transmission was also evaluated in the guinea-pig atrium (-logIC(50) = 4.47 ± 0.12 M) and did not differ from the -logIC(50) value obtained in the rat anococcygeus muscle. This study demonstrated that coniine exerts inhibitory effects on nicotinic receptor-mediated nitrergic and noradrenergic transmitter response.

The release of acetylcholine from post-ganglionic cell bodies in response to depolarization.

PubMed Central

Johnson, D A; Pilar, G

1980-01-01

1. Acetylcholine (Ach) release from parasympathetic ganglia cell somata was investigated in denervated avian ciliary ganglia. Three days after the input to the ganglion (the oculomotor nerve) was sectioned, all presynaptic nerve terminals had degenerated. 2. Denervated ganglia were shown to contain endogenous ACh and to be capable of synthesizing [3H]ACh from [3H]choline added to the incubation medium. 3. In response to depolarization induced by incubation in 50 mM-[K+]o, denervated ganglia released [3H]ACh into bath effluents in amounts approximately 15% of the non-denervated contralateral control. This release was shown to be Ca2+ dependent in both intact and denervated ganglia. 4. Antidromic electrical stimulation of ciliary nerves also elicited [3H]ACh release. Nicotine (1 microgram/microliter.) depolarized denervated ciliary ganglion cells and evoked release of the transmitter and this release was antagonized by curare. 5. It is concluded that the ganglionic cell bodies sysnthesized ACh and released the transmitter in response to K+ depolarization, antidromic stimulation and cholinergic agonists, despite the lack of morphological specializations usually associated with stimulus-induced release of neurotransmitter. The evidence suggests the existence of a mechanism of transmitter release which is Ca2+ dependent, probably from a cytoplasmic pool and therefore distinct from the usual vesicular release at the nerve terminal. Images Plate 1 Plate 2 PMID:6247485

Presynaptic muscarinic receptors, calcium channels, and protein kinase C modulate the functional disconnection of weak inputs at polyinnervated neonatal neuromuscular synapses.

PubMed

Santafe, M M; Garcia, N; Lanuza, M A; Tomàs, M; Besalduch, N; Tomàs, J

2009-04-01

We studied the relation among calcium inflows, voltage-dependent calcium channels (VDCC), presynaptic muscarinic acetylcholine receptors (mAChRs), and protein kinase C (PKC) activity in the modulation of synapse elimination. We used intracellular recording to determine the synaptic efficacy in dually innervated endplates of the levator auris longus muscle of newborn rats during axonal competition in the postnatal synaptic elimination period. In these dual junctions, the weak nerve terminal was potentiated by partially reducing calcium entry (P/Q-, N-, or L-type VDCC-specific block or 500 muM magnesium ions), M1- or M4-type selective mAChR block, or PKC block. Moreover, reducing calcium entry or blocking PKC or mAChRs results in unmasking functionally silent nerve endings that now recover neurotransmitter release. Our results show interactions between these molecules and indicate that there is a release inhibition mechanism based on an mAChR-PKC-VDCC intracellular cascade. When it is fully active in certain weak motor axons, it can depress ACh release and even disconnect synapses. We suggest that this mechanism plays a central role in the elimination of redundant neonatal synapses, because functional axonal withdrawal can indeed be reversed by mAChRs, VDCCs, or PKC block.

Ferulic Acid Suppresses Glutamate Release Through Inhibition of Voltage-Dependent Calcium Entry in Rat Cerebrocortical Nerve Terminals

PubMed Central

Lin, Tzu Yu; Lu, Cheng Wei; Huang, Shu-Kuei

2013-01-01

Abstract This study investigated the effects and possible mechanism of ferulic acid, a naturally occurring phenolic compound, on endogenous glutamate release in the nerve terminals of the cerebral cortex in rats. Results show that ferulic acid inhibited the release of glutamate evoked by the K+ channel blocker 4-aminopyridine (4-AP). The effect of ferulic acid on the evoked glutamate release was prevented by chelating the extracellular Ca2+ ions, but was insensitive to the glutamate transporter inhibitor DL-threo-beta-benzyl-oxyaspartate. Ferulic acid suppressed the depolarization-induced increase in a cytosolic-free Ca2+ concentration, but did not alter 4-AP–mediated depolarization. Furthermore, the effect of ferulic acid on evoked glutamate release was abolished by blocking the Cav2.2 (N-type) and Cav2.1 (P/Q-type) channels, but not by blocking ryanodine receptors or mitochondrial Na+/Ca2+ exchange. These results show that ferulic acid inhibits glutamate release from cortical synaptosomes in rats through the suppression of presynaptic voltage-dependent Ca2+ entry. PMID:23342970

Lycopene depresses glutamate release through inhibition of voltage-dependent Ca2+ entry and protein kinase C in rat cerebrocortical nerve terminals.

PubMed

Lu, Cheng-Wei; Hung, Chi-Feng; Jean, Wei-Horng; Lin, Tzu-Yu; Huang, Shu-Kuei; Wang, Su-Jane

2018-05-01

Lycopene is a natural dietary carotenoid that was reported to exhibit a neuroprotective profile. Considering that excitotoxicity and cell death induced by glutamate are involved in many brain disorders, the effect of lycopene on glutamate release in rat cerebrocortical nerve terminals and the possible mechanism involved in such effect was investigated. We observed here that lycopene inhibited 4-aminopyridine (4-AP)-evoked glutamate release and intrasynaptosomal Ca 2+ concentration elevation. The inhibitory effect of lycopene on 4-AP-evoked glutamate release was markedly reduced in the presence of the Ca v 2.2 (N-type) and Ca v 2.1 (P/Q-type) channel blocker ω-conotoxin MVIIC, but was insensitive to the intracellular Ca 2+ -release inhibitors dantrolene and CGP37157. Furthermore, in the presence of the protein kinase C inhibitors GF109203X and Go6976, the action of lycopene on evoked glutamate release was prevented. These results are the first to suggest that lycopene inhibits glutamate release from rat cortical synaptosomes by suppressing presynaptic Ca 2+ entry and protein kinase C activity.

Characterization and regulation of (/sup 3/H)-serotonin uptake and release in rodent spinal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stauderman, K.A.

1986-01-01

The uptake and release of (/sup 3/H)-serotonin were investigated in rat spinal cord synaptosomes. In the uptake experiments, sodium-dependent and sodium-independent (/sup 3/H)-serotonin accumulation processes were found. Sodium-dependent (/sup 3/H)-serotonin accumulation was: linear with sodium concentrations up to 180 mM; decreased by disruption of membrane integrity or ionic gradients; associated with purified synaptosomal fractions; and reduced after description of descending serotonergic neurons in the spinal cord. Of the uptake inhibitors tested, the most potent was fluoxetine (IC/sub 50/ 75 nM), followed by desipramine (IC/sub 50/ 430 nM) and nomifensine (IC/sub 50/ 950 nM). The sodium-independent (/sup 3/H)-serotonin accumulation process wasmore » insensitive to most treatments and probably represents nonspecific membrane binding. Thus, only sodium-dependent (/sup 3/H)-serotonin uptake represents the uptake process of serotonergic nerve terminals in rat spinal cord homogenates. In the release experiments, K/sup +/-induced release of previously accumulated (/sup 3/H)-serotonin was Ca/sup 2 +/-dependent, and originated from serotonergic synaptosomes. Exogenous serotonin and 5-methyoxy-N,N-dimethyltryptamine inhibited (/sup 3/H)-serotonin release in a concentration-dependent way. Of the antagonists tested, only methiothepin effectively blocked the effect of serotonin. These data support the existence of presynaptic serotonin autoreceptors on serotonergic nerve terminals in the rat spinal cord that act to inhibit a voltage and Ca/sup 2 +/-sensitive process linked to serotonin release. Alteration of spinai cord serotonergic function may therefore be possible by drugs acting on presynaptic serotonin autoreceptors in the spinal cord.« less

Presynaptic and postsynaptic effects of local cathodal DC polarization within the spinal cord in anaesthetized animal preparations

PubMed Central

Bolzoni, F; Jankowska, E

2015-01-01

The present study aimed to compare presynaptic and postsynaptic actions of direct current polarization in the spinal cord, focusing on DC effects on primary afferents and motoneurons. To reduce the directly affected spinal cord region, a weak polarizing direct current (0.1–0.3 μA) was applied locally in deeply anaesthetized cats and rats; within the hindlimb motor nuclei in the caudal lumbar segments, or in the dorsal horn within the terminal projection area of low threshold skin afferents. Changes in the excitability of primary afferents activated by intraspinal stimuli (20–50 μA) were estimated using increases or decreases in compound action potentials recorded from the dorsal roots or peripheral nerves as their measure. Changes in the postsynaptic actions of the afferents were assessed from intracellularly recorded monosynaptic EPSPs in hindlimb motoneurons and monosynaptic extracellular field potentials (evoked by group Ia afferents in motor nuclei, or by low threshold cutaneous afferents in the dorsal horn). The excitability of motoneurons activated by intraspinal stimuli was assessed using intracellular records or motoneuronal discharges recorded from a ventral root or a muscle nerve. Cathodal polarization was found to affect motoneurons and afferents providing input to them to a different extent. The excitability of both was markedly increased during DC application, although post-polarization facilitation was found to involve presynaptic afferents and some of their postsynaptic actions, but only negligibly motoneurons themselves. Taken together, these results indicate that long-lasting post-polarization facilitation of spinal activity induced by locally applied cathodal current primarily reflects the facilitation of synaptic transmission. PMID:25416625

Activity Induces Fmr1-Sensitive Synaptic Capture of Anterograde Circulating Neuropeptide Vesicles

PubMed Central

Cavolo, Samantha L.; Bulgari, Dinara; Deitcher, David L.

2016-01-01

Synaptic neuropeptide and neurotrophin stores are maintained by constitutive bidirectional capture of dense-core vesicles (DCVs) as they circulate in and out of the nerve terminal. Activity increases DCV capture to rapidly replenish synaptic neuropeptide stores following release. However, it is not known whether this is due to enhanced bidirectional capture. Here experiments at the Drosophila neuromuscular junction, where DCVs contain neuropeptides and a bone morphogenic protein, show that activity-dependent replenishment of synaptic neuropeptides following release is evident after inhibiting the retrograde transport with the dynactin disruptor mycalolide B or photobleaching DCVs entering a synaptic bouton by retrograde transport. In contrast, photobleaching anterograde transport vesicles entering a bouton inhibits neuropeptide replenishment after activity. Furthermore, tracking of individual DCVs moving through boutons shows that activity selectively increases capture of DCVs undergoing anterograde transport. Finally, upregulating fragile X mental retardation 1 protein (Fmr1, also called FMRP) acts independently of futsch/MAP-1B to abolish activity-dependent, but not constitutive, capture. Fmr1 also reduces presynaptic neuropeptide stores without affecting activity-independent delivery and evoked release. Therefore, presynaptic motoneuron neuropeptide storage is increased by a vesicle capture mechanism that is distinguished from constitutive bidirectional capture by activity dependence, anterograde selectivity, and Fmr1 sensitivity. These results show that activity recruits a separate mechanism than used at rest to stimulate additional synaptic capture of DCVs for future release of neuropeptides and neurotrophins. SIGNIFICANCE STATEMENT Synaptic release of neuropeptides and neurotrophins depends on presynaptic accumulation of dense-core vesicles (DCVs). At rest, DCVs are captured bidirectionally as they circulate through Drosophila motoneuron terminals by anterograde and retrograde transport. Here we show that activity stimulates further synaptic capture that is distinguished from basal capture by its selectivity for anterograde DCVs and its inhibition by overexpression of the fragile X retardation protein Fmr1. Fmr1 dramatically lowers DCV numbers in synaptic boutons. Therefore, activity-dependent anterograde capture is a major determinant of presynaptic peptide stores. PMID:27852784

Short-term effects of beta-amyloid25-35 peptide aggregates on transmitter release in neuromuscular synapses.

PubMed

Garcia, Neus; Santafé, Manel M; Tomàs, Marta; Lanuza, Maria A; Tomàs, Josep

2008-03-01

The beta-amyloid (AB) peptide25-35 contains the functional domain of the AB precursor protein that is both required for neurotrophic effects in normal neural tissues and is involved in the neurotoxic effects in Alzheimer disease. We demonstrated the presence of the amyloid precursor protein/AB peptide in intramuscular axons, presynaptic motor nerve terminals, terminal and myelinating Schwann cells, and the postsynaptic and subsarcolemmal region in the Levator auris longus muscle of adult rats by immunocytochemistry. Using intracellular recording, we investigated possible short-term functional effects of the AB fragment (0.1-10 micromol/L) on acetylcholine release in adult and newborn motor end plates. We found no change in evoked, spontaneous transmitter release or resting membrane potential of the muscle cells. A previous block of the presynaptic muscarinic receptor subtypes and a previous block or stimulation of protein kinase C revealed no masked effect of the peptide on the regulation of transmitter release. The aggregated form of AB peptide25-35, however, interfered acutely with acetylcholine release (quantal content reduction) when synaptic activity was maintained by electric stimulation. The possible relevance of this inhibition of neurotransmission by AB peptide25-35 to the pathogenesis of Alzheimer remains to be determined.

Functional maturation of motor nerve terminals in the avian iris: ultrastructure, transmitter metabolism and synaptic reliability

PubMed Central

Pilar, Guillermo; Tuttle, Jeremy; Vaca, Ken

1981-01-01

1. The transformation of easily fatigued embryonic neuromuscular junctions into highly reliable mature terminals was examined by studying functional and morphological changes during development of the avian iris. The mature ability to follow repetitive electrical nerve stimulation was correlated with the rate of acetylcholine (ACh) synthesis and choline uptake, and with the fine structure of the nerve terminals and the post-synaptic elements. 2. The terminals of the ciliary nerve of the chick initially form functional synaptic contacts with the iris muscle at embryonic St. 34-40. At the onset of this period, no Na+-dependent high affinity choline uptake can be demonstrated, and the low level of ACh synthesis present is sensitive to Na+ removal. At St. 36 [3H]ACh synthesis begins to increase, the increment being Na+-dependent. 3. ACh synthesis in the embryonic iris was insensitive to a conditioning [K+]o depolarization even as late as St. 43. Just before hatching, depolarization elicits some augmentation in synthesis, but by 2 days ex ovo this release-induced response has increased by an order of magnitude. 4. Concurrently with the acquisition of the ability to respond to depolarization with accelerated synthesis, neuromuscular transmission in the iris becomes reliable and secure during stimulation at 20 Hz. Embryonic junctions rapidly block during such stimulation, and the failure is shown to be presynaptic in origin, resulting most probably from failure to sustain adequate levels of transmitter release. 5. Ultrastructural examination of the developing ciliary terminals revealed few synaptic vesicles at early stages, and a dearth of other specializations. The sequence of development from these small structurally undistinguished endings to large en plaque junctions completely filled with vesicles was reconstructed and compared to other neuromuscular junctions. Morphological maturation appears progressive with little evidence of discontinuity signalling functional status, but it is only after the terminals enlarge and become closely packed with vesicles that mature synaptic reliability is found. 6. The temporal correlation between responsiveness of transmitter synthesis to depolarization and reliable neuromuscular transmission suggests that modulation of neurotransmitter metabolism in response to demand signals the achievement of junctional maturity. ImagesABPlate 2Plate 3Plate 4 PMID:6279822

Presynaptic neurones may contribute a unique glycoprotein to the extracellular matrix at the synapse

NASA Astrophysics Data System (ADS)

Caroni, Pico; Carlson, Steven S.; Schweitzer, Erik; Kelly, Regis B.

1985-04-01

As the extracellular matrix at the original site of a neuromuscular junction seems to play a major part in the specificity of synaptic regeneration1-5, considerable attention has been paid to unique molecules localized to this region6-11. Here we describe an extracellular matrix glycoprotein of the elasmobranch electric organ that is localized near the nerve endings. By immunological criteria, it is synthesized in the cell bodies, transported down the axons and is related to a glycoprotein in the synaptic vesicles of the neurones that innervate the electric organ. It is apparently specific for these neurones, as it cannot be detected elsewhere in the nervous system of the fish. Therefore, neurones seem to contribute unique extracellular matrix glycoproteins to the synaptic region. Synaptic vesicles could be involved in transporting these glycoproteins to or from the nerve terminal surface.

Endogenous cannabinoids mediate retrograde signals from depolarized postsynaptic neurons to presynaptic terminals.

PubMed

Ohno-Shosaku, T; Maejima, T; Kano, M

2001-03-01

Endogenous cannabinoids are considered to function as diffusible and short-lived modulators that may transmit signals retrogradely from postsynaptic to presynaptic neurons. To evaluate this possibility, we have made a paired whole-cell recording from cultured hippocampal neurons with inhibitory synaptic connections. In about 60% of pairs, a cannabinoid agonist greatly reduced the release of the inhibitory neurotransmitter GABA from presynaptic terminals. In most of such pairs but not in those insensitive to the agonist, depolarization of postsynaptic neurons and the resultant elevation of intracellular Ca2+ concentration caused transient suppression of inhibitory synaptic currents, which is mainly due to reduction of GABA release. This depolarization-induced suppression was completely blocked by selective cannabinoid antagonists. Our results reveal that endogenous cannabinoids mediate retrograde signals from depolarized postsynaptic neurons to presynaptic terminals to cause the reduction of transmitter release.

Schwann Cells in Neuromuscular Junction Formation and Maintenance.

PubMed

Barik, Arnab; Li, Lei; Sathyamurthy, Anupama; Xiong, Wen-Cheng; Mei, Lin

2016-09-21

The neuromuscular junction (NMJ) is a tripartite synapse that is formed by motor nerve terminals, postjunctional muscle membranes, and terminal Schwann cells (TSCs) that cover the nerve-muscle contact. NMJ formation requires intimate communications among the three different components. Unlike nerve-muscle interaction, which has been well characterized, less is known about the role of SCs in NMJ formation and maintenance. We show that SCs in mice lead nerve terminals to prepatterned AChRs. Ablating SCs at E8.5 (i.e., prior nerve arrival at the clusters) had little effect on aneural AChR clusters at E13.5, suggesting that SCs may not be necessary for aneural clusters. SC ablation at E12.5, a time when phrenic nerves approach muscle fibers, resulted in smaller and fewer nerve-induced AChR clusters; however, SC ablation at E15.5 reduced AChR cluster size but had no effect on cluster density, suggesting that SCs are involved in AChR cluster maturation. Miniature endplate potential amplitude, but not frequency, was reduced when SCs were ablated at E15.5, suggesting that postsynaptic alterations may occur ahead of presynaptic deficits. Finally, ablation of SCs at P30, after NMJ maturation, led to NMJ fragmentation and neuromuscular transmission deficits. Miniature endplate potential amplitude was reduced 3 d after SC ablation, but both amplitude and frequency were reduced 6 d after. Together, these results indicate that SCs are not only required for NMJ formation, but also necessary for its maintenance; and postsynaptic function and structure appeared to be more sensitive to SC ablation. Neuromuscular junctions (NMJs) are critical for survival and daily functioning. Defects in NMJ formation during development or maintenance in adulthood result in debilitating neuromuscular disorders. The role of Schwann cells (SCs) in NMJ formation and maintenance was not well understood. We genetically ablated SCs during development and after NMJ formation to investigate the consequences of the ablation. This study reveals a critical role of SCs in NMJ formation as well as maintenance. Copyright © 2016 the authors 0270-6474/16/369770-12$15.00/0.

Differentiation in the effects of the angiotensin II receptor blocker class on autonomic function.

PubMed

Esler, Murray

2002-06-01

Measurement of regional sympathetic activity with nerve recording and noradrenaline spillover isotope dilution techniques demonstrates activation of the sympathetic nerves of the heart, kidneys and skeletal muscle vasculature in younger patients with essential hypertension. Sympathetic overactivity in the renal sympathetic outflow is a prominent pathophysiological feature in obesity-related hypertensives of any age. This increase in sympathetic activity is thought to both initiate and sustain the blood pressure elevation, and, in addition, contributes to adverse cardiovascular events. Sympathetic overactivity seems to particularly influence systolic pressure, by increasing the rate of left ventricular ejection, by reducing arterial compliance through increasing neural arterial tone, and via arteriolar vasoconstriction, by promoting rebound of the reflected arterial wave from the periphery. Inhibition of the renin-angiotensin system in certain circumstances appears to be able to reduce sympathetic nervous activity. Claims have been made for such an action at virtually every site in the sympathetic neuraxis. In reality, renin-angiotensin actions on the sympathetic nervous system are probably much more circumscribed than this, with the case perhaps being strongest for a presynaptic action of angiotensin on sympathetic nerves, to augment noradrenaline release. The ability of angiotensin receptor blockers to antagonize neural presynaptic angiotensin AT1 receptors appears to differ markedly between the individual agents in this drug class. In experimental models, such as the pithed rat, neural presynaptic actions are particularly evident with eprosartan. In a blinded study of crossover design, the effects of eprosartan and losartan on sympathetic nerve firing, measured by microneurography, and whole body noradrenaline spillover to plasma is currently being measured in patients with essential hypertension. A reduction in noradrenaline spillover disproportionate to any possible fall in nerve firing would document the presence of presynaptic antagonism of noradrenaline release.

PACAP/PAC1R signaling modulates acetylcholine release at neuronal nicotinic synapses

PubMed Central

Pugh, Phyllis C.; Jayakar, Selwyn S.; Margiotta, Joseph F.

2009-01-01

Neuropeptides collaborate with conventional neurotransmitters to regulate synaptic output. Pituitary adenylate cyclase-activating polypeptide (PACAP) co-localizes with acetylcholine in presynaptic nerve terminals, is released by stimulation, and enhances nicotinic acetylcholine receptor- (nAChR-) mediated responses. Such findings implicate PACAP in modulating nicotinic neurotransmission, but relevant synaptic mechanisms have not been explored. We show here that PACAP acts via selective high-affinity G-protein coupled receptors (PAC1Rs) to enhance transmission at nicotinic synapses on parasympathetic ciliary ganglion (CG) neurons by rapidly and persistently increasing the frequency and amplitude of spontaneous, impulse-dependent nicotinic excitatory postsynaptic currents (sEPSCs). Of the canonical adenylate cyclase (AC) and phospholipase-C (PLC) transduction cascades stimulated by PACAP/PAC1R signaling, only AC-generated signals are critical for synaptic modulation since the increases in sEPSC frequency and amplitude were mimicked by 8-Bromo-cAMP, blocked by inhibiting AC or cAMP-dependent protein kinase (PKA), and unaffected by inhibiting PLC. Despite its ability to increase agonist-induced nAChR currents, PACAP failed to influence nAChR-mediated impulse-independent miniature EPSC amplitudes (quantal size). Instead, evoked transmission assays reveal that PACAP/PAC1R signaling increased quantal content, indicating it modulates synaptic function by increasing vesicular ACh release from presynaptic terminals. Lastly, signals generated by the retrograde messenger, nitric oxide- (NO-) are critical for the synaptic modulation since the PACAP-induced increases in spontaneous EPSC frequency, amplitude and quantal content were mimicked by NO donor and absent after inhibiting NO synthase (NOS). These results indicate that PACAP/PAC1R activation recruits AC-dependent signaling that stimulates NOS to increase NO production and control presynaptic transmitter output at neuronal nicotinic synapses. PMID:19958833

Ethanol Mediated Inhibition of Synaptic Vesicle Recycling at Amygdala Glutamate Synapses Is Dependent upon Munc13-2

PubMed Central

Gioia, Dominic A.; Alexander, Nancy; McCool, Brian A.

2017-01-01

Chronic exposure to alcohol produces adaptations within the basolateral amygdala (BLA) that are associated with the development of anxiety-like behaviors during withdrawal. In part, these adaptations are mediated by plasticity in glutamatergic synapses occurring through an AMPA receptor mediated form of post-synaptic facilitation in addition to a unique form of presynaptic facilitation. In comparison to the post-synaptic compartment, relatively less is understood about the mechanisms involved in the acute and chronic effects of ethanol in the presynaptic terminal. Previous research has demonstrated that glutamatergic terminals in the mouse BLA are sensitive to ethanol mediated inhibition of synaptic vesicle recycling in a strain-dependent fashion. Importantly, the strain-dependent differences in presynaptic ethanol sensitivity are in accordance with known strain-dependent differences in ethanol/anxiety interactions. In the present study, we have used a short-hairpin RNA to knockdown the expression of the presynaptic Munc13-2 protein in C57BL/6J mice, whose BLA glutamate terminals are normally ethanol-insensitive. We injected this shRNA, or a scrambled control virus, into the medial prefrontal cortex (mPFC) which sends dense projections to the BLA. Accordingly, this knockdown strategy reduces the expression of the Munc13-2 isoform in mPFC terminals within the BLA and alters presynaptic terminal function in C57BL/6J mice in a manner that phenocopies DBA/2J glutamate terminals which are normally ethanol-sensitive. Here, we provide evidence that manipulation of this single protein, Munc13-2, renders C57BL/6J terminals sensitive to ethanol mediated inhibition of synaptic vesicle recycling and post-tetanic potentiation. Furthermore, we found that this ethanol inhibition was dose dependent. Considering the important role of Munc13 proteins in synaptic plasticity, this study potentially identifies a molecular mechanism regulating the acute presynaptic effects of ethanol to the long lasting adaptations in the BLA that occur during chronic ethanol exposure. PMID:28785200

Central projections and entries of capsaicin-sensitive muscle afferents.

PubMed

Della Torre, G; Lucchi, M L; Brunetti, O; Pettorossi, V E; Clavenzani, P; Bortolami, R

1996-03-25

The entry pathway and central distribution of A delta and C muscle afferents within the central nervous system (CNS) were investigated by combining electron microscopy and electrophysiological analysis after intramuscular injection of capsaicin. The drug was injected into the rat lateral gastrocnemius (LG) and extraocular (EO) muscles. The compound action potentials of LG nerve and the evoked field potentials recorded in semilunar ganglion showed an immediate and permanent reduction in A delta and C components. The morphological data revealed degenerating unmyelinated axons and terminals in the inner sublamina II and in the border of laminae I-II of the dorsal horn at L4-L5 and C1-C2 (subnucleus caudalis trigemini) spinal cord segments. Most degenerating terminals were the central bouton (C) of type I and II synaptic glomeruli. Furthermore, degenerating peripheral axonal endings (V2) presynaptic to normal C were found. Since V2 were previously found degenerated after cutting the oculomotor nerve (ON) or L4 ventral root, we conclude that some A delta and C afferents from LG and EO muscles entering the CNS by ON or ventral roots make axoaxonic synapses on other primary afferents to promote an afferent control of sensory input.

Acute effects of moclobemide and deprenyl on 5-HT synthesis rates in the rat brain: An autoradiographic study.

PubMed

Nishi, Kyoko; Mück-Seler, Dorotea; Hasegawa, Shu; Watanabe, Arata; Diksic, Mirko

2006-10-16

Serotonin (5-HT), norepinephrine (NE) and dopamine (DA) released from nerve terminals in the brain are primarily removed from the synaptic cleft by a reuptake mechanism. In part, the homeostasis is maintained by monoamine oxidase (MAO) deamination achieved primarily intracellularly. The present study's aim was to examine the effect of the acute administration of the MAO inhibitors, moclobemide (a MAO-A inhibitor) and deprenyl (a MAO-B inhibitor), on 5-HT synthesis rates, measured in discrete regions of the rat brain by an autoradiographic method, using alpha-[14C]methyl-l-tryptophan as a tracer. MAO inhibitors have different effects on 5-HT synthesis rates in the cell bodies and areas of the nerve terminals. Moclobemide (10 mg/kg, i.p. 30 min before the tracer injection) and deprenyl (3 mg/kg, i.p. 2 h before the tracer injection) decreased the 5-HT synthesis rates in the dorsal (-18% and -22%) and median (-22% and -33%) raphe, respectively. Moclobemide also significantly decreased 5-HT synthesis in the entire nerve terminal areas investigated. The reductions were between 23% (cingulate cortex) and 50% (locus coeruleus). Deprenyl did not significantly affect 5-HT synthesis in the nerve terminals. The present results suggest that MAO-A, and to a lesser extent, MAO-B, are involved in the regulation of 5-HT synthesis in the rat brain. The mechanism(s) of MAO inhibitors' action on 5-HT synthesis in the raphe nuclei are probably related to an increase in the extraneuronal 5-HT concentration and also to the interaction between the serotonergic and catecholaminergic neurons. The reduction of 5-HT synthesis in the raphe nuclei likely occurs by an action of extracellular 5-HT via the dendritic autoreceptors with a possible contribution from the action of extracellular DA and NE. In the terminal regions, the most likely mechanism is via the presynaptic autoreceptors through which elevated extraneuronal 5-HT acts on synthesis control. However, there is also a possibility that the elevation in intraneuronal 5-HT directly inhibits its synthesis, especially following deprenyl treatment. A great influence of moclobemide on 5-HT synthesis could be related to its antidepressant action.

[Effect of trimebutine on cholinergic transmission in neurons of the inferior mesenteric ganglion of the rabbit].

PubMed

Julé, Y

1987-01-01

We analyzed the effects of trimebutine on the synaptic activity of neurons of the rabbit inferior mesenteric ganglion, using intracellular recording techniques. The synaptic activity was produced by subthreshold stimuli (0.5 Hz) applied individually, on lumbar splanchnic and lumbar colonic nerves. These stimuli triggered cholinergic responses corresponding to fast excitatory postsynaptic potentials. In 8 of 20 neurones tested trimebutine (10(-6) g/ml) produced an inhibition of excitatory postsynaptic potentials, without any change in the resting membrane potential. In 6 of 20 neurons tested, trimebutine produced, successively, an early facilitation followed by a late inhibition of excitatory postsynaptic potentials. Both effects occurred without change in the resting membrane potential. The inhibitory and facilitatory effects of trimebutine were accompanied, by an increase and a decrease in the number of failures of nerve stimulation respectively. These results indicate that inhibitory and facilitatory effects of trimebutine correspond respectively to a decrease and an increase in the amount of acetylcholine released from presynaptic nerve terminals originating from the spinal cord and the distal colon.

Actions of Acute and Chronic Ethanol on Presynaptic Terminals

PubMed Central

Roberto, Marisa; Treistman, Steven N.; Pietrzykowski, Andrzej Z.; Weiner, Jeff; Galindo, Rafael; Mameli, Manuel; Valenzuela, Fernando; Zhu, Ping Jun; Lovinger, David; Zhang, Tao A.; Hendricson, Adam H.; Morrisett, Richard; Siggins, George Robert

2014-01-01

This article presents the proceedings of a symposium entitled “The Tipsy Terminal: Presynaptic Effects of Ethanol” (held at the annual meeting of the Research Society on Alcoholism, in Santa Barbara, CA, June 27, 2005). The objective of this symposium was to focus on a cellular site of ethanol action underrepresented in the alcohol literature, but quickly becoming a “hot” topic. The chairs of the session were Marisa Roberto and George Robert Siggins. Our speakers were chosen on the basis of the diverse electrophysiological and other methods used to discern the effects of acute and chronic ethanol on presynaptic terminals and on the basis of significant insights that their data provide for understanding ethanol actions on neurons in general, as mechanisms underlying problematic behavioral effects of alcohol. The 5 presenters drew from their recent studies examining the effects of acute and chronic ethanol using a range of sophisticated methods from electrophysiological analysis of paired-pulse facilitation and spontaneous and miniature synaptic currents (Drs. Weiner, Valenzuela, Zhu, and Morrisett), to direct recording of ion channel activity and peptide release from acutely isolated synaptic terminals (Dr. Treistman), to direct microscopic observation of vesicular release (Dr. Morrisett). They showed that ethanol administration could both increase and decrease the probability of release of different transmitters from synaptic terminals. The effects of ethanol on synaptic terminals could often be correlated with important behavioral or developmental actions of alcohol. These and other novel findings suggest that future analyses of synaptic effects of ethanol should attempt to ascertain, in multiple brain regions, the role of presynaptic terminals, relevant presynaptic receptors and signal transduction linkages, exocytotic mechanisms, and their involvement in alcohol’s behavioral actions. Such studies could lead to new treatment strategies for alcohol intoxication, alcohol abuse, and alcoholism. PMID:16441271

Neurotrophin trafficking by anterograde transport.

PubMed

Altar, C A; DiStefano, P S

1998-10-01

The ever-unfolding biology of NGF is consistent with a target-derived retrograde mode of action in peripheral and central neurons. However, another member of the neurotrophin family, brain-derived neurotrophic factor (BDNF), is present within nerve terminals in certain regions of the brain and PNS that do not contain the corresponding mRNA. Recent studies have shown that the endogenous neurotrophins, BDNF and neurotrophin-3 (NT-3), are transported anterogradely by central and peripheral neurons. The supply of BDNF by afferents is consistent with their presynaptic synthesis, vesicular storage, release and postsynaptic actions. Anterograde axonal transport provides an 'afferent supply' of BDNF and NT-3 to neurons and target tissues, where they function as trophic factors and as neurotransmitters.

Presynaptic mGlu1 and mGlu5 autoreceptors facilitate glutamate exocytosis from mouse cortical nerve endings.

PubMed

Musante, Veronica; Neri, Elisa; Feligioni, Marco; Puliti, Aldamaria; Pedrazzi, Marco; Conti, Valerio; Usai, Cesare; Diaspro, Alberto; Ravazzolo, Roberto; Henley, Jeremy M; Battaglia, Giuseppe; Pittaluga, Anna

2008-09-01

The effects of mGlu1 and mGlu5 receptor activation on the depolarization-evoked release of [3H]d-aspartate ([3H]D-ASP) from mouse cortical synaptosomes were investigated. The mGlu1/5 receptor agonist 3,5-DHPG (0.1-100microM) potentiated the K+(12mM)-evoked [3H]D-ASP overflow. The potentiation occurred in a concentration-dependent manner showing a biphasic pattern. The agonist potentiated [3H]D-ASP exocytosis when applied at 0.3microM; the efficacy of 3,5-DHPG then rapidly declined and reappeared at 30-100microM. The fall of efficacy of agonist at intermediate concentration may be consistent with 3,5-DHPG-induced receptor desensitization. Facilitation of [3H]D-ASP exocytosis caused by 0.3microM 3,5-DHPG was prevented by the selective mGlu5 receptor antagonist MPEP, but was insensitive to the selective mGlu1 receptor antagonist CPCCOEt. In contrast, CPCCOEt prevented the potentiation by 50microM 3,5-DHPG, while MPEP had minimal effect. Unexpectedly, LY 367385 antagonized both the 3,5-DHPG-induced effects. A total of 0.3microM 3,5-DHPG failed to facilitate the K+-evoked [3H]D-ASP overflow from mGlu5 receptor knockout (mGlu5-/-) cortical synaptosomes, but not from nerve terminals prepared from the cortex of animals lacking the mGlu1 receptors, the crv4/crv4 mice. On the contrary, 50microM 3,5-DHPG failed to affect the [3H]D-ASP exocytosis from cortical synaptosomes obtained from crv4/crv4 and mGlu5-/-mice. Western blot analyses in subsynaptic fractions support the existence of both mGlu1 and mGlu5 autoreceptors located presynaptically, while immunocytochemistry revealed their presence at glutamatergic terminals. We propose that mGlu1 and mGlu5 autoreceptors exist on mouse glutamatergic cortical terminals; mGlu5 receptors may represent the "high affinity" binding sites for 3,5-DHPG, while mGlu1 autoreceptors represent the "low affinity" binding sites.

Pre-synaptic kainate receptor-mediated facilitation of glutamate release involves PKA and Ca(2+) -calmodulin at thalamocortical synapses.

PubMed

Andrade-Talavera, Yuniesky; Duque-Feria, Paloma; Sihra, Talvinder S; Rodríguez-Moreno, Antonio

2013-09-01

We have investigated the mechanisms underlying the facilitatory modulation mediated by kainate receptor (KAR) activation in the cortex, using isolated nerve terminals (synaptosomes) and slice preparations. In cortical nerve terminals, kainate (KA, 100 μM) produced an increase in 4-aminopyridine (4-AP)-evoked glutamate release. In thalamocortical slices, KA (1 μM) produced an increase in the amplitude of evoked excitatory post-synaptic currents (eEPSCs) at synapses established between thalamic axon terminals from the ventrobasal nucleus onto stellate neurons of L4 of the somatosensory cortex. In both, synaptosomes and slices, the effect of KA was antagonized by 6-cyano-7-nitroquinoxaline-2,3-dione, and persisted after pre-treatment with a cocktail of antagonists of other receptors whose activation could potentially have produced facilitation of release indirectly. Mechanistically, the observed effects of KA appear to be congruent in synaptosomal and slice preparations. Thus, the facilitation by KA of synaptosomal glutamate release and thalamocortical synaptic transmission were suppressed by the inhibition of protein kinase A and occluded by the stimulation of adenylyl cyclase. Dissecting this G-protein-independent regulation further in thalamocortical slices, the KAR-mediated facilitation of synaptic transmission was found to be sensitive to the block of Ca(2+) permeant KARs by philanthotoxin. Intriguingly, the synaptic facilitation was abrogated by depletion of intracellular Ca(2+) stores by thapsigargin, or inhibition of Ca(2+) -induced Ca(2+) -release by ryanodine. Thus, the KA-mediated modulation was contingent on both Ca(2+) entry through Ca(2+) -permeable KARs and liberation of intracellular Ca(2+) stores. Finally, sensitivity to W-7 indicated that the increased cytosolic [Ca(2+) ] underpinning KAR-mediated regulation of synaptic transmission at thalamocortical synapses, requires downstream activation of calmodulin. We conclude that neocortical pre-synaptic KARs mediate the facilitation of glutamate release and synaptic transmission by a Ca(2+) -calmodulin dependent activation of an adenylyl cyclase/cAMP/protein kinase A signalling cascade, independent of G-protein involvement. © 2013 International Society for Neurochemistry.

A heterogeneous population of nuclear-encoded mitochondrial mRNAs is present in the axons of primary sympathetic neurons.

PubMed

Aschrafi, Armaz; Kar, Amar N; Gale, Jenna R; Elkahloun, Abdel G; Vargas, Jose Noberto S; Sales, Naomi; Wilson, Gabriel; Tompkins, Miranda; Gioio, Anthony E; Kaplan, Barry B

2016-09-01

Mitochondria are enriched in subcellular regions of high energy consumption, such as axons and pre-synaptic nerve endings. Accumulating evidence suggests that mitochondrial maintenance in these distal structural/functional domains of the neuron depends on the "in-situ" translation of nuclear-encoded mitochondrial mRNAs. In support of this notion, we recently provided evidence for the axonal targeting of several nuclear-encoded mRNAs, such as cytochrome c oxidase, subunit 4 (COXIV) and ATP synthase, H+ transporting and mitochondrial Fo complex, subunit C1 (ATP5G1). Furthermore, we showed that axonal trafficking and local translation of these mRNAs plays a critical role in the generation of axonal ATP. Using a global gene expression analysis, this study identified a highly diverse population of nuclear-encoded mRNAs that were enriched in the axon and presynaptic nerve terminals. Among this population of mRNAs, fifty seven were found to be at least two-fold more abundant in distal axons, as compared with the parental cell bodies. Gene ontology analysis of the nuclear-encoded mitochondrial mRNAs suggested functions for these gene products in molecular and biological processes, including but not limited to oxidoreductase and electron carrier activity and proton transport. Based on these results, we postulate that local translation of nuclear-encoded mitochondrial mRNAs present in the axons may play an essential role in local energy production and maintenance of mitochondrial function. Published by Elsevier B.V.

Effects of Levetiracetam, Carbamazepine, Phenytoin, Valproate, Lamotrigine, Oxcarbazepine, Topiramate, Vinpocetine and Sertraline on Presynaptic Hippocampal Na(+) and Ca(2+) Channels Permeability.

PubMed

Sitges, María; Chiu, Luz María; Reed, Ronald C

2016-04-01

Ion channels are targets of various antiepileptic drugs. In cerebral presynaptic nerve endings Na(+) and Ca(2+) channels are particularly abundant, as they control neurotransmitter release, including the release of glutamate (Glu), the most concentrated excitatory amino acid neurotransmitter in the brain. Several pre-synaptic channels are implicated in the mechanism of action of the pro-convulsive agent, 4-aminopyridine (4-AP). In the present study the effects of levetiracetam and other established and newer (vinpocetine) anti-epileptic drugs, as well as of the anti-depressant, sertraline on the increase in Ca(2+) induced by 4-AP in hippocampal isolated nerve endings were investigated. Also the effects of some of the anti-seizure drugs on the selective increase in Ca(2+) induced by high K(+), or on the selective increase in Na(+) induced by veratridine were tested. Sertraline and vinpocetine effectively inhibited the rise in Ca(2+) induced by 4-AP, which was dependent on the out-in Na(+) gradient and tetrodotoxin sensitive. Carbamazepine, phenytoin, lamotrigine and oxcarbazepine inhibited the rise in Ca(2+) induced by 4-AP too, but at higher concentrations than sertraline and vinpocetine, whereas levetiracetam, valproic acid and topiramate did not. The three latter antiepileptic drugs also failed in modifying other responses mediated by the activation of brain presynaptic Na(+) or Ca(2+) channels, including Glu release. This indicates that levetiracetam, valproic acid and topiramate mechanisms of action are unrelated with a decrease in presynaptic Na(+) or Ca(2+) channels permeability. It is concluded that depolarized cerebral isolated nerve endings represent a useful tool to unmask potential antiepileptic drugs targeting presynaptic Na(+) and/or Ca(2+) channels in the brain; such as vinpocetine or the anti-depressant sertraline, which high effectiveness to control seizures in the animal in vivo has been demonstrated.

Activity Induces Fmr1-Sensitive Synaptic Capture of Anterograde Circulating Neuropeptide Vesicles.

PubMed

Cavolo, Samantha L; Bulgari, Dinara; Deitcher, David L; Levitan, Edwin S

2016-11-16

Synaptic neuropeptide and neurotrophin stores are maintained by constitutive bidirectional capture of dense-core vesicles (DCVs) as they circulate in and out of the nerve terminal. Activity increases DCV capture to rapidly replenish synaptic neuropeptide stores following release. However, it is not known whether this is due to enhanced bidirectional capture. Here experiments at the Drosophila neuromuscular junction, where DCVs contain neuropeptides and a bone morphogenic protein, show that activity-dependent replenishment of synaptic neuropeptides following release is evident after inhibiting the retrograde transport with the dynactin disruptor mycalolide B or photobleaching DCVs entering a synaptic bouton by retrograde transport. In contrast, photobleaching anterograde transport vesicles entering a bouton inhibits neuropeptide replenishment after activity. Furthermore, tracking of individual DCVs moving through boutons shows that activity selectively increases capture of DCVs undergoing anterograde transport. Finally, upregulating fragile X mental retardation 1 protein (Fmr1, also called FMRP) acts independently of futsch/MAP-1B to abolish activity-dependent, but not constitutive, capture. Fmr1 also reduces presynaptic neuropeptide stores without affecting activity-independent delivery and evoked release. Therefore, presynaptic motoneuron neuropeptide storage is increased by a vesicle capture mechanism that is distinguished from constitutive bidirectional capture by activity dependence, anterograde selectivity, and Fmr1 sensitivity. These results show that activity recruits a separate mechanism than used at rest to stimulate additional synaptic capture of DCVs for future release of neuropeptides and neurotrophins. Synaptic release of neuropeptides and neurotrophins depends on presynaptic accumulation of dense-core vesicles (DCVs). At rest, DCVs are captured bidirectionally as they circulate through Drosophila motoneuron terminals by anterograde and retrograde transport. Here we show that activity stimulates further synaptic capture that is distinguished from basal capture by its selectivity for anterograde DCVs and its inhibition by overexpression of the fragile X retardation protein Fmr1. Fmr1 dramatically lowers DCV numbers in synaptic boutons. Therefore, activity-dependent anterograde capture is a major determinant of presynaptic peptide stores. Copyright © 2016 the authors 0270-6474/16/3611781-07$15.00/0.

Altered mechanisms underlying the abnormal glutamate release in amyotrophic lateral sclerosis at a pre-symptomatic stage of the disease.

PubMed

Bonifacino, Tiziana; Musazzi, Laura; Milanese, Marco; Seguini, Mara; Marte, Antonella; Gallia, Elena; Cattaneo, Luca; Onofri, Franco; Popoli, Maurizio; Bonanno, Giambattista

2016-11-01

Abnormal Glu release occurs in the spinal cord of SOD1(G93A) mice, a transgenic animal model for human ALS. Here we studied the mechanisms underlying Glu release in spinal cord nerve terminals of SOD1(G93A) mice at a pre-symptomatic disease stage (30days) and found that the basal release of Glu was more elevated in SOD1(G93A) with respect to SOD1 mice, and that the surplus of release relies on synaptic vesicle exocytosis. Exposure to high KCl or ionomycin provoked Ca(2+)-dependent Glu release that was likewise augmented in SOD1(G93A) mice. Equally, the Ca(2+)-independent hypertonic sucrose-induced Glu release was abnormally elevated in SOD1(G93A) mice. Also in this case, the surplus of Glu release was exocytotic in nature. We could determine elevated cytosolic Ca(2+) levels, increased phosphorylation of Synapsin-I, which was causally related to the abnormal Glu release measured in spinal cord synaptosomes of pre-symptomatic SOD1(G93A) mice, and increased phosphorylation of glycogen synthase kinase-3 at the inhibitory sites, an event that favours SNARE protein assembly. Western blot experiments revealed an increased number of SNARE protein complexes at the nerve terminal membrane, with no changes of the three SNARE proteins and increased expression of synaptotagmin-1 and β-Actin, but not of an array of other release-related presynaptic proteins. These results indicate that the abnormal exocytotic Glu release in spinal cord of pre-symptomatic SOD1(G93A) mice is mainly based on the increased size of the readily releasable pool of vesicles and release facilitation, supported by plastic changes of specific presynaptic mechanisms. Copyright © 2016 Elsevier Inc. All rights reserved.

FM Dye Cycling at the Synapse: Comparing High Potassium Depolarization, Electrical and Channelrhodopsin Stimulation.

PubMed

Kopke, Danielle L; Broadie, Kendal

2018-05-24

FM dyes are used to study the synaptic vesicle (SV) cycle. These amphipathic probes have a hydrophilic head and hydrophobic tail, making them water-soluble with the ability to reversibly enter and exit membrane lipid bilayers. These styryl dyes are relatively non-fluorescent in aqueous medium, but insertion into the outer leaflet of the plasma membrane causes a >40X increase in fluorescence. In neuronal synapses, FM dyes are internalized during SV endocytosis, trafficked both within and between SV pools, and released with SV exocytosis, providing a powerful tool to visualize presynaptic stages of neurotransmission. A primary genetic model of glutamatergic synapse development and function is the Drosophila neuromuscular junction (NMJ), where FM dye imaging has been used extensively to quantify SV dynamics in a wide range of mutant conditions. The NMJ synaptic terminal is easily accessible, with a beautiful array of large synaptic boutons ideal for imaging applications. Here, we compare and contrast the three ways to stimulate the Drosophila NMJ to drive activity-dependent FM1-43 dye uptake/release: 1) bath application of high [K + ] to depolarize neuromuscular tissues, 2) suction electrode motor nerve stimulation to depolarize the presynaptic nerve terminal, and 3) targeted transgenic expression of channelrhodopsin variants for light-stimulated, spatial control of depolarization. Each of these methods has benefits and disadvantages for the study of genetic mutation effects on the SV cycle at the Drosophila NMJ. We will discuss these advantages and disadvantages to assist the selection of the stimulation approach, together with the methodologies specific to each strategy. In addition to fluorescent imaging, FM dyes can be photoconverted to electron-dense signals visualized using transmission electron microscopy (TEM) to study SV cycle mechanisms at an ultrastructural level. We provide the comparisons of confocal and electron microscopy imaging from the different methods of Drosophila NMJ stimulation, to help guide the selection of future experimental paradigms.

The interaction between tropomyosin-related kinase B receptors and presynaptic muscarinic receptors modulates transmitter release in adult rodent motor nerve terminals.

PubMed

Garcia, Neus; Tomàs, Marta; Santafé, Manel M; Besalduch, Nuria; Lanuza, Maria A; Tomàs, Josep

2010-12-08

The neurotrophin brain-derived neurotrophic factor (BDNF), neurotrophin-4 (NT-4) and the receptors tropomyosin-related kinase B (trkB) and p75(NTR) are present in the nerve terminals on the neuromuscular junctions (NMJs) of the levator auris longus muscle of the adult mouse. Exogenously added BDNF or NT-4 increased evoked ACh release after 3 h. This presynaptic effect (the size of the spontaneous potentials is not affected) is specific because it is not produced by neurotrophin-3 (NT-3) and is prevented by preincubation with trkB-IgG chimera or by pharmacological block of trkB [K-252a (C₂₇H₂₁N₃O₅)] or p75(NTR) [Pep5 (C₈₆H₁₁₁N₂₅O₁₉S₂] signaling. The effect of BDNF depends on the M₁ and M₂ muscarinic acetylcholine autoreceptors (mAChRs) because it is prevented by atropine, pirenzepine and methoctramine. We found that K-252a incubation reduces ACh release (~50%) in a short time (1 h), but the p75(NTR) signaling inhibitor Pep5 does not have this effect. The specificity of the K-252a blocking effect on trkB was confirmed with the anti-trkB antibody 47/trkB, which reduces evoked ACh release, like K-252a, whereas the nonpermeant tyrosine kinase blocker K-252b does not. Neither does incubation with the fusion protein trkB-IgG (to chelate endogenous BDNF/NT-4), anti-BDNF or anti-NT-4 change ACh release. Thus, the trkB receptor normally seems to be coupled to ACh release when there is no short-term local effect of neurotrophins at the NMJ. The normal function of the mAChR mechanism is a permissive prerequisite for the trkB pathway to couple to ACh release. Reciprocally, the normal function of trkB modulates M₁- and M₂-subtype muscarinic pathways.

alpha2-Adrenoceptors control the release of noradrenaline but not neuropeptide Y from perivascular nerve terminals.

PubMed

Donoso, M Veronica; Carvajal, Andrés; Paredes, Alfonso; Tomic, Alexander; Koenig, Cecilia S; Huidobro-Toro, J Pablo

2002-09-01

Neuropeptide Y (NPY) and noradrenaline (NA) are co-transmitters at many sympathetic synapses, but it is not yet clear if their release is independently regulated. To address this question, we quantified the electrically evoked release of these co-transmitters from perivascular nerve terminals to the mesenteric circulation in control and drug-treated rats. 6-Hydroxydopamine reduced the tissue content and the electrically evoked release of ir-NPY and NA as well as the rise in perfusion pressure. A 0.001 mg/kg reserpine reduced the content of ir-NPY and NA, but did not modify their release nor altered the rise in perfusion pressure elicited by the electrical stimuli. However, 0.1mg/kg reserpine reduced both the content and release of NA but decreased only the content but not the release of ir-NPY; the rise in perfusion pressure was halved. Clonidine did not affect the release of ir-NPY while it lowered the outflow of NA, not altering the rise in perfusion pressure elicited by the electrical stimuli. Yohimbine, did not modify the release of ir-NPY but increased the NA outflow, it antagonized the clonidine effect. Therefore, presynaptic alpha2-adrenoceptors modulate the release of NA but not NPY, implying separate regulatory mechanisms.

Paired associative stimulation induces change in presynaptic inhibition of Ia terminals in wrist flexors in humans.

PubMed

Lamy, Jean-Charles; Russmann, Heike; Shamim, Ejaz A; Meunier, Sabine; Hallett, Mark

2010-08-01

Enhancements in the strength of corticospinal projections to muscles are induced in conscious humans by paired associative stimulation (PAS) to the motor cortex. Although most of the previous studies support the hypothesis that the increase of the amplitude of motor evoked potentials (MEPs) by PAS involves long-term potentiation (LTP)-like mechanism in cortical synapses, changes in spinal excitability after PAS have been reported, suggestive of parallel modifications in both cortical and spinal excitability. In a first series of experiments (experiment 1), we confirmed that both flexor carpi radialis (FCR) MEPs and FCR H reflex recruitment curves are enhanced by PAS. To elucidate the mechanism responsible for this change in the H reflex amplitude, we tested, using the same subjects, the hypothesis that enhanced H reflexes are caused by a down-regulation of the efficacy of mechanisms controlling Ia afferent discharge, including presynaptic Ia inhibition and postactivation depression. To address this question, amounts of both presynaptic Ia inhibition of FCR Ia terminals (D1 and D2 inhibitions methods; experiment 2) and postactivation depression (experiment 3) were determined before and after PAS. Results showed that PAS induces a significant decrease of presynaptic Ia inhibition of FCR terminals, which was concomitant with the facilitation of the H reflex. Postactivation depression was unaffected by PAS. It is argued that enhancement of segmental excitation by PAS relies on a selective effect of PAS on the interneurons controlling presynaptic inhibition of Ia terminals.

Na+ current in presynaptic terminals of the crayfish opener cannot initiate action potentials.

PubMed

Lin, Jen-Wei

2016-01-01

Action potential (AP) propagation in presynaptic axons of the crayfish opener neuromuscular junction (NMJ) was investigated by simultaneously recording from a terminal varicosity and a proximal branch. Although orthodromically conducting APs could be recorded in terminals with amplitudes up to 70 mV, depolarizing steps in terminals to -20 mV or higher failed to fire APs. Patch-clamp recordings did detect Na(+) current (INa) in most terminals. The INa exhibited a high threshold and fast activation rate. Local perfusion of Na(+)-free saline showed that terminal INa contributed to AP waveform by slightly accelerating the rising phase and increasing the peak amplitude. These findings suggest that terminal INa functions to "touch up" but not to generate APs. Copyright © 2016 the American Physiological Society.

The Role of Neurotrophins in Neurotransmitter Release

PubMed Central

Tyler, William J.; Perrett, Stephen P.; Pozzo-Miller, Lucas D.

2009-01-01

The neurotrophins (NTs) have recently been shown to elicit pronounced effects on quantal neurotransmitter release at both central and peripheral nervous system synapses. Due to their activity-dependent release, as well as the subcellular localization of both protein and receptor, NTs are ideally suited to modify the strength of neuronal connections by “fine-tuning” synaptic activity through direct actions at presynaptic terminals. Here, using BDNF as a prototypical example, the authors provide an update of recent evidence demonstrating that NTs enhance quantal neurotransmitter release at synapses through presynaptic mechanisms. The authors further propose that a potential target for NT actions at presynaptic terminals is the mechanism by which terminals retrieve synaptic vesicles after exocytosis. Depending on the temporal demands placed on synapses during high-frequency synaptic transmission, synapses may use two alternative modes of synaptic vesicle retrieval, the conventional slow endosomal recycling or a faster rapid retrieval at the active zone, referred to as “kiss-and-run.” By modulating Ca2+ microdomains associated with voltage-gated Ca2+ channels at active zones, NTs may elicit a switch from the slow to the fast mode of endocytosis of vesicles at presynaptic terminals during high-frequency synaptic transmission, allowing more reliable information transfer and neuronal signaling in the central nervous system. PMID:12467374

The role of neurotrophins in neurotransmitter release.

PubMed

Tyler, William J; Perrett, Stephen P; Pozzo-Miller, Lucas D

2002-12-01

The neurotrophins (NTs) have recently been shown to elicit pronounced effects on quantal neurotransmitter release at both central and peripheral nervous system synapses. Due to their activity-dependent release, as well as the subcellular localization of both protein and receptor, NTs are ideally suited to modify the strength of neuronal connections by "fine-tuning" synaptic activity through direct actions at presynaptic terminals. Here, using BDNF as a prototypical example, the authors provide an update of recent evidence demonstrating that NTs enhance quantal neurotransmitter release at synapses through presynaptic mechanisms. The authors further propose that a potential target for NT actions at presynaptic terminals is the mechanism by which terminals retrieve synaptic vesicles after exocytosis. Depending on the temporal demands placed on synapses during high-frequency synaptic transmission, synapses may use two alternative modes of synaptic vesicle retrieval, the conventional slow endosomal recycling or a faster rapid retrieval at the active zone, referred to as "kiss-and-run." By modulating Ca2+ microdomains associated with voltage-gated Ca2+ channels at active zones, NTs may elicit a switch from the slow to the fast mode of endocytosis of vesicles at presynaptic terminals during high-frequency synaptic transmission, allowing more reliable information transfer and neuronal signaling in the central nervous system.

Combined Changes in Chloride Regulation and Neuronal Excitability Enable Primary Afferent Depolarization to Elicit Spiking without Compromising its Inhibitory Effects

PubMed Central

2016-01-01

The central terminals of primary afferent fibers experience depolarization upon activation of GABAA receptors (GABAAR) because their intracellular chloride concentration is maintained above electrochemical equilibrium. Primary afferent depolarization (PAD) normally mediates inhibition via sodium channel inactivation and shunting but can evoke spikes under certain conditions. Antidromic (centrifugal) conduction of these spikes may contribute to neurogenic inflammation while orthodromic (centripetal) conduction could contribute to pain in the case of nociceptive fibers. PAD-induced spiking is assumed to override presynaptic inhibition. Using computer simulations and dynamic clamp experiments, we sought to identify which biophysical changes are required to enable PAD-induced spiking and whether those changes necessarily compromise PAD-mediated inhibition. According to computational modeling, a depolarizing shift in GABA reversal potential (EGABA) and increased intrinsic excitability (manifest as altered spike initiation properties) were necessary for PAD-induced spiking, whereas increased GABAAR conductance density (ḡGABA) had mixed effects. We tested our predictions experimentally by using dynamic clamp to insert virtual GABAAR conductances with different EGABA and kinetics into acutely dissociated dorsal root ganglion (DRG) neuron somata. Comparable experiments in central axon terminals are prohibitively difficult but the biophysical requirements for PAD-induced spiking are arguably similar in soma and axon. Neurons from naïve (i.e. uninjured) rats were compared before and after pharmacological manipulation of intrinsic excitability, and against neurons from nerve-injured rats. Experimental data confirmed that, in most neurons, both predicted changes were necessary to yield PAD-induced spiking. Importantly, such changes did not prevent PAD from inhibiting other spiking or from blocking spike propagation. In fact, since the high value of ḡGABA required for PAD-induced spiking still mediates strong inhibition, we conclude that PAD-induced spiking does not represent failure of presynaptic inhibition. Instead, diminished PAD caused by reduction of ḡGABA poses a greater risk to presynaptic inhibition and the sensory processing that relies upon it. PMID:27835641

Presynaptic Membrane Receptors Modulate ACh Release, Axonal Competition and Synapse Elimination during Neuromuscular Junction Development.

PubMed

Tomàs, Josep; Garcia, Neus; Lanuza, Maria A; Santafé, Manel M; Tomàs, Marta; Nadal, Laura; Hurtado, Erica; Simó, Anna; Cilleros, Víctor

2017-01-01

During the histogenesis of the nervous system a lush production of neurons, which establish an excessive number of synapses, is followed by a drop in both neurons and synaptic contacts as maturation proceeds. Hebbian competition between axons with different activities leads to the loss of roughly half of the neurons initially produced so connectivity is refined and specificity gained. The skeletal muscle fibers in the newborn neuromuscular junction (NMJ) are polyinnervated but by the end of the competition, 2 weeks later, the NMJ are innervated by only one axon. This peripheral synapse has long been used as a convenient model for synapse development. In the last few years, we have studied transmitter release and the local involvement of the presynaptic muscarinic acetylcholine autoreceptors (mAChR), adenosine autoreceptors (AR) and trophic factor receptors (TFR, for neurotrophins and trophic cytokines) during the development of NMJ and in the adult. This review article brings together previously published data and proposes a molecular background for developmental axonal competition and loss. At the end of the first week postnatal, these receptors modulate transmitter release in the various nerve terminals on polyinnervated NMJ and contribute to axonal competition and synapse elimination.

Effect of rocuronium on the level and mode of pre-synaptic acetylcholine release by facial and somatic nerves, and changes following facial nerve injury in rabbits.

PubMed

Tan, Jinghua; Xu, Jing; Xing, Yian; Chen, Lianhua; Li, Shitong

2015-01-01

Muscles innervated by the facial nerve show differential sensitivities to muscle relaxants than muscles innervated by somatic nerves. The evoked electromyography (EEMG) response is also proportionally reduced after facial nerve injury. This forms the theoretical basis for proper utilization of muscle relaxants to balance EEMG monitoring and immobility under general anesthesia. (1) To observe the relationships between the level and mode of acetylcholine (ACh) release and the duration of facial nerve injury, and the influence of rocuronium in an in vitro rabbit model. (2) To explore the pre-synaptic mechanisms of discrepant responses to a muscle relaxant. Quantal and non-quantal ACh release were measured by using intracellular microelectrode recording in the orbicularis oris 1 to 42 days after graded facial nerve injury and in the gastrocnemius with/without rocuronium. Quantal ACh release was significantly decreased by rocuronium in the orbicularis oris and gastrocnemius, but significantly more so in gastrocnemius. Quantal release was reduced after facial nerve injury, which was significantly correlated with the severity of nerve injury in the absence but not in the presence of rocuronium. Non-quantal ACh release was reduced after facial nerve injury, with many relationships observed depending on the extent of the injury. The extent of inhibition of non-quantal release by rocuronium correlated with the grade of facial nerve injury. These findings may explain why EEMG amplitude might be diminished after acute facial nerve injury but relatively preserved after chronic injury and differential responses in sensitivity to rocuronium.

Effect of rocuronium on the level and mode of pre-synaptic acetylcholine release by facial and somatic nerves, and changes following facial nerve injury in rabbits

PubMed Central

Tan, Jinghua; Xu, Jing; Xing, Yian; Chen, Lianhua; Li, Shitong

2015-01-01

Muscles innervated by the facial nerve show differential sensitivities to muscle relaxants than muscles innervated by somatic nerves. The evoked electromyography (EEMG) response is also proportionally reduced after facial nerve injury. This forms the theoretical basis for proper utilization of muscle relaxants to balance EEMG monitoring and immobility under general anesthesia. (1) To observe the relationships between the level and mode of acetylcholine (ACh) release and the duration of facial nerve injury, and the influence of rocuronium in an in vitro rabbit model. (2) To explore the pre-synaptic mechanisms of discrepant responses to a muscle relaxant. Quantal and non-quantal ACh release were measured by using intracellular microelectrode recording in the orbicularis oris 1 to 42 days after graded facial nerve injury and in the gastrocnemius with/without rocuronium. Quantal ACh release was significantly decreased by rocuronium in the orbicularis oris and gastrocnemius, but significantly more so in gastrocnemius. Quantal release was reduced after facial nerve injury, which was significantly correlated with the severity of nerve injury in the absence but not in the presence of rocuronium. Non-quantal ACh release was reduced after facial nerve injury, with many relationships observed depending on the extent of the injury. The extent of inhibition of non-quantal release by rocuronium correlated with the grade of facial nerve injury. These findings may explain why EEMG amplitude might be diminished after acute facial nerve injury but relatively preserved after chronic injury and differential responses in sensitivity to rocuronium. PMID:25973033

Glucose and lactate as metabolic constraints on presynaptic transmission at an excitatory synapse.

PubMed

Lucas, Sarah J; Michel, Christophe B; Marra, Vincenzo; Smalley, Joshua L; Hennig, Matthias H; Graham, Bruce P; Forsythe, Ian D

2018-05-01

Synapses have high energy demands which increase during intense activity. We show that presynaptic terminals can utilise extracellular glucose or lactate to generate energy to maintain synaptic transmission. Reducing energy substrates induces a metabolic stress: presynaptic ATP depletion impaired synaptic transmission through a reduction in the number of functional synaptic vesicle release sites and a slowing of vesicle pool replenishment, without a consistent change in release probability. Metabolic function is compromised in many pathological conditions (e.g. stroke, traumatic brain injury and neurodegeneration). Knowledge of how synaptic transmission is constrained by metabolic stress, especially during intense brain activity, will provide insights to improve cognition following pathological insults. The synapse has high energy demands, which increase during intense activity. Presynaptic ATP production depends on substrate availability and usage will increase during activity, which in turn could influence transmitter release and information transmission. We investigated transmitter release at the mouse calyx of Held synapse using glucose or lactate (10, 1 or 0 mm) as the extracellular substrates while inducing metabolic stress. High-frequency stimulation (HFS) and recovery paradigms evoked trains of EPSCs monitored under voltage-clamp. Whilst postsynaptic intracellular ATP was stabilised by diffusion from the patch pipette, depletion of glucose increased EPSC depression during HFS and impaired subsequent recovery. Computational modelling of these data demonstrated a reduction in the number of functional release sites and slowed vesicle pool replenishment during metabolic stress, with little change in release probability. Directly depleting presynaptic terminal ATP impaired transmitter release in an analogous manner to glucose depletion. In the absence of glucose, presynaptic terminal metabolism could utilise lactate from the aCSF and this was blocked by inhibition of monocarboxylate transporters (MCTs). MCT inhibitors significantly suppressed transmission in low glucose, implying that lactate is a presynaptic substrate. Additionally, block of glycogenolysis accelerated synaptic transmission failure in the absence of extracellular glucose, consistent with supplemental supply of lactate by local astrocytes. We conclude that both glucose and lactate support presynaptic metabolism and that limited availability, exacerbated by high-intensity firing, constrains presynaptic ATP, impeding transmission through a reduction in functional presynaptic release sites as vesicle recycling slows when ATP levels are low. © 2018 The Authors. The Journal of Physiology © 2018 The Physiological Society.

Cellular localization of the atypical isoforms of protein kinase C (aPKCζ/PKMζ and aPKCλ/ι) on the neuromuscular synapse.

PubMed

Besalduch, Núria; Lanuza, Maria A; Garcia, Neus; Obis, Teresa; Santafe, Manel M; Tomàs, Marta; Priego, Mercedes; Tomàs, Josep

2013-11-27

Several classic and novel protein kinase C (PKC) isoforms are selectively distributed in specific cell types of the adult neuromuscular junction (NMJ), in the neuron, glia and muscle components, and are involved in many functions, including neurotransmission. Here, we investigate the presence in this paradigmatic synapse of atypical PKCs, full-length atypical PKC zeta (aPKCζ), its separated catalytic part (PKMζ) and atypical lambda-iota PKC (aPKCλ/ι). High resolution immunohistochemistry was performed using a pan-atypical PKC antibody. Our results show moderate immunolabeling on the three cells (presynaptic motor nerve terminal, teloglial Schwann cell and postsynaptic muscle cell) suggesting the complex involvement of atypical PKCs in synaptic function. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

The neurite outgrowth inhibitor Nogo-A promotes denervation in an amyotrophic lateral sclerosis model

PubMed Central

Jokic, Natasa; Gonzalez de Aguilar, Jose-Luis; Dimou, Leda; Lin, Shuo; Fergani, Anissa; Ruegg, Markus A; Schwab, Martin E; Dupuis, Luc; Loeffler, Jean-Philippe

2006-01-01

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by motor neuron loss and muscle wasting. In muscles of ALS patients, Nogo-A—a protein known to inhibit axon regeneration—is ectopically expressed at levels that correlate with the severity of the clinical symptoms. We now show that the genetic ablation of Nogo-A extends survival and reduces muscle denervation in a mouse model of ALS. In turn, overexpression of Nogo-A in wild-type muscle fibres leads to shrinkage of the postsynapse and retraction of the presynaptic motor ending. This suggests that the expression of Nogo-A occurring early in ALS skeletal muscle could cause repulsion and destabilization of the motor nerve terminals, and subsequent dying back of the axons and motor neurons. PMID:17039253

Ultrastructural localization of ChAT-like immunoreactivity in the human vestibular periphery.

PubMed

Kong, W J; Hussl, B; Thumfart, W F; Schrott-Fischer, A

1998-05-01

Acetylcholine (ACh) has long been considered a neurotransmitter candidate in the efferent vestibular system of mammals. Recently, choline acetyltransferase (ChAT), the synthesizing enzyme for ACh, was immunocytochemically localized in all five end-organs of the rat vestibule (Kong et al. (1994) Hear. Res. 75, 192-200). However, there is little information in the literature concerning the cholinergic innervation in the vestibular periphery of man. In the present study the ultrastructural localization of the ChAT-like immunoreactivity in the human vestibular periphery was investigated in order to reveal the cholinergic innervation in the human vestibular end-organs. A modified method of pre-embedding immunoelectron microscopy was applied. It was found that the ChAT-like immunoreactivity was located in the bouton-type vesiculated nerve terminals in the vestibular neurosensory epithelia of man. These ChAT-like immunostained nerve terminals make synaptic contacts either with afferent chalices surrounding type I vestibular sensory hair cells, or with type II vestibular sensory hair cells. These results show that the ChAT-like immunoreactivity in the human vestibular periphery is confined to the efferent vestibular system. The ChAT-containing efferents innervate both type I hair cells and type II hair cells, making postsynaptic and presynaptic contacts, respectively. This study presents evidence that ACh is a neurotransmitter candidate in the efferent vestibular system of man.

Serotonin uptake inhibitors: uses in clinical therapy and in laboratory research.

PubMed

Fuller, R W

1995-01-01

Fluoxetine, zimelidine, sertraline, paroxetine, fluvoxamine, indalpine and citalopram are the selective inhibitors of serotonin uptake that have been most widely studied. Some of these compounds are or have been used clinically in the treatment of mental depression, obsessive-compulsive disorder and bulimia, and therapeutic benefit has been claimed in additional diseases as well. By blocking the membrane uptake carrier which transports serotonin from the extracellular space to inside the serotonin nerve terminals, these compounds increase extracellular concentrations of serotonin and amplify signals sent by serotonin neurons. Because serotonin neurons are widespread in the central nervous system, the functional consequences of blocking serotonin uptake are diverse, but are generally subtle. Animals treated with serotonin uptake inhibitors look normal in gross appearance, but effects such as reduced aggressive behavior, decreased food intake and altered food selection, analgesia, anticonvulsant activity, endocrine changes and neurochemical changes have been demonstrated and characterized. Serotonin uptake inhibitors have helped in revealing some dynamics of serotonin neurons; for example, when uptake is inhibited and extracellular serotonin concentration increases, presynaptic as well as postsynaptic receptors for serotonin are activated to a greater degree. A consequence of increased activation of autoreceptors on serotonin cell bodies and nerve terminals is a reduction in firing of serotonin neurons and a decrease in serotonin synthesis and release. The result is a limit on the degree to which extracellular serotonin and serotonergic neurotransmission are increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Activity-induced Ca2+ signaling in perisynaptic Schwann cells of the early postnatal mouse is mediated by P2Y1 receptors and regulates muscle fatigue

PubMed Central

Heredia, Dante J; Feng, Cheng-Yuan; Hennig, Grant W; Renden, Robert B

2018-01-01

Perisynaptic glial cells respond to neural activity by increasing cytosolic calcium, but the significance of this pathway is unclear. Terminal/perisynaptic Schwann cells (TPSCs) are a perisynaptic glial cell at the neuromuscular junction that respond to nerve-derived substances such as acetylcholine and purines. Here, we provide genetic evidence that activity-induced calcium accumulation in neonatal TPSCs is mediated exclusively by one subtype of metabotropic purinergic receptor. In P2ry1 mutant mice lacking these responses, postsynaptic, rather than presynaptic, function was altered in response to nerve stimulation. This impairment was correlated with a greater susceptibility to activity-induced muscle fatigue. Interestingly, fatigue in P2ry1 mutants was more greatly exacerbated by exposure to high potassium than in control mice. High potassium itself increased cytosolic levels of calcium in TPSCs, a response which was also reduced P2ry1 mutants. These results suggest that activity-induced calcium responses in TPSCs regulate postsynaptic function and muscle fatigue by regulating perisynaptic potassium. PMID:29384476

Myasthenic decrement and myasthenic myopathy. A study on the effects of thymectomy.

PubMed Central

Pinelli, P; Arrigo, A; Moglia, A

1975-01-01

Motor unit action potentials, M responses to repetitive nerve stimulation, and anticholinesterase tests were investigated in 12 myasthenic patients before and after thymectomy. In six of them the endarterial acetylcholine test was also carried out. Responsiveness to ACTH or to prednisone treatment was evaluated before and after thymectomy. The typical myasthenic presynaptic disorders were improved by thymectomy, while signs of myasthenic myopathy (according to Rowland's definition) were apparently increased. This process of 'functional myopathophanerosis' is discussed and explained in terms of a previous presynaptic disorder blocking the voluntary recruitment threshold of those motor units which are most affected at both presynaptic and postsynaptic level. Images PMID:168321

Interaction between P2X and nicotinic acetylcholine receptors in glutamate nerve terminals of the rat hippocampus.

PubMed

Rodrigues, Ricardo J; Almeida, Teresa; de Mendonça, Alexandre; Cunha, Rodrigo A

2006-01-01

Nicotinic acetylcholine receptors (nAChRs [constituted by pentameric association of alpha2-10 and beta2-4 subunits]) and P2X receptors (P2XRs [activated by ATP and constituted by multimeric association of P2X1-7 subunits]) are both ionotropic receptors permeable to cations, which have in common the disparity between the wealth of data showing their presence in the brain and little evidence of their participation in mediating synaptic transmission. This has led to the proposal that both nAChRs and P2XRs might primarily modulate rather than directly mediate synaptic transmission, which is in accordance with the predominant presynaptic localization of both receptor subtypes (Role and Berg, 1996; Cunha and Ribeiro, 2000). Interestingly, both functional neurochemical (Allgaier et al., 1995; Salgado et al., 2000; Diáz-Hernández et al., 2002) and electrophysiological studies (Barajas-Lopez et al., 1998; Searl et al., 1998; Zhou and Calligan, 1998; Khakh et al., 2000) indicated a close interaction between nAChRs and P2XRs, which is paralleled by a co-release of ATPand ACh from central terminals (e.g., Richardson and Brown, 1987). Because glutamate release in the hippocampus is controlled by both nAChRs (e.g., McGehee et al., 1995) and P2XRs (Khakh et al., 2003; Rodrigues et al., 2005), we investigated if there was a functional interaction between these two presynaptic ionotropic receptors in the control of glutamate release in the rat hippocampus.

Serotonin in the solitary tract nucleus shortens the laryngeal chemoreflex in anesthetized neonatal rats

PubMed Central

Donnelly, William T.; Bartlett, Donald; Leiter, J.C.

2017-01-01

The laryngeal chemoreflex (LCR), an airway protective reflex that causes apnea and bradycardia, has long been suspected as an initiating event in the sudden infant death syndrome (SIDS). Serotonin (5-HT) and 5-HT receptors may be deficient in the brainstems of babies who die of SIDS, and 5-HT seems to be important in terminating apneas directly or in causing arousals or as part of the process of autoresuscitation. We hypothesized that 5-HT in the brainstem would limit the duration of the LCR. We studied anesthetized rat pups between 7 and 21 days of age and made microinjections into the cisterna magna or into the nucleus of the solitary tract (NTS). Focal, bilateral microinjections of 5-HT into the caudal NTS significantly shortened the LCR. The 5-HT 1a receptor antagonist, WAY 100635, did not affect the LCR consistently, nor did a 5-HT2 receptor antagonist, ketanserin, alter the duration of the LCR. The 5-HT3 specific agonist, 1-(3-chlorophenyl)-biguanide, microinjected bilaterally into the caudal NTS significantly shortened the LCR. Thus, endogenous 5-HT released within the NTS may curtail the respiratory depression that is part of the LCR, and serotonergic shortening of the LCR may be attributed to activation of 5-HT3 receptors within the NTS. 5-HT3 receptors are expressed presynaptically on C-fiber afferents of the superior laryngeal nerve, and serotonergic shortening of the LCR may be mediated presynaptically by enhanced activation of inhibitory interneurons within the NTS that terminate during the LCR. PMID:27121960

Harmful impact on presynaptic glutamate and GABA transport by carbon dots synthesized from sulfur-containing carbohydrate precursor.

PubMed

Borisova, Tatiana; Dekaliuk, Mariia; Pozdnyakova, Natalia; Pastukhov, Artem; Dudarenko, Marina; Borysov, Arsenii; Vari, Sandor G; Demchenko, Alexander P

2017-07-01

Carbon nanoparticles that may be potent air pollutants with adverse effects on human health often contain heteroatoms including sulfur. In order to study in detail their effects on different physiological and biochemical processes, artificially produced carbon dots (CDs) with well-controlled composition that allows fluorescence detection may be of great use. Having been prepared from different types of organic precursors, CDs expose different atoms at their surface suggesting a broad variation of functional groups. Recently, we demonstrated neurotoxic properties of CDs synthesized from the amino acid β-alanine, and it is of importance to analyze whether CDs obtained from different precursors and particularly those exposing sulfur atoms induce similar neurotoxic effects. This study focused on synthesis of CDs from the sulfur-containing precursor thiourea-CDs (TU-CDs) with a size less than 10 nm, their characterization, and neuroactivity assessment. Neuroactive properties of TU-CDs were analyzed based on their effects on the key characteristics of glutamatergic and γ-aminobutyric acid (GABA) neurotransmission in isolated rat brain nerve terminals. It was observed that TU-CDs (0.5-1.0 mg/ml) attenuated the initial velocity of Na + -dependent transporter-mediated uptake and accumulation of L-[ 14 C]glutamate and [ 3 H]GABA by nerve terminals in a dose-dependent manner and increased the ambient level of the neurotransmitters. Starting from the concentration of 0.2 mg/ml, TU-CDs evoked a gradual dose-dependent depolarization of the plasma membrane of nerve terminals measured with the cationic potentiometric dye rhodamine 6G. Within the concentration range of 0.1-0.5 mg/ml, TU-CDs caused an "unphysiological" step-like increase in fluorescence intensity of the рН-sensitive fluorescent dye acridine orange accumulated by synaptic vesicles. Therefore, despite different surface properties and fluorescent features of CDs prepared from different starting materials (thiourea and β-alanine), their principal neurotoxic effects are analogous but displayed at a different level of efficiency. Sulfur-containing TU-CDs exhibit lower effects (by ~30%) on glutamate and GABA transport in the nerve terminals in comparison with sulfur-free β-alanine CDs. Our results suggest considering that an uncontrolled presence of carbon-containing particulate matter in the human environment may pose a toxicity risk for the central nervous system.

Dendritic position is a major determinant of presynaptic strength

PubMed Central

de Jong, Arthur P.H.; Schmitz, Sabine K.; Toonen, Ruud F.G.

2012-01-01

Different regulatory principles influence synaptic coupling between neurons, including positional principles. In dendrites of pyramidal neurons, postsynaptic sensitivity depends on synapse location, with distal synapses having the highest gain. In this paper, we investigate whether similar rules exist for presynaptic terminals in mixed networks of pyramidal and dentate gyrus (DG) neurons. Unexpectedly, distal synapses had the lowest staining intensities for vesicular proteins vGlut, vGAT, Synaptotagmin, and VAMP and for many nonvesicular proteins, including Bassoon, Munc18, and Syntaxin. Concomitantly, distal synapses displayed less vesicle release upon stimulation. This dependence of presynaptic strength on dendritic position persisted after chronically blocking action potential firing and postsynaptic receptors but was markedly reduced on DG dendrites compared with pyramidal dendrites. These data reveal a novel rule, independent of neuronal activity, which regulates presynaptic strength according to dendritic position, with the strongest terminals closest to the soma. This gradient is opposite to postsynaptic gradients observed in pyramidal dendrites, and different cell types apply this rule to a different extent. PMID:22492722

Action potential broadening in a presynaptic channelopathy

NASA Astrophysics Data System (ADS)

Begum, Rahima; Bakiri, Yamina; Volynski, Kirill E.; Kullmann, Dimitri M.

2016-07-01

Brain development and interictal function are unaffected in many paroxysmal neurological channelopathies, possibly explained by homoeostatic plasticity of synaptic transmission. Episodic ataxia type 1 is caused by missense mutations of the potassium channel Kv1.1, which is abundantly expressed in the terminals of cerebellar basket cells. Presynaptic action potentials of small inhibitory terminals have not been characterized, and it is not known whether developmental plasticity compensates for the effects of Kv1.1 dysfunction. Here we use visually targeted patch-clamp recordings from basket cell terminals of mice harbouring an ataxia-associated mutation and their wild-type littermates. Presynaptic spikes are followed by a pronounced afterdepolarization, and are broadened by pharmacological blockade of Kv1.1 or by a dominant ataxia-associated mutation. Somatic recordings fail to detect such changes. Spike broadening leads to increased Ca2+ influx and GABA release, and decreased spontaneous Purkinje cell firing. We find no evidence for developmental compensation for inherited Kv1.1 dysfunction.

A Dynamic Analysis of Secretory Granules Containing Proteins Involved In Learning

NASA Astrophysics Data System (ADS)

Prahl, Louis; Simon, Alex; Jacobs, Conor; Fulwiler, Audrey; Hilken, Lindsay; Scalettar, Bethe; Lochner, Janis

2010-10-01

Formation and encoding of long-term memories requires a series of structural changes at synapses, or sites of neuronal communication, in the hippocampus; these changes are mediated by neuromodulatory proteins and serve to strengthen synapses to improve communication. Two prominent neuromodulators, tissue plasminogen activator (tPA) and brain-derived neurotrophic factor (BDNF), are copackaged into secretory granules (SGs) in the body of nerve cells and are transported to distal synapses by motor proteins. At synapses, particularly presynaptic sites, the fate of tPA and BDNF is largely unknown. Motivated by this, and by recent data implicating presynaptic BDNF in early phases of learning, we used fluorescence microscopy to elucidate dynamic properties of presynaptic tPA and BDNF. We find that presynaptic SGs containing tPA and/or BDNF undergo Brownian and anomalous diffusive motion that, in 75% of cases, is so slow that it typically would be classified as immobility. These results suggest that tPA and BDNF are retained at presynaptic sites to facilitate their corelease and role in learning.

Effects of Ca2+ channel blockers on transmitter release and presynaptic currents at the frog neuromuscular junction.

PubMed Central

Katz, E; Ferro, P A; Cherksey, B D; Sugimori, M; Llinás, R; Uchitel, O D

1995-01-01

1. The effects of the calcium channel blockers, funnel-web spider toxin (FTX), omega-agatoxin IVA (omega-Aga IVA) and omega-conotoxin GVIA (omega-CgTX), were tested on transmitter release and presynaptic currents in frog motor nerve endings. 2. Evoked transmitter release was blocked by FTX (IC50 = 0.02 microliter ml-1) and omega-CgTX (1 microM) but was not affected by omega-Aga IVA (0.5 microM). When FTX (0.1 microliter ml-1) was assayed on spontaneous release either in normal Ringer solution or in low Ca(2+)-high Mg2+ solution, it was found not to affect miniature endplate potential (MEPP) amplitude but to increase MEPP frequency by approximately 2-fold in both conditions. 3. Presynaptic calcium currents (ICa), measured by the perineurial technique in the presence of 10 mM tetraethylammonium chloride (TEA) and 200 microM BaCl2 to block K+ currents, were blocked by omega-CgTX (5 microM), partially blocked by FTX (1 microliter ml-1) and not affected by omega-Aga IVA (0.5 microM). 4. The presynaptic calcium-activated potassium current (IK(Ca)) measured by the perineurial technique in the presence of 0.5 microM 3,4-aminopyridine (DAP) to block voltage-dependent K+ currents, was strongly affected by charybdotoxin (ChTX) (300 nM) and completely abolished by BaCl2 (200 microM). This current was also blocked by omega-CgTX (5 microM) and by CdCl2 (200 microM) but was not affected by FTX (1 microliter ml-1). The blockade by omega-CgTX could not be reversed by elevating [Ca]o to 10 mM. 5. The results suggest that in frog synaptic terminals two omega-CgTX-sensitive populations might coexist. The transmitter release process seems to be mediated by calcium influx through a omega-CgTX- and FTX-sensitive population. PMID:7473230

Effects of Ca2+ channel blockers on transmitter release and presynaptic currents at the frog neuromuscular junction.

PubMed

Katz, E; Ferro, P A; Cherksey, B D; Sugimori, M; Llinás, R; Uchitel, O D

1995-08-01

1. The effects of the calcium channel blockers, funnel-web spider toxin (FTX), omega-agatoxin IVA (omega-Aga IVA) and omega-conotoxin GVIA (omega-CgTX), were tested on transmitter release and presynaptic currents in frog motor nerve endings. 2. Evoked transmitter release was blocked by FTX (IC50 = 0.02 microliter ml-1) and omega-CgTX (1 microM) but was not affected by omega-Aga IVA (0.5 microM). When FTX (0.1 microliter ml-1) was assayed on spontaneous release either in normal Ringer solution or in low Ca(2+)-high Mg2+ solution, it was found not to affect miniature endplate potential (MEPP) amplitude but to increase MEPP frequency by approximately 2-fold in both conditions. 3. Presynaptic calcium currents (ICa), measured by the perineurial technique in the presence of 10 mM tetraethylammonium chloride (TEA) and 200 microM BaCl2 to block K+ currents, were blocked by omega-CgTX (5 microM), partially blocked by FTX (1 microliter ml-1) and not affected by omega-Aga IVA (0.5 microM). 4. The presynaptic calcium-activated potassium current (IK(Ca)) measured by the perineurial technique in the presence of 0.5 microM 3,4-aminopyridine (DAP) to block voltage-dependent K+ currents, was strongly affected by charybdotoxin (ChTX) (300 nM) and completely abolished by BaCl2 (200 microM). This current was also blocked by omega-CgTX (5 microM) and by CdCl2 (200 microM) but was not affected by FTX (1 microliter ml-1). The blockade by omega-CgTX could not be reversed by elevating [Ca]o to 10 mM. 5. The results suggest that in frog synaptic terminals two omega-CgTX-sensitive populations might coexist. The transmitter release process seems to be mediated by calcium influx through a omega-CgTX- and FTX-sensitive population.

Synaptic Vesicle Recycling Is Unaffected in the Ts65Dn Mouse Model of Down Syndrome.

PubMed

Marland, Jamie R K; Smillie, Karen J; Cousin, Michael A

2016-01-01

Down syndrome (DS) is the most common genetic cause of intellectual disability, and arises from trisomy of human chromosome 21. Accumulating evidence from studies of both DS patient tissue and mouse models has suggested that synaptic dysfunction is a key factor in the disorder. The presence of several genes within the DS trisomy that are either directly or indirectly linked to synaptic vesicle (SV) endocytosis suggested that presynaptic dysfunction could underlie some of these synaptic defects. Therefore we determined whether SV recycling was altered in neurons from the Ts65Dn mouse, the best characterised model of DS to date. We found that SV exocytosis, the size of the SV recycling pool, clathrin-mediated endocytosis, activity-dependent bulk endocytosis and SV generation from bulk endosomes were all unaffected by the presence of the Ts65Dn trisomy. These results were obtained using battery of complementary assays employing genetically-encoded fluorescent reporters of SV cargo trafficking, and fluorescent and morphological assays of fluid-phase uptake in primary neuronal culture. The absence of presynaptic dysfunction in central nerve terminals of the Ts65Dn mouse suggests that future research should focus on the established alterations in excitatory / inhibitory balance as a potential route for future pharmacotherapy.

Synaptic Vesicle Recycling Is Unaffected in the Ts65Dn Mouse Model of Down Syndrome

PubMed Central

Marland, Jamie R. K.; Smillie, Karen J.; Cousin, Michael A.

2016-01-01

Down syndrome (DS) is the most common genetic cause of intellectual disability, and arises from trisomy of human chromosome 21. Accumulating evidence from studies of both DS patient tissue and mouse models has suggested that synaptic dysfunction is a key factor in the disorder. The presence of several genes within the DS trisomy that are either directly or indirectly linked to synaptic vesicle (SV) endocytosis suggested that presynaptic dysfunction could underlie some of these synaptic defects. Therefore we determined whether SV recycling was altered in neurons from the Ts65Dn mouse, the best characterised model of DS to date. We found that SV exocytosis, the size of the SV recycling pool, clathrin-mediated endocytosis, activity-dependent bulk endocytosis and SV generation from bulk endosomes were all unaffected by the presence of the Ts65Dn trisomy. These results were obtained using battery of complementary assays employing genetically-encoded fluorescent reporters of SV cargo trafficking, and fluorescent and morphological assays of fluid-phase uptake in primary neuronal culture. The absence of presynaptic dysfunction in central nerve terminals of the Ts65Dn mouse suggests that future research should focus on the established alterations in excitatory / inhibitory balance as a potential route for future pharmacotherapy. PMID:26808141

Manipulation of norepinephrine metabolism with yohimbine in the treatment of autonomic failure

NASA Technical Reports Server (NTRS)

Biaggioni, I.; Robertson, R. M.; Robertson, D.

1994-01-01

It has been postulated that alpha 2-adrenergic receptors play a modulatory role in the regulation of blood pressure. Activation of alpha 2-receptors located in the central nervous system results in inhibition of sympathetic tone and decrease of blood pressure. This indeed may be the mechanism of action of central sympatholytic antihypertensives such as alpha-methyldopa. Presynaptic alpha 2-receptors also are found in adrenergic nerve terminals. These receptors act as a negative feedback mechanism by inhibiting the release of norepinephrine. The relevance of alpha 2-adrenergic receptors for blood pressure regulation can be explored with yohimbine, a selective antagonist of these receptors. Yohimbine increases blood pressure in resting normal volunteers. This effect is associated with an increase in both sympathetic nerve activity, reflecting an increase in central sympathetic outflow, and in norepinephrine spillover, reflecting potentiation of the release of norepinephrine from adrenergic nerve terminals. These actions, therefore, underscore the importance of alpha 2-adrenergic receptors for blood pressure regulation even under resting conditions. Patients with autonomic failure, even those with severe sympathetic deprivation, are hypersensitive to the pressor effects of yohimbine. This increased responsiveness can be explained by sensitization of adrenergic receptors, analogous to denervation supersensitivity, and by the lack of autonomic reflexes that would normally buffer any increase in blood pressure. Preliminary studies suggest that the effectiveness of yohimbine in autonomic failure can be enhanced with monoamine oxidase inhibitors. Used in combination, yohimbine increases norepinephrine release, whereas monoamine oxidase inhibitors inhibit its degradation. Therefore, yohimbine is not only a useful tool in the study of blood pressure regulation, but may offer a therapeutic option in autonomic dysfunction.

Region-specific changes in presynaptic agmatine and glutamate levels in the aged rat brain.

PubMed

Jing, Y; Liu, P; Leitch, B

2016-01-15

During the normal aging process, the brain undergoes a range of biochemical and structural alterations, which may contribute to deterioration of sensory and cognitive functions. Age-related deficits are associated with altered efficacy of synaptic neurotransmission. Emerging evidence indicates that levels of agmatine, a putative neurotransmitter in the mammalian brain, are altered in a region-specific manner during the aging process. The gross tissue content of agmatine in the prefrontal cortex (PFC) of aged rat brains is decreased whereas levels in the temporal cortex (TE) are increased. However, it is not known whether these changes in gross tissue levels are also mirrored by changes in agmatine levels at synapses and thus could potentially contribute to altered synaptic function with age. In the present study, agmatine levels in presynaptic terminals in the PFC and TE regions (300 terminals/region) of young (3month; n=3) and aged (24month; n=3) brains of male Sprague-Dawley rats were compared using quantitative post-embedding immunogold electron-microscopy. Presynaptic levels of agmatine were significantly increased in the TE region (60%; p<0.001) of aged rats compared to young rats, however no significant differences were detected in synaptic levels in the PFC region. Double immunogold labeling indicated that agmatine and glutamate were co-localized in the same synaptic terminals, and quantitative analyses revealed significantly reduced glutamate levels in agmatine-immunopositive synaptic terminals in both regions in aged rats compared to young animals. This study, for the first time, demonstrates differential effects of aging on agmatine and glutamate in the presynaptic terminals of PFC and TE. Future research is required to understand the functional significance of these changes and the underlying mechanisms. Copyright © 2015 IBRO. Published by Elsevier Ltd. All rights reserved.

Cell Biology and Pathophysiology of α-Synuclein

PubMed Central

Burré, Jacqueline; Sharma, Manu; Südhof, Thomas C.

2017-01-01

α-Synuclein is an abundant neuronal protein that is highly enriched in presynaptic nerve terminals. Genetics and neuropathology studies link α-synuclein to Parkinson’s disease (PD) and other neurodegenerative disorders. Accumulation of misfolded oligomers and larger aggregates of α-synuclein defines multiple neurodegenerative diseases called synucleino-pathies, but the mechanisms by which α-synuclein acts in neurodegeneration are unknown. Moreover, the normal cellular function of α-synuclein remains debated. In this perspective, we review the structural characteristics of α-synuclein, its developmental expression pattern, its cellular and subcellular localization, and its function in neurons. We also discuss recent progress on secretion of α-synuclein, which may contribute to its interneuronal spread in a prion-like fashion, and describe the neurotoxic effects of α-synuclein that are thought to be responsible for its role in neurodegeneration. PMID:28108534

Bassoon-disruption slows vesicle replenishment and induces homeostatic plasticity at a CNS synapse

PubMed Central

Mendoza Schulz, Alejandro; Jing, Zhizi; María Sánchez Caro, Juan; Wetzel, Friederike; Dresbach, Thomas; Strenzke, Nicola; Wichmann, Carolin; Moser, Tobias

2014-01-01

Endbulb of Held terminals of auditory nerve fibers (ANF) transmit auditory information at hundreds per second to bushy cells (BCs) in the anteroventral cochlear nucleus (AVCN). Here, we studied the structure and function of endbulb synapses in mice that lack the presynaptic scaffold bassoon and exhibit reduced ANF input into the AVCN. Endbulb terminals and active zones were normal in number and vesicle complement. Postsynaptic densities, quantal size and vesicular release probability were increased while vesicle replenishment and the standing pool of readily releasable vesicles were reduced. These opposing effects canceled each other out for the first evoked EPSC, which showed unaltered amplitude. We propose that ANF activity deprivation drives homeostatic plasticity in the AVCN involving synaptic upscaling and increased intrinsic BC excitability. In vivo recordings from individual mutant BCs demonstrated a slightly improved response at sound onset compared to ANF, likely reflecting the combined effects of ANF convergence and homeostatic plasticity. Further, we conclude that bassoon promotes vesicular replenishment and, consequently, a large standing pool of readily releasable synaptic vesicles at the endbulb synapse. PMID:24442636

Neuromodulatory changes in short-term synaptic dynamics may be mediated by two distinct mechanisms of presynaptic calcium entry.

PubMed

Oh, Myongkeun; Zhao, Shunbing; Matveev, Victor; Nadim, Farzan

2012-12-01

Although synaptic output is known to be modulated by changes in presynaptic calcium channels, additional pathways for calcium entry into the presynaptic terminal, such as non-selective channels, could contribute to modulation of short term synaptic dynamics. We address this issue using computational modeling. The neuropeptide proctolin modulates the inhibitory synapse from the lateral pyloric (LP) to the pyloric dilator (PD) neuron, two slow-wave bursting neurons in the pyloric network of the crab Cancer borealis. Proctolin enhances the strength of this synapse and also changes its dynamics. Whereas in control saline the synapse shows depression independent of the amplitude of the presynaptic LP signal, in proctolin, with high-amplitude presynaptic LP stimulation the synapse remains depressing while low-amplitude stimulation causes facilitation. We use simple calcium-dependent release models to explore two alternative mechanisms underlying these modulatory effects. In the first model, proctolin directly targets calcium channels by changing their activation kinetics which results in gradual accumulation of calcium with low-amplitude presynaptic stimulation, leading to facilitation. The second model uses the fact that proctolin is known to activate a non-specific cation current I ( MI ). In this model, we assume that the MI channels have some permeability to calcium, modeled to be a result of slow conformation change after binding calcium. This generates a gradual increase in calcium influx into the presynaptic terminals through the modulatory channel similar to that described in the first model. Each of these models can explain the modulation of the synapse by proctolin but with different consequences for network activity.

Postvibration depression of the H-reflex as a result of a dual mechanism: an experimental study in humans.

PubMed

Abbruzzese, M; Minatel, C; Reni, L; Favale, E

2001-09-01

Changes in amplitude of the soleus H (S(H))-reflex and its neurographic correlates (P(1) and P(2) waves) after vibration of the soleus muscle have been evaluated as a function of mechanical stimulation frequency, duration of the conditioning train, and test stimulus intensity. Additional experiments aimed at assessing the nervous system mechanisms underlying the postvibration depression (PVD) have been performed. In particular, homonymous (S(HMR) or S(H)) versus heteronymous (S(HTR)) soleus response, evoked respectively by tibial nerve and femoral nerve electrical stimulation, the effectiveness of sub-H threshold tibial nerve conditioning volleys on the S(HTR), and the respective effects of a brief passive stretching of the quadriceps and soleus muscles on the recovery of both the S(HMR) and S(HTR) after vibration of the homologous muscle were investigated under suitable experimental conditions. It was found that PVD occurs in the absence of changes in amplitude of the P(1) wave and the S(HTR), is paralleled by a reduced effectiveness of tibial nerve-conditioning volleys on the S(HTR) and is shortened consistently by brief passive stretching of the homologous muscle. It follows that PVD may be the result of a long-lasting reduction of the transmitter release from Ia presynaptic terminals depending, at least in part, on a protracted postvibration Ia afferent discharge caused by spindles thixotropy. These findings may provide a better understanding of the pathophysiologic mechanisms underlying spasticity in humans.

The effects of atropine and oxotremorine on acetylcholine release in rat phrenic nerve-diaphragm preparations.

PubMed Central

Abbs, E. T.; Joseph, D. N.

1981-01-01

1 Atropine (10(-5) M) enhanced the release of [3H]-acetylcholine from rat isolated hemidiaphragms, previously incubated with [3H-methyl]-choline, stimulated via their phrenic nerves. 2 Oxotremorine (10(-5) M) did not affect the stimulated release of [3H]-acetylcholine but antagonized the facilitatory effects of atropine (10(-5) M). 3 It is suggested that there are presynaptic inhibitory muscarinic receptors that modulate the release of acetylcholine in the phrenic nerves of the rat. PMID:7236997

Profiling Synaptic Proteins Identifies Regulators of Insulin Secretion and Lifespan

PubMed Central

Kaplan, Joshua M.

2008-01-01

Cells are organized into distinct compartments to perform specific tasks with spatial precision. In neurons, presynaptic specializations are biochemically complex subcellular structures dedicated to neurotransmitter secretion. Activity-dependent changes in the abundance of presynaptic proteins are thought to endow synapses with different functional states; however, relatively little is known about the rules that govern changes in the composition of presynaptic terminals. We describe a genetic strategy to systematically analyze protein localization at Caenorhabditis elegans presynaptic specializations. Nine presynaptic proteins were GFP-tagged, allowing visualization of multiple presynaptic structures. Changes in the distribution and abundance of these proteins were quantified in 25 mutants that alter different aspects of neurotransmission. Global analysis of these data identified novel relationships between particular presynaptic components and provides a new method to compare gene functions by identifying shared protein localization phenotypes. Using this strategy, we identified several genes that regulate secretion of insulin-like growth factors (IGFs) and influence lifespan in a manner dependent on insulin/IGF signaling. PMID:19043554

Interplay between glucose and leptin signaling determines the strength of GABAergic synapses at POMC neurons

PubMed Central

Lee, Dong Kun; Jeong, Jae Hoon; Chun, Sung-Kun; Chua, Streamson; Jo, Young-Hwan

2015-01-01

Regulation of GABAergic inhibitory inputs and alterations in POMC neuron activity by nutrients and adiposity signals regulate energy and glucose homeostasis. Thus, understanding how POMC neurons integrate these two signal molecules at the synaptic level is important. Here we show that leptin’s action on GABA release to POMC neurons is influenced by glucose levels. Leptin stimulates the JAK2-PI3K pathway in both presynaptic GABAergic terminals and postsynaptic POMC neurons. Inhibition of AMPK activity in presynaptic terminals decreases GABA release at 10 mM glucose. However, postsynaptic TRPC channel opening by the PI3K-PLC signaling pathway in POMC neurons enhances spontaneous GABA release via activation of presynaptic MC3/4 and mGlu receptors at 2.5 mM glucose. High-fat feeding blunts AMPK-dependent presynaptic inhibition, whereas PLC-mediated GABAergic feedback inhibition remains responsive to leptin. Our data indicate that the interplay between glucose and leptin signaling in glutamatergic POMC neurons is critical for determining the strength of inhibitory tone towards POMC neurons. PMID:25808323

Interplay between glucose and leptin signalling determines the strength of GABAergic synapses at POMC neurons.

PubMed

Lee, Dong Kun; Jeong, Jae Hoon; Chun, Sung-Kun; Chua, Streamson; Jo, Young-Hwan

2015-03-26

Regulation of GABAergic inhibitory inputs and alterations in POMC neuron activity by nutrients and adiposity signals regulate energy and glucose homeostasis. Thus, understanding how POMC neurons integrate these two signal molecules at the synaptic level is important. Here we show that leptin's action on GABA release to POMC neurons is influenced by glucose levels. Leptin stimulates the JAK2-PI3K pathway in both presynaptic GABAergic terminals and postsynaptic POMC neurons. Inhibition of AMPK activity in presynaptic terminals decreases GABA release at 10 mM glucose. However, postsynaptic TRPC channel opening by the PI3K-PLC signalling pathway in POMC neurons enhances spontaneous GABA release via activation of presynaptic MC3/4 and mGlu receptors at 2.5 mM glucose. High-fat feeding blunts AMPK-dependent presynaptic inhibition, whereas PLC-mediated GABAergic feedback inhibition remains responsive to leptin. Our data indicate that the interplay between glucose and leptin signalling in glutamatergic POMC neurons is critical for determining the strength of inhibitory tone towards POMC neurons.

The effect of potassium on exocytosis of transmitter at the frog neuromuscular junction.

PubMed Central

Ceccarelli, B; Fesce, R; Grohovaz, F; Haimann, C

1988-01-01

1. Electrophysiology and morphology have been combined to investigate the time course of the exocytosis of quanta of neurotransmitter induced by elevated concentrations of K+ at the frog neuromuscular junction. 2. Replicas of freeze-fractured resting nerve terminals fixed in the presence of 20 mM-K+ showed images of fusion of synaptic vesicles with the presynaptic axolemma which were closely associated with the active zones. After 1 min in 20 nM-K+ fusions appeared also outside the active zones, and by 5 min they became uniformly distributed over the presynaptic membrane. 3. The average total density of fusions was not significantly different at the various times examined since it decreased at the active zones while it increased over the rest of the membrane. 4. Resting terminals fixed in 20 mM-K+ released 33,000-45,000 quanta after the addition of fixative; terminals stimulated by 20 mM-K+ for 1-5 min released 50,000-100,000 quanta during fixation. The fixative potentiated K+-induced transmitter release. 5. Fusions were uniformly distributed in terminals pre-incubated for 5 min in 20 mM-K+ without added Ca2+, stimulated by adding Ca2+ for 30 s, and then fixed. Conversely, after 5 min stimulation in hypertonic Ringer solution fusions remained predominantly located near the active zones. A similar distribution was observed after 15 min stimulation by a lower concentration of K+ (15 mM). 6. At all concentrations of K+ tested (10, 15, 20, 25 mM) miniature end-plate potential (MEPP) rate attained a steady-state value within 10-15 min. Values from a single junction were generally lower at higher concentrations of K+, which indicates partial inactivation of the secretion-recycling process. 7. The data indicate that K+ initially activates exocytosis at the active zones. Subsequently, ectopic exocytosis is activated while sites at the active zones appear to undergo partial inactivation. These phenomena are not related to the intensity or to the amount of previous secretion. Images Fig. 1 Fig. 2 Fig. 3 Fig. 8 Fig. 10 PMID:2902217

High resolution labeling of cholinergic nerve terminals using a specific fully active biotinylated botulinum neurotoxin type A.

PubMed

Arribas, M; Blasi, J; Egea, G; Fariñas, I; Solsona, C; Marsal, J

1993-12-15

We report here on the synthesis and characterization of a fully active biotinylated derivative of the botulinum neurotoxin type A. Different ratios of biotin: botulinum toxin were tested to optimize derivatizing conditions and a ratio of 35:1 was selected for further experiments. The average number of biotin groups per toxin molecule was estimated to be 7.8, occurring at both heavy and light chains, and almost all externally located and easily accessible to recognition by streptavidin. The modified toxin retained its toxicity and its ability to interact with biological membranes. Apart from its suitability for detection in Western blots and in microtiter well plates, biotinylated botulinum toxin proved to be adequate for morphological labeling studies at both light and electron microscopy. Peroxidase histochemistry in cryostat sections of intoxicated rat hemidiaphragm muscles showed a distinct labeling of end-plates. Electron microscopy studies were performed on the electric organ of Torpedo marmorata using colloidal gold-conjugated streptavidin for detection. After intoxication of electric organ fragments with the modified toxin, gold labels were found associated with the presynaptic plasma membrane of nerve terminals and with the membrane of synaptic vesicles. Moreover, the distribution of biotinylated botulinum toxin binding sites over the membrane of synaptosomes isolated from the electric organ of Torpedo and their relationship with intramembrane particles were analyzed using the replica-staining label-fracture technique. It was found that the toxin is never associated with intramembrane particles.

Influence of oculomotor nerve afferents on central endings of primary trigeminal fibers.

PubMed

Manni, E; Bortolami, R; Pettorossi, V E; Lucchi, M L; Callegari, E; Draicchio, F

1987-12-01

Painful fibers running in the third nerve and originating from the ophthalmic trigeminal area send their central projections at level of substantia gelatinosa of nucleus caudalis trigemini. The central endings of these fibers form axoaxonic synapses with trigeminal fibers entering the brain stem through the trigeminal root. The effect of electrical stimulation of the third nerve central stump on the central endings of trigeminal afferent fibers consists in an increased excitability, possibly resulting in a presynaptic inhibition. This inhibitory influence is due to both direct and indirect connections of the third nerve afferent fibers with the trigeminal ones.

Disruption of the Axonal Trafficking of Tyrosine Hydroxylase mRNA Impairs Catecholamine Biosynthesis in the Axons of Sympathetic Neurons

PubMed Central

Gioio, Anthony E.

2017-01-01

Abstract Tyrosine hydroxylase (TH) is the enzyme that catalyzes the rate-limiting step in the biosynthesis of the catecholamine neurotransmitters. In a previous communication, evidence was provided that TH mRNA is trafficked to the axon, where it is locally translated. In addition, a 50-bp sequence element in the 3′untranslated region (3’UTR) of TH mRNA was identified that directs TH mRNA to distal axons (i.e., zip-code). In the present study, the hypothesis was tested that local translation of TH plays an important role in the biosynthesis of the catecholamine neurotransmitters in the axon and/or presynaptic nerve terminal. Toward this end, a targeted deletion of the axonal transport sequence element was developed, using the lentiviral delivery of the CRISPR/Cas9 system, and two guide RNA (gRNA) sequences flanking the 50-bp cis-acting regulatory element in rat superior cervical ganglion (SCG) neurons. Deletion of the axonal transport element reduced TH mRNA levels in the distal axons and reduced the axonal protein levels of TH and TH activity as measured by phosphorylation of SER40 in SCG neurons. Moreover, deletion of the zip-code diminished the axonal levels of dopamine (DA) and norepinephrine (NE). Conversely, the local translation of exogenous TH mRNA in the distal axon enhanced TH levels and activity, and elevated axonal NE levels. Taken together, these results provide direct evidence to support the hypothesis that TH mRNA trafficking and local synthesis of TH play an important role in the synthesis of catecholamines in the axon and presynaptic terminal. PMID:28630892

Disruption of the Axonal Trafficking of Tyrosine Hydroxylase mRNA Impairs Catecholamine Biosynthesis in the Axons of Sympathetic Neurons.

PubMed

Aschrafi, Armaz; Gioio, Anthony E; Dong, Lijin; Kaplan, Barry B

2017-01-01

Tyrosine hydroxylase (TH) is the enzyme that catalyzes the rate-limiting step in the biosynthesis of the catecholamine neurotransmitters. In a previous communication, evidence was provided that TH mRNA is trafficked to the axon, where it is locally translated. In addition, a 50-bp sequence element in the 3'untranslated region (3'UTR) of TH mRNA was identified that directs TH mRNA to distal axons (i.e., zip-code). In the present study, the hypothesis was tested that local translation of TH plays an important role in the biosynthesis of the catecholamine neurotransmitters in the axon and/or presynaptic nerve terminal. Toward this end, a targeted deletion of the axonal transport sequence element was developed, using the lentiviral delivery of the CRISPR/Cas9 system, and two guide RNA (gRNA) sequences flanking the 50-bp cis- acting regulatory element in rat superior cervical ganglion (SCG) neurons. Deletion of the axonal transport element reduced TH mRNA levels in the distal axons and reduced the axonal protein levels of TH and TH activity as measured by phosphorylation of SER40 in SCG neurons. Moreover, deletion of the zip-code diminished the axonal levels of dopamine (DA) and norepinephrine (NE). Conversely, the local translation of exogenous TH mRNA in the distal axon enhanced TH levels and activity, and elevated axonal NE levels. Taken together, these results provide direct evidence to support the hypothesis that TH mRNA trafficking and local synthesis of TH play an important role in the synthesis of catecholamines in the axon and presynaptic terminal.

Substance P presynaptically depresses the transmission of sensory input to bronchopulmonary neurons in the guinea pig nucleus tractus solitarii

PubMed Central

Sekizawa, Shin-ichi; Joad, Jesse P; Bonham, Ann C

2003-01-01

Substance P modulates the reflex regulation of respiratory function by its actions both peripherally and in the CNS, particularly in the nucleus tractus solitarii (NTS), the first central site for synaptic contact of the lung and airway afferent fibres. There is considerable evidence that the actions of substance P in the NTS augment respiratory reflex output, but the precise effects on synaptic transmission have not yet been determined. Therefore, we determined the effects of substance P on synaptic transmission at the first central synapses by using whole-cell voltage clamping in an NTS slice preparation. Studies were performed on second-order neurons in the slice anatomically identified as receiving monosynaptic input from sensory nerves in the lungs and airways. This was done by the fluorescent labelling of terminal boutons after 1,1′-dioctadecyl-3,3,3′,3′-tetra-methylindocarbo-cyanine perchlorate (DiI) was applied via tracheal instillation. Substance P (1.0, 0.3 and 0.1 μM) significantly decreased the amplitude of excitatory postsynaptic currents (eEPSCs) evoked by stimulation of the tractus solitarius, in a concentration-dependent manner. The decrease was accompanied by an increase in the paired-pulse ratio of two consecutive eEPSCs, and a decrease in the frequency, but not the amplitude, of spontaneous EPSCs and miniature EPSCs, findings consistent with a presynaptic site of action. The effects were consistently and significantly attenuated by a neurokinin-1 (NK1) receptor antagonist (SR140333, 3 μM). The data suggest a new site of action for substance P in the NTS (NK1 receptors on the central terminals of sensory fibres) and a new mechanism (depression of synaptic transmission) for regulating respiratory reflex function. PMID:14561836

Antivenom for Neuromuscular Paralysis Resulting From Snake Envenoming

PubMed Central

Silva, Anjana; Hodgson, Wayne C.; Isbister, Geoffrey K.

2017-01-01

Antivenom therapy is currently the standard practice for treating neuromuscular dysfunction in snake envenoming. We reviewed the clinical and experimental evidence-base for the efficacy and effectiveness of antivenom in snakebite neurotoxicity. The main site of snake neurotoxins is the neuromuscular junction, and the majority are either: (1) pre-synaptic neurotoxins irreversibly damaging the presynaptic terminal; or (2) post-synaptic neurotoxins that bind to the nicotinic acetylcholine receptor. Pre-clinical tests of antivenom efficacy for neurotoxicity include rodent lethality tests, which are problematic, and in vitro pharmacological tests such as nerve-muscle preparation studies, that appear to provide more clinically meaningful information. We searched MEDLINE (from 1946) and EMBASE (from 1947) until March 2017 for clinical studies. The search yielded no randomised placebo-controlled trials of antivenom for neuromuscular dysfunction. There were several randomised and non-randomised comparative trials that compared two or more doses of the same or different antivenom, and numerous cohort studies and case reports. The majority of studies available had deficiencies including poor case definition, poor study design, small sample size or no objective measures of paralysis. A number of studies demonstrated the efficacy of antivenom in human envenoming by clearing circulating venom. Studies of snakes with primarily pre-synaptic neurotoxins, such as kraits (Bungarus spp.) and taipans (Oxyuranus spp.) suggest that antivenom does not reverse established neurotoxicity, but early administration may be associated with decreased severity or prevent neurotoxicity. Small studies of snakes with mainly post-synaptic neurotoxins, including some cobra species (Naja spp.), provide preliminary evidence that neurotoxicity may be reversed with antivenom, but placebo controlled studies with objective outcome measures are required to confirm this. PMID:28422078

Inhibition of presynaptic activity by zinc released from mossy fiber terminals during tetanic stimulation.

PubMed

Minami, Akira; Sakurada, Naomi; Fuke, Sayuri; Kikuchi, Kazuya; Nagano, Tetsuo; Oku, Naoto; Takeda, Atsushi

2006-01-01

Zinc exists in high densities in the giant boutons of hippocampal mossy fibers. On the basis of the evidence that zinc decreases extracellular glutamate concentration in the hippocampus, the presynaptic action of zinc released from mossy fibers during high-frequency (tetanic) stimulation was examined using hippocampal slices. The increase in zinc-specific fluorescent signals was observed in both extracellular and intracellular compartments in the mossy fiber terminals during the delivery of tetanic stimuli (100 Hz, 1 sec) to the dentate granule cell layer, suggesting that zinc released from mossy fibers is immediately retaken up by mossy fibers. When mossy fiber terminals were preferentially double-stained with zinc and calcium indicators and tetanic stimuli (100 Hz, 1 sec) were delivered to the dentate granule cell layer, the increase in calcium orange signal during the stimulation was enhanced in mossy fiber terminals by addition of CaEDTA, a membrane-impermeable zinc chelator, and was suppressed by addition of zinc. The decrease in FM4-64 signal (vesicular exocytosis) during tetanic stimulation (10 Hz, 180 sec), which induced mossy fiber long-term potentiation, was also enhanced in mossy fiber terminals by addition of CaEDTA and was suppressed by addition of zinc. The present study demonstrates that zinc released from mossy fibers may be a negative-feedback factor against presynaptic activity during tetanic stimulation.

Myasthenia gravis and related disorders: Pathology and molecular pathogenesis.

PubMed

Ha, James C; Richman, David P

2015-04-01

Disorders affecting the presynaptic, synaptic, and postsynaptic portions of the neuromuscular junction arise from various mechanisms in children and adults, including acquired autoimmune or toxic processes as well as genetic mutations. Disorders include autoimmune myasthenia gravis associated with acetylcholine receptor, muscle specific kinase or Lrp4 antibodies, Lambert-Eaton myasthenic syndrome, nerve terminal hyperexcitability syndromes, Guillain Barré syndrome, botulism, organophosphate poisoning and a number of congenital myasthenic syndromes. This review focuses on the various molecular and pathophysiological mechanisms of these disorders, characterization of which has been crucial to the development of treatment strategies specific for each pathogenic mechanism. In the future, further understanding of the underlying processes may lead to more effective and targeted therapies of these disorders. This article is part of a Special Issue entitled: Neuromuscular Diseases: Pathology and Molecular Pathogenesis. Copyright © 2014 Elsevier B.V. All rights reserved.

Studies on the cellular localization of spinal cord substance P receptors.

PubMed

Helke, C J; Charlton, C G; Wiley, R G

1986-10-01

Substance P-immunoreactivity and specific substance P binding sites are present in the spinal cord. Receptor autoradiography showed the discrete localization of substance P binding sites in both sensory and motor regions of the spinal cord and functional studies suggested an important role for substance P receptor activation in autonomic outflow, nociception, respiration and somatic motor function. In the current studies, we investigated the cellular localization of substance P binding sites in rat spinal cord using light microscopic autoradiography combined with several lesioning techniques. Unilateral injections of the suicide transport agent, ricin, into the superior cervical ganglion reduced substance P binding and cholinesterase-stained preganglionic sympathetic neurons in the intermediolateral cell column. However, unilateral electrolytic lesions of ventral medullary substance P neurons which project to the intermediolateral cell column did not alter the density of substance P binding in the intermediolateral cell column. Likewise, 6-hydroxydopamine and 5,7-dihydroxytryptamine, which destroy noradrenergic and serotonergic nerve terminals, did not reduce the substance P binding in the intermediolateral cell column. It appears, therefore, that the substance P binding sites are located postsynaptically on preganglionic sympathetic neurons rather than presynaptically on substance P-immunoreactive processes (i.e. as autoreceptors) or on monoamine nerve terminals. Unilateral injections of ricin into the phrenic nerve resulted in the unilateral destruction of phrenic motor neurons in the cervical spinal cord and caused a marked reduction in the substance P binding in the nucleus. Likewise, sciatic nerve injections of ricin caused a loss of associated motor neurons in the lateral portion of the ventral horn of the lumbar spinal cord and a reduction in the substance P binding. Sciatic nerve injections of ricin also destroyed afferent nerves of the associated dorsal root ganglia and increased the density of substance P binding in the dorsal horn. Capsaicin, which destroys small diameter primary sensory neurons, similarly increased the substance P binding in the dorsal horn. These studies show that the cellular localization of substance P binding sites can be determined by analysis of changes in substance P binding to discrete regions of spinal cord after selective lesions of specific groups of neurons. The data show the presence of substance P binding sites on preganglionic sympathetic neurons in the intermediolateral cell column and on somatic motor neurons in the ventral horn, including the phrenic motor nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Shank3 is localized in axons and presynaptic specializations of developing hippocampal neurons and involved in the modulation of NMDA receptor levels at axon terminals.

PubMed

Halbedl, Sonja; Schoen, Michael; Feiler, Marisa S; Boeckers, Tobias M; Schmeisser, Michael J

2016-04-01

Autism-related Shank1, Shank2, and Shank3 are major postsynaptic scaffold proteins of excitatory glutamatergic synapses. A few studies, however, have already indicated that within a neuron, the presence of Shank family members is not limited to the postsynaptic density. By separating axons from dendrites of developing hippocampal neurons in microfluidic chambers, we show that RNA of all three Shank family members is present within axons. Immunostaining confirms these findings as all three Shanks are indeed found within separated axons and further co-localize with well-known proteins of the presynaptic specialization in axon terminals. Therefore, Shank proteins might not only serve as postsynaptic scaffold proteins, but also play a crucial role during axonal outgrowth and presynaptic development and function. This is supported by our findings that shRNA-mediated knockdown of Shank3 results in up-regulation of the NMDA receptor subunit GluN1 in axon terminals. Taken together, our findings will have major implications for the future analysis of neuronal Shank biology in both health and disease. Shank1, Shank2, and Shank3 are major postsynaptic scaffold proteins of excitatory glutamatergic synapses strongly related to several neuropsychiatric disorders. However, a few studies have already implicated a functional role of the Shanks beyond the postsynaptic density (PSD). We here show that all three Shanks are localized in both axons and pre-synaptic specializiations of developing hippocampal neurons in culture. We further provide evidence that Shank3 is involved in the modulation of NMDA receptor levels at axon terminals. Taken together, our study will open up novel avenues for the future analysis of neuronal Shank biology in both health and disease. © 2016 International Society for Neurochemistry.

Trifurcation of the tibial nerve within the tarsal tunnel.

PubMed

Develi, Sedat

2018-05-01

The tibial nerve is the larger terminal branch of the sciatic nerve and it terminates in the tarsal tunnel by giving lateral and medial plantar nerves. We present a rare case of trifurcation of the tibial nerve within the tarsal tunnel. The variant nerve curves laterally after branching from the tibial nerve and courses deep to quadratus plantae muscle. Interestingly, posterior tibial artery was also terminating by giving three branches. These branches were accompanying the terminal branches of the tibial nerve.

G-protein-coupled inward rectifier potassium channels involved in corticostriatal presynaptic modulation.

PubMed

Meneses, David; Mateos, Verónica; Islas, Gustavo; Barral, Jaime

2015-09-01

Presynaptic modulation has been associated mainly with calcium channels but recent data suggests that inward rectifier potassium channels (K(IR)) also play a role. In this work we set to characterize the role of presynaptic K(IR) channels in corticostriatal synaptic transmission. We elicited synaptic potentials in striatum by stimulating cortical areas and then determined the synaptic responses of corticostriatal synapsis by using paired pulse ratio (PPR) in the presence and absence of several potassium channel blockers. Unspecific potassium channels blockers Ba(2+) and Cs(+) reduced the PPR, suggesting that these channels are presynaptically located. Further pharmacological characterization showed that application of tertiapin-Q, a specific K(IR)3 channel family blocker, also induced a reduction of PPR, suggesting that K(IR)3 channels are present at corticostriatal terminals. In contrast, exposure to Lq2, a specific K(IR)1.1 inward rectifier potassium channel, did not induce any change in PPR suggesting the absence of these channels in the presynaptic corticostriatal terminals. Our results indicate that K(IR)3 channels are functionally expressed at the corticostriatal synapses, since blockage of these channels result in PPR decrease. Our results also help to explain how synaptic activity may become sensitive to extracellular signals mediated by G-protein coupled receptors. A vast repertoire of receptors may influence neurotransmitter release in an indirect manner through regulation of K(IR)3 channels. © 2015 Wiley Periodicals, Inc.

Presynaptic mechanisms of lead neurotoxicity: effects on vesicular release, vesicle clustering and mitochondria number.

PubMed

Zhang, Xiao-Lei; Guariglia, Sara R; McGlothan, Jennifer L; Stansfield, Kirstie H; Stanton, Patric K; Guilarte, Tomás R

2015-01-01

Childhood lead (Pb2+) intoxication is a global public health problem and accounts for 0.6% of the global burden of disease associated with intellectual disabilities. Despite the recognition that childhood Pb2+ intoxication contributes significantly to intellectual disabilities, there is a fundamental lack of knowledge on presynaptic mechanisms by which Pb2+ disrupts synaptic function. In this study, using a well-characterized rodent model of developmental Pb2+ neurotoxicity, we show that Pb2+ exposure markedly inhibits presynaptic vesicular release in hippocampal Schaffer collateral-CA1 synapses in young adult rats. This effect was associated with ultrastructural changes which revealed a reduction in vesicle number in the readily releasable/docked vesicle pool, disperse vesicle clusters in the resting pool, and a reduced number of presynaptic terminals with multiple mitochondria with no change in presynaptic calcium influx. These studies provide fundamental knowledge on mechanisms by which Pb2+ produces profound inhibition of presynaptic vesicular release that contribute to deficits in synaptic plasticity and intellectual development.

Active zone density is conserved during synaptic growth but impaired in aged mice

PubMed Central

Chen, Jie; Mizushige, Takafumi; Nishimune, Hiroshi

2013-01-01

Presynaptic active zones are essential structures for synaptic vesicle release, but the developmental regulation of their number and maintenance during aging at mammalian neuromuscular junctions (NMJs) remains unknown. Here, we analyzed the distribution of active zones in developing, mature, and aged mouse NMJs by immunohistochemical detection of the active zone-specific protein Bassoon. Bassoon is a cytosolic scaffolding protein essential for the active zone assembly in ribbon synapses and some brain synapses. Bassoon staining showed a punctate pattern in nerve terminals and axons at the nascent NMJ on embryonic days 16.5–18.5. Three-dimensional reconstruction of NMJs revealed that the majority of Bassoon puncta within an NMJ were attached to the presynaptic membrane from postnatal day 0 to adulthood, and colocalized with another active zone protein Piccolo. During postnatal development, the number of Bassoon puncta increased as the size of the synapses increased. Importantly, the density of Bassoon puncta remained relatively constant from postnatal day 0 to 54 at 2.3 puncta/μm2, while the synapse size increased 3.3-fold. However, Bassoon puncta density and signal intensity were significantly attenuated at the NMJs of 27-month-old aged mice. These results suggest that synapses maintain the density of synaptic vesicle release sites while the synapse size changes, but this density becomes impaired during aging. PMID:21935939

Targeting Chronic and Neuropathic Pain: The N-type Calcium Channel Comes of Age

PubMed Central

Snutch, Terrance P.

2005-01-01

Summary: The rapid entry of calcium into cells through activation of voltage-gated calcium channels directly affects membrane potential and contributes to electrical excitability, repetitive firing patterns, excitation-contraction coupling, and gene expression. At presynaptic nerve terminals, calcium entry is the initial trigger mediating the release of neurotransmitters via the calcium-dependent fusion of synaptic vesicles and involves interactions with the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex of synaptic release proteins. Physiological factors or drugs that affect either presynaptic calcium channel activity or the efficacy of calcium-dependent vesicle fusion have dramatic consequences on synaptic transmission, including that mediating pain signaling. The N-type calcium channel exhibits a number of characteristics that make it an attractive target for therapeutic intervention concerning chronic and neuropathic pain conditions. Within the past year, both U.S. and European regulatory agencies have approved the use of the cationic peptide Prialt for the treatment of intractable pain. Prialt is the first N-type calcium channel blocker approved for clinical use and represents the first new proven mechanism of action for chronic pain intervention in many years. The present review discusses the rationale behind targeting the N-type calcium channel, some of the limitations confronting the widespread clinical application of Prialt, and outlines possible strategies to improve upon Prialt's relatively narrow therapeutic window. PMID:16489373

Robust presynaptic serotonin 5-HT1B receptor inhibition of the striatonigral output and its sensitization by chronic fluoxetine treatment

PubMed Central

Ding, Shengyuan; Li, Li

2015-01-01

The striatonigral projection is a striatal output pathway critical to motor control, cognition, and emotion regulation. Its axon terminals in the substantia nigra pars reticulata (SNr) express a high level of serotonin (5-HT) type 1B receptors (5-HT1BRs), whereas the SNr also receives an intense 5-HT innervation that expresses 5-HT transporters, providing an anatomic substrate for 5-HT and selective 5-HT reuptake inhibitor (SSRI)-based antidepressant treatment to regulate the striatonigral output. In this article we show that 5-HT, by activating presynaptic 5-HT1BRs on the striatonigral axon terminals, potently inhibited the striatonigral GABA output, as reflected in the reduction of the striatonigral inhibitory postsynaptic currents in SNr GABA neurons. Functionally, 5-HT1BR agonism reduced the striatonigral GABA output-induced pause of the spontaneous high-frequency firing in SNr GABA neurons. Equally important, chronic SSRI treatment with fluoxetine enhanced this presynaptic 5-HT1BR-mediated pause reduction in SNr GABA neurons. Taken together, these results indicate that activation of the 5-HT1BRs on the striatonigral axon terminals can limit the motor-promoting GABA output. Furthermore, in contrast to the desensitization of 5-HT1 autoreceptors, chronic SSRI-based antidepressant treatment sensitizes this presynaptic 5-HT1BR-mediated effect in the SNr, a novel cellular mechanism that alters the striatonigral information transfer, potentially contributing to the behavioral effects of chronic SSRI treatment. PMID:25787955

Hispidulin inhibits the release of glutamate in rat cerebrocortical nerve terminals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Tzu-Yu; Department of Mechanical Engineering, Yuan Ze University, Taoyuan, 320, Taiwan; Lu, Cheng-Wei

2012-09-01

Hispidulin, a naturally occurring flavone, has been reported to have an antiepileptic profile. An excessive release of glutamate is considered to be related to neuropathology of epilepsy. We investigated whether hispidulin affected endogenous glutamate release in rat cerebral cortex nerve terminals (synaptosomes) and explored the possible mechanism. Hispidulin inhibited the release of glutamate evoked by the K{sup +} channel blocker 4-aminopyridine (4-AP). The effects of hispidulin on the evoked glutamate release were prevented by the chelation of extracellular Ca{sup 2+} ions and the vesicular transporter inhibitor bafilomycin A1. However, the glutamate transporter inhibitor DL-threo-beta-benzyl-oxyaspartate did not have any effect onmore » hispidulin action. Hispidulin reduced the depolarization-induced increase in cytosolic free Ca{sup 2+} concentration ([Ca{sup 2+}]{sub C}), but did not alter 4-AP-mediated depolarization. Furthermore, the effect of hispidulin on evoked glutamate release was abolished by blocking the Ca{sub v}2.2 (N-type) and Ca{sub v}2.1 (P/Q-type) channels, but not by blocking ryanodine receptors or mitochondrial Na{sup +}/Ca{sup 2+} exchange. Mitogen-activated protein kinase kinase (MEK) inhibition also prevented the inhibitory effect of hispidulin on evoked glutamate release. Western blot analyses showed that hispidulin decreased the 4-AP-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and synaptic vesicle-associated protein synapsin I, a major presynaptic substrate for ERK; this decrease was also blocked by the MEK inhibitor. Moreover, the inhibition of glutamate release by hispidulin was strongly attenuated in mice without synapsin I. These results show that hispidulin inhibits glutamate release from cortical synaptosomes in rats through the suppression of presynaptic voltage-dependent Ca{sup 2+} entry and ERK/synapsin I signaling pathway. -- Highlights: ► Hispidulin inhibited glutamate release from rat cerebrocortical synaptosomes. ► This action did not involve the participation of GABA{sub A} receptors. ► A decrease in the Ca{sup 2+} influx through Ca{sub v}2.2 and Ca{sub v}2.1 channels was involved. ► A role for the MAPK/ERK/synapsin I pathway in the action of hispidulin was suggested. ► This study provided further understanding of the mode of hispidulin action in the brain.« less

Calcium released by photolysis of DM-nitrophen stimulates transmitter release at squid giant synapse.

PubMed

Delaney, K R; Zucker, R S

1990-07-01

1. Transmitter release at the squid giant synapse was stimulated by photolytic release of Ca2+ from the 'caged' Ca2+ compound DM-nitrophen (Kaplan & Ellis-Davies, 1988) inserted into presynaptic terminals. 2. Competing binding reactions cause the amount of Ca2+ released by DM-nitrophen photolysis to depend on the concentrations of DM-nitrophen, total Ca2+, Mg+, ATP and native cytoplasmic Ca2+ buffer. Measurements of presynaptic [Ca2+] changes by co-injection of the fluorescent indicator dye Fura-2 show that DM-nitrophen photolysis causes a transient rise in Ca2+ followed by decay within about 150 ms to an increased steady-state level. 3. Rapid photolysis of Ca2(+)-loaded nitrophen within the presynaptic terminal was followed in less than a millisecond by depolarization of the postsynaptic membrane. As with action potential-evoked excitatory postsynaptic potentials (EPSPs), the light-evoked response was partially and reversibly blocked by 1-3 mM-kainic acid which desensitizes postsynaptic glutamate receptors. 4. Release was similar in magnitude and rate to normal action potential-mediated EPSPs. 5. The release of transmitter by photolysis of Ca2(+)-loaded DM-nitrophen was not affected by removal of Ca2+ from the saline or addition of tetrodotoxin. Photolysis of DM-nitrophen injected into presynaptic terminals without added Ca2+ did not stimulate release of transmitter nor did it interfere with normal action potential-mediated release. 6. Stimulation of presynaptic action potentials in Ca2(+)-free saline during the light-evoked response did not elicit increased release of transmitter if the ganglion was bathed in Ca2(+)-free saline, i.e. in the absence of Ca2+ influx. Increasing the intensity of the light or stimulating presynaptic action potentials in Ca2(+)-containing saline increased the release of transmitter. Therefore the failure of presynaptic voltage change to increase transmitter release resulting from release of caged Ca2+ was not due to saturation or inhibition of the release mechanism by light-released Ca2+. 7. Decreasing the temperature of the preparation increased the delay to onset of the light-evoked response and reduced its amplitude and rate of rise to an extent similar to that observed for action potential-evoked EPSPs.

Task- and time-dependent modulation of Ia presynaptic inhibition during fatiguing contractions performed by humans

PubMed Central

Maerz, Adam H.; Gould, Jeffrey R.; Enoka, Roger M.

2011-01-01

Presynaptic modulation of Ia afferents converging onto the motor neuron pool of the extensor carpi radialis (ECR) was compared during contractions (20% of maximal force) sustained to failure as subjects controlled either the angular position of the wrist while supporting an inertial load (position task) or exerted an equivalent force against a rigid restraint (force task). Test Hoffmann (H) reflexes were evoked in the ECR by stimulating the radial nerve above the elbow. Conditioned H reflexes were obtained by stimulating either the median nerve above the elbow or at the wrist (palmar branch) to assess presynaptic inhibition of homonymous (D1 inhibition) and heteronymous Ia afferents (heteronymous Ia facilitation), respectively. The position task was briefer than the force task (P = 0.001), although the maximal voluntary force and electromyograph for ECR declined similarly at failure for both tasks. Changes in the amplitude of the conditioned H reflex were positively correlated between the two conditioning methods (P = 0.02) and differed between the two tasks (P < 0.05). The amplitude of the conditioned H reflex during the position task first increased (129 ± 20.5% of the initial value, P < 0.001) before returning to its initial value (P = 0.22), whereas it increased progressively during the force task to reach 122 ± 17.4% of the initial value at failure (P < 0.001). Moreover, changes in conditioned H reflexes were associated with the time to task failure and force fluctuations. The results suggest a task- and time-dependent modulation of presynaptic inhibition of Ia afferents during fatiguing contractions. PMID:21543747

On the pharmacology of ascending, descending and recurrent postsynatic inhibition of the cuneothalamic relay cells in the cat

PubMed Central

Kelly, J. S.; Renaud, L. P.

1973-01-01

1. In cats decerebrated or anaesthetized with pentobarbitone, cells of the middle third of the cuneate nucleus that were excited by tactile stimulation of the ipsilateral forelimb (responding to displacement of hairs, skin or joints) and inhibited by electrical stimulation of the contralateral pyramid, were invariably inhibited by electrical stimulation of the ipsilateral forepaw and the contralateral forelimb nerves. 2. In 50% of the cats, the cells were more fully identified by placing electrodes stereotaxically in the contralateral medial lemniscus. Recurrent inhibition was always a concomitant of the antidromic action potential. 3. The intensity and the duration of inhibition evoked by all of these pathways was totally resistant to iontophoretic and intravenous strychnine in doses at least 5 times that required to block completely the response of the same cells to iontophoretic glycine and was extremely sensitive to either iontophoretic bicuculline or picrotoxin. 4. Although the inhibition was invariably sensitive to intravenous picrotoxin, no significant change occurred in the duration or intensity of the inhibition when bicuculline was administered intravenously (5 or 6 times) as repeated doses of 0·2 mg/kg. 5. Postsynaptic inhibition in the cuneate may be mediated by γ-aminobutyric acid released from the nerve terminals of a common pool of interneurones shared by ascending, descending and recurrent pathways. Since the receptors involved in this pathway are resistant to intravenous bicuculline, they may well be distinct from those responsible for changes in the primary afferent terminal excitability, usually believed to be associated with presynaptic inhibition. PMID:4357959

Target-specific expression of presynaptic NMDA receptors in neocortical microcircuits.

PubMed

Buchanan, Katherine A; Blackman, Arne V; Moreau, Alexandre W; Elgar, Dale; Costa, Rui P; Lalanne, Txomin; Tudor Jones, Adam A; Oyrer, Julia; Sjöström, P Jesper

2012-08-09

Traditionally, NMDA receptors are located postsynaptically; yet, putatively presynaptic NMDA receptors (preNMDARs) have been reported. Although implicated in controlling synaptic plasticity, their function is not well understood and their expression patterns are debated. We demonstrate that, in layer 5 of developing mouse visual cortex, preNMDARs specifically control synaptic transmission at pyramidal cell inputs to other pyramidal cells and to Martinotti cells, while leaving those to basket cells unaffected. We also reveal a type of interneuron that mediates ascending inhibition. In agreement with synapse-specific expression, we find preNMDAR-mediated calcium signals in a subset of pyramidal cell terminals. A tuned network model predicts that preNMDARs specifically reroute information flow in local circuits during high-frequency firing, in particular by impacting frequency-dependent disynaptic inhibition mediated by Martinotti cells, a finding that we experimentally verify. We conclude that postsynaptic cell type determines presynaptic terminal molecular identity and that preNMDARs govern information processing in neocortical columns. Copyright © 2012 Elsevier Inc. All rights reserved.

Crimpy enables discrimination of presynaptic and postsynaptic pools of a BMP at the Drosophila neuromuscular junction.

PubMed

James, Rebecca E; Hoover, Kendall M; Bulgari, Dinara; McLaughlin, Colleen N; Wilson, Christopher G; Wharton, Kristi A; Levitan, Edwin S; Broihier, Heather T

2014-12-08

Distinct pools of the bone morphogenetic protein (BMP) Glass bottom boat (Gbb) control structure and function of the Drosophila neuromuscular junction. Specifically, motoneuron-derived Gbb regulates baseline neurotransmitter release, whereas muscle-derived Gbb regulates neuromuscular junction growth. Yet how cells differentiate between these ligand pools is not known. Here we present evidence that the neuronal Gbb-binding protein Crimpy (Cmpy) permits discrimination of pre- and postsynaptic ligand by serving sequential functions in Gbb signaling. Cmpy first delivers Gbb to dense core vesicles (DCVs) for activity-dependent release from presynaptic terminals. In the absence of Cmpy, Gbb is no longer associated with DCVs and is not released by activity. Electrophysiological analyses demonstrate that Cmpy promotes Gbb's proneurotransmission function. Surprisingly, the Cmpy ectodomain is itself released upon DCV exocytosis, arguing that Cmpy serves a second function in BMP signaling. In addition to trafficking Gbb to DCVs, we propose that Gbb/Cmpy corelease from presynaptic terminals defines a neuronal protransmission signal. Copyright © 2014 Elsevier Inc. All rights reserved.

Influence of transcutaneous electrical nerve stimulation conditions on disynaptic reciprocal Ia inhibition and presynaptic inhibition in healthy adults.

PubMed

Takeda, Kazuya; Tanabe, Shigeo; Koyama, Soichiro; Ushiroyama, Kosuke; Naoi, Yuki; Motoya, Ikuo; Sakurai, Hiroaki; Kanada, Yoshikiyo

2017-03-01

This study investigated the influence of stimulus conditions of transcutaneous electrical nerve stimulation (TENS) on disynaptic reciprocal Ia inhibition (RI) and presynaptic inhibition (D1 inhibition) in healthy adults. Eight healthy participants received TENS (stimulus frequencies of 50, 100, and 200 Hz) over the deep peroneal nerve and tibialis anterior (TA) muscle in the resting condition for 30 min. At pre- and post-intervention, the RI from the TA to the soleus (SOL) and D1 inhibition of the SOL alpha motor neuron were assessed by evoked electromyography. The results showed that RI was not changed by TENS at any stimulus frequency condition. Conversely, D1 inhibition was significantly changed by TENS regardless of the stimulus frequency. The present results and previous studies pertaining to RI suggest that the resting condition might strongly influence the lack of pre- vs. post-intervention change in the RI. Regarding the D1 inhibition, the present results suggest that the effect of TENS might be caused by post-tetanic potentiation. The knowledge gained from the present study might contribute to a better understanding of fundamental studies of TENS in healthy adults and its clinical application for stroke survivors.

Simultaneous monitoring of presynaptic transmitter release and postsynaptic receptor trafficking reveals an enhancement of presynaptic activity in metabotropic glutamate receptor-mediated long-term depression.

PubMed

Xu, Wei; Tse, Yiu Chung; Dobie, Frederick A; Baudry, Michel; Craig, Ann Marie; Wong, Tak Pan; Wang, Yu Tian

2013-03-27

Although the contribution of postsynaptic mechanisms to long-term synaptic plasticity has been studied extensively, understanding the contribution of presynaptic modifications to this process lags behind, primarily because of a lack of techniques with which to directly and quantifiably measure neurotransmitter release from synaptic terminals. Here, we developed a method to measure presynaptic activity through the biotinylation of vesicular transporters in vesicles fused with presynaptic membranes during neurotransmitter release. This method allowed us for the first time to selectively quantify the spontaneous or evoked release of glutamate or GABA at their respective synapses. Using this method to investigate presynaptic changes during the expression of group I metabotropic glutamate receptor (mGluR1/5)-mediated long-term depression (LTD) in cultured rat hippocampal neurons, we discovered that this form of LTD was associated with increased presynaptic release of glutamate, despite reduced miniature EPSCs measured with whole-cell recording. Moreover, we found that specific blockade of AMPA receptor (AMPAR) endocytosis with a membrane-permeable GluR2-derived peptide not only prevented the expression of LTD but also eliminated LTD-associated increase in presynaptic release. Thus, our work not only demonstrates that mGluR1/5-mediated LTD is associated with increased endocytosis of postsynaptic AMPARs but also reveals an unexpected homeostatic/compensatory increase in presynaptic release. In addition, this study indicates that biotinylation of vesicular transporters in live cultured neurons is a valuable tool for studying presynaptic function.

The final stage of cholinergic differentiation occurs below inner hair cells during development of the rodent cochlea.

PubMed

Bergeron, Adam L; Schrader, Angela; Yang, Dan; Osman, Abdullah A; Simmons, Dwayne D

2005-12-01

To gain further insights into the cholinergic differentiation of presynaptic efferent terminals in the inner ear, we investigated the expression of the high-affinity choline transporter (ChT1) in comparison to other presynaptic and cholinergic markers. In the adult mammalian cochlea, cholinergic axons from medial olivocochlear (OC) neurons form axosomatic synapses with outer hair cells (OHCs), whereas axons from lateral OC neurons form axodendritic synapses on afferent fibers below inner hair cells (IHCs). Mouse brain and cochlea homogenates reveal at least two ChT1 isoforms: a nonglycosylated approximately 73 kDa protein and a glycosylated approximately 45 kDa protein. In mouse brain, ChT1 is preferentially expressed by neurons in periolivary regions of the superior olive consistent with the location of medial OC neurons. In the adult mouse cochlea, ChT1-positive terminals are located almost exclusively below OHCs consistent with a medial OC innervation. Between postnatal day 2 (P2) and P4, ChT1-positive terminals are below IHCs and occur after the expression of growth-associated protein 43, synapsin, and the vesicular acetylcholine transporter. By P15, ChT1-positive terminals are mostly on OHCs. Accounting for differences in gestational age, the developmental expression of ChT1 in the rat cochlea is similar to the mouse. However, in older rats ChT1-positive terminals are below IHCs and OHCs. In both rat and mouse, our observations indicate that the onset of ChT1 expression occurs after efferent terminals are below IHCs and express other presynaptic and cholinergic markers. In the mouse, but not in the rat, ChT1 may preferentially identify medial OC neurons.

SAD-B kinase regulates pre-synaptic vesicular dynamics at hippocampal Schaffer collateral synapses and affects contextual fear memory.

PubMed

Watabe, Ayako M; Nagase, Masashi; Hagiwara, Akari; Hida, Yamato; Tsuji, Megumi; Ochiai, Toshitaka; Kato, Fusao; Ohtsuka, Toshihisa

2016-01-01

Synapses of amphids defective (SAD)-A/B kinases control various steps in neuronal development and differentiation, such as axon specifications and maturation in central and peripheral nervous systems. At mature pre-synaptic terminals, SAD-B is associated with synaptic vesicles and the active zone cytomatrix; however, how SAD-B regulates neurotransmission and synaptic plasticity in vivo remains unclear. Thus, we used SAD-B knockout (KO) mice to study the function of this pre-synaptic kinase in the brain. We found that the paired-pulse ratio was significantly enhanced at Shaffer collateral synapses in the hippocampal CA1 region in SAD-B KO mice compared with wild-type littermates. We also found that the frequency of the miniature excitatory post-synaptic current was decreased in SAD-B KO mice. Moreover, synaptic depression following prolonged low-frequency synaptic stimulation was significantly enhanced in SAD-B KO mice. These results suggest that SAD-B kinase regulates vesicular release probability at pre-synaptic terminals and is involved in vesicular trafficking and/or regulation of the readily releasable pool size. Finally, we found that hippocampus-dependent contextual fear learning was significantly impaired in SAD-B KO mice. These observations suggest that SAD-B kinase plays pivotal roles in controlling vesicular release properties and regulating hippocampal function in the mature brain. Synapses of amphids defective (SAD)-A/B kinases control various steps in neuronal development and differentiation, but their roles in mature brains were only partially known. Here, we demonstrated, at mature pre-synaptic terminals, that SAD-B regulates vesicular release probability and synaptic plasticity. Moreover, hippocampus-dependent contextual fear learning was significantly impaired in SAD-B KO mice, suggesting that SAD-B kinase plays pivotal roles in controlling vesicular release properties and regulating hippocampal function in the mature brain. © 2015 International Society for Neurochemistry.

Modulation of the Cholinergic Mechanisms in the Bronchial Smooth Muscle.

DTIC Science & Technology

1984-06-01

after addition of the muscarinic agonist oxotremorine . Presynaptic Ach receptors were first reported to occur on nor- adrenergic terminals...muscarinic agonist, oxotremorine , reduced the output of [3H,-Ach by only 20% (Paper IV, Figure 4). This is a strong indication for the existence of...presynaptic muscarinic receptors, which modulate the release of Ach. The oxotremorine reduced release of [3H]-Ach upon stimulation was not mediated by a

Botulinum Toxin for Rhinitis.

PubMed

Ozcan, Cengiz; Ismi, Onur

2016-08-01

Rhinitis is a common clinical entity. Besides nasal obstruction, itching, and sneezing, one of the most important symptoms of rhinitis is nasal hypersecretion produced by nasal glands and exudate from the nasal vascular bed. Allergic rhinitis is an IgE-mediated inflammatory reaction of nasal mucosa after exposure to environmental allergens. Idiopathic rhinitis describes rhinitis symptoms that occur after non-allergic, noninfectious irritants. Specific allergen avoidance, topical nasal decongestants, nasal corticosteroids, immunotherapy, and sinonasal surgery are the main treatment options. Because the current treatment modalities are not enough for reducing rhinorrhea in some patients, novel treatment options are required to solve this problem. Botulinum toxin is an exotoxin generated by Clostridium botulinum. It disturbs the signal transmission at the neuromuscular and neuroglandular junction by inhibiting the acetylcholine release from the presynaptic nerve terminal. It has been widely used in neuromuscular, hypersecretory, and autonomic nerve system disorders. There have been a lot of published articles concerning the effect of this toxin on rhinitis symptoms. Based on the results of these reports, intranasal botulinum toxin A administration appears to be a safe and effective treatment method for decreasing rhinitis symptoms in rhinitis patients with a long-lasting effect. Botulinum toxin type A will be a good treatment option for the chronic rhinitis patients who are resistant to other treatment methods.

Neuromuscular paralysis by the basic phospholipase A2 subunit of crotoxin from Crotalus durissus terrificus snake venom needs its acid chaperone to concurrently inhibit acetylcholine release and produce muscle blockage.

PubMed

Cavalcante, Walter L G; Noronha-Matos, José B; Timóteo, Maria A; Fontes, Marcos R M; Gallacci, Márcia; Correia-de-Sá, Paulo

2017-11-01

Crotoxin (CTX), a heterodimeric phospholipase A 2 (PLA 2 ) neurotoxin from Crotalus durissus terrificus snake venom, promotes irreversible blockade of neuromuscular transmission. Indirect electrophysiological evidence suggests that CTX exerts a primary inhibitory action on transmitter exocytosis, yet contribution of a postsynaptic action of the toxin resulting from nicotinic receptor desensitization cannot be excluded. Here, we examined the blocking effect of CTX on nerve-evoked transmitter release measured directly using radioisotope neurochemistry and video microscopy with the FM4-64 fluorescent dye. Experiments were conducted using mice phrenic-diaphragm preparations. Real-time fluorescence video microscopy and liquid scintillation spectrometry techniques were used to detect transmitter exocytosis and nerve-evoked [ 3 H]-acetylcholine ([ 3 H]ACh) release, respectively. Nerve-evoked myographic recordings were also carried out for comparison purposes. Both CTX (5μg/mL) and its basic PLA 2 subunit (CB, 20μg/mL) had biphasic effects on nerve-evoked transmitter exocytosis characterized by a transient initial facilitation followed by a sustained decay. CTX and CB reduced nerve-evoked [ 3 H]ACh release by 60% and 69%, respectively, but only the heterodimer, CTX, decreased the amplitude of nerve-evoked muscle twitches. Data show that CTX exerts a presynaptic inhibitory action on ACh release that is highly dependent on its intrinsic PLA 2 activity. Given the high safety margin of the neuromuscular transmission, one may argue that the presynaptic block caused by the toxin is not enough to produce muscle paralysis unless a concurrent postsynaptic inhibitory action is also exerted by the CTX heterodimer. Copyright © 2017. Published by Elsevier Inc.

The neuromuscular activity of Bothriopsis bilineata smaragdina (forest viper) venom and its toxin Bbil-TX (Asp49 phospholipase A2) on isolated mouse nerve-muscle preparations.

PubMed

Floriano, Rafael Stuani; Rocha, Thalita; Carregari, Victor Corasolla; Marangoni, Sergio; da Cruz-Höfling, Maria Alice; Hyslop, Stephen; Rodrigues-Simioni, Léa; Rowan, Edward G

2015-03-01

The presynaptic action of Bothriopsis bilineata smaragdina (forest viper) venom and Bbil-TX, an Asp49 PLA2 from this venom, was examined in detail in mouse phrenic nerve-muscle (PND) preparations in vitro and in a neuroblastoma cell line (SK-N-SH) in order to gain a better insight into the mechanism of action of the venom and associated Asp49 PLA2. In low Ca(2+) solution, venom (3μg/ml) caused a quadriphasic response in PND twitch height whilst at 10μg/ml the venom additionally induced an abrupt and marked initial contracture followed by neuromuscular facilitation, rhythmic oscillations of nerve-evoked twitches, alterations in baseline and progressive blockade. The venom slowed the relaxation phase of muscle twitches. In low Ca(2+), Bbil-TX [210nM (3μg/ml)] caused a progressive increase in PND twitch amplitude but no change in the decay time constant. Venom (10μg/ml) and Bbil-TX (210nM) caused minor changes in the compound action potential (CAP) amplitude recorded from sciatic nerve preparations, with no significant effect on rise time and latency; tetrodotoxin (3.1nM) blocked the CAP at the end of the experiments. In mouse triangularis sterni nerve-muscle (TSn-m) preparations, venom (10μg/ml) and Bbil-TX (210nM) significantly reduced the perineural waveform associated with the outward K(+) current while the amplitude of the inward Na(+) current was not significantly affected. Bbil-TX (210nM) caused a progressive increase in the quantal content of TSn-m preparations maintained in low Ca(2+) solution. Venom (3μg/ml) and toxin (210nM) increased the calcium fluorescence in SK-N-SH neuroblastoma cells loaded with Fluo3 AM and maintained in low or normal Ca(2+) solution. In normal Ca(2+), the increase in fluorescence amplitude was accompanied by irregular and frequent calcium transients. In TSn-m preparations loaded with Fluo4 AM, venom (10μg/ml) caused an immediate increase in intracellular Ca(2+) followed by oscillations in fluorescence and muscle contracture; Bbil-TX did not change the calcium fluorescence in TSn-m preparations. Immunohistochemical analysis of toxin-treated PND preparations revealed labeling of junctional ACh receptors but a loss of the presynaptic proteins synaptophysin and SNAP25. Together, these data confirm the presynaptic action of Bbil-TX and show that it involves modulation of K(+) channel activity and presynaptic protein expression. Copyright © 2015 Elsevier Ltd. All rights reserved.

On the Role of Glutamate in Presynaptic Development: Possible Contributions of Presynaptic NMDA Receptors.

PubMed

Fedder, Karlie N; Sabo, Shasta L

2015-12-14

Proper formation and maturation of synapses during development is a crucial step in building the functional neural circuits that underlie perception and behavior. It is well established that experience modifies circuit development. Therefore, understanding how synapse formation is controlled by synaptic activity is a key question in neuroscience. In this review, we focus on the regulation of excitatory presynaptic terminal development by glutamate, the predominant excitatory neurotransmitter in the brain. We discuss the evidence that NMDA receptor activation mediates these effects of glutamate and present the hypothesis that local activation of presynaptic NMDA receptors (preNMDARs) contributes to glutamate-dependent control of presynaptic development. Abnormal glutamate signaling and aberrant synapse development are both thought to contribute to the pathogenesis of a variety of neurodevelopmental disorders, including autism spectrum disorders, intellectual disability, epilepsy, anxiety, depression, and schizophrenia. Therefore, understanding how glutamate signaling and synapse development are linked is important for understanding the etiology of these diseases.

Dynamics of Multiple Trafficking Behaviors of Individual Synaptic Vesicles Revealed by Quantum-Dot Based Presynaptic Probe

PubMed Central

Lee, Suho; Jung, Kyung Jin; Jung, Hyun Suk; Chang, Sunghoe

2012-01-01

Although quantum dots (QDs) have provided invaluable information regarding the diffusive behaviors of postsynaptic receptors, their application in presynaptic terminals has been rather limited. In addition, the diffraction-limited nature of the presynaptic bouton has hampered detailed analyses of the behaviors of synaptic vesicles (SVs) at synapses. Here, we created a quantum-dot based presynaptic probe and characterized the dynamic behaviors of individual SVs. As previously reported, the SVs exhibited multiple exchanges between neighboring boutons. Actin disruption induced a dramatic decrease in the diffusive behaviors of SVs at synapses while microtubule disruption only reduced extrasynaptic mobility. Glycine-induced synaptic potentiation produced significant increases in synaptic and inter-boutonal trafficking of SVs, which were NMDA receptor- and actin-dependent while NMDA-induced synaptic depression decreased the mobility of the SVs at synapses. Together, our results show that sPH-AP-QD revealed previously unobserved trafficking properties of SVs around synapses, and the dynamic modulation of SV mobility could regulate presynaptic efficacy during synaptic activity. PMID:22666444

Neurotoxins from venoms of the Hymenoptera--twenty-five years of research in Amsterdam.

PubMed

Piek, T

1990-01-01

1. In co-operation with colleagues in Europe, Japan and the U.S.A., 25 years of research in Amsterdam have provided new views on the way some hymenopteran insects incapacitate their prey by a diversity of neurotoxins, resulting in block of synaptic transmission in CNS or neuromuscular junctions, or affecting voltage dependent phenomena in nerve and muscle fibers. 2. Nicotinic synaptic transmission in the insect CNS is irreversibly blocked at the presynaptic side by kinins, or reversibly and postsynaptically blocked by philanthotoxins. 3. Glutamatergic neuromuscular transmission is reversibly blocked by philanthotoxins at the pre- and/or postsynaptic side. 4. A presynaptic block of neuromuscular transmission was found with the Microbracon toxins. 5. An irreversible deactivation, without paralysis, of cockroaches is caused by a sting of Ampulex compressa into the suboesophageal ganglion. 6. Poneratoxin, a 25 amino acid residue polypeptide, isolated from an ant venom, is the first described hymenopteran neurotoxin affecting excitability of nerve and muscle fibres by changing the kinetics of the voltage-dependent sodium channel.

Single and combined effects of carbamazepine and vinpocetine on depolarization-induced changes in Na+, Ca2+ and glutamate release in hippocampal isolated nerve endings.

PubMed

Sitges, María; Chiu, Luz María; Nekrassov, Vladimir

2006-07-01

The single and combined effects of carbamazepine and vinpocetine on the release of the excitatory amino acid neurotransmitter glutamate, on the rise in internal Na+ (Na(i), as determined with SBFI), and on the rise in internal Ca2+ (Ca(i), as determined with fura-2) induced by an increased permeability of presynaptic Na+ channels, with veratridine, or by an increased permeability of presynaptic Ca2+ channels with high K+, were investigated in isolated hippocampal nerve endings. The present study shows that carbamazepine and vinpocetine, both inhibit dose dependently the release of preloaded [3H]Glu induced by veratridine. However, carbamazepine is two orders of magnitude less potent than vinpocetine. The calculated IC(50)'s for carbamazepine and vinpocetine to inhibit veratridine-induced [3H]Glu release are 200 and 2 microM, respectively. Consistently 150 microM carbamazepine and 1.5 microM vinpocetine reduce the veratridine-induced rise in Na(i) in a similar extent. The single effects of carbamazepine and of vinpocetine on the presynaptic Na+ channel mediated responses, namely the rise in Na(i) and the release of Glu induced by veratridine, are additive. Responses that depend on the entrance of external Ca2+ via presynaptic Ca2+ channels, such as the release of [3H]Glu and the rise in Ca(i) induced by high K+, are insensitive to 300 microM carbamazepine and slightly reduced by 5 microM vinpocetine. It is concluded that the additive effects of carbamazepine, which is one of the most common antiepileptic drugs, and vinpocetine that besides its known neuroprotective action and antiepileptic potential is a memory enhancer, may perhaps be advantageous in the treatment of epileptic patients.

Neuropeptide Y as a presynaptic modulator of norepinephrine release from the sympathetic nerve fibers in the pig pineal gland.

PubMed

Ziółkowska, N; Lewczuk, B; Przybylska-Gornowicz, B

2015-01-01

Norepinephrine (NE) released from the sympathetic nerve endings is the main neurotransmitter controlling melatonin synthesis in the mammalian pineal gland. Although neuropeptide Y (NPY) co-exists with NE in the pineal sympathetic nerve fibers it also occurs in a population of non-adrenergic nerve fibers located in this gland. The role of NPY in pineal physiology is still enigmatic. The present study characterizes the effect of NPY on the depolarization-evoked 3H-NE release from the pig pineal explants. The explants of the pig pineal gland were loaded with 3H-NE in the presence of pargyline and superfused with Tyrode medium. They were exposed twice to the modified Tyrode medium containing 60 mM of K+ to evoke the 3H-NE release via depolarization. NPY, specific agonists of Y1- and Y2- receptors and pharmacologically active ligands of α2-adrenoceptors were added to the medium before and during the second depolarization. The radioactivity was measured in medium fractions collected every 2 minutes during the superfusion. NPY (0.1-10 μM) significantly decreased the depolarization-induced 3H-NE release. Similar effect was observed after the treatment with Y2-agonist: NPY13-36, but not with Y1-agonist: [Leu31,Pro34]-NPY. The tritium overflow was lower in the explants exposed to the 5 μM NPY and 1 μM rauwolscine than to rauwolscine only. The effects of 5 μM NPY and 0.05 μM UK 14,304 on the depolarization-evoked 3H-NE release were additive. The results show that NPY is involved in the regulation of NE release from the sympathetic terminals in the pig pineal gland, inhibiting this process via Y2-receptors.

Role of different types of Ca2+ channels and a reticulum-like Ca2+ pump in neurotransmitter release.

PubMed

Fossier, P; Baux, G; Tauc, L

1993-01-01

The factors controlling the Ca2+ concentration directly responsible for triggering acetylcholine (ACh) release were investigated at an identified neuro-neuronal synapse of the Aplysia buccal ganglion. The types of presynaptic voltage-gated Ca2+ channels associated with transmitter release were determined by using selective blockers such as nifedipine, omega-conotoxin and a partially purified extract from the venom of a funnel web spider (FTx). L-type, N-type and P-type Ca2+ channels are present in the presynaptic neuron. The influx of Ca2+ through both N- and P-types induces the release of ACh whereas Ca2+ flowing through L-type channels modulates the duration of the presynaptic action potential by controlling the Ca(2+)-dependent K+ current. tBuBHQ, a blocker of the reticulum Ca2+ pump, induces a potentiation of evoked release without modifying the presynaptic Ca2+ influx. This seems to indicate that a part of the Ca2+ entering the presynaptic terminal through N- and P-type Ca2+ channels is sequestered in a presynaptic reticulum-like Ca2+ buffer preventing these ions from contributing to ACh release. To exert its control, this Ca2+ buffer must be located close to both the presynaptic Ca2+ channels and the transmitter release mechanism.

Biochemistry of snake venom neurotoxins and their application to the study of synapse. [Neurotoxins isolated from venom of the Formosan banded krait

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanley, M.R.

1978-11-01

The crude venom of the Formosan banded krait, Bungarus multicinctus, was separated into eleven lethal protein fractions. Nine fractions were purified to final homogeneous toxins, designated ..cap alpha..-bungarotoxin, ..beta..-bungarotoxin, and toxins 7, 8, 9A, 11, 12, 13, and 14. Three of the toxins, ..cap alpha..-bungarotoxin, 7, and 8, were identified as post-synaptic curarimimetic neurotoxins. The remaining toxins were identified as pre-synaptic neurotoxins. ..cap alpha..-Bungarotoxin, toxin 7, and toxin 8 are all highly stable basic polypeptides of approx. 8000 daltons molecular weight. The pre-synaptic toxins fell into two structural groups: toxin 9A and 14 which were single basic chains of approx.more » 14,000 daltons, and ..beta..-bungarotoxin, and toxins 11 thru 13 which were composed of two chains of approx. 8000 and approx. 13,000 daltons covalently linked by disulfides. All the pre-synaptic neurotoxins were shown to have intrinsic calcium-dependent phospholipase A activities. Under certain conditions, intact synaptic membranes were hydrolyzed more rapidly than protein-free extracted synaptic-lipid liposomes which, in turn, were hydrolyzed more rapidly than any other tested liposomes. It was speculated that cell-surface arrays of phosphatidyl serine/glycolipids created high affinity target sites for ..beta..-bungarotoxin. Single-chain toxins were found to be qualitatively different from the two-chain toxins in their ability to block the functioning of acetylcholine receptors, and were quantitatively different in their enzymatic and membrane disruptive activities. ..beta..-Bungarotoxin was shown to be an extremely potent neuronal lesioning agent. There was no apparent selectivity for cholinergic over non-cholinergic neurons, nor for nerve terminals over cell bodies. It was suggested that ..beta..-bungarotoxin can be considered a useful new histological tool, which may exhibit some regional selectivity.« less

Transient release kinetics of rod bipolar cells revealed by capacitance measurement of exocytosis from axon terminals in rat retinal slices.

PubMed

Oltedal, Leif; Hartveit, Espen

2010-05-01

Presynaptic transmitter release has mostly been studied through measurements of postsynaptic responses, but a few synapses offer direct access to the presynaptic terminal, thereby allowing capacitance measurements of exocytosis. For mammalian rod bipolar cells, synaptic transmission has been investigated in great detail by recording postsynaptic currents in AII amacrine cells. Presynaptic measurements of the dynamics of vesicular cycling have so far been limited to isolated rod bipolar cells in dissociated preparations. Here, we first used computer simulations of compartmental models of morphologically reconstructed rod bipolar cells to adapt the 'Sine + DC' technique for capacitance measurements of exocytosis at axon terminals of intact rod bipolar cells in retinal slices. In subsequent physiological recordings, voltage pulses that triggered presynaptic Ca(2+) influx evoked capacitance increases that were proportional to the pulse duration. With pulse durations 100 ms, the increase saturated at 10 fF, corresponding to the size of a readily releasable pool of vesicles. Pulse durations 400 ms evoked additional capacitance increases, probably reflecting recruitment from additional pools of vesicles. By using Ca(2+) tail current stimuli, we separated Ca(2+) influx from Ca(2+) channel activation kinetics, allowing us to estimate the intrinsic release kinetics of the readily releasable pool, yielding a time constant of 1.1 ms and a maximum release rate of 2-3 vesicles (release site)(1) ms(1). Following exocytosis, we observed endocytosis with time constants ranging from 0.7 to 17 s. Under physiological conditions, it is likely that release will be transient, with the kinetics limited by the activation kinetics of the voltage-gated Ca(2+) channels.

Patterns of primary afferent depolarization of segmental and ascending intraspinal collaterals of single joint afferents in the cat.

PubMed

Rudomin, P; Lomelí, J

2007-01-01

We have examined in the anesthetized cat the threshold changes produced by sensory and supraspinal stimuli on intraspinal collaterals of single afferents from the posterior articular nerve (PAN). Forty-eight fibers were tested in the L3 segment, in or close to Clarke's column, and 70 fibers in the L6-L7 segments within the intermediate zone. Of these, 15 pairs of L3 and L6-L7 collaterals were from the same afferent. Antidromically activated fibers had conduction velocities between 23 and 74 m/s and peripheral thresholds between 1.1 and 4.7 times the threshold of the most excitable fibers (xT), most of them below 3 xT. PAN afferents were strongly depolarized by stimulation of muscle afferents and by cutaneous afferents, as well as by stimulation of the bulbar reticular formation and the midline raphe nuclei. Stimulation of muscle nerves (posterior biceps and semitendinosus, quadriceps) produced a larger PAD (primary afferent depolarization) in the L6-L7 than in the L3 terminations. Group II were more effective than group I muscle afferents. As with group I muscle afferents, the PAD elicited in PAN afferents by stimulation of muscle nerves could be inhibited by conditioning stimulation of cutaneous afferents. Stimulation of the cutaneous sural and superficial peroneal nerves increased the threshold of few terminations (i.e., produced primary afferent hyperpolarization, PAH) and reduced the threshold of many others, particularly of those tested in the L6-L7 segments. Yet, there was a substantial number of terminals where these conditioning stimuli had minor or no effects. Autogenetic stimulation of the PAN with trains of pulses increased the intraspinal threshold in 46% and reduced the threshold in 26% of fibers tested in the L6-L7 segments (no tests were made with trains of pulses on fibers ending in L3). These observations indicate that PAN afferents have a rather small autogenetic PAD, particularly if this is compared with the effects of heterogenetic stimulation. Therefore, the depression of the PAN intraspinal fields produced by autogenetic stimulation described by Rudomin et al. (Exp Brain Res DOI 10.1007/s00221-006-0600-x, 2006) may be ascribed to other mechanisms besides a GABAa PAD. It is suggested that the small or no autogenetic PAD displayed by the examined joint afferents prevents presynaptic filtering of their synaptic actions and preserves the original information generated in the periphery. This could be important for proper adjustment of limb position.

Lack of Change in Markers of Presynaptic Terminal Abundance Alongside Subtle Reductions in Markers of Presynaptic Terminal Plasticity in Prefrontal Cortex of Schizophrenia Patients

PubMed Central

Fung, Samantha J.; Sivagnanasundaram, Sinthuja; Shannon Weickert, Cynthia

2010-01-01

Background Reduced synaptic connectivity in frontal cortex may contribute to schizophrenia symptoms. While altered mRNA and protein expression of various synaptic genes has been found, discrepancies between studies mean a generalisable synaptic pathology in schizophrenia has not been identified. Methods We determined if mRNAs encoding presynaptic proteins enriched in inhibitory [vesicular GABA transporter (VGAT) and complexin 1] and/or excitatory [vesicular glutamate transporter (VGluT1) and complexin 2] terminals are altered in the dorsolateral prefrontal cortex of subjects with schizophrenia (n=37 patients, n=37 controls). We also measured mRNA expression of markers associated with synaptic plasticity/neurite outgrowth [growth associated protein 43 (GAP43) and neuronal navigators 1 and 2 (NAV1 and NAV2)]; and mRNAs of other synaptic-associated proteins previously implicated in schizophrenia: dysbindin and vesicle-associated membrane protein (VAMP1) mRNAs using quantitative RT-PCR. Results No significant changes in complexin 1, VGAT, complexin 2, VGluT1, dysbindin, NAV2, or VAMP1 mRNA expression were found, however we observed reduced expression of mRNAs associated with plasticity/cytoskeletal modification (GAP43 and NAV1) in schizophrenia. Although dysbindin mRNA did not differ in schizophrenia compared to controls, dysbindin mRNA positively correlated with GAP-43 and NAV1 in schizophrenia, but not in controls, suggesting low levels of dysbindin may be linked to reduced plasticity in the disease state. No relationships between three dysbindin genetic polymorphisms previously associated with dysbindin mRNA levels were found. Conclusions A reduction in the plasticity of synaptic terminals supports the hypothesis that reduced modifiability of synaptic terminals may contribute to neuropathology and working memory deficits in schizophrenia. PMID:21145444

Fragile X mental retardation protein controls synaptic vesicle exocytosis by modulating N-type calcium channel density

NASA Astrophysics Data System (ADS)

Ferron, Laurent; Nieto-Rostro, Manuela; Cassidy, John S.; Dolphin, Annette C.

2014-04-01

Fragile X syndrome (FXS), the most common heritable form of mental retardation, is characterized by synaptic dysfunction. Synaptic transmission depends critically on presynaptic calcium entry via voltage-gated calcium (CaV) channels. Here we show that the functional expression of neuronal N-type CaV channels (CaV2.2) is regulated by fragile X mental retardation protein (FMRP). We find that FMRP knockdown in dorsal root ganglion neurons increases CaV channel density in somata and in presynaptic terminals. We then show that FMRP controls CaV2.2 surface expression by targeting the channels to the proteasome for degradation. The interaction between FMRP and CaV2.2 occurs between the carboxy-terminal domain of FMRP and domains of CaV2.2 known to interact with the neurotransmitter release machinery. Finally, we show that FMRP controls synaptic exocytosis via CaV2.2 channels. Our data indicate that FMRP is a potent regulator of presynaptic activity, and its loss is likely to contribute to synaptic dysfunction in FXS.

Synapse-specific and compartmentalized expression of presynaptic homeostatic potentiation

PubMed Central

Li, Xiling; Goel, Pragya; Chen, Catherine; Angajala, Varun; Chen, Xun

2018-01-01

Postsynaptic compartments can be specifically modulated during various forms of synaptic plasticity, but it is unclear whether this precision is shared at presynaptic terminals. Presynaptic homeostatic plasticity (PHP) stabilizes neurotransmission at the Drosophila neuromuscular junction, where a retrograde enhancement of presynaptic neurotransmitter release compensates for diminished postsynaptic receptor functionality. To test the specificity of PHP induction and expression, we have developed a genetic manipulation to reduce postsynaptic receptor expression at one of the two muscles innervated by a single motor neuron. We find that PHP can be induced and expressed at a subset of synapses, over both acute and chronic time scales, without influencing transmission at adjacent release sites. Further, homeostatic modulations to CaMKII, vesicle pools, and functional release sites are compartmentalized and do not spread to neighboring pre- or post-synaptic structures. Thus, both PHP induction and expression mechanisms are locally transmitted and restricted to specific synaptic compartments. PMID:29620520

Kinetics, Ca2+ dependence, and biophysical properties of integrin-mediated mechanical modulation of transmitter release from frog motor nerve terminals

NASA Technical Reports Server (NTRS)

Chen, B. M.; Grinnell, A. D.

1997-01-01

Neurotransmitter release from frog motor nerve terminals is strongly modulated by change in muscle length. Over the physiological range, there is an approximately 10% increase in spontaneous and evoked release per 1% muscle stretch. Because many muscle fibers do not receive suprathreshold synaptic inputs at rest length, this stretch-induced enhancement of release constitutes a strong peripheral amplifier of the spinal stretch reflex. The stretch modulation of release is inhibited by peptides that block integrin binding of natural ligands. The modulation varies linearly with length, with a delay of no more than approximately 1-2 msec and is maintained constant at the new length. Moreover, the stretch modulation persists in a zero Ca2+ Ringer and, hence, is not dependent on Ca2+ influx through stretch activated channels. Eliminating transmembrane Ca2+ gradients and buffering intraterminal Ca2+ to approximately normal resting levels does not eliminate the modulation, suggesting that it is not the result of release of Ca2+ from internal stores. Finally, changes in temperature have no detectable effect on the kinetics of stretch-induced changes in endplate potential (EPP) amplitude or miniature EPP (mEPP) frequency. We conclude, therefore, that stretch does not act via second messenger pathways or a chemical modification of molecules involved in the release pathway. Instead, there is direct mechanical modulation of release. We postulate that tension on integrins in the presynaptic membrane is transduced mechanically into changes in the position or conformation of one or more molecules involved in neurotransmitter release, altering sensitivity to Ca2+ or the equilibrium for a critical reaction leading to vesicle fusion.

Dopamine disposition in the presynaptic process regulates the severity of methamphetamine-induced neurotoxicity.

PubMed

Kuhn, Donald M; Francescutti-Verbeem, Dina M; Thomas, David M

2008-10-01

Methamphetamine (METH) is well known for its ability to cause damage to dopamine (DA) nerve endings of the striatum. The mechanisms by which METH causes neurotoxicity are not fully understood, but likely candidates are increased oxidative and nitrosative stress and mitochondrial dysfunction. Microglial activation is also emerging as an important element of the METH neurotoxic cascade, and it appears that extensive cross-talk between these cells and DA nerve endings is an early event in this process. It may seem paradoxical, but DA itself is also thought to be an essential factor in the neuronal damaging effects of METH, but issues relating to its precise role in this regard remain unanswered. We present in this overview a summary of studies that tested how alterations in the disposition of presynaptic DA (injections of reserpine, L-DOPA, or clorgyline) modulate METH neurotoxicity. In all cases, these drugs significantly increased the magnitude of microglial activation as well as the severity of damage to striatal DA nerve endings caused by METH. The enhancement of METH effects in striatum by reserpine, L-DOPA, and clorgyline persisted for 14 days and showed no evidence of recovery. These data establish that subtle shifts in the newly synthesized pool of DA can cause substantial changes in the severity of METH-induced neurotoxicity. DA released into the synapse by METH is very likely the source of downstream reactants that provoke microglial activation and the ensuing damage to DA nerve endings.

Comparison of Glutamate Turnover in Nerve Terminals and Brain Tissue During [1,6-13C2]Glucose Metabolism in Anesthetized Rats.

PubMed

Patel, Anant B; Lai, James C K; Chowdhury, Golam I M; Rothman, Douglas L; Behar, Kevin L

2017-01-01

The 13 C turnover of neurotransmitter amino acids (glutamate, GABA and aspartate) were determined from extracts of forebrain nerve terminals and brain homogenate, and fronto-parietal cortex from anesthetized rats undergoing timed infusions of [1,6- 13 C 2 ]glucose or [2- 13 C]acetate. Nerve terminal 13 C fractional labeling of glutamate and aspartate was lower than those in whole cortical tissue at all times measured (up to 120 min), suggesting either the presence of a constant dilution flux from an unlabeled substrate or an unlabeled (effectively non-communicating on the measurement timescale) glutamate pool in the nerve terminals. Half times of 13 C labeling from [1,6- 13 C 2 ]glucose, as estimated by least squares exponential fitting to the time course data, were longer for nerve terminals (Glu C4 , 21.8 min; GABA C2 21.0 min) compared to cortical tissue (Glu C4 , 12.4 min; GABA C2 , 14.5 min), except for Asp C3 , which was similar (26.5 vs. 27.0 min). The slower turnover of glutamate in the nerve terminals (but not GABA) compared to the cortex may reflect selective effects of anesthesia on activity-dependent glucose use, which might be more pronounced in the terminals. The 13 C labeling ratio for glutamate-C4 from [2- 13 C]acetate over that of 13 C-glucose was twice as large in nerve terminals compared to cortex, suggesting that astroglial glutamine under the 13 C glucose infusion was the likely source of much of the nerve terminal dilution. The net replenishment of most of the nerve terminal amino acid pools occurs directly via trafficking of astroglial glutamine.

Structural and functional investigations of the murine cavernosal nerve: a model system for serial spatio-temporal study of autonomic neuropathy.

PubMed

Schaumburg, Herbert H; Zotova, Elena; Cannella, Barbara; Raine, Cedric S; Arezzo, Joseph; Tar, Moses; Melman, Arnold

2007-04-01

To illustrate the ultrastructural fibre composition of the rat cavernosal nerve at serial levels, from its origin in the main pelvic ganglion to its termination in the corpus cavernosum of the distal penile shaft, and to develop a technique that permits repeated electrophysiological recording from the fibres that form the cavernosal nerve distinct from the axons of the dorsal nerve of the penis (DNP). For the light microscope and ultrastructural studies, Sprague-Dawley rats were anaesthetized and the pelvic organs and lower limbs were perfused with glutaraldehyde through the distal aorta. Tissue samples were embedded in epoxy resin and prepared for light and electron microscopy. Frozen tissue was used for the immunohistochemical studies and sections were stained with rabbit anti-nitric oxide synthetase 1 (NOS1). For the electrophysiology, anaesthetized rats were used in sterile conditions. Nerve conduction velocity for the cavernosal nerve was assessed from a point 2 mm below the main (major) pelvic ganglion after stimulating the nerve at the crus penis; multi-unit averaging techniques were used to enhance the recording of slow-conduction activity. Recordings from the DNP were obtained over the proximal shaft after stimulation at the base of the penis. Step-serial sections of the cavernosal nerve revealed numerous ganglion cells in the initial segments and gradually fewer myelinated fibres at distal levels. At the point of crural entry, the nerve contained almost exclusively unmyelinated axons. As it descended the penile shaft, the nerve separated into small fascicles containing only one to four axons at the level of the distal shaft. In the corpus cavernosum, vesicle-filled presynaptic axon preterminals were close to smooth muscle fibres, but did not seem to be in direct contact. Immunohistochemical evaluation of NOS1 activity showed intense staining of the fibres of the DNP and most of the neurones in the main pelvic ganglion. There was also scattered NOS1 activity in the nerve bundles of the corpus cavernosum. Electrophysiology identified activity in C fibres on the cavernosal nerve and in Aalpha-Adelta fibres in the DNP. These results show that it is possible to perform integrated cavernosal pressure monitoring and ultrastructural and electrophysiological studies in this model. These yielded accurate data about the erectile status of the penis, and the state of unmyelinated and myelinated fibres in the DNP and cavernosal nerves of the same animal. This study provides a useful template for future studies of experimental diabetic autonomic neuropathy.

Presynaptic Protein Synthesis Is Required for Long-Term Plasticity of GABA Release.

PubMed

Younts, Thomas J; Monday, Hannah R; Dudok, Barna; Klein, Matthew E; Jordan, Bryen A; Katona, István; Castillo, Pablo E

2016-10-19

Long-term changes of neurotransmitter release are critical for proper brain function. However, the molecular mechanisms underlying these changes are poorly understood. While protein synthesis is crucial for the consolidation of postsynaptic plasticity, whether and how protein synthesis regulates presynaptic plasticity in the mature mammalian brain remain unclear. Here, using paired whole-cell recordings in rodent hippocampal slices, we report that presynaptic protein synthesis is required for long-term, but not short-term, plasticity of GABA release from type 1 cannabinoid receptor (CB 1 )-expressing axons. This long-term depression of inhibitory transmission (iLTD) involves cap-dependent protein synthesis in presynaptic interneuron axons, but not somata. Translation is required during the induction, but not maintenance, of iLTD. Mechanistically, CB 1 activation enhances protein synthesis via the mTOR pathway. Furthermore, using super-resolution STORM microscopy, we revealed eukaryotic ribosomes in CB 1 -expressing axon terminals. These findings suggest that presynaptic local protein synthesis controls neurotransmitter release during long-term plasticity in the mature mammalian brain. Copyright © 2016 Elsevier Inc. All rights reserved.

Chlorpyrifos, chlorpyrifos-oxon, and diisopropylfluorophosphate inhibit kinesin-dependent microtubule motility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gearhart, Debra A.; Sickles, Dale W.; Buccafusco, Jerry J.

2007-01-01

Diisopropylfluorophosphate, originally developed as a chemical warfare agent, is structurally similar to nerve agents, and chlorpyrifos has extensive worldwide use as an agricultural pesticide. While inhibition of cholinesterases underlies the acute toxicity of these organophosphates, we previously reported impaired axonal transport in the sciatic nerves from rats treated chronically with subthreshold doses of chlorpyrifos. Those data indicate that chlorpyrifos (and/or its active metabolite, chlorpyrifos-oxon) might directly affect the function of kinesin and/or microtubules-the principal proteins that mediate anterograde axonal transport. The current report describes in vitro assays to assess the concentration-dependent effects of chlorpyrifos (0-10 {mu}M), chlorpyrifos-oxon (0-10 {mu}M), andmore » diisopropylfluorophosphate (0-0.59 nM) on kinesin-dependent microtubule motility. Preincubating bovine brain microtubules with the organophosphates did not alter kinesin-mediated microtubule motility. In contrast, preincubation of bovine brain kinesin with diisopropylfluorophosphate, chlorpyrifos, or chlorpyrifos-oxon produced a concentration-dependent increase in the number of locomoting microtubules that detached from the kinesin-coated glass cover slip. Our data suggest that the organophosphates-chlorpyrifos-oxon, chlorpyrifos, and diisopropylfluorophosphate-directly affect kinesin, thereby disrupting kinesin-dependent transport on microtubules. Kinesin-dependent movement of vesicles, organelles, and other cellular components along microtubules is fundamental to the organization of all eukaryotic cells, especially in neurons where organelles and proteins synthesized in the cell body must move down long axons to pre-synaptic sites in nerve terminals. We postulate that disruption of kinesin-dependent intracellular transport could account for some of the long-term effects of organophosphates on the peripheral and central nervous system.« less

In vitro and ex vivo screening of candidate therapeutics to restore neurotransmission in nerve terminals intoxicated by botulinum neurotoxin serotype A1.

PubMed

Beske, Phillip H; Bradford, Aaron B; Hoffman, Katie M; Mason, Sydney J; McNutt, Patrick M

2018-06-01

Botulinum neurotoxins (BoNTs) are exceedingly potent neurological poisons that block cholinergic release in the peripheral nervous system and cause death by asphyxiation. While post-exposure prophylaxis can effectively eliminate toxin in the bloodstream, there are no clinically effective treatments to prevent or reverse disease once BoNT has entered the neuron. To address the need for post-symptomatic countermeasures, we designed and developed an in vitro assay based on whole-cell, patch-clamp electrophysiological monitoring of miniature excitatory post-synaptic currents in synaptically active murine embryonic stem cell-derived neurons. This synaptic function-based assay was used to assess the efficacy of rationally selected drugs to restore neurotransmission in neurons comprehensively intoxicated by BoNT/A. Based on clinical reports suggesting that elevated Ca 2+ signaling promotes symptomatic relief from botulism, we identified seven candidate drugs that modulate presynaptic Ca 2+ signaling and assessed their ability to reverse BoNT/A-induced synaptic blockade. The most effective drugs from the screen were found to phasically agonize voltage-gated calcium channel (VGCC) activity. Lead candidates were then applied to ex vivo studies in BoNT/A-paralyzing mouse phrenic nerve-hemidiaphragm (PND) preparations. Treatment of PNDs with VGCC agonists after paralytic onset transiently potentiated nerve-elicited muscle contraction and delayed progression to neuromuscular failure. Collectively, this study suggests that Ca 2+ -modulating drugs represent a novel symptomatic treatment for neuromuscular paralysis following BoNT/A poisoning. Published by Elsevier Ltd.

Characterization of substance P release from the intermediate area of rat thoracic spinal cord.

PubMed

Yang, L; Thomas, N D; Helke, C J

1996-08-01

Substance P (SP) nerve terminals innervate the intermediolateral cell column (IML) of the thoracic spinal cord, where SP coexists with serotonin (5-HT), neurokinin A (NKA) and thyrotropin-releasing hormone (TRH). Neither the depolarization-induced release of SP nor the presence of other neurochemicals in the regulation of SP release has been directly studied in this system. In the present study, basal and K(+)-stimulated release of SP from the microdissected intermediate area (including the IML, intercalated nucleus and central autonomic nucleus) of the rat thoracic spinal cord, and the regulation of SP release by presynaptic autoreceptors and by coexisting neurochemicals (5-HT, NKA and TRH) were studied using an in vitro superfusion system. Potassium evoked a concentration- and extracellular Ca(2+)-dependent release of SP. In rats pretreated with the serotoninergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), both SP content and the absolute amount of SP released were decreased. However, the fraction of the remaining tissue content of SP released by K+ depolarization was not changed subsequent to 5,7-DHT treatment. Moreover, 5-HT, 5-HT1B agonists (CGS-12066B and RU 24969) and a 5-HT3 agonist (2-methyl-5-HT) did not alter the K(+)-evoked release of SP. These data demonstrate that SP is released from the intermediate area of the rat thoracic spinal cord and some of the SP released comes from serotoninergic nerve terminals. Although 5-HT coexists with SP in the IML, neither endogenous 5-HT nor 5-HT receptor ligands appear to regulate the release of SP. Other colocalized neuropeptides (NKA and TRH) are not involved in the regulation of SP release because neither NKA, a NK2 agonist (GR 64349) nor a TRH analog (MK-771) changed the K(+)-evoked release of SP. A neurokinin-1 (NK1) antagonist (GR 82334) dose-dependently (10(-9)-10(-7) M) increased the K(+)-stimulated release of SP. These data suggest the presence of presynaptic inhibitory NK1 autoreceptors. Whereas, NK1 agonists, [GR 73632 (10(-9)-10(-6) M) and [Sar9, Met (O2)11]SP (10(-8)-10(-6) M)], increased the basal and K(+)-stimulated release of SP, the excitatory effects of GR 73632 were not blocked by the NK1 antagonist. Moreover, GR 73632 increased the efflus of SP to a greater extent in the absence of peptidase inhibitors. Thus, the effect of NK1 agonists on the release of SP may be related to an inhibition of peptide degradation rather than activation of NK1 autoreceptors.

Presynaptic Active Zone Density during Development and Synaptic Plasticity.

PubMed

Clarke, Gwenaëlle L; Chen, Jie; Nishimune, Hiroshi

2012-01-01

Neural circuits transmit information through synapses, and the efficiency of synaptic transmission is closely related to the density of presynaptic active zones, where synaptic vesicles are released. The goal of this review is to highlight recent insights into the molecular mechanisms that control the number of active zones per presynaptic terminal (active zone density) during developmental and stimulus-dependent changes in synaptic efficacy. At the neuromuscular junctions (NMJs), the active zone density is preserved across species, remains constant during development, and is the same between synapses with different activities. However, the NMJ active zones are not always stable, as exemplified by the change in active zone density during acute experimental manipulation or as a result of aging. Therefore, a mechanism must exist to maintain its density. In the central nervous system (CNS), active zones have restricted maximal size, exist in multiple numbers in larger presynaptic terminals, and maintain a constant density during development. These findings suggest that active zone density in the CNS is also controlled. However, in contrast to the NMJ, active zone density in the CNS can also be increased, as observed in hippocampal synapses in response to synaptic plasticity. Although the numbers of known active zone proteins and protein interactions have increased, less is known about the mechanism that controls the number or spacing of active zones. The following molecules are known to control active zone density and will be discussed herein: extracellular matrix laminins and voltage-dependent calcium channels, amyloid precursor proteins, the small GTPase Rab3, an endocytosis mechanism including synaptojanin, cytoskeleton protein spectrins and β-adducin, and a presynaptic web including spectrins. The molecular mechanisms that organize the active zone density are just beginning to be elucidated.

Presynaptic Active Zone Density during Development and Synaptic Plasticity

PubMed Central

Clarke, Gwenaëlle L.; Chen, Jie; Nishimune, Hiroshi

2012-01-01

Neural circuits transmit information through synapses, and the efficiency of synaptic transmission is closely related to the density of presynaptic active zones, where synaptic vesicles are released. The goal of this review is to highlight recent insights into the molecular mechanisms that control the number of active zones per presynaptic terminal (active zone density) during developmental and stimulus-dependent changes in synaptic efficacy. At the neuromuscular junctions (NMJs), the active zone density is preserved across species, remains constant during development, and is the same between synapses with different activities. However, the NMJ active zones are not always stable, as exemplified by the change in active zone density during acute experimental manipulation or as a result of aging. Therefore, a mechanism must exist to maintain its density. In the central nervous system (CNS), active zones have restricted maximal size, exist in multiple numbers in larger presynaptic terminals, and maintain a constant density during development. These findings suggest that active zone density in the CNS is also controlled. However, in contrast to the NMJ, active zone density in the CNS can also be increased, as observed in hippocampal synapses in response to synaptic plasticity. Although the numbers of known active zone proteins and protein interactions have increased, less is known about the mechanism that controls the number or spacing of active zones. The following molecules are known to control active zone density and will be discussed herein: extracellular matrix laminins and voltage-dependent calcium channels, amyloid precursor proteins, the small GTPase Rab3, an endocytosis mechanism including synaptojanin, cytoskeleton protein spectrins and β-adducin, and a presynaptic web including spectrins. The molecular mechanisms that organize the active zone density are just beginning to be elucidated. PMID:22438837

Membrane potentials in pinched-off presynaptic nerve ternimals monitored with a fluorescent probe: evidence that synaptosomes have potassium diffusion potentials.

PubMed Central

Blaustein, M P; Goldring, J M

1975-01-01

1. Some physiological properties of tissue fractions from rat brain homogenates have been examined. Of the three fractions studied (presynaptic nerve terminals, mitochondria and fragmented membranes), only the nerve terminals (synaptosomes) have the ability to accumulate 42K from physiological salt solutions. 2. The ability to accumulate and retain K is lost if synaptosomes are exposed to very hypotonic solutions. The K uptake and total K content is reduced by ouabain and by inhibitors of glycolysis and oxidative phosphorylation. 3. These results suggest that synaptosomes in physiological saline accumulate K against a concentration gradient, and may have K diffusion potentials across their surface membranes. The voltage-sensitive fluorescent probe, 3,3'-dipentyl 2,2'-oxacarbocyanine (CC5), was used to test this possibility. 4. In the squid axon, the fluorescent emission of CC5 is directly proportional to membrane potential; depolarization causes an increase in fluorescence. 5. The fluorescence of synaptosomes ('synaptosome fluorescence') treated with CC5 is increased when [K]o is increased or [K]o is reduced; replacement of external Na by Li or choline has little effect on the synaptosome fluorescence. In quantitative terms, synaptosome fluorescence is proportional to log ([K]o plus 0-05[Na]o). Rb is about as effective as K in enhancing synaptosome fluorescence; Cs is about 1/4 as effective. The effect of increased [K]o is reversible. 6. The fluorescence data provide corroborative evidence that there is normally a large K gradient ([K]o smaller than [I]i) across the synaptosome surface membrane. The data suggest the [K]i may be in excess of 100 mM. 7. Replacement of Cl- by methylsulphate did not significantly affect the relationship between synaptosome fluorescence and [K]o, nor did removal of external Ca. 8. The fluorescence of CC5-treated mitochondria, membrane fragmnets, or lysed synaptosomes is unaffected by changes in the K concentration of the medium. 9. Veratridine and gramicidin D, both of which enhance Na permeability (PNa) in some intact tissues, increase synaptosome fluorescence when added to the standard medium. The increment is greatly reduced or abolished when external Na is replaced by choline. 10. If synaptosomes are first Na-loaded (by pre-treatment with cyanide + iodoacetate), and then placed in a choline medium, addition of gramicidin D significantly decreases fluorescence. This effect could be explained if, with [Na]o smaller than [Na]i, the increase in PNa causes the synaptosomes to hyperpolarize. 11. The veratridine-induced increase in synaptosome fluorescence was prevented by 3 times 10- minus 7M tetrodotoxin, which also blocks the depolarizing effect of veratridine in intact neurones. 12. The main conclusion is that synaptosomes may retain resting membrane potentials and the ability to increase Na permeability. PMID:49421

Vesicular Glutamate Transporters: Spatio-Temporal Plasticity following Hearing Loss

PubMed Central

Fyk-Kolodziej, Bozena; Shimano, Takashi; Gong, Tzy-Wen; Holt, Avril Genene

2011-01-01

An immunocytochemical comparison of vGluT1 and vGluT3 in the cochlear nucleus (CN) of deafened versus normal hearing rats showed the first example of vGluT3 immunostaining in the dorsal and ventral CN and revealed temporal and spatial changes in vGluT1 localization in the CN after cochlear injury. In normal hearing rats vGluT1 immunostaining was restricted to terminals on CN neurons while vGluT3 immunolabeled the somata of the neurons. This changed in the VCN three days following deafness, where vGluT1 immunostaining was no longer seen in large auditory nerve terminals but was instead found in somata of VCN neurons. In the DCN, while vGluT1 labeling of terminals decreased, there was no labeling of neuronal somata. Therefore, loss of peripheral excitatory input results in co-localization of vGluT1 and vGluT3 in VCN neuronal somata. Postsynaptic glutamatergic neurons can use retrograde signaling to control their presynaptic inputs and these results suggest vGluTs could play a role in regulating retrograde signaling in the CN under different conditions of excitatory input. Changes in vGluT gene expression in CN neurons were found three weeks following deafness using qRT-PCR with significant increases in vGluT1 gene expression in both ventral and dorsal CN while vGluT3 gene expression decreased in VCN but increased in DCN. PMID:21211553

Adaptations of Presynaptic Dopamine Terminals Induced by Psychostimulant Self-Administration

PubMed Central

2015-01-01

A great deal of research has focused on investigating neurobiological alterations induced by chronic psychostimulant use in an effort to describe, understand, and treat the pathology of psychostimulant addiction. It has been known for several decades that dopamine neurotransmission in the nucleus accumbens is integrally involved in the selection and execution of motivated and goal-directed behaviors, and that psychostimulants act on this system to exert many of their effects. As such, a large body of work has focused on defining the consequences of psychostimulant use on dopamine signaling in the striatum as it relates to addictive behaviors. Here, we review presynaptic dopamine terminal alterations observed following self-administration of cocaine and amphetamine, as well as possible mechanisms by which these alterations occur and their impact on the progression of addiction. PMID:25491345

Distal axotomy enhances retrograde presynaptic excitability onto injured pyramidal neurons via trans-synaptic signaling.

PubMed

Nagendran, Tharkika; Larsen, Rylan S; Bigler, Rebecca L; Frost, Shawn B; Philpot, Benjamin D; Nudo, Randolph J; Taylor, Anne Marion

2017-09-20

Injury of CNS nerve tracts remodels circuitry through dendritic spine loss and hyper-excitability, thus influencing recovery. Due to the complexity of the CNS, a mechanistic understanding of injury-induced synaptic remodeling remains unclear. Using microfluidic chambers to separate and injure distal axons, we show that axotomy causes retrograde dendritic spine loss at directly injured pyramidal neurons followed by retrograde presynaptic hyper-excitability. These remodeling events require activity at the site of injury, axon-to-soma signaling, and transcription. Similarly, directly injured corticospinal neurons in vivo also exhibit a specific increase in spiking following axon injury. Axotomy-induced hyper-excitability of cultured neurons coincides with elimination of inhibitory inputs onto injured neurons, including those formed onto dendritic spines. Netrin-1 downregulation occurs following axon injury and exogenous netrin-1 applied after injury normalizes spine density, presynaptic excitability, and inhibitory inputs at injured neurons. Our findings show that intrinsic signaling within damaged neurons regulates synaptic remodeling and involves netrin-1 signaling.Spinal cord injury can induce synaptic reorganization and remodeling in the brain. Here the authors study how severed distal axons signal back to the cell body to induce hyperexcitability, loss of inhibition and enhanced presynaptic release through netrin-1.

Preferential accumulation of amyloid-beta in presynaptic glutamatergic terminals (VGluT1 and VGluT2) in Alzheimer's disease cortex.

PubMed

Sokolow, Sophie; Luu, Sanh H; Nandy, Karabi; Miller, Carol A; Vinters, Harry V; Poon, Wayne W; Gylys, Karen H

2012-01-01

Amyloid-beta (Aβ) is thought to play a central role in synaptic dysfunction (e.g. neurotransmitter release) and synapse loss. Glutamatergic dysfunction is involved in the pathology of Alzheimer's disease (AD) and perhaps plays a central role in age-related cognitive impairment. Yet, it is largely unknown whether Aβ accumulates in excitatory boutons. To assess the possibility that glutamatergic terminals are lost in AD patients, control and AD synaptosomes were immunolabeled for the most abundant vesicular glutamate transporters (VGluT1 and VGluT2) and quantified by flow cytometry and immunoblot methods. In post-mortem parietal cortex from aged control subjects, glutamatergic boutons are fairly abundant as approximately 40% were immunoreactive for VGluT1 (37%) and VGluT2 (39%). However, the levels of these specific markers of glutamatergic synapses were not significantly different among control and AD cases. To test the hypothesis that Aβ is associated with excitatory terminals, AD synaptosomes were double-labeled for Aβ and for VGluT1 and VGluT2, and analyzed by flow cytometry and confocal microscopy. Our study demonstrated that Aβ immunoreactivity (IR) was present in glutamatergic terminals of AD patients. Quantification of Aβ and VGluT1 in a large population of glutamatergic nerve terminals was performed by flow cytometry, showing that 42% of VGluT1 synaptosomes were immunoreactive for Aβ compared to 9% of VGluT1 synaptosomes lacking Aβ-IR. Percentage of VGluT2 synaptosomes immunoreactive for Aβ (21%) was significantly higher than VGluT2 synaptosomes lacking Aβ-IR (9%). Moreover, Aβ preferentially affects VGluT1 (42% positive) compared to VGluT2 terminals (21%). These data represent the first evidence of high levels of Aβ in excitatory boutons in AD cortex and support the hypothesis that Aβ may play a role in modulating glutamate transmission in AD terminals. Copyright © 2011 Elsevier Inc. All rights reserved.

Preferential accumulation of amyloid-beta in presynaptic glutamatergic terminals (VGluT1 and VGluT2) in Alzheimer’s disease cortex

PubMed Central

Sokolow, Sophie; Luu, Sanh H.; Nandy, Karabi; Miller, Carol A.; Vinters, Harry V.; Poon, Wayne W.; Gylys, Karen H.

2011-01-01

Amyloid-beta (Aβ) is thought to play a central role in synaptic dysfunction (e.g. neurotransmitter release) and synapse loss. Glutamatergic dysfunction is involved in the pathology of Alzheimer’s disease (AD) and perhaps plays a central role in age-related cognitive impairment. Yet, it is largely unknown whether Aβ accumulates in excitatory boutons. To assess the possibility that glutamatergic terminals are lost in AD patients, control and AD synaptosomes were immunolabeled for the most abundant vesicular glutamate transporters (VGluT1 and VGluT2) and quantified by flow cytometry and immunoblot methods. In post-mortem parietal cortex from aged control subjects, glutamatergic boutons are fairly abundant as approximately 40% were immunoreactive for VGluT1 (37%) and VGluT2 (39%). However, the levels of these specific markers of glutamatergic synapses were not significantly different among control and AD cases. To test the hypothesis that Aβ is associated with excitatory terminals, AD synaptosomes were double-labeled for Aβ and for VGluT1 and VGluT2, and analyzed by flow cytometry and confocal microscopy. Our study demonstrated that Aβ immunoreactivity (IR) was present in glutamatergic terminals of AD patients. Quantification of Aβ and VGluT1 in a large population of glutamatergic nerve terminals was performed by flow cytometry, showing that 42% of VGluT1 synaptosomes were immunoreactive for Aβ compared to 9% of VGluT1 synaptosomes lacking Aβ-IR. Percentage of VGluT2 synaptosomes immunoreactive for Aβ (21%) was significantly higher than VGluT2 synaptosomes lacking Aβ-IR (9%). Moreover, Aβ preferentially affects VGluT1 (42% positive) compared to VGluT2 terminals (21%). These data represent the first evidence of high levels of Aβ in excitatory boutons in AD cortex and support the hypothesis that Aβ may play a role in modulating glutamate transmission in AD terminals. PMID:21914482

APP is cleaved by Bace1 in pre-synaptic vesicles and establishes a pre-synaptic interactome, via its intracellular domain, with molecular complexes that regulate pre-synaptic vesicles functions.

PubMed

Del Prete, Dolores; Lombino, Franco; Liu, Xinran; D'Adamio, Luciano

2014-01-01

Amyloid Precursor Protein (APP) is a type I membrane protein that undergoes extensive processing by secretases, including BACE1. Although mutations in APP and genes that regulate processing of APP, such as PSENs and BRI2/ITM2B, cause dementias, the normal function of APP in synaptic transmission, synaptic plasticity and memory formation is poorly understood. To grasp the biochemical mechanisms underlying the function of APP in the central nervous system, it is important to first define the sub-cellular localization of APP in synapses and the synaptic interactome of APP. Using biochemical and electron microscopy approaches, we have found that APP is localized in pre-synaptic vesicles, where it is processed by Bace1. By means of a proteomic approach, we have characterized the synaptic interactome of the APP intracellular domain. We focused on this region of APP because in vivo data underline the central functional and pathological role of the intracellular domain of APP. Consistent with the expression of APP in pre-synaptic vesicles, the synaptic APP intracellular domain interactome is predominantly constituted by pre-synaptic, rather than post-synaptic, proteins. This pre-synaptic interactome of the APP intracellular domain includes proteins expressed on pre-synaptic vesicles such as the vesicular SNARE Vamp2/Vamp1 and the Ca2+ sensors Synaptotagmin-1/Synaptotagmin-2, and non-vesicular pre-synaptic proteins that regulate exocytosis, endocytosis and recycling of pre-synaptic vesicles, such as target-membrane-SNAREs (Syntaxin-1b, Syntaxin-1a, Snap25 and Snap47), Munc-18, Nsf, α/β/γ-Snaps and complexin. These data are consistent with a functional role for APP, via its carboxyl-terminal domain, in exocytosis, endocytosis and/or recycling of pre-synaptic vesicles.

ONR Far East Scientific Bulletin. Volume 6, Number 4, October - December 1981,

DTIC Science & Technology

1981-12-01

been found to delay dark adaptation in the absence of calcium; this makes it unlikely that the darK adaptation process after bleaching is related to...presynaptically in a gastropod nerve cell. Calcium ions are involved, but the mechanisms underlying the effect are still not clear. The effects of

Involvement of the cGMP pathway in the osthole-facilitated glutamate release in rat hippocampal nerve endings.

PubMed

Lin, Tzu Yu; Lu, Cheng Wei; Huang, Wei-Jan; Wang, Su-Jane

2012-03-01

Osthole, an active constituent isolated from Cnidium monnieri (L.) Cusson, has previously been shown to have the capacity to increase depolarization-evoked glutamate release in rat hippocampal nerve terminals. As cGMP-dependent signaling cascade has been found to modulate glutamate release at the presynaptic level, the aim of this study was to further examine the role of cGMP signaling pathway in the regulation of osthole on glutamate release in hippocampal synaptosomes. Results showed that osthole dose-dependently increased intrasynaptosomal cGMP levels. The elevation of cGMP levels by osthole was prevented by the phosphodiesterase 5 inhibitor sildenafil but was insensitive to the guanylyl cyclase inhibitor ODQ. In addition, osthole-induced facilitation of 4-aminopyridine (4-AP)-evoked glutamate release was completely prevented by the cGMP-dependent protein kinase (PKG) inhibitors, KT5823, and Rp-8-Br-PET-cGMPS. Direct activation of PKG with 8-Br-cGMP or 8-pCPT-cGMP also occluded the osthole-mediated facilitation of 4-AP-evoked glutamate release. Furthermore, sildenafil exhibited a dose-dependent facilitation of 4-AP-evoked release of glutamate and occluded the effect of osthole on the 4-AP-evoked glutamate release. Collectively, our findings suggest that osthole-mediated facilitation of glutamate release involves the activation of cGMP/PKG-dependent pathway. Copyright © 2011 Wiley Periodicals, Inc.

Presynaptic congenital myasthenic syndrome with a homozygous sequence variant in LAMA5 combines myopia, facial tics, and failure of neuromuscular transmission.

PubMed

Maselli, Ricardo A; Arredondo, Juan; Vázquez, Jessica; Chong, Jessica X; Bamshad, Michael J; Nickerson, Deborah A; Lara, Marian; Ng, Fiona; Lo, Victoria L; Pytel, Peter; McDonald, Craig M

2017-08-01

Defects in genes encoding the isoforms of the laminin alpha subunit have been linked to various phenotypic manifestations, including brain malformations, muscular dystrophy, ocular defects, cardiomyopathy, and skin abnormalities. We report here a severe defect of neuromuscular transmission in a consanguineous patient with a homozygous variant in the laminin alpha-5 subunit gene (LAMA5). The variant c.8046C>T (p.Arg2659Trp) is rare and has a predicted deleterious effect. The affected individual, who also carries a rare homozygous sequence variant in LAMA1, had muscle weakness, myopia, and facial tics. Magnetic resonance imaging of brain showed mild volume loss and periventricular T2 prolongation. Repetitive nerve stimulation revealed 50% decrement of compound muscle action potential amplitudes and 250% facilitation immediately after exercise, Endplate studies identified a profound reduction of the endplate potential quantal content and endplates with normal postsynaptic folding that were denuded or partially occupied by small nerve terminals. Expression studies revealed that p.Arg2659Trp caused decreased binding of laminin alpha-5 to SV2A and impaired laminin-521 cell-adhesion and cell projection support in primary neuronal cultures. In summary, this report describing severe neuromuscular transmission failure in a patient with a LAMA5 mutation expands the list of phenotypes associated with defects in genes encoding alpha-laminins. © 2017 Wiley Periodicals, Inc.

High-voltage-activated calcium current subtypes in mouse DRG neurons adapt in a subpopulation-specific manner after nerve injury.

PubMed

Murali, Swetha S; Napier, Ian A; Mohammadi, Sarasa A; Alewood, Paul F; Lewis, Richard J; Christie, MacDonald J

2015-03-01

Changes in ion channel function and expression are characteristic of neuropathic pain. Voltage-gated calcium channels (VGCCs) are integral for neurotransmission and membrane excitability, but relatively little is known about changes in their expression after nerve injury. In this study, we investigate whether peripheral nerve ligation is followed by changes in the density and proportion of high-voltage-activated (HVA) VGCC current subtypes in dorsal root ganglion (DRG) neurons, the contribution of presynaptic N-type calcium channels in evoked excitatory postsynaptic currents (EPSCs) recorded from dorsal horn neurons in the spinal cord, and the changes in expression of mRNA encoding VGCC subunits in DRG neurons. Using C57BL/6 mice [8- to 11-wk-old males (n = 91)] for partial sciatic nerve ligation or sham surgery, we performed whole cell patch-clamp recordings on isolated DRG neurons and dorsal horn neurons and measured the expression of all VGCC subunits with RT-PCR in DRG neurons. After nerve injury, the density of P/Q-type current was reduced overall in DRG neurons. There was an increase in the percentage of N-type and a decrease in that of P/Q-type current in medium- to large-diameter neurons. No changes were found in the contribution of presynaptic N-type calcium channels in evoked EPSCs recorded from dorsal horn neurons. The α2δ-1 subunit was upregulated by 1.7-fold and γ-3, γ-2, and β-4 subunits were all downregulated 1.7-fold in injured neurons compared with sham-operated neurons. This comprehensive characterization of HVA VGCC subtypes in mouse DRG neurons after nerve injury revealed changes in N- and P/Q-type current proportions only in medium- to large-diameter neurons. Copyright © 2015 the American Physiological Society.

Molecular Mechanism of Acrylamide Neurotoxicity: Lessons Learned from Organic Chemistry

PubMed Central

Gavin, Terrence

2012-01-01

Background: Acrylamide (ACR) produces cumulative neurotoxicity in exposed humans and laboratory animals through a direct inhibitory effect on presynaptic function. Objectives: In this review, we delineate how knowledge of chemistry provided an unprecedented understanding of the ACR neurotoxic mechanism. We also show how application of the hard and soft, acids and bases (HSAB) theory led to the recognition that the α,β-unsaturated carbonyl structure of ACR is a soft electrophile that preferentially forms covalent bonds with soft nucleophiles. Methods: In vivo proteomic and in chemico studies demonstrated that ACR formed covalent adducts with highly nucleophilic cysteine thiolate groups located within active sites of presynaptic proteins. Additional research showed that resulting protein inactivation disrupted nerve terminal processes and impaired neurotransmission. Discussion: ACR is a type-2 alkene, a chemical class that includes structurally related electrophilic environmental pollutants (e.g., acrolein) and endogenous mediators of cellular oxidative stress (e.g., 4-hydroxy-2-nonenal). Members of this chemical family produce toxicity via a common molecular mechanism. Although individual environmental concentrations might not be toxicologically relevant, exposure to an ambient mixture of type-2 alkene pollutants could pose a significant risk to human health. Furthermore, environmentally derived type-2 alkenes might act synergistically with endogenously generated unsaturated aldehydes to amplify cellular damage and thereby accelerate human disease/injury processes that involve oxidative stress. Conclusions: These possibilities have substantial implications for environmental risk assessment and were realized through an understanding of ACR adduct chemistry. The approach delineated here can be broadly applied because many toxicants of different chemical classes are electrophiles that produce toxicity by interacting with cellular proteins. PMID:23060388

Muscle-derived collagen XIII regulates maturation of the skeletal neuromuscular junction.

PubMed

Latvanlehto, Anne; Fox, Michael A; Sormunen, Raija; Tu, Hongmin; Oikarainen, Tuomo; Koski, Anu; Naumenko, Nikolay; Shakirzyanova, Anastasia; Kallio, Mika; Ilves, Mika; Giniatullin, Rashid; Sanes, Joshua R; Pihlajaniemi, Taina

2010-09-15

Formation, maturation, stabilization, and functional efficacy of the neuromuscular junction (NMJ) are orchestrated by transsynaptic and autocrine signals embedded within the synaptic cleft. Here, we demonstrate that collagen XIII, a nonfibrillar transmembrane collagen, is another such signal. We show that collagen XIII is expressed by muscle and its ectodomain can be proteolytically shed into the extracellular matrix. The collagen XIII protein was found present in the postsynaptic membrane and synaptic basement membrane. To identify a role for collagen XIII at the NMJ, mice were generated lacking this collagen. Morphological and ultrastructural analysis of the NMJ revealed incomplete adhesion of presynaptic and postsynaptic specializations in collagen XIII-deficient mice of both genders. Strikingly, Schwann cells erroneously enwrapped nerve terminals and invaginated into the synaptic cleft, resulting in a decreased contact surface for neurotransmission. Consistent with morphological findings, electrophysiological studies indicated both postsynaptic and presynaptic defects in Col13a1(-/-) mice, such as decreased amplitude of postsynaptic potentials, diminished probabilities of spontaneous release and reduced readily releasable neurotransmitter pool. To identify the role of collagen XIII at the NMJ, shed ectodomain of collagen XIII was applied to cultured myotubes, and it was found to advance acetylcholine receptor (AChR) cluster maturation. Together with the delay in AChR cluster development observed in collagen XIII-deficient mutants in vivo, these results suggest that collagen XIII plays an autocrine role in postsynaptic maturation of the NMJ. Altogether, the results presented here reveal that collagen XIII is a novel muscle-derived cue necessary for the maturation and function of the vertebrate NMJ.

Peripheral Nerve Injury Leads to Working Memory Deficits and Dysfunction of the Hippocampus by Upregulation of TNF-α in Rodents

PubMed Central

Ren, Wen-Jie; Liu, Yong; Zhou, Li-Jun; Li, Wei; Zhong, Yi; Pang, Rui-Ping; Xin, Wen-Jun; Wei, Xu-Hong; Wang, Jun; Zhu, He-Quan; Wu, Chang-You; Qin, Zhi-Hai; Liu, Guosong; Liu, Xian-Guo

2011-01-01

Patients with chronic pain usually suffer from working memory deficits, which may decrease their intellectual ability significantly. Despite intensive clinical studies, the mechanism underlying this form of memory impairment remains elusive. In this study, we investigated this issue in the spared nerve injury (SNI) model of neuropathic pain, a most common form of chronic pain. We found that SNI impaired working memory and short-term memory in rats and mice. To explore the potential mechanisms, we studied synaptic transmission/plasticity in hippocampus, a brain region critically involved in memory function. We found that frequency facilitation, a presynaptic form of short-term plasticity, and long-term potentiation at CA3–CA1 synapses were impaired after SNI. Structurally, density of presynaptic boutons in hippocampal CA1 synapses was reduced significantly. At the molecular level, we found that tumor necrosis factor-α (TNF-α) increased in cerebrospinal fluid, in hippocampal tissue and in plasma after SNI. Intracerebroventricular or intrahippocampal injection of recombinant rat TNF mimicked the effects of SNI in naive rats, whereas inhibition of TNF-α or genetic deletion of TNF receptor 1 prevented both memory deficits and synaptic dysfunction induced by SNI. As TNF-α is critical for development of neuropathic pain, we suggested that the over-production of TNF-α following peripheral nerve injury might lead to neuropathic pain and memory deficits, simultaneously. PMID:21289602

Central projections of the lateral line and eighth nerves in the bowfin, Amia calva.

PubMed

McCormick, C A

1981-03-20

The first-order connections of the anterior and posterior lateral line nerves and of the eighth nerve were determined in the bowfin, Amia calva, using experimental degeneration and anterograde HRP transport techniques. The termination sites of these nerves define a dorsal lateralis cell column and a ventral octavus cell column. The anterior and posterior lateralis nerves distribute ipsilaterally to two medullary nuclei-nucleus medialis and nucleus caudalis. Nucleus medialis comprises the rostral two-thirds of the lateralis column and contains large, Purkinje-like cells dorsally and polygonal, granule, and fusiform cells ventrally. Nucleus caudalis is located posterior to nucleus medialis and consists of small, granule cells. Anterior lateralis fibers terminate ventrally to ventromedially in both nucleus medialis and nucleus caudalis. Posterior lateralis fibers terminate dorsally to dorsolaterally within these two nuclei. A sparse anterior lateralis input may also be present on the dendrites of one of the nuclei within the octavus cell column, nucleus magnocellularis. In contrast, the anterior and posterior rami of the eighth nerve each terminate within four medullary nuclei which comprise the octavus cell column: the anterior, magnocellular, descending, and posterior octavus nuclei. An eighth nerve projection to the medial reticular formation is also present. Some fibers of the lateralis and eighth nerves terminate within the ipsilateral eminentia granularis of the cerebellum. Lateralis fibers distribute to approximately the lateral half of this structure with posterior lateral line fibers terminating laterally and anterior lateral line fibers terminating medially. Eighth nerve fibers distribute to the medial half of the eminentia granularis.

The synaptic terminations of certain midbrain-olivary fibers in the opossum.

PubMed

King, J S; Hamos, J E; Maley, B E

1978-11-15

The nuclear origin and distribution of midbrain-olivary fibers has been described in a previous study utilizing axonal transport techniques (Linauts and Martin, '78a). The present report extends their results to the electron microscopic level and details the postsynaptic distribution of such fibers. Lesions within the ventral periaqueductal grey and adjacent tegmentum, the red nucleus or the nucleus subparafascicularis result in electron dense axon terminals within the olive at survival times of 48, 72 and 96 hours. At 72 hours, many degenerating presynaptic profiles shrink, become irregular in shape and are totally or partially surrounded by glial processes. The principal olivary nucleus contains the majority of these profiles. However, the subparafascicular terminals are more abundant in the rostral and intermediate parts of the medial accessory nucleus and the rubral terminals are concentrated within the dorsal lamella of the principal nucleus. The nuclear location of the degenerating terminals was determined by examination of 1 micrometer plastic sections cut in the transverse plane from each block face prior to thin sectioning. Degenerating terminals were counted in three cases, one from each of the three lesion sites described above. When taken together these cases show that just over 50% of the degenerating terminals are presynaptic to spiny appendages and are located within the synaptic clusters (glomeruli) described previously (King, '76). The percentage of degenerating terminals in the glomeruli increases to 70% when the lesion is in the ventral periaqueductal grey and adjacent tegmentum. The remaining degenerating terminals contact dendritic shafts outside the astrocytic boundaries of the synaptic clusters. The synpatic vesicle populations within the degenerating terminals vary with the location of the lesion. Lesions in the ventral periaqueductal grey and the adjacent tegmentum result in the degeneration of terminals with either clear spherical vesicles or endings with both clear spherical vesicles and a variable number of large dense core vesicles. In contrast, the primary degenerative changes that occur after destruction of the red nucleus or the nucleus subparafascicularis are in terminals with clear spherical vesicles. When the synaptic complex was present in the plane of section, regardless of the site of the lesion, the degenerating terminals could be classified as Gray's type I. Thus, we have demonstrated that afferents from the mesencephalon terminate within synpatic clusters located in the principal and medial accessory (part A) subnuclei of the inferior olive. Although the mesencephalic afferents have multiple origins (Linauts and Martin, '78a), many of their synaptic terminals contact spiny appendages within the synaptic clusters. This postsynaptic site also receives cerebellar terminals (King et al., '76). The origin of presynaptic profiles within the synaptic clusters that contain clear pleomorphlic vesicles is yet to be determined.

Acute corneal epithelial debridement unmasks the corneal stromal nerve responses to ocular stimulation in rats: implications for abnormal sensations of the eye.

PubMed

Hirata, Harumitsu; Mizerska, Kamila; Dallacasagrande, Valentina; Guaiquil, Victor H; Rosenblatt, Mark I

2017-05-01

It is widely accepted that the mechanisms for transducing sensory information reside in the nerve terminals. Occasionally, however, studies have appeared demonstrating that similar mechanisms may exist in the axon to which these terminals are connected. We examined this issue in the cornea, where nerve terminals in the epithelial cell layers are easily accessible for debridement, leaving the underlying stromal (axonal) nerves undisturbed. In isoflurane-anesthetized rats, we recorded extracellularly from single trigeminal ganglion neurons innervating the cornea that are excited by ocular dryness and cooling: low-threshold (<2°C cooling) and high-threshold (>2°C) cold-sensitive plus dry-sensitive neurons playing possible roles in tearing and ocular pain. We found that the responses in both types of neurons to dryness, wetness, and menthol stimuli were effectively abolished by the debridement, indicating that their transduction mechanisms lie in the nerve terminals. However, some responses to the cold, heat, and hyperosmolar stimuli in low-threshold cold-sensitive plus dry-sensitive neurons still remained. Surprisingly, the responses to heat in approximately half of the neurons were augmented after the debridement. We were also able to evoke these residual responses and follow the trajectory of the stromal nerves, which we subsequently confirmed histologically. The residual responses always disappeared when the stromal nerves were cut at the limbus, suggesting that the additional transduction mechanisms for these sensory modalities originated most likely in stromal nerves. The functional significance of these residual and enhanced responses from stromal nerves may be related to the abnormal sensations observed in ocular disease. NEW & NOTEWORTHY In addition to the traditional view that the sensory transduction mechanisms exist in the nerve terminals, we report here that the proximal axons (stromal nerves in the cornea from which these nerve terminals originate) may also be capable of transducing sensory information. We arrived at this conclusion by removing the epithelial cell layers of the cornea in which the nerve terminals reside but leaving the underlying stromal nerves undisturbed. Copyright © 2017 the American Physiological Society.

Acute corneal epithelial debridement unmasks the corneal stromal nerve responses to ocular stimulation in rats: implications for abnormal sensations of the eye

PubMed Central

Mizerska, Kamila; Dallacasagrande, Valentina; Guaiquil, Victor H.; Rosenblatt, Mark I.

2017-01-01

It is widely accepted that the mechanisms for transducing sensory information reside in the nerve terminals. Occasionally, however, studies have appeared demonstrating that similar mechanisms may exist in the axon to which these terminals are connected. We examined this issue in the cornea, where nerve terminals in the epithelial cell layers are easily accessible for debridement, leaving the underlying stromal (axonal) nerves undisturbed. In isoflurane-anesthetized rats, we recorded extracellularly from single trigeminal ganglion neurons innervating the cornea that are excited by ocular dryness and cooling: low-threshold (<2°C cooling) and high-threshold (>2°C) cold-sensitive plus dry-sensitive neurons playing possible roles in tearing and ocular pain. We found that the responses in both types of neurons to dryness, wetness, and menthol stimuli were effectively abolished by the debridement, indicating that their transduction mechanisms lie in the nerve terminals. However, some responses to the cold, heat, and hyperosmolar stimuli in low-threshold cold-sensitive plus dry-sensitive neurons still remained. Surprisingly, the responses to heat in approximately half of the neurons were augmented after the debridement. We were also able to evoke these residual responses and follow the trajectory of the stromal nerves, which we subsequently confirmed histologically. The residual responses always disappeared when the stromal nerves were cut at the limbus, suggesting that the additional transduction mechanisms for these sensory modalities originated most likely in stromal nerves. The functional significance of these residual and enhanced responses from stromal nerves may be related to the abnormal sensations observed in ocular disease. NEW & NOTEWORTHY In addition to the traditional view that the sensory transduction mechanisms exist in the nerve terminals, we report here that the proximal axons (stromal nerves in the cornea from which these nerve terminals originate) may also be capable of transducing sensory information. We arrived at this conclusion by removing the epithelial cell layers of the cornea in which the nerve terminals reside but leaving the underlying stromal nerves undisturbed. PMID:28250152

Development of the terminal nerve system in the shark Scyliorhinus canicula.

PubMed

Quintana-Urzainqui, Idoia; Anadón, Ramón; Candal, Eva; Rodríguez-Moldes, Isabel

2014-01-01

The nervus terminalis (or terminal nerve) system was discovered in an elasmobranch species more than a century ago. Over the past century, it has also been recognized in other vertebrate groups, from agnathans to mammals. However, its origin, functions or relationship with the olfactory system are still under debate. Despite the abundant literature about the nervus terminalis system in adult elasmobranchs, its development has been overlooked. Studies in other vertebrates have reported newly differentiated neurons of the terminal nerve system migrating from the olfactory epithelium to the telencephalon as part of a 'migratory mass' of cells associated with the olfactory nerve. Whether the same occurs in developing elasmobranchs (adults showing anatomically separated nervus terminalis and olfactory systems) has not yet been determined. In this work we characterized for the first time the development of the terminal nerve and ganglia in an elasmobranch, the lesser spotted dogfish (Scyliorhinus canicula), by means of tract-tracing techniques combined with immunohistochemical markers for the terminal nerve (such as FMRF-amide peptide), for the developing components of the olfactory system (Gα0 protein, GFAP, Pax6), and markers for early postmitotic neurons (HuC/D) and migrating immature neurons (DCX). We discriminated between embryonic olfactory and terminal nerve systems and determined that both components may share a common origin in the migratory mass. We also localized the exact point where they split off near the olfactory nerve-olfactory bulb junction. The study of the development of the terminal nerve system in a basal gnathostome contributes to the knowledge of the ancestral features of this system in vertebrates, shedding light on its evolution and highlighting the importance of elasmobranchs for developmental and evolutionary studies. © 2014 S. Karger AG, Basel.

Facial diplegia, pharyngeal paralysis, and ophthalmoplegia after a timber rattlesnake envenomation.

PubMed

Madey, Jason J; Price, Amanda B; Dobson, Joseph V; Stickler, David E; McSwain, S David

2013-11-01

The timber rattlesnake, also known as Crotalus horridus, is well known to cause significant injury from toxins stored within its venom. During envenomation, toxic systemic effects immediately begin to cause damage to many organ systems including cardiovascular, hematologic, musculoskeletal, respiratory, and neurologic. One defining characteristic of the timber rattlesnake is a specific neurotoxin called crotoxin, or the "canebrake toxin," which is a potent β-neurotoxin affecting presynaptic nerves that can cause paralysis by inhibiting appropriate neuromuscular transmission. We present an unusual case of an 8-year-old boy bitten twice on his calf by a timber rattlesnake, who presented with a life-threatening envenomation and suffered multisystem organ failure as well as a prominent presynaptic neurotoxicity resulting in facial diplegia, pharyngeal paralysis, and ophthalmoplegia.

Synapse Formation in Monosynaptic Sensory–Motor Connections Is Regulated by Presynaptic Rho GTPase Cdc42

PubMed Central

Imai, Fumiyasu; Ladle, David R.; Leslie, Jennifer R.; Duan, Xin; Rizvi, Tilat A.; Ciraolo, Georgianne M.; Zheng, Yi

2016-01-01

Spinal reflex circuit development requires the precise regulation of axon trajectories, synaptic specificity, and synapse formation. Of these three crucial steps, the molecular mechanisms underlying synapse formation between group Ia proprioceptive sensory neurons and motor neurons is the least understood. Here, we show that the Rho GTPase Cdc42 controls synapse formation in monosynaptic sensory–motor connections in presynaptic, but not postsynaptic, neurons. In mice lacking Cdc42 in presynaptic sensory neurons, proprioceptive sensory axons appropriately reach the ventral spinal cord, but significantly fewer synapses are formed with motor neurons compared with wild-type mice. Concordantly, electrophysiological analyses show diminished EPSP amplitudes in monosynaptic sensory–motor circuits in these mutants. Temporally targeted deletion of Cdc42 in sensory neurons after sensory–motor circuit establishment reveals that Cdc42 does not affect synaptic transmission. Furthermore, addition of the synaptic organizers, neuroligins, induces presynaptic differentiation of wild-type, but not Cdc42-deficient, proprioceptive sensory neurons in vitro. Together, our findings demonstrate that Cdc42 in presynaptic neurons is required for synapse formation in monosynaptic sensory–motor circuits. SIGNIFICANCE STATEMENT Group Ia proprioceptive sensory neurons form direct synapses with motor neurons, but the molecular mechanisms underlying synapse formation in these monosynaptic sensory–motor connections are unknown. We show that deleting Cdc42 in sensory neurons does not affect proprioceptive sensory axon targeting because axons reach the ventral spinal cord appropriately, but these neurons form significantly fewer presynaptic terminals on motor neurons. Electrophysiological analysis further shows that EPSPs are decreased in these mice. Finally, we demonstrate that Cdc42 is involved in neuroligin-dependent presynaptic differentiation of proprioceptive sensory neurons in vitro. These data suggest that Cdc42 in presynaptic sensory neurons is essential for proper synapse formation in the development of monosynaptic sensory–motor circuits. PMID:27225763

Cytosolic Calcium Coordinates Mitochondrial Energy Metabolism with Presynaptic Activity

PubMed Central

Chouhan, Amit K.; Ivannikov, Maxim V.; Lu, Zhongmin; Sugimori, Mutsuyuki; Llinas, Rodolfo R.; Macleod, Gregory T.

2012-01-01

Most neurons fire in bursts, imposing episodic energy demands, but how these demands are coordinated with oxidative phosphorylation is still unknown. Here, using fluorescence imaging techniques on presynaptic termini of Drosophila motor neurons (MNs), we show that mitochondrial matrix pH (pHm), inner membrane potential (Δψm), and NAD(P)H levels ([NAD(P)H]m) increase within seconds of nerve stimulation. The elevations of pHm, Δψm, and [NAD(P)H]m indicate an increased capacity for ATP production. Elevations in pHm were blocked by manipulations which blocked mitochondrial Ca2+ uptake, including replacement of extracellular Ca2+ with Sr2+, and application of either tetraphenylphosphonium chloride or KB-R7943, indicating that it is Ca2+ that stimulates presynaptic mitochondrial energy metabolism. To place this phenomenon within the context of endogenous neuronal activity, the firing rates of a number of individually identified MNs were determined during fictive locomotion. Surprisingly, although endogenous firing rates are significantly different, there was little difference in presynaptic cytosolic Ca2+ levels ([Ca2+]c) between MNs when each fires at its endogenous rate. The average [Ca2+]c level (329±11nM) was slightly above the average Ca2+ affinity of the mitochondria (281±13nM). In summary, we show that when MNs fire at endogenous rates [Ca2+]c is driven into a range where mitochondria rapidly acquire Ca2+. As we also show that Ca2+ stimulates presynaptic mitochondrial energy metabolism, we conclude that [Ca2+]c levels play an integral role in coordinating mitochondrial energy metabolism with presynaptic activity in Drosophila MNs. PMID:22279208

Neural and receptor cochlear potentials obtained by transtympanic electrocochleography in auditory neuropathy.

PubMed

Santarelli, Rosamaria; Starr, Arnold; Michalewski, Henry J; Arslan, Edoardo

2008-05-01

Transtympanic electrocochleography (ECochG) was recorded bilaterally in children and adults with auditory neuropathy (AN) to evaluate receptor and neural generators. Test stimuli were clicks from 60 to 120dB p.e. SPL. Measures obtained from eight AN subjects were compared to 16 normally hearing children. Receptor cochlear microphonics (CMs) in AN were of normal or enhanced amplitude. Neural compound action potentials (CAPs) and receptor summating potentials (SPs) were identified in five AN ears. ECochG potentials in those ears without CAPs were of negative polarity and of normal or prolonged duration. We used adaptation to rapid stimulus rates to distinguish whether the generators of the negative potentials were of neural or receptor origin. Adaptation in controls resulted in amplitude reduction of CAP twice that of SP without affecting the duration of ECochG potentials. In seven AN ears without CAP and with prolonged negative potential, adaptation was accompanied by reduction of both amplitude and duration of the negative potential to control values consistent with neural generation. In four ears without CAP and with normal duration potentials, adaptation was without effect consistent with receptor generation. In five AN ears with CAP, there was reduction in amplitude of CAP and SP as controls but with a significant decrease in response duration. Three patterns of cochlear potentials were identified in AN: (1) presence of receptor SP without CAP consistent with pre-synaptic disorder of inner hair cells; (2) presence of both SP and CAP consistent with post-synaptic disorder of proximal auditory nerve; (3) presence of prolonged neural potentials without a CAP consistent with post-synaptic disorder of nerve terminals. Cochlear potential measures may identify pre- and post-synaptic disorders of inner hair cells and auditory nerves in AN.

Enkephalin modulation of neural transmission in the cat stellate ganglion: pharmacological actions of exogenous opiates.

PubMed

Prosdocimi, M; Finesso, M; Gorio, A

1986-11-01

Neural ganglionic transmission was studied in vivo in the cat, using closed chest anesthetized preparations. The right stellate ganglion and its branches were exposed retropleurally and prepared for electrical stimulation of pre- and postganglionic nerve fibers. The axillary artery was cannulated allowing direct administration of drugs in the arterial blood supplying the ganglion. Stimulation of postjunctional receptors could thus be obtained by local administration of selective agents. Local administration of nicotinic, muscarinic or histaminergic agents increased heart rate and blood pressure. Opiates were given either i.v. or locally through the axillary artery: we tested the effects of morphine, Leu-enkephalin (Leu-enk), Met-enkephalin (Met-enk), [D-ala2]-Met-enkephalinamide (DAME) and etorphine. When given locally, Leu-enk (from 10 micrograms), Met-enk (from 20 micrograms), DAME (from 5 micrograms) and etorphine (from 0.2 micrograms) inhibited tachycardia induced by preganglionic stimulation and reduced the amplitude of the compound action potential recorded from the postganglionic nerve. Morphine (10-200 micrograms) had no effect. On the other hand, tachycardia induced by postganglionic nerve stimulation was unaffected by opiates in the same experimental conditions. Intravenous administration of similar doses of opiates had no effect on ganglionic transmission. When tachycardia was induced by chemical stimulation of nicotinic (DMPP), muscarinic (McN-A-343-11) or histamine receptors in the stellate ganglia, opiates were still active in reducing the effect of these chemicals. These data provide evidence that exogenous opiates exert a depressing action on postsynaptic responses of sympathetic ganglia tested in vivo, although an additional action on presynaptic terminals is not excluded. As endogenous opiates are normally present in various sympathetic ganglia, including the stellate ganglion of the cat, it is possible that they play some modulatory role on ganglionic transmission in physiological conditions.

Acute hyperbilirubinaemia induces presynaptic neurodegeneration at a central glutamatergic synapse

PubMed Central

Haustein, Martin D; Read, David J; Steinert, Joern R; Pilati, Nadia; Dinsdale, David; Forsythe, Ian D

2010-01-01

There is a well-established link between hyperbilirubinaemia and hearing loss in paediatrics, but the cellular mechanisms have not been elucidated. Here we used the Gunn rat model of hyperbilirubinaemia to investigate bilirubin-induced hearing loss. In vivo auditory brainstem responses revealed that Gunn rats have severe auditory deficits within 18 h of exposure to high bilirubin levels. Using an in vitro preparation of the auditory brainstem from these rats, extracellular multi-electrode array recording from the medial nucleus of the trapezoid body (MNTB) showed longer latency and decreased amplitude of evoked field potentials following bilirubin exposure, suggestive of transmission failure at this synaptic relay. Whole-cell patch-clamp recordings confirmed that the electrophysiological properties of the postsynaptic MNTB neurons were unaffected by bilirubin, with no change in action potential waveforms or current–voltage relationships. However, stimulation of the trapezoid body was unable to elicit large calyceal EPSCs in MNTB neurons of hyperbilirubinaemic rats, indicative of damage at a presynaptic site. Multi-photon imaging of anterograde-labelled calyceal projections revealed axonal staining and presynaptic profiles around MNTB principal neuron somata. Following induction of hyperbilirubinaemia the giant synapses were largely destroyed. Electron microscopy confirmed loss of presynaptic calyceal terminals and supported the electrophysiological evidence for healthy postsynaptic neurons. MNTB neurons express high levels of neuronal nitric oxide synthase (nNOS). Nitric oxide has been implicated in mechanisms of bilirubin toxicity elsewhere in the brain, and antagonism of nNOS by 7-nitroindazole protected hearing during bilirubin exposure. We conclude that bilirubin-induced deafness is caused by degeneration of excitatory synaptic terminals in the auditory brainstem. PMID:20937712

Acute hyperbilirubinaemia induces presynaptic neurodegeneration at a central glutamatergic synapse.

PubMed

Haustein, Martin D; Read, David J; Steinert, Joern R; Pilati, Nadia; Dinsdale, David; Forsythe, Ian D

2010-12-01

There is a well-established link between hyperbilirubinaemia and hearing loss in paediatrics, but the cellular mechanisms have not been elucidated. Here we used the Gunn rat model of hyperbilirubinaemia to investigate bilirubin-induced hearing loss. In vivo auditory brainstem responses revealed that Gunn rats have severe auditory deficits within 18 h of exposure to high bilirubin levels. Using an in vitro preparation of the auditory brainstem from these rats, extracellular multi-electrode array recording from the medial nucleus of the trapezoid body (MNTB) showed longer latency and decreased amplitude of evoked field potentials following bilirubin exposure, suggestive of transmission failure at this synaptic relay. Whole-cell patch-clamp recordings confirmed that the electrophysiological properties of the postsynaptic MNTB neurons were unaffected by bilirubin, with no change in action potential waveforms or current-voltage relationships. However, stimulation of the trapezoid body was unable to elicit large calyceal EPSCs in MNTB neurons of hyperbilirubinaemic rats, indicative of damage at a presynaptic site. Multi-photon imaging of anterograde-labelled calyceal projections revealed axonal staining and presynaptic profiles around MNTB principal neuron somata. Following induction of hyperbilirubinaemia the giant synapses were largely destroyed. Electron microscopy confirmed loss of presynaptic calyceal terminals and supported the electrophysiological evidence for healthy postsynaptic neurons. MNTB neurons express high levels of neuronal nitric oxide synthase (nNOS). Nitric oxide has been implicated in mechanisms of bilirubin toxicity elsewhere in the brain, and antagonism of nNOS by 7-nitroindazole protected hearing during bilirubin exposure. We conclude that bilirubin-induced deafness is caused by degeneration of excitatory synaptic terminals in the auditory brainstem.

Presynaptic dystroglycan-pikachurin complex regulates the proper synaptic connection between retinal photoreceptor and bipolar cells.

PubMed

Omori, Yoshihiro; Araki, Fumiyuki; Chaya, Taro; Kajimura, Naoko; Irie, Shoichi; Terada, Koji; Muranishi, Yuki; Tsujii, Toshinori; Ueno, Shinji; Koyasu, Toshiyuki; Tamaki, Yasuhiro; Kondo, Mineo; Amano, Shiro; Furukawa, Takahisa

2012-05-02

Dystroglycan (DG) is a key component of the dystrophin-glycoprotein complex (DGC) at the neuromuscular junction postsynapse. In the mouse retina, the DGC is localized at the presynapse of photoreceptor cells, however, the function of presynaptic DGC is poorly understood. Here, we developed and analyzed retinal photoreceptor-specific DG conditional knock-out (DG CKO) mice. We found that the DG CKO retina showed a reduced amplitude and a prolonged implicit time of the ERG b-wave. Electron microscopic analysis revealed that bipolar dendrite invagination into the photoreceptor terminus is perturbed in the DG CKO retina. In the DG CKO retina, pikachurin, a DG ligand in the retina, is markedly decreased at photoreceptor synapses. Interestingly, in the Pikachurin(-/-) retina, the DG signal at the ribbon synaptic terminus was severely reduced, suggesting that pikachurin is required for the presynaptic accumulation of DG at the photoreceptor synaptic terminus, and conversely DG is required for pikachurin accumulation. Furthermore, we found that overexpression of pikachurin induces formation and clustering of a DG-pikachurin complex on the cell surface. The Laminin G repeats of pikachurin, which are critical for its oligomerization and interaction with DG, were essential for the clustering of the DG-pikachurin complex as well. These results suggest that oligomerization of pikachurin and its interaction with DG causes DG assembly on the synapse surface of the photoreceptor synaptic terminals. Our results reveal that the presynaptic interaction of pikachurin with DG at photoreceptor terminals is essential for both the formation of proper photoreceptor ribbon synaptic structures and normal retinal electrophysiology.

The relationship of choline acetyltransferase activity at the neuromuscular junction to changes in muscle mass and function

PubMed Central

Diamond, Ivan; Franklin, Gary M.; Milfay, Dale

1974-01-01

1. The role of muscle mass and function in the regulation of choline acetyltransferase activity at the neuromuscular junction has been investigated in the rat. 2. Choline acetyltransferase (ChAc) is located in presynaptic nerve terminals and is a specific enzymatic marker of cholinergic innervation in muscle. 3. ChAc activity increased co-ordinately with developmental growth of the soleus muscle. However, another form of muscle growth, work hypertrophy, did not produce an increase in ChAc. 4. Growth arrest of muscle by hypophysectomy did not alter the normal development of ChAc activity, and cortisone-induced muscle atrophy did not reduce ChAc activity in the soleus or plantaris. 5. Tenotomy-induced muscle atrophy provoked a significant fall in ChAc in the soleus and plantaris. 6. The tonic soleus had significantly greater ChAc activity than the phasic plantaris. 7. These observations suggest that muscle mass per se does not influence the development and regulation of ChAc in muscle but that the quality of muscle contraction may modulate enzyme activity. PMID:4818500

Implications and mechanism of action of gabapentin in neuropathic pain.

PubMed

Kukkar, Ankesh; Bali, Anjana; Singh, Nirmal; Jaggi, Amteshwar Singh

2013-03-01

Gabapentin is an anti-epileptic agent but now it is also recommended as first line agent in neuropathic pain, particularly in diabetic neuropathy and post herpetic neuralgia. α2δ-1, an auxillary subunit of voltage gated calcium channels, has been documented as its main target and its specific binding to this subunit is described to produce different actions responsible for pain attenuation. The binding to α2δ-1 subunits inhibits nerve injury-induced trafficking of α1 pore forming units of calcium channels (particularly N-type) from cytoplasm to plasma membrane (membrane trafficking) of pre-synaptic terminals of dorsal root ganglion (DRG) neurons and dorsal horn neurons. Furthermore, the axoplasmic transport of α2δ-1 subunits from DRG to dorsal horns neurons in the form of anterograde trafficking is also inhibited in response to gabapentin administration. Gabapentin has also been shown to induce modulate other targets including transient receptor potential channels, NMDA receptors, protein kinase C and inflammatory cytokines. It may also act on supra-spinal region to stimulate noradrenaline mediated descending inhibition, which contributes to its anti-hypersensitivity action in neuropathic pain.

Zinc transporter ZnT-3 regulates presynaptic Erk1/2 signaling and hippocampus-dependent memory.

PubMed

Sindreu, Carlos; Palmiter, Richard D; Storm, Daniel R

2011-02-22

The physiological role of vesicular zinc at central glutamatergic synapses remains poorly understood. Here we show that mice lacking the synapse-specific vesicular zinc transporter ZnT3 (ZnT3KO mice) have reduced activation of the Erk1/2 MAPK in hippocampal mossy fiber terminals, disinhibition of zinc-sensitive MAPK tyrosine phosphatase activity, and impaired MAPK signaling during hippocampus-dependent learning. Activity-dependent exocytosis is required for the effect of zinc on presynaptic MAPK and phosphatase activity. ZnT3KO mice have complete deficits in contextual discrimination and spatial working memory. Local blockade of zinc or MAPK in the mossy fiber pathway of wild-type mice impairs contextual discrimination. We conclude that ZnT3 is important for zinc homeostasis modulating presynaptic MAPK signaling and is required for hippocampus-dependent memory.

Zinc transporter ZnT-3 regulates presynaptic Erk1/2 signaling and hippocampus-dependent memory

PubMed Central

Sindreu, Carlos; Palmiter, Richard D.; Storm, Daniel R.

2011-01-01

The physiological role of vesicular zinc at central glutamatergic synapses remains poorly understood. Here we show that mice lacking the synapse-specific vesicular zinc transporter ZnT3 (ZnT3KO mice) have reduced activation of the Erk1/2 MAPK in hippocampal mossy fiber terminals, disinhibition of zinc-sensitive MAPK tyrosine phosphatase activity, and impaired MAPK signaling during hippocampus-dependent learning. Activity-dependent exocytosis is required for the effect of zinc on presynaptic MAPK and phosphatase activity. ZnT3KO mice have complete deficits in contextual discrimination and spatial working memory. Local blockade of zinc or MAPK in the mossy fiber pathway of wild-type mice impairs contextual discrimination. We conclude that ZnT3 is important for zinc homeostasis modulating presynaptic MAPK signaling and is required for hippocampus-dependent memory. PMID:21245308

GABAB receptor-mediated frequency-dependent and circadian changes in synaptic plasticity modulate retinal input to the suprachiasmatic nucleus

PubMed Central

Moldavan, Mykhaylo G; Allen, Charles N

2013-01-01

Light is the most important environmental signal that entrains the circadian clock located in the hypothalamic suprachiasmatic nucleus (SCN). The retinohypothalamic tract (RHT) was stimulated to simulate the light intensity-dependent discharges of intrinsically photosensitive retinal ganglion cells projecting axons to the hypothalamus. EPSCs were evoked by paired-pulse stimulation or by application of stimulus trains, and recorded from SCN neurons in rat brain slices. Initial release probability (Pr) and synaptic plasticity changes depended on the strength of GABAB receptor (GABABR)-mediated presynaptic inhibition and could be different at the same GABABR agonist concentration. Facilitation caused by frequency-dependent relief of GABABR-mediated inhibition was observed when the initial Pr was decreased to less than 15% of control during strong activation of presynaptic GABAB receptors by (±)baclofen (10 μm), GABA (≥2 mm) or by GABA uptake inhibitor nipecotic acid (≥5 mm). In contrast, short-term synaptic depression appeared during baclofen (10 μm) application when initial Pr was greater than 30% of control. Block of 4-aminopyridine-sensitive K+ currents increased the amplitude and time constant of decay of evoked EPSCs (eEPSCs), and decreased the GABABR-mediated presynaptic inhibition. The GABAB receptor antagonist CGP55845 (3 μm) increased the eEPSCs amplitude 30% throughout the light−dark cycle. During light and dark phases the RHT inputs to 55% and 33% of recorded neurons, respectively, were under GABAB inhibitory control indicating that the tonic inhibition induced by local changes of endogenous GABA concentration contributes to the circadian variation of RHT transmitter release. We conclude that GABABR-mediated presynaptic inhibition decreased with increasing frequency and broadening of presynaptic action potentials, and depended on the sensitivity of RHT terminals to GABABR agonists, and diurnal changes of the extracellular GABA concentration around RHT axon terminals in the SCN. PMID:23401614

Ciproxifan, a histamine H{sub 3} receptor antagonist and inverse agonist, presynaptically inhibits glutamate release in rat hippocampus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Cheng-Wei; Lin, Tzu-Yu

2017-03-15

Ciproxifan is an H{sub 3} receptor antagonist and inverse agonist with antipsychotic effects in several preclinical models; its effect on glutamate release has been investigated in the rat hippocampus. In a synaptosomal preparation, ciproxifan reduced 4-aminopyridine (4-AP)-evoked Ca{sup 2+}-dependent glutamate release and cytosolic Ca{sup 2+} concentration elevation but did not affect the membrane potential. The inhibitory effect of ciproxifan on 4-AP-evoked glutamate release was prevented by the Gi/Go-protein inhibitor pertussis toxin and Ca{sub v}2.2 (N-type) and Ca{sub v}2.1 (P/Q-type) channel blocker ω-conotoxin MVIIC, but was not affected by the intracellular Ca{sup 2+}-release inhibitors dantrolene and CGP37157. Furthermore, the phospholipase A{submore » 2} (PLA{sub 2}) inhibitor OBAA, prostaglandin E{sub 2} (PGE{sub 2}), PGE2 subtype 2 (EP{sub 2}) receptor antagonist PF04418948, and extracellular signal-regulated kinase (ERK) inhibitor FR180204 eliminated the inhibitory effect of ciproxifan on glutamate release. Ciproxifan reduced the 4-AP-evoked phosphorylation of ERK and synapsin I, a presynaptic target of ERK. The ciproxifan-mediated inhibition of glutamate release was prevented in synaptosomes from synapsin I-deficient mice. Moreover, ciproxifan reduced the frequency of miniature excitatory postsynaptic currents without affecting their amplitude in hippocampal slices. Our data suggest that ciproxifan, acting through the blockade of Gi/Go protein-coupled H{sub 3} receptors present on hippocampal nerve terminals, reduces voltage-dependent Ca{sup 2+} entry by diminishing PLA{sub 2}/PGE{sub 2}/EP{sub 2} receptor pathway, which subsequently suppresses the ERK/synapsin I cascade to decrease the evoked glutamate release. - Highlights: • Ciproxifan presynaptically reduces glutamate release in the hippocampus in vitro. • Decrease in voltage-dependent Ca{sup 2+} influx is involved. • A role for the PLA{sub 2}/PGE{sub 2}/EP{sub 2} pathway in the action of ciproxifan is suggested. • Decreased ERK and synapsin I activity is also involved. • This study provides new insight into the mode by which ciproxifan acts in the brain.« less

Sufentanil, Morphine, Met-enkephalin, and κ-Agonist (U-50,488H) Inhibit Substance P Release from Primary Sensory-Neurons: A Model for Presynaptic Spinal Opioid Actions

PubMed Central

Chang, H. Ming; Berde, Charles B.; Holz, George G.; Steward, Grieg F.; Kream, Richard M.

2010-01-01

An in vitro model system for analysis of presynaptic inhibitory actions of spinal opioids has been applied. Embryonic sensory neurons derived from chick dorsal root ganglia were grown in primary cell culture, and the release of substance P was evoked by electrical field stimulation during exposure to drugs with well-demonstrated affinity for opioid receptors. This allowed a pharmacologic characterization of the inhibitory actions of specific opioid agonists on the release of substance P as measured by radioimmunoassay (RIA). Sufentanil (0.5 µm), a high affinity µ receptor agonist, U-50,488H (25 µm), a selective κ receptor agonist, and morphine (10 µm), an agonist with high affinity for µ and δ receptors, inhibited the evoked release of substance P by approximately 60%, 40%, and 50%, respectively. For sufentanil the response was demonstrated to be dose-dependent. As is the case for its analgesic action in vivo, morphine was approximately 50-fold less potent than sufentanil on a molar basis in this assay. The actions of sufentanil, U-50-488H and morphine were mimicked by the endogenous opioid peptide met-enkephalin, and its stable synthetic analog D-ala2-met5-enkephalinamide (DAME). Naloxone (25 µm), an opioid receptor antagonist, blocked the inhibitory action of sufentanil (0.5 µm), morphine (5 µm), and DAME (5 µm), but not U-50,488H (10 µm). The action of U-50,488H was partially blocked by the antagonist naltrexone (25 µm). Stereo-selectivity of agonist action was confirmed by the failure of dextrorphan (50 µm), an inactive opioid isomer, to inhibit the release of substance P. Actions mediated by specific opioid receptors were thus demonstrated by high affinity responses to agonists, blockade of agonist responses by opioid antagonists, and stereoselectivity. These findings suggest that in the spinal cord presynaptic inhibition of evoked substance P release is mediated by µ, K and δ opioid receptors located on primary sensory nerve terminals. Activation of these receptors may explain, at least in part, the spinal analgesic actions of specific opioid agonists. PMID:2467589

N-type Ca2+ channels mediate transmitter release at the electromotoneuron-electrocyte synapses of the weakly electric fish Gymnotus carapo.

PubMed

Sierra, F; Lorenzo, D; Macadar, O; Buño, W

1995-06-19

The effects of omega-conotoxin-GVIA (omega-CgTX) on synaptic transmission were studied in the electromotoneuron-electrocyte synapses of the electric organ (EO) of the weakly electric fish Gymnotus carapo. omega-CgTX selectively and irreversibly blocked excitatory postsynaptic potentials (EPSPs) in a dose dependent-manner. The toxin had no effect on: (a) resting postsynaptic membrane potential and conductance; (b) postsynaptic action potentials elicited by depolarizing transmembrane current pulses; (c) the action potential conduction in the presynaptic fiber; (d) acetylcholine (ACh)-induced postsynaptic responses. Nifedipine - a selective dihydropyridine antagonist of the L-type voltage-dependent Ca2+ channels (VDCCs) - did not affect synaptic transmission. Transmission was also undisturbed by the peptide omega-Agatoxin (omega-Aga-IVA), the low molecular weight polyamine, funnel-web toxin (FTX) - both included in the venom of the spider Agelenopsis aperta - and its synthetic analog sFTX, all selective blockers of P-type VDCCs. Since omega-CgTX irreversibly blocks the N-type VDCCs, we conclude that presynaptic N-type VDCCs mediate transmitter release at electromotoneuron terminals. The VDCCs involved in fish peripheral electromotoneuron-electrocyte presynaptic transmitter release are therefore similar to those in amphibian, reptilian and avian peripheral synapses, but differ from mammalian and invertebrate motoneuron terminals.

Astrocyte lipid metabolism is critical for synapse development and function in vivo.

PubMed

van Deijk, Anne-Lieke F; Camargo, Nutabi; Timmerman, Jaap; Heistek, Tim; Brouwers, Jos F; Mogavero, Floriana; Mansvelder, Huibert D; Smit, August B; Verheijen, Mark H G

2017-04-01

The brain is considered to be autonomous in lipid synthesis with astrocytes producing lipids far more efficiently than neurons. Accordingly, it is generally assumed that astrocyte-derived lipids are taken up by neurons to support synapse formation and function. Initial confirmation of this assumption has been obtained in cell cultures, but whether astrocyte-derived lipids support synapses in vivo is not known. Here, we address this issue and determined the role of astrocyte lipid metabolism in hippocampal synapse formation and function in vivo. Hippocampal protein expression for the sterol regulatory element-binding protein (SREBP) and its target gene fatty acid synthase (Fasn) was found in astrocytes but not in neurons. Diminishing SREBP activity in astrocytes using mice in which the SREBP cleavage-activating protein (SCAP) was deleted from GFAP-expressing cells resulted in decreased cholesterol and phospholipid secretion by astrocytes. Interestingly, SCAP mutant mice showed more immature synapses, lower presynaptic protein SNAP-25 levels as well as reduced numbers of synaptic vesicles, indicating impaired development of the presynaptic terminal. Accordingly, hippocampal short-term and long-term synaptic plasticity were defective in mutant mice. These findings establish a critical role for astrocyte lipid metabolism in presynaptic terminal development and function in vivo. GLIA 2017;65:670-682. © 2017 Wiley Periodicals, Inc.

On the nature of the afferent fibers of oculomotor nerve.

PubMed

Manni, E; Draicchio, F; Pettorossi, V E; Carobi, C; Grassi, S; Bortolami, R; Lucchi, M L

1989-03-01

The oculogyric nerves contain afferent fibers originating from the ophthalmic territory, the somata of which are located in the ipsilateral semilunar ganglion. These primary sensory neurons project to the Subnucleus Gelatinosus of the Nucleus Caudalis Trigemini, where they make presynaptic contact with the central endings of the primary trigeminal afferents running in the fifth cranial nerve. After complete section of the trigeminal root, the antidromic volleys elicited in the trunk of the third cranial nerve by stimulating SG of NCT consisted of two waves belonging to the A delta and C groups. The area of both components of the antidromic volleys decreased both after bradykinin and hystamine injection into the corresponding cutaneous region and after thermic stimulation of the ipsilateral trigeminal ophthalmic territory. The reduction of such potentials can be explained in terms of collision between the antidromic volleys and those elicited orthodromically by chemical and thermic stimulation. Also, capsaicin applied on the nerve induced an immediate increase, followed by a long lasting decrease, of orthodromic evoked response area. These findings bring further support to the nociceptive nature of the afferent fibers running into the oculomotor nerve.

Cortical presynaptic control of dorsal horn C-afferents in the rat.

PubMed

Moreno-López, Yunuen; Pérez-Sánchez, Jimena; Martínez-Lorenzana, Guadalupe; Condés-Lara, Miguel; Rojas-Piloni, Gerardo

2013-01-01

Lamina 5 sensorimotor cortex pyramidal neurons project to the spinal cord, participating in the modulation of several modalities of information transmission. A well-studied mechanism by which the corticospinal projection modulates sensory information is primary afferent depolarization, which has been characterized in fast muscular and cutaneous, but not in slow-conducting nociceptive skin afferents. Here we investigated whether the inhibition of nociceptive sensory information, produced by activation of the sensorimotor cortex, involves a direct presynaptic modulation of C primary afferents. In anaesthetized male Wistar rats, we analyzed the effects of sensorimotor cortex activation on post tetanic potentiation (PTP) and the paired pulse ratio (PPR) of dorsal horn field potentials evoked by C-fiber stimulation in the sural (SU) and sciatic (SC) nerves. We also explored the time course of the excitability changes in nociceptive afferents produced by cortical stimulation. We observed that the development of PTP was completely blocked when C-fiber tetanic stimulation was paired with cortex stimulation. In addition, sensorimotor cortex activation by topical administration of bicuculline (BIC) produced a reduction in the amplitude of C-fiber responses, as well as an increase in the PPR. Furthermore, increases in the intraspinal excitability of slow-conducting fiber terminals, produced by sensorimotor cortex stimulation, were indicative of primary afferent depolarization. Topical administration of BIC in the spinal cord blocked the inhibition of C-fiber neuronal responses produced by cortical stimulation. Dorsal horn neurons responding to sensorimotor cortex stimulation also exhibited a peripheral receptive field and responded to stimulation of fast cutaneous myelinated fibers. Our results suggest that corticospinal inhibition of nociceptive responses is due in part to a modulation of the excitability of primary C-fibers by means of GABAergic inhibitory interneurons.

Cortical Presynaptic Control of Dorsal Horn C–Afferents in the Rat

PubMed Central

Martínez-Lorenzana, Guadalupe; Condés-Lara, Miguel; Rojas-Piloni, Gerardo

2013-01-01

Lamina 5 sensorimotor cortex pyramidal neurons project to the spinal cord, participating in the modulation of several modalities of information transmission. A well-studied mechanism by which the corticospinal projection modulates sensory information is primary afferent depolarization, which has been characterized in fast muscular and cutaneous, but not in slow-conducting nociceptive skin afferents. Here we investigated whether the inhibition of nociceptive sensory information, produced by activation of the sensorimotor cortex, involves a direct presynaptic modulation of C primary afferents. In anaesthetized male Wistar rats, we analyzed the effects of sensorimotor cortex activation on post tetanic potentiation (PTP) and the paired pulse ratio (PPR) of dorsal horn field potentials evoked by C–fiber stimulation in the sural (SU) and sciatic (SC) nerves. We also explored the time course of the excitability changes in nociceptive afferents produced by cortical stimulation. We observed that the development of PTP was completely blocked when C-fiber tetanic stimulation was paired with cortex stimulation. In addition, sensorimotor cortex activation by topical administration of bicuculline (BIC) produced a reduction in the amplitude of C–fiber responses, as well as an increase in the PPR. Furthermore, increases in the intraspinal excitability of slow-conducting fiber terminals, produced by sensorimotor cortex stimulation, were indicative of primary afferent depolarization. Topical administration of BIC in the spinal cord blocked the inhibition of C–fiber neuronal responses produced by cortical stimulation. Dorsal horn neurons responding to sensorimotor cortex stimulation also exhibited a peripheral receptive field and responded to stimulation of fast cutaneous myelinated fibers. Our results suggest that corticospinal inhibition of nociceptive responses is due in part to a modulation of the excitability of primary C–fibers by means of GABAergic inhibitory interneurons. PMID:23935924

Choline transporter mutations in severe congenital myasthenic syndrome disrupt transporter localization.

PubMed

Wang, Haicui; Salter, Claire G; Refai, Osama; Hardy, Holly; Barwick, Katy E S; Akpulat, Ugur; Kvarnung, Malin; Chioza, Barry A; Harlalka, Gaurav; Taylan, Fulya; Sejersen, Thomas; Wright, Jane; Zimmerman, Holly H; Karakaya, Mert; Stüve, Burkhardt; Weis, Joachim; Schara, Ulrike; Russell, Mark A; Abdul-Rahman, Omar A; Chilton, John; Blakely, Randy D; Baple, Emma L; Cirak, Sebahattin; Crosby, Andrew H

2017-11-01

The presynaptic, high-affinity choline transporter is a critical determinant of signalling by the neurotransmitter acetylcholine at both central and peripheral cholinergic synapses, including the neuromuscular junction. Here we describe an autosomal recessive presynaptic congenital myasthenic syndrome presenting with a broad clinical phenotype due to homozygous choline transporter missense mutations. The clinical phenotype ranges from the classical presentation of a congenital myasthenic syndrome in one patient (p.Pro210Leu), to severe neurodevelopmental delay with brain atrophy (p.Ser94Arg) and extend the clinical outcomes to a more severe spectrum with infantile lethality (p.Val112Glu). Cells transfected with mutant transporter construct revealed a virtually complete loss of transport activity that was paralleled by a reduction in transporter cell surface expression. Consistent with these findings, studies to determine the impact of gene mutations on the trafficking of the Caenorhabditis elegans choline transporter orthologue revealed deficits in transporter export to axons and nerve terminals. These findings contrast with our previous findings in autosomal dominant distal hereditary motor neuropathy of a dominant-negative frameshift mutation at the C-terminus of choline transporter that was associated with significantly reduced, but not completely abrogated choline transporter function. Together our findings define divergent neuropathological outcomes arising from different classes of choline transporter mutation with distinct disease processes and modes of inheritance. These findings underscore the essential role played by the choline transporter in sustaining acetylcholine neurotransmission at both central and neuromuscular synapses, with important implications for treatment and drug selection. © The Author (2017). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Presynaptic Inhibition of Diverse Afferents to the Locus Coeruleus by Kappa Opiate Receptors: a Novel Mechanism for Regulating the Central Norepinephrine System

PubMed Central

Kreibich, Arati S.; Reyes, Beverly A. S.; Curtis, Andre L.; Ecke, Laurel; Chavkin, Charles; Van Bockstaele, Elisabeth J.; Valentino, Rita J.

2008-01-01

The norepinephrine nucleus, locus coeruleus (LC), is activated by diverse stimuli and modulates arousal and behavioral strategies in response to these stimuli through its divergent efferent system. Afferents communicating information to the LC include excitatory amino acids (EAA), corticotropin-releasing factor (CRF) and endogenous opioids acting at μ-opiate receptors. As the LC is also innervated by the endogenous κ-opiate receptor (κ-OR) ligand, dynorphin, and expresses κ-ORs, this study investigated κ-OR regulation of LC neuronal activity in rat. Immunoelectron microscopy revealed a prominent localization of κ-ORs in axon terminals in the LC that also contained either the vesicular glutamate transporter or CRF. Microinfusion of the κ-OR agonist, U50488, into the LC did not alter LC spontaneous discharge but attenuated phasic discharge evoked by stimuli that engage EAA afferents to the LC, including sciatic nerve stimulation and auditory stimuli and the tonic activation associated with opiate withdrawal. Inhibitory effects of the κ-OR agonist were not restricted to EAA afferents, as U50488 also attenuated tonic LC activation by hypotensive stress, an effect mediated by CRF afferents. Together, these results indicate that κ-ORs are poised to presynaptically inhibit diverse afferent signaling to the LC. This is a novel and potentially powerful means of regulating the LC-NE system that can impact on forebrain processing of stimuli and the organization of behavioral strategies in response to environmental stimuli. The results implicate κ-ORs as a novel target for alleviating symptoms of opiate withdrawal, stress-related disorders or disorders characterized by abnormal sensory responses, such as autism. PMID:18562623

Presynaptic inhibition of diverse afferents to the locus ceruleus by kappa-opiate receptors: a novel mechanism for regulating the central norepinephrine system.

PubMed

Kreibich, Arati; Reyes, Beverly A S; Curtis, Andre L; Ecke, Laurel; Chavkin, Charles; Van Bockstaele, Elisabeth J; Valentino, Rita J

2008-06-18

The norepinephrine nucleus, locus ceruleus (LC), is activated by diverse stimuli and modulates arousal and behavioral strategies in response to these stimuli through its divergent efferent system. Afferents communicating information to the LC include excitatory amino acids (EAAs), corticotropin-releasing factor (CRF), and endogenous opioids acting at mu-opiate receptors. Because the LC is also innervated by the endogenous kappa-opiate receptor (kappa-OR) ligand dynorphin and expresses kappa-ORs, this study investigated kappa-OR regulation of LC neuronal activity in rat. Immunoelectron microscopy revealed a prominent localization of kappa-ORs in axon terminals in the LC that also contained either the vesicular glutamate transporter or CRF. Microinfusion of the kappa-OR agonist (trans)-3,4-dichloro-N-methyl-N-[2-1-pyrrolidinyl)-cyclo-hexyl] benzeneacetamide (U50488) into the LC did not alter LC spontaneous discharge but attenuated phasic discharge evoked by stimuli that engage EAA afferents to the LC, including sciatic nerve stimulation and auditory stimuli and the tonic activation associated with opiate withdrawal. Inhibitory effects of the kappa-OR agonist were not restricted to EAA afferents, as U50488 also attenuated tonic LC activation by hypotensive stress, an effect mediated by CRF afferents. Together, these results indicate that kappa-ORs are poised to presynaptically inhibit diverse afferent signaling to the LC. This is a novel and potentially powerful means of regulating the LC-norepinephrine system that can impact on forebrain processing of stimuli and the organization of behavioral strategies in response to environmental stimuli. The results implicate kappa-ORs as a novel target for alleviating symptoms of opiate withdrawal, stress-related disorders, or disorders characterized by abnormal sensory responses, such as autism.

The novel protein kinase C epsilon isoform at the adult neuromuscular synapse: location, regulation by synaptic activity-dependent muscle contraction through TrkB signaling and coupling to ACh release.

PubMed

Obis, Teresa; Besalduch, Núria; Hurtado, Erica; Nadal, Laura; Santafe, Manel M; Garcia, Neus; Tomàs, Marta; Priego, Mercedes; Lanuza, Maria A; Tomàs, Josep

2015-02-10

Protein kinase C (PKC) regulates a variety of neural functions, including neurotransmitter release. Although various PKC isoforms can be expressed at the synaptic sites and specific cell distribution may contribute to their functional diversity, little is known about the isoform-specific functions of PKCs in neuromuscular synapse. The present study is designed to examine the location of the novel isoform nPKCε at the neuromuscular junction (NMJ), their synaptic activity-related expression changes, its regulation by muscle contraction, and their possible involvement in acetylcholine release. We use immunohistochemistry and confocal microscopy to demonstrate that the novel isoform nPKCε is exclusively located in the motor nerve terminals of the adult rat NMJ. We also report that electrical stimulation of synaptic inputs to the skeletal muscle significantly increased the amount of nPKCε isoform as well as its phosphorylated form in the synaptic membrane, and muscle contraction is necessary for these nPKCε expression changes. The results also demonstrate that synaptic activity-induced muscle contraction promotes changes in presynaptic nPKCε through the brain-derived neurotrophic factor (BDNF)-mediated tyrosine kinase receptor B (TrkB) signaling. Moreover, nPKCε activity results in phosphorylation of the substrate MARCKS involved in actin cytoskeleton remodeling and related with neurotransmission. Finally, blocking nPKCε with a nPKCε-specific translocation inhibitor peptide (εV1-2) strongly reduces phorbol ester-induced ACh release potentiation, which further indicates that nPKCε is involved in neurotransmission. Together, these results provide a mechanistic insight into how synaptic activity-induced muscle contraction could regulate the presynaptic action of the nPKCε isoform and suggest that muscle contraction is an important regulatory step in TrkB signaling at the NMJ.

The newly synthesized pool of dopamine determines the severity of methamphetamine-induced neurotoxicity.

PubMed

Thomas, David M; Francescutti-Verbeem, Dina M; Kuhn, Donald M

2008-05-01

The neurotransmitter dopamine (DA) has long been implicated as a participant in the neurotoxicity caused by methamphetamine (METH), yet, its mechanism of action in this regard is not fully understood. Treatment of mice with the tyrosine hydroxylase (TH) inhibitor alpha-methyl-p-tyrosine (AMPT) lowers striatal cytoplasmic DA content by 55% and completely protects against METH-induced damage to DA nerve terminals. Reserpine, by disrupting vesicle amine storage, depletes striatal DA by more than 95% and accentuates METH-induced neurotoxicity. l-DOPA reverses the protective effect of AMPT against METH and enhances neurotoxicity in animals with intact TH. Inhibition of MAO-A by clorgyline increases pre-synaptic DA content and enhances METH striatal neurotoxicity. In all conditions of altered pre-synaptic DA homeostasis, increases or decreases in METH neurotoxicity paralleled changes in striatal microglial activation. Mice treated with AMPT, l-DOPA, or clorgyline + METH developed hyperthermia to the same extent as animals treated with METH alone, whereas mice treated with reserpine + METH were hypothermic, suggesting that the effects of alterations in cytoplasmic DA on METH neurotoxicity were not strictly mediated by changes in core body temperature. Taken together, the present data reinforce the notion that METH-induced release of DA from the newly synthesized pool of transmitter into the extracellular space plays an essential role in drug-induced striatal neurotoxicity and microglial activation. Subtle alterations in intracellular DA content can lead to significant enhancement of METH neurotoxicity. Our results also suggest that reactants derived from METH-induced oxidation of released DA may serve as neuronal signals that lead to microglial activation early in the neurotoxic process associated with METH.

Enhancement by oxotremorine of acetylcholine release from the rat phrenic nerve.

PubMed Central

Das, M; Ganguly, D K; Vedasiromoni, J R

1978-01-01

Oxotremorine (10.5 micron) produced a paralytic effect on twitch responses of rat diaphragm in vitro to direct and indirect stimulation. 2 The paralytic effect of oxotremorine was absent when the diaphragm was stimulated directly in the presence of hemicholinium-3 (0.42 mM), at a time when twitch responses to indirect stimulation ceased completely. 3 Oxotremorine, at two different pharmacologically active doses, strikingly increased the resting as well as electrically evoked release of acetylcholine into the bathing fluid from the phrenic nerve-diaphragm preparation. 4 This presynaptic effect of oxotremorine may explain its pharmacological effects at the cholinergic synapses studied so far. PMID:203356

Modifications of Gustatory Nerve Synapses onto Nucleus of the Solitary Tract Neurons Induced by Dietary Sodium-Restriction During Development

PubMed Central

MAY, OLIVIA L.; ERISIR, ALEV; HILL, DAVID L.

2008-01-01

The terminal fields of nerves carrying gustatory information to the rat brainstem show a remarkable amount of expansion in the nucleus of the solitary tract (NTS) as a result of early dietary sodium restriction. However, the extent to which these axonal changes represent corresponding changes in synapses is not known. To identify the synaptic characteristics that accompany the terminal field expansion, the greater superficial petrosal (GSP), chorda tympani (CT), and glossopharyngeal (IX) nerves were labeled in rats fed a sodium-restricted diet during pre- and postnatal development. The morphology of these nerve terminals within the NTS region where the terminal fields of all three nerves overlap was evaluated by transmission electron microscopy. Compared to data from control rats, CT axons were the most profoundly affected. The density of CT arbors and synapses quadrupled as a result of the near life-long dietary manipulation. In contrast, axon and synapse densities of GSP and IX nerves were not modified in sodium-restricted rats. Furthermore, compared to controls, CT terminals displayed more instances of contacts with postsynaptic dendritic protrusions and IX terminals synapsed more frequently with dendritic shafts. Thus, dietary sodium restriction throughout pre- and postnatal development had differential effects on the synaptic organization of the three nerves in the NTS. These anatomical changes may underlie the impact of sensory restriction during development on the functional processing of taste information and taste-related behaviors. PMID:18366062

Modifications of gustatory nerve synapses onto nucleus of the solitary tract neurons induced by dietary sodium-restriction during development.

PubMed

May, Olivia L; Erisir, Alev; Hill, David L

2008-06-01

The terminal fields of nerves carrying gustatory information to the rat brainstem show a remarkable amount of expansion in the nucleus of the solitary tract (NTS) as a result of early dietary sodium restriction. However, the extent to which these axonal changes represent corresponding changes in synapses is not known. To identify the synaptic characteristics that accompany the terminal field expansion, the greater superficial petrosal (GSP), chorda tympani (CT), and glossopharyngeal (IX) nerves were labeled in rats fed a sodium-restricted diet during pre- and postnatal development. The morphology of these nerve terminals within the NTS region where the terminal fields of all three nerves overlap was evaluated by transmission electron microscopy. Compared to data from control rats, CT axons were the most profoundly affected. The density of CT arbors and synapses quadrupled as a result of the near life-long dietary manipulation. In contrast, axon and synapse densities of GSP and IX nerves were not modified in sodium-restricted rats. Furthermore, compared to controls, CT terminals displayed more instances of contacts with postsynaptic dendritic protrusions and IX terminals synapsed more frequently with dendritic shafts. Thus, dietary sodium restriction throughout pre- and postnatal development had differential effects on the synaptic organization of the three nerves in the NTS. These anatomical changes may underlie the impact of sensory restriction during development on the functional processing of taste information and taste-related behaviors.

Drug interactions with neuromuscular blockers.

PubMed

Feldman, S; Karalliedde, L

1996-10-01

Drugs administered to patients undergoing anaesthesia may complicate the use of the neuromuscular blockers that are given to provide good surgical conditions. The various sites of interaction include actions on motor nerve conduction and spinal reflexes, acetylcholine (ACh) synthesis, mobilisation and release, sensitivity of the motor end plate to ACh and the ease of propagation of the motor action potential. In addition, many drugs affect the pharmacokinetics of neuromuscular blockers, especially as most drugs depend to a greater or lesser extent upon renal excretion. The clinically significant interaction between nondepolarisers and depolarisers may be due to blockade of the pre-synaptic nicotinic receptors by the depolarisers, leading to decreased ACh mobilisation and release. Synergism between nondepolarisers probably results from post-synaptic receptor mechanisms. Volatile anaesthetic agents affect the sensitivity of the motor end-plate (post-synaptic receptor blockade) in addition to having effects on pre-synaptic nicotinic function. The effects of nondepolarisers are likely to be potentiated and their action prolonged by large doses of local anaesthetics due to depression of nerve conduction, depression of ACh formation, mobilisation and release, decreases in post-synaptic receptor channel opening times and reductions in muscular contraction. Most antibacterials have effects on pre-synaptic mechanisms. Procainamide and quinidine principally block nicotinic receptor channels. Magnesium has a marked inhibitory effect on ACh release. Calcium antagonists could theoretically interfere with neurotransmitter release and muscle contractility. Phenytoin and lithium decrease ACh release, whilst corticosteroids and furosemide (frusemide) tend to increase the release of the transmitter. Ecothiopate, tacrine, organophosphates, propanidid, metoclopramide and bambuterol depress cholinesterase activity and prolong the duration of the neuromuscular block. The probability of clinically significant interactions increases in patients receiving several drugs with possible effects on neuromuscular transmission and muscle contraction.

Inhibition of noradrenaline release by lysergic acid diethylamide

PubMed Central

Hughes, J.

1973-01-01

Lysergic acid diethylamide (LSD) inhibits the release of labelled noradrenaline from the guinea-pig vas deferens during intramural nerve stimulation and causes a corresponding reduction in the contractions of the smooth muscle. These effects of LSD are most prominent at low stimulus frequencies and they are prevented by treatment with phentolamine. It is concluded that LSD inhibits noradrenaline release by interacting with presynaptic α-adrenoceptors. PMID:4788042

Adenosine A(2A) receptor antagonists are broad facilitators of antinicotinic neuromuscular blockade monitored either with 2 Hz train-of-four or 50 Hz tetanic stimuli.

PubMed

Pereira, Monalisa W; Correia-de-Sá, Paulo; Alves-Do-Prado, Wilson

2012-10-01

1. The 2 Hz train-of-four ratio (TOF(ratio)) is used to monitor the degree of patient curarization. Using a rat phrenic nerve-hemidiaphragm preparation, we showed that antinicotinic agents, such as hexamethonium, d-tubocurarine and pancuronium, but not cisatracurium, decreased contractions produced by physiological nerve activity patterns (50 Hz) more efficiently than those caused by 2 Hz trains. Uncertainty about the usefulness of the TOF(ratio) to control safe recovery from curarization prompted us to investigate the muscarinic and adenosine neuromodulation of tetanic (50 Hz) fade induced by antinicotinic agents at concentrations that cause a 25% reduction in the TOF(ratio) (TOF(fade)). 2. Tetanic fade caused by d-tubocurarine (1.1 μmol/L), pancuronium (3 μmol/L) and hexamethonium (5.47 mmol/L) was attenuated by blocking presynaptic inhibitory muscarinic M(2) and adenosine A(1) receptors with methoctramine (1 μmol/L) and 1,3-dipropyl-8-cyclopentylxanthine (2.5 nmol/L), respectively. These compounds enhanced rather than decreased tetanic fade induced by cisatracurium (2.2 μmol/L), but they consistently attenuated cisatracurium-induced TOF(fade). The effect of the M(1) receptor antagonist pirenzepine (10 nmol/L) on fade produced by antinicotinic agents at 50 Hz was opposite to that observed with TOF stimulation. Blockade of adenosine A(2A) receptors with ZM 241385 (10 nmol/L) attenuated TOF(fade) caused by all antinicotinic drugs tested, with the exception of the 'pure' presynaptic nicotinic antagonist hexamethonium. ZM 241385 was the only compound tested in this series that facilitated recovery from tetanic fade produced by cisatracurium. 3. The data suggest that distinct antinicotinic relaxants interfere with fine-tuning neuromuscular adaptations to motor nerve stimulation patterns via activation of presynaptic muscarinic and adenosine receptors. These results support the use of A(2A) receptor antagonists together with atropine to facilitate recovery from antinicotinic neuromuscular blockade. © 2012 The Authors Clinical and Experimental Pharmacology and Physiology © 2012 Wiley Publishing Asia Pty Ltd.

[Changes in the innervation of the taste buds in diabetic rats].

PubMed

Hevér, Helén; Altdorfer, Károly; Zelles, Tivadar; Batbayar, Bayarchimeg; Fehér, Erzsébet

2013-03-24

Abnormal sensations such as pain and impairment of taste are symptoms of approximately 10% of patients having diabetes mellitus. The aim of the study was to investigate and quantify the different neuropeptide containing nerve fibres in the vallate papilla of the diabetic rat. Immunohistochemical methods were used to study the changes of the number of different neuropeptide containing nerve terminals located in the vallate papillae in diabetic rats. Diabetes was induced in the rats with streptozotocin. Two weeks after streptozotocin treatment the number of the substance P, galanin, vasoactive intestinal polypeptide and neuropeptide Y immunoreactive nerve terminals was significantly increased (p<0.05) in the tunica mucosa of the tongue. The number of the lymphocytes and mast cells was also increased significantly. Some of the immunoreactive nerve terminals were located in the lingual epithelium both intragemmally and extragemmally and were seen to comprise dense bundles in the lamina propria just beneath the epithelium. No taste cells were immunoreactive for any of the investigated peptides. Vasoactive intestinal polypeptide and neuropeptide Y immunoreactive nerve fibres were not detected in the taste buds. For weeks after streptozotocin administration the number of the substance P, calcitonin gene related peptide and galanin immunoreactive nerve terminals was decreased both intragemmally and intergemmally. In case of immediate insulin treatment, the number of the immunoreactive nerve terminals was similar to that of the controls, however, insulin treatment given 1 week later to diabetic rats produced a decreased number of nerve fibers. Morphometry revealed no significant difference in papilla size between the control and diabetic groups, but there were fewer taste buds (per papilla). Increased number of immunoreactive nerve terminals and mast cells 2 weeks after the development of diabetes was the consequence of neurogenic inflammation which might cause vasoconstriction and lesions of the oral mucosa. Taste impairment, which developed 4 weeks after streptozotocin treatment could be caused by neuropathic defects and degeneration or morphological changes in the taste buds and nerve fibres.

Dopaminergic Presynaptic Modulation of Nigral Afferents: Its Role in the Generation of Recurrent Bursting in Substantia Nigra Pars Reticulata Neurons

PubMed Central

de Jesús Aceves, José; Rueda-Orozco, Pavel E.; Hernández, Ricardo; Plata, Víctor; Ibañez-Sandoval, Osvaldo; Galarraga, Elvira; Bargas, José

2011-01-01

Previous work has shown the functions associated with activation of dopamine presynaptic receptors in some substantia nigra pars reticulata (SNr) afferents: (i) striatonigral terminals (direct pathway) posses presynaptic dopamine D1-class receptors whose action is to enhance inhibitory postsynaptic currents (IPSCs) and GABA transmission. (ii) Subthalamonigral terminals posses D1- and D2-class receptors where D1-class receptor activation enhances and D2-class receptor activation decreases excitatory postsynaptic currents. Here we report that pallidonigral afferents posses D2-class receptors (D3 and D4 types) that decrease inhibitory synaptic transmission via presynaptic modulation. No action of D1-class agonists was found on pallidonigral synapses. In contrast, administration of D1-receptor antagonists greatly decreased striatonigral IPSCs in the same preparation, suggesting that tonic dopamine levels help in maintaining the function of the striatonigral (direct) pathway. When both D3 and D4 type receptors were blocked, pallidonigral IPSCs increased in amplitude while striatonigral connections had no significant change, suggesting that tonic dopamine levels are repressing a powerful inhibition conveyed by pallidonigral synapses (a branch of the indirect pathway). We then blocked both D1- and D2-class receptors to acutely decrease direct pathway (striatonigral) and enhance indirect pathways (subthalamonigral and pallidonigral) synaptic force. The result was that most SNr projection neurons entered a recurrent bursting firing mode similar to that observed during Parkinsonism in both patients and animal models. These results raise the question as to whether the lack of dopamine in basal ganglia output nuclei is enough to generate some pathological signs of Parkinsonism. PMID:21347219

Enhanced pre-synaptic glutamate release in deep-dorsal horn contributes to calcium channel alpha-2-delta-1 protein-mediated spinal sensitization and behavioral hypersensitivity

PubMed Central

Nguyen, David; Deng, Ping; Matthews, Elizabeth A; Kim, Doo-Sik; Feng, Guoping; Dickenson, Anthony H; Xu, Zao C; Luo, Z David

2009-01-01

Nerve injury-induced expression of the spinal calcium channel alpha-2-delta-1 subunit (Cavα2δ1) has been shown to mediate behavioral hypersensitivity through a yet identified mechanism. We examined if this neuroplasticity modulates behavioral hypersensitivity by regulating spinal glutamatergic neurotransmission in injury-free transgenic mice overexpressing the Cavα2δ1 proteins in neuronal tissues. The transgenic mice exhibited hypersensitivity to mechanical stimulation (allodynia) similar to the spinal nerve ligation injury model. Intrathecally delivered antagonists for N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxyl-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptors, but not for the metabotropic glutamate receptors, caused a dose-dependent allodynia reversal in the transgenic mice without changing the behavioral sensitivity in wild-type mice. This suggests that elevated spinal Cavα2δ1 mediates allodynia through a pathway involving activation of selective glutamate receptors. To determine if this is mediated by enhanced spinal neuronal excitability or pre-synaptic glutamate release in deep-dorsal horn, we examined wide-dynamic-range (WDR) neuron excitability with extracellular recording and glutamate-mediated excitatory postsynaptic currents with whole-cell patch recording in deep-dorsal horn of the Cavα2δ1 transgenic mice. Our data indicated that overexpression of Cavα2δ1 in neuronal tissues led to increased frequency, but not amplitude, of miniature excitatory post synaptic currents mediated mainly by AMPA/kainate receptors at physiological membrane potentials, and also by NMDA receptors upon depolarization, without changing the excitability of WDR neurons to high intensity stimulation. Together, these findings support a mechanism of Cavα2δ1-mediated spinal sensitization in which elevated Cavα2δ1 causes increased pre-synaptic glutamate release that leads to reduced excitation thresholds of post-synaptic dorsal horn neurons to innocuous stimuli. This spinal sensitization mechanism may mediate at least partially the neuropathic pain states derived from increased pre-synaptic Cavα2δ1 expression. PMID:19216737

Presynaptic Dopamine D2 Receptors Modulate [3H]GABA Release at StriatoPallidal Terminals via Activation of PLC → IP3 → Calcineurin and Inhibition of AC → cAMP → PKA Signaling Cascades.

PubMed

Jijón-Lorenzo, Rafael; Caballero-Florán, Isaac Hiram; Recillas-Morales, Sergio; Cortés, Hernán; Avalos-Fuentes, José Arturo; Paz-Bermúdez, Francisco Javier; Erlij, David; Florán, Benjamín

2018-02-21

Striatal dopamine D2 receptors activate the PLC → IP3 → Calcineurin-signaling pathway to modulate the neural excitability of En+ Medium-sized Spiny GABAergic neurons (MSN) through the regulation of L-type Ca 2+ channels. Presynaptic dopaminergic D2 receptors modulate GABA release at striatopallidal terminals through L-type Ca 2+ channels as well, but their signaling pathway is still undetermined. Since D2 receptors are Gi/o-coupled and negatively modulate adenylyl cyclase (AC), we investigated whether presynaptic D2 receptors modulate GABA release through the same signaling cascade that controls excitability in the striatum or by the inhibition of AC and decreased PKA activity. Activation of D2 receptors stimulated formation of [ 3 H]IP 1 and decreased Forskolin-stimulated [ 3 H]cAMP accumulation in synaptosomes from rat Globus Pallidus. D2 receptor activation with Quinpirole in the presence of L 745,870 decreased, in a dose-dependent manner, K + -induced [ 3 H]GABA release in pallidal slices. The effect was prevented by the pharmacological blockade of Gi/o βγ subunit effects with Gallein, PLC with U 73122, IP3 receptor activation with 4-APB, Calcineurin with FK506. In addition, when release was stimulated with Forskolin to activate AC, D2 receptors also decreased K + -induced [ 3 H]GABA release, an effect occluded with the effect of the blockade of PKA with H89 or stimulation of release with the cAMP analog 8-Br-cAMP. These data indicate that D2 receptors modulate [ 3 H]GABA release at striatopallidal terminals by activating the PLC → IP3 → Calcineurin-signaling cascade, the same one that modulates excitability in soma. Additionally, D2 receptors inhibit release when AC is active. Both mechanisms appear to converge to regulate the activity of presynaptic L-type Ca 2+ channels. Copyright © 2018 IBRO. Published by Elsevier Ltd. All rights reserved.

The terminal latency of the phrenic nerve correlates with respiratory symptoms in amyotrophic lateral sclerosis.

PubMed

Park, Jin-Sung; Park, Donghwi

2017-09-01

The aim of the study was to investigate the electrophysiological parameters in phrenic nerve conduction studies (NCS) that sensitively reflect latent respiratory insufficiency present in amyotrophic lateral sclerosis (ALS). Forty-nine patients with ALS were examined, and after exclusion, 21 patients with ALS and their phrenic NCS results were reviewed. The patients were divided into two groups according to their respiratory sub-score in the ALS functional rating scale - revised (Group A, sub-score 12vs. Group B, sub-score 11). We compared the parameters of phrenic NCS between the two groups. There were no significant differences in the clinical characteristics between the two groups. Using a multivariate model, we found that the terminal latency of the phrenic nerve was the only parameter that was associated with early symptoms of respiratory insufficiency (p<0.05). The optimal cutoff value for the terminal latency of the phrenic nerve was 7.65ms (sensitivity 80%, specificity 68.2%). The significantly prolonged terminal latency of the phrenic nerve in our study may reflect a profound distal motor axonal dysfunction of the phrenic nerve in patients with ALS in the early stage of respiratory insufficiency that can be used as a sensitive electrophysiological marker reflecting respiratory symptoms in ALS. The terminal latency of the phrenic nerve is useful for early detection of respiratory insufficiency in patients with ALS. Copyright © 2017. Published by Elsevier B.V.

Prophylactic versus Therapeutic Fingolimod: Restoration of Presynaptic Defects in Mice Suffering from Experimental Autoimmune Encephalomyelitis

PubMed Central

Merega, Elisa; Di Prisco, Silvia; Padolecchia, Cristina; Grilli, Massimo; Milanese, Marco; Di Cesare Mannelli, Lorenzo; Ghelardini, Carla; Bonanno, Giambattista; Marchi, Mario

2017-01-01

Fingolimod, the first oral, disease-modifying therapy for MS, has been recently proposed to modulate glutamate transmission in the central nervous system (CNS) of mice suffering from Experimental Autoimmune Encephalomyelitis (EAE) and in MS patients. Our study aims at investigating whether oral fingolimod recovers presynaptic defects that occur at different stages of disease in the CNS of EAE mice. In vivo prophylactic (0.3 mg/kg for 14 days, from the 7th day post immunization, d.p.i, the drug dissolved in the drinking water) fingolimod significantly reduced the clinical symptoms and the anxiety-related behaviour in EAE mice. Spinal cord inflammation, demyelination and glial cell activation are markers of EAE progression. These signs were ameliorated following oral fingolimod administration. Glutamate exocytosis was shown to be impaired in cortical and spinal cord terminals isolated from EAE mice at 21 ± 1 d.p.i., while GABA alteration emerged only at the spinal cord level. Prophylactic fingolimod recovered these presynaptic defects, restoring altered glutamate and GABA release efficiency. The beneficial effect occurred in a dose-dependent, region-specific manner, since lower (0.1–0.03 mg/kg) doses restored, although to a different extent, synaptic defects in cortical but not spinal cord terminals. A delayed reduction of glutamate, but not of GABA, exocytosis was observed in hippocampal terminals of EAE mice at 35 d.p.i. Therapeutic (0.3 mg/kg, from 21 d.p.i. for 14 days) fingolimod restored glutamate exocytosis in the cortex and in the hippocampus of EAE mice at 35 ± 1 d.p.i. but not in the spinal cord, where also GABAergic defects remained unmodified. These results improve our knowledge of the molecular events accounting for the beneficial effects elicited by fingolimod in demyelinating disorders. PMID:28125677

Ultrastructural and molecular biologic comparison of classic proprioceptors and palisade endings in sheep extraocular muscles.

PubMed

Rungaldier, Stefanie; Heiligenbrunner, Stefan; Mayer, Regina; Hanefl-Krivanek, Christiane; Lipowec, Marietta; Streicher, Johannes; Blumer, Roland

2009-12-01

To analyze and compare the structural and molecular features of classic proprioceptors like muscle spindles and Golgi tendon organs (GTOs) and putative proprioceptors (palisade endings) in sheep extraocular muscle (EOMs). The EOMs of four sheep were analyzed. Frozen sections or wholemount preparations of the samples were immunohistochemically labeled and analyzed by confocal laser scanning microscopy. Triple labeling with different combinations of antibodies against neurofilament, synaptophysin, and choline acetyltransferase (ChAT), as well as alpha-bungarotoxin and phalloidin, was performed. Microscopic anatomy of the nerve end organs was analyzed by transmission electron microscopy. The microscopic anatomy demonstrated that muscle spindles and GTOs had a perineural capsule and palisade endings a connective tissue capsule. Sensory nerve terminals in muscle spindles and GTOs contained only a few vesicles, whereas palisade nerve terminals were full of clear vesicles. Likewise, motor terminals in the muscle spindles' polar regions were full of clear vesicles. Immunohistochemistry showed that sensory nerve fibers as well as their sensory nerve terminals in muscle spindles and GTOs were ChAT-negative. Palisade endings were supplied by ChAT-positive nerve fibers, and the palisade complexes including palisade nerve terminals were also ChAT-immunoreactive. Motor terminals in muscle spindles were ChAT and alpha-bungarotoxin positive. The present study demonstrated in sheep EOMs that palisade endings are innervated by cholinergic axons exhibiting characteristics typical of motoneurons, whereas muscle spindles (except the polar regions) and GTOs are supplied by noncholinergic axons. These results raise the question of whether palisade endings are candidates for proprioceptors in EOMs.

Ultrastructural and molecular biologic comparison of classical proprioceptors and palisade endings in sheep extraocular muscles

PubMed Central

RUNGALDIER, Stefanie; HEILIGENBRUNNER, Stefan; MAYER, Regina; HANEFL-KRIVANEK, Christiane; LIPOWEC, Marietta; STREICHER, Johannes; BLUMER, Roland

2016-01-01

Purpose To analyze and compare the structural and molecular features of classical proprioceptors like muscle spindles and Golgi tendon organs (GTOs) and putative proprioceptors (palisade endings) in sheep extraocular muscle (EOMs). Methods The EOMs of four sheep were analyzed. Frozen sections or whole mount preparations of the samples were immunohistochemically labeled and analyzed by confocal laser scanning microscopy. Triple labeling with different combinations of antibodies against neurofilament, synaptophysin and choline acetyltransferase (ChAT) as well as α-bungarotoxin and phalloidin was performed. Microscopic anatomy of the nerve end organs was analyzed by transmission electron microscopy. Results The microscopic anatomy demonstrated that muscle spindles and GTOs had a perineural capsule and palisade endings a connective tissue capsule. Sensory nerve terminals in muscle spindles and GTOs contained only few vesicles whereas palisade nerve terminals were full of clear vesicles. Likewise, motor terminals in the muscle spindles’ polar regions were full of clear vesicles. Immunohistochemistry showed that sensory nerve fibers as well as their sensory nerve terminals in muscle spindles and GTOs were ChAT-negative. Palisade endings were supplied by ChAT-positive nerve fibers and the palisade complexes including palisade nerve terminals were also ChAT-immunoreactive. Motor terminals in muscle spindles were ChAT and α-bungarotoxin -positive. Conclusions The present study demonstrated in sheep EOMs that palisade endings are innervated by cholinergic axons exhibiting characteristics typical for motoneurons whereas muscle spindles (except the polar regions) and GTOs are supplied by non-cholinergic axons. These results question whether palisade endings are candidates for proprioceptors in EOMs. PMID:19553627

The PLC/IP3R/PKC Pathway is Required for Ethanol-enhanced GABA Release

PubMed Central

Kelm, M. Katherine; Weinberg, Richard J.; Criswell, Hugh E.; Breese, George R.

2010-01-01

Summary Research on the actions of ethanol at the GABAergic synapse has traditionally focused on postsynaptic mechanisms, but recent data demonstrate that ethanol also increases both evoked and spontaneous GABA release in many brain regions. Using whole-cell voltage-clamp recordings, we previously showed that ethanol increases spontaneous GABA release at the rat interneuron-Purkinje cell synapse. This presynaptic ethanol effect is dependent on calcium release from internal stores, possibly through activation of inositol 1,4,5-trisphosphate receptors (IP3Rs). After confirming that ethanol targets vesicular GABA release, in the present study we used electron microscopic immunohistochemistry to demonstrate that IP3Rs are located in presynaptic terminals of cerebellar interneurons. Activation of IP3Rs requires binding of IP3, generated through activation of phospholipase C (PLC). We find that the PLC antagonist edelfosine prevents ethanol from increasing spontaneous GABA release. Diacylglycerol generated by PLC and calcium released by activation of the IP3R activate protein kinase C (PKC). Ethanol-enhanced GABA release was blocked by two PKC antagonists, chelerythrine and calphostin C. When a membrane impermeable PKC antagonist, PKC (19-36), was delivered intracellularly to the postsynaptic neuron, ethanol continued to increase spontaneous GABA release. Overall, these results suggest that activation of the PLC/IP3R/PKC pathway is necessary for ethanol to increase spontaneous GABA release from presynaptic terminals onto Purkinje cells. PMID:20206640

Contributions of SERCA pump and ryanodine-sensitive stores to presynaptic residual Ca2+

PubMed Central

Scullin, Chessa S.; Partridge, L. Donald

2010-01-01

The presynaptic Ca2+ signal, which triggers vesicle release, disperses to a broadly distributed residual [Ca2+] ([Ca2+]res) that plays an important role in synaptic plasticity. We have previously reported a slowing in the decay timecourse of [Ca2+]res during the second of paired pulses. In this study, we investigated the contributions of organelle and plasma membrane Ca2+ flux pathways to the reduction of effectiveness of [Ca2+]res clearance during short-term plasticity in Schaffer collateral terminals in the CA1 field of the hippocampus. We show that the slowed decay timecourse is mainly the result of a transport-dependent Ca2+ clearance process; that presynaptic caffeine-sensitive Ca2+ stores are not functionally loaded in the unstimulated terminal, but that these stores can effectively take up Ca2+ even during high frequency trains of stimuli; and that a rate limiting step of sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) kinetics following the first pulse is responsible for a large portion of the observed slowing of [Ca2+]res clearance during the second pulse. We were able to accurately fit our [Ca2+]res data with a kinetic model based on these observations and this model predicted a reduction in availability of unbound SERCA during paired pulses, but no saturation of Ca2+ buffer in the endoplasmic reticulum. PMID:20153896

Presynaptic establishment of the synaptic cleft extracellular matrix is required for post-synaptic differentiation

PubMed Central

Rohrbough, Jeffrey; Rushton, Emma; Woodruff, Elvin; Fergestad, Tim; Vigneswaran, Krishanthan; Broadie, Kendal

2007-01-01

Formation and regulation of excitatory glutamatergic synapses is essential for shaping neural circuits throughout development. In a Drosophila genetic screen for synaptogenesis mutants, we identified mind the gap (mtg), which encodes a secreted, extracellular N-glycosaminoglycan-binding protein. MTG is expressed neuronally and detected in the synaptic cleft, and is required to form the specialized transsynaptic matrix that links the presynaptic active zone with the post-synaptic glutamate receptor (GluR) domain. Null mtg embryonic mutant synapses exhibit greatly reduced GluR function, and a corresponding loss of localized GluR domains. All known post-synaptic signaling/scaffold proteins functioning upstream of GluR localization are also grossly reduced or mislocalized in mtg mutants, including the dPix–dPak–Dock cascade and the Dlg/PSD-95 scaffold. Ubiquitous or neuronally targeted mtg RNA interference (RNAi) similarly reduce post-synaptic assembly, whereas post-synaptically targeted RNAi has no effect, indicating that presynaptic MTG induces and maintains the post-synaptic pathways driving GluR domain formation. These findings suggest that MTG is secreted from the presynaptic terminal to shape the extracellular synaptic cleft domain, and that the cleft domain functions to mediate transsynaptic signals required for post-synaptic development. PMID:17901219

Crimpy enables discrimination of pre and postsynaptic pools of a BMP at the Drosophila NMJ

PubMed Central

James, Rebecca E.; Hoover, Kendall M.; Bulgari, Dinara; McLaughlin, Colleen N.; Wilson, Christopher G.; Wharton, Kristi A.; Levitan, Edwin S.; Broihier, Heather T.

2014-01-01

Summary Distinct pools of the BMP Glass bottom boat (Gbb) control structure and function of the Drosophila neuromuscular junction. Specifically, motoneuron-derived Gbb regulates baseline neurotransmitter release, while muscle-derived Gbb regulates NMJ growth. Yet how cells differentiate between these ligand pools is not known. Here we present evidence that the neuronal Gbb-binding protein Crimpy (Cmpy) permits discrimination of pre and postsynaptic ligand by serving sequential functions in Gbb signaling. Cmpy first delivers Gbb to dense core vesicles (DCVs) for activity-dependent release from presynaptic terminals. In the absence of Cmpy, Gbb is no longer associated with DCVs and is not released by activity. Electrophysiological analyses demonstrate that Cmpy promotes Gbb's pro-neurotransmission function. Surprisingly, the Cmpy ectodomain is itself released upon DCV exocytosis, arguing that Cmpy serves a second function in BMP signaling. In addition to trafficking Gbb to DCVs, we propose that Gbb/Cmpy co-release from presynaptic terminals defines a neuronal pro-transmission signal. PMID:25453556

Clarinet (CLA-1), a novel active zone protein required for synaptic vesicle clustering and release

PubMed Central

Nelson, Jessica; Richmond, Janet E; Colón-Ramos, Daniel A; Shen, Kang

2017-01-01

Active zone proteins cluster synaptic vesicles at presynaptic terminals and coordinate their release. In forward genetic screens, we isolated a novel Caenorhabditis elegans active zone gene, clarinet (cla-1). cla-1 mutants exhibit defects in synaptic vesicle clustering, active zone structure and synapse number. As a result, they have reduced spontaneous vesicle release and increased synaptic depression. cla-1 mutants show defects in vesicle distribution near the presynaptic dense projection, with fewer undocked vesicles contacting the dense projection and more docked vesicles at the plasma membrane. cla-1 encodes three isoforms containing common C-terminal PDZ and C2 domains with homology to vertebrate active zone proteins Piccolo and RIM. The C-termini of all isoforms localize to the active zone. Specific loss of the ~9000 amino acid long isoform results in vesicle clustering defects and increased synaptic depression. Our data indicate that specific isoforms of clarinet serve distinct functions, regulating synapse development, vesicle clustering and release. PMID:29160205

Expanded Terminal Fields of Gustatory Nerves Accompany Embryonic BDNF Overexpression in Mouse Oral Epithelia

PubMed Central

Sun, Chengsan; Dayal, Arjun

2015-01-01

Brain-derived neurotrophic factor (BDNF) is expressed in gustatory epithelia and is required for gustatory neurons to locate and innervate their correct target during development. When BDNF is overexpressed throughout the lingual epithelium, beginning embryonically, chorda tympani fibers are misdirected and innervate inappropriate targets, leading to a loss of taste buds. The remaining taste buds are hyperinnervated, demonstrating a disruption of nerve/target matching in the tongue. We tested the hypothesis here that overexpression of BDNF peripherally leads to a disrupted terminal field organization of nerves that carry taste information to the brainstem. The chorda tympani, greater superficial petrosal, and glossopharyngeal nerves were labeled in adult wild-type (WT) mice and in adult mice in which BDNF was overexpressed (OE) to examine the volume and density of their central projections in the nucleus of the solitary tract. We found that the terminal fields of the chorda tympani and greater superficial petrosal nerves and overlapping fields that included these nerves in OE mice were at least 80% greater than the respective field volumes in WT mice. The shapes of terminal fields were similar between the two groups; however, the density and spread of labels were greater in OE mice. Unexpectedly, there were also group-related differences in chorda tympani nerve function, with OE mice showing a greater relative taste response to a concentration series of sucrose. Overall, our results show that disruption in peripheral innervation patterns of sensory neurons have significant effects on peripheral nerve function and central organization of their terminal fields. PMID:25568132

An immunoelectron microscopic study of methionine-enkephalin structures in cat prevertebral ganglia.

PubMed

Benfares, J; Henry, M; Cupo, A; Julé, Y

1995-03-01

Methionine-enkephalin-like immunoreactivity was detected in presynaptic nerve fibers and SIF cells in cat prevertebral ganglia. The immunoreactive nerve fibers contained a mixture of numerous small clear vesicles and a few large vesicles; the immunoreactivity was only confined to the large vesicles. Most of the immunoreactive fibers were in apposition with non-immunoreactive neuronal profiles, without any detectable synaptic membrane specializations. The other immunoreactive fibers formed synaptic contacts mainly with non-immunostained dendrites and to a lesser extent with axons and neuronal soma. The characterization at the ultrastructural level of the enkephalin-like immunoreactive structures is discussed as regards the modalities whereby opiates may be involved in sympathetic ganglionic transmission.

Cationic influences upon synaptic transmission at the hair cell-afferent fiber synapse of the frog

NASA Technical Reports Server (NTRS)

Cochran, S. L.

1995-01-01

The concentrations of inorganic cations (K+, Na+, and Ca2+) bathing the isolated frog labyrinth were varied in order to assess their role in influencing and mediating synaptic transmission at the hair cell-afferent fiber synapse. Experiments employed intracellular recordings of synaptic activity from VIIIth nerve afferents. Recordings were digitized continuously at 50 kHz, and excitatory postsynaptic potentials were detected and parameters quantified by computer algorithms. Particular attention was focused on cationic effects upon excitatory postsynaptic potential frequency of occurrence and excitatory postsynaptic potential amplitude, in order to discriminate between pre- and postsynaptic actions. Because the small size of afferents preclude long term stable recordings, alterations in cationic concentrations were applied transiently and their peak effects on synaptic activity were assessed. Increases in extracellular K+ concentration of a few millimolar produced a large increase in the frequency of occurrence of excitatory postsynaptic potentials with little change in amplitude, indicating that release of transmitter from the hair cell is tightly coupled to its membrane potential. Increasing extracellular Na+ concentration resulted in an increase in excitatory postsynaptic potential amplitude with no significant change in excitatory postsynaptic potential frequency of occurrence, suggesting that the transmitter-gated subsynaptic channel conducts Na+ ions. Decreases in extracellular Ca2+ concentration had little effect upon excitatory postsynaptic potential frequency, but increased excitatory postsynaptic potential frequency and amplitude. These findings suggest that at higher concentrations Ca2+ act presynaptically to prevent transmitter release and postsynaptically to prevent Na+ influx during the generation of the excitatory postsynaptic potential. The influences of these ions on synaptic activity at this synapse are remarkably similar to those reported at the vertebrate neuromuscular junction. The major differences between these two synapses are the neurotransmitters and the higher resting release rate and higher sensitivity of release to increased K+ concentrations of the hair cells over that of motor nerve terminals. These differences reflect the functional roles of the two synapses: the motor nerve terminal response in an all-or-nothing signal consequent from action potential invasion, while the hair cell releases transmitter in a graded fashion, proportionate to the extent of stereocilial deflection. Despite these differences between the two junctions, the similar actions of these elemental cations upon synaptic function at each implies that these ions may participate similarly in the operations of other synapses, independent of the neurotransmitter type.(ABSTRACT TRUNCATED AT 400 WORDS).

Mechanisms of α-Synuclein Induced Synaptopathy in Parkinson's Disease

PubMed Central

Bridi, Jessika C.; Hirth, Frank

2018-01-01

Parkinson's disease (PD) is characterized by intracellular inclusions of aggregated and misfolded α-Synuclein (α-Syn), and the loss of dopaminergic (DA) neurons in the brain. The resulting motor abnormalities mark the progression of PD, while non-motor symptoms can already be identified during early, prodromal stages of disease. Recent studies provide evidence that during this early prodromal phase, synaptic and axonal abnormalities occur before the degenerative loss of neuronal cell bodies. These early phenotypes can be attributed to synaptic accumulation of toxic α-Syn. Under physiological conditions, α-Syn functions in its native conformation as a soluble monomer. However, PD patient brains are characterized by intracellular inclusions of insoluble fibrils. Yet, oligomers and protofibrils of α-Syn have been identified to be the most toxic species, with their accumulation at presynaptic terminals affecting several steps of neurotransmitter release. First, high levels of α-Syn alter the size of synaptic vesicle pools and impair their trafficking. Second, α-Syn overexpression can either misregulate or redistribute proteins of the presynaptic SNARE complex. This leads to deficient tethering, docking, priming and fusion of synaptic vesicles at the active zone (AZ). Third, α-Syn inclusions are found within the presynaptic AZ, accompanied by a decrease in AZ protein levels. Furthermore, α-Syn overexpression reduces the endocytic retrieval of synaptic vesicle membranes during vesicle recycling. These presynaptic alterations mediated by accumulation of α-Syn, together impair neurotransmitter exocytosis and neuronal communication. Although α-Syn is expressed throughout the brain and enriched at presynaptic terminals, DA neurons are the most vulnerable in PD, likely because α-Syn directly regulates dopamine levels. Indeed, evidence suggests that α-Syn is a negative modulator of dopamine by inhibiting enzymes responsible for its synthesis. In addition, α-Syn is able to interact with and reduce the activity of VMAT2 and DAT. The resulting dysregulation of dopamine levels directly contributes to the formation of toxic α-Syn oligomers. Together these data suggest a vicious cycle of accumulating α-Syn and deregulated dopamine that triggers synaptic dysfunction and impaired neuronal communication, ultimately causing synaptopathy and progressive neurodegeneration in Parkinson's disease. PMID:29515354

Modeling neuropeptide transport in various types of nerve terminals containing en passant boutons.

PubMed

Kuznetsov, I A; Kuznetsov, A V

2015-03-01

We developed a mathematical model for simulating neuropeptide transport inside dense core vesicles (DCVs) in axon terminals containing en passant boutons. The motivation for this research is a recent experimental study by Levitan and colleagues (Bulgari et al., 2014) which described DCV transport in nerve terminals of type Ib and type III as well as in nerve terminals of type Ib with the transcription factor DIMM. The goal of our modeling is validating the proposition put forward by Levitan and colleagues that the dramatic difference in DCV number in type Ib and type III terminals can be explained by the difference in DCV capture in type Ib and type III boutons rather than by differences in DCV anterograde transport and half-life of resident DCVs. The developed model provides a tool for studying the dynamics of DCV transport in various types of nerve terminals. The model is also an important step in gaining a better mechanistic understanding of transport processes in axons and identifying directions for the development of new models in this area. Copyright © 2014 Elsevier Inc. All rights reserved.

Desmin and nerve terminal expression during embryonic development of the lateral pterygoid muscle in mice.

PubMed

Yamamoto, Masahito; Shinomiya, Takashi; Kishi, Asuka; Yamane, Shigeki; Umezawa, Takashi; Ide, Yoshinobu; Abe, Shinichi

2014-09-01

In adults, the lateral pterygoid muscle (LPM) is usually divided into the upper and lower head, between which the buccal nerve passes. Recent investigations have demonstrated foetal developmental changes in the topographical relationship between the human LPM and buccal nerve. However, as few studies have investigated this issue, we clarified the expression of desmin and nerve terminal distribution during embryonic development of the LPM in mice. We utilized immunohistochemical staining and reverse transcription chain reaction (RT-PCR) to clarify the expression of desmin and nerve terminal distribution. We observed weak expression of desmin in the LPM at embryonic day (ED) 11, followed by an increase in expression from embryonic days 12-15. In addition, starting at ED 12, we observed preferential accumulation of desmin in the vicinity of the myotendinous junction, a trend that did not change up to ED 15. Nerve terminal first appeared at ED 13 and formed regularly spaced linear arrays at the centre of the muscle fibre by ED 15. The results of immunohistochemical staining agreed with those of RT-PCR analysis. We found that desmin accumulated in the vicinity of the myotendinous junction starting at ED 12, prior to the onset of jaw movement. We speculate that the accumulation of desmin is due to factors other than mechanical stress experienced during early muscle contraction. Meanwhile, the time point at which nerve terminals first appeared roughly coincided with the onset of jaw movement. Copyright © 2014 Elsevier Ltd. All rights reserved.

Effects of early nerve repair on experimental brachial plexus injury in neonatal rats.

PubMed

Bourke, Gráinne; McGrath, Aleksandra M; Wiberg, Mikael; Novikov, Lev N

2018-03-01

Obstetrical brachial plexus injury refers to injury observed at the time of delivery, which may lead to major functional impairment in the upper limb. In this study, the neuroprotective effect of early nerve repair following complete brachial plexus injury in neonatal rats was examined. Brachial plexus injury induced 90% loss of spinal motoneurons and 70% decrease in biceps muscle weight at 28 days after injury. Retrograde degeneration in spinal cord was associated with decreased density of dendritic branches and presynaptic boutons and increased density of astrocytes and macrophages/microglial cells. Early repair of the injured brachial plexus significantly delayed retrograde degeneration of spinal motoneurons and reduced the degree of macrophage/microglial reaction but had no effect on muscle atrophy. The results demonstrate that early nerve repair of neonatal brachial plexus injury could promote survival of injured motoneurons and attenuate neuroinflammation in spinal cord.

Alzheimer's Disease: Targeting the Cholinergic System

PubMed Central

Ferreira-Vieira, Talita H.; Guimaraes, Isabella M.; Silva, Flavia R.; Ribeiro, Fabiola M.

2016-01-01

Acetylcholine (ACh) has a crucial role in the peripheral and central nervous systems. The enzyme choline acetyltransferase (ChAT) is responsible for synthesizing ACh from acetyl-CoA and choline in the cytoplasm and the vesicular acetylcholine transporter (VAChT) uptakes the neurotransmitter into synaptic vesicles. Following depolarization, ACh undergoes exocytosis reaching the synaptic cleft, where it can bind its receptors, including muscarinic and nicotinic receptors. ACh present at the synaptic cleft is promptly hydrolyzed by the enzyme acetylcholinesterase (AChE), forming acetate and choline, which is recycled into the presynaptic nerve terminal by the high-affinity choline transporter (CHT1). Cholinergic neurons located in the basal forebrain, including the neurons that form the nucleus basalis of Meynert, are severely lost in Alzheimer’s disease (AD). AD is the most ordinary cause of dementia affecting 25 million people worldwide. The hallmarks of the disease are the accumulation of neurofibrillary tangles and amyloid plaques. However, there is no real correlation between levels of cortical plaques and AD-related cognitive impairment. Nevertheless, synaptic loss is the principal correlate of disease progression and loss of cholinergic neurons contributes to memory and attention deficits. Thus, drugs that act on the cholinergic system represent a promising option to treat AD patients. PMID:26813123

Evidence for postsynaptic modulation of muscle contraction by a Drosophila neuropeptide.

PubMed

Clark, Julie; Milakovic, Maja; Cull, Amanda; Klose, Markus K; Mercier, A Joffre

2008-07-01

DPKQDFMRFamide, the most abundant FMRFamide-like peptide in Drosophila melanogaster, has been shown previously to enhance contractions of larval body wall muscles elicited by nerve stimulation and to increase excitatory junction potentials (EJPs). The present work investigated the possibility that this peptide can also stimulate muscle contraction by a direct action on muscle fibers. DPKQDFMRFamide induced slow contractions and increased tonus in body wall muscles of Drosophila larvae from which the central nervous system had been removed. The threshold for this effect was approximately 10(-8)M. The increase in tonus persisted in the presence of 7x10(-3)M glutamate, which desensitized postsynaptic glutamate receptors. Thus, the effect on tonus could not be explained by enhanced release of glutamate from synaptic terminals and, thus, may represent a postsynaptic effect. The effect on tonus was abolished in calcium-free saline and by treatment with L-type calcium channel blockers, nifedipine and nicardipine, but not by T-type blockers, amiloride and flunarizine. The present results provide evidence that this Drosophila peptide can act postsynaptically in addition to its apparent presynaptic effects, and that the postsynaptic effect requires influx through L-type calcium channels.

Selectivity of the uptake of glutamate and GABA in two morphologically distinct insect neuromuscular synapses.

PubMed

van Marle, J; Piek, T; Lammertse, T; Lind, A; Van Weeren-Kramer, J

1985-11-25

The common inhibitor (CI) and slow excitor tibiae (SETi) innervated slow muscles 135cd of the locust Schistocerca gregaria were incubated under high-affinity uptake conditions either in [3H]GABA or in [3H]glutamate. [3H]GABA is accumulated in the glia of the nerve endings of the CI as well as the SETi; however, it is accumulated only in the terminal axons of the CI, not in the terminal axons of the SETi. The grain densities above the glia and above the CI terminal axons are approximately 2 grains/micron2. After incubation in [3H]glutamate the grain densities above the CI terminal axons and the SETi terminal axons are approximately 4 grains/micron2; the grain densities above the glia of both types of nerve endings are approximately 17 grains/micron2. The relatively high labeling (3 grains/micron2) of the muscles after incubation in the presence of glutamate is ascribed to the high metabolic requirements of slow muscles. The conclusion is drawn that a high-affinity uptake system for GABA is present in the CI terminal axons and in the glia of both the CI and SETi nerve endings. However, while the glutamate uptake in the CI and SETi nerve endings of the slow 135cd is comparable to the high-affinity uptake of glutamate in the fast excitor tibiae (FETi) nerve endings of the fast retractor unguis muscle, a high-affinity uptake of glutamate was only demonstrated in the glia of both types of nerve endings. A high-affinity uptake in the terminal axons of the CI and SETi may be masked by an extensively low-affinity uptake of glutamate by the muscles.

Amino-Terminal β-Amyloid Antibody Blocks β-Amyloid-Mediated Inhibition of the High-Affinity Choline Transporter CHT.

PubMed

Cuddy, Leah K; Seah, Claudia; Pasternak, Stephen H; Rylett, R Jane

2017-01-01

Alzheimer's disease (AD) is a common age-related neurodegenerative disorder that is characterized by progressive cognitive decline. The deficits in cognition and attentional processing that are observed clinically in AD are linked to impaired function of cholinergic neurons that release the neurotransmitter acetylcholine (ACh). The high-affinity choline transporter (CHT) is present at the presynaptic cholinergic nerve terminal and is responsible for the reuptake of choline produced by hydrolysis of ACh following its release. Disruption of CHT function leads to decreased choline uptake and ACh synthesis, leading to impaired cholinergic neurotransmission. We report here that cell-derived β-amyloid peptides (Aβ) decrease choline uptake activity and cell surface CHT protein levels in SH-SY5Y neural cells. Moreover, we make the novel observation that the amount of CHT protein localizing to early endosomes and lysosomes is decreased significantly in cells that have been treated with cell culture medium that contains Aβ peptides released from neural cells. The Aβ-mediated loss of CHT proteins from lysosomes is prevented by blocking lysosomal degradation of CHT with the lysosome inhibitor bafilomycin A1 (BafA 1 ). BafA 1 also attenuated the Aβ-mediated decrease in CHT cell surface expression. Interestingly, however, lysosome inhibition did not block the effect of Aβ on CHT activity. Importantly, neutralizing Aβ using an anti-Aβ antibody directed at the N-terminal amino acids 1-16 of Aβ, but not by an antibody directed at the mid-region amino acids 22-35 of Aβ, attenuates the effect of Aβ on CHT activity and trafficking. This indicates that a specific N-terminal Aβ epitope, or specific conformation of soluble Aβ, may impair CHT activity. Therefore, Aβ immunotherapy may be a more effective therapeutic strategy for slowing the progression of cognitive decline in AD than therapies designed to promote CHT cell surface levels.

Inhibition of botulinum neurotoxins interchain disulfide bond reduction prevents the peripheral neuroparalysis of botulism.

PubMed

Zanetti, Giulia; Azarnia Tehran, Domenico; Pirazzini, Marcon; Binz, Thomas; Shone, Clifford C; Fillo, Silvia; Lista, Florigio; Rossetto, Ornella; Montecucco, Cesare

2015-12-01

Botulinum neurotoxins (BoNTs) form a growing family of metalloproteases with a unique specificity either for VAMP, SNAP25 or syntaxin. The BoNTs are grouped in seven different serotypes indicated by letters from A to G. These neurotoxins enter the cytosol of nerve terminals via a 100 kDa chain which binds to the presynaptic membrane and assists the translocation of a 50 kDa metalloprotease chain. These two chains are linked by a single disulfide bridge which plays an essential role during the entry of the metalloprotease chain in the cytosol, but thereafter it has to be reduced to free the proteolytic activity. Its reduction is mediated by thioredoxin which is continuously regenerated by its reductase. Here we show that inhibitors of thioredoxin reductase or of thioredoxin prevent the specific proteolysis of VAMP by the four VAMP-specific BoNTs: type B, D, F and G. These compounds are effective not only in primary cultures of neurons, but also in preventing the in vivo mouse limb neuroparalysis. In addition, one of these inhibitors, Ebselen, largely protects mice from the death caused by a systemic injection. Together with recent results obtained with BoNTs specific for SNAP25 and syntaxin, the present data demonstrate the essential role of the thioredoxin-thioredoxin reductase system in reducing the interchain disulfide during the nerve intoxication mechanism of all serotypes. Therefore its inhibitors should be considered for a possible use to prevent botulism and for treating infant botulism. Copyright © 2015 Elsevier Inc. All rights reserved.

Effects of short-term continuous positive airway pressure on myocardial sympathetic nerve function and energetics in patients with heart failure and obstructive sleep apnea: a randomized study.

PubMed

Hall, Allison B; Ziadi, Maria C; Leech, Judith A; Chen, Shin-Yee; Burwash, Ian G; Renaud, Jennifer; deKemp, Robert A; Haddad, Haissam; Mielniczuk, Lisa M; Yoshinaga, Keiichiro; Guo, Ann; Chen, Li; Walter, Olga; Garrard, Linda; DaSilva, Jean N; Floras, John S; Beanlands, Rob S B

2014-09-09

Heart failure with reduced ejection fraction and obstructive sleep apnea (OSA), 2 states of increased metabolic demand and sympathetic nervous system activation, often coexist. Continuous positive airway pressure (CPAP), which alleviates OSA, can improve ventricular function. It is unknown whether this is due to altered oxidative metabolism or presynaptic sympathetic nerve function. We hypothesized that short-term (6-8 weeks) CPAP in patients with OSA and heart failure with reduced ejection fraction would improve myocardial sympathetic nerve function and energetics. Forty-five patients with OSA and heart failure with reduced ejection fraction (left ventricular ejection fraction 35.8±9.7% [mean±SD]) were evaluated with the use of echocardiography and 11C-acetate and 11C-hydroxyephedrine positron emission tomography before and ≈6 to 8 weeks after randomization to receive short-term CPAP (n=22) or no CPAP (n=23). Work metabolic index, an estimate of myocardial efficiency, was calculated as follows: (stroke volume index×heart rate×systolic blood pressure÷Kmono), where Kmono is the monoexponential function fit to the myocardial 11C-acetate time-activity data, reflecting oxidative metabolism. Presynaptic sympathetic nerve function was measured with the use of the 11C-hydroxyephedrine retention index. CPAP significantly increased hydroxyephedrine retention versus no CPAP (Δretention: +0.012 [0.002, 0.021] versus -0.006 [-0.013, 0.005] min(-1); P=0.003). There was no significant change in work metabolic index between groups. However, in those with more severe OSA (apnea-hypopnea index>20 events per hour), CPAP significantly increased both work metabolic index and systolic blood pressure (P<0.05). In patients with heart failure with reduced ejection fraction and OSA, short-term CPAP increased hydroxyephedrine retention, indicating improved myocardial sympathetic nerve function, but overall did not affect energetics. In those with more severe OSA, CPAP may improve cardiac efficiency. Further outcome-based investigation of the consequences of CPAP is warranted. http://www.clinicaltrials.gov. Unique identifier: NCT00756366. © 2014 American Heart Association, Inc.

Presynaptic DLG regulates synaptic function through the localization of voltage-activated Ca2+ Channels

PubMed Central

Astorga, César; Jorquera, Ramón A.; Ramírez, Mauricio; Kohler, Andrés; López, Estefanía; Delgado, Ricardo; Córdova, Alex; Olguín, Patricio; Sierralta, Jimena

2016-01-01

The DLG-MAGUK subfamily of proteins plays a role on the recycling and clustering of glutamate receptors (GLUR) at the postsynaptic density. discs-large1 (dlg) is the only DLG-MAGUK gene in Drosophila and originates two main products, DLGA and DLGS97 which differ by the presence of an L27 domain. Combining electrophysiology, immunostaining and genetic manipulation at the pre and postsynaptic compartments we study the DLG contribution to the basal synaptic-function at the Drosophila larval neuromuscular junction. Our results reveal a specific function of DLGS97 in the regulation of the size of GLUR fields and their subunit composition. Strikingly the absence of any of DLG proteins at the presynaptic terminal disrupts the clustering and localization of the calcium channel DmCa1A subunit (Cacophony), decreases the action potential-evoked release probability and alters short-term plasticity. Our results show for the first time a crucial role of DLG proteins in the presynaptic function in vivo. PMID:27573697

Presynaptic DLG regulates synaptic function through the localization of voltage-activated Ca(2+) Channels.

PubMed

Astorga, César; Jorquera, Ramón A; Ramírez, Mauricio; Kohler, Andrés; López, Estefanía; Delgado, Ricardo; Córdova, Alex; Olguín, Patricio; Sierralta, Jimena

2016-08-30

The DLG-MAGUK subfamily of proteins plays a role on the recycling and clustering of glutamate receptors (GLUR) at the postsynaptic density. discs-large1 (dlg) is the only DLG-MAGUK gene in Drosophila and originates two main products, DLGA and DLGS97 which differ by the presence of an L27 domain. Combining electrophysiology, immunostaining and genetic manipulation at the pre and postsynaptic compartments we study the DLG contribution to the basal synaptic-function at the Drosophila larval neuromuscular junction. Our results reveal a specific function of DLGS97 in the regulation of the size of GLUR fields and their subunit composition. Strikingly the absence of any of DLG proteins at the presynaptic terminal disrupts the clustering and localization of the calcium channel DmCa1A subunit (Cacophony), decreases the action potential-evoked release probability and alters short-term plasticity. Our results show for the first time a crucial role of DLG proteins in the presynaptic function in vivo.

MCTP is an ER-resident calcium sensor that stabilizes synaptic transmission and homeostatic plasticity

PubMed Central

Genç, Özgür; Dickman, Dion K; Ma, Wenpei; Tong, Amy; Fetter, Richard D; Davis, Graeme W

2017-01-01

Presynaptic homeostatic plasticity (PHP) controls synaptic transmission in organisms from Drosophila to human and is hypothesized to be relevant to the cause of human disease. However, the underlying molecular mechanisms of PHP are just emerging and direct disease associations remain obscure. In a forward genetic screen for mutations that block PHP we identified mctp (Multiple C2 Domain Proteins with Two Transmembrane Regions). Here we show that MCTP localizes to the membranes of the endoplasmic reticulum (ER) that elaborate throughout the soma, dendrites, axon and presynaptic terminal. Then, we demonstrate that MCTP functions downstream of presynaptic calcium influx with separable activities to stabilize baseline transmission, short-term release dynamics and PHP. Notably, PHP specifically requires the calcium coordinating residues in each of the three C2 domains of MCTP. Thus, we propose MCTP as a novel, ER-localized calcium sensor and a source of calcium-dependent feedback for the homeostatic stabilization of neurotransmission. DOI: http://dx.doi.org/10.7554/eLife.22904.001 PMID:28485711

Study of axonal dystrophy. II Dystrophy and atrophy of the presynaptic boutons: a dual pathology.

PubMed

Fujisawa, K; Shiraki, H

1980-01-01

In succession to the previous quantitative work, a qualitative study has been carried out on the nature of a dual pathology affecting presynaptic boutons in the posterior tract nuclei of ageing rats. Based on the morphology of dystrophic boutons in early stage, it is concluded that the initial and therefore essential characteristic of dystrophic process is an abnormal increase of normal axonal components within the presynaptic boutons, and that various abnormal substructures of spheroids hitherto reported in the literature are probably the results of their secondary metamorphosis. The dystrophic process within the posterior tract nuclei is a selective one, involving presynaptic boutons and preterminal axons only of the posterior tract fibres. Comparison of the frequency of early dystrophic boutons and of fully grown-up spheroids indicates that a small percentage of boutons deriving from posterior tract fibres become dystrophic and of these dystrophic boutons only a small percentage again continue to develop unto large spheroids, throughout lifespan of the animals. On the other hand, in search of a morphological counterpart for the age-related decrease of volume ratio of presynaptic boutons to the neuropil, some dubious atrophic changes were also found in presynaptic boutons, which could have been easily missed from observation if studied qualitatively alone. Accordingly, no less numerous boutons other than dystrophic ones are supposed to atrophy 'independently' and to disappear 'silently' during the same period. The dystrophic and the atrophic changes involve different boutons (of different or the same terminal axons) within the same gray matter. This dual pathology of boutons needs further elucidation of its neurocytopathological as well as neurobiological background in the future.

Single cocaine exposure does not alter striatal pre-synaptic dopamine function in mice: an [18 F]-FDOPA PET study.

PubMed

Bonsall, David R; Kokkinou, Michelle; Veronese, Mattia; Coello, Christopher; Wells, Lisa A; Howes, Oliver D

2017-12-01

Cocaine is a recreational drug of abuse that binds to the dopamine transporter, preventing reuptake of dopamine into pre-synaptic terminals. The increased presence of synaptic dopamine results in stimulation of both pre- and post-synaptic dopamine receptors, considered an important mechanism by which cocaine elicits its reinforcing properties. However, the effects of acute cocaine administration on pre-synaptic dopamine function remain unclear. Non-invasive imaging techniques such as positron emission tomography have revealed impaired pre-synaptic dopamine function in chronic cocaine users. Similar impairments have been seen in animal studies, with microdialysis experiments indicating decreased basal dopamine release. Here we use micro positron emission tomography imaging techniques in mice to measure dopamine synthesis capacity and determine the effect of acute cocaine administration of pre-synaptic dopamine function. We show that a dose of 20 mg/kg cocaine is sufficient to elicit hyperlocomotor activity, peaking 15-20 min post treatment (p < 0.001). However, dopamine synthesis capacity in the striatum was not significantly altered by acute cocaine treatment (KiCer: 0.0097 per min vs. 0.0112 per min in vehicle controls, p > 0.05). Furthermore, expression levels of two key enzymes related to dopamine synthesis, tyrosine hydroxylase and aromatic l-amino acid decarboxylase, within the striatum of scanned mice were not significantly affected by acute cocaine pre-treatment (p > 0.05). Our findings suggest that while the regulation of dopamine synthesis and release in the striatum have been shown to change with chronic cocaine use, leading to a reduced basal tone, these adaptations to pre-synaptic dopaminergic neurons are not initiated following a single exposure to the drug. © 2017 International Society for Neurochemistry.

Protons are a neurotransmitter that regulates synaptic plasticity in the lateral amygdala.

PubMed

Du, Jianyang; Reznikov, Leah R; Price, Margaret P; Zha, Xiang-ming; Lu, Yuan; Moninger, Thomas O; Wemmie, John A; Welsh, Michael J

2014-06-17

Stimulating presynaptic terminals can increase the proton concentration in synapses. Potential receptors for protons are acid-sensing ion channels (ASICs), Na(+)- and Ca(2+)-permeable channels that are activated by extracellular acidosis. Those observations suggest that protons might be a neurotransmitter. We found that presynaptic stimulation transiently reduced extracellular pH in the amygdala. The protons activated ASICs in lateral amygdala pyramidal neurons, generating excitatory postsynaptic currents. Moreover, both protons and ASICs were required for synaptic plasticity in lateral amygdala neurons. The results identify protons as a neurotransmitter, and they establish ASICs as the postsynaptic receptor. They also indicate that protons and ASICs are a neurotransmitter/receptor pair critical for amygdala-dependent learning and memory.

Somato-dendritic synapses in the nucleus reticularis thalami of the rat.

PubMed

Csillik, B; Pálfi, A; Gulya, K; Mihály, A; Knyihár-Csillik, Elizabeth

2002-01-01

In the reticular nucleus of the rat thalamus, about 30% of the synapses are brought about by the perikarya of parvalbumin-immunopositive neurons, which establish somato-dendritic synapses with large dendrites of nerve cells of specific thalamic nuclei. Although the parvalbumin-immunopositive presynaptic structures bear resemblance to goblet-like or calyciform axonal endings, electron microscopic immunocytochemistry and in situ hybridization revealed that these structures are parts of the perikaryal cytoplasm studded with synaptic vesicles. In about 15% of the somato-dendritic synapses, axons are seen to be in synaptic contact with the parvalbumin-immunoreactive perikaryon. Double immunohistochemical staining revealed that the parvalbumin immunoreactive presynaptic perikarya and dendrites contained GABA. It is assumed that the peculiar somato-dendritic synaptic complexes subserve the goal of filtration of impulses arriving at the reticular nucleus from various thalamic nuclei, thus processing them for further sampling.

Cluster of wound botulism in California: clinical, electrophysiologic, and pathologic study.

PubMed

Maselli, R A; Ellis, W; Mandler, R N; Sheikh, F; Senton, G; Knox, S; Salari-Namin, H; Agius, M; Wollmann, R L; Richman, D P

1997-10-01

Over a period of 15 months we have seen 6 patients with long-standing history of subcutaneous heroin injections who experienced acute blurred vision, dysphagia, dysarthria, and generalized weakness. Decreased or absent deep tendon reflexes, pupillary abnormalities, incremental responses to fast repetitive nerve stimulation, and positive serology for Clostridia botulinum toxin A were found, but not in all cases. Muscle biopsies showed variable signs of neurogenic atrophy. In vitro electrophysiology studies revealed decreased end-plate potentials quantal content, confirming the presynaptic nature of the disorder. Mechanical ventilation was required in 5 patients. Half of the patients were treated with polyvalent antitoxiin. Prognosis was favorable, though recovery was slow. In conclusion, acute bulbar weakness with visual symptoms in patients with subcutaneous heroin abuse strongly suggets the possibility of wound botulism. High diagnostic suspicion combined with histology and in vitro electrophysiology confirmation of presynaptic failure, especially in seronegative cases, may significantly improve morbidity.

[Morphologic studies of the protective role of catechin on kanamycin otoneurotoxicity in SD rats].

PubMed

Liu, Guo-hui; Xie, Ding-hua; Wu, Wei-jing

2002-12-28

To determine the protection of catechin on aminoglycoside antibiotics otoneurotoxicity in SD rats, and observe the morphologic changes of cochlear efferent nerve terminals and outer hair cells after the injection of kanamycin and the feeding of catechin by the stomach tube. Thirty-eight SD rats were randomly assigned into three experimental groups (KM-treated, catechin-treated, KM and catechin in combination) and one control group. The KM-treated group was given kanamycin in a dose of 500 mg.(kg.d)-1 for 14 days. The catechin-treated group was given catechin once by the stomach tube in a dose of 400 mg.(kg.d)-1. Two kinds of medicine were simultaneously given in the KM+ catechin group. Transmission electron microscopy was utilized to observe the subcellular structure of efferent nerve fibers and outer hair cells. The densities of efferent nerve fibers and terminals were examined and the numbers of efferent nerve fibers and terminals were numerated by the surface preparation using modified histochemical staining for acetylcholinesterase (AchE). The damage in the group protected by catechin was relieved compared with the unprotected group. No damage was found in the catechin-treated alone group and controls. The densities and numbers of efferent nerve fibers and terminals were obviously fewer in the unprotected group than in the protected group and controls(P < 0.05). There was no significant difference in the numbers of efferent nerve fibers and terminals of the group protected by catechin compared with the controls and the catechin-treated group (P > 0.05). Catechin significantly protects MOC efferent nerves in kanamycin otoneurotoxicity.

Calcitonin Gene-Related Peptide Reduces Taste-Evoked ATP Secretion from Mouse Taste Buds.

PubMed

Huang, Anthony Y; Wu, Sandy Y

2015-09-16

Immunoelectron microscopy revealed that peripheral afferent nerve fibers innervating taste buds contain calcitonin gene-related peptide (CGRP), which may be as an efferent transmitter released from peripheral axon terminals. In this report, we determined the targets of CGRP within taste buds and studied what effect CGRP exerts on taste bud function. We isolated mouse taste buds and taste cells, conducted functional imaging using Fura-2, and used cellular biosensors to monitor taste-evoked transmitter release. The findings showed that a subset of Presynaptic (Type III) taste cells (53%) responded to 0.1 μm CGRP with an increase in intracellular Ca(2+). In contrast, Receptor (Type II) taste cells rarely (4%) responded to 0.1 μm CGRP. Using pharmacological tools, the actions of CGRP were probed and elucidated by the CGRP receptor antagonist CGRP(8-37). We demonstrated that this effect of CGRP was dependent on phospholipase C activation and was prevented by the inhibitor U73122. Moreover, applying CGRP caused taste buds to secrete serotonin (5-HT), a Presynaptic (Type III) cell transmitter, but not ATP, a Receptor (Type II) cell transmitter. Further, our previous studies showed that 5-HT released from Presynaptic (Type III) cells provides negative paracrine feedback onto Receptor (Type II) cells by activating 5-HT1A receptors, and reducing ATP secretion. Our data showed that CGRP-evoked 5-HT release reduced taste-evoked ATP secretion. The findings are consistent with a role for CGRP as an inhibitory transmitter that shapes peripheral taste signals via serotonergic signaling during processing gustatory information in taste buds. The taste sensation is initiated with a highly complex set of interactions between a variety of cells located within the taste buds before signal propagation to the brain. Afferent signals from the oral cavity are carried to the brain in chemosensory fibers that contribute to chemesthesis, the general chemical sensitivity of the mucus membranes in the oronasal cavities and being perceived as pungency, irritation, or heat. This is a study of a fundamental question in neurobiology: how are signals processed in sensory end organs, taste buds? More specifically, taste-modifying interactions, via transmitters, between gustatory and chemosensory afferents inside taste buds will help explain how a coherent output is formed before being transmitted to the brain. Copyright © 2015 the authors 0270-6474/15/3512714-11$15.00/0.

The dimensions and characteristics of the subepidermal nerve plexus in human skin--terminal Schwann cells constitute a substantial cell population within the superficial dermis.

PubMed

Reinisch, Christina M; Tschachler, Erwin

2012-03-01

The skin constitutes the largest sensorial organ. Its nervous system consists of different types of afferent nerve fibers which spread out immediately beneath the skin surface to sense temperature, touch and pain. Our aim was to investigate the dimension and topographic relationship of the different nerve fibers of the subepidermal nerve plexus in human hairy skin and to analyze numbers and marker expression of terminal Schwann cells. Nerve fibers and Schwann cells were investigated on dermal sheet preparations and thick sections of skin from various body regions of 10 individuals. The dimension of subepidermal nerve fibers varied between different body sites with highest values in chest skin (100 ± 18 mm/mm(2)) and lowest in posterior forearm skin (53 ± 10 mm/mm(2)). The majority of fibers (85.79%) were unmyelinated, thus representing C-fibers, of which 7.84% were peptidergic. Neurofilament-positive fibers (A-fibers) accounted for 14.21% and fibers positive for both neurofilament and myelin (Aβ-fibers) for only 0.18%. The number of Schwann cells varied in accordance with nerve fiber length from 453 ± 108 on chest skin to 184 ± 58/mm(2) in skin of the posterior forearm. Terminal Schwann cells showed a marker profile comparable to Schwann cells in peripheral nerves with the notable exception of expression of NGFr, NCAM, L1CAM and CD146 on myelinating Schwann cells in the dermis but not in peripheral nerves. Our data show that terminal Schwann cells constitute a substantial cell population within the papillary dermis and that both nerve fiber length and Schwann cell numbers vary considerably between different body sites. Copyright © 2011 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.

Structure, Distribution, and Function of Neuronal/Synaptic Spinules and Related Invaginating Projections

PubMed Central

Petralia, Ronald S.; Wang, Ya-Xian; Mattson, Mark P.; Yao, Pamela J.

2015-01-01

Neurons and especially their synapses often project long thin processes that can invaginate neighboring neuronal or glial cells. These “invaginating projections” can occur in almost any combination of postsynaptic, presynaptic, and glial processes. Invaginating projections provide a precise mechanism for one neuron to communicate or exchange material exclusively at a highly localized site on another neuron, e.g., to regulate synaptic plasticity. The best-known types are postsynaptic projections called “spinules” that invaginate into presynaptic terminals. Spinules seem to be most prevalent at large very active synapses. Here, we present a comprehensive review of all kinds of invaginating projections associated with both neurons in general and more specifically with synapses; we describe them in all animals including simple, basal metazoans. These structures may have evolved into more elaborate structures in some higher animal groups exhibiting greater synaptic plasticity. In addition to classic spinules and filopodial invaginations, we describe a variety of lesser-known structures such as amphid microvilli, spinules in giant mossy terminals and en marron/brush synapses, the highly specialized fish retinal spinules, the trophospongium, capitate projections, and fly gnarls, as well as examples in which the entire presynaptic or postsynaptic process is invaginated. These various invaginating projections have evolved to modify the function of a particular synapse, or to channel an effect to one specific synapse or neuron, without affecting those nearby. We discuss how they function in membrane recycling, nourishment, and cell signaling and explore how they might change in aging and disease. PMID:26007200

Short term memory may be the depletion of the readily releasable pool of presynaptic neurotransmitter vesicles of a metastable long term memory trace pattern.

PubMed

Tarnow, Eugen

2009-09-01

The Tagging/Retagging model of short term memory was introduced earlier (Tarnow in Cogn Neurodyn 2(4):347-353, 2008) to explain the linear relationship between response time and correct response probability for word recall and recognition: At the initial stimulus presentation the words displayed tag the corresponding long term memory locations. The tagging process is linear in time and takes about one second to reach a tagging level of 100%. After stimulus presentation the tagging level decays logarithmically with time to 50% after 14 s and to 20% after 220 s. If a probe word is reintroduced the tagging level has to return to 100% for the word to be properly identified, which leads to a delay in response time. This delay is proportional to the tagging loss. The tagging level is directly related to the probability of correct word recall and recognition. Evidence presented suggests that the tagging level is the level of depletion of the Readily Releasable Pool (RRP) of neurotransmitter vesicles at presynaptic terminals. The evidence includes the initial linear relationship between tagging level and time as well as the subsequent logarithmic decay of the tagging level. The activation of a short term memory may thus be the depletion of RRP (exocytosis) and short term memory decay may be the ensuing recycling of the neurotransmitter vesicles (endocytosis). The pattern of depleted presynaptic terminals corresponds to the long term memory trace.

Blocking Effects of Human Tau on Squid Giant Synapse Transmission and Its Prevention by T-817 MA

PubMed Central

Moreno, Herman; Choi, Soonwook; Yu, Eunah; Brusco, Janaina; Avila, Jesus; Moreira, Jorge E.; Sugimori, Mutsuyuki; Llinás, Rodolfo R.

2011-01-01

Filamentous tau inclusions are hallmarks of Alzheimer's disease and related neurodegenerative tauopathies, but the molecular mechanisms involved in tau-mediated changes in neuronal function and their possible effects on synaptic transmission are unknown. We have evaluated the effects of human tau protein injected directly into the presynaptic terminal axon of the squid giant synapse, which affords functional, structural, and biochemical analysis of its action on the synaptic release process. Indeed, we have found that at physiological concentration recombinant human tau (h-tau42) becomes phosphorylated, produces a rapid synaptic transmission block, and induces the formation of clusters of aggregated synaptic vesicles in the vicinity of the active zone. Presynaptic voltage clamp recordings demonstrate that h-tau42 does not modify the presynaptic calcium current amplitude or kinetics. Analysis of synaptic noise at the post-synaptic axon following presynaptic h-tau42 microinjection revealed an initial phase of increase spontaneous transmitter release followed by a marked reduction in noise. Finally, systemic administration of T-817MA, a proposed neuro-protective agent, rescued tau-induced synaptic abnormalities. Our results show novel mechanisms of h-tau42 mediated synaptic transmission failure and identify a potential therapeutic agent to treat tau-related neurotoxicity. PMID:21629767

High-Bandwidth Atomic Force Microscopy Reveals A Mechanical spike Accompanying the Action Potential in mammalian Nerve Terminals

NASA Astrophysics Data System (ADS)

Salzberg, Brian M.

2008-03-01

Information transfer from neuron to neuron within nervous systems occurs when the action potential arrives at a nerve terminal and initiates the release of a chemical messenger (neurotransmitter). In the mammalian neurohypophysis (posterior pituitary), large and rapid changes in light scattering accompany secretion of transmitter-like neuropeptides. In the mouse, these intrinsic optical signals are intimately related to the arrival of the action potential (E-wave) and the release of arginine vasopressin and oxytocin (S-wave). We have used a high bandwidth (20 kHz) atomic force microscope (AFM) to demonstrate that these light scattering signals are associated with changes in nerve terminal volume, detected as nanometer-scale movements of a cantilever positioned on top of the neurohypophysis. The most rapid mechanical response, the ``spike'', has duration comparable to that of the action potential (˜2 ms) and probably reflects an increase in terminal volume due to H2O movement associated with Na^+-influx. Elementary calculations suggest that two H2O molecules accompanying each Na^+-ion could account for the ˜0.5-1.0 å increase in the diameter of each terminal during the action potential. Distinguishable from the mechanical ``spike'', a slower mechanical event, the ``dip'', represents a decrease in nerve terminal volume, depends upon Ca^2+-entry, as well as on intra-terminal Ca^2+-transients, and appears to monitor events associated with secretion. A simple hypothesis is that this ``dip'' reflects the extrusion of the dense core granule that comprises the secretory products. These dynamic high bandwidth AFM recordings are the first to monitor mechanical events in nervous systems and may provide novel insights into the mechanism(s) by which excitation is coupled to secretion at nerve terminals.

Dopamine D1 and D2 Receptor Immunoreactivities in the Arcuate-Median Eminence Complex and their Link to the Tubero-Infundibular Dopamine Neurons

PubMed Central

Romero-Fernandez, W.; Borroto-Escuela, D.O.; Vargas-Barroso, V.; Narváez, M.; Di Palma, M.; Agnati, L.F.; Sahd, J. Larriva

2014-01-01

Dopamine D1 and D2 receptor immunohistochemistry and Golgi techniques were used to study the structure of the adult rat arcuate-median eminence complex, and determine the distribution of the dopamine D1 and D2 receptor immunoreactivities therein, particularly in relation to the tubero-infundibular dopamine neurons. Punctate dopamine D1 and D2 receptor immunoreactivities, likely located on nerve terminals, were enriched in the lateral palisade zone built up of nerve terminals, while the densities were low to modest in the medial palisade zone. A codistribution of dopamine D1 receptor or dopamine D2 receptor immunoreactive puncta with tyrosine hydroxylase immunoreactive nerve terminals was demonstrated in the external layer. Dopamine D1 receptor but not dopamine D2 receptor immnunoreactivites nerve cell bodies were found in the ventromedial part of the arcuate nucleus and in the lateral part of the internal layer of the median eminence forming a continuous cell mass presumably representing neuropeptide Y immunoreactive nerve cell bodies. The major arcuate dopamine/ tyrosine hydroxylase nerve cell group was found in the dorsomedial part. A large number of tyrosine hydroxylase immunoreactive nerve cell bodies in this region demonstrated punctate dopamine D1 receptor immunoreactivity but only a few presented dopamine D2 receptor immunoreactivity which were mainly found in a substantial number of tyrosine hydroxylase cell bodies of the ventral periventricular hypothalamic nucleus, also belonging to the tuberoinfundibular dopamine neurons. Structural evidence for projections of the arcuate nerve cells into the median eminence was also obtained. Distal axons formed horizontal axons in the internal layer issuing a variable number of collaterals classified into single or multiple strands located in the external layer increasing our understanding of the dopamine nerve terminal networks in this region. Dopamine D1 and D2 receptors may therefore directly and differentially modulate the activity and/or Dopamine synthesis of substantial numbers of tubero-infundibular dopamine neurons at the somatic and terminal level. The immunohistochemical work also gives support to the view that dopamine D1 receptors and/or dopamine D2 receptors in the lateral palisade zone by mediating dopamine volume transmission may contribute to the inhibition of luteinizing hormone releasing hormone release from nerve terminals in this region. PMID:25308843

Dopamine D1 and D2 receptor immunoreactivities in the arcuate-median eminence complex and their link to the tubero-infundibular dopamine neurons.

PubMed

Romero-Fernandez, W; Borroto-Escuela, D O; Vargas-Barroso, V; Narváez, M; Di Palma, M; Agnati, L F; Larriva Sahd, J; Fuxe, K

2014-07-18

Dopamine D1 and D2 receptor immunohistochemistry and Golgi techniques were used to study the structure of the adult rat arcuate-median eminence complex, and determine the distribution of the dopamine D1 and D2 receptor immunoreactivities therein, particularly in relation to the tubero-infundibular dopamine neurons. Punctate dopamine D1 and D2 receptor immunoreactivities, likely located on nerve terminals, were enriched in the lateral palisade zone built up of nerve terminals, while the densities were low to modest in the medial palisade zone. A codistribution of dopamine D1 receptor or dopamine D2 receptor immunoreactive puncta with tyrosine hydroxylase immunoreactive nerve terminals was demonstrated in the external layer. Dopamine D1 receptor but not dopamine D2 receptor immnunoreactivites nerve cell bodies were found in the ventromedial part of the arcuate nucleus and in the lateral part of the internal layer of the median eminence forming a continuous cell mass presumably representing neuropeptide Y immunoreactive nerve cell bodies. The major arcuate dopamine/ tyrosine hydroxylase nerve cell group was found in the dorsomedial part. A large number of tyrosine hydroxylase immunoreactive nerve cell bodies in this region demonstrated punctate dopamine D1 receptor immunoreactivity but only a few presented dopamine D2 receptor immunoreactivity which were mainly found in a substantial number of tyrosine hydroxylase cell bodies of the ventral periventricular hypothalamic nucleus, also belonging to the tubero-infundibular dopamine neurons. Structural evidence for projections of the arcuate nerve cells into the median eminence was also obtained. Distal axons formed horizontal axons in the internal layer issuing a variable number of collaterals classified into single or multiple strands located in the external layer increasing our understanding of the dopamine nerve terminal networks in this region.  Dopamine D1 and D2 receptors may therefore directly and differentially modulate the activity and /or Dopamine synthesis of substantial numbers of tubero-infundibular dopamine neurons at the somatic and terminal level. The immunohistochemical work also gives support to the view that dopamine D1 receptors and/or dopamine D2 receptors in the lateral palisade zone by mediating dopamine volume transmission may contribute to the inhibition of luteinizing hormone releasing hormone release from nerve terminals in this region.

Mechanistic insights on spider neurotoxins.

PubMed

Luch, Andreas

2010-01-01

In physiology research, animal neurotoxins historically have served as valuable tools for identification, purification, and functional characterization of voltage-dependent ion channels. In particular, toxins from scorpions, sea anemones and cone snails were at the forefront of work aimed at illuminating the three-dimensional architecture of sodium channels. To date, at least six different receptor binding sites have been identified and--most of them--structurally assigned in terms of protein sequence and spatial disposition. Recent work on Australian funnel-web spiders identified certain peptidic ingredients as being responsible for the neurotoxicity of the crude venom. These peptides, termed delta-atracotoxins (delta-ACTX), consist of 42 amino acids and bind to voltage-gated sodium channels in the same way as classical scorpion alpha-toxins. According to the 'voltage-sensor trapping model' proposed in the literature, delta-ACTX isoforms interact with the voltage sensor S4 transmembrane segment of alpha-subunit domain IV, thereby preventing its normal outward movement and concurrent conformational changes required for inactivation of the channel. As consequence prolonged action potentials at autonomic or somatic synapses induce massive transmitter release, resulting in clinical correlates of neuroexcitation (e.g., muscle fasciculation, spasms, paresthesia, tachycardia, diaphoresis, etc.). On the other hand, the major neurotoxin isolated from black widow spiders, alpha-latrotoxin (alpha-LTX), represents a 132 kDa protein consisting of a unique N-terminal sequence and a C-terminal part harboring multiple ankyrin-like repeats. Upon binding to one of its specific presynaptic receptors, alpha-LTX has been shown to tetramerize under physiological conditions to form Ca2+-permeable pores in presynaptic membranes. The molecular model worked out during recent years separates two distinguishable receptor-mediated effects. According to current knowledge, binding of the N terminus of alpha-LTX at one of its specific receptors either triggers intracellular signaling cascades, resulting in phospholipase C-mediated mobilization of presynaptic Ca2+ stores, or leads to the formation of tetrameric pore complexes, allowing extracellular Ca2+ to enter the presynaptic terminal. Alpha-LTX-triggered exocytosis and fulminant transmitter release at autonomic synapses may then provoke a clinical syndrome referred to as 'latrodectism', characterized by local and incapacitating pain, diaphoresis, muscle fasciculation, tremor, anxiety, and so forth. The present review aims at providing a short introduction into some of the exciting molecular effects induced by neurotoxins isolated from black widow and funnel-web spiders.

Serotonin in the solitary tract nucleus shortens the laryngeal chemoreflex in anaesthetized neonatal rats.

PubMed

Donnelly, William T; Bartlett, Donald; Leiter, J C

2016-07-01

What is the central question of this study? Failure to terminate apnoea and arouse is likely to contribute to sudden infant death syndrome (SIDS). Serotonin is deficient in the brainstems of babies who died of SIDS. Therefore, we tested the hypothesis that serotonin in the nucleus of the solitary tract (NTS) would shorten reflex apnoea. What is the main finding and its importance? Serotonin microinjected into the NTS shortened the apnoea and respiratory inhibition associated with the laryngeal chemoreflex. Moreover, this effect was achieved through a 5-HT3 receptor. This is a new insight that is likely to be relevant to the pathogenesis of SIDS. The laryngeal chemoreflex (LCR), an airway-protective reflex that causes apnoea and bradycardia, has long been suspected as an initiating event in the sudden infant death syndrome. Serotonin (5-HT) and 5-HT receptors may be deficient in the brainstems of babies who die of sudden infant death syndrome, and 5-HT seems to be important in terminating apnoeas directly or in causing arousals or as part of the process of autoresuscitation. We hypothesized that 5-HT in the brainstem would limit the duration of the LCR. We studied anaesthetized rat pups between 7 and 21 days of age and made microinjections into the cisterna magna or into the nucleus of the solitary tract (NTS). Focal, bilateral microinjections of 5-HT into the caudal NTS significantly shortened the LCR. The 5-HT1a receptor antagonist, WAY 100635, did not affect the LCR consistently, nor did a 5-HT2 receptor antagonist, ketanserin, alter the duration of the LCR. The 5-HT3 specific agonist, 1-(3-chlorophenyl)-biguanide, microinjected bilaterally into the caudal NTS significantly shortened the LCR. Thus, endogenous 5-HT released within the NTS may curtail the respiratory depression that is part of the LCR, and serotonergic shortening of the LCR may be attributed to activation of 5-HT3 receptors within the NTS. 5-HT3 receptors are expressed presynaptically on C fibre afferents of the superior laryngeal nerve, and serotonergic shortening of the LCR may be mediated presynaptically by enhanced activation of inhibitory interneurons within the NTS. © 2016 The Authors. Experimental Physiology © 2016 The Physiological Society.

Palisade endings in extraocular muscles of the monkey are immunoreactive for choline acetyltransferase and vesicular acetylcholine transporter.

PubMed

Konakci, Kadriye Zeynep; Streicher, Johannes; Hoetzenecker, Wolfram; Haberl, Ines; Blumer, Michael Josef Franz; Wieczorek, Grazyna; Meingassner, Josef Gottfried; Paal, Szabolcs Levente; Holzinger, Daniel; Lukas, Julius-Robert; Blumer, Roland

2005-12-01

To analyze palisade endings in extraocular muscles (EOMs) of a primate species and to examine our previous findings in cat that palisade endings are putative effector organs. Eleven monkeys (Macaca fascicularis) of both sexes, between 4 and 6 years of age were analyzed. Whole EOM myotendons were immunostained with four combinations of triple-fluorescent labeling and examined by confocal laser scanning microscopy. Labeling included antibodies against choline acetyltransferase (ChAT), vesicular acetylcholine transporter (VAChT), neurofilament, and synaptophysin. Muscle fibers were counterstained with phalloidin. Palisade endings were observed in all monkey EOMs. Nerve fibers extended from the muscle into the tendon and looped back to divide into a terminal arborization (palisade ending) around a single muscle fiber tip. In approximately 30% of the cases, nerve fibers supplying palisade endings often established motor terminals outside the palisade complex. Nerve fibers forming palisade endings were ChAT-neurofilament positive. Axonal branches of palisade endings were ChAT-neurofilament positive as well. All palisade nerve terminals exhibited ChAT-synaptophysin immunoreactivity. Within the palisade complex, palisade nerve terminals exhibited VAChT immunoreactivity. All palisade nerve terminals were VAChT-synaptophysin immunoreactive. The results confirm that in the monkey, palisade endings contain acetylcholine and are therefore most likely effector organs. Palisade endings are also present in human EOMs and because of their location at the myotendinous junction, these organs are of crucial interest for strabismus surgery.

GLT-1: The elusive presynaptic glutamate transporter

PubMed Central

Rimmele, Theresa S.; Rosenberg, Paul A.

2016-01-01

Historically, glutamate uptake in the CNS was mainly attributed to glial cells for three reasons: 1) none of the glutamate transporters were found to be located in presynaptic terminals of excitatory synapses; 2) the putative glial transporters, GLT-1 and GLAST are expressed at high levels in astrocytes; 3) studies of the constitutive GLT-1 knockout as well as pharmacological studies demonstrated that >90% of glutamate uptake into forebrain synaptosomes is mediated by the operation of GLT-1. Here we summarize the history leading up to the recognition of GLT-1a as a presynaptic glutamate transporter. A major issue now is understanding the physiological and pathophysiologial significance of the expression of GLT-1 in presynaptic terminals. To elucidate the cell-type specific functions of GLT-1, a conditional knockout was generated with which to inactivate the GLT-1 gene in different cell types using Cre/lox technology. Astrocytic knockout led to an 80% reduction of GLT-1 expression, resulting in intractable seizures and early mortality as seen also in the constitutive knockout. Neuronal knockout was associated with no obvious phenotype. Surprisingly, synaptosomal uptake capacity (Vmax) was found to be significantly reduced, by 40%, in the neuronal knockout, indicating that the contribution of neuronal GLT-1 to synaptosomal uptake is disproportionate to its protein expression (5–10%). Conversely, the contribution of astrocytic GLT-1 to synaptosomal uptake was much lower than expected. In contrast, the loss of uptake into liposomes prepared from brain protein from astrocyte and neuronal knockouts was proportionate with the loss of GLT-1 protein, suggesting that a large portion of GLT-1 in astrocytic membranes in synaptosomal preparations is not functional, possibly because of a failure to reseal. These results suggest the need to reinterpret many previous studies using synaptosomal uptake to investigate glutamate transport itself as well as changes in glutamate homeostasis associated with normal functions, neurodegeneration, and response to drugs. PMID:27129805

Molecular Machines Determining the Fate of Endocytosed Synaptic Vesicles in Nerve Terminals

PubMed Central

Fassio, Anna; Fadda, Manuela; Benfenati, Fabio

2016-01-01

The cycle of a synaptic vesicle (SV) within the nerve terminal is a step-by-step journey with the final goal of ensuring the proper synaptic strength under changing environmental conditions. The SV cycle is a precisely regulated membrane traffic event in cells and, because of this, a plethora of membrane-bound and cytosolic proteins are devoted to assist SVs in each step of the journey. The cycling fate of endocytosed SVs determines both the availability for subsequent rounds of release and the lifetime of SVs in the terminal and is therefore crucial for synaptic function and plasticity. Molecular players that determine the destiny of SVs in nerve terminals after a round of exo-endocytosis are largely unknown. Here we review the functional role in SV fate of phosphorylation/dephosphorylation of SV proteins and of small GTPases acting on membrane trafficking at the synapse, as they are emerging as key molecules in determining the recycling route of SVs within the nerve terminal. In particular, we focus on: (i) the cyclin-dependent kinase-5 (cdk5) and calcineurin (CN) control of the recycling pool of SVs; (ii) the role of small GTPases of the Rab and ADP-ribosylation factor (Arf) families in defining the route followed by SV in their nerve terminal cycle. These regulatory proteins together with their synaptic regulators and effectors, are molecular nanomachines mediating homeostatic responses in synaptic plasticity and potential targets of drugs modulating the efficiency of synaptic transmission. PMID:27242505

Molecular Machines Determining the Fate of Endocytosed Synaptic Vesicles in Nerve Terminals.

PubMed

Fassio, Anna; Fadda, Manuela; Benfenati, Fabio

2016-01-01

The cycle of a synaptic vesicle (SV) within the nerve terminal is a step-by-step journey with the final goal of ensuring the proper synaptic strength under changing environmental conditions. The SV cycle is a precisely regulated membrane traffic event in cells and, because of this, a plethora of membrane-bound and cytosolic proteins are devoted to assist SVs in each step of the journey. The cycling fate of endocytosed SVs determines both the availability for subsequent rounds of release and the lifetime of SVs in the terminal and is therefore crucial for synaptic function and plasticity. Molecular players that determine the destiny of SVs in nerve terminals after a round of exo-endocytosis are largely unknown. Here we review the functional role in SV fate of phosphorylation/dephosphorylation of SV proteins and of small GTPases acting on membrane trafficking at the synapse, as they are emerging as key molecules in determining the recycling route of SVs within the nerve terminal. In particular, we focus on: (i) the cyclin-dependent kinase-5 (cdk5) and calcineurin (CN) control of the recycling pool of SVs; (ii) the role of small GTPases of the Rab and ADP-ribosylation factor (Arf) families in defining the route followed by SV in their nerve terminal cycle. These regulatory proteins together with their synaptic regulators and effectors, are molecular nanomachines mediating homeostatic responses in synaptic plasticity and potential targets of drugs modulating the efficiency of synaptic transmission.

Selective binding, uptake, and retrograde transport of tetanus toxin by nerve terminals in the rat iris. An electron microscope study using colloidal gold as a tracer

PubMed Central

1978-01-01

A series of specific macromolecules (tetanus toxin, cholera toxin, nerve growth factor [NGF], and several lectins) have been shown to be transported retrogradely with high selectivity from terminals to cell bodies in various types of neurons. Under identical experimental conditions (low protein concentrations injected), most other macromolecules, e.g. horseradish peroxidase (HRP), albumin, ferritin, are not transported in detectable amounts. In the present EM study, we demonstrate selective binding of tetanus toxin to the surface membrane of nerve terminals, followed by uptake and subsequent retorgrade axonal transport. Tetanus toxin or albumin was adsorbed to colloidal gold particles (diam 200 A). The complex was shown to be stable and well suited as an EM tracer. 1-4 h after injection into the anterior eye chamber of adult rats, tetanus toxin-gold particles were found to be selectively associated with membranes of nerve terminals and preterminal axons. Inside terminals and axons, the tracer was localized mainly in smooth endoplasmic reticulum (SER)-like membrane compartments. In contrast, association of albumin-gold complexes with nervous structures was never observed, in spite of extensive uptake into fibroblasts. Electron microscope and biochemical experiments showed selective retrograde transport of tetanus toxin-gold complexes to the superior cervical ganglion. Specific binding to membrane components at nerve terminals and subsequent internalization and retrograde transport may represent an important pathway for macromolecules carrying information from target organs to the perikarya of their innervating neurons. PMID:659508

What Is Transmitted in "Synaptic Transmission"?

ERIC Educational Resources Information Center

Montagna, Erik; de Azevedo, Adriana M. S.; Romano, Camilla; Ranvaud, Ronald

2010-01-01

Even students that obtain a high grade in neurophysiology often carry away a serious misconception concerning the final result of the complex set of events that follows the arrival of an action potential at the presynaptic terminal. The misconception consists in considering that "at a synapse, information is passed on from one neuron to the next"…

THE EFFECT OF GESTATIONAL MERCURY VAPOR EXPOSURE ON RAT BRAIN A-SYNUCLEIN EXPRESSION.

EPA Science Inventory

Alpha-synuclein is a highly conserved protein that localizes to pre-synaptic terminals and is thought to play a role in neuronal plasticity. It is upregulated developmentally and continues to be expressed at high levels in the adult brain. Its presence in a number of neuronal (A...

The C-terminal heavy-chain domain of botulinum neurotoxin a is not the only site that binds neurons, as the N-terminal heavy-chain domain also plays a very active role in toxin-cell binding and interactions.

PubMed

Ayyar, B Vijayalakshmi; Aoki, K Roger; Atassi, M Zouhair

2015-04-01

Botulinum neurotoxins (BoNTs) possess unique specificity for nerve terminals. They bind to the presynaptic membrane and then translocate intracellularly, where the light-chain endopeptidase cleaves the SNARE complex proteins, subverting the synaptic exocytosis responsible for acetylcholine release to the synaptic cleft. This inhibits acetylcholine binding to its receptor, causing paralysis. Binding, an obligate event for cell intoxication, is believed to occur through the heavy-chain C-terminal (HC) domain. It is followed by toxin translocation and entry into the cell cytoplasm, which is thought to be mediated by the heavy-chain N-terminal (HN) domain. Submolecular mapping analysis by using synthetic peptides spanning BoNT serotype A (BoNT/A) and mouse brain synaptosomes (SNPs) and protective antibodies against toxin from mice and cervical dystonia patients undergoing BoNT/A treatment revealed that not only regions of the HC domain but also regions of the HN domain are involved in the toxin binding process. Based on these findings, we expressed a peptide corresponding to the BoNT/A region comprising HN domain residues 729 to 845 (HN729-845). HN729-845 bound directly to mouse brain SNPs and substantially inhibited BoNT/A binding to SNPs. The binding involved gangliosides GT1b and GD1a and a few membrane lipids. The peptide bound to human or mouse neuroblastoma cells within 1 min. Peptide HN729-845 protected mice completely against a lethal BoNT/A dose (1.05 times the 100% lethal dose). This protective activity was obtained at a dose comparable to that of the peptide from positions 967 to 1296 in the HC domain. These findings strongly indicate that HN729-845 and, by extension, the HN domain are fully programmed and equipped to bind to neuronal cells and in the free state can even inhibit the binding of the toxin. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

Relative roles of different mechanisms of depression at the mouse endbulb of Held

PubMed Central

Yang, Hua; Xu-Friedman, Matthew A.

2010-01-01

Several mechanisms can underlie short-term synaptic depression, including vesicle depletion, receptor desensitization, and changes in presynaptic release probability. To determine which mechanisms affect depression under physiological conditions, we studied the synapse formed by auditory nerve fibers onto bushy cells in the anteroventral cochlear nucleus (the “endbulb of Held”) using voltage-clamp recordings of brain slices from P15–21 mice near physiological temperatures. Depression of both AMPA and NMDA EPSCs showed two phases of recovery. The fast component of depression for the AMPA EPSC was eliminated by cyclothiazide and aniracetam, suggesting it results from desensitization. The fast component of depression for the NMDA EPSC was reduced by the low-affinity antagonist L-AP5, suggesting it results from saturation. The remaining depression in AMPA and NMDA components is identical and therefore presynaptic in origin. It is likely to result from presynaptic vesicle depletion. Recovery from depression after trains of activity was slowed by the application of EGTA-AM, suggesting that the endbulb has a residual-calcium-dependent form of recovery. We developed a model that incorporates depletion, desensitization, and calcium-dependent recovery. This model replicated experimental findings over a range of experimental conditions. The model further indicated that desensitization plays only a minor role during prolonged activity, in large part because presynaptic release is so depleted. Thus, depletion appears to be the dominant mechanism of depression at the endbulb during normal activity. Furthermore, calcium-dependent recovery at the endbulb is critical to prevent complete run-down during high activity and to preserve the reliability of information transmission. PMID:18367696

Protons are a neurotransmitter that regulates synaptic plasticity in the lateral amygdala

PubMed Central

Du, Jianyang; Reznikov, Leah R.; Price, Margaret P.; Zha, Xiang-ming; Lu, Yuan; Moninger, Thomas O.; Wemmie, John A.; Welsh, Michael J.

2014-01-01

Stimulating presynaptic terminals can increase the proton concentration in synapses. Potential receptors for protons are acid-sensing ion channels (ASICs), Na+- and Ca2+-permeable channels that are activated by extracellular acidosis. Those observations suggest that protons might be a neurotransmitter. We found that presynaptic stimulation transiently reduced extracellular pH in the amygdala. The protons activated ASICs in lateral amygdala pyramidal neurons, generating excitatory postsynaptic currents. Moreover, both protons and ASICs were required for synaptic plasticity in lateral amygdala neurons. The results identify protons as a neurotransmitter, and they establish ASICs as the postsynaptic receptor. They also indicate that protons and ASICs are a neurotransmitter/receptor pair critical for amygdala-dependent learning and memory. PMID:24889629

Morphology of presumptive rapidly adapting receptors in the rat bronchus.

PubMed Central

Kappagoda, C T; Skepper, J N; McNaughton, L; Siew, E E; Navaratnam, V

1990-01-01

The present investigation was undertaken in rats to determine whether sensory nerves exist in apposition to the bronchial microvessels which may function as rapidly adapting receptors (RAR). The primary and secondary bronchi on both sides were removed and processed for light and electron microscopy. Nerves were frequently found in relation to venules external to the muscle coat of bronchi. They comprised myelinated axons which ended individually as non-myelinated convoluted terminals enclosed within a loose capsule of attenuated cells. Serial sections showed that these terminals were not related to ganglion cells. Cervical vagal section and injection of HRP-WGA into the nodose ganglion provided corroborative evidence of the sensory nature of these terminals. Vagal section caused degenerative changes in the encapsulated nerve terminals in the bronchial walls and horseradish peroxidase labelling was demonstrable in such terminals. Moreover, immunocytochemical studies demonstrated the presence of calcitonin gene regulated peptide and substance P in these structures. It is suggested that they comprise the RAR. Encapsulated nerve terminals were not found in the epithelial layer, in the submucous coat or in the muscularis of bronchi. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10 Fig. 11 Fig. 12 PMID:1691164

Passive Diffusion as a Mechanism Underlying Ribbon Synapse Vesicle Release and Resupply

PubMed Central

Graydon, Cole W.; Zhang, Jun; Oesch, Nicholas W.; Sousa, Alioscka A.; Leapman, Richard D.

2014-01-01

Synaptic ribbons are presynaptic protein structures found at many synapses that convey graded, “analog” sensory signals in the visual, auditory, and vestibular pathways. Ribbons, typically anchored to the presynaptic membrane and surrounded by tethered synaptic vesicles, are thought to regulate or facilitate vesicle delivery to the presynaptic membrane. No direct evidence exists, however, to indicate how vesicles interact with the ribbon or, once attached, move along the ribbon's surface to reach the presynaptic release sites at its base. To address these questions, we have created, validated, and tested a passive vesicle diffusion model of retinal rod bipolar cell ribbon synapses. We used axial (bright-field) electron tomography in the scanning transmission electron microscopy to obtain 3D structures of rat rod bipolar cell terminals in 1-μm-thick sections of retinal tissue at an isotropic spatial resolution of ∼3 nm. The resulting structures were then incorporated with previously published estimates of vesicle diffusion dynamics into numerical simulations that accurately reproduced electrophysiologically measured vesicle release/replenishment rates and vesicle pool sizes. The simulations suggest that, under physiologically realistic conditions, diffusion of vesicles crowded on the ribbon surface gives rise to a flow field that enhances delivery of vesicles to the presynaptic membrane without requiring an active transport mechanism. Numerical simulations of ribbon–vesicle interactions predict that transient binding and unbinding of multiple tethers to each synaptic vesicle may achieve sufficiently tight association of vesicles to the ribbon while permitting the fast diffusion along the ribbon that is required to sustain high release rates. PMID:24990916

Passive diffusion as a mechanism underlying ribbon synapse vesicle release and resupply.

PubMed

Graydon, Cole W; Zhang, Jun; Oesch, Nicholas W; Sousa, Alioscka A; Leapman, Richard D; Diamond, Jeffrey S

2014-07-02

Synaptic ribbons are presynaptic protein structures found at many synapses that convey graded, "analog" sensory signals in the visual, auditory, and vestibular pathways. Ribbons, typically anchored to the presynaptic membrane and surrounded by tethered synaptic vesicles, are thought to regulate or facilitate vesicle delivery to the presynaptic membrane. No direct evidence exists, however, to indicate how vesicles interact with the ribbon or, once attached, move along the ribbon's surface to reach the presynaptic release sites at its base. To address these questions, we have created, validated, and tested a passive vesicle diffusion model of retinal rod bipolar cell ribbon synapses. We used axial (bright-field) electron tomography in the scanning transmission electron microscopy to obtain 3D structures of rat rod bipolar cell terminals in 1-μm-thick sections of retinal tissue at an isotropic spatial resolution of ∼3 nm. The resulting structures were then incorporated with previously published estimates of vesicle diffusion dynamics into numerical simulations that accurately reproduced electrophysiologically measured vesicle release/replenishment rates and vesicle pool sizes. The simulations suggest that, under physiologically realistic conditions, diffusion of vesicles crowded on the ribbon surface gives rise to a flow field that enhances delivery of vesicles to the presynaptic membrane without requiring an active transport mechanism. Numerical simulations of ribbon-vesicle interactions predict that transient binding and unbinding of multiple tethers to each synaptic vesicle may achieve sufficiently tight association of vesicles to the ribbon while permitting the fast diffusion along the ribbon that is required to sustain high release rates. Copyright © 2014 the authors 0270-6474/14/348948-15$15.00/0.

The Biogenic Amine Tyramine and its Receptor (AmTyr1) in Olfactory Neuropils in the Honey Bee (Apis mellifera) Brain

PubMed Central

Sinakevitch, Irina T.; Daskalova, Sasha M.; Smith, Brian H.

2017-01-01

This article describes the cellular sources for tyramine and the cellular targets of tyramine via the Tyramine Receptor 1 (AmTyr1) in the olfactory learning and memory neuropils of the honey bee brain. Clusters of approximately 160 tyramine immunoreactive neurons are the source of tyraminergic fibers with small varicosities in the optic lobes, antennal lobes, lateral protocerebrum, mushroom body (calyces and gamma lobes), tritocerebrum and subesophageal ganglion (SEG). Our tyramine mapping study shows that the primary sources of tyramine in the antennal lobe and calyx of the mushroom body are from at least two Ventral Unpaired Median neurons (VUMmd and VUMmx) with cell bodies in the SEG. To reveal AmTyr1 receptors in the brain, we used newly characterized anti-AmTyr1 antibodies. Immunolocalization studies in the antennal lobe with anti-AmTyr1 antibodies showed that the AmTyr1 expression pattern is mostly in the presynaptic sites of olfactory receptor neurons (ORNs). In the mushroom body calyx, anti-AmTyr1 mapped the presynaptic sites of uniglomerular Projection Neurons (PNs) located primarily in the microglomeruli of the lip and basal ring calyx area. Release of tyramine/octopamine from VUM (md and mx) neurons in the antennal lobe and mushroom body calyx would target AmTyr1 expressed on ORN and uniglomerular PN presynaptic terminals. The presynaptic location of AmTyr1, its structural similarity with vertebrate alpha-2 adrenergic receptors, and previous pharmacological evidence suggests that it has an important role in the presynaptic inhibitory control of neurotransmitter release. PMID:29114209

Effect of capsaicin on thermoregulation: an update with new aspects

PubMed Central

Szolcsányi, János

2015-01-01

Capsaicin, a selective activator of the chemo- and heat-sensitive transient receptor potential (TRP) V1 cation channel, has characteristic feature of causing long-term functional and structural impairment of neural elements supplied by TRPV1/capsaicin receptor. In mammals, systemic application of capsaicin induces complex heat-loss response characteristic for each species and avoidance of warm environment. Capsaicin activates cutaneous warm receptors and polymodal nociceptors but has no effect on cold receptors or mechanoreceptors. In this review, thermoregulatory features of capsaicin-pretreated rodents and TRPV1-mediated neural elements with innocuous heat sensitivity are summarized. Recent data support a novel hypothesis for the role of visceral warmth sensors in monitoring core body temperature. Furthermore, strong evidence suggests that central presynaptic nerve terminals of TRPV1-expressing cutaneous, thoracic and abdominal visceral receptors are activated by innocuous warmth stimuli and capsaicin. These responses are absent in TRPV1 knockout mice. Thermoregulatory disturbance induced by systemic capsaicin pretreatment lasts for months and is characterized by a normal body temperature at cool environment up to a total dose of 150 mg/kg s.c. Upward differential shift of set points for activation vasodilation, other heat-loss effectors and thermopreference develops. Avoidance of warm ambient temperature (35°C, 40°C) is severely impaired but thermopreference at cool ambient temperatures (Tas) are not altered. TRPV1 knockout or knockdown and genetically altered TRPV1, TRPV2 and TRPM8 knockout mice have normal core temperature in thermoneutral or cool environments, but the combined mutant mice have impaired regulation in warm or cold (4°C) environments. Several lines of evidence support that in the preoptic area warmth sensitive neurons are activated and desensitized by capsaicin, but morphological evidence for it is controversial. It is suggested that these neurons have also integrator function. Fever is enhanced in capsaicin-desensitized rats and the inhibition observed after pretreatment with low i.p. doses does not support in the light of their warmth sensitivity the concept that abdominal TRPV1-expressing nerve terminals serve as nonthermal chemosensors for reference signals in thermoregulation. PMID:27227029

Drosophila Syd-1, Liprin-α, and Protein Phosphatase 2A B′ Subunit Wrd Function in a Linear Pathway to Prevent Ectopic Accumulation of Synaptic Materials in Distal Axons

PubMed Central

Li, Long; Tian, Xiaolin; Zhu, Mingwei; Bulgari, Dinara; Böhme, Mathias A.; Goettfert, Fabian; Wichmann, Carolin; Sigrist, Stephan J.; Levitan, Edwin S.

2014-01-01

During synaptic development, presynaptic differentiation occurs as an intrinsic property of axons to form specialized areas of plasma membrane [active zones (AZs)] that regulate exocytosis and endocytosis of synaptic vesicles. Genetic and biochemical studies in vertebrate and invertebrate model systems have identified a number of proteins involved in AZ assembly. However, elucidating the molecular events of AZ assembly in a spatiotemporal manner remains a challenge. Syd-1 (synapse defective-1) and Liprin-α have been identified as two master organizers of AZ assembly. Genetic and imaging analyses in invertebrates show that Syd-1 works upstream of Liprin-α in synaptic assembly through undefined mechanisms. To understand molecular pathways downstream of Liprin-α, we performed a proteomic screen of Liprin-α-interacting proteins in Drosophila brains. We identify Drosophila protein phosphatase 2A (PP2A) regulatory subunit B′ [Wrd (Well Rounded)] as a Liprin-α-interacting protein, and we demonstrate that it mediates the interaction of Liprin-α with PP2A holoenzyme and the Liprin-α-dependent synaptic localization of PP2A. Interestingly, loss of function in syd-1, liprin-α, or wrd shares a common defect in which a portion of synaptic vesicles, dense-core vesicles, and presynaptic cytomatrix proteins ectopically accumulate at the distal, but not proximal, region of motoneuron axons. Strong genetic data show that a linear syd-1/liprin-α/wrd pathway in the motoneuron antagonizes glycogen synthase kinase-3β kinase activity to prevent the ectopic accumulation of synaptic materials. Furthermore, we provide data suggesting that the syd-1/liprin-α/wrd pathway stabilizes AZ specification at the nerve terminal and that such a novel function is independent of the roles of syd-1/liprin-α in regulating the morphology of the T-bar structural protein BRP (Bruchpilot). PMID:24948803

Drosophila Syd-1, liprin-α, and protein phosphatase 2A B' subunit Wrd function in a linear pathway to prevent ectopic accumulation of synaptic materials in distal axons.

PubMed

Li, Long; Tian, Xiaolin; Zhu, Mingwei; Bulgari, Dinara; Böhme, Mathias A; Goettfert, Fabian; Wichmann, Carolin; Sigrist, Stephan J; Levitan, Edwin S; Wu, Chunlai

2014-06-18

During synaptic development, presynaptic differentiation occurs as an intrinsic property of axons to form specialized areas of plasma membrane [active zones (AZs)] that regulate exocytosis and endocytosis of synaptic vesicles. Genetic and biochemical studies in vertebrate and invertebrate model systems have identified a number of proteins involved in AZ assembly. However, elucidating the molecular events of AZ assembly in a spatiotemporal manner remains a challenge. Syd-1 (synapse defective-1) and Liprin-α have been identified as two master organizers of AZ assembly. Genetic and imaging analyses in invertebrates show that Syd-1 works upstream of Liprin-α in synaptic assembly through undefined mechanisms. To understand molecular pathways downstream of Liprin-α, we performed a proteomic screen of Liprin-α-interacting proteins in Drosophila brains. We identify Drosophila protein phosphatase 2A (PP2A) regulatory subunit B' [Wrd (Well Rounded)] as a Liprin-α-interacting protein, and we demonstrate that it mediates the interaction of Liprin-α with PP2A holoenzyme and the Liprin-α-dependent synaptic localization of PP2A. Interestingly, loss of function in syd-1, liprin-α, or wrd shares a common defect in which a portion of synaptic vesicles, dense-core vesicles, and presynaptic cytomatrix proteins ectopically accumulate at the distal, but not proximal, region of motoneuron axons. Strong genetic data show that a linear syd-1/liprin-α/wrd pathway in the motoneuron antagonizes glycogen synthase kinase-3β kinase activity to prevent the ectopic accumulation of synaptic materials. Furthermore, we provide data suggesting that the syd-1/liprin-α/wrd pathway stabilizes AZ specification at the nerve terminal and that such a novel function is independent of the roles of syd-1/liprin-α in regulating the morphology of the T-bar structural protein BRP (Bruchpilot). Copyright © 2014 the authors 0270-6474/14/348474-14$15.00/0.

Presynaptic M1, M2, and A1 receptors play roles in tetanic fade induced by pancuronium or cisatracurium.

PubMed

Bornia, Elaine Campana Sanches; Bando, Erika; Machinski, Miguel; Pereira, Monalisa Wolski; Alves-Do-Prado, Wilson

2009-01-01

We investigated whether presynaptic facilitatory M1 and/or inhibitory M2 muscarinic receptors contributed to pancuronium- and cisatracurium-induced tetanic fade. Phrenic nerve-diaphragm muscle preparations of rats were indirectly stimulated with tetanic frequency (75 +/- 3.3 Hz; mean +/- SD). Doses of pancuronium, cisatracurium, hexamethonium, and d-tubocurarine for producing approximately 25% fade were determined. The effects of pirenzepine and methoctramine, blockers of presynaptic M1 and M2 receptors, respectively, on the tetanic fade were investigated. The concentrations required for approximately 25% fade were 413 microM for hexamethonium (26.8 +/- 2.4% 4% fade), 55 nM for d-tubocurarine (28.7 +/- 2.55% fade), 0.32 microM for pancuronium (25.4 +/- 2.2% fade), and 0.32 microM for cisatracurium (24.7 +/- 0.8% fade). Pirenzepine or methoctramine alone did not produce the fade. Methoctramine, 1 microM, attenuated the fade induced by hexamethonium (to 16.0 +/- 2.5% fade), d-tubocurarine (to 6.0 +/- 1.6 fade), pancuronium (to 8.0 +/- 4.0% fade), and cisatracurium (to 11.0 +/- 3.3% fade). 10 nM pirenzepine attenuated only the fades produced by pancuronium (to 5.0 +/- 0.11% fade) and cisatracurium (to 13.3 +/- 5.3% fade). Cisatracurium (0.32 microM) showed antiacetylcholinesterase activity (in plasma, 14.2 +/- 1.6%; 6%; in erythrocyt 17.2 +/- 2.66%) similar to that of pancuronium (0.32 microM). The selective A1 receptor blocker, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 2.5 nM), also attenuated the fades induced by pancuronium and cisatracurium. The tetanic fades produced by pancuronium and cisatracurium depend on the activation of presynaptic inhibitory M2 receptors; these agents also have anticholinesterase activities. The fades induced by these agents also depend on the activation of presynaptic inhibitory A1 receptors through the activation of stimulatory M1 receptors by acetylcholine.

Palisade endings are present in canine extraocular muscles and have a cholinergic phenotype

PubMed Central

RUNGALDIER, Stefanie; POMIKAL, Christine; STREICHER, Johannes; BLUMER, Roland

2016-01-01

Classical proprioceptors, like Golgi tendon organs and muscle spindles are absent in the extraocular muscles (EOMs) of most mammals. Instead, a nerve end organ was detected in the EOMs of each species including sheep, cats, rabbits, rats, monkeys, and man examined so far: the palisade ending. Until now no evidence appeared that palisade endings are present in canine EOMs. We analyzed dog EOMs by confocal laser scanning microscopy, 3D reconstruction, and transmission electron microscopy. In EOM wholemount preparations stained with antibodies against neurofilament and synaptophysin we found typical palisade endings. Nerve fibers coming from the muscle extended into the tendon. There, the nerve fibers turned 180° and returned to branch into preterminal axons which established nerve terminals around a single muscle fiber tip. Fine structural analyses revealed that each palisade ending in dog EOMs established nerve terminals on the tendon. In some palisade endings we found nerve terminals contacting the muscle fiber as well. Such neuromuscular contacts had a basal lamina in the synaptic cleft thereby resembling motor terminals. By using antibodies against choline acetyltransferase (ChAT) we proved that canine palisade endings are ChAT-immunoreactive. This study shows that palisade endings are present in canine EOMs. In line with prior findings in cat and monkey, palisade endings in dog have a cholinergic phenotype. PMID:19766165

Compartmentalized beta subunit distribution determines characteristics and ethanol sensitivity of somatic, dendritic, and terminal large-conductance calcium-activated potassium channels in the rat central nervous system.

PubMed

Wynne, P M; Puig, S I; Martin, G E; Treistman, S N

2009-06-01

Neurons are highly differentiated and polarized cells, whose various functions depend upon the compartmentalization of ion channels. The rat hypothalamic-neurohypophysial system (HNS), in which cell bodies and dendrites reside in the hypothalamus, physically separated from their nerve terminals in the neurohypophysis, provides a particularly powerful preparation in which to study the distribution and regional properties of ion channel proteins. Using electrophysiological and immunohistochemical techniques, we characterized the large-conductance calcium-activated potassium (BK) channel in each of the three primary compartments (soma, dendrite, and terminal) of HNS neurons. We found that dendritic BK channels, in common with somatic channels but in contrast to nerve terminal channels, are insensitive to iberiotoxin. Furthermore, analysis of dendritic BK channel gating kinetics indicates that they, like somatic channels, have fast activation kinetics, in contrast to the slow gating of terminal channels. Dendritic and somatic channels are also more sensitive to calcium and have a greater conductance than terminal channels. Finally, although terminal BK channels are highly potentiated by ethanol, somatic and dendritic channels are insensitive to the drug. The biophysical and pharmacological properties of somatic and dendritic versus nerve terminal channels are consistent with the characteristics of exogenously expressed alphabeta1 versus alphabeta4 channels, respectively. Therefore, one possible explanation for our findings is a selective distribution of auxiliary beta1 subunits to the somatic and dendritic compartments and beta4 to the terminal compartment. This hypothesis is supported immunohistochemically by the appearance of distinct punctate beta1 or beta4 channel clusters in the membrane of somatic and dendritic or nerve terminal compartments, respectively.

Homeostatic Presynaptic Plasticity Is Specifically Regulated by P/Q-type Ca2+ Channels at Mammalian Hippocampal Synapses.

PubMed

Jeans, Alexander F; van Heusden, Fran C; Al-Mubarak, Bashayer; Padamsey, Zahid; Emptage, Nigel J

2017-10-10

Voltage-dependent Ca 2+ channels (VGCC) represent the principal source of Ca 2+ ions driving evoked neurotransmitter release at presynaptic boutons. In mammals, presynaptic Ca 2+ influx is mediated mainly via P/Q-type and N-type VGCC, which differ in their properties. Changes in their relative contributions tune neurotransmission both during development and in Hebbian plasticity. However, whether this represents a functional motif also present in other forms of activity-dependent regulation is unknown. Here, we study the role of VGCC in homeostatic plasticity (HSP) in mammalian hippocampal neurons using optical techniques. We find that changes in evoked Ca 2+ currents specifically through P/Q-type, but not N-type, VGCC mediate bidirectional homeostatic regulation of both neurotransmitter release efficacy and the size of the major synaptic vesicle pools. Selective dependence of HSP on P/Q-type VGCC in mammalian terminals has important implications for phenotypes associated with P/Q-type channelopathies, including migraine and epilepsy. Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.

The epilepsy-linked Lgi1 protein assembles into presynaptic Kv1 channels and inhibits inactivation by Kvbeta1.

PubMed

Schulte, Uwe; Thumfart, Jörg-Oliver; Klöcker, Nikolaj; Sailer, Claudia A; Bildl, Wolfgang; Biniossek, Martin; Dehn, Doris; Deller, Thomas; Eble, Silke; Abbass, Karen; Wangler, Tanja; Knaus, Hans-Günther; Fakler, Bernd

2006-03-02

The voltage-gated potassium (Kv) channel subunit Kv1.1 is a major constituent of presynaptic A-type channels that modulate synaptic transmission in CNS neurons. Here, we show that Kv1.1-containing channels are complexed with Lgi1, the functionally unassigned product of the leucine-rich glioma inactivated gene 1 (LGI1), which is causative for an autosomal dominant form of lateral temporal lobe epilepsy (ADLTE). In the hippocampal formation, both Kv1.1 and Lgi1 are coassembled with Kv1.4 and Kvbeta1 in axonal terminals. In A-type channels composed of these subunits, Lgi1 selectively prevents N-type inactivation mediated by the Kvbeta1 subunit. In contrast, defective Lgi1 molecules identified in ADLTE patients fail to exert this effect resulting in channels with rapid inactivation kinetics. The results establish Lgi1 as a novel subunit of Kv1.1-associated protein complexes and suggest that changes in inactivation gating of presynaptic A-type channels may promote epileptic activity.

Increase of transcription factor EB (TFEB) and lysosomes in rat DRG neurons and their transportation to the central nerve terminal in dorsal horn after nerve injury.

PubMed

Jung, J; Uesugi, N; Jeong, N Y; Park, B S; Konishi, H; Kiyama, H

2016-01-28

In the spinal dorsal horn (DH), nerve injury activates microglia and induces neuropathic pain. Several studies clarified an involvement of adenosine triphosphate (ATP) in the microglial activation. However, the origin of ATP together with the release mechanism is unclear. Recent in vitro study revealed that an ATP marker, quinacrine, in lysosomes was released from neurite terminal of dorsal root ganglion (DRG) neurons to extracellular space via lysosomal exocytosis. Here, we demonstrate a possibility that the lysosomal ingredient including ATP released from DRG neurons by lysosomal-exocytosis is an additional source of the glial activation in DH after nerve injury. After rat L5 spinal nerve ligation (SNL), mRNA for transcription factor EB (TFEB), a transcription factor controlling lysosomal activation and exocytosis, was induced in the DRG. Simultaneously both lysosomal protein, LAMP1- and vesicular nuclear transporter (VNUT)-positive vesicles were increased in L5 DRG neurons and ipsilateral DH. The quinacrine staining in DH was increased and co-localized with LAMP1 immunoreactivity after nerve injury. In DH, LAMP1-positive vesicles were also co-localized with a peripheral nerve marker, Isolectin B4 (IB4) lectin. Injection of the adenovirus encoding mCherry-LAMP1 into DRG showed that mCherry-positive lysosomes are transported to the central nerve terminal in DH. These findings suggest that activation of lysosome synthesis including ATP packaging in DRG, the central transportation of the lysosome, and subsequent its exocytosis from the central nerve terminal of DRG neurons in response to nerve injury could be a partial mechanism for activation of microglia in DH. This lysosome-mediated microglia activation mechanism may provide another clue to control nociception and pain. Copyright © 2015 IBRO. Published by Elsevier Ltd. All rights reserved.

Contribution of presynaptic HCN channels to excitatory inputs of spinal substantia gelatinosa neurons.

PubMed

Peng, S-C; Wu, J; Zhang, D-Y; Jiang, C-Y; Xie, C-N; Liu, T

2017-09-01

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are pathological pain-associated voltage-gated ion channels. They are widely expressed in central nervous system including spinal lamina II (also named the substantia gelatinosa, SG). Here, we examined the distribution of HCN channels in glutamatergic synaptic terminals as well as their role in the modulation of synaptic transmission in SG neurons from SD rats and glutamic acid decarboxylase-67 (GAD67)-GFP mice. We found that the expression of the HCN channel isoforms was varied in SG. The HCN4 isoform showed the highest level of co-localization with VGLUT2 (23±3%). In 53% (n=21/40 neurons) of the SG neurons examined in SD rats, application of HCN channel blocker, ZD7288 (10μM), decreased the frequency of spontaneous (s) and miniature (m) excitatory postsynaptic currents (EPSCs) by 37±4% and 33±4%, respectively. Consistently, forskolin (FSK) (an activator of adenylate cyclase) significantly increased the frequency of mEPSCs by 225±34%, which could be partially inhibited by ZD7288. Interestingly, the effects of ZD7288 and FSK on sEPSC frequency were replicated in non-GFP-expressing neurons, but not in GFP-expressing GABAergic SG neurons, in GAD67-GFP transgenic C57/BL6 mice. In summary, our results represent a previously unknown cellular mechanism by which presynaptic HCN channels, especially HCN4, regulate the glutamate release from presynaptic terminals that target excitatory, but not inhibitory SG interneurons. Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.

Prejunctional and postjunctional actions of heptanol and 18 beta-glycyrretinic acid in the rodent vas deferens.

PubMed

Rahman, Faisal; Manchanda, Rohit; Brain, Keith L

2009-06-15

Heptanol and 18 beta-glycyrrhetinic acid (18 beta GA) block gap junctions, but have other actions on transmitter release that have not been characterised. This study investigates the prejunctional and postjunctional effects of these compounds in guinea pig and mouse vas deferens using intracellular electrophysiological recording and confocal Ca(2+) imaging of sympathetic nerve terminals. In mice, heptanol (2 mM) reversibly decreased the amplitude of purinergic excitatory junction potentials (EJPs; 52+/-5%, P<0.05) while having little effect on spontaneous excitatory junction potentials (sEJPs). Heptanol (2 mM) reversibly abolished the nerve terminal Ca(2+) transient in 52% of terminals. 18 beta GA (10 microM) decreased the mean EJP amplitude, and increased input resistance in both mouse (137+/-17%, P<0.05) and guinea pig (354+/-50%, P<0.001) vas deferens indicating gap junction blockade. Further, 18 beta GA increased the sEJP frequency significantly in guinea pigs (by 71+/-25%, P<0.05) and in 5 out of 6 tissues in mice (19+/-3%, P<0.05). Moreover, 18 beta GA depolarised cells from both mice (11+/-1%, P<0.01) and guinea pigs (8+/-1%, P<0.005). Therefore, we conclude that heptanol (2 mM) decreases neurotransmitter release (given the decrease in EJP amplitude) by abolishing the nerve terminal action potential in a proportion of nerve terminals. 18 betaGA (10 microM) effectively blocks the gap junctions, but the increase in sEJP frequency suggests an additional prejunctional effect, which might involve the induction of spontaneous nerve terminal action potentials.

[Experimental studies for the improvement of facial nerve regeneration].

PubMed

Guntinas-Lichius, O; Angelov, D N

2008-02-01

Using a combination of the following, it is possible to investigate procedures to improve the morphological and functional regeneration of the facial nerve in animal models: 1) retrograde fluorescence tracing to analyse collateral axonal sprouting and the selectivity of reinnervation of the mimic musculature, 2) immunohistochemistry to analyse both the terminal axonal sprouting in the muscles and the axon reaction within the nucleus of the facial nerve, the peripheral nerve, and its environment, and 3) digital motion analysis of the muscles. To obtain good functional facial nerve regeneration, a reduction of terminal sprouting in the mimic musculature seems to be more important than a reduction of collateral sprouting at the lesion site. Promising strategies include acceleration of nerve regeneration, forced induced use of the paralysed face, mechanical stimulation of the face, and transplantation of nerve-growth-promoting olfactory epithelium at the lesion site.

Cholesterol-Independent Effects of Methyl-β-Cyclodextrin on Chemical Synapses

PubMed Central

Ormerod, Kiel G.; Coorssen, Jens R.; Mercier, A. Joffre

2012-01-01

The cholesterol chelating agent, methyl-β-cyclodextrin (MβCD), alters synaptic function in many systems. At crayfish neuromuscular junctions, MβCD is reported to reduce excitatory junctional potentials (EJPs) by impairing impulse propagation to synaptic terminals, and to have no postsynaptic effects. We examined the degree to which physiological effects of MβCD correlate with its ability to reduce cholesterol, and used thermal acclimatization as an alternative method to modify cholesterol levels. MβCD impaired impulse propagation and decreased EJP amplitude by 40% (P<0.05) in preparations from crayfish acclimatized to 14°C but not from those acclimatized to 21°C. The reduction in EJP amplitude in the cold-acclimatized group was associated with a 49% reduction in quantal content (P<0.05). MβCD had no effect on input resistance in muscle fibers but decreased sensitivity to the neurotransmitter L-glutamate in both warm- and cold-acclimatized groups. This effect was less pronounced and reversible in the warm-acclimatized group (90% reduction in cold, P<0.05; 50% reduction in warm, P<0.05). MβCD reduced cholesterol in isolated nerve and muscle from cold- and warm-acclimatized groups by comparable amounts (nerve: 29% cold, 25% warm; muscle: 20% cold, 18% warm; P<0.05). This effect was reversed by cholesterol loading, but only in the warm-acclimatized group. Thus, effects of MβCD on glutamate-sensitivity correlated with its ability to reduce cholesterol, but effects on impulse propagation and resulting EJP amplitude did not. Our results indicate that MβCD can affect both presynaptic and postsynaptic properties, and that some effects of MβCD are unrelated to cholesterol chelation. PMID:22590538

A Role for Synapsin in Associative Learning: The "Drosophila" Larva as a Study Case

ERIC Educational Resources Information Center

Michels, Birgit; Diegelmann, Soren; Tanimoto, Hiromu; Schwenkert, Isabell; Buchner, Erich; Gerber, Bertram

2005-01-01

Synapsins are evolutionarily conserved, highly abundant vesicular phosphoproteins in presynaptic terminals. They are thought to regulate the recruitment of synaptic vesicles from the reserve pool to the readily-releasable pool, in particular when vesicle release is to be maintained at high spiking rates. As regulation of transmitter release is a…

Dysbindin-1 is reduced in intrinsic, glutamatergic terminals of the hippocampal formation in schizophrenia

PubMed Central

Talbot, Konrad; Eidem, Wess L.; Tinsley, Caroline L.; Benson, Matthew A.; Thompson, Edward W.; Smith, Rachel J.; Hahn, Chang-Gyu; Siegel, Steven J.; Trojanowski, John Q.; Gur, Raquel E.; Blake, Derek J.; Arnold, Steven E.

2004-01-01

Eleven studies now report significant associations between schizophrenia and certain haplotypes of single-nucleotide polymorphisms in the gene encoding dysbindin-1 at 6p22.3. Dysbindin-1 is best known as dystrobrevin-binding protein 1 (DTNBP1) and may thus be associated with the dystrophin glycoprotein complex found at certain postsynaptic sites in the brain. Contrary to expectations, however, we found that when compared to matched, nonpsychiatric controls, 73–93% of cases in two schizophrenia populations displayed presynaptic dysbindin-1 reductions averaging 18–42% (P = 0.027–0.0001) at hippocampal formation sites lacking neuronal dystrobrevin (i.e., β-dystrobrevin). The reductions, which were not observed in the anterior cingulate of the same schizophrenia cases, occurred specifically in terminal fields of intrinsic, glutamatergic afferents of the subiculum, the hippocampus proper, and especially the inner molecular layer of the dentate gyrus (DGiml). An inversely correlated increase in vesicular glutamate transporter-1 (VGluT-1) occurred in DGiml of the same schizophrenia cases. Those changes occurred without evidence of axon terminal loss or neuroleptic effects on dysbindin-1 or VGluT-1. Our findings indicate that presynaptic dysbindin-1 reductions independent of the dystrophin glycoprotein complex are frequent in schizophrenia and are related to glutamatergic alterations in intrinsic hippocampal formation connections. Such changes may contribute to the cognitive deficits common in schizophrenia. PMID:15124027

Dysbindin-1 is reduced in intrinsic, glutamatergic terminals of the hippocampal formation in schizophrenia.

PubMed

Talbot, Konrad; Eidem, Wess L; Tinsley, Caroline L; Benson, Matthew A; Thompson, Edward W; Smith, Rachel J; Hahn, Chang-Gyu; Siegel, Steven J; Trojanowski, John Q; Gur, Raquel E; Blake, Derek J; Arnold, Steven E

2004-05-01

Eleven studies now report significant associations between schizophrenia and certain haplotypes of single-nucleotide polymorphisms in the gene encoding dysbindin-1 at 6p22.3. Dysbindin-1 is best known as dystrobrevin-binding protein 1 (DTNBP1) and may thus be associated with the dystrophin glycoprotein complex found at certain postsynaptic sites in the brain. Contrary to expectations, however, we found that when compared to matched, nonpsychiatric controls, 73-93% of cases in two schizophrenia populations displayed presynaptic dysbindin-1 reductions averaging 18-42% (P = 0.027-0.0001) at hippocampal formation sites lacking neuronal dystrobrevin (i.e., beta-dystrobrevin). The reductions, which were not observed in the anterior cingulate of the same schizophrenia cases, occurred specifically in terminal fields of intrinsic, glutamatergic afferents of the subiculum, the hippocampus proper, and especially the inner molecular layer of the dentate gyrus (DGiml). An inversely correlated increase in vesicular glutamate transporter-1 (VGluT-1) occurred in DGiml of the same schizophrenia cases. Those changes occurred without evidence of axon terminal loss or neuroleptic effects on dysbindin-1 or VGluT-1. Our findings indicate that presynaptic dysbindin-1 reductions independent of the dystrophin glycoprotein complex are frequent in schizophrenia and are related to glutamatergic alterations in intrinsic hippocampal formation connections. Such changes may contribute to the cognitive deficits common in schizophrenia.

The nervus terminalis in the chick: a FMRFamide-immunoreactive and AChE-positive nerve.

PubMed

Wirsig-Wiechmann, C R

1990-07-16

The chick terminal nerve (TN) was examined by immunocytochemical and histochemical methods. Molluscan cardioexcitatory peptide-immunoreactive (FMRFamide-ir) and acetylcholinesterase (AChE)-positive TN perikarya and fibers were distributed along olfactory and trigeminal nerves. FMRFamide-ir TN fibers terminated in the olfactory lamina propria and epithelium and in ganglia along the rostroventral nasal septum. This initial description of several populations of avian TN neurons should provide the foundation for future developmental studies of this system.

Peripheral nerve hyperexcitability with preterminal nerve and neuromuscular junction remodeling is a hallmark of Schwartz-Jampel syndrome.

PubMed

Bauché, Stéphanie; Boerio, Delphine; Davoine, Claire-Sophie; Bernard, Véronique; Stum, Morgane; Bureau, Cécile; Fardeau, Michel; Romero, Norma Beatriz; Fontaine, Bertrand; Koenig, Jeanine; Hantaï, Daniel; Gueguen, Antoine; Fournier, Emmanuel; Eymard, Bruno; Nicole, Sophie

2013-12-01

Schwartz-Jampel syndrome (SJS) is a recessive disorder with muscle hyperactivity that results from hypomorphic mutations in the perlecan gene, a basement membrane proteoglycan. Analyses done on a mouse model have suggested that SJS is a congenital form of distal peripheral nerve hyperexcitability resulting from synaptic acetylcholinesterase deficiency, nerve terminal instability with preterminal amyelination, and subtle peripheral nerve changes. We investigated one adult patient with SJS to study this statement in humans. Perlecan deficiency due to hypomorphic mutations was observed in the patient biological samples. Electroneuromyography showed normal nerve conduction, neuromuscular transmission, and compound nerve action potentials while multiple measures of peripheral nerve excitability along the nerve trunk did not detect changes. Needle electromyography detected complex repetitive discharges without any evidence for neuromuscular transmission failure. The study of muscle biopsies containing neuromuscular junctions showed well-formed post-synaptic element, synaptic acetylcholinesterase deficiency, denervation of synaptic gutters with reinnervation by terminal sprouting, and long nonmyelinated preterminal nerve segments. These data support the notion of peripheral nerve hyperexcitability in SJS, which would originate distally from synergistic actions of peripheral nerve and neuromuscular junction changes as a result of perlecan deficiency. Copyright © 2013 Elsevier B.V. All rights reserved.

Cyfip1 Regulates Presynaptic Activity during Development.

PubMed

Hsiao, Kuangfu; Harony-Nicolas, Hala; Buxbaum, Joseph D; Bozdagi-Gunal, Ozlem; Benson, Deanna L

2016-02-03

Copy number variations encompassing the gene encoding Cyfip1 have been associated with a variety of human diseases, including autism and schizophrenia. Here we show that juvenile mice hemizygous for Cyfip1 have altered presynaptic function, enhanced protein translation, and increased levels of F-actin. In developing hippocampus, reduced Cyfip1 levels serve to decrease paired pulse facilitation and increase miniature EPSC frequency without a change in amplitude. Higher-resolution examination shows these changes to be caused primarily by an increase in presynaptic terminal size and enhanced vesicle release probability. Short hairpin-mediated knockdown of Cyfip1 coupled with expression of mutant Cyfip1 proteins indicates that the presynaptic alterations are caused by dysregulation of the WAVE regulatory complex. Such dysregulation occurs downstream of Rac1 as acute exposure to Rac1 inhibitors rescues presynaptic responses in culture and in hippocampal slices. The data serve to highlight an early and essential role for Cyfip1 in the generation of normally functioning synapses and suggest a means by which changes in Cyfip1 levels could impact the generation of neural networks and contribute to abnormal and maladaptive behaviors. Several developmental brain disorders have been associated with gene duplications and deletions that serve to increase or decrease levels of encoded proteins. Cyfip1 is one such protein, but the role it plays in brain development is poorly understood. We asked whether decreased Cyfip1 levels altered the function of developing synapses. The data show that synapses with reduced Cyfip1 are larger and release neurotransmitter more rapidly. These effects are due to Cyfip1's role in actin polymerization and are reversed by expression of a Cyfip1 mutant protein retaining actin regulatory function or by inhibiting Rac1. Thus, Cyfip1 has a more prominent early role regulating presynaptic activity during a stage of development when activity helps to define neural pathways. Copyright © 2016 the authors 0270-6474/16/361564-13$15.00/0.

Integration of Synaptic Vesicle Cargo Retrieval with Endocytosis at Central Nerve Terminals

PubMed Central

Cousin, Michael A.

2017-01-01

Central nerve terminals contain a limited number of synaptic vesicles (SVs) which mediate the essential process of neurotransmitter release during their activity-dependent fusion. The rapid and accurate formation of new SVs with the appropriate cargo is essential to maintain neurotransmission in mammalian brain. Generating SVs containing the correct SV cargo with the appropriate stoichiometry is a significant challenge, especially when multiple modes of endocytosis exist in central nerve terminals, which occur at different locations within the nerve terminals. These endocytosis modes include ultrafast endocytosis, clathrin-mediated endocytosis (CME) and activity-dependent bulk endocytosis (ADBE) which are triggered by specific patterns of neuronal activity. This review article will assess the evidence for the role of classical adaptor protein complexes in SV retrieval, discuss the role of monomeric adaptors and how interactions between specific SV cargoes can facilitate retrieval. In addition it will consider the evidence for preassembled plasma membrane cargo complexes and their role in facilitating these endocytosis modes. Finally it will present a unifying model for cargo retrieval at the presynapse, which integrates endocytosis modes in time and space. PMID:28824381

Does trans‐spinal and local DC polarization affect presynaptic inhibition and post‐activation depression?

PubMed Central

Kaczmarek, D.; Ristikankare, J.

2017-01-01

Key points Trans‐spinal polarization was recently introduced as a means to improve deficient spinal functions. However, only a few attempts have been made to examine the mechanisms underlying DC actions. We have now examined the effects of DC on two spinal modulatory systems, presynaptic inhibition and post‐activation depression, considering whether they might weaken exaggerated spinal reflexes and enhance excessively weakened ones.Direct current effects were evoked by using local intraspinal DC application (0.3–0.4 μA) in deeply anaesthetized rats and were compared with the effects of trans‐spinal polarization (0.8–1.0 mA).Effects of local intraspinal DC were found to be polarity dependent, as locally applied cathodal polarization enhanced presynaptic inhibition and post‐activation depression, whereas anodal polarization weakened them. In contrast, both cathodal and anodal trans‐spinal polarization facilitated them.The results suggest some common DC‐sensitive mechanisms of presynaptic inhibition and post‐activation depression, because both were facilitated or depressed by DC in parallel. Abstract Direct current (DC) polarization has been demonstrated to alleviate the effects of various deficits in the operation of the central nervous system. However, the effects of trans‐spinal DC stimulation (tsDCS) have been investigated less extensively than the effects of transcranial DC stimulation, and their cellular mechanisms have not been elucidated. The main objectives of this study were, therefore, to extend our previous analysis of DC effects on the excitability of primary afferents and synaptic transmission by examining the effects of DC on two spinal modulatory feedback systems, presynaptic inhibition and post‐activation depression, in an anaesthetized rat preparation. Other objectives were to compare the effects of locally and trans‐spinally applied DC (locDC and tsDCS). Local polarization at the sites of terminal branching of afferent fibres was found to induce polarity‐dependent actions on presynaptic inhibition and post‐activation depression, as cathodal locDC enhanced them and anodal locDC depressed them. In contrast, tsDCS modulated presynaptic inhibition and post‐activation depression in a polarity‐independent fashion because both cathodal and anodal tsDCS facilitated them. The results show that the local presynaptic actions of DC might counteract both excessively strong and excessively weak monosynaptic actions of group Ia and cutaneous afferents. However, they indicate that trans‐spinally applied DC might counteract the exaggerated spinal reflexes but have an adverse effect on pathologically weakened spinal activity by additional presynaptic weakening. The results are also relevant for the analysis of the basic properties of presynaptic inhibition and post‐activation depression because they indicate that some common DC‐sensitive mechanisms contribute to them. PMID:27891626

Identification of a human synaptotagmin-1 mutation that perturbs synaptic vesicle cycling

PubMed Central

Baker, Kate; Gordon, Sarah L.; Grozeva, Detelina; van Kogelenberg, Margriet; Roberts, Nicola Y.; Pike, Michael; Blair, Edward; Hurles, Matthew E.; Chong, W. Kling; Baldeweg, Torsten; Kurian, Manju A.; Boyd, Stewart G.; Cousin, Michael A.; Raymond, F. Lucy

2015-01-01

Synaptotagmin-1 (SYT1) is a calcium-binding synaptic vesicle protein that is required for both exocytosis and endocytosis. Here, we describe a human condition associated with a rare variant in SYT1. The individual harboring this variant presented with an early onset dyskinetic movement disorder, severe motor delay, and profound cognitive impairment. Structural MRI was normal, but EEG showed extensive neurophysiological disturbances that included the unusual features of low-frequency oscillatory bursts and enhanced paired-pulse depression of visual evoked potentials. Trio analysis of whole-exome sequence identified a de novo SYT1 missense variant (I368T). Expression of rat SYT1 containing the equivalent human variant in WT mouse primary hippocampal cultures revealed that the mutant form of SYT1 correctly localizes to nerve terminals and is expressed at levels that are approximately equal to levels of endogenous WT protein. The presence of the mutant SYT1 slowed synaptic vesicle fusion kinetics, a finding that agrees with the previously demonstrated role for I368 in calcium-dependent membrane penetration. Expression of the I368T variant also altered the kinetics of synaptic vesicle endocytosis. Together, the clinical features, electrophysiological phenotype, and in vitro neuronal phenotype associated with this dominant negative SYT1 mutation highlight presynaptic mechanisms that mediate human motor control and cognitive development. PMID:25705886

Muscle Expression of SOD1G93A Triggers the Dismantlement of Neuromuscular Junction via PKC-Theta.

PubMed

Dobrowolny, Gabriella; Martini, Martina; Scicchitano, Bianca Maria; Romanello, Vanina; Boncompagni, Simona; Nicoletti, Carmine; Pietrangelo, Laura; De Panfilis, Simone; Catizone, Angela; Bouchè, Marina; Sandri, Marco; Rudolf, Rüdiger; Protasi, Feliciano; Musarò, Antonio

2018-04-20

Neuromuscular junction (NMJ) represents the morphofunctional interface between muscle and nerve. Several chronic pathologies such as aging and neurodegenerative diseases, including muscular dystrophy and amyotrophic lateral sclerosis, display altered NMJ and functional denervation. However, the triggers and the molecular mechanisms underlying the dismantlement of NMJ remain unclear. Here we provide evidence that perturbation in redox signaling cascades, induced by muscle-specific accumulation of mutant SOD1 G93A in transgenic MLC/SOD1 G93A mice, is causally linked to morphological alterations of the neuromuscular presynaptic terminals, high turnover rate of acetylcholine receptor, and NMJ dismantlement. The analysis of potential molecular mechanisms that mediate the toxic activity of SOD1 G93A revealed a causal link between protein kinase Cθ (PKCθ) activation and NMJ disintegration. The study discloses the molecular mechanism that triggers functional denervation associated with the toxic activity of muscle SOD1 G93A expression and suggests the possibility of developing a new strategy to counteract age- and pathology-associated denervation based on pharmacological inhibition of PKCθ activity. Collectively, these data indicate that muscle-specific accumulation of oxidative damage can affect neuromuscular communication and induce NMJ dismantlement through a PKCθ-dependent mechanism. Antioxid. Redox Signal. 28, 1105-1119.

Immunolocalization of a tachykinin-receptor-like protein in the central nervous system of Locusta migratoria migratorioides and neobellieria bullata.

PubMed

Veelaert, D; Oonk, H B; Vanden Eynde, G; Torfs, H; Meloen, R H; Schoofs, L; Parmentier, M; De Loof, A; Vanden Broeck, J

1999-05-10

Antisera raised against two distinct peptide regions of the Drosophila neurokinin-like receptor NKD were used to immunolocalize tachykinin-receptor-like proteins in the central nervous system of two insect species: the African migratory locust, Locusta migratoria, and the gray fleshfly, Neobellieria bullata. The resulting immunopositive staining patterns were identical for both antisera. Moreover, a very similar distribution of the immunoreactive material was observed in fleshflies and locusts. Immunoreactivity was found in nerve terminals of the retrocerebral complex, suggesting a presynaptic localization of the receptor in this part of the brain. Cell bodies were stained in the subesophageal ganglion: an anterior group of four larger cells and a posterior group of about 20 cells. These cells have axons projecting into the contralateral nervus corporis allati (NCA) II, bypassing the corpus allatum and projecting through the NCA I into the storage part of the corpus cardiacum. In the glandular part of the corpus cardiacum, the glandular adipokinetic hormone-producing cells did not show any immunopositive staining. In the locust, additional immunopositive staining was observed in internolaterally located neurons of the tritocerebrum and in important integrative parts of the neuropil such as the central body and the mushroom bodies.

Presynaptic Muscarinic Acetylcholine Receptors and TrkB Receptor Cooperate in the Elimination of Redundant Motor Nerve Terminals during Development.

PubMed

Nadal, Laura; Garcia, Neus; Hurtado, Erica; Simó, Anna; Tomàs, Marta; Lanuza, Maria A; Cilleros, Victor; Tomàs, Josep

2017-01-01

The development of the nervous system involves the overproduction of synapses but connectivity is refined by Hebbian activity-dependent axonal competition. The newborn skeletal muscle fibers are polyinnervated but, at the end of the competition process, some days later, become innervated by a single axon. We used quantitative confocal imaging of the autofluorescent axons from transgenic B6.Cg-Tg (Thy1-YFP)16 Jrs/J mice to investigate the possible cooperation of the muscarinic autoreceptors (mAChR, M 1 -, M 2 - and M 4 -subtypes) and the tyrosine kinase B (TrkB) receptor in the control of axonal elimination after the mice Levator auris longus (LAL) muscle had been exposed to several selective antagonist of the corresponding receptor pathways in vivo . Our previous results show that M 1 , M 2 and TrkB signaling individually increase axonal loss rate around P9. Here we show that although the M 1 and TrkB receptors cooperate and add their respective individual effects to increase axonal elimination rate even more, the effect of the M 2 receptor is largely independent of both M 1 and TrkB receptors. Thus both, cooperative and non-cooperative signaling mechanisms contribute to developmental synapse elimination.

Presynaptic Muscarinic Acetylcholine Receptors and TrkB Receptor Cooperate in the Elimination of Redundant Motor Nerve Terminals during Development

PubMed Central

Nadal, Laura; Garcia, Neus; Hurtado, Erica; Simó, Anna; Tomàs, Marta; Lanuza, Maria A.; Cilleros, Victor; Tomàs, Josep

2017-01-01

The development of the nervous system involves the overproduction of synapses but connectivity is refined by Hebbian activity-dependent axonal competition. The newborn skeletal muscle fibers are polyinnervated but, at the end of the competition process, some days later, become innervated by a single axon. We used quantitative confocal imaging of the autofluorescent axons from transgenic B6.Cg-Tg (Thy1-YFP)16 Jrs/J mice to investigate the possible cooperation of the muscarinic autoreceptors (mAChR, M1-, M2- and M4-subtypes) and the tyrosine kinase B (TrkB) receptor in the control of axonal elimination after the mice Levator auris longus (LAL) muscle had been exposed to several selective antagonist of the corresponding receptor pathways in vivo. Our previous results show that M1, M2 and TrkB signaling individually increase axonal loss rate around P9. Here we show that although the M1 and TrkB receptors cooperate and add their respective individual effects to increase axonal elimination rate even more, the effect of the M2 receptor is largely independent of both M1 and TrkB receptors. Thus both, cooperative and non-cooperative signaling mechanisms contribute to developmental synapse elimination. PMID:28228723

Identification and Characterization of ML352: A Novel, Noncompetitive Inhibitor of the Presynaptic Choline Transporter

PubMed Central

2015-01-01

The high-affinity choline transporter (CHT) is the rate-limiting determinant of acetylcholine (ACh) synthesis, yet the transporter remains a largely undeveloped target for the detection and manipulation of synaptic cholinergic signaling. To expand CHT pharmacology, we pursued a high-throughput screen for novel CHT-targeted small molecules based on the electrogenic properties of transporter-mediated choline transport. In this effort, we identified five novel, structural classes of CHT-specific inhibitors. Chemical diversification and functional analysis of one of these classes identified ML352 as a high-affinity (Ki = 92 nM) and selective CHT inhibitor. At concentrations that fully antagonized CHT in transfected cells and nerve terminal preparations, ML352 exhibited no inhibition of acetylcholinesterase (AChE) or cholineacetyltransferase (ChAT) and also lacked activity at dopamine, serotonin, and norepinephrine transporters, as well as many receptors and ion channels. ML352 exhibited noncompetitive choline uptake inhibition in intact cells and synaptosomes and reduced the apparent density of hemicholinium-3 (HC-3) binding sites in membrane assays, suggesting allosteric transporter interactions. Pharmacokinetic studies revealed limited in vitro metabolism and significant CNS penetration, with features predicting rapid clearance. ML352 represents a novel, potent, and specific tool for the manipulation of CHT, providing a possible platform for the development of cholinergic imaging and therapeutic agents. PMID:25560927

Tachycardia, reduced vagal capacity, and age-dependent ventricular dysfunction arising from diminished expression of the presynaptic choline transporter.

PubMed

English, Brett A; Appalsamy, Martin; Diedrich, Andre; Ruggiero, Alicia M; Lund, David; Wright, Jane; Keller, Nancy R; Louderback, Katherine M; Robertson, David; Blakely, Randy D

2010-09-01

Healthy cardiovascular function relies on a balanced and responsive integration of noradrenergic and cholinergic innervation of the heart. High-affinity choline uptake by cholinergic terminals is pivotal for efficient ACh production and release. To date, the cardiovascular impact of diminished choline transporter (CHT) expression has not been directly examined, largely due to the transporter's inaccessibility in vivo. Here, we describe findings from cardiovascular experiments using transgenic mice that bear a CHT genetic deficiency. Whereas CHT knockout (CHT(-/-)) mice exhibit early postnatal lethality, CHT heterozygous (CHT(+/-)) mice survive, grow, and reproduce normally and exhibit normal spontaneous behaviors. However, the CHT(+/-) mouse heart displays significantly reduced levels of high-affinity choline uptake accompanied by significantly reduced levels of ACh. Telemeterized recordings of cardiovascular function in these mice revealed tachycardia and hypertension at rest. After treadmill exercise, CHT(+/-) mice exhibited slower heart rate recovery, consistent with a diminished cholinergic reserve, a contention validated through direct vagal nerve stimulation. Echocardiographic and histological experiments revealed an age-dependent decrease in fractional shortening, increased left ventricular dimensions, and increased ventricular fibrosis, consistent with ventricular dysfunction. These cardiovascular phenotypes of CHT(+/-) mice encourage an evaluation of humans bearing reduced CHT expression for their resiliency in maintaining proper heart function as well as risk for cardiovascular disease.

Behavioral impact of neurotransmitter-activated GPCRs: Muscarinic and GABAB receptors regulate C. elegans locomotion

PubMed Central

Dittman, Jeremy S; Kaplan, Joshua M

2008-01-01

Neurotransmitter released from presynaptic terminals activates both ligand-gated ion channels (ionotropic receptors) and a variety of G protein-coupled receptors (GPCRs). These neurotransmitter receptors are expressed on both pre- and postsynaptic cells. Thus, each neurotransmitter acts on multiple receptor classes, generating a large repertoire of physiological responses. The impact of many ionotropic receptors on neuronal activity and behavior has been clearly elucidated; however, much less is known about how neurotransmitter-gated GPCRs regulate neurons and circuits. In C. elegans, both Acetylcholine (ACh) and GABA are released in the nerve cord and mediate fast neuromuscular excitation and inhibition during locomotion. Here we identify a muscarinic receptor (GAR-2) and the GABAB receptor dimer (GBB-1/2) that detect synaptically released ACh and GABA, respectively. Both GAR-2 and GBB-1/2 inhibited cholinergic motor neurons when ACh and GABA levels were enhanced. Loss of either GPCR resulted in movement defects, suggesting that these receptors are activated during locomotion. When the negative feedback provided by GAR-2 was replaced with positive feedback, animals became highly sensitive to ACh levels and locomotion was severely impaired. Thus, conserved GPCRs act in the nematode motor circuit to provide negative feedback and to regulate locomotory behaviors that underlie navigation. PMID:18614679

The subtype of alpha-adrenoceptor involved in the neural control of renal tubular sodium reabsorption in the rabbit.

PubMed Central

Hesse, I F; Johns, E J

1984-01-01

A study was undertaken in pentobarbitone anaesthetized rabbits, undergoing a saline diuresis, to determine the subtype of alpha-adrenoceptor mediating renal tubular sodium reabsorption. Stimulation of the renal nerves at low rates, to cause an 11% fall in renal blood flow, did not change glomerular filtration rate but significantly reduced urine flow rate, and absolute and fractional sodium excretions by approximately 40%. These responses were reproducible in different groups of animals and with time. Renal nerve stimulation during an intra-renal arterial infusion of prazosin, to block alpha 1-adrenoceptors, had no effect on the renal haemodynamic response but completely abolished the reductions in urine flow rate, and absolute and fractional sodium excretion. During intra-renal arterial infusion of yohimbine, to block renal alpha 2-adrenoceptors, stimulation of the renal nerves to cause similar renal haemodynamic changes resulted in significantly larger reductions in urine flow rate, and absolute and fractional sodium excretion of about 52-58%. These results indicate that in the rabbit alpha 1-adrenoceptors are present on the renal tubules, which mediate the increase in sodium reabsorption caused by renal nerve stimulation. They further suggest the presence of presynaptic alpha 2-adrenoceptors on those nerves innervating the renal tubules. PMID:6086915

Lacosamide diminishes dryness-induced hyperexcitability of corneal cold sensitive nerve terminals.

PubMed

Kovács, Illés; Dienes, Lóránt; Perényi, Kristóf; Quirce, Susana; Luna, Carolina; Mizerska, Kamila; Acosta, M Carmen; Belmonte, Carlos; Gallar, Juana

2016-09-15

Lacosamide is an anti-epileptic drug that is also used for the treatment of painful diabetic neuropathy acting through voltage-gated sodium channels. The aim of this work was to evaluate the effects of acute application of lacosamide on the electrical activity of corneal cold nerve terminals in lacrimo-deficient guinea pigs. Four weeks after unilateral surgical removal of the main lachrimal gland in guinea pigs, corneas were excised and superfused in vitro at 34°C for extracellular electrophysiological recording of nerve terminal impulse activity of cold thermosensitive nerve terminals. The characteristics of the spontaneous and the stimulus-evoked (cooling ramps from 34°C to 15°C) activity before and in presence of lacosamide 100µM and lidocaine 100µM were compared. Cold nerve terminals (n=34) recorded from dry eye corneas showed significantly enhanced spontaneous activity (8.0±1.1 vs. 5.2±0.7imp/s; P<0.05) and cold response (21.2±1.7 vs. 16.8±1.3imp/s; P<0.05) as well as reduced cold threshold (1.5±0.1 vs. 2.8±0.2 Δ°C; P<0.05) to cooling ramps compared to terminals (n=58) from control animals. Both lacosamide and lidocaine decreased spontaneous activity and peak response to cooling ramps significantly (P<0.05). Temperature threshold was increased by the addition of lidocaine (P<0.05) but not lacosamide (P>0.05) to the irrigation fluid. In summary, the application of lacosamide results in a significant decrease of the augmented spontaneous activity and responsiveness to cold of corneal sensory nerves from tear-deficient animals. Based on these promising results we speculate that lacosamide might be used to reduce the hyperexcitability of corneal cold receptors caused by prolonged ocular surface dryness due to hyposecretory or evaporative dry eye disease. Copyright © 2016 Elsevier B.V. All rights reserved.

Coincident postsynaptic activity gates presynaptic dopamine release to induce plasticity in Drosophila mushroom bodies

PubMed Central

Ueno, Kohei; Suzuki, Ema; Naganos, Shintaro; Ofusa, Kyoko; Horiuchi, Junjiro; Saitoe, Minoru

2017-01-01

Simultaneous stimulation of the antennal lobes (ALs) and the ascending fibers of the ventral nerve cord (AFV), two sensory inputs to the mushroom bodies (MBs), induces long-term enhancement (LTE) of subsequent AL-evoked MB responses. LTE induction requires activation of at least three signaling pathways to the MBs, mediated by nicotinic acetylcholine receptors (nAChRs), NMDA receptors (NRs), and D1 dopamine receptors (D1Rs). Here, we demonstrate that inputs from the AL are transmitted to the MBs through nAChRs, and inputs from the AFV are transmitted by NRs. Dopamine signaling occurs downstream of both nAChR and NR activation, and requires simultaneous stimulation of both pathways. Dopamine release requires the activity of the rutabaga adenylyl cyclase in postsynaptic MB neurons, and release is restricted to MB neurons that receive coincident stimulation. Our results indicate that postsynaptic activity can gate presynaptic dopamine release to regulate plasticity. DOI: http://dx.doi.org/10.7554/eLife.21076.001 PMID:28117664

Synaptic transmission block by presynaptic injection of oligomeric amyloid beta

PubMed Central

Moreno, Herman; Yu, Eunah; Pigino, Gustavo; Hernandez, Alejandro I.; Kim, Natalia; Moreira, Jorge E.; Sugimori, Mutsuyuki; Llinás, Rodolfo R.

2009-01-01

Early Alzheimer's disease (AD) pathophysiology is characterized by synaptic changes induced by degradation products of amyloid precursor protein (APP). The exact mechanisms of such modulation are unknown. Here, we report that nanomolar concentrations of intraaxonal oligomeric (o)Aβ42, but not oAβ40 or extracellular oAβ42, acutely inhibited synaptic transmission at the squid giant synapse. Further characterization of this phenotype demonstrated that presynaptic calcium currents were unaffected. However, electron microscopy experiments revealed diminished docked synaptic vesicles in oAβ42-microinjected terminals, without affecting clathrin-coated vesicles. The molecular events of this modulation involved casein kinase 2 and the synaptic vesicle rapid endocytosis pathway. These findings open the possibility of a new therapeutic target aimed at ameliorating synaptic dysfunction in AD. PMID:19304802

Timing and efficacy of Ca2+ channel activation in hippocampal mossy fiber boutons.

PubMed

Bischofberger, Josef; Geiger, Jörg R P; Jonas, Peter

2002-12-15

The presynaptic Ca2+ signal is a key determinant of transmitter release at chemical synapses. In cortical synaptic terminals, however, little is known about the kinetic properties of the presynaptic Ca2+ channels. To investigate the timing and magnitude of the presynaptic Ca2+ inflow, we performed whole-cell patch-clamp recordings from mossy fiber boutons (MFBs) in rat hippocampus. MFBs showed large high-voltage-activated Ca(2+) currents, with a maximal amplitude of approximately 100 pA at a membrane potential of 0 mV. Both activation and deactivation were fast, with time constants in the submillisecond range at a temperature of approximately 23 degrees C. An MFB action potential (AP) applied as a voltage-clamp command evoked a transient Ca2+ current with an average amplitude of approximately 170 pA and a half-duration of 580 microsec. A prepulse to +40 mV had only minimal effects on the AP-evoked Ca2+ current, indicating that presynaptic APs open the voltage-gated Ca2+ channels very effectively. On the basis of the experimental data, we developed a kinetic model with four closed states and one open state, linked by voltage-dependent rate constants. Simulations of the Ca2+ current could reproduce the experimental data, including the large amplitude and rapid time course of the current evoked by MFB APs. Furthermore, the simulations indicate that the shape of the presynaptic AP and the gating kinetics of the Ca2+ channels are tuned to produce a maximal Ca2+ influx during a minimal period of time. The precise timing and high efficacy of Ca2+ channel activation at this cortical glutamatergic synapse may be important for synchronous transmitter release and temporal information processing.

Quantitative monitoring of activity-dependent bulk endocytosis of synaptic vesicle membrane by fluorescent dextran imaging

PubMed Central

Clayton, Emma Louise; Cousin, Michael Alan

2012-01-01

Activity-dependent bulk endocytosis (ADBE) is the dominant synaptic vesicle (SV) retrieval mode in central nerve terminals during periods of intense neuronal activity. Despite this fact there are very few real time assays that report the activity of this critical SV retrieval mode. In this paper we report a simple and quantitative assay of ADBE using uptake of large flourescent dextrans as fluid phase markers. We show that almost all dextran uptake occurs in nerve terminals, using co-localisation with the fluorescent probe FM1-43. We also demonstrate that accumulated dextran cannot be unloaded by neuronal stimulation, indicating its specific loading into bulk endosomes and not SVs. Quantification of dextran uptake was achieved by using thresholding analysis to count the number of loaded nerve terminals, since monitoring the average fluorescence intensity of these nerve terminals did not accurately report the extent of ADBE. Using this analysis we showed that dextran uptake occurs very soon after stimulation and that it does not persist when stimulation terminates. Thus we have devised a simple and quantitative method to monitor ADBE in living neurones, which will be ideal for real time screening of small molecule inhibitors of this key SV retrieval mode. PMID:19766140

Heterogeneity of glutamatergic and GABAergic release machinery in cerebral cortex: analysis of synaptogyrin, vesicle-associated membrane protein, and syntaxin.

PubMed

Bragina, L; Giovedì, S; Barbaresi, P; Benfenati, F; Conti, F

2010-02-03

To define whether cortical glutamatergic and GABAergic release machineries can be differentiated on the basis of the nature and amount of proteins they express, we studied the degree of co-localization of synaptogyrin (SGYR) 1 and 3, vesicle-associated membrane protein (VAMP) 1 and 2, syntaxin (STX) 1A and 1B in vesicular glutamate transporter (VGLUT)1-, VGLUT2- and vesicular GABA transporter (VGAT)-positive (+) puncta and synaptic vesicles in the rat cerebral cortex. Co-localization studies showed that SGYR1 and 3 were expressed in about 90% of VGLUT1+, 70% of VGLUT2+ and 80% of VGAT+ puncta; VAMP1 was expressed in approximately 45% of VGLUT1+, 55% of VGLUT2+, and 80% of VGAT+ puncta; VAMP2 in about 95% of VGLUT1+, 75% of VGLUT2+, and 80% of VGAT+ puncta; STX1A in about 65% of VGLUT1+, 30% of VGLUT2+, and 3% of VGAT+ puncta, and STX1B in approximately 45% of VGLUT1+, 35% of VGLUT2+, and 70% of VGAT+ puncta. Immunoisolation studies showed that while STX1A was completely segregated and virtually absent from VGAT synaptic vesicles, STX1B, VAMP1/VAMP2, SGYR1/SGYR3 showed a similar pattern with the highest expression in VGLUT1 immunoisolated vesicles and the lowest in VGAT immunoisolated vesicles. Moreover, we studied the localization of STX1B at the electron microscope and found that a population of axon terminals forming symmetric synapses were STX1B-positive.These results extend our previous observations on the differential expression of presynaptic proteins involved in neurotransmitter release in GABAergic and glutamatergic terminals and indicate that heterogeneity of glutamatergic and GABAergic release machinery can be contributed by both the presence or absence of a given protein in a nerve terminal and the amount of protein expressed by synaptic vesicles. Copyright 2010 IBRO. Published by Elsevier Ltd. All rights reserved.

Chronic treatment with agomelatine or venlafaxine reduces depolarization-evoked glutamate release from hippocampal synaptosomes

PubMed Central

2013-01-01

Background Growing compelling evidence from clinical and preclinical studies has demonstrated the primary role of alterations of glutamatergic transmission in cortical and limbic areas in the pathophysiology of mood disorders. Chronic antidepressants have been shown to dampen endogenous glutamate release from rat hippocampal synaptic terminals and to prevent the marked increase of glutamate overflow induced by acute behavioral stress in frontal/prefrontal cortex. Agomelatine, a new antidepressant endowed with MT1/MT2 agonist and 5-HT2C serotonergic antagonist properties, has shown efficacy at both preclinical and clinical levels. Results Chronic treatment with agomelatine, or with the reference drug venlafaxine, induced a marked decrease of depolarization-evoked endogenous glutamate release from purified hippocampal synaptic terminals in superfusion. No changes were observed in GABA release. This effect was accompanied by reduced accumulation of SNARE protein complexes, the key molecular effector of vesicle docking, priming and fusion at presynaptic membranes. Conclusions Our data suggest that the novel antidepressant agomelatine share with other classes of antidepressants the ability to modulate glutamatergic transmission in hippocampus. Its action seems to be mediated by molecular mechanisms located on the presynaptic membrane and related with the size of the vesicle pool ready for release. PMID:23895555

Muscular innervation of the proximal duodenum of the guinea pig.

PubMed

Iino, S

2000-10-01

We investigated the muscular structure and innervation of the gastroduodenal junction in the guinea pig. In the gastroduodenal junction, the innermost layer of the circular muscle contained numerous nerve fibers and terminals. Since this nerve network continued onto the deep muscular plexus (DMP) of the duodenum, we surmised that the numerous nerve fibers in the gastroduodenal junction were specialized DMP in the most proximal part of the duodenum. The innermost layer containing many nerve fibers was about 1,000 microm in length and 100 microm in thickness in the proximal duodenum. This layer contained numerous connective tissue fibers composed of collagen and elastic fibers. Five to 30 smooth muscle cells lay in contact with each other and were surrounded by fine connective tissue. The nerve fibers in the proximal duodenum contained nerve terminals immunoreactive for choline acetyltransferase, dynorphin, enkephalin, galanin, gastrin-releasing peptide, nitric oxide synthase, substance P, and vasoactive intestinal polypeptide. Adrenergic fibers which contained tyrosine hydroxylase immunoreactivity were rare in the proximal duodenum. In the innermost layer of the proximal duodenum, there were numerous c-Kit immunopositive cells that were in contact with nerve terminals. This study allowed us to clarify the specific architecture of the most proximal portion of the duodenum. The functional significance of the proximal duodenum in relation to the electrical connection and neural cooperation of the musculature between the antrum and the duodenum is also discussed.

Localization and characterization of (/sup 3/H)desmethylimipramine binding sites in rat brain by quantitative autoradiography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biegon, A.; Rainbow, T.C.

1983-05-01

The high affinity binding sites for the antidepressant desmethlyimipramine (DMI) have been localized in rat brain by quantitative autoradiography. There are high concentrations of binding sites in the locus ceruleus, the anterior ventral thalamus, the ventral portion of the bed nucleus of the stria terminalis, the paraventricular and the dorsomedial nuclei of the hypothalamus. The distribution of DMI binding sites is in striking accord with the distribution of norepinephrine terminals. Pretreatment of rats with the neurotoxin 6-hydroxydopamine, which causes a selective degeneration of catecholamine terminals, results in 60 to 90% decrease in DMI binding. These data support the idea thatmore » high affinity binding sites for DMI are located on presynaptic noradrenergic terminals.« less

Pre-synaptic glycine GlyT1 transporter--NMDA receptor interaction: relevance to NMDA autoreceptor activation in the presence of Mg2+ ions.

PubMed

Musante, Veronica; Summa, Maria; Cunha, Rodrigo A; Raiteri, Maurizio; Pittaluga, Anna

2011-05-01

Rat hippocampal glutamatergic terminals possess NMDA autoreceptors whose activation by low micromolar NMDA elicits glutamate exocytosis in the presence of physiological Mg(2+) (1.2 mM), the release of glutamate being significantly reduced when compared to that in Mg(2+)-free condition. Both glutamate and glycine were required to evoke glutamate exocytosis in 1.2 mM Mg(2+), while dizocilpine, cis-4-[phosphomethyl]-piperidine-2-carboxylic acid and 7-Cl-kynurenic acid prevented it, indicating that occupation of both agonist sites is needed for receptor activation. D-serine mimicked glycine but also inhibited the NMDA/glycine-induced release of [(3H]D-aspartate, thus behaving as a partial agonist. The NMDA/glycine-induced release in 1.2 mM Mg(2+) strictly depended on glycine uptake through the glycine transporter type 1 (GlyT1), because the GlyT1 blocker N-[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl])sarcosine hydrochloride, but not the GlyT2 blocker Org 25534, prevented it. Accordingly, [(3)H]glycine was taken up during superfusion, while lowering the external concentration of Na(+), the monovalent cation co-transported with glycine by GlyT1, abrogated the NMDA-induced effect. Western blot analysis of subsynaptic fractions confirms that GlyT1 and NMDA autoreceptors co-localize at the pre-synaptic level, where GluN3A subunits immunoreactivity was also recovered. It is proposed that GlyT1s coexist with NMDA autoreceptors on rat hippocampal glutamatergic terminals and that glycine taken up by GlyT1 may permit physiological activation of NMDA pre-synaptic autoreceptors. © 2011 The Authors. Journal of Neurochemistry © 2011 International Society for Neurochemistry.

Activation of inactivation process initiates rapid eye movement sleep.

PubMed

Mallick, Birendra Nath; Singh, Abhishek; Khanday, Mudasir Ahmad

2012-06-01

Interactions among REM-ON and REM-OFF neurons form the basic scaffold for rapid eye movement sleep (REMS) regulation; however, precise mechanism of their activation and cessation, respectively, was unclear. Locus coeruleus (LC) noradrenalin (NA)-ergic neurons are REM-OFF type and receive GABA-ergic inputs among others. GABA acts postsynaptically on the NA-ergic REM-OFF neurons in the LC and presynaptically on the latter's projection terminals and modulates NA-release on the REM-ON neurons. Normally during wakefulness and non-REMS continuous release of NA from the REM-OFF neurons, which however, is reduced during the latter phase, inhibits the REM-ON neurons and prevents REMS. At this stage GABA from substantia nigra pars reticulate acting presynaptically on NA-ergic terminals on REM-ON neurons withdraws NA-release causing the REM-ON neurons to escape inhibition and being active, may be even momentarily. A working-model showing neurochemical-map explaining activation of inactivation process, showing contribution of GABA-ergic presynaptic inhibition in withdrawing NA-release and dis-inhibition induced activation of REM-ON neurons, which in turn activates other GABA-ergic neurons and shutting-off REM-OFF neurons for the initiation of REMS-generation has been explained. Our model satisfactorily explains yet unexplained puzzles (i) why normally REMS does not appear during waking, rather, appears following non-REMS; (ii) why cessation of LC-NA-ergic-REM-OFF neurons is essential for REMS-generation; (iii) factor(s) which does not allow cessation of REM-OFF neurons causes REMS-loss; (iv) the association of changes in levels of GABA and NA in the brain during REMS and its deprivation and associated symptoms; v) why often dreams are associated with REMS. Copyright © 2012 Elsevier Ltd. All rights reserved.

The 'glial' glutamate transporter, EAAT2 (Glt-1) accounts for high affinity glutamate uptake into adult rodent nerve endings.

PubMed

Suchak, Sachin K; Baloyianni, Nicoletta V; Perkinton, Michael S; Williams, Robert J; Meldrum, Brian S; Rattray, Marcus

2003-02-01

The excitatory amino acid transporters (EAAT) removes neurotransmitters glutamate and aspartate from the synaptic cleft. Most CNS glutamate uptake is mediated by EAAT2 into glia, though nerve terminals show evidence for uptake, through an unknown transporter. Reverse-transcriptase PCR identified the expression of EAAT1, EAAT2, EAAT3 and EAAT4 mRNAs in primary cultures of mouse cortical or striatal neurones. We have used synaptosomes and glial plasmalemmal vesicles (GPV) from adult mouse and rat CNS to identify the nerve terminal transporter. Western blotting showed detectable levels of the transporters EAAT1 (GLAST) and EAAT2 (Glt-1) in both synaptosomes and GPVs. Uptake of [3H]D-aspartate or [3H]L-glutamate into these preparations revealed sodium-dependent uptake in GPV and synaptosomes which was inhibited by a range of EAAT blockers: dihydrokainate, serine-o-sulfate, l-trans-2,4-pyrrolidine dicarboxylate (PDC) (+/-)-threo-3-methylglutamate and (2S,4R )-4-methylglutamate. The IC50 values found for these compounds suggested functional expression of the 'glial, transporter, EAAT2 in nerve terminals. Additionally blockade of the majority EAAT2 uptake sites with 100 micro m dihydrokainate, failed to unmask any functional non-EAAT2 uptake sites. The data presented in this study indicate that EAAT2 is the predominant nerve terminal glutamate transporter in the adult rodent CNS.

Palisade endings are present in canine extraocular muscles and have a cholinergic phenotype.

PubMed

Rungaldier, Stefanie; Pomikal, Christine; Streicher, Johannes; Blumer, Roland

2009-11-20

Classical proprioceptors, like Golgi tendon organs and muscle spindles are absent in the extraocular muscles (EOMs) of most mammals. Instead, a nerve end organ was detected in the EOMs of each species including sheep, cat, rabbit, rat, monkey, and human examined so far: the palisade ending. Until now no clear evidence appeared that palisade endings are also present in canine EOMs. Here, we analyzed dog EOMs by confocal laser scanning microscopy, 3D reconstruction, and transmission electron microscopy. In EOM wholemount preparations stained with antibodies against neurofilament and synaptophysin we could demonstrate typical palisade endings. Nerve fibers coming from the muscle extend into the tendon. There, the nerve fibers turn 180 degrees and return to branch into preterminal axons which establish nerve terminals around a single muscle fiber tip. Fine structural analysis revealed that each palisade ending in dog EOMs establish nerve terminals on the tendon. In some palisade endings we found nerve terminals contacting the muscle fiber as well. Such neuromuscular contacts have a basal lamina in the synaptic cleft. By using an antibody against choline acetyltransferase (ChAT) we proved that canine palisade endings are ChAT-immunoreactive. This study shows that palisade endings are present in canine EOMs. In line with prior findings in cat and monkey, palisade endings in dog have a cholinergic phenotype.

Renal dopamine containing nerves. What is their functional significance?

PubMed

DiBona, G F

1990-06-01

Biochemical and morphological studies indicate that there are nerves within the kidney that contain dopamine and that various structures within the kidney contain dopamine receptors. However, the functional significance of these renal dopamine containing nerves in relation to renal dopamine receptors is unknown. The functional significance could be defined by demonstrating that an alteration in one or more renal functions occurring in response to reflex or electrical activation of efferent renal nerves is dependent on release of dopamine as the neurotransmitter from the renal nerve terminals acting on renal dopamine receptors. Thus, the hypothesis becomes: reflex or electrical activation of efferent renal nerves causes alterations in renal function (eg, renal blood flow, water and solute handling) that are inhibited by specific and selective dopamine receptor antagonists. As reviewed herein, the published experimental data do not support the hypothesis. Therefore, the view that alterations in one or more renal functions occurring in response to reflex or electrical activation of efferent renal nerves are dependent on release of dopamine as the neurotransmitter from the renal nerve terminals acting on renal dopamine receptors remains unproven.

Presynaptic Neuronal Nicotinic Receptors Differentially Shape Select Inputs to Auditory Thalamus and Are Negatively Impacted by Aging.

PubMed

Sottile, Sarah Y; Hackett, Troy A; Cai, Rui; Ling, Lynne; Llano, Daniel A; Caspary, Donald M

2017-11-22

Acetylcholine (ACh) is a potent neuromodulator capable of modifying patterns of acoustic information flow. In auditory cortex, cholinergic systems have been shown to increase salience/gain while suppressing extraneous information. However, the mechanism by which cholinergic circuits shape signal processing in the auditory thalamus (medial geniculate body, MGB) is poorly understood. The present study, in male Fischer Brown Norway rats, seeks to determine the location and function of presynaptic neuronal nicotinic ACh receptors (nAChRs) at the major inputs to MGB and characterize how nAChRs change during aging. In vitro electrophysiological/optogenetic methods were used to examine responses of MGB neurons after activation of nAChRs during a paired-pulse paradigm. Presynaptic nAChR activation increased responses evoked by stimulation of excitatory corticothalamic and inhibitory tectothalamic terminals. Conversely, nAChR activation appeared to have little effect on evoked responses from inhibitory thalamic reticular nucleus and excitatory tectothalamic terminals. In situ hybridization data showed nAChR subunit transcripts in GABAergic inferior colliculus neurons and glutamatergic auditory cortical neurons supporting the present slice findings. Responses to nAChR activation at excitatory corticothalamic and inhibitory tectothalamic inputs were diminished by aging. These findings suggest that cholinergic input to the MGB increases the strength of tectothalamic inhibitory projections, potentially improving the signal-to-noise ratio and signal detection while increasing corticothalamic gain, which may facilitate top-down identification of stimulus identity. These mechanisms appear to be affected negatively by aging, potentially diminishing speech perception in noisy environments. Cholinergic inputs to the MGB appear to maximize sensory processing by adjusting both top-down and bottom-up mechanisms in conditions of attention and arousal. SIGNIFICANCE STATEMENT The pedunculopontine tegmental nucleus is the source of cholinergic innervation for sensory thalamus and is a critical part of an ascending arousal system that controls the firing mode of thalamic cells based on attentional demand. The present study describes the location and impact of aging on presynaptic neuronal nicotinic acetylcholine receptors (nAChRs) within the circuitry of the auditory thalamus (medial geniculate body, MGB). We show that nAChRs are located on ascending inhibitory and descending excitatory presynaptic inputs onto MGB neurons, likely increasing gain selectively and improving temporal clarity. In addition, we show that aging has a deleterious effect on nAChR efficacy. Cholinergic dysfunction at the level of MGB may affect speech understanding negatively in the elderly population. Copyright © 2017 the authors 0270-6474/17/3711378-13$15.00/0.

Presynaptic Neuronal Nicotinic Receptors Differentially Shape Select Inputs to Auditory Thalamus and Are Negatively Impacted by Aging

PubMed Central

Sottile, Sarah Y.; Hackett, Troy A.

2017-01-01

Acetylcholine (ACh) is a potent neuromodulator capable of modifying patterns of acoustic information flow. In auditory cortex, cholinergic systems have been shown to increase salience/gain while suppressing extraneous information. However, the mechanism by which cholinergic circuits shape signal processing in the auditory thalamus (medial geniculate body, MGB) is poorly understood. The present study, in male Fischer Brown Norway rats, seeks to determine the location and function of presynaptic neuronal nicotinic ACh receptors (nAChRs) at the major inputs to MGB and characterize how nAChRs change during aging. In vitro electrophysiological/optogenetic methods were used to examine responses of MGB neurons after activation of nAChRs during a paired-pulse paradigm. Presynaptic nAChR activation increased responses evoked by stimulation of excitatory corticothalamic and inhibitory tectothalamic terminals. Conversely, nAChR activation appeared to have little effect on evoked responses from inhibitory thalamic reticular nucleus and excitatory tectothalamic terminals. In situ hybridization data showed nAChR subunit transcripts in GABAergic inferior colliculus neurons and glutamatergic auditory cortical neurons supporting the present slice findings. Responses to nAChR activation at excitatory corticothalamic and inhibitory tectothalamic inputs were diminished by aging. These findings suggest that cholinergic input to the MGB increases the strength of tectothalamic inhibitory projections, potentially improving the signal-to-noise ratio and signal detection while increasing corticothalamic gain, which may facilitate top-down identification of stimulus identity. These mechanisms appear to be affected negatively by aging, potentially diminishing speech perception in noisy environments. Cholinergic inputs to the MGB appear to maximize sensory processing by adjusting both top-down and bottom-up mechanisms in conditions of attention and arousal. SIGNIFICANCE STATEMENT The pedunculopontine tegmental nucleus is the source of cholinergic innervation for sensory thalamus and is a critical part of an ascending arousal system that controls the firing mode of thalamic cells based on attentional demand. The present study describes the location and impact of aging on presynaptic neuronal nicotinic acetylcholine receptors (nAChRs) within the circuitry of the auditory thalamus (medial geniculate body, MGB). We show that nAChRs are located on ascending inhibitory and descending excitatory presynaptic inputs onto MGB neurons, likely increasing gain selectively and improving temporal clarity. In addition, we show that aging has a deleterious effect on nAChR efficacy. Cholinergic dysfunction at the level of MGB may affect speech understanding negatively in the elderly population. PMID:29061702

Congenital Myasthenic Syndrome Type 19 Is Caused by Mutations in COL13A1, Encoding the Atypical Non-fibrillar Collagen Type XIII α1 Chain.

PubMed

Logan, Clare V; Cossins, Judith; Rodríguez Cruz, Pedro M; Parry, David A; Maxwell, Susan; Martínez-Martínez, Pilar; Riepsaame, Joey; Abdelhamed, Zakia A; Lake, Alice V R; Moran, Maria; Robb, Stephanie; Chow, Gabriel; Sewry, Caroline; Hopkins, Philip M; Sheridan, Eamonn; Jayawant, Sandeep; Palace, Jacqueline; Johnson, Colin A; Beeson, David

2015-12-03

The neuromuscular junction (NMJ) consists of a tripartite synapse with a presynaptic nerve terminal, Schwann cells that ensheathe the terminal bouton, and a highly specialized postsynaptic membrane. Synaptic structural integrity is crucial for efficient signal transmission. Congenital myasthenic syndromes (CMSs) are a heterogeneous group of inherited disorders that result from impaired neuromuscular transmission, caused by mutations in genes encoding proteins that are involved in synaptic transmission and in forming and maintaining the structural integrity of NMJs. To identify further causes of CMSs, we performed whole-exome sequencing (WES) in families without an identified mutation in known CMS-associated genes. In two families affected by a previously undefined CMS, we identified homozygous loss-of-function mutations in COL13A1, which encodes the alpha chain of an atypical non-fibrillar collagen with a single transmembrane domain. COL13A1 localized to the human muscle motor endplate. Using CRISPR-Cas9 genome editing, modeling of the COL13A1 c.1171delG (p.Leu392Sfs(∗)71) frameshift mutation in the C2C12 cell line reduced acetylcholine receptor (AChR) clustering during myotube differentiation. This highlights the crucial role of collagen XIII in the formation and maintenance of the NMJ. Our results therefore delineate a myasthenic disorder that is caused by loss-of-function mutations in COL13A1, encoding a protein involved in organization of the NMJ, and emphasize the importance of appropriate symptomatic treatment for these individuals. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.

Accelerated intoxication of GABAergic synapses by botulinum neurotoxin A disinhibits stem cell-derived neuron networks prior to network silencing

PubMed Central

Beske, Phillip H.; Scheeler, Stephen M.; Adler, Michael; McNutt, Patrick M.

2015-01-01

Botulinum neurotoxins (BoNTs) are extremely potent toxins that specifically cleave SNARE proteins in peripheral synapses, preventing neurotransmitter release. Neuronal responses to BoNT intoxication are traditionally studied by quantifying SNARE protein cleavage in vitro or monitoring physiological paralysis in vivo. Consequently, the dynamic effects of intoxication on synaptic behaviors are not well-understood. We have reported that mouse embryonic stem cell-derived neurons (ESNs) are highly sensitive to BoNT based on molecular readouts of intoxication. Here we study the time-dependent changes in synapse- and network-level behaviors following addition of BoNT/A to spontaneously active networks of glutamatergic and GABAergic ESNs. Whole-cell patch-clamp recordings indicated that BoNT/A rapidly blocked synaptic neurotransmission, confirming that ESNs replicate the functional pathophysiology responsible for clinical botulism. Quantitation of spontaneous neurotransmission in pharmacologically isolated synapses revealed accelerated silencing of GABAergic synapses compared to glutamatergic synapses, which was consistent with the selective accumulation of cleaved SNAP-25 at GAD1+ pre-synaptic terminals at early timepoints. Different latencies of intoxication resulted in complex network responses to BoNT/A addition, involving rapid disinhibition of stochastic firing followed by network silencing. Synaptic activity was found to be highly sensitive to SNAP-25 cleavage, reflecting the functional consequences of the localized cleavage of the small subpopulation of SNAP-25 that is engaged in neurotransmitter release in the nerve terminal. Collectively these findings illustrate that use of synaptic function assays in networked neurons cultures offers a novel and highly sensitive approach for mechanistic studies of toxin:neuron interactions and synaptic responses to BoNT. PMID:25954159

Whole-body vibration induces distinct reflex patterns in human soleus muscle.

PubMed

Karacan, Ilhan; Cidem, Muharrem; Cidem, Mehmet; Türker, Kemal S

2017-06-01

The neuronal mechanisms underlying whole body vibration (WBV)-induced muscular reflex (WBV-IMR) are not well understood. To define a possible pathway for WBV-IMR, this study investigated the effects of WBV amplitude on WBV-IMR latency by surface electromyography analysis of the soleus muscle in human adult volunteers. The tendon (T) reflex was also induced to evaluate the level of presynaptic Ia inhibition during WBV. WBV-IMR latency was shorter when induced by low- as compared to medium- or high-amplitude WBV (33.9±5.3msvs. 43.8±3.6 and 44.1±4.2ms, respectively). There was no difference in latencies between T-reflex elicited before WBV (33.8±2.4ms) and WBV-IMR induced by low-amplitude WBV. Presynaptic Ia inhibition was absent during low-amplitude WBV but was present during medium- and high-amplitude WBV. Consequently, WBV induces short- or long-latency reflexes depending on the vibration amplitude. During low-amplitude WBV, muscle spindle activation may induce the short- but not the long-latency WBV-IMR. Furthermore, unlike the higher amplitude WBV, low-amplitude WBV does not induce presynaptic inhibition at the Ia synaptic terminals. Copyright © 2017 Elsevier Ltd. All rights reserved.

Drosophila Atlastin in motor neurons is required for locomotion and presynaptic function.

PubMed

De Gregorio, Cristian; Delgado, Ricardo; Ibacache, Andrés; Sierralta, Jimena; Couve, Andrés

2017-10-15

Hereditary spastic paraplegias (HSPs) are characterized by spasticity and weakness of the lower limbs, resulting from length-dependent axonopathy of the corticospinal tracts. In humans, the HSP-related atlastin genes ATL1 - ATL3 catalyze homotypic membrane fusion of endoplasmic reticulum (ER) tubules. How defects in neuronal Atlastin contribute to axonal degeneration has not been explained satisfactorily. Using Drosophila , we demonstrate that downregulation or overexpression of Atlastin in motor neurons results in decreased crawling speed and contraction frequency in larvae, while adult flies show progressive decline in climbing ability. Broad expression in the nervous system is required to rescue the atlastin -null Drosophila mutant ( atl 2 ) phenotype. Importantly, both spontaneous release and the reserve pool of synaptic vesicles are affected. Additionally, axonal secretory organelles are abnormally distributed, whereas presynaptic proteins diminish at terminals and accumulate in distal axons, possibly in lysosomes. Our findings suggest that trafficking defects produced by Atlastin dysfunction in motor neurons result in redistribution of presynaptic components and aberrant mobilization of synaptic vesicles, stressing the importance of ER-shaping proteins and the susceptibility of motor neurons to their mutations or depletion. © 2017. Published by The Company of Biologists Ltd.

Regulation of synaptic activity by snapin-mediated endolysosomal transport and sorting

PubMed Central

Di Giovanni, Jerome; Sheng, Zu-Hang

2015-01-01

Recycling synaptic vesicles (SVs) transit through early endosomal sorting stations, which raises a fundamental question: are SVs sorted toward endolysosomal pathways? Here, we used snapin mutants as tools to assess how endolysosomal sorting and trafficking impact presynaptic activity in wild-type and snapin−/− neurons. Snapin acts as a dynein adaptor that mediates the retrograde transport of late endosomes (LEs) and interacts with dysbindin, a subunit of the endosomal sorting complex BLOC-1. Expressing dynein-binding defective snapin mutants induced SV accumulation at presynaptic terminals, mimicking the snapin−/− phenotype. Conversely, over-expressing snapin reduced SV pool size by enhancing SV trafficking to the endolysosomal pathway. Using a SV-targeted Ca2+ sensor, we demonstrate that snapin–dysbindin interaction regulates SV positional priming through BLOC-1/AP-3-dependent sorting. Our study reveals a bipartite regulation of presynaptic activity by endolysosomal trafficking and sorting: LE transport regulates SV pool size, and BLOC-1/AP-3-dependent sorting fine-tunes the Ca2+ sensitivity of SV release. Therefore, our study provides new mechanistic insights into the maintenance and regulation of SV pool size and synchronized SV fusion through snapin-mediated LE trafficking and endosomal sorting. PMID:26108535

Ca2+-independent Activation of Ca2+/Calmodulin-dependent Protein Kinase II Bound to the C-terminal Domain of CaV2.1 Calcium Channels*

PubMed Central

Magupalli, Venkat G.; Mochida, Sumiko; Yan, Jin; Jiang, Xin; Westenbroek, Ruth E.; Nairn, Angus C.; Scheuer, Todd; Catterall, William A.

2013-01-01

Ca2+/calmodulin-dependent protein kinase II (CaMKII) forms a major component of the postsynaptic density where its functions in synaptic plasticity are well established, but its presynaptic actions are poorly defined. Here we show that CaMKII binds directly to the C-terminal domain of CaV2.1 channels. Binding is enhanced by autophosphorylation, and the kinase-channel signaling complex persists after dephosphorylation and removal of the Ca2+/CaM stimulus. Autophosphorylated CaMKII can bind the CaV2.1 channel and synapsin-1 simultaneously. CaMKII binding to CaV2.1 channels induces Ca2+-independent activity of the kinase, which phosphorylates the enzyme itself as well as the neuronal substrate synapsin-1. Facilitation and inactivation of CaV2.1 channels by binding of Ca2+/CaM mediates short term synaptic plasticity in transfected superior cervical ganglion neurons, and these regulatory effects are prevented by a competing peptide and the endogenous brain inhibitor CaMKIIN, which blocks binding of CaMKII to CaV2.1 channels. These results define the functional properties of a signaling complex of CaMKII and CaV2.1 channels in which both binding partners are persistently activated by their association, and they further suggest that this complex is important in presynaptic terminals in regulating protein phosphorylation and short term synaptic plasticity. PMID:23255606

Action potentials reliably invade axonal arbors of rat neocortical neurons

PubMed Central

Cox, Charles L.; Denk, Winfried; Tank, David W.; Svoboda, Karel

2000-01-01

Neocortical pyramidal neurons have extensive axonal arborizations that make thousands of synapses. Action potentials can invade these arbors and cause calcium influx that is required for neurotransmitter release and excitation of postsynaptic targets. Thus, the regulation of action potential invasion in axonal branches might shape the spread of excitation in cortical neural networks. To measure the reliability and extent of action potential invasion into axonal arbors, we have used two-photon excitation laser scanning microscopy to directly image action-potential-mediated calcium influx in single varicosities of layer 2/3 pyramidal neurons in acute brain slices. Our data show that single action potentials or bursts of action potentials reliably invade axonal arbors over a range of developmental ages (postnatal 10–24 days) and temperatures (24°C-30°C). Hyperpolarizing current steps preceding action potential initiation, protocols that had previously been observed to produce failures of action potential propagation in cultured preparations, were ineffective in modulating the spread of action potentials in acute slices. Our data show that action potentials reliably invade the axonal arbors of neocortical pyramidal neurons. Failures in synaptic transmission must therefore originate downstream of action potential invasion. We also explored the function of modulators that inhibit presynaptic calcium influx. Consistent with previous studies, we find that adenosine reduces action-potential-mediated calcium influx in presynaptic terminals. This reduction was observed in all terminals tested, suggesting that some modulatory systems are expressed homogeneously in most terminals of the same neuron. PMID:10931955

Characterization, localization and function of pertussis toxin-sensitive G proteins in the nervous systems of Aplysia and Loligo

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vogel, S.S.

1989-01-01

The author has characterized pertussis toxin-sensitive G proteins in the nervous systems of the gastropod mollusc Aplysia and the cephalopod Loligo using ({sup 32}P)ADP-ribosylation and immunoblotting with G protein specific antisera. As in vertebrates, this class of G protein is associated with membranes and enriched in nervous tissue in Aplysia. Analysis of dissected Aplysia ganglia reveal that it is enriched in neuropil, a region containing most of the central nervous system synapses. Because both Aplysia and Loligo synaptosomes are enriched in pertussis toxin-sensitive G proteins, it is likely that they are found in synaptic terminals. Fractionation of Aplysia synaptosomes intomore » membrane and vesicle fractions reveals that, although the majority of G protein is recovered in the plasma membrane fraction, a small proportion is recovered in the vesicle fraction. He shows that G proteins are on intracellular membranes by ADP-ribosylating extruded axoplasm with pertussis toxin. A plausible explanation for vesicular localization of G protein in axoplasm is that G proteins are transported to terminals on vesicles. He has shown, using ligature experiments with Aplysia connectives and temperature block experiments in the giant axon of Loligo, that G proteins move by anterograde fast axonal transport. Injection of pertussis toxin into the identified Aplysia neuron L10 blocks histamine-induced presynaptic inhibition of transmitter release. This suggests that pertussis toxin sensitive G proteins play a role in modulating transmitter release at synaptic terminals. In the giant synapse of Loligo, he presents preliminary data that demonstrates that the activation of G proteins in the presynaptic terminal results in decreased transmitter release.« less

Triazines facilitate neurotransmitter release of synaptic terminals located in hearts of frog (Rana ridibunda) and honeybee (Apis mellifera) and in the ventral nerve cord of a beetle (Tenebrio molitor).

PubMed

Papaefthimiou, Chrisovalantis; Zafeiridou, Georgia; Topoglidi, Aglaia; Chaleplis, George; Zografou, Stella; Theophilidis, George

2003-07-01

Three triazine herbicides, atrazine, simazine and metribuzine, and some of their major metabolites (cyanuric acid and 6-azauracil) were investigated for their action on synaptic terminals using three different isolated tissue preparations from the atria of the frog, Rana ridibunda, the heart of the honeybee, Apis mellifera macedonica, and the ventral nerve cord of the beetle, Tenebrio molitor. The results indicate that triazines facilitate the release of neurotransmitters from nerve terminals, as already reported for the mammalian central nervous system. The no observed effect concentration, the maximum concentration of the herbicide diluted in the saline that has no effect on the physiological properties of the isolated tissue, was estimated for each individual preparation. According to their relative potency, the three triazines tested can be ranked as follows: atrazine (cyanuric acid), simazine>metribuzine (6-azauracil). The action of these compounds on the cholinergic (amphibians, insects), adrenergic (amphibian) and octopaminergic (insects) synaptic terminals is discussed.

Excitatory and inhibitory synaptic mechanisms at the first stage of integration in the electroreception system of the shark

PubMed Central

Rotem, Naama; Sestieri, Emanuel; Hounsgaard, Jorn; Yarom, Yosef

2014-01-01

High impulse rate in afferent nerves is a common feature in many sensory systems that serve to accommodate a wide dynamic range. However, the first stage of integration should be endowed with specific properties that enable efficient handling of the incoming information. In elasmobranches, the afferent nerve originating from the ampullae of Lorenzini targets specific neurons located at the Dorsal Octavolateral Nucleus (DON), the first stage of integration in the electroreception system. Using intracellular recordings in an isolated brainstem preparation from the shark we analyze the properties of this afferent pathway. We found that stimulating the afferent nerve activates a mixture of excitatory and inhibitory synapses mediated by AMPA-like and GABAA receptors, respectively. The excitatory synapses that are extremely efficient in activating the postsynaptic neurons display unusual voltage dependence, enabling them to operate as a current source. The inhibitory input is powerful enough to completely eliminate the excitatory action of the afferent nerve but is ineffective regarding other excitatory inputs. These observations can be explained by the location and efficiency of the synapses. We conclude that the afferent nerve provides powerful and reliable excitatory input as well as a feed-forward inhibitory input, which is partially presynaptic in origin. These results question the cellular location within the DON where cancelation of expected incoming signals occurs. PMID:24639631

Extralaryngeal division of the recurrent laryngeal nerve: a new description for the inferior laryngeal nerve.

PubMed

Yalcin, Bulent; Tunali, Selcuk; Ozan, Hasan

2008-05-01

Extralaryngeal division of the recurrent laryngeal nerve was contradictory in the literature. We aimed to investigate extralaryngeal division of the nerve, and also propose a new description for the inferior laryngeal nerve. Sixty specimens (120 sides) were examined for this project, including 41 men and 19 women cadavers between the ages of 40 and 89 years at death. In one right side, terminal segment of the nerve gave off many small branches surrounding the inferior thyroid artery then reaching the larynx, trachea, thyroid gland and esophagus. In eight sides, terminal segment of the nerve had no extralaryngeal division and entered the larynx as a single trunk. In 110 sides, the nerve had extralaryngeal division. One hundred and three nerves had two laryngeal and one to three extralaryngeal branches. Two types were described in this group. In type I (66 nerves), both branches arose from the same level of nerve. Type I had two subtypes: type Ia, the origin of the branches was just below the inferior constrictor muscle; type Ib, the origin of the branches was 15-35 mm below the muscle. In type II (37 nerves), the laryngeal branches arose just 3-5 mm above the extralaryngeal branches. We observed that the laryngeal and extralaryngeal branches arose generally from the same point of the recurrent laryngeal nerve. The inferior laryngeal nerve is thus very short, or even nonexistent. Therefore, we suggest that if the term "superior laryngeal nerve" is a given, standard, and accepted term, then the term "inferior laryngeal nerve" should also be accepted instead of the term "recurrent laryngeal nerve."

Surgical Approaches to Facial Nerve Deficits

PubMed Central

Birgfeld, Craig; Neligan, Peter

2011-01-01

The facial nerve is one of the most commonly injured cranial nerves. Once injured, the effects on form, function, and psyche are profound. We review the anatomy of the facial nerve from the brain stem to its terminal branches. We also discuss the physical exam findings of facial nerve injury at various levels. Finally, we describe various reconstructive options for reanimating the face and restoring both form and function. PMID:22451822

Occlusion of carotid artery and hypergravity loading of animals caused similar effects on L-[14C]glutamate uptake in rat brain nerve terminals

NASA Astrophysics Data System (ADS)

Borisova, Tatiana; Sivko, Roman; Krisanova, Natalia

Changes in sodium-dependent L-[14C]glutamate uptake in rat brain nerve terminals was com-paratively analysed after hypergravity loading of animals (centrifugation of rats in special con-tainers at 10 G for 1 hour) and unilateral occlusion of carotid artery (20 min). The initial velocity of L-[14C]glutamate uptake was decreased from 2.5 ± 0.2 nmol x min-1 x mg-1 of proteins to 2.05 ± 0.1 nmol x min-1 x mg-1 of proteins after hypergravity and after occlusion -up to 2.25 ± 0.1 nmol x min-1 x mg-1 of proteins. Recently, we have shown that a decrease in L-[14C]glutamate uptake was at least partially caused by the redaction in the membrane potential of nerve terminals and the proton gradient of synaptic vesicles. These parameters were analysed after unilateral occlusion of carotid artery, where one brain hemisphere was used as a control, whereas the second one as subjected to ischemic/hypoxic conditions. Similarly with hypergravity, we revealed a decrease in the membrane potential of nerve terminals by ˜ 10 % and a reduction of the proton gradient of synaptic vesicles by ˜ 5 % after occlusion of carotid artery. Thus, a decrease in the activity of glutamate transporters after hypergrav-ity and unilateral occlusion of carotid artery was at least partially caused by changes in the membrane potential of nerve terminals and the proton gradient of synaptic vesicles. This fact may be considered in support of the suggestion that ischemia/hypoxia was a main unspecific stressor, which caused the alterations in glutamatergic neurotransmission under conditions of hypergravity.

Maintenance of Mouse Gustatory Terminal Field Organization Is Disrupted following Selective Removal of Peripheral Sodium Salt Taste Activity at Adulthood

PubMed Central

Sun, Chengsan

2017-01-01

Neural activity plays a critical role in the development of central circuits in sensory systems. However, the maintenance of these circuits at adulthood is usually not dependent on sensory-elicited neural activity. Recent work in the mouse gustatory system showed that selectively deleting the primary transduction channel for sodium taste, the epithelial sodium channel (ENaC), throughout development dramatically impacted the organization of the central terminal fields of three nerves that carry taste information to the nucleus of the solitary tract. More specifically, deleting ENaCs during development prevented the normal maturation of the fields. The present study was designed to extend these findings by testing the hypothesis that the loss of sodium taste activity impacts the maintenance of the normal adult terminal field organization in male and female mice. To do this, we used an inducible Cre-dependent genetic recombination strategy to delete ENaC function after terminal field maturation occurred. We found that removal of sodium taste neural activity at adulthood resulted in significant reorganization of mature gustatory afferent terminal fields in the nucleus of the solitary tract. Specifically, the chorda tympani and greater superficial petrosal nerve terminal fields were 1.4× and 1.6× larger than age-matched controls, respectively. By contrast, the glossopharyngeal nerve, which is not highly sensitive to sodium taste stimulation, did not undergo terminal field reorganization. These surprising results suggest that gustatory nerve terminal fields remain plastic well into adulthood, which likely impacts central coding of taste information and taste-related behaviors with altered taste experience. SIGNIFICANCE STATEMENT Neural activity plays a major role in the development of sensory circuits in the mammalian brain. However, the importance of sensory-driven activity in maintaining these circuits at adulthood, especially in subcortical structures, appears to be much less. Here, we tested whether the loss of sodium taste activity in adult mice impacts the maintenance of how taste nerves project to the first central relay. We found that specific loss of sodium-elicited taste activity at adulthood produced dramatic and selective reorganization of terminal fields in the brainstem. This demonstrates, for the first time, that taste-elicited activity is necessary for the normal maintenance of central gustatory circuits at adulthood and highlights a level of plasticity not seen in other sensory system subcortical circuits. PMID:28676575

Short-Term Facilitation at a Detonator Synapse Requires the Distinct Contribution of Multiple Types of Voltage-Gated Calcium Channels.

PubMed

Chamberland, Simon; Evstratova, Alesya; Tóth, Katalin

2017-05-10

Neuronal calcium elevations are shaped by several key parameters, including the properties, density, and the spatial location of voltage-gated calcium channels (VGCCs). These features allow presynaptic terminals to translate complex firing frequencies and tune the amount of neurotransmitter released. Although synchronous neurotransmitter release relies on both P/Q- and N-type VGCCs at hippocampal mossy fiber-CA3 synapses, the specific contribution of VGCCs to calcium dynamics, neurotransmitter release, and short-term facilitation remains unknown. Here, we used random-access two-photon calcium imaging together with electrophysiology in acute mouse hippocampal slices to dissect the roles of P/Q- and N-type VGCCs. Our results show that N-type VGCCs control glutamate release at a limited number of release sites through highly localized Ca 2+ elevations and support short-term facilitation by enhancing multivesicular release. In contrast, Ca 2+ entry via P/Q-type VGCCs promotes the recruitment of additional release sites through spatially homogeneous Ca 2+ elevations. Altogether, our results highlight the specialized contribution of P/Q- and N-types VGCCs to neurotransmitter release. SIGNIFICANCE STATEMENT In presynaptic terminals, neurotransmitter release is dynamically regulated by the transient opening of different types of voltage-gated calcium channels. Hippocampal giant mossy fiber terminals display extensive short-term facilitation during repetitive activity, with a large several fold postsynaptic response increase. Though, how giant mossy fiber terminals leverage distinct types of voltage-gated calcium channels to mediate short-term facilitation remains unexplored. Here, we find that P/Q- and N-type VGCCs generate different spatial patterns of calcium elevations in giant mossy fiber terminals and support short-term facilitation through specific participation in two mechanisms. Whereas N-type VGCCs contribute only to the synchronization of multivesicular release, P/Q-type VGCCs act through microdomain signaling to recruit additional release sites. Copyright © 2017 the authors 0270-6474/17/374913-15$15.00/0.

Muscarinic acetylcholine receptor subtype expression in avian vestibular hair cells, nerve terminals and ganglion cells.

PubMed

Li, G Q; Kevetter, G A; Leonard, R B; Prusak, D J; Wood, T G; Correia, M J

2007-04-25

Muscarinic acetylcholine receptors (mAChRs) are widely expressed in the CNS and peripheral nervous system and play an important role in modulating the cell activity and function. We have shown that the cholinergic agonist carbachol reduces the pigeon's inwardly rectifying potassium channel (pKir2.1) ionic currents in native vestibular hair cells. We have cloned and sequenced pigeon mAChR subtypes M2-M5 and we have studied the expression of all five mAChR subtypes (M1-M5) in the pigeon vestibular end organs (semicircular canal ampullary cristae and utricular maculae), vestibular nerve fibers and the vestibular (Scarpa's) ganglion using tissue immunohistochemistry (IH), dissociated single cell immunocytochemistry (IC) and Western blotting (WB). We found that vestibular hair cells, nerve fibers and ganglion cells each expressed all five (M1-M5) mAChR subtypes. Two of the three odd-numbered mAChRs (M1, M5) were present on the hair cell cilia, supporting cells and nerve terminals. And all three odd numbered mAChRs (M1, M3 and M5) were expressed on cuticular plates, myelin sheaths and Schwann cells. Even-numbered mAChRs were seen on the nerve terminals. M2 was also shown on the cuticular plates and supporting cells. Vestibular efferent fibers and terminals were not identified in our studies. Results from WB of the dissociated vestibular epithelia, nerve fibers and vestibular ganglia were consistent with the results from IH and IC. Our findings suggest that there is considerable co-expression of the subtypes on the neural elements of the labyrinth. Further electrophysiological and pharmacological studies should delineate the mechanisms of action of muscarinic acetylcholine receptors on structures in the labyrinth.

Peripheral axotomy of the rat mandibular trigeminal nerve leads to an increase in VIP and decrease of other primary afferent neuropeptides in the spinal trigeminal nucleus.

PubMed

Atkinson, M E; Shehab, S A

1986-12-01

In the vasoactive intestinal polypeptide (VIP)-rich lumbosacral spinal cord, VIP increases at the expense of other neuropeptides after primary sensory nerve axotomy. This study was undertaken to ascertain whether similar changes occur in peripherally axotomised cranial sensory nerves. VIP immunoreactivity increased in the terminal region of the mandibular nerve in the trigeminal nucleus caudalis following unilateral section of the sensory root of the mandibular trigeminal nerve at the foramen orale. Other primary afferent neuropeptides (substance P, cholecystokinin and somatostatin) were depleted and fluoride-resistant acid phosphatase activity was abolished in the same circumscribed areas of the nucleus caudalis. The rise in VIP and depletion of other markers began 4 days postoperatively and was maximal by 10 days, these levels remaining unchanged up to 1 year postoperatively. VIP-immunoreactive cell bodies were absent from trigeminal ganglia from the unoperated side but small and medium cells stained intensely in the ganglia of the operated side after axotomy. These observations indicate that increase of VIP in sensory nerve terminals is a general phenomenon occurring in both cranial and spinal sensory terminal areas. The intense VIP immunoreactivity in axotomised trigeminal ganglia suggests that the increased levels of VIP in the nucleus caudalis are of peripheral origin, indicating a change in expression of neuropeptides within primary afferent neurons following peripheral axotomy.

Prevention and Treatment of Noise-Induced Tinnitus. Revision

DTIC Science & Technology

2013-07-01

CTBP2 immunolabeling) for their loss following noise. Sub-Task 1c: Assessment of Auditory Nerve ( VGLUT1 immunolabel) terminals on neurons in Ventral...and Dorsal Cochlear Nucleus (VCN, DCN) for their loss following noise. Sub-Task 1d: Assessment of VGLUT2 , VAT & VGAT immunolabeled terminals in VCN...significant reduction in connections compared to animals without noise exposure. Sub-Task 1c: Assessment of Auditory Nerve ( VGLUT1 immunolabel

Direct evidence for activity-dependent glucose phosphorylation in neurons with implications for the astrocyte-to-neuron lactate shuttle

PubMed Central

Patel, Anant B.; Lai, James C. K.; Chowdhury, Golam M. I.; Hyder, Fahmeed; Rothman, Douglas L.; Shulman, Robert G.; Behar, Kevin L.

2014-01-01

Previous 13C magnetic resonance spectroscopy experiments have shown that over a wide range of neuronal activity, approximately one molecule of glucose is oxidized for every molecule of glutamate released by neurons and recycled through astrocytic glutamine. The measured kinetics were shown to agree with the stoichiometry of a hypothetical astrocyte-to-neuron lactate shuttle model, which predicted negligible functional neuronal uptake of glucose. To test this model, we measured the uptake and phosphorylation of glucose in nerve terminals isolated from rats infused with the glucose analog, 2-fluoro-2-deoxy-d-glucose (FDG) in vivo. The concentrations of phosphorylated FDG (FDG6P), normalized with respect to known neuronal metabolites, were compared in nerve terminals, homogenate, and cortex of anesthetized rats with and without bicuculline-induced seizures. The increase in FDG6P in nerve terminals agreed well with the increase in cortical neuronal glucose oxidation measured previously under the same conditions in vivo, indicating that direct uptake and oxidation of glucose in nerve terminals is substantial under resting and activated conditions. These results suggest that neuronal glucose-derived pyruvate is the major oxidative fuel for activated neurons, not lactate-derived from astrocytes, contradicting predictions of the original astrocyte-to-neuron lactate shuttle model under the range of study conditions. PMID:24706914

Direct evidence for activity-dependent glucose phosphorylation in neurons with implications for the astrocyte-to-neuron lactate shuttle.

PubMed

Patel, Anant B; Lai, James C K; Chowdhury, Golam M I; Hyder, Fahmeed; Rothman, Douglas L; Shulman, Robert G; Behar, Kevin L

2014-04-08

Previous (13)C magnetic resonance spectroscopy experiments have shown that over a wide range of neuronal activity, approximately one molecule of glucose is oxidized for every molecule of glutamate released by neurons and recycled through astrocytic glutamine. The measured kinetics were shown to agree with the stoichiometry of a hypothetical astrocyte-to-neuron lactate shuttle model, which predicted negligible functional neuronal uptake of glucose. To test this model, we measured the uptake and phosphorylation of glucose in nerve terminals isolated from rats infused with the glucose analog, 2-fluoro-2-deoxy-D-glucose (FDG) in vivo. The concentrations of phosphorylated FDG (FDG6P), normalized with respect to known neuronal metabolites, were compared in nerve terminals, homogenate, and cortex of anesthetized rats with and without bicuculline-induced seizures. The increase in FDG6P in nerve terminals agreed well with the increase in cortical neuronal glucose oxidation measured previously under the same conditions in vivo, indicating that direct uptake and oxidation of glucose in nerve terminals is substantial under resting and activated conditions. These results suggest that neuronal glucose-derived pyruvate is the major oxidative fuel for activated neurons, not lactate-derived from astrocytes, contradicting predictions of the original astrocyte-to-neuron lactate shuttle model under the range of study conditions.

Adenosine A2B and A3 receptor location at the mouse neuromuscular junction.

PubMed

Garcia, Neus; Priego, Mercedes; Hurtado, Erica; Obis, Teresa; Santafe, Manel M; Tomàs, Marta; Lanuza, Maria Angel; Tomàs, Josep

2014-07-01

To date, four subtypes of adenosine receptors have been cloned (A(1)R, A(2A)R, A(2B)R, and A(3)R). In a previous study we used confocal immunocytochemistry to identify A(1)R and A(2A)R receptors at mouse neuromuscular junctions (NMJs). The data shows that these receptors are localized differently in the three cells (muscle, nerve and glia) that configure the NMJs. A(1)R localizes in the terminal teloglial Schwann cell and nerve terminal, whereas A(2A)R localizes in the postsynaptic muscle and in the axon and nerve terminal. Here, we use Western blotting to investigate the presence of A(2B)R and A(3)R receptors in striated muscle and immunohistochemistry to localize them in the three cells of the adult neuromuscular synapse. The data show that A(2B)R and A(3)R receptors are present in the nerve terminal and muscle cells at the NMJs. Neither A(2B)R nor A(3)R receptors are localized in the Schwann cells. Thus, the four subtypes of adenosine receptors are present in the motor endings. The presence of these receptors in the neuromuscular synapse allows the receptors to be involved in the modulation of transmitter release. © 2014 Anatomical Society.

Ulcerative colitis: ultrastructure of interstitial cells in myenteric plexus.

PubMed

Rumessen, J J; Vanderwinden, J-M; Horn, T

2010-10-01

Interstitial cells of Cajal (ICC) are key regulatory cells in the gut. In the colon of patients with severe ulcerative colitis (UC), myenteric ICC had myoid ultrastructural features and were in close contact with nerve terminals. In all patients as opposed to controls, some ICC profiles showed degenerative changes, such as lipid droplets and irregular vacuoles. Nerve terminals often appeared swollen and empty. Glial cells, muscle cells, and fibroblast-like cells (FLC) showed no alterations. FLC enclosed macrophages (MLC), which were in close contact with naked axon terminals. The organization and cytological changes may be of pathophysiological significance in patients with UC.

Presynaptic muscarinic control of glutamatergic synaptic transmission.

PubMed

Buño, W; Cabezas, C; Fernández de Sevilla, D

2006-01-01

The hippocampus receives cholinergic projections from the medial septal nucleus and Broca's diagonal band that terminate in the CA1, CA3, and dentate gyrus regions (Frotscher and Leranth, 1985). Glutamatergic synapses between CA3 and CA1 pyramidal neurons are presynaptically inhibited by acetylcholine (ACh), via activation of muscarinic ACh receptors (mAChRs) at the terminals of Schaffer collaterals (SCs) (Hounsgaard, 1978; Fernández de Sevilla et al., 2002, 2003). There are two types of SC-CA1 pyramidal neuron synapses. One type, called functional synapse, shows postsynaptic alpha- amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-receptor mediated currents at resting potential (Vm) and both AMPA and N-methyl-D-aspartate receptor (NMDAR)-mediated currents when depolarized. The other type, termed silent synapse, only displays postsynaptic NMDAR-mediated currents at depolarized Vms, but does not respond at the resting Vm (Isaac et al., 1995). Using hippocampal slices obtained from young Wistar rats, we examined the effects of activation of cholinergic afferents at the stratum oriens/alveus on excitatory postsynaptic currents (EPSCs) evoked in CA1 pyramidal neurons by stimulation of SCs. We also tested the action of the nonhydrolyzable cholinergic agonist carbamylcholine chloride (CCh) on EPSCs evoked by minimal stimulation of SCs (which activates a single or very few synapses) in functional and silent synapses.

Non-random nature of spontaneous mIPSCs in mouse auditory brainstem neurons revealed by recurrence quantification analysis

PubMed Central

Leao, Richardson N; Leao, Fabricio N; Walmsley, Bruce

2005-01-01

A change in the spontaneous release of neurotransmitter is a useful indicator of processes occurring within presynaptic terminals. Linear techniques (e.g. Fourier transform) have been used to analyse spontaneous synaptic events in previous studies, but such methods are inappropriate if the timing pattern is complex. We have investigated spontaneous glycinergic miniature synaptic currents (mIPSCs) in principal cells of the medial nucleus of the trapezoid body. The random versus deterministic (or periodic) nature of mIPSCs was assessed using recurrence quantification analysis. Nonlinear methods were then used to quantify any detected determinism in spontaneous release, and to test for chaotic or fractal patterns. Modelling demonstrated that this procedure is much more sensitive in detecting periodicities than conventional techniques. mIPSCs were found to exhibit periodicities that were abolished by blockade of internal calcium stores with ryanodine, suggesting calcium oscillations in the presynaptic inhibitory terminals. Analysis indicated that mIPSC occurrences were chaotic in nature. Furthermore, periodicities were less evident in congenitally deaf mice than in normal mice, indicating that appropriate neural activity during development is necessary for the expression of deterministic chaos in mIPSC patterns. We suggest that chaotic oscillations of mIPSC occurrences play a physiological role in signal processing in the auditory brainstem. PMID:16271982

Observations on the elimination of polyneuronal innervation in developing mammalian skeletal muscle.

PubMed Central

O'Brien, R A; Ostberg, A J; Vrbová, G

1978-01-01

1. The mechanism responsible for the elimination of polyneuronal innervation in developing rat soleus muscles was studied electrophysiologically and histologically. 2. Initially all the axons contacting a single end-plate have simple bulbous terminals. As elimination proceeds one axon develops terminal branches while the other terminals remain bulbous and may be seen in contact with, or a short distance away from, the end-plate. It is suggested that the branched terminal remains in contact with the muscle fibre while the other terminals withdraw. 3. At a time when polyneuronal innervation can no longer be detected electrophysiologically, the histological technique still shows the presence of end-plates contacted by more than one nerve terminal. 4. The effect of activity on the disappearance of polyneuronal innervation was examined. Activity was increased by electrical stimulation of the right sciatic nerve. This procedure also produced reflex activity in the contralateral limb. In both cases polyneuronal innervation was eliminated more rapidly in the active muscles. 5. The finding that proteolytic enzymes are released from muscles treated with acetylcholine (ACh), and the observation of the more rapid elimination of supernumerary terminals at the end-plates of active muscles, lead to the suggestion that superfluous nerve-muscle contacts are removed by the proteolytic enzymes in response to neuromuscular activity. The selective stabilization of only one of the terminals is discussed in the light of these results. Images Plate 1 Plate 2 PMID:722562

Neuronal activity-dependent membrane traffic at the neuromuscular junction

PubMed Central

Miana-Mena, Francisco Javier; Roux, Sylvie; Benichou, Jean-Claude; Osta, Rosario; Brûlet, Philippe

2002-01-01

During development and also in adulthood, synaptic connections are modulated by neuronal activity. To follow such modifications in vivo, new genetic tools are designed. The nontoxic C-terminal fragment of tetanus toxin (TTC) fused to a reporter gene such as LacZ retains the retrograde and transsynaptic transport abilities of the holotoxin itself. In this work, the hybrid protein is injected intramuscularly to analyze in vivo the mechanisms of intracellular and transneuronal traffics at the neuromuscular junction (NMJ). Traffic on both sides of the synapse are strongly dependent on presynaptic neural cell activity. In muscle, a directional membrane traffic concentrates β-galactosidase-TTC hybrid protein into the NMJ postsynaptic side. In neurons, the probe is sorted across the cell to dendrites and subsequently to an interconnected neuron. Such fusion protein, sensitive to presynaptic neuronal activity, would be extremely useful to analyze morphological changes and plasticity at the NMJ. PMID:11880654

Altered cortical GABA neurotransmission in schizophrenia: insights into novel therapeutic strategies.

PubMed

Stan, Ana D; Lewis, David A

2012-06-01

Altered markers of cortical GABA neurotransmission are among the most consistently observed abnormalities in postmortem studies of schizophrenia. The altered markers are particularly evident between the chandelier class of GABA neurons and their synaptic targets, the axon initial segment (AIS) of pyramidal neurons. For example, in the dorsolateral prefrontal cortex of subjects with schizophrenia immunoreactivity for the GABA membrane transporter is decreased in presynaptic chandelier neuron axon terminals, whereas immunoreactivity for the GABAA receptor α2 subunit is increased in postsynaptic AIS. Both of these molecular changes appear to be compensatory responses to a presynaptic deficit in GABA synthesis, and thus could represent targets for novel therapeutic strategies intended to augment the brain's own compensatory mechanisms. Recent findings that GABA inputs from neocortical chandelier neurons can be powerfully excitatory provide new ideas about the role of these neurons in the pathophysiology of cortical dysfunction in schizophrenia, and consequently in the design of pharmacological interventions.

Neuronal Depolarization Drives Increased Dopamine Synaptic Vesicle Loading via VGLUT.

PubMed

Aguilar, Jenny I; Dunn, Matthew; Mingote, Susana; Karam, Caline S; Farino, Zachary J; Sonders, Mark S; Choi, Se Joon; Grygoruk, Anna; Zhang, Yuchao; Cela, Carolina; Choi, Ben Jiwon; Flores, Jorge; Freyberg, Robin J; McCabe, Brian D; Mosharov, Eugene V; Krantz, David E; Javitch, Jonathan A; Sulzer, David; Sames, Dalibor; Rayport, Stephen; Freyberg, Zachary

2017-08-30

The ability of presynaptic dopamine terminals to tune neurotransmitter release to meet the demands of neuronal activity is critical to neurotransmission. Although vesicle content has been assumed to be static, in vitro data increasingly suggest that cell activity modulates vesicle content. Here, we use a coordinated genetic, pharmacological, and imaging approach in Drosophila to study the presynaptic machinery responsible for these vesicular processes in vivo. We show that cell depolarization increases synaptic vesicle dopamine content prior to release via vesicular hyperacidification. This depolarization-induced hyperacidification is mediated by the vesicular glutamate transporter (VGLUT). Remarkably, both depolarization-induced dopamine vesicle hyperacidification and its dependence on VGLUT2 are seen in ventral midbrain dopamine neurons in the mouse. Together, these data suggest that in response to depolarization, dopamine vesicles utilize a cascade of vesicular transporters to dynamically increase the vesicular pH gradient, thereby increasing dopamine vesicle content. Copyright © 2017 Elsevier Inc. All rights reserved.

Neuronal Depolarization Drives Increased Dopamine Synaptic Vesicle Loading via VGLUT

PubMed Central

Aguilar, Jenny I.; Dunn, Matthew; Mingote, Susana; Karam, Caline S.; Farino, Zachary J.; Sonders, Mark S.; Choi, Se Joon; Grygoruk, Anna; Zhang, Yuchao; Cela, Carolina; Choi, Ben Jiwon; Flores, Jorge; Freyberg, Robin J.; McCabe, Brian D.; Mosharov, Eugene V.; Krantz, David E.; Javitch, Jonathan A.; Sulzer, David; Sames, Dalibor; Rayport, Stephen; Freyberg, Zachary

2017-01-01

SUMMARY The ability of presynaptic dopamine terminals to tune neurotransmitter release to meet the demands of neuronal activity is critical to neurotransmission. Although vesicle content has been assumed to be static, in vitro data increasingly suggest that cell activity modulates vesicle content. Here, we use a coordinated genetic, pharmacological, and imaging approach in Drosophila to study the presynaptic machinery responsible for these vesicular processes in vivo. We show that cell depolarization increases synaptic vesicle dopamine content prior to release via vesicular hyperacidification. This depolarization-induced hyperacidification is mediated by the vesicular glutamate transporter (VGLUT). Remarkably, both depolarization-induced dopamine vesicle hyperacidification and its dependence on VGLUT2 are seen in ventral midbrain dopamine neurons in the mouse. Together, these data suggest that in response to depolarization, dopamine vesicles utilize a cascade of vesicular transporters to dynamically increase the vesicular pH gradient, thereby increasing dopamine vesicle content. PMID:28823729

Development of serotonergic and adrenergic receptors in the rat spinal cord: effects of neonatal chemical lesions and hyperthyroidism.

PubMed

Lau, C; Pylypiw, A; Ross, L L

1985-03-01

The sympathetic preganglionic neurons in the spinal cord receive dense serotonergic (5-HT) and catecholaminergic (CA) afferent inputs from the descending supraspinal pathways. In the rat spinal cord, the levels of these biogenic amines and their receptors are low at birth, but undergo rapid ontogenetic increases in the ensuing 2-3 postnatal weeks until the adult levels are reached. In many systems it has been shown that denervation of presynaptic neurons leads to an up-regulation of the number of postsynaptic receptors. To determine whether the 5-HT and CA receptors in the developing spinal cord are also subject to such transsynaptic regulation, we examined the ontogeny of serotonergic receptors and alpha- and beta-adrenergic receptors in thoracolumbar spinal cord of rats given neurotoxins which destroy serotonergic (5,7-dihydroxytryptamine (5,7-DHT)) or noradrenergic (6-hydroxydopamine (6-OHDA)) nerve terminals. Intracisternal administration of 5,7-DHT or 6-OHDA at 1 and 6 days of age prevented, respectively, the development of 5-HT and CA levels in the spinal cord. Rats lesioned with 5,7-DHT displayed a marked elevation of 5-HT receptors with a binding of 50% greater than controls at 1 week and a continuing increase to twice normal by 4 weeks. A similar pattern of up-regulation was also detected with the alpha-adrenergic receptor, as rats lesioned with 6-OHDA exhibited persistent increases in receptor concentration. However, in these same animals ontogeny of the beta-adrenergic receptor in the spinal cord remained virtually unaffected by the chemical lesion. In several other parts of the nervous system, it has been demonstrated that the beta-adrenergic sensitivity can be modulated by hormonal signals, particularly that of the thyroid hormones. This phenomenon was examined in the spinal cord and in confirmation with previous studies neonatal treatment of triiodothyronine (0.1 mg/kg, s.c. daily) was capable of evoking persistent increases in beta-adrenergic receptor binding. These results suggest that: (a) development of the postjunctional serotonergic and alpha-adrenergic receptors in the rat spinal cord can occur in the absence of the prejunctional nerve terminals and are subject to transsynaptic modulation; (b) beta-adrenergic receptors in the spinal cord also can develop after prejunctional lesions but are regulated by hormonal rather than neuronal factors.

Ablation of the presynaptic organizer Bassoon in excitatory neurons retards dentate gyrus maturation and enhances learning performance.

PubMed

Annamneedi, Anil; Caliskan, Gürsel; Müller, Sabrina; Montag, Dirk; Budinger, Eike; Angenstein, Frank; Fejtova, Anna; Tischmeyer, Wolfgang; Gundelfinger, Eckart D; Stork, Oliver

2018-06-18

Bassoon is a large scaffolding protein of the presynaptic active zone involved in the development of presynaptic terminals and in the regulation of neurotransmitter release at both excitatory and inhibitory brain synapses. Mice with constitutive ablation of the Bassoon (Bsn) gene display impaired presynaptic function, show sensory deficits and develop severe seizures. To specifically study the role of Bassoon at excitatory forebrain synapses and its relevance for control of behavior, we generated conditional knockout (Bsn cKO) mice by gene ablation through an Emx1 promoter-driven Cre recombinase. In these animals, we confirm selective loss of Bassoon from glutamatergic neurons of the forebrain. Behavioral assessment revealed that, in comparison to wild-type littermates, Bsn cKO mice display selectively enhanced contextual fear memory and increased novelty preference in a spatial discrimination/pattern separation task. These changes are accompanied by an augmentation of baseline synaptic transmission at medial perforant path to dentate gyrus (DG) synapses, as indicated by increased ratios of field excitatory postsynaptic potential slope to fiber volley amplitude. At the structural level, an increased complexity of apical dendrites of DG granule cells can be detected in Bsn cKO mice. In addition, alterations in the expression of cellular maturation markers and a lack of age-dependent decrease in excitability between juvenile and adult Bsn cKO mice are observed. Our data suggest that expression of Bassoon in excitatory forebrain neurons is required for the normal maturation of the DG and important for spatial and contextual memory.

Synaptically evoked Ca2+ release from intracellular stores is not influenced by vesicular zinc in CA3 hippocampal pyramidal neurones.

PubMed

Evstratova, Alesya; Tóth, Katalin

2011-12-01

The co-release of neuromodulatory substances in combination with classic neurotransmitters such as glutamate and GABA from individual presynaptic nerve terminals has the capacity to dramatically influence synaptic efficacy and plasticity. At hippocampal mossy fibre synapses vesicular zinc is suggested to serve as a cotransmitter capable of regulating calcium release from internal stores in postsynaptic CA3 pyramidal cells. Here we investigated this possibility using combined intracellular ratiometric calcium imaging and patch-clamp recording techniques. In acute hippocampal slices a brief train of mossy fibre stimulation produced a large, delayed postsynaptic Ca(2+) wave that was spatially restricted to the proximal apical dendrites of CA3 pyramidal cells within stratum lucidum. This calcium increase was sensitive to intracellularly applied heparin indicating reliance upon release from internal stores and was triggered by activation of both group I metabotropic glutamate and NMDA receptors. Importantly, treatment of slices with the membrane-impermeant zinc chelator CaEDTA did not influence the synaptically evoked postsynaptic Ca(2+) waves. Moreover, mossy fibre stimulus evoked postsynaptic Ca(2+) signals were not significantly different between wild-type and zinc transporter 3 (ZnT3) knock-out animals. Considered together our data do not support a role for vesicular zinc in regulating mossy fibre evoked Ca(2+) release from CA3 pyramidal cell internal stores.

Synaptically evoked Ca2+ release from intracellular stores is not influenced by vesicular zinc in CA3 hippocampal pyramidal neurones

PubMed Central

Evstratova, Alesya; Tóth, Katalin

2011-01-01

Abstract The co-release of neuromodulatory substances in combination with classic neurotransmitters such as glutamate and GABA from individual presynaptic nerve terminals has the capacity to dramatically influence synaptic efficacy and plasticity. At hippocampal mossy fibre synapses vesicular zinc is suggested to serve as a cotransmitter capable of regulating calcium release from internal stores in postsynaptic CA3 pyramidal cells. Here we investigated this possibility using combined intracellular ratiometric calcium imaging and patch-clamp recording techniques. In acute hippocampal slices a brief train of mossy fibre stimulation produced a large, delayed postsynaptic Ca2+ wave that was spatially restricted to the proximal apical dendrites of CA3 pyramidal cells within stratum lucidum. This calcium increase was sensitive to intracellularly applied heparin indicating reliance upon release from internal stores and was triggered by activation of both group I metabotropic glutamate and NMDA receptors. Importantly, treatment of slices with the membrane-impermeant zinc chelator CaEDTA did not influence the synaptically evoked postsynaptic Ca2+ waves. Moreover, mossy fibre stimulus evoked postsynaptic Ca2+ signals were not significantly different between wild-type and zinc transporter 3 (ZnT3) knock-out animals. Considered together our data do not support a role for vesicular zinc in regulating mossy fibre evoked Ca2+ release from CA3 pyramidal cell internal stores. PMID:21986206

Liprin-α3 controls vesicle docking and exocytosis at the active zone of hippocampal synapses.

PubMed

Wong, Man Yan; Liu, Changliang; Wang, Shan Shan H; Roquas, Aram C F; Fowler, Stephen C; Kaeser, Pascal S

2018-02-27

The presynaptic active zone provides sites for vesicle docking and release at central nervous synapses and is essential for speed and accuracy of synaptic transmission. Liprin-α binds to several active zone proteins, and loss-of-function studies in invertebrates established important roles for Liprin-α in neurodevelopment and active zone assembly. However, Liprin-α localization and functions in vertebrates have remained unclear. We used stimulated emission depletion superresolution microscopy to systematically determine the localization of Liprin-α2 and Liprin-α3, the two predominant Liprin-α proteins in the vertebrate brain, relative to other active-zone proteins. Both proteins were widely distributed in hippocampal nerve terminals, and Liprin-α3, but not Liprin-α2, had a prominent component that colocalized with the active-zone proteins Bassoon, RIM, Munc13, RIM-BP, and ELKS. To assess Liprin-α3 functions, we generated Liprin-α3-KO mice by using CRISPR/Cas9 gene editing. We found reduced synaptic vesicle tethering and docking in hippocampal neurons of Liprin-α3-KO mice, and synaptic vesicle exocytosis was impaired. Liprin-α3 KO also led to mild alterations in active zone structure, accompanied by translocation of Liprin-α2 to active zones. These findings establish important roles for Liprin-α3 in active-zone assembly and function, and suggest that interplay between various Liprin-α proteins controls their active-zone localization.

Phytocannabinoids and endocannabinoids.

PubMed

Fisar, Zdenek

2009-01-01

Progress in understanding the molecular mechanisms of cannabis action was made after discovery of cannabinoid receptors in the brain and the finding of endogenous metabolites with affinity to them. Activation of cannabinoid receptors on synaptic terminals results in regulation of ion channels, neurotransmitter release and synaptic plasticity. Neuromodulation of synapses by the cannabinoids is proving to have a wide range of functional effects, making them potential targets as medical preparations in a variety of illnesses, including some mental disorders and neurodegenerative illnesses. Cannabis contains a large amount of substances with affinity for the cannabinoid receptors. The endocannabinoids are a family of lipid neurotransmitters that engage the same membrane receptors targeted by tetrahydrocannabinol and that mediate retrograde signal from postsynaptic neurons to presynaptic ones. Discovery of endogenous cannabinoids and studies of the physiological functions of the cannabinoid system in the brain and body are producing a number of important findings about the role of membrane lipids and fatty acids in nerve signal transduction. Plant, endogenous and synthetic cannabinoids are using in these studies. The role of lipid membranes in the cannabinoid system follows from the fact that the source and supply of endogenous cannabinoids are derived from arachidonic acid, an important membrane constituent. The study of structure-activity relationships of molecules which influence the cannabinoid system in the brain and body is crucial in search of medical preparations with the therapeutic effects of the phytocannabinoids without the negative effects on cognitive function attributed to cannabis.

Tachycardia, reduced vagal capacity, and age-dependent ventricular dysfunction arising from diminished expression of the presynaptic choline transporter

PubMed Central

English, Brett A.; Appalsamy, Martin; Diedrich, Andre; Ruggiero, Alicia M.; Lund, David; Wright, Jane; Keller, Nancy R.; Louderback, Katherine M.; Robertson, David

2010-01-01

Healthy cardiovascular function relies on a balanced and responsive integration of noradrenergic and cholinergic innervation of the heart. High-affinity choline uptake by cholinergic terminals is pivotal for efficient ACh production and release. To date, the cardiovascular impact of diminished choline transporter (CHT) expression has not been directly examined, largely due to the transporter's inaccessibility in vivo. Here, we describe findings from cardiovascular experiments using transgenic mice that bear a CHT genetic deficiency. Whereas CHT knockout (CHT−/−) mice exhibit early postnatal lethality, CHT heterozygous (CHT+/−) mice survive, grow, and reproduce normally and exhibit normal spontaneous behaviors. However, the CHT+/− mouse heart displays significantly reduced levels of high-affinity choline uptake accompanied by significantly reduced levels of ACh. Telemeterized recordings of cardiovascular function in these mice revealed tachycardia and hypertension at rest. After treadmill exercise, CHT+/− mice exhibited slower heart rate recovery, consistent with a diminished cholinergic reserve, a contention validated through direct vagal nerve stimulation. Echocardiographic and histological experiments revealed an age-dependent decrease in fractional shortening, increased left ventricular dimensions, and increased ventricular fibrosis, consistent with ventricular dysfunction. These cardiovascular phenotypes of CHT+/− mice encourage an evaluation of humans bearing reduced CHT expression for their resiliency in maintaining proper heart function as well as risk for cardiovascular disease. PMID:20601463

Lack of functional and morphological susceptibility of the greater superficial petrosal nerve to developmental dietary sodium restriction.

PubMed

Sollars, S I; Hill, D L

2000-12-01

Restriction of dietary sodium during gestation has major effects on taste function and anatomy in the offspring. The chorda tympani nerve of offspring that are maintained on sodium-reduced chow throughout life (NaDep) has reduced neurophysiological responses to sodium and altered morphology of its terminal field in the nucleus of the solitary tract. There are many anatomical and physiological similarities between the chorda tympani nerve that innervates taste buds on the anterior tongue and the greater superficial petrosal nerve (GSP) that innervates taste buds on the palate. To determine if the GSP is similarly susceptible to the effects of dietary sodium restriction, the present study examined neurophysiological responses and the terminal field of the GSP in NaDep and control rats. Neurophysiological responses of the GSP to a variety of sodium and non-sodium stimuli did not differ between NaDep and control rats. Furthermore, the volume and shape of the GSP terminal field in the nucleus of the solitary tract did not differ between the groups. Therefore, despite the high degree of functional and anatomical correspondence between the chorda tympani nerve and the GSP, the GSP does not appear to be susceptible to the effects of lifelong dietary sodium restriction.

[Type B botulism: a family outbreak].

PubMed

Lamboley, G; Mandel, R; Müller, S; Douard, P; Métral, S; Durand, P

2001-03-01

Three cases of an outbreak of familial foodborne botulism are reported. The food incriminated could not be identified despite a careful investigation into the food history of the patients. The outcome was good following endotracheal ventilation and botulism antitoxin trivalent therapy. In France, foodborne botulism is an uncommon public health disease, and with a good prognosis when the diagnosis is promptly performed. The value of emergency electromyographic findings is emphasized, particularly when the repetitive stimulation of the motor nerve shows a presynaptic block of neuromuscular transmission. Management depends on the symptomatology, and trivalent antitoxin therapy is the only specific treatment.

Clostridium botulinum and the ophthalmologist: a review of botulism, including biological warfare ramifications of botulinum toxin.

PubMed

Caya, J G

2001-01-01

The anaerobic bacterium Clostridium botulinum causes disease by elaborating an extremely potent neurotoxin that inhibits release of acetylcholine at presynaptic nerve endings, thereby resulting in a descending flaccid paralysis and autonomic nervous system dysfunction. Possible ophthalmological effects of this neurotoxin are many and typically constitute the earliest manifestations of botulism. This review summarizes the medical literature on botulism with regard to historical perspective, epidemiology, clinical manifestations, and treatment. Ophthalmological findings of botulism are tabulated and their frequencies are provided. Finally, the bioterrorism/biologic warfare ramifications of botulinum toxin are briefly discussed.

Parallel processing of afferent olfactory sensory information

PubMed Central

Vaaga, Christopher E.

2016-01-01

Key points The functional synaptic connectivity between olfactory receptor neurons and principal cells within the olfactory bulb is not well understood.One view suggests that mitral cells, the primary output neuron of the olfactory bulb, are solely activated by feedforward excitation.Using focal, single glomerular stimulation, we demonstrate that mitral cells receive direct, monosynaptic input from olfactory receptor neurons.Compared to external tufted cells, mitral cells have a prolonged afferent‐evoked EPSC, which serves to amplify the synaptic input.The properties of presynaptic glutamate release from olfactory receptor neurons are similar between mitral and external tufted cells.Our data suggest that afferent input enters the olfactory bulb in a parallel fashion. Abstract Primary olfactory receptor neurons terminate in anatomically and functionally discrete cortical modules known as olfactory bulb glomeruli. The synaptic connectivity and postsynaptic responses of mitral and external tufted cells within the glomerulus may involve both direct and indirect components. For example, it has been suggested that sensory input to mitral cells is indirect through feedforward excitation from external tufted cells. We also observed feedforward excitation of mitral cells with weak stimulation of the olfactory nerve layer; however, focal stimulation of an axon bundle entering an individual glomerulus revealed that mitral cells receive monosynaptic afferent inputs. Although external tufted cells had a 4.1‐fold larger peak EPSC amplitude, integration of the evoked currents showed that the synaptic charge was 5‐fold larger in mitral cells, reflecting the prolonged response in mitral cells. Presynaptic afferents onto mitral and external tufted cells had similar quantal amplitude and release probability, suggesting that the larger peak EPSC in external tufted cells was the result of more synaptic contacts. The results of the present study indicate that the monosynaptic afferent input to mitral cells depends on the strength of odorant stimulation. The enhanced spiking that we observed in response to brief afferent input provides a mechanism for amplifying sensory information and contrasts with the transient response in external tufted cells. These parallel input paths may have discrete functions in processing olfactory sensory input. PMID:27377344

Acetylcholine Encodes Long-Lasting Presynaptic Plasticity at Glutamatergic Synapses in the Dorsal Striatum after Repeated Amphetamine Exposure

PubMed Central

Wang, Wengang; Darvas, Martin; Storey, Granville P.; Bamford, Ian J.; Gibbs, Jeffrey T.; Palmiter, Richard D.

2013-01-01

Locomotion and cue-dependent behaviors are modified through corticostriatal signaling whereby short-term increases in dopamine availability can provoke persistent changes in glutamate release that contribute to neuropsychiatric disorders, including Parkinson's disease and drug dependence. We found that withdrawal of mice from repeated amphetamine treatment caused a chronic presynaptic depression (CPD) in glutamate release that was most pronounced in corticostriatal terminals with a low probability of release and lasted >50 d in treated mice. An amphetamine challenge reversed CPD via a dopamine D1-receptor-dependent paradoxical presynaptic potentiation (PPP) that increased corticostriatal activity in direct pathway medium spiny neurons. This PPP was correlated with locomotor responses after a drug challenge, suggesting that it may underlie the sensitization process. Experiments in brain slices and in vivo indicated that dopamine regulation of acetylcholine release from tonically active interneurons contributes to CPD, PPP, locomotor sensitization, and cognitive ability. Therefore, a chronic decrease in corticostriatal activity during withdrawal is regulated around a new physiological range by tonically active interneurons and returns to normal upon reexposure to amphetamine, suggesting that this paradoxical return of striatal activity to a more stable, normalized state may represent an additional source of drug motivation during abstinence. PMID:23785153

Terminal-Nerve-Derived Neuropeptide Y Modulates Physiological Responses in the Olfactory Epithelium of Hungry Axolotls (Ambystoma mexicanum)

PubMed Central

Mousley, Angela; Polese, Gianluca; Marks, Nikki J.; Eisthen, Heather L.

2007-01-01

The vertebrate brain actively regulates incoming sensory information, effectively filtering input and focusing attention toward environmental stimuli that are most relevant to the animal's behavioral context or physiological state. Such centrifugal modulation has been shown to play an important role in processing in the retina and cochlea, but has received relatively little attention in olfaction. The terminal nerve, a cranial nerve that extends underneath the lamina propria surrounding the olfactory epithelium, displays anatomical and neurochemical characteristics that suggest that it modulates activity in the olfactory epithelium. Using immunocytochemical techniques, we demonstrate that neuropeptide Y (NPY) is abundantly present in the terminal nerve in the axolotl (Ambystoma mexicanum), an aquatic salamander. Because NPY plays an important role in regulating appetite and hunger in many vertebrates, we investigated the possibility that NPY modulates activity in the olfactory epithelium in relation to the animal's hunger level. We therefore characterized the full length NPY gene from axolotls to enable synthesis of authentic axolotl NPY for use in electrophysiological experiments. We find that axolotl NPY modulates olfactory epithelial responses evoked by L-glutamic acid, a food-related odorant, but only in hungry animals. Similarly, whole-cell patch-clamp recordings demonstrate that bath application of axolotl NPY enhances the magnitude of a tetrodotoxin-sensitive inward current, but only in hungry animals. These results suggest that expression or activity of NPY receptors in the olfactory epithelium may change with hunger level, and that terminal nerve-derived peptides modulate activity in the olfactory epithelium in response to an animal's changing behavioral and physiological circumstances. PMID:16855098

Terminal nerve-derived neuropeptide y modulates physiological responses in the olfactory epithelium of hungry axolotls (Ambystoma mexicanum).

PubMed

Mousley, Angela; Polese, Gianluca; Marks, Nikki J; Eisthen, Heather L

2006-07-19

The vertebrate brain actively regulates incoming sensory information, effectively filtering input and focusing attention toward environmental stimuli that are most relevant to the animal's behavioral context or physiological state. Such centrifugal modulation has been shown to play an important role in processing in the retina and cochlea, but has received relatively little attention in olfaction. The terminal nerve, a cranial nerve that extends underneath the lamina propria surrounding the olfactory epithelium, displays anatomical and neurochemical characteristics that suggest that it modulates activity in the olfactory epithelium. Using immunocytochemical techniques, we demonstrate that neuropeptide Y (NPY) is abundantly present in the terminal nerve in the axolotl (Ambystoma mexicanum), an aquatic salamander. Because NPY plays an important role in regulating appetite and hunger in many vertebrates, we investigated the possibility that NPY modulates activity in the olfactory epithelium in relation to the animal's hunger level. We therefore characterized the full-length NPY gene from axolotls to enable synthesis of authentic axolotl NPY for use in electrophysiological experiments. We find that axolotl NPY modulates olfactory epithelial responses evoked by l-glutamic acid, a food-related odorant, but only in hungry animals. Similarly, whole-cell patch-clamp recordings demonstrate that bath application of axolotl NPY enhances the magnitude of a tetrodotoxin-sensitive inward current, but only in hungry animals. These results suggest that expression or activity of NPY receptors in the olfactory epithelium may change with hunger level, and that terminal nerve-derived peptides modulate activity in the olfactory epithelium in response to an animal's changing behavioral and physiological circumstances.

Intramuscular Distribution of the Abducens Nerve in the Lateral Rectus Muscle for the Management of Strabismus.

PubMed

Shin, Hyun Jin; Lee, Shin-Hyo; Shin, Kang-Jae; Koh, Ki-Seok; Song, Wu-Chul

2018-06-01

To elucidate the intramuscular distribution and branching patterns of the abducens nerve in the lateral rectus (LR) muscle so as to provide anatomical confirmation of the presence of compartmentalization, including for use in clinical applications such as botulinum toxin injections. Thirty whole-mount human cadaver specimens were dissected and then Sihler's stain was applied. The basic dimensions of the LR and its intramuscular nerve distribution were investigated. The distances from the muscle insertion to the point at which the abducens nerve enters the LR and to the terminal nerve plexus were also measured. The LR was 46.0 mm long. The abducens nerve enters the muscle on the posterior one-third of the LR and then typically divides into a few branches (average of 1.8). This supports a segregated abducens nerve selectively innervating compartments of the LR. The intramuscular nerve distribution showed a Y-shaped ramification with root-like arborization. The intramuscular nerve course finished around the middle of the LR (24.8 mm posterior to the insertion point) to form the terminal nerve plexus. This region should be considered the optimal target site for botulinum toxin injections. We have also identified the presence of an overlapping zone and communicating nerve branches between the neighboring LR compartments. Sihler's staining is a useful technique for visualizing the entire nerve network of the LR. Improving the knowledge of the nerve distribution patterns is important not only for researchers but also clinicians to understand the functions of the LR and the diverse pathophysiology of strabismus.

Afferent fibers and sensory ganglion cells within the oculomotor nerve in some mammals and man. II. Electrophysiological investigations.

PubMed

Manni, E; Bortolami, R; Pettorossi, V E; Lucchi, M L; Callegari, E

1978-01-01

The main aim of the present study was to localize with electrophysiological techniques the central projections and terminations of the aberrant trigeminal fibres contained in the oculomotor nerve of the lamb. After severing a trigeminal root, single-shock electrical stimulation of the trigeminal axons present in the central stump of the ipsilateral oculomotor nerve evoked field potentials in the area of, i) the subnucleus gelatinosus of the nucleus caudalis trigemini at the level of C1-C2; ii) the main sensory trigeminal nucleus; iii) the descending trigeminal nucleus and tract; iv) the adjacent reticular formation. Units whose discharge rate was influenced by such a stimulation were also found in the same territories. These regions actually exhibited degenerations after cutting an oculomotor nerve. We conclude, therefore, that the trigeminal fibres which leave the Vth nerve at the level of the cavernous sinus and enter the brain stem through the IIIrd nerve, end in the same structures which receive the terminations of the afferent fibres entering the brain stem through the sensory trigeminal root.

Maintenance of Mouse Gustatory Terminal Field Organization Is Disrupted following Selective Removal of Peripheral Sodium Salt Taste Activity at Adulthood.

PubMed

Skyberg, Rolf; Sun, Chengsan; Hill, David L

2017-08-09

Neural activity plays a critical role in the development of central circuits in sensory systems. However, the maintenance of these circuits at adulthood is usually not dependent on sensory-elicited neural activity. Recent work in the mouse gustatory system showed that selectively deleting the primary transduction channel for sodium taste, the epithelial sodium channel (ENaC), throughout development dramatically impacted the organization of the central terminal fields of three nerves that carry taste information to the nucleus of the solitary tract. More specifically, deleting ENaCs during development prevented the normal maturation of the fields. The present study was designed to extend these findings by testing the hypothesis that the loss of sodium taste activity impacts the maintenance of the normal adult terminal field organization in male and female mice. To do this, we used an inducible Cre-dependent genetic recombination strategy to delete ENaC function after terminal field maturation occurred. We found that removal of sodium taste neural activity at adulthood resulted in significant reorganization of mature gustatory afferent terminal fields in the nucleus of the solitary tract. Specifically, the chorda tympani and greater superficial petrosal nerve terminal fields were 1.4× and 1.6× larger than age-matched controls, respectively. By contrast, the glossopharyngeal nerve, which is not highly sensitive to sodium taste stimulation, did not undergo terminal field reorganization. These surprising results suggest that gustatory nerve terminal fields remain plastic well into adulthood, which likely impacts central coding of taste information and taste-related behaviors with altered taste experience. SIGNIFICANCE STATEMENT Neural activity plays a major role in the development of sensory circuits in the mammalian brain. However, the importance of sensory-driven activity in maintaining these circuits at adulthood, especially in subcortical structures, appears to be much less. Here, we tested whether the loss of sodium taste activity in adult mice impacts the maintenance of how taste nerves project to the first central relay. We found that specific loss of sodium-elicited taste activity at adulthood produced dramatic and selective reorganization of terminal fields in the brainstem. This demonstrates, for the first time, that taste-elicited activity is necessary for the normal maintenance of central gustatory circuits at adulthood and highlights a level of plasticity not seen in other sensory system subcortical circuits. Copyright © 2017 the authors 0270-6474/17/377619-12$15.00/0.

Activation of alpha-latrotoxin receptors in neuromuscular synapses leads to a prolonged splash acetylcholine release.

PubMed

Lelyanova, V G; Thomson, D; Ribchester, R R; Tonevitsky, E A; Ushkaryov, Y A

2009-06-01

The mechanisms of acetylcholine release in presynaptic terminals of motoneurons induced by mutant alpha-latrotoxin (LT(N4C)) were analyzed. In contrast to wild-type alpha-latrotoxin that causes both continuous and splash secretion of acetylcholine and necessarity block neuromuscular transmission, LT(N4C) causes only splash release lasting over many hours. Thus, activation of alpha-latrotoxin receptors controls long-lasting enhanced secretion of acetylcholine.

Neuromodulatory properties of fluorescent carbon dots: effect on exocytotic release, uptake and ambient level of glutamate and GABA in brain nerve terminals.

PubMed

Borisova, Tatiana; Nazarova, Anastasia; Dekaliuk, Mariia; Krisanova, Natalia; Pozdnyakova, Natalia; Borysov, Arsenii; Sivko, Roman; Demchenko, Alexander P

2015-02-01

Carbon dots (C-dots), a recently discovered class of fluorescent nano-sized particles with pure carbon core, have great bioanalytical potential. Neuroactive properties of fluorescent C-dots obtained from β-alanine by microwave heating were assessed based on the analysis of their effects on the key characteristics of GABA- and glutamatergic neurotransmission in isolated rat brain nerve terminals. It was found that C-dots (40-800 μg/ml) in dose-dependent manner: (1) decreased exocytotic release of [(3)H]GABA and L-[(14)C]glutamate; (2) reduced acidification of synaptic vesicles; (3) attenuated the initial velocity of Na(+)-dependent transporter-mediated uptake of [(3)H]GABA and L-[(14)C]glutamate; (4) increased the ambient level of the neurotransmitters, nevertheless (5) did not change significantly the potential of the plasma membrane of nerve terminals. Almost complete suppression of exocytotic release of the neurotransmitters was caused by C-dots at a concentration of 800 μg/ml. Fluorescent and neuromodulatory features combined in C-dots create base for their potential usage for labeling and visualization of key processes in nerve terminals, and also in theranostics. In addition, natural presence of carbon-containing nanoparticles in the human food chain and in the air may provoke the development of neurologic consequences. Copyright © 2014 Elsevier Ltd. All rights reserved.

High probability neurotransmitter release sites represent an energy efficient design

PubMed Central

Lu, Zhongmin; Chouhan, Amit K.; Borycz, Jolanta A.; Lu, Zhiyuan; Rossano, Adam J; Brain, Keith L.; Zhou, You; Meinertzhagen, Ian A.; Macleod, Gregory T.

2016-01-01

Nerve terminals contain multiple sites specialized for the release of neurotransmitters. Release usually occurs with low probability, a design thought to confer many advantages. High probability release sites are not uncommon but their advantages are not well understood. Here we test the hypothesis that high probability release sites represent an energy efficient design. We examined release site probabilities and energy efficiency at the terminals of two glutamatergic motor neurons synapsing on the same muscle fiber in Drosophila larvae. Through electrophysiological and ultrastructural measurements we calculated release site probabilities to differ considerably between terminals (0.33 vs. 0.11). We estimated the energy required to release and recycle glutamate from the same measurements. The energy required to remove calcium and sodium ions subsequent to nerve excitation was estimated through microfluorimetric and morphological measurements. We calculated energy efficiency as the number of glutamate molecules released per ATP molecule hydrolyzed, and high probability release site terminals were found to be more efficient (0.13 vs. 0.06). Our analytical model indicates that energy efficiency is optimal (~0.15) at high release site probabilities (~0.76). As limitations in energy supply constrain neural function, high probability release sites might ameliorate such constraints by demanding less energy. Energy efficiency can be viewed as one aspect of nerve terminal function, in balance with others, because high efficiency terminals depress significantly during episodic bursts of activity. PMID:27593375

Recovery of the sub-basal nerve plexus and superficial nerve terminals after corneal epithelial injury in mice.

PubMed

Downie, Laura E; Naranjo Golborne, Cecilia; Chen, Merry; Ho, Ngoc; Hoac, Cam; Liyanapathirana, Dasun; Luo, Carol; Wu, Ruo Bing; Chinnery, Holly R

2018-06-01

Our aim was to compare regeneration of the sub-basal nerve plexus (SBNP) and superficial nerve terminals (SNT) following corneal epithelial injury. We also sought to compare agreement when quantifying nerve parameters using different image analysis techniques. Anesthetized, female C57BL/6 mice received central 1-mm corneal epithelial abrasions. Four-weeks post-injury, eyes were enucleated and processed for PGP9.5 to visualize the corneal nerves using wholemount immunofluorescence staining and confocal microscopy. The percentage area of the SBNP and SNT were quantified using: ImageJ automated thresholds, ImageJ manual thresholds and manual tracings in NeuronJ. Nerve sum length was quantified using NeuronJ and Imaris. Agreement between methods was considered with Bland-Altman analyses. Four-weeks post-injury, the sum length of nerve fibers in the SBNP, but not the SNT, was reduced compared with naïve eyes. In the periphery, but not central cornea, of both naïve and injured eyes, nerve fiber lengths in the SBNP and SNT were strongly correlated. For quantifying SBNP nerve axon area, all image analysis methods were highly correlated. In the SNT, there was poor correlation between manual methods and auto-thresholding, with a trend towards underestimating nerve fiber area using auto-thresholding when higher proportions of nerve fibers were present. In conclusion, four weeks after superficial corneal injury, there is differential recovery of epithelial nerve axons; SBNP sum length is reduced, however the sum length of SNTs is similar to naïve eyes. Care should be taken when selecting image analysis methods to compare nerve parameters in different depths of the corneal epithelium due to differences in background autofluorescence. Copyright © 2018 Elsevier Ltd. All rights reserved.

Immunocytochemical localization of glutamic acid decarboxylase (GAD) and substance P in neural areas mediating motion-induced emesis: Effects of vagal stimulation on GAD immunoreactivity

NASA Technical Reports Server (NTRS)

Damelio, F.; Gibbs, M. A.; Mehler, W. R.; Daunton, Nancy G.; Fox, Robert A.

1991-01-01

Immunocytochemical methods were employed to localize the neurotransmitter amino acid gamma-aminobutyric acid (GABA) by means of its biosynthetic enzyme glutamic acid decarboxylase (GAD) and the neuropeptide substance P in the area postrema (AP), area subpostrema (ASP), nucleus of the tractus solitarius (NTS), and gelatinous nucleus (GEL). In addition, electrical stimulation was applied to the night vagus nerve at the cervical level to assess the effects on GAD-immunoreactivity (GAR-IR). GAD-IR terminals and fibers were observed in the AP, ASP, NTS, and GEL. They showed pronounced density at the level of the ASP and gradual decrease towards the solitary complex. Nerve cells were not labelled in our preparations. Ultrastructural studies showed symmetric or asymmetric synaptic contracts between labelled terminals and non-immunoreactive dendrites, axons, or neurons. Some of the labelled terminals contained both clear- and dense-core vesicles. Our preliminary findings, after electrical stimulation of the vagus nerve, revealed a bilateral decrease of GAD-IR that was particularly evident at the level of the ASP. SP-immunoreactive (SP-IR) terminals and fibers showed varying densities in the AP, ASP, NTS, and GEL. In our preparations, the lateral sub-division of the NTS showed the greatest accumulation. The ASP showed medium density of immunoreactive varicosities and terminals and the AP and GEL displayed scattered varicose axon terminals. The electron microscopy revealed that all immunoreactive terminals contained clear-core vesicles which make symmetric or asymmetric synaptic contact with unlabelled dendrites. It is suggested that the GABAergic terminals might correspond to vagal afferent projections and that GAD/GABA and substance P might be co-localized in the same terminal allowing the possibility of a regulated release of the transmitters in relation to demands.

Agrin mutations lead to a congenital myasthenic syndrome with distal muscle weakness and atrophy.

PubMed

Nicole, Sophie; Chaouch, Amina; Torbergsen, Torberg; Bauché, Stéphanie; de Bruyckere, Elodie; Fontenille, Marie-Joséphine; Horn, Morten A; van Ghelue, Marijke; Løseth, Sissel; Issop, Yasmin; Cox, Daniel; Müller, Juliane S; Evangelista, Teresinha; Stålberg, Erik; Ioos, Christine; Barois, Annie; Brochier, Guy; Sternberg, Damien; Fournier, Emmanuel; Hantaï, Daniel; Abicht, Angela; Dusl, Marina; Laval, Steven H; Griffin, Helen; Eymard, Bruno; Lochmüller, Hanns

2014-09-01

Congenital myasthenic syndromes are a clinically and genetically heterogeneous group of rare diseases resulting from impaired neuromuscular transmission. Their clinical hallmark is fatigable muscle weakness associated with a decremental muscle response to repetitive nerve stimulation and frequently related to postsynaptic defects. Distal myopathies form another clinically and genetically heterogeneous group of primary muscle disorders where weakness and atrophy are restricted to distal muscles, at least initially. In both congenital myasthenic syndromes and distal myopathies, a significant number of patients remain genetically undiagnosed. Here, we report five patients from three unrelated families with a strikingly homogenous clinical entity combining congenital myasthenia with distal muscle weakness and atrophy reminiscent of a distal myopathy. MRI and neurophysiological studies were compatible with mild myopathy restricted to distal limb muscles, but decrement (up to 72%) in response to 3 Hz repetitive nerve stimulation pointed towards a neuromuscular transmission defect. Post-exercise increment (up to 285%) was observed in the distal limb muscles in all cases suggesting presynaptic congenital myasthenic syndrome. Immunofluorescence and ultrastructural analyses of muscle end-plate regions showed synaptic remodelling with denervation-reinnervation events. We performed whole-exome sequencing in two kinships and Sanger sequencing in one isolated case and identified five new recessive mutations in the gene encoding agrin. This synaptic proteoglycan with critical function at the neuromuscular junction was previously found mutated in more typical forms of congenital myasthenic syndrome. In our patients, we found two missense mutations residing in the N-terminal agrin domain, which reduced acetylcholine receptors clustering activity of agrin in vitro. Our findings expand the spectrum of congenital myasthenic syndromes due to agrin mutations and show an unexpected correlation between the mutated gene and the associated phenotype. This provides a good rationale for examining patients with apparent distal myopathy for a neuromuscular transmission disorder and agrin mutations. © The Author (2014). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Uptake and metabolism of fructose by rat neocortical cells in vivo and by isolated nerve terminals in vitro.

PubMed

Hassel, Bjørnar; Elsais, Ahmed; Frøland, Anne-Sofie; Taubøll, Erik; Gjerstad, Leif; Quan, Yi; Dingledine, Raymond; Rise, Frode

2015-05-01

Fructose reacts spontaneously with proteins in the brain to form advanced glycation end products (AGE) that may elicit neuroinflammation and cause brain pathology, including Alzheimer's disease. We investigated whether fructose is eliminated by oxidative metabolism in neocortex. Injection of [(14) C]fructose or its AGE-prone metabolite [(14) C]glyceraldehyde into rat neocortex in vivo led to formation of (14) C-labeled alanine, glutamate, aspartate, GABA, and glutamine. In isolated neocortical nerve terminals, [(14) C]fructose-labeled glutamate, GABA, and aspartate, indicating uptake of fructose into nerve terminals and oxidative fructose metabolism in these structures. This was supported by high expression of hexokinase 1, which channels fructose into glycolysis, and whose activity was similar with fructose or glucose as substrates. By contrast, the fructose-specific ketohexokinase was weakly expressed. The fructose transporter Glut5 was expressed at only 4% of the level of neuronal glucose transporter Glut3, suggesting transport across plasma membranes of brain cells as the limiting factor in removal of extracellular fructose. The genes encoding aldose reductase and sorbitol dehydrogenase, enzymes of the polyol pathway that forms glucose from fructose, were expressed in rat neocortex. These results point to fructose being transported into neocortical cells, including nerve terminals, and that it is metabolized and thereby detoxified primarily through hexokinase activity. We asked how the brain handles fructose, which may react spontaneously with proteins to form 'advanced glycation end products' and trigger inflammation. Neocortical cells took up and metabolized extracellular fructose oxidatively in vivo, and isolated nerve terminals did so in vitro. The low expression of fructose transporter Glut5 limited uptake of extracellular fructose. Hexokinase was a main pathway for fructose metabolism, but ketohexokinase (which leads to glyceraldehyde formation) was expressed too. Neocortical cells also took up and metabolized glyceraldehyde oxidatively. © 2015 International Society for Neurochemistry.

Pre- and post-alpha motoneuronal control of the soleus H-reflex during sinusoidal hip movements in human spinal cord injury

PubMed Central

Knikou, Maria; Chaudhuri, Debjani; Kay, Elizabeth; Schmit, Brian D.

2006-01-01

The aim of this study was to establish the contribution of hip-mediated sensory feedback to spinal interneuronal circuits during dynamic conditions in people with incomplete spinal cord injury (SCI). Specifically, we investigated the effects of synergistic and antagonistic group I afferents on the soleus H-reflex during imposed sinusoidal hip movements. The soleus H-reflex was conditioned by stimulating the common peroneal nerve (CPN) at short (2, 3, and 4 ms) and long (80, 100, and 120 ms) conditioning test (C-T) intervals to assess the reciprocal and pre-synaptic inhibition of the soleus H-reflex, respectively. The soleus H-reflex was also conditioned by medial gastrocnemius (MG) nerve stimulation at C-T intervals ranging from 4 to 7 ms to assess changes in autogenic Ib inhibition during hip movement. Sinusoidal hip movements were imposed to the right hip joint at 0.2 Hz by the Biodex system while subjects were supine. The effects of sinusoidal hip movement on five leg muscles along with hip, knee, and ankle joint torques were also established during sensorimotor conditioning of the reflex. Phase-dependent modulation of antagonistic and synergistic muscle afferents was present during hip movement, with the reciprocal, pre-synaptic, and Ib inhibition to be significantly reduced during hip extension and reinforced during hip flexion. Reflexive muscle and joint torque responses – induced by the hip movement – were entrained to specific phases of hip movement. This study provides evidence that hip-mediated input acts as a controlling signal of pre- and post-alpha motoneuronal control of the soleus H-reflex. The expression of these spinal interneuronal circuits during imposed sinusoidal hip movements is discussed with respect to motor recovery in humans after SCI. PMID:16782072

Acid-Sensing Ion Channels Activated by Evoked Released Protons Modulate Synaptic Transmission at the Mouse Calyx of Held Synapse.

PubMed

González-Inchauspe, Carlota; Urbano, Francisco J; Di Guilmi, Mariano N; Uchitel, Osvaldo D

2017-03-08

Acid-sensing ion channels (ASICs) regulate synaptic activities and play important roles in neurodegenerative diseases. We found that these channels can be activated in neurons of the medial nucleus of the trapezoid body (MNTB) of the auditory system in the CNS. A drop in extracellular pH induces transient inward ASIC currents (I ASIC s) in postsynaptic MNTB neurons from wild-type mice. The inhibition of I ASIC s by psalmotoxin-1 (PcTx1) and the absence of these currents in knock-out mice for ASIC-1a subunit (ASIC1a -/- ) suggest that homomeric ASIC-1as are mediating these currents in MNTB neurons. Furthermore, we detect ASIC1a-dependent currents during synaptic transmission, suggesting an acidification of the synaptic cleft due to the corelease of neurotransmitter and H + from synaptic vesicles. These currents are capable of eliciting action potentials in the absence of glutamatergic currents. A significant characteristic of these homomeric ASIC-1as is their permeability to Ca 2+ Activation of ASIC-1a in MNTB neurons by exogenous H + induces an increase in intracellular Ca 2+ Furthermore, the activation of postsynaptic ASIC-1as during high-frequency stimulation (HFS) of the presynaptic nerve terminal leads to a PcTx1-sensitive increase in intracellular Ca 2+ in MNTB neurons, which is independent of glutamate receptors and is absent in neurons from ASIC1a -/- mice. During HFS, the lack of functional ASICs in synaptic transmission results in an enhanced short-term depression of glutamatergic EPSCs. These results strongly support the hypothesis of protons as neurotransmitters and demonstrate that presynaptic released protons modulate synaptic transmission by activating ASIC-1as at the calyx of Held-MNTB synapse. SIGNIFICANCE STATEMENT The manuscript demonstrates that postsynaptic neurons of the medial nucleus of the trapezoid body at the mouse calyx of Held synapse express functional homomeric Acid-sensing ion channel-1a (ASIC-1as) that can be activated by protons (coreleased with neurotransmitter from acidified synaptic vesicles). These ASIC-1as contribute to the generation of postsynaptic currents and, more relevant, to calcium influx, which could be involved in the modulation of presynaptic transmitter release. Inhibition or deletion of ASIC-1a leads to enhanced short-term depression, demonstrating that they are concerned with short-term plasticity of the synapse. ASICs represent a widespread communication system with unique properties. We expect that our experiments will have an impact in the neurobiology field and will spread in areas related to neuronal plasticity. Copyright © 2017 the authors 0270-6474/17/372589-11$15.00/0.

Morphology of P2X3-immunoreactive nerve endings in the rat laryngeal mucosa.

PubMed

Takahashi, Natsumi; Nakamuta, Nobuaki; Yamamoto, Yoshio

2016-02-01

The morphological characteristics of P2X3-immunoreactive nerve endings in the laryngeal mucosa were herein examined using immunohistochemistry with confocal laser microscopy. Ramified intraepithelial nerve endings immunoreactive to P2X3 were distributed in the epiglottis and arytenoid region. The axon terminals of P2X3-immunoreactive ramified endings were beaded or flat in shape. These endings were also immunoreactive to P2X2 and not identical to the nerve endings immunoreactive to Na(+)-K(+)-ATPase α3-subunit, substance P (SP), and calcitonin gene-related peptide (CGRP). P2X3-immunoreactive axon terminals were also immunoreactive to vGLUT1, vGLUT2, and vGLUT3. In addition to ramified endings, P2X3-immunoreactive nerve endings were associated with α-gustducin-immunoreactive solitary chemosensory cells and/or SNAP25-immunoreactive neuroendocrine cells. Furthermore, P2X3-immunoreactive nerve endings were also observed in the taste bud-like chemosensory cell clusters of the stratified squamous epithelium covering epiglottic and arytenoid cartilage. The P2X3-immunoreactive nerve endings that associated with sensory and/or endocrine cells and chemosensory cell clusters were also immunoreactive to P2X2, vGLUT1, vGLUT2, and vGLUT3, but not to SP or CGRP. In conclusion, P2X3-immunoreactive nerve endings may be classified into two types, i.e., intraepithelial ramified nerve endings and nerve endings associated with chemosensory cells and neuroendocrine cells.

IL-1β impairs retrograde flow of BDNF signaling by attenuating endosome trafficking.

PubMed

Carlos, Anthony J; Tong, Liqi; Prieto, G Aleph; Cotman, Carl W

2017-02-02

Pro-inflammatory cytokines accumulate in the brain with age and Alzheimer's disease and can impair neuron health and cognitive function. Brain-derived neurotrophic factor (BDNF) is a key neurotrophin that supports neuron health, function, and synaptic plasticity. The pro-inflammatory cytokine interleukin-1β (IL-1β) impairs BDNF signaling but whether it affects BDNF signaling endosome trafficking has not been studied. This study uses an in vitro approach in primary hippocampal neurons to evaluate the effect of IL-1β on BDNF signaling endosome trafficking. Neurons were cultured in microfluidic chambers that separate the environments of the cell body and its axon terminal, enabling us to specifically treat in axon compartments and trace vesicle trafficking in real-time. We found that IL-1β attenuates BDNF signaling endosomes throughout networks in cultures. In IL-1β-treated cells, overall BDNF endosomal density was decreased, and the colocalization of BDNF endosomes with presynaptic terminals was found to be more than two times higher than in control cultures. Selective IL-1β treatment to the presynaptic compartment in microfluidic chamber attenuated BDNF endosome flux, as measured by reduced BDNF-GFP endosome counts in the somal compartment. Further, IL-1β decreased the BDNF-induced phosphorylation of Erk5, a known BDNF retrograde trafficking target. Mechanistically, the deficiency in trafficking was not due to impaired endocytosis of the BDNF-TrkB complex, or impaired transport rate, since BDNF endosomes traveled at the same rate in both control and IL-1β treatment groups. Among the regulators of presynaptic endosome sorting is the post-translational modification, ubiquitination. In support of this possibility, the IL-1β-mediated suppression of BDNF-induced Erk5 phosphorylation can be rescued by exogenous ubiquitin C-terminal hydrolase L1 (UCH-L1), a deubiquitinating enzyme that regulates ubiquitin and endosomal trafficking. We observed a state of neurotrophic resistance whereby, in the prolonged presence of IL-1β, BDNF is not effective in delivering long-distance signaling via the retrograde transport of signaling endosomes. Since IL-1β accumulation is an invariant feature across many neurodegenerative diseases, our study suggest that compromised BDNF retrograde transport-dependent signaling may have important implications in neurodegenerative diseases.

Modulation of the release of ( sup 3 H)norepinephrine from the base and body of the rat urinary bladder by endogenous adrenergic and cholinergic mechanisms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Somogyi, G.T.; de Groat, W.C.

Modulation of (3H)NE release was studied in rat urinary bladder strips prelabeled with (3H)NE. (3H)NE uptake occurred in strips from the bladder base and body, but was very prominent in the base where the noradrenergic innervation is most dense. Electrical field stimulation markedly increased (3H)NE outflow from the superfused tissue. The quantity of (3H)NE release was approximately equal during three consecutive periods of stimulation. Activation of presynaptic muscarinic receptors by 1.0 microM oxotremorine reduced (3H)NE release to 46% of the control. Atropine (1 microM) blocked the effect of oxotremorine and increased the release to 147% of predrug control levels. Activationmore » of presynaptic alpha-2 adrenoceptors by 1 microM clonidine reduced (3H)NE release to 55% of control. Yohimbine blocked the action of clonidine and increased the release to 148% of control. The release of (3H)NE from the bladder base and body was increased by both 1 microM atropine (to 167% and 174% of control, respectively) and 1 microM yohimbine (to 286% and 425% of control, respectively). Atropine and yohimbine administered in combination had similar facilitatory effects as when administered alone. We conclude that the release of (3H)NE from adrenergic nerve endings in electrically stimulated bladder strips is modulated via endogenous transmitters acting on both muscarinic and alpha-2 adrenergic presynaptic receptors and that the latter provide the most prominent control.« less

Presynaptic strontium dynamics and synaptic transmission.

PubMed Central

Xu-Friedman, M A; Regehr, W G

1999-01-01

Strontium can replace calcium in triggering neurotransmitter release, although peak release is reduced and the duration of release is prolonged. Strontium has therefore become useful in probing release, but its mechanism of action is not well understood. Here we study the action of strontium at the granule cell to Purkinje cell synapse in mouse cerebellar slices. Presynaptic residual strontium levels were monitored with fluorescent indicators, which all responded to strontium (fura-2, calcium orange, fura-2FF, magnesium green, and mag-fura-5). When calcium was replaced by equimolar concentrations of strontium in the external bath, strontium and calcium both entered presynaptic terminals. Contaminating calcium was eliminated by including EGTA in the extracellular bath, or by loading parallel fibers with EGTA, enabling the actions of strontium to be studied in isolation. After a single stimulus, strontium reached higher peak free levels than did calcium (approximately 1.7 times greater), and decayed more slowly (half-decay time 189 ms for strontium and 32 ms for calcium). These differences in calcium and strontium dynamics are likely a consequence of greater strontium permeability through calcium channels, lower affinity of the endogenous buffer for strontium, and less efficient extrusion of strontium. Measurements of presynaptic divalent levels help to explain properties of release evoked by strontium. Parallel fiber synaptic currents triggered by strontium are smaller in amplitude and longer in duration than those triggered by calcium. In both calcium and strontium, release consists of two components, one more steeply dependent on divalent levels than the other. Strontium drives both components less effectively than does calcium, suggesting that the affinities of the sensors involved in both phases of release are lower for strontium than for calcium. Thus, the larger and slower strontium transients account for the prominent slow component of release triggered by strontium. PMID:10096899

Presynaptic Muscarinic M2 Receptors Modulate Glutamatergic Transmission in the Bed Nucleus of the Stria Terminalis

PubMed Central

Guo, Ji-Dong; Hazra, Rimi; Dabrowska, Joanna; Muly, E. Chris; Wess, Jürgen; Rainnie, Donald G.

2012-01-01

The anterolateral cell group of the bed nucleus of the stria terminalis (BNSTALG) serves as an important relay station in stress circuitry. Limbic inputs to the BNSTALG are primarily glutamatergic and activity-dependent changes in this input have been implicated in abnormal behaviors associated with chronic stress and addiction. Significantly, local infusion of acetylcholine (ACh) receptor agonists into the BNST trigger stress-like cardiovascular responses, however, little is known about the effects of these agents on glutamatergic transmission in the BNSTALG. Here, we show that glutamate- and ACh-containing fibers are found in close association in the BNSTALG. Moreover, in the presence of the acetylcholinesterase inhibitor, eserine, endogenous ACh release evoked a long-lasting reduction of the amplitude of stimulus-evoked EPSCs. This effect was mimicked by exogenous application of the ACh analogue, carbachol, which caused a reversible, dose-dependent, reduction of the evoked EPSC amplitude, and an increase in both the paired pulse ratio and coefficient of variation, suggesting a presynaptic site of action. Uncoupling of postsynaptic G-proteins with intracellular GDP-β-S, or application of the nicotinic receptor antagonist, tubocurarine, failed to block the carbachol effect. In contrast, the carbachol effect was blocked by prior application of atropine or M2 receptor-preferring antagonists, and was absent in M2/M4 receptor knockout mice, suggesting that presynaptic M2 receptors mediate the effect of ACh. Immuno-electron microscopy studies further revealed the presence of M2 receptors on axon terminals that formed asymmetric synapses with BNST neurons. Our findings suggest that presynaptic M2 receptors might be an important modulator of the stress circuit and hence a novel target for drug development. PMID:22166222

Facilitatory effects of piracetam on excitability of motor nerve terminals and neuromuscular transmission.

PubMed

Hall, E D; Von Voigtlander, P F

1987-11-01

The possible in vivo facilitatory effects of the pyrrolidine acetamide no-otropic agent piracetam on neuromuscular transmission, were studied based upon reports of enhancement of central cholinergic function. Piracetam was shown to antagonize the lethal effects of the neuromuscular blocking agent hemicholinium-3 (HC-3), in female CF-1 mice when administered in a dose of 100 mg/kg (i.p.) simultaneously with HC-3. A 30 mg/kg (i.p.) dose of piracetam was ineffective by itself, although it potentiated the protective effects of choline (25 mg/kg i.p.). The analogs of piracetam, aniracetam, oxiracetam, pramiracetam and dupracetam also significantly antagonized the lethality of HC-3 at doses over a 30-300 mg/kg range. The acute facilitatory properties of piracetam on neuromuscular transmission were examined in more detail in vivo in the soleus nerve muscle preparation of the cat. A 100 mg/kg (i.v.) dose of piracetam, while having no effect on its own, significantly enhanced the ability of a 200 micrograms/kg (i.v.) dose of edrophonium to produce a potentiation of muscle contraction dependent on repetitive discharges in the soleus motor nerve terminals. In preparations in which the motor nerve terminals of the soleus were in a partially degenerated state as a result of section of the motor axons 48 hr earlier, piracetam acted to restore their sensitivity to edrophonium. Furthermore, in both normal and partially degenerated preparations, piracetam significantly decreased the neuromuscular blocking effects of a 150 micrograms/kg (i.v.) dose of d-tubocurarine. The mechanism of the neuromuscular facilitatory effects of piracetam on neuromuscular transmission is discussed in terms of an enhanced excitability of motor nerve terminals together with an action to increase the synthesis and/or release of acetylcholine.

The origin of the post-tetanic hyperpolarization of mammalian motor nerve terminals

PubMed Central

Gage, P. W.; Hubbard, J. I.

1966-01-01

1. Motor nerve terminals in magnesium-poisoned rat hemidiaphragm-phrenic nerve preparations in vitro were stimulated with short depolarizing pulses of approximately threshold strength and the evoked antidromic responses recorded from the phrenic nerve. The percentage of these 1/sec or 0·5/sec stimuli to which there was no antidromic response was used as a quantitative measure of the terminal excitability. After standard tetanic stimulation (1000 impulses at 100/sec) the excitability of the terminals was depressed for an average duration of 60-70 sec, during most of which time no antidromic responses to stimuli of pretetanic intensity were recorded. There was no significant interaction between stimuli to the terminals at rates of 1 or 0·5/sec. 2. Potassium-free solutions at first increased, then decreased, the post-tetanic depression of excitability. Raising [K]o threefold (15 mM) abolished the post-tetanic depression and often converted it to an exaltation of excitability. 3. Polarizing currents were applied to the terminals with a second electrode. Depolarizing currents increased, while hyperpolarizing currents decreased, the post-tetanic depression of excitability. 4. In solutions with 70% of the normal NaCl content replaced by sucrose, the post-tetanic depression of excitability was reversibly prolonged. 5. In the presence of 7·7 × 10-6 M digoxin or 0·42 mM ouabain there was a small reversible reduction of post-tetanic excitability. 6. After exposure to solutions containing no glucose or to solutions containing 3-5 mM sodium azide the excitability of the terminals was not altered by the tetanus. After washing with the control solution, post-tetanic depression of excitability returned. Antimycin-A (1·8 × 10-6 M) had little or no effect upon post-tetanic excitability. 7. It was concluded that the post-tetanic depression of excitability reflected hyperpolarization of the terminals and that this hyperpolarization was caused by a shift of the membrane potential towards the potassium equilibrium potential because of an increase in potassium permeability. ImagesFig. 1 PMID:5921834

Cell types and synaptic organization of the medullary electromotor nucleus in a constant frequency weakly electric fish, Sternarchus albifrons.

PubMed

Tokunaga, A; Akert, K; Sandri, C; Bennett, M V

1980-08-01

The medullary electromotor nucleus (EMN) of Sternarchus albifrons was studied at the light and electron microscopic levels. The EMN consists of a dense meshwork of myelinated axons and glial elements with interposed large neurons; it is provided with an abundant supply of capillaries. Two types of essentially adrendritic nerve cells were distinguished on the basis of size: giant neurons (approx. 70 micrometers in diameter) and large neurons (approx. 30 micrometers in diameter). Their population ratio is 1:4. Only giant cells are labelled following the injection of retrograde tracer into the spinal cord; they are therefore identified with the so-called "relay cells" of other gymnotids. Tracer experiments further suggest that the descending axons of these relay cells give off collateral branches throughout the elongated spinal electromotor nucleus. In contrast, the large cells remain unlabelled and therefore lack spinal projections; they most likely correspond to "pacemaker cells." The perikaryal surface, including axon hillock and proximal part of initial segment of both types of EMN cells, is contacted by clusters of synaptic terminals and astrocytic processes. Two main varieties of synaptic terminals occur: (1) large endings and (2) ordinary end feet with standard size (S-type) and variable size (Sv-type) clear, spherical vesicles. The junction between large endings and EMN cells is characterized by the combination of gap junctions and surrounding intermediate junctions whose freeze-fracture characteristics were morphometrically analyzed. The large endings were formed by nodes of Ranvier as well as by fiber terminations, and synchronization within the EMN may be achieved by presynaptic fibers. Some of the contacts occur directly on the initial segment, which could allow activity to bypass the soma. It is concluded that the elctromotor system of Sternarchus is comprised of a rapid conduction pathway where medullary pacemaker and relay cells as well as spinal electromotor neurons are coupled by synapses with gap junctions. In contrast to the spinal electromotor neurons, the medullary EMN cells receive synapses with morphological characteristics of chemical transmission, and the S-type and SV-type terminals may possibly correspond to Gray's Type I and Type II synapses, respectively. These synapses may be involved in modulation of the electric organ discharge frequency.

Variation in Lingual Nerve Course: A Human Cadaveric Study

PubMed Central

Al-Amery, Samah M.; Nambiar, Phrabhakaran; Naidu, Murali

2016-01-01

The lingual nerve is a terminal branch of the mandibular nerve. It is varied in its course and in its relationship to the mandibular alveolar crest, submandibular duct and also the related muscles in the floor of the mouth. This study aims to understand the course of the lingual nerve from the molar area until its insertion into the tongue muscle. This cadaveric research involved the study of 14 hemi-mandibles and consisted of two parts: (i) obtaining morphometrical measurements of the lingual nerve to three landmarks on the alveolar ridge, and (b) understanding non-metrical or morphological appearance of its terminal branches inserting in the ventral surface of the tongue. The mean distance between the fourteen lingual nerves and the alveolar ridge was 12.36 mm, and they were located 12.03 mm from the lower border of the mandible. These distances were varied when near the first molar (M1), second molar (M2) and third molar (M3). The lingual nerve coursed on the floor of the mouth for approximately 25.43 mm before it deviated toward the tongue anywhere between the mesial of M1 and distal of M2. Thirteen lingual nerves were found to loop around the submandibular duct for an average distance of 6.92 mm (95% CI: 5.24 to 8.60 mm). Their looping occurred anywhere between the M2 and M3. In 76.9% of the cases the loop started around the M3 region and the majority (69.2%) of these looping ended at between the first and second molars and at the lingual developmental groove of the second molar. It gave out as many as 4 branches at its terminal end at the ventral surface of the tongue, with the presence of 2 branches being the most common pattern. An awareness of the variations of the lingual nerve is important to prevent any untoward complications or nerve injury and it is hoped that these findings will be useful for planning of surgical procedures related to the alveolar crest, submandibular gland/ duct and surrounding areas. PMID:27662622

Evidence for crustacean cardioactive peptide-like innervation of the gut in Locusta migratoria.

PubMed

Donini, Andrew; Ngo, Caroline; Lange, Angela B

2002-11-01

Hindguts from female Vth instar larvae, young adults (1-2 days) and old adults (>10 days) are equally sensitive to the crustacean cardioactive peptide (CCAP), with changes in contraction occurring at a threshold concentration of 10(-9)M and maximal responses observed at concentrations ranging between 10(-7) and 5x10(-6)M. An immunohistochemical examination of the gut of Locusta migratoria with an antiserum raised against CCAP revealed an extensive network of CCAP-like immunoreactive processes on the hindgut and posterior midgut via the 11th sternal nerve arising from the terminal abdominal ganglion. Anterograde filling of the 11th sternal nerve with neurobiotin revealed extensive processes and terminals on the hindgut. Retrograde filling of the branch of the 11th sternal nerve which innervates the hindgut with neurobiotin revealed two bilaterally paired cells in the terminal abdominal ganglion which co-localized with CCAP-like immunoreactivity. Results suggest that a CCAP-like substance acts as a neurotransmitter/neuromodulator at the locust hindgut.

LIM Kinase, a Newly Identified Regulator of Presynaptic Remodeling by Rod Photoreceptors After Injury

PubMed Central

Wang, Weiwei; Townes-Anderson, Ellen

2015-01-01

Purpose Rod photoreceptors retract their axon terminals and develop neuritic sprouts in response to retinal detachment and reattachment, respectively. This study examines the role of LIM kinase (LIMK), a component of RhoA and Rac pathways, in the presynaptic structural remodeling of rod photoreceptors. Methods Phosphorylated LIMK (p-LIMK), the active form of LIMK, was examined in salamander retina with Western blot and confocal microscopy. Axon length within the first 7 hours and process growth after 3 days of culture were assessed in isolated rod photoreceptors treated with inhibitors of upstream regulators ROCK and p21-activated kinase (Pak) (Y27632 and IPA-3) and a direct LIMK inhibitor (BMS-5). Porcine retinal explants were also treated with BMS-5 and analyzed 24 hours after detachment. Because Ca2+ influx contributes to axonal retraction, L-type channels were blocked in some experiments with nicardipine. Results Phosphorylated LIMK is present in rod terminals during retraction and in newly formed processes. Axonal retraction over 7 hours was significantly reduced by inhibition of LIMK or its regulators, ROCK and Pak. Process growth was reduced by LIMK or Pak inhibition especially at the basal (axon-bearing) region of the rod cells. Combining Ca2+ channel and LIMK inhibition had no additional effect on retraction but did further inhibit sprouting after 3 days. In detached porcine retina, LIMK inhibition reduced rod axonal retraction and improved retinal morphology. Conclusions Thus structural remodeling, in the form of either axonal retraction or neuritic growth, requires LIMK activity. LIM kinase inhibition may have therapeutic potential for reducing pathologic rod terminal plasticity after retinal injury. PMID:26658506

St. John’s Wort enhances the synaptic activity of the nucleus of the solitary tract

PubMed Central

Vance, Katie M.; Ribnicky, David M.; Hermann, Gerlinda E.; Rogers, Richard C.

2014-01-01

Objective St. John’s Wort extract, which is commonly used to treat depression, inhibits the reuptake of several neurotransmitters, including glutamate, serotonin, norepinephrine, and dopamine. Glutamatergic visceral vagal afferents synapse upon neurons of the solitary tract (NST); thus, we evaluated whether St. John’s Wort extract modulates glutamatergic neurotransmission within the NST. Materials and Methods We used live cell calcium imaging to evaluate whether St. John’s Wort and its isolated components hypericin and hyperforin increase the excitability of pre-labeled vagal afferent terminals synapsing upon the NST. We used voltage-clamp recordings of spontaneous miniature excitatory postsynaptic currents (mEPSCs) to evaluate whether St. John’s Wort alters glutamate release from vagal afferents onto NST neurons. Results Our imaging data show that St. John’s Wort (50 μg/mL) increased the intracellular calcium levels of stimulated vagal afferent terminals compared to the bath control. This increase in presynaptic vagal afferent calcium by the extract coincides with an increase in neurotransmitter release within the nucleus of the solitary tract, as the frequency of mEPSCs is significantly higher in the presence of the extract compared to the control. Finally, our imaging data show that hyperforin, a known component of St. John’s Wort extract, also significantly increases terminal calcium levels. Conclusion These data suggest that St. John’s Wort extract can significantly increase the probability of glutamate release from vagal afferents onto the NST by increasing presynaptic calcium. The in vitro vagal afferent synapse with NST neurons is an ideal model system to examine the mechanism of action of botanical agents on glutamatergic neurotransmission. PMID:24985104

[Regulation of acetylcholine synthesis in presynaptic endings of cholinergic neurons of the central nervous system].

PubMed

Tuchek, S; Dolezhal, V; Richny, Ia

1984-01-01

Data on the acetylcholine (ACh) synthesis in nerve cells with special attention to its control are summarized in the paper. At rest or during moderate synaptic activity, the concentration of ACh in the compartment of its synthesis probably corresponds to the equilibrium between the substrates and products in the reaction catalysed by choline acetyltransferase. The release of ACh is followed by a transfer of ACh from the compartment of its synthesis to the compartment of release, and, automatically, by the synthesis of new ACh until a new equilibrium is reached in the compartment of synthesis. In addition, synaptic activity and the release of ACh support the synthesis of new ACh in the following ways: choline carriers are disinhibited by lowering the concentration of ACh in the nerve endings, and the transport of choline from the extracellular fluid to the cell interior according to its electro-chemical gradient is thus facilitated; the concentration of choline in the extracellular fluid is increased in the vicinity of the nerve endings as a consequence of the hydrolysis of the released ACh; postactivation hyperpolarization of the nerve endings brings about an increase of the choline transport and concentration in the nerve endings; presumably, the stimulation of muscarinic receptors brings about a further increase in the choline concentration in the vicinity of the nerve endings by the phosphatidylcholine hydrolysis intensification in postsynaptic cells; the decrease in the concentration of acetyl-CoA (as a consequence of the resynthesis of ACh) increases the activity of pyruvate dehydrogenase and the production of acetyl-CoA; conceivably, the increase in the concentration of Ca2+ ions in the nerve endings assists direct passage of acetyl-CoA from the mitochondria to the cytosol of the nerve endings, where the synthesis of ACh occurs.(ABSTRACT TRUNCATED AT 250 WORDS)

[Molecular mechanisms of neurotransmission].

PubMed

Nagatsu, T

2000-12-01

Neurotransmission is regulated by neurotransmitters at the synapses in the neuronal circuits. Main neurotransmitters are classified into the groups of amino acids, amines, purines, peptides, and nitric oxide. In principle, neurotransmitters except peptides are synthesized in the presynaptic neuroterminals from the precursors by the synthesizing enzymes, stored in the synaptic vesicles, released by exocytosis into the synaptic cleft, combined with the postsynaptic membrane receptors, and induce a series of signal transduction to produce acute, short-term, or long-term physiological effects. Termination of the neurotransmission is carried out either by re-uptake into presynaptic nerve terminals through plasma membrane transporters and storage into synaptic vesicles through vesicular transporters or by degradation through metabolizing enzymes (acetylcholine and peptides). Almost all genes related to neurotransmitters have been cloned and the structures of the genes and the protein products have been characterized. Molecular mechanisms of neurotransmission have been elucidated by mouse molecular genetics such as transgenic or knockout mice. Over-expression of human tyrosine hydroxylase (TH). the rate-limiting enzyme of catecholamine synthesis, in transgenic mice (Kaneda et al, Neuron 6, 583-584, 1991) or conversion of norepinephrine neurons to epinephrine neurons (Kobayashi et al, Proc Natl Acad Sci USA 89, 1631-1635, 1992) does not significantly change the phenotype due to compensatory mechanisms such as receptor down-regulation. In contrast, TH (-/-) mutant mice die at perinatal period due to heart failure caused by norepinephrine deficiency in the sympathetic neurons (Kobayashi et al, J Biol Chem 270, 27235-27243, 1995). TH (+/-) mice show a partial decrease in norepinephrine and a modest memory impairment (Kobayashi et al, J Neurosci 20, 2418-2426, 2000). One problem with adult phenotype in transgenic or knockout mice is that mutations cause the confounding effect of the developmental compensation. Thus conditional knockout of a specific type of neurons at a definite time after birth is required. Immunotoxin mediated conditional cell targeting (IMCT) (Kobayashi et al, Proc Natl Acad Sci 92, 1132-1136, 1995) is a novel transgenic technique for elucidating the function of a neuron in a neuronal circuit. Human molecular genetics of genetic neurological diseases are also useful for elucidating molecular mechanisms of neurotransmission. Autosomal dominant dopa-responsive dystonia (DRD) (Segawa's disease) with mutations of GTP cyclohydrolase I (Ichinose et al, Nature Genet 8, 236-242, 1994) causes a partial decrease in dopamine in the nigrostriatal dopamine neurons and produces a dystonia phenotype (Segawa's syndrome). In contrast, autosomal recessive GTP cyclohydrolase I deficiency with complete loss of the enzyme activity produces deficiencies of dopamine, norepinephrine, and serotonin and complex phenotypes with severe neurological symptoms (Ichinose et al, J Biol Chem 270, 10062-10071, 1995).

Immunohistochemical demonstration of enkephalin-containing nerve fibers in guinea pig and rat lungs.

PubMed

Shimosegawa, T; Foda, H D; Said, S I

1989-08-01

Met-enkephalin (Met-Enk) and Leu-enkephalin (Leu-Enk), the opioid peptides originally isolated from the brain, are believed to act as inhibitory neuromodulators at various synaptic sites. In this immunohistochemical study, we have investigated the localization and distribution of Met- and Leu-Enk immunoreactivities in airways and pulmonary vessels of guinea pigs and rats. Immunoreactivities to both peptides were found in nerve fibers and nerve terminals distributed mainly to the trachea and major bronchi, and were especially prevalent in the smooth muscle layer, in the lamina propria, and around tracheal and bronchial glands, but not in the epithelium. Few immunoreactive nerve fibers were detected in smaller bronchi, bronchioles, and alveoli. Enkephalin-immunoreactive nerve fibers were also localized in the walls of pulmonary and bronchial vessels. Within airway microganglia, immunoreactivity was observed in a few nerve terminals, but not in ganglion cell bodies. Met- and Leu-Enk immunoreactive nerve fibers showed similar distribution patterns, though minor differences were noted between the two species: Enk-immunoreactive nerve fibers in the smooth muscle layer were more abundant in guinea pigs than in rats, whereas those in mucous glands were richer in rats than in guinea pigs. These results document the presence of Met- and Leu-Enk immunoreactivity in nerve fibers supplying guinea pig and rat airways and pulmonary vessels, and provide a morphologic basis for the view that enkephalins are likely neurotransmitters or neuromodulators in the lung.

Quantum aspects of brain activity and the role of consciousness.

PubMed Central

Beck, F; Eccles, J C

1992-01-01

The relationship of brain activity to conscious intentions is considered on the basis of the functional microstructure of the cerebral cortex. Each incoming nerve impulse causes the emission of transmitter molecules by the process of exocytosis. Since exocytosis is a quantal phenomenon of the presynaptic vesicular grid with a probability much less than 1, we present a quantum mechanical model for it based on a tunneling process of the trigger mechanism. Consciousness manifests itself in mental intentions. The consequent voluntary actions become effective by momentary increases of the probability of vesicular emission in the thousands of synapses on each pyramidal cell by quantal selection. PMID:1333607

Enhancement of GABA release through endogenous activation of axonal GABA(A) receptors in juvenile cerebellum.

PubMed

Trigo, Federico F; Chat, Mireille; Marty, Alain

2007-11-14

Recent evidence indicates the presence of presynaptic GABA(A) receptors (GABA(A)Rs) in the axon domain of several classes of central neurons, including cerebellar basket and stellate cells. Here, we investigate the possibility that these receptors could be activated in the absence of electrical or chemical stimulation. We find that low concentrations of GABA increase the frequency of miniature GABAergic synaptic currents. Submaximal concentrations of a GABA(A)R blocker, gabazine, decrease both the miniature current frequency and the probability of evoked GABA release. Zolpidem, an agonist of the benzodiazepine binding site, and NO-711 (1-[2-[[(diphenylmethylene)imino]oxy]ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride), a blocker of GABA uptake, both increase the frequency of miniature currents. These effects occur up to postnatal day 14, but not later. Immunohistochemistry indicates the presence of alpha1-containing GABA(A)Rs in interneuron presynaptic terminals with a similar age dependence. We conclude that, under resting conditions, axonal GABA(A)Rs are significantly activated, that this activation results in enhanced GABA release, and that it can be augmented by increasing the affinity of GABA(A)Rs or reducing GABA uptake. Our findings suggest the existence of a positive-feedback mechanism involving presynaptic GABA(A)Rs that maintains a high release rate and a high local GABA concentration in the immature cerebellar network.

Stereotyped initiation of retinal waves by bipolar cells via presynaptic NMDA autoreceptors

PubMed Central

Zhang, Rong-wei; Li, Xiao-quan; Kawakami, Koichi; Du, Jiu-lin

2016-01-01

Glutamatergic retinal waves, the spontaneous patterned neural activities propagating among developing retinal ganglion cells (RGCs), instruct the activity-dependent refinement of visuotopic maps. However, its initiation and underlying mechanism remain largely elusive. Here using larval zebrafish and multiple in vivo approaches, we discover that bipolar cells (BCs) are responsible for the generation of glutamatergic retinal waves. The wave originates from BC axon terminals (ATs) and propagates laterally to nearby BCs and vertically to downstream RGCs and the optic tectum. Its initiation is triggered by the activation of and consequent glutamate release from BC ATs, and is mediated by the N-methyl-D-aspartate subtype of glutamate receptors (NMDARs) expressed at these ATs. Intercellular asymmetry of NMDAR expression at BC ATs enables the preferential initiation of waves at the temporal retina, where BC ATs express more NMDARs. Thus, our findings indicate that glutamatergic retinal waves are initiated by BCs through a presynaptic NMDA autoreceptor-dependent process. PMID:27586999

N-cadherin expression in palisade nerve endings of rat vellus hairs.

PubMed

Kaidoh, Toshiyuki; Inoué, Takao

2008-02-01

Palisade nerve endings (PNs) are mechanoreceptors around vellus hairs of mammals. Each lanceolate nerve ending (LN) of the PN is characterized by a sensory nerve ending symmetrically sandwiched by two processes of type II terminal Schwann cells (tSCIIs). However, the molecular mechanisms underlying the structural organization of the PN are poorly understood. Electron microscopy showed that adherens junctions appeared to adhere to the sensory nerve ending and tSCII processes, so we examined the location of the N-cadherin adhesion system in PNs of rat vellus hairs by using immunoelectron microscopy. N-cadherin localized near both ends of the cell boundary between sensory nerve ending and tSCII processes, which corresponded to the sites of adherens junctions. We further found cadherin-associated proteins, alpha- and beta-catenins, at the linings of adherens junctions. Three-dimensional reconstruction of immunoelectron microscopic serial thin sections showed four linear arrays of N-cadherin arranged longitudinally along the LN beneath the four longitudinal borders of two tSCII processes. In contrast, sensory nerve fibers just proximal to the LNs formed common unmyelinated nerve fibers, in which N-cadherin was located mainly at the mesaxon of type I terminal Schwann cells (tSCIs). These results suggest that the four linear arrays of N-cadherin-mediated junctions adhere the sensory nerve ending and tSCII processes side by side to form the characteristic structure of the LN, and the structural differences between the LNs and the proximal unmyelinated nerve fibers possibly are due to the difference in the pattern of N-cadherin expression between sensory nerve endings and tSCII or tSCI processes. (c) 2007 Wiley-Liss, Inc.

Functional interactions between endogenous cannabinoid and opioid systems: focus on alcohol, genetics and drug-addicted behaviors.

PubMed

López-Moreno, J A; López-Jiménez, A; Gorriti, M A; de Fonseca, F Rodríguez

2010-04-01

Although the first studies regarding the endogenous opioid system and addiction were published during the 1940s, addiction and cannabinoids were not addressed until the 1970s. Currently, the number of opioid addiction studies indexed in PubMed-Medline is 16 times greater than the number of cannabinoid addiction reports. More recently, functional interactions have been demonstrated between the endogenous cannabinoid and opioid systems. For example, the cannabinoid brain receptor type 1 (CB1) and mu opioid receptor type 1 (MOR1) co-localize in the same presynaptic nerve terminals and signal through a common receptor-mediated G-protein pathway. Here, we review a great variety of behavioral models of drug addiction and alcohol-related behaviors. We also include data providing clear evidence that activation of the cannabinoid and opioid endogenous systems via WIN 55,512-2 (0.4-10 mg/kg) and morphine (1.0-10 mg/kg), respectively, produces similar levels of relapse to alcohol in operant alcohol self-administration tasks. Finally, we discuss genetic studies that reveal significant associations between polymorphisms in MOR1 and CB1 receptors and drug addiction. For example, the SNP A118G, which changes the amino acid aspartate to asparagine in the MOR1 gene, is highly associated with altered opioid system function. The presence of a microsatellite polymorphism of an (AAT)n triplet near the CB1 gene is associated with drug addiction phenotypes. But, studies exploring haplotypes with regard to both systems, however, are lacking.

Melatonin modulates rat myotube-acetylcholine receptors by inhibiting calmodulin.

PubMed

de Almeida-Paula, Lidiana Duarte; Costa-Lotufo, Leticia V; Silva Ferreira, Zulma; Monteiro, Amanda Elisa G; Isoldi, Mauro Cesar; Godinho, Rosely O; Markus, Regina P

2005-11-21

Melatonin, the pineal gland hormone, modulates alpha-bungarotoxin sensitive nicotinic acetylcholine receptors in sympathetic nerve terminals, cerebellum and chick retina imposing a diurnal variation in functional responses [Markus, R.P., Zago, W.M., Carneiro, R.C., 1996. Melatonin modulation of presynaptic nicotinic acetylcholine receptors in the rat vas deferens. J. Pharmacol. Exp. Ther. 279, 18-22; Markus, R.P., Santos, J.M., Zago, W., Reno, L.A., 2003. Melatonin nocturnal surge modulates nicotinic receptors and nicotine-induced [3HI] glutamate release in rat cerebellum slices. J. Pharmacol. Exp. Ther. 305, 525-530; Sampaio, L.F.S., Hamassaki-Britto, D.E., Markus, R.P., 2005. Influence of melatonin on the development of functional nicotinic acetylcholine receptors in cultured chick retinal cells. Braz. J. Med. Biol. Res. 38, 603-613]. Here we show that in rat myotubes forskolin and melatonin reduced the number of nicotinic acetylcholine receptors expressed in plasma membrane. In addition, these cells expressed melatonin MT1 receptors, which are known to be coupled to G(i)-protein. However, the pharmacological profile of melatonin analogs regarding the reduction in cyclic AMP accumulation and number of nicotinic acetylcholine receptors did not point to a mechanism mediated by activation of G(i)-protein coupled receptors. On the other hand, calmidazolium, a classical inhibitor of calmodulin, reduced in a similar manner both effects. Considering that one isoform of adenylyl cyclase present in rat myotubes is regulated by Ca2+/calmodulin, we propose that melatonin modulates the number of nicotinic acetylcholine receptors via reduction in cyclic AMP accumulation.

Human autoantibodies specific for the α1A calcium channel subunit reduce both P-type and Q-type calcium currents in cerebellar neurons

PubMed Central

Pinto, Ashwin; Gillard, Samantha; Moss, Fraser; Whyte, Kathryn; Brust, Paul; Williams, Mark; Stauderman, Ken; Harpold, Michael; Lang, Bethan; Newsom-Davis, John; Bleakman, David; Lodge, David; Boot, John

1998-01-01

The pharmacological properties of voltage-dependent calcium channel (VDCC) subtypes appear mainly to be determined by the α1 pore-forming subunit but, whether P-and Q-type VDCCs are encoded by the same α1 gene presently is unresolved. To investigate this, we used IgG antibodies to presynaptic VDCCs at motor nerve terminals that underlie muscle weakness in the autoimmune Lambert–Eaton myasthenic syndrome (LEMS). We first studied their action on changes in intracellular free Ca2+ concentration [Ca2+]i in human embryonic kidney (HEK293) cell lines expressing different combinations of human recombinant VDCC subunits. Incubation for 18 h with LEMS IgG (2 mg/ml) caused a significant dose-dependent reduction in the K+-stimulated [Ca2+]i increase in the α1A cell line but not in the α1B, α1C, α1D, and α1E cell lines, establishing the α1A subunit as the target for these autoantibodies. Exploiting this specificity, we incubated cultured rat cerebellar neurones with LEMS IgG and observed a reduction in P-type current in Purkinje cells and both P- and Q-type currents in granule cells. These data are consistent with the hypothesis that the α1A gene encodes for the pore-forming subunit of both P-type and Q-type VDCCs. PMID:9653186

On the translocation of botulinum and tetanus neurotoxins across the membrane of acidic intracellular compartments.

PubMed

Pirazzini, Marco; Azarnia Tehran, Domenico; Leka, Oneda; Zanetti, Giulia; Rossetto, Ornella; Montecucco, Cesare

2016-03-01

Tetanus and botulinum neurotoxins are produced by anaerobic bacteria of the genus Clostridium and are the most poisonous toxins known, with 50% mouse lethal dose comprised within the range of 0.1-few nanograms per Kg, depending on the individual toxin. Botulinum neurotoxins are similarly toxic to humans and can therefore be considered for potential use in bioterrorism. At the same time, their neurospecificity and reversibility of action make them excellent therapeutics for a growing and heterogeneous number of human diseases that are characterized by a hyperactivity of peripheral nerve terminals. The complete crystallographic structure is available for some botulinum toxins, and reveals that they consist of four domains functionally related to the four steps of their mechanism of neuron intoxication: 1) binding to specific receptors of the presynaptic membrane; 2) internalization via endocytic vesicles; 3) translocation across the membrane of endocytic vesicles into the neuronal cytosol; 4) catalytic activity of the enzymatic moiety directed towards the SNARE proteins. Despite the many advances in understanding the structure-mechanism relationship of tetanus and botulinum neurotoxins, the molecular events involved in the translocation step have been only partially elucidated. Here we will review recent advances that have provided relevant insights on the process and discuss possible models that can be experimentally tested. This article is part of a Special Issue entitled: Pore-Forming Toxins edited by Mauro Dalla Serra and Franco Gambale. Copyright © 2015. Published by Elsevier B.V.

Stimulation of spinal dorsal horn β2-adrenergic receptor ameliorates neuropathic mechanical hypersensitivity through a reduction of phosphorylation of microglial p38 MAP kinase and astrocytic c-jun N-terminal kinase.

PubMed

Zhang, Fang Fang; Morioka, Norimitsu; Abe, Hiromi; Fujii, Shiori; Miyauchi, Kazuki; Nakamura, Yoki; Hisaoka-Nakashima, Kazue; Nakata, Yoshihiro

2016-12-01

The noradrenaline-adrenergic system has a crucial role in controlling nociceptive transduction at the spinal level. While α-adrenergic receptors are known to regulate nociceptive neurotransmitter release at the spinal presynaptic level, it is not entirely clear whether β-adrenergic receptors are involved in controlling pain transduction at the spinal level as well. The current study elucidated a role of β-adrenergic receptors in neuropathic pain in mice following a partial sciatic nerve ligation (PSNL). In addition, the cellular and intracellular signaling cascade induced by β-adrenergic receptors in neuropathic mice was elaborated. Intrathecal injection of isoproterenol (1 nmol), a nonselective β-adrenergic receptor agonist, briefly ameliorated hind paw mechanical hypersensitivity of PSNL mice. Isoproterenol's antinociceptive effect was mediated through β2-adrenergic receptors since pretreatment with ICI118551, a selective β2-adrenergic receptor antagonist, but not with CGP20712A, a selective β1-adrenergic receptor antagonist, significantly attenuated isoproterenol's effect. Furthermore, intrathecal treatment with a selective β2-adrenergic receptor agonist, terbutaline, but not a selective β1-adrenergic receptor agonist, dobutamine, also significantly ameliorated neuropathic pain. Fourteen days after PSNL, increased phosphorylation of both p38 Mitogen-activated protein kinase (MAPK) in microglia and c-jun N-terminal kinase (JNK) in astrocytes of ipsilateral spinal dorsal horn were observed. Phosphorylation of both microglial p38 MAPK and astrocytic JNK were downregulated by stimulation of the β2-adrenergic receptor. Together, these results suggest that spinal β2-adrenergic receptor have an inhibitory role in neuropathic nociceptive transduction at the spinal level through a downregulation of glial activity, perhaps through modulation of MAP kinases phosphorylation. Thus, targeting of β2-adrenergic receptors could be an effective therapeutic strategy in treating neuropathic pain. Copyright © 2016 Elsevier Ltd. All rights reserved.

Active uptake of substance P carboxy-terminal heptapeptide (5-11) into rat brain and rabbit spinal cord slices.

PubMed

Nakata, Y; Kusaka, Y; Yajima, H; Segawa, T

1981-12-01

We previously reported that nerve terminals and glial cells lack an active uptake system capable of terminating transmitter action of substance P (SP). In the present study, we demonstrated the existence of an active uptake system for SP carboxy-terminal heptapeptide, (5-11)SP. When the slices from either rat brain or rabbit spinal cord were incubated with [3H](5-11)SP, the uptake of (5-11)SP into slices was observed. The uptake system has the properties of an active transport mechanism: it is dependent on temperature and sensitive to hypoosmotic treatment and is inhibited by ouabain and dinitrophenol (DNP). In the brain, (5-11)SP was accumulated by means of a high-affinity and a low-affinity uptake system. The Km and the Vmax values for the high-affinity system were 4.20 x 10(-8) M and 7.59 fmol/10 mg wet weight/min, respectively, whereas these values for the low-affinity system were 1.00 x 10(-6) M and 100 fmol/10 mg wet weight/min, respectively. In the spinal cord, there was only one uptake system, with a Km value of 2.16 x 10(-7) M and Vmax value of 26.2 fmol/10 mg wet weight/min. These results suggest that when SP is released from nerve terminals, it is hydrolysed into (5-11)SP before or after acting as a neurotransmitter, which is in turn accumulated into nerve terminals. Therefore, the uptake system may represent a possible mechanism for the inactivation of SP.

Effect of 1 GeV/n Fe particles on cocaine-stimulated locomotor activity

NASA Astrophysics Data System (ADS)

Vazquez, M.; Bruneus, M.; Gatley, J.; Russell, S.; Billups, A.

Space travel beyond the Earth's protective magnetic field (for example, to Mars) will involve exposure of astronauts to irradiation by high-energy nuclei such as 56Fe (HZE radiation), which are a component of galactic cosmic rays. These particles have high linear energy transfer (LET) and are expected to irreversibly damage cells they traverse. Our working hypothesis is that long-term behavioral alterations are induced after exposure of the brain to 1 GeV/n iron particles with fluences of 1 to 8 particles/cell targets. Previous studies support this notion but are not definitive, especially with regard to long-term effects. Using the Alternating Gradient Synchrotron (AGS) we expose C57 mice to 1 GeV/n 56Fe radiation (head only) at doses of 0, 15, 30, 60, 120 and 240 cGy. There were originally 19 mice per group. The ability of cocaine to increase locomotor activity in 16 of these animals in response to an intraperitoneal injection of cocaine has been measured so far at 1, 4, 8, 12, 16, 20, 24 and 28 weeks. Cocaine-stimulated locomotor activity was chosen in part because it is a behavioral assay with which we have considerable experience. More importantly, the ability to respond to cocaine is a complex behavior involving many neurotransmitter systems and brain circuits. Therefore, the probability of alteration of this behavior by HZE particles was considered high. However, the central circuit is the nigrostriatal dopamine system, in which dopamine is released in striatum from nerve terminals whose cell bodies are located in the substantia nigra. Cocaine activates behavior by blocking dopamine transporters on striatal nerve terminals and therefore elevating the concentration of dopamine in the synapse. Dopamine activates receptors on striatal GABAergic cells that project via other brain regions to the thalamus. Activation of the motor cortex by glutamatergic projections from the thalamus leads ultimately to increased locomotion. The experimental paradigm involves placing mice in a plexiglass box fitted with arrays of photocells. A mouse placed in the box exhibits exploratory behavior that diminishes to a low level over the course of about 20 min. Iron particle irradiation caused dose related reductions in locomotor activity stimulated by cocaine, as evidenced by the group data presented here. The impairments after HZE radiation appeared to be persistent. Irradiation using a 137Co source also led to alterations in cocaine-stimulated locomotion at early times, but, unlike the situation for HZE radiation, these disappeared at later times. These studies were very recently terminated and data analysis is not yet complete. For example, spontaneous activity was also monitored, and it is possible that comparison of stimulated and spontaneous locomotion for each animal may expose larger changes. Most of the mice were sacrificed and their brains stored for histology and neurochemistry. Ex vivo determination of dopamine transporter status in striata of some of the mice indicated no large decrease in this marker of pre-synaptic dopamine terminals, supporting an earlier pilot study in rats.

Iatrogenic nerve injuries during shoulder surgery.

PubMed

Carofino, Bradley C; Brogan, David M; Kircher, Michelle F; Elhassan, Bassem T; Spinner, Robert J; Bishop, Allen T; Shin, Alexander Y

2013-09-18

The current literature indicates that neurologic injuries during shoulder surgery occur infrequently and result in little if any morbidity. The purpose of this study was to review one institution's experience treating patients with iatrogenic nerve injuries after shoulder surgery. A retrospective review of the records of patients evaluated in a brachial plexus specialty clinic from 2000 to 2010 identified twenty-six patients with iatrogenic nerve injury secondary to shoulder surgery. The records were reviewed to determine the operative procedure, time to presentation, findings on physical examination, treatment, and outcome. The average age was forty-three years (range, seventeen to seventy-two years), and the average delay prior to referral was 5.4 months (range, one to fifteen months). Seven nerve injuries resulted from open procedures done to treat instability; nine, from arthroscopic surgery; four, from total shoulder arthroplasty; and six, from a combined open and arthroscopic operation. The injury occurred at the level of the brachial plexus in thirteen patients and at a terminal nerve branch in thirteen. Fifteen patients (58%) did not recover nerve function after observation and required surgical management. A structural nerve injury (laceration or suture entrapment) occurred in nine patients (35%), including eight of the thirteen who presented with a terminal nerve branch injury and one of the thirteen who presented with an injury at the level of the brachial plexus. Nerve injuries occurring during shoulder surgery can produce severe morbidity and may require surgical management. Injuries at the level of a peripheral nerve are more likely to be surgically treatable than injuries of the brachial plexus. A high index of suspicion and early referral and evaluation should be considered when evaluating patients with iatrogenic neurologic deficits after shoulder surgery.

Receptosecretory nature of type III cells in the taste bud.

PubMed

Yoshie, Sumio

2009-01-01

Type III cells in taste buds form chemical synapses with intragemmal afferent nerve fibers and are characterized by the presence of membrane-bound vesicles in the cytoplasm. Although the vesicles differ in shape and size among species, they are primarily categorized into small clear (40 nm in diameter) and large dense-cored (90-200 nm) types. As such vesicles tend to be closely juxtaposed to the synaptic membrane of the cells, it is reasonable to consider that the vesicles include transmitter(s) towards the gustatory nerve. In the guinea-pig taste bud, stimulation with various taste substances (sucrose, sodium chloride, quinine hydrochloride, or monosodium L-glutamate) causes ultrastructural alterations of the type III cells. At the synapse, the presynaptic plasma membrane often displays invaginations of 90 nm in a mean diameter towards the cytoplasm, which indicates the dense-cored vesicles opening into the synaptic cleft by means of exocytosis. The vesicles are also exocytosed at the non-synaptic region into the intercellular space. These findings strongly suggest that the transmitters presumably contained in the vesicles are released to conduct the excitement of the type III cells to the nerves and also to exert their paracrine effects upon the surroundings, such as the Ebner's salivary gland, acting as local hormones.

Changes in VGLUT1 and VGLUT2 expression in rat dorsal root ganglia and spinal cord following spared nerve injury.

PubMed

Wang, Hong-Sheng; Yu, Gang; Wang, Zhi-Tong; Yi, Shou-Pu; Su, Rui-Bin; Gong, Ze-Hui

2016-10-01

Disturbance of glutamate homeostasis is a well-characterized mechanism of neuropathic pain. Vesicular glutamate transporters (VGLUTs) determine glutamate accumulation in synaptic vesicles and their roles in neuropathic pain have been suggested by gene-knockout studies. Here, we investigated the spatio-temporal changes in VGLUT expression during the development of neuropathic pain in wild-type rats. Spared nerve injury (SNI) induced mechanical allodynia from postoperative day 1 to at least day 14. Expression of VGLUT1 and VGLUT2 in dorsal root ganglia and spinal cord was examined by western blot analyses on different postoperative days. We observed that VGLUT2 were selectively upregulated in crude vesicle fractions from the ipsilateral lumbar enlargement on postoperative days 7 and 14, while VGLUT1 was transiently downregulated in ipsilateral DRG (day 4) and contralateral lumbar enlargement (day 1). Upregulation of VGLUT2 was not accompanied by alterations in vesicular expression of synaptotagmin or glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Thus, VGLUTs expression, especially VGLUT2, is regulated following peripheral nerve injury. Temporal regulation of VGLUT2 expression in spinal cord may represent a novel presynaptic mechanism contributing to injury-induced glutamate imbalance and associated neuropathic pain. Copyright © 2016 Elsevier Ltd. All rights reserved.

Microglial activation is a pharmacologically specific marker for the neurotoxic amphetamines.

PubMed

Thomas, David M; Dowgiert, Jennifer; Geddes, Timothy J; Francescutti-Verbeem, Dina; Liu, Xiuli; Kuhn, Donald M

2004-09-09

Neurotoxic amphetamines cause damage to monoamine nerve terminals of the striatum by unknown mechanisms. Microglial activation contributes to the neuronal damage that accompanies injury, disease, and inflammation, but a role for these cells in amphetamine-induced neurotoxicity has received little attention. We show presently that D-methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA), D-amphetamine, and p-chloroamphetamine, each of which has been linked to dopamine (DA) or serotonin nerve terminal damage, result in microglial activation in the striatum. The non-neurotoxic amphetamines l-methamphetamine, fenfluramine, and DOI do not have this effect. All drugs that cause microglial activation also increase expression of glial fibrillary acidic protein (GFAP). At a minimum, microglial activation serves as a pharmacologically specific marker for striatal nerve terminal damage resulting only from those amphetamines that exert neurotoxicity. Because microglia are known to produce many of the reactive species (e.g., nitric oxide, superoxide, cytokines) that mediate the neurotoxicity of the amphetamine-class of drugs, their activation could represent an early and essential event in the neurotoxic cascade associated with high-dose amphetamine intoxication.

Presynaptic Na+-dependent transport and exocytose of GABA and glutamate in brain in hypergravity.

NASA Astrophysics Data System (ADS)

Borisova, T.; Pozdnyakova, N.; Krisanova, N.; Himmelreich, N.

γ-Aminobutyric acid (GABA) and L-glutamate are the most widespread neurotransmitter amino acids in the mammalian central nervous system. GABA is now widely recognized as the major inhibitory neurotransmitter. L-glutamate mediates the most of excitatory synaptic neurotransmission in the brain. They involved in the main aspects of normal brain function. The nerve terminals (synaptosomes) offer several advantages as a model system for the study of general mechanisms of neurosecretion. Our data allowed to conclude that exposure of animals to hypergravity (centrifugation of rats at 10G for 1 hour) had a profound effect on synaptic processes in brain. Comparative analysis of uptake and release of GABA and glutamate have demonstrated that hypergravity loading evokes oppositely directed alterations in inhibitory and excitatory signal transmission. We studied the maximal velocities of [^3H]GABA reuptake and revealed more than twofold enhancement of GABA transporter activity (Vmax rises from 1.4 |pm 0.3 nmol/min/mg of protein in the control group to 3.3 ± 0.59 nmol/min/mg of protein for animals exposed to hypergravity (P ≤ 0.05)). Recently we have also demonstrated the significant lowering of glutamate transporter activity (Vmax of glutamate reuptake decreased from 12.5 ± 3.2 nmol/min/mg of protein in the control group to 5.6 ± 0.9 nmol/min/mg of protein in the group of animals, exposed to the hypergravity stress (P ≤ 0.05)). Significant changes occurred in release of neurotransmitters induced by stimulating exocytosis with the agents, which depolarized nerve terminal plasma membrane. Depolarization-evoked Ca2+-stimulated release was more abundant for GABA (7.2 ± 0.54% and 11,74 ±1,2 % of total accumulated label for control and hypergravity, respectively (P≤0.05)) and was essentially less for glutamate (14.4 ± 0.7% and 6.2 ± 1.9%) after exposure of animals to centrifuge induced artificial gravity. Changes observed in depolarization-evoked exocytotic release seem to be in a concert with alterations of plasma membrane transporters activity studied. Perhaps, lowering of glutamate transporter activity and increase of the velocity of GABA uptake correlated with diminution and augmentation of exocytotic release of these neurotransmitters, respectively. It is possible to suggest that observed changes in the activity of the processes responsible for the uptake and release of excitatory and inhibitory neurotransmitters are likely to be physiologically important and reflect making protective mechanisms more active for neutralization of harm influence of hypergravity stress.

Constitutive and ghrelin-dependent GHSR1a activation impairs CaV2.1 and CaV2.2 currents in hypothalamic neurons

PubMed Central

López Soto, Eduardo Javier; Agosti, Francina; Cabral, Agustina; Mustafa, Emilio Roman; Damonte, Valentina Martínez; Gandini, Maria Alejandra; Rodríguez, Silvia; Castrogiovanni, Daniel; Felix, Ricardo; Perelló, Mario

2015-01-01

The growth hormone secretagogue receptor type 1a (GHSR1a) has the highest known constitutive activity of any G protein–coupled receptor (GPCR). GHSR1a mediates the action of the hormone ghrelin, and its activation increases transcriptional and electrical activity in hypothalamic neurons. Although GHSR1a is present at GABAergic presynaptic terminals, its effect on neurotransmitter release remains unclear. The activities of the voltage-gated calcium channels, CaV2.1 and CaV2.2, which mediate neurotransmitter release at presynaptic terminals, are modulated by many GPCRs. Here, we show that both constitutive and agonist-dependent GHSR1a activity elicit a strong impairment of CaV2.1 and CaV2.2 currents in rat and mouse hypothalamic neurons and in a heterologous expression system. Constitutive GHSR1a activity reduces CaV2 currents by a Gi/o-dependent mechanism that involves persistent reduction in channel density at the plasma membrane, whereas ghrelin-dependent GHSR1a inhibition is reversible and involves altered CaV2 gating via a Gq-dependent pathway. Thus, GHSR1a differentially inhibits CaV2 channels by Gi/o or Gq protein pathways depending on its mode of activation. Moreover, we present evidence suggesting that GHSR1a-mediated inhibition of CaV2 attenuates GABA release in hypothalamic neurons, a mechanism that could contribute to neuronal activation through the disinhibition of postsynaptic neurons. PMID:26283199

Molecular characteristics suggest an effector function of palisade endings in extraocular muscles.

PubMed

Konakci, Kadriye Zeynep; Streicher, Johannes; Hoetzenecker, Wolfram; Blumer, Michael Josef Franz; Lukas, Julius-Robert; Blumer, Roland

2005-01-01

To analyze palisade endings in cat extraocular muscles (EOMs) and to clarify whether these EOM-specific organs are sensory or motor. Twelve cats aged between 1 and 16 years were analyzed. Whole EOM tendons were immunostained using four different combinations of triple fluorescence labeling. Triple labeling included antibodies against choline acetyltransferase (ChAT), neurofilament, synaptophysin, and alpha-bungarotoxin. Preparations were examined by confocal laser scanning microscopy. ChAT-labeled EOMs were also analyzed by immunoelectron microscopy. Three-dimensional reconstructions were made of palisade endings. Palisade endings were found in the distal and proximal myotendinous regions of cat EOMs. These endings arose from thin nerve fibers coming from the muscle and extending into the tendon. There, the nerve fibers turned back 180 degrees to divide into terminal branches around the muscle fiber tips. Terminal branches established numerous contacts with the tendon attached to the muscle fiber tip and only a few contacts with the muscle fiber. Often, nerve fibers forming palisade endings on muscle fiber tips were observed to establish multiple motor contacts on muscle fibers outside palisade endings. Three-dimensional reconstructions depicted the complex morphology of the palisade endings. All nerve fibers supplying palisade endings stained positively for ChAT and neurofilament. All nerve terminals in palisade endings were ChAT and synaptophysin positive. Only neuromuscular contacts in palisade endings were positive for alpha-bungarotoxin, as well. This study provides evidence that palisade endings in cat EOMs have effector function. The findings may be of significance for strabismus surgery because palisade endings are also found in human EOMs.

Presynaptic membrane potential affects transmitter release in an identified neuron in Aplysia by modulating the Ca2+ and K+ currents.

PubMed

Shapiro, E; Castellucci, V F; Kandel, E R

1980-01-01

We have examined the relationships between the modulation of transmitter release and of specific ionic currents by membrane potential in the cholinergic interneuron L10 of the abdominal ganglion of Aplysia californica. The presynaptic cell body was voltage-clamped under various pharmacological conditions and transmitter release from the terminals was assayed simultaneously by recording the synaptic potentials in the postsynaptic cell. When cell L10 was voltage-clamped from a holding potential of -60 mV in the presence of tetrodotoxin, graded transmitter release was evoked by depolarizing command pulses in the membrane voltage range (-35 mV to + 10 mV) in which the Ca(2+) current was also increasing. Depolarizing the holding potential of L10 results in increased transmitter output. Two ionic mechanisms contribute to this form of plasticity. First, depolarization inactivates some K(+) channels so that depolarizing command pulses recruit a smaller K(+) current. In unclamped cells the decreased K(+) conductance causes spike-broadening and increased influx of Ca(2+) during each spike. Second, small depolarizations around resting potential (-55 mV to -35 mV) activate a steady-state Ca(2+) current that also contributes to the modulation of transmitter release, because, even with most presynaptic K(+) currents blocked pharmacologically, depolarizing the holding potential still increases transmitter release. In contrast to the steady-state Ca(2+) current, the transient inward Ca(2+) current evoked by depolarizing clamp steps is relatively unchanged from various holding potentials.

Protective Effects of Testosterone on Presynaptic Terminals against Oligomeric β-Amyloid Peptide in Primary Culture of Hippocampal Neurons

PubMed Central

Lau, Chi-Fai; Ho, Yuen-Shan; Hung, Clara Hiu-Ling; Poon, Chun-Hei; Chiu, Kin; Yang, Xifei

2014-01-01

Increasing lines of evidence support that testosterone may have neuroprotective effects. While observational studies reported an association between higher bioavailable testosterone or brain testosterone levels and reduced risk of Alzheimer's disease (AD), there is limited understanding of the underlying neuroprotective mechanisms. Previous studies demonstrated that testosterone could alleviate neurotoxicity induced by β-amyloid (Aβ), but these findings mainly focused on neuronal apoptosis. Since synaptic dysfunction and degeneration are early events during the pathogenesis of AD, we aim to investigate the effects of testosterone on oligomeric Aβ-induced synaptic changes. Our data suggested that exposure of primary cultured hippocampal neurons to oligomeric Aβ could reduce the length of neurites and decrease the expression of presynaptic proteins including synaptophysin, synaptotagmin, and synapsin-1. Aβ also disrupted synaptic vesicle recycling and protein folding machinery. Testosterone preserved the integrity of neurites and the expression of presynaptic proteins. It also attenuated Aβ-induced impairment of synaptic exocytosis. By using letrozole as an aromatase antagonist, we further demonstrated that the effects of testosterone on exocytosis were unlikely to be mediated through the estrogen receptor pathway. Furthermore, we showed that testosterone could attenuate Aβ-induced reduction of HSP70, which suggests a novel mechanism that links testosterone and its protective function on Aβ-induced synaptic damage. Taken together, our data provide further evidence on the beneficial effects of testosterone, which may be useful for future drug development for AD. PMID:25045655

Different role of TTX-sensitive voltage-gated sodium channel (NaV 1) subtypes in action potential initiation and conduction in vagal airway nociceptors.

PubMed

Kollarik, M; Sun, H; Herbstsomer, R A; Ru, F; Kocmalova, M; Meeker, S N; Undem, B J

2018-04-15

The action potential initiation in the nerve terminals and its subsequent conduction along the axons of afferent nerves are not necessarily dependent on the same voltage-gated sodium channel (Na V 1) subunits. The action potential initiation in jugular C-fibres within airway tissues is not blocked by TTX; nonetheless, conduction of action potentials along the vagal axons of these nerves is often dependent on TTX-sensitive channels. This is not the case for nodose airway Aδ-fibres and C-fibres, where both action potential initiation and conduction is abolished by TTX or selective Na V 1.7 blockers. The difference between the initiation of action potentials within the airways vs. conduction along the axons should be considered when developing Na V 1 blocking drugs for topical application to the respiratory tract. The action potential (AP) initiation in the nerve terminals and its subsequent AP conduction along the axons do not necessarily depend on the same subtypes of voltage-gated sodium channels (Na V 1s). We evaluated the role of TTX-sensitive and TTX-resistant Na V 1s in vagal afferent nociceptor nerves derived from jugular and nodose ganglia innervating the respiratory system. Single cell RT-PCR was performed on vagal afferent neurons retrogradely labelled from the guinea pig trachea. Almost all of the jugular neurons expressed the TTX-sensitive channel Na V 1.7 along with TTX-resistant Na V 1.8 and Na V 1.9. Tracheal nodose neurons also expressed Na V 1.7 but, less frequently, Na V 1.8 and Na V 1.9. Na V 1.6 were expressed in ∼40% of the jugular and 25% of nodose tracheal neurons. Other Na V 1 α subunits were only rarely expressed. Single fibre recordings were made from the vagal nodose and jugular nerve fibres innervating the trachea or lung in the isolated perfused vagally-innervated preparations that allowed for selective drug delivery to the nerve terminal compartment (AP initiation) or to the desheathed vagus nerve (AP conduction). AP initiation in jugular C-fibres was unaffected by TTX, although it was inhibited by Na V 1.8 blocker (PF-01247324) and abolished by combination of TTX and PF-01247324. However, AP conduction in the majority of jugular C-fibres was abolished by TTX. By contrast, both AP initiation and conduction in nodose nociceptors was abolished by TTX or selective Na V 1.7 blockers. Distinction between the effect of a drug with respect to inhibiting AP in the nerve terminals within the airways vs. at conduction sites along the vagus nerve is relevant to therapeutic strategies involving inhaled Na V 1 blocking drugs. © 2018 The Authors. The Journal of Physiology © 2018 The Physiological Society.

Ultrastructural studies of vasopressin neurons of the paraventricular nucleus of the hypothalamus using a monoclonal antibody to vasopressin: analysis of synaptic input.

PubMed

Silverman, A J; Hou-Yu, A; Zimmerman, E A

1983-05-01

The ultrastructure of the vasopressin neurons of the paraventricular nucleus of the hypothalamus was studied by immunocytochemical techniques. Tissue antigen was detected in unembedded tissue sections using a monoclonal antibody that recognizes vasopressin but not oxytocin or vasotocin. At the light-microscopic level, reaction product was seen to fill the cytoplasm of the neuron cell body as well as large portions of the dendrite and axon. Immunoreactive spines were seen on both somatic and dendritic surfaces and their presence was confirmed at the ultrastructural level. In the light-microscope, axonal processes do not have spines and are thinner and more varicose than dendritic processes. At the electron-microscopic level, both axons and dendrites of the vasopressin cells are filled with reactive neurosecretory granules. The presence of large numbers of these organelles made it difficult to distinguish proximal dendrites from Herring bodies (axonal swellings). At the ultrastructural level, reaction product was also observed in the cytoplasm of all segments of the vasopressin cells. The presence of reaction product outside of membranous compartments is undoubtably due to disruption of membranes by detergent treatment or exposure to basic pH. However, the staining procedure used did allow us to examine the synaptic input to the vasopressin cells. All portions of the vasopressin neuron receive a diverse innervation. The somata have synapses on their surfaces and on spines. These axo-somatic terminals are primarily, but not exclusively, symmetrical and the presynaptic elements contain spherical or elongate vesicles. On the dendrites, terminals again were observed on the surface or on spines. these axo-dendritic synapses were usually asymmetrical. The presynaptic elements contained clear spherical, elongate or pleomorphic vesicles. Occasional varicosities with dense-core granules were seen to make en passant contacts with dendrites; these contacts did not have obvious membrane specializations. Input to vasopressin axons was studied both along the paraventricular-neurohypophysial tract and in the median eminence. Vasopressin axons receive a synaptic input (axo-axonic), predominately of the asymmetric variety with clear, spherical vesicles in the presynaptic element. These findings demonstrate that the vasopressin neurons of the paraventricular nucleus receive a diverse innervation.

Axon Termination, Pruning, and Synaptogenesis in the Giant Fiber System of Drosophila melanogaster Is Promoted by Highwire.

PubMed

Borgen, Melissa; Rowland, Kimberly; Boerner, Jana; Lloyd, Brandon; Khan, Aruna; Murphey, Rodney

2017-03-01

The ubiquitin ligase Highwire has a conserved role in synapse formation. Here, we show that Highwire coordinates several facets of central synapse formation in the Drosophila melanogaster giant fiber system, including axon termination, axon pruning, and synaptic function. Despite the similarities to the fly neuromuscular junction, the role of Highwire and the underlying signaling pathways are distinct in the fly's giant fiber system. During development, branching of the giant fiber presynaptic terminal occurs and, normally, the transient branches are pruned away. However, in highwire mutants these ectopic branches persist, indicating that Highwire promotes axon pruning. highwire mutants also exhibit defects in synaptic function. Highwire promotes axon pruning and synaptic function cell-autonomously by attenuating a mitogen-activated protein kinase pathway including Wallenda, c-Jun N-terminal kinase/Basket, and the transcription factor Jun. We also show a novel role for Highwire in non-cell autonomous promotion of synaptic function from the midline glia. Highwire also regulates axon termination in the giant fibers, as highwire mutant axons exhibit severe overgrowth beyond the pruning defect. This excessive axon growth is increased by manipulating Fos expression in the cells surrounding the giant fiber terminal, suggesting that Fos regulates a trans -synaptic signal that promotes giant fiber axon growth. Copyright © 2017 by the Genetics Society of America.

Optogenetic versus electrical stimulation of dopamine terminals in the nucleus accumbens reveals local modulation of presynaptic release

PubMed Central

Melchior, James R.; Ferris, Mark J.; Stuber, Garret D.; Riddle, David R.; Jones, Sara R.

2015-01-01

The nucleus accumbens is highly heterogeneous, integrating regionally distinct afferent projections and accumbal interneurons, resulting in diverse local microenvironments. Dopamine (DA) neuron terminals similarly express a heterogeneous collection of terminal receptors that modulate DA signaling. Cyclic voltammetry is often used to probe DA terminal dynamics in brain slice preparations; however, this method traditionally requires electrical stimulation to induce DA release. Electrical stimulation excites all of the neuronal processes in the stimulation field, potentially introducing simultaneous, multi-synaptic modulation of DA terminal release. We used optogenetics to selectively stimulate DA terminals and used voltammetry to compare DA responses from electrical and optical stimulation of the same area of tissue around a recording electrode. We found that with multiple pulse stimulation trains, optically stimulated DA release increasingly exceeded that of electrical stimulation. Furthermore, electrical stimulation produced inhibition of DA release across longer duration stimulations. The GABAB antagonist, CGP 55845, increased electrically stimulated DA release significantly more than light stimulated release. The nicotinic acetylcholine receptor antagonist, dihydro-β-erythroidine hydrobromide, inhibited single pulse electrically stimulated DA release while having no effect on optically stimulated DA release. Our results demonstrate that electrical stimulation introduces local multi-synaptic modulation of DA release that is absent with optogenetically targeted stimulation. PMID:26011081

Semi-quantitative ultrastructural analysis of the localization and neuropeptide content of gonadotropin releasing hormone nerve terminals in the median eminence throughout the estrous cycle of the rat.

PubMed

Prevot, V; Dutoit, S; Croix, D; Tramu, G; Beauvillain, J C

1998-05-01

The ultrastructural appearance of gonadotropin releasing hormone-immunoreactive elements was studied in the external zone of the median eminence of adult female Wistar rats. On the one hand, the purpose of the study was to determine the distribution of gonadotropin releasing hormone terminals towards the parenchymatous basal lamina at the level of hypothalamo-hypophyseal portal vessels, throughout the estrous cycle. On the other hand, we have semi-quantified the gonadotropin releasing hormone content in nerve terminals or preterminals during this physiological condition. A morphometric study was coupled to a colloidal 15 mn gold postembedding immunocytochemistry procedure. Animals were killed at 09.00 on diestrus II, 0.900, 10.00, 13.00, 17.00 and 18.00 on proestrus and 09.00 on estrus (n = 4-8 rats/group). A preliminary light microscopic study was carried out to identify an antero-posterior part of median eminence strongly immunostained by anti-gonadotropin releasing hormone antibodies but which was, in addition, easily spotted. This last condition was necessary to make a good comparison between each animal. Contacts between gonadotropin releasing hormone nerve terminals and the basal lamina were observed only the day of proestrus. Such contacts, however, were rare and in the great majority of cases, gonadotropin releasing hormone terminals are separated from basal lamina by tanycytic end feet. The morphometric analysis showed no significant variation in average distance between gonadotropin releasing hormone terminals and capillaries throughout the estrous cycle. Consequently, it did not appear that a large neuroglial plasticity exists during the estrous cycle. However, the observation of contacts only on proestrus together with some ultrastructural images evoke the possibility of a slight plasticity. The semi-quantitative results show that the content of gonadotropin releasing hormone in the nerve endings presented two peaks on proestrus: one at 09.00 (23 +/- 5 particles/micrograms2, P < 0.03) before the onset of luteinizing hormone surge, and the second at 18.00 (16 +/- 2 particles/micrograms2, P < 0.01) concomitantly with the luteinizing hormone surge, when compared to baseline values on proestrus 10.00 (8 +/- particles/micrograms2).

The metabotropic glutamate receptor activates the lipid kinase PI3K in Drosophila motor neurons through the calcium/calmodulin-dependent protein kinase II and the nonreceptor tyrosine protein kinase DFak.

PubMed

Chun-Jen Lin, Curtis; Summerville, James B; Howlett, Eric; Stern, Michael

2011-07-01

Ligand activation of the metabotropic glutamate receptor (mGluR) activates the lipid kinase PI3K in both the mammalian central nervous system and Drosophila motor nerve terminal. In several subregions of the mammalian brain, mGluR-mediated PI3K activation is essential for a form of synaptic plasticity termed long-term depression (LTD), which is implicated in neurological diseases such as fragile X and autism. In Drosophila larval motor neurons, ligand activation of DmGluRA, the sole Drosophila mGluR, similarly mediates a PI3K-dependent downregulation of neuronal activity. The mechanism by which mGluR activates PI3K remains incompletely understood in either mammals or Drosophila. Here we identify CaMKII and the nonreceptor tyrosine kinase DFak as critical intermediates in the DmGluRA-dependent activation of PI3K at Drosophila motor nerve terminals. We find that transgene-induced CaMKII inhibition or the DFak(CG1) null mutation each block the ability of glutamate application to activate PI3K in larval motor nerve terminals, whereas transgene-induced CaMKII activation increases PI3K activity in motor nerve terminals in a DFak-dependent manner, even in the absence of glutamate application. We also find that CaMKII activation induces other PI3K-dependent effects, such as increased motor axon diameter and increased synapse number at the larval neuromuscular junction. CaMKII, but not PI3K, requires DFak activity for these increases. We conclude that the activation of PI3K by DmGluRA is mediated by CaMKII and DFak.

Central Projections of Antennal and Labial Palp Sensory Neurons in the Migratory Armyworm Mythimna separata

PubMed Central

Ma, Bai-Wei; Zhao, Xin-Cheng; Berg, Bente G.; Xie, Gui-Ying; Tang, Qing-Bo; Wang, Gui-Rong

2017-01-01

The oriental armyworm, Mythimna separata (Walker), is a polyphagous, migratory pest relying on olfactory cues to find mates, locate nectar, and guide long-distance flight behavior. In the present study, a combination of neuroanatomical techniques were utilized on this species, including backfills, confocal microscopy, and three-dimensional reconstructions, to trace the central projections of sensory neurons from the antenna and the labial pit organ, respectively. As previously shown, the axons of the labial sensory neurons project via the ipsilateral labial nerve and terminate in three main areas of the central nervous system: (1) the labial-palp pit organ glomerulus of each antennal lobe, (2) the gnathal ganglion, and (3) the prothoracic ganglion of the ventral nerve cord. Similarly, the antennal sensory axons project to multiple areas of the central nervous system. The ipsilateral antennal nerve targets mainly the antennal lobe, the antennal mechanosensory and motor center, and the prothoracic and mesothoracic ganglia. Specific staining experiments including dye application to each of the three antennal segments indicate that the antennal lobe receives input from flagellar olfactory neurons exclusively, while the antennal mechanosensory and motor center is innervated by mechanosensory neurons from the whole antenna, comprising the flagellum, pedicle, and scape. The terminals in the mechanosensory and motor center are organized in segregated zones relating to the origin of neurons. The flagellar mechanosensory axons target anterior zones, while the pedicular and scapal axons terminate in posterior zones. In the ventral nerve cord, the processes from the antennal sensory neurons terminate in the motor area of the thoracic ganglia, suggesting a close connection with motor neurons. Taken together, the numerous neuropils innervated by axons both from the antenna and labial palp indicate the multiple roles these sensory organs serve in insect behavior. PMID:29209176

Three variations of the laryngeal nerve in the same patient: a case report

PubMed Central

2011-01-01

Introduction A non-recurrent course is a rare anatomic variation of the inferior laryngeal nerve (ILN). Bilateral extra-laryngeal bifurcation of the ILN seldom occurs before its laryngeal entry. Anastomosis between the ILN and cervical sympathetic chain is another rare anatomic feature. The prevalence of extra-laryngeal branching of the non-recurrent nerve is unknown. We present an example of triple anatomic variations of ILNs in the same patient, and also two anatomic variations in the same nerve. Case presentation A 56-year-old Caucasian man with a large toxic multi-nodular goiter was surgically treated with total thyroidectomy. Both his right and left ILNs were identified, fully exposed and preserved along their cervical courses. We discovered many variations during bilateral exploration of the two ILNs. His right ILN was non-recurrent. This non-recurrent ILN showed a terminal division before laryngeal entry. The left nerve had a usual course as a recurrent laryngeal nerve (RLN) at his tracheaesophageal groove. We also discovered bifurcation of his RLN beginning at a neurovascular (RLN and inferior thyroid artery) crossing point. Anterior and posterior branches of both nerves entered his larynx separately. The sympathetic inferior laryngeal anastomotic branch (SILAB) between the posterior branch of his left ILN and the cervical sympathetic chain was established in the distal part of the nerve before laryngeal entry. Conclusion A non-recurrent nerve and extra-laryngeal branching of the ILN are two different variations. The coincidence of a right non-recurrent ILN and bilateral bifurcation of both nerves is a very interesting feature. SILAB is a rare additional finding as a third anatomic variation in the same patient. Extra-laryngeal terminal division of a non-recurrent ILN is an extremely unusual anatomic finding. Two anatomic variations have occurred in the same nerve, like "the variation of the variation". PMID:21722360

Daily Electrical Muscle Stimulation Enhances Functional Recovery Following Nerve Transection and Repair in Rats.

PubMed

Willand, Michael P; Chiang, Cameron D; Zhang, Jennifer J; Kemp, Stephen W P; Borschel, Gregory H; Gordon, Tessa

2015-08-01

Incomplete recovery following surgical reconstruction of damaged peripheral nerves is common. Electrical muscle stimulation (EMS) to improve functional outcomes has not been effective in previous studies. To evaluate the efficacy of a new, clinically translatable EMS paradigm over a 3-month period following nerve transection and immediate repair. Rats were divided into 6 groups based on treatment (EMS or no treatment) and duration (1, 2, or 3 months). A tibial nerve transection injury was immediately repaired with 2 epineurial sutures. The right gastrocnemius muscle in all rats was implanted with intramuscular electrodes. In the EMS group, the muscle was electrically stimulated with 600 contractions per day, 5 days a week. Terminal measurements were made after 1, 2, or 3 months. Rats in the 3-month group were assessed weekly using skilled and overground locomotion tests. Neuromuscular junction reinnervation patterns were also examined. Muscles that received daily EMS had significantly greater numbers of reinnervated motor units with smaller average motor unit sizes. The majority of muscle endplates were reinnervated by a single axon arising from a nerve trunk with significantly fewer numbers of terminal sprouts in the EMS group, the numbers being small. Muscle mass and force were unchanged but EMS improved behavioral outcomes. Our results demonstrated that EMS using a moderate stimulation paradigm immediately following nerve transection and repair enhances electrophysiological and behavioral recovery. © The Author(s) 2014.

[Targeted inactivation of gamma-synuclein gene affects anxiety and exploratory behaviour of mice].

PubMed

Kokhan, V S; Bolkunov, A V; Ustiugov, A A; Van'kin, G I; Shelkovnikova, T A; Redkozubova, O M; Strekalova, T V; Bukhman, V L; Ninkina, N N; Bachurin, S O

2011-01-01

Gamma(gamma)-synuclein is a member of synuclein family of cytoplasmic and predominantly neuronal proteins found only in vertebrates. Gamma-synuclein is abundant in axons and presynaptic terminals of neurons localized in brain regions involved in emotions, learning and memory. However, the role of gamma-synuclein in these brain functions was not previously assessed. We have demonstrated for the first time that the loss of gamma-synuclein results in a significant increase in the level of orientation response in novel environment and decrease in the level of state anxiety.

Neuropeptide Y in the adult and fetal human pineal gland.

PubMed

Møller, Morten; Phansuwan-Pujito, Pansiri; Badiu, Corin

2014-01-01

Neuropeptide Y was isolated from the porcine brain in 1982 and shown to be colocalized with noradrenaline in sympathetic nerve terminals. The peptide has been demonstrated to be present in sympathetic nerve fibers innervating the pineal gland in many mammalian species. In this investigation, we show by use of immunohistochemistry that neuropeptide Y is present in nerve fibers of the adult human pineal gland. The fibers are classical neuropeptidergic fibers endowed with large boutons en passage and primarily located in a perifollicular position with some fibers entering the pineal parenchyma inside the follicle. The distance from the immunoreactive terminals to the pinealocytes indicates a modulatory function of neuropeptide Y for pineal physiology. Some of the immunoreactive fibers might originate from neurons located in the brain and be a part of the central innervation of the pineal gland. In a series of human fetuses, neuropeptide Y-containing nerve fibers was present and could be detected as early as in the pineal of four- to five-month-old fetuses. This early innervation of the human pineal is different from most rodents, where the innervation starts postnatally.

Neuropeptide Y in the Adult and Fetal Human Pineal Gland

PubMed Central

Møller, Morten; Phansuwan-Pujito, Pansiri

2014-01-01

Neuropeptide Y was isolated from the porcine brain in 1982 and shown to be colocalized with noradrenaline in sympathetic nerve terminals. The peptide has been demonstrated to be present in sympathetic nerve fibers innervating the pineal gland in many mammalian species. In this investigation, we show by use of immunohistochemistry that neuropeptide Y is present in nerve fibers of the adult human pineal gland. The fibers are classical neuropeptidergic fibers endowed with large boutons en passage and primarily located in a perifollicular position with some fibers entering the pineal parenchyma inside the follicle. The distance from the immunoreactive terminals to the pinealocytes indicates a modulatory function of neuropeptide Y for pineal physiology. Some of the immunoreactive fibers might originate from neurons located in the brain and be a part of the central innervation of the pineal gland. In a series of human fetuses, neuropeptide Y-containing nerve fibers was present and could be detected as early as in the pineal of four- to five-month-old fetuses. This early innervation of the human pineal is different from most rodents, where the innervation starts postnatally. PMID:24757681

Macrophage Depletion Ameliorates Peripheral Neuropathy in Aging Mice.

PubMed

Yuan, Xidi; Klein, Dennis; Kerscher, Susanne; West, Brian L; Weis, Joachim; Katona, Istvan; Martini, Rudolf

2018-05-09

Aging is known as a major risk factor for the structure and function of the nervous system. There is urgent need to overcome such deleterious effects of age-related neurodegeneration. Here we show that peripheral nerves of 24-month-old aging C57BL/6 mice of either sex show similar pathological alterations as nerves from aging human individuals, whereas 12-month-old adult mice lack such alterations. Specifically, nerve fibers showed demyelination, remyelination and axonal lesion. Moreover, in the aging mice, neuromuscular junctions showed features typical for dying-back neuropathies, as revealed by a decline of presynaptic markers, associated with α-bungarotoxin-positive postsynapses. In line with these observations were reduced muscle strengths. These alterations were accompanied by elevated numbers of endoneurial macrophages, partially comprising the features of phagocytosing macrophages. Comparable profiles of macrophages could be identified in peripheral nerve biopsies of aging persons. To determine the pathological impact of macrophages in aging mice, we selectively targeted the cells by applying an orally administered CSF-1R specific kinase (c-FMS) inhibitor. The 6-month-lasting treatment started before development of degenerative changes at 18 months and reduced macrophage numbers in mice by ∼70%, without side effects. Strikingly, nerve structure was ameliorated and muscle strength preserved. We show, for the first time, that age-related degenerative changes in peripheral nerves are driven by macrophages. These findings may pave the way for treating degeneration in the aging peripheral nervous system by targeting macrophages, leading to reduced weakness, improved mobility, and eventually increased quality of life in the elderly. SIGNIFICANCE STATEMENT Aging is a major risk factor for the structure and function of the nervous system. Here we show that peripheral nerves of 24-month-old aging mice show similar degenerative alterations as nerves from aging human individuals. Both in mice and humans, these alterations were accompanied by endoneurial macrophages. To determine the pathological impact of macrophages in aging mice, we selectively targeted the cells by blocking a cytokine receptor, essential for macrophage survival. The treatment strongly reduced macrophage numbers and substantially improved nerve structure and muscle strength. We show, for the first time, that age-related degenerative changes in peripheral nerves are driven by macrophages. These findings may be helpful for treatment weakness and reduced mobility in the elderly. Copyright © 2018 the authors 0270-6474/18/384610-11$15.00/0.

The Scaffolding Protein, Grb2-associated Binder-1, in Skeletal Muscles and Terminal Schwann Cells Regulates Postnatal Neuromuscular Synapse Maturation

PubMed Central

Park, So Young; Jang, So Young; Shin, Yoon Kyoung; Jung, Dong Keun; Yoon, Byeol A; Kim, Jong Kook; Jo, Young Rae; Lee, Hye Jeong

2017-01-01

The vertebrate neuromuscular junction (NMJ) is considered as a “tripartite synapse” consisting of a motor axon terminal, a muscle endplate, and terminal Schwann cells that envelope the motor axon terminal. The neuregulin 1 (NRG1)-ErbB2 signaling pathway plays an important role in the development of the NMJ. We previously showed that Grb2-associated binder 1 (Gab1), a scaffolding mediator of receptor tyrosine kinase signaling, is required for NRG1-induced peripheral nerve myelination. Here, we determined the role of Gab1 in the development of the NMJ using muscle-specific conditional Gab1 knockout mice. The mutant mice showed delayed postnatal maturation of the NMJ. Furthermore, the selective loss of the gab1 gene in terminal Schwann cells produced delayed synaptic elimination with abnormal morphology of the motor endplate, suggesting that Gab1 in both muscles and terminal Schwann cells is required for proper NMJ development. Gab1 in terminal Schwann cells appeared to regulate the number and process elongation of terminal Schwann cells during synaptic elimination. However, Gab2 knockout mice did not show any defects in the development of the NMJ. Considering the role of Gab1 in postnatal peripheral nerve myelination, our findings suggest that Gab1 is a pleiotropic and important component of NRG1 signals during postnatal development of the peripheral neuromuscular system. PMID:28680299

The Scaffolding Protein, Grb2-associated Binder-1, in Skeletal Muscles and Terminal Schwann Cells Regulates Postnatal Neuromuscular Synapse Maturation.

PubMed

Park, So Young; Jang, So Young; Shin, Yoon Kyoung; Jung, Dong Keun; Yoon, Byeol A; Kim, Jong Kook; Jo, Young Rae; Lee, Hye Jeong; Park, Hwan Tae

2017-06-01

The vertebrate neuromuscular junction (NMJ) is considered as a "tripartite synapse" consisting of a motor axon terminal, a muscle endplate, and terminal Schwann cells that envelope the motor axon terminal. The neuregulin 1 (NRG1)-ErbB2 signaling pathway plays an important role in the development of the NMJ. We previously showed that Grb2-associated binder 1 (Gab1), a scaffolding mediator of receptor tyrosine kinase signaling, is required for NRG1-induced peripheral nerve myelination. Here, we determined the role of Gab1 in the development of the NMJ using muscle-specific conditional Gab1 knockout mice. The mutant mice showed delayed postnatal maturation of the NMJ. Furthermore, the selective loss of the gab1 gene in terminal Schwann cells produced delayed synaptic elimination with abnormal morphology of the motor endplate, suggesting that Gab1 in both muscles and terminal Schwann cells is required for proper NMJ development. Gab1 in terminal Schwann cells appeared to regulate the number and process elongation of terminal Schwann cells during synaptic elimination. However, Gab2 knockout mice did not show any defects in the development of the NMJ. Considering the role of Gab1 in postnatal peripheral nerve myelination, our findings suggest that Gab1 is a pleiotropic and important component of NRG1 signals during postnatal development of the peripheral neuromuscular system.

Palisade endings: cholinergic sensory organs or effector organs?

PubMed

Blumer, Roland; Konakci, Kadriye Zeynep; Pomikal, Christine; Wieczorek, Grazyna; Lukas, Julius-Robert; Streicher, Johannes

2009-03-01

This study aims to complement the authors' prior findings on palisade endings in extraocular muscles (EOMs) of monkeys, and to clarify whether palisade endings are cholinergic motor or cholinergic sensory. Macaque monkeys (Macaca fascicularis, n = 10) of both sexes were analyzed using three-dimensional (3D) reconstructions, confocal laser scanning microscopy (CLSM), and conventional/immuno transmission electron microscopy (TEM). For CLSM, we used three combinations of triple fluorescent labeling. EOM wholemounts were labeled with cholinergic markers, including choline acetyltransferase (ChAT), choline transporter (ChT), vesicular acetylcholine transporter (VAChT), and a classical postsynaptic marker for motor terminals, namely alpha-bungarotoxin. Muscle fibers were counterstained with phalloidin. 3D reconstructions were done of triple-labeled palisade endings. For immuno TEM, tissue was labeled with antibody against ChAT. Concordant with prior findings, the authors demonstrated that palisade endings at the muscle fiber tips arose from nerve fibers that are ChAT-positive. In 25% of the cases, axons forming palisade endings established multiple neuromuscular contacts outside the palisade complex. Such additional neuromuscular contacts were motor terminals, as demonstrated by alpha-bungarotoxin binding. All palisade endings established nerve terminals on the tendon. In 40% of the palisade endings, nerve terminals were observed on the muscle fiber as well. Neurotendinous contacts and neuromuscular contacts in palisade endings were ChT/ChAT/VAChT-immunoreactive. Neuromuscular contacts exhibited structural features of motor terminals and were also alpha-bungarotoxin positive. The present study ascertained that palisade endings are cholinergic motor organs. Therefore, it was concluded that palisade endings are not candidates to provide eye-position signals.

Ionotropic and metabotropic receptor mediated airway sensory nerve activation.

PubMed

Lee, Min-Goo; Kollarik, Marian; Chuaychoo, Benjamas; Undem, Bradley J

2004-01-01

There are several receptors capable of inducing activating generator potentials in cough-associated afferent terminals in the airways. The chemical receptors leading to generator potentials can be subclassified into ionotropic and metabotropic types. An ionotropic receptor has an agonist-binding domain, and also serves directly as an ion channel that is opened upon binding of the agonist. Examples of ionotropic receptors found in airway sensory nerve terminals include receptors for serotonin (5-HT3 receptors), ATP (P2X receptors), acetylcholine (nicotinic receptors), receptors for capsaicin and related vanilloids (TRPV1 receptors), and acid receptors (acid sensing ion channels). Afferent nerve terminals can also be depolarized via activation of metabotropic or G-protein coupled receptors (GPCRs). Among the GPCRs that can lead to activation of airway afferent fibers include bradykinin B2 and adenosine A1 receptors. The signaling events leading to GPCR-mediated membrane depolarization are more complex than that seen with ionotropic receptors. The GPCR-mediated effects are thought to occur through classical second messenger systems such as activation of phospholipase C. This may lead to membrane depolarization through interaction with specific ionotropic receptors (such as TRPV1) and/or various types of calcium activated channels.

Evidence for presynaptically silent synapses in the immature hippocampus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoon, Jae Young; Choi, Sukwoo

Silent synapses show NMDA receptor (NMDAR)-mediated synaptic responses, but not AMPAR-mediated synaptic responses. A prevailing hypothesis states that silent synapses contain NMDARs, but not AMPARs. However, alternative presynaptic hypotheses, according to which AMPARs are present at silent synapses, have been proposed; silent synapses show slow glutamate release via a fusion pore, and glutamate spillover from the neighboring synaptic terminals. Consistent with these presynaptic hypotheses, the peak glutamate concentrations at silent synapses have been estimated to be ≪170 μM, much lower than those seen at functional synapses. Glutamate transients predicted based on the two presynaptic mechanisms have been shown to activate onlymore » high-affinity NMDARs, but not low-affinity AMPARs. Interestingly, a previous study has developed a new approach to distinguish between the two presynaptic mechanisms using dextran, an inert macromolecule that reduces the diffusivity of released glutamate: postsynaptic responses through the fusion pore mechanism, but not through the spillover mechanism, are potentiated by reduced glutamate diffusivity. Therefore, we reasoned that if the fusion pore mechanism underlies silent synapses, dextran application would reveal AMPAR-mediated synaptic responses at silent synapses. In the present study, we recorded AMPAR-mediated synaptic responses at the CA3-CA1 synapses in neonatal rats in the presence of blockers for NMDARs and GABAARs. Bath application of dextran revealed synaptic responses at silent synapses. GYKI53655, a selective AMPAR-antagonist, completely inhibited the unsilenced synaptic responses, indicating that the unsilenced synaptic responses are mediated by AMPARs. The dextran-mediated reduction in glutamate diffusivity would also lead to the activation of metabotropic glutamate receptors (mGluRs), which might induce unsilencing via the activation of unknown intracellular signaling. Hence, we determined whether mGluR-blockers alter the dextran-induced unsilencing. However, dextran application continued to produce significant synaptic unsilencing in the presence of a cocktail of the blockers for all subtypes of mGluRs. Our findings provide evidence that slowed glutamate diffusion produces synaptic unsilencing by enhancing the peak glutamate occupancy of pre-existing AMPARs, supporting the fusion pore mechanism of silent synapses. - Highlights: • Slowed glutamate diffusion by dextran reveals synaptic responses at silent synapses. • Unsilenced synaptic responses are mediated by AMPA receptors. • Dextran-induced unsilencing is independent of metabotropic glutamate receptors.« less

Endogenous calcitonin gene-related peptide (CGRP) mediates adrenergic-dependent vasodilation induced by nicotine in mesenteric resistance arteries of the rat

PubMed Central

Shiraki, Hinako; Kawasaki, Hiromu; Tezuka, Satoko; Nakatsuma, Akira; Kurosaki, Yuji

2000-01-01

The mechanisms underlying vasodilator effect of nicotine on mesenteric resistance blood vessels and the role of calcitonin gene-related peptide (CGRP)-containing (CGRPergic) vasodilator nerves were studied in the rat. Mesenteric vascular beds isolated from Wistar rats were perfused with Krebs solution, and perfusion pressure was measured with a pressure transducer. In preparations with intact endothelium and contracted by perfusion with Krebs solution containing methoxamine, perfusion of nicotine (1–100 μM) for 1 min caused a concentration-dependent vasodilator response without vasoconstriction. The nicotine-induced vasodilation was markedly inhibited by hexamethonium (nicotinic cholinoceptor antagonist, 10 μM) and blocked by guanethidine (adrenergic neuron blocker, 5 μM). Either denervation by cold storage (4°C for 72 h) or adrenergic denervation by 6-hydroxydopamine (toxin for adrenergic neurons, 2 mM for 20 min incubation, twice) blocked the nicotine-induced vasodilation. Neither endothelium removal with perfusion of sodium deoxycholate (1.80 mg ml−1, for 30 s) nor treatment with Nω-nitro-L-arginine (nitric oxide synthase inhibitor, 100 μM), atropine (muscarinic cholinoceptor antagonist, 10 nM) or propranolol (β-adrenoceptor antagonist, 100 nM) affected the nicotine-induced vasodilation. In preparations without endothelium, treatment with capsaicin (depleting CGRP-containing sensory nerves, 1 μM) or human CGRP[8–37] (CGRP receptor antagonist, 0.5 μM) markedly inhibited the nicotine-induced vasodilation. These results suggest that, in the mesenteric resistance artery of the rat, nicotine induces vasodilation, which is independent of the function of the endothelium and is involved in activation of CGRPergic nerves. It is also suggested that nicotine stimulates presynaptic nicotinic cholinoceptors on adrenergic nerves to release adrenergic neurotransmitters, which then act on CGRPergic nerves to release endogenous CGRP from the nerve. PMID:10882393

Morphologically mixed chemical-electrical synapses formed by primary afferents in rodent vestibular nuclei as revealed by immunofluorescence detection of connexin36 and vesicular glutamate transporter-1

PubMed Central

Nagy, James I.; Bautista, Wendy; Blakley, Brian; Rash, John E.

2013-01-01

Axon terminals forming mixed chemical/electrical synapses in the lateral vestibular nucleus of rat were described over forty years ago. Because gap junctions formed by connexins are the morphological correlate of electrical synapses, and with demonstrations of widespread expression of the gap junction protein connexin36 (Cx36) in neurons, we investigated the distribution and cellular localization of electrical synapses in the adult and developing rodent vestibular nuclear complex, using immunofluorescence detection of Cx36 as a marker for these synapses. In addition, we examined Cx36 localization in relation to that of the nerve terminal marker vesicular glutamate transporter-1 (vglut-1). An abundance of immunolabelling for Cx36 in the form of Cx36-puncta was found in each of the four major vestibular nuclei of adult rat and mouse. Immunolabelling was associated with somata and initial dendrites of medium and large neurons, and was absent in vestibular nuclei of Cx36 knockout mice. Cx36-puncta were seen either dispersed or aggregated into clusters on the surface of neurons, and were never found to occur intracellularly. Nearly all Cx36-puncta were localized to large nerve terminals immunolabelled for vglut-1. These terminals and their associated Cx36-puncta were substantially depleted after labyrinthectomy. Developmentally, labelling for Cx36 was already present in the vestibular nuclei at postnatal day 5, where it was only partially co-localized with vglut-1, and did not become fully associated with vglut-1-positive terminals until postnatal day 20 to 25. The results show that vglut-1-positive primary afferent nerve terminals form mixed synapses throughout the vestibular nuclear complex, that the gap junction component of these synapses contain Cx36, that multiple Cx36-containing gap junctions are associated with individual vglut-1 terminals and that the development of these mixed synapses is protracted over several postnatal weeks. PMID:23912039

Sodium Channel β2 Subunits Prevent Action Potential Propagation Failures at Axonal Branch Points.

PubMed

Cho, In Ha; Panzera, Lauren C; Chin, Morven; Hoppa, Michael B

2017-09-27

Neurotransmitter release depends on voltage-gated Na + channels (Na v s) to propagate an action potential (AP) successfully from the axon hillock to a synaptic terminal. Unmyelinated sections of axon are very diverse structures encompassing branch points and numerous presynaptic terminals with undefined molecular partners of Na + channels. Using optical recordings of Ca 2+ and membrane voltage, we demonstrate here that Na + channel β2 subunits (Na v β2s) are required to prevent AP propagation failures across the axonal arborization of cultured rat hippocampal neurons (mixed male and female). When Na v β2 expression was reduced, we identified two specific phenotypes: (1) membrane excitability and AP-evoked Ca 2+ entry were impaired at synapses and (2) AP propagation was severely compromised with >40% of axonal branches no longer responding to AP-stimulation. We went on to show that a great deal of electrical signaling heterogeneity exists in AP waveforms across the axonal arborization independent of axon morphology. Therefore, Na v β2 is a critical regulator of axonal excitability and synaptic function in unmyelinated axons. SIGNIFICANCE STATEMENT Voltage-gated Ca 2+ channels are fulcrums of neurotransmission that convert electrical inputs into chemical outputs in the form of vesicle fusion at synaptic terminals. However, the role of the electrical signal, the presynaptic action potential (AP), in modulating synaptic transmission is less clear. What is the fidelity of a propagating AP waveform in the axon and what molecules shape it throughout the axonal arborization? Our work identifies several new features of AP propagation in unmyelinated axons: (1) branches of a single axonal arborization have variable AP waveforms independent of morphology, (2) Na + channel β2 subunits modulate AP-evoked Ca 2+ -influx, and (3) β2 subunits maintain successful AP propagation across the axonal arbor. These findings are relevant to understanding the flow of excitation in the brain. Copyright © 2017 the authors 0270-6474/17/379519-15$15.00/0.

Comparative effects of aluminum and ouabain on synaptosomal choline uptake, acetylcholine release and (Na+/K+)ATPase.

PubMed

Silva, Virgília S; Nunes, M Alexandra; Cordeiro, J Miguel; Calejo, Ana I; Santos, Sofia; Neves, Paulo; Sykes, António; Morgado, Fernando; Dunant, Yves; Gonçalves, Paula P

2007-07-17

Closing the gap between adverse health effects of aluminum and its mechanisms of action still represents a huge challenge. Cholinergic dysfunction has been implicated in neuronal injury induced by aluminum. Previously reported data also indicate that in vivo and in vitro exposure to aluminum inhibits the mammalian (Na(+)/K(+))ATPase, an ubiquitous plasma membrane pump. This study was undertaken with the specific aim of determining whether in vitro exposure to AlCl(3) and ouabain, the foremost utilized selective inhibitor of (Na(+)/K(+))ATPase, induce similar functional modifications of cholinergic presynaptic nerve terminals, by comparing their effects on choline uptake, acetylcholine release and (Na(+)/K(+))ATPase activity, on subcellular fractions enriched in synaptic nerve endings isolated from rat brain, cuttlefish optic lobe and torpedo electric organ. Results obtained show that choline uptake by rat synaptosomes was inhibited by submillimolar AlCl(3), whereas the amount of choline taken up by synaptosomes isolated from cuttlefish and torpedo remained unchanged. Conversely, choline uptake was reduced by ouabain to a large extent in all synaptosomal preparations analyzed. In contrast to ouabain, which modified the K(+) depolarization evoked release of acetylcholine by rat, cuttlefish and torpedo synaptosomal fractions, AlCl(3) induced reduction of stimulated acetylcholine release was only observed when rat synaptosomes were challenged. Finally, it was observed that the aluminum effect on cuttlefish and torpedo synaptosomal (Na(+)/K(+))ATPase activity was slight when compared to its inhibitory action on mammalian (Na(+)/K(+))ATPase. In conclusion, inhibition of (Na(+)/K(+))ATPase by AlCl(3) and ouabain jeopardized the high-affinity (Na(+)-dependent, hemicholinium-3 sensitive) uptake of choline and the Ca(2+)-dependent, K(+) depolarization evoked release of acetylcholine by rat, cuttlefish and torpedo synaptosomal fractions. The effects of submillimolar AlCl(3) on choline uptake and acetylcholine release only resembled those of ouabain when rat synaptosomes were assayed. Therefore, important differences were found between the species regarding the cholinotoxic action of aluminum. The variability of (Na(+)/K(+))ATPase sensitivity to aluminum of cholinergic neurons might contribute to their differential susceptibility to this neurotoxic agent.

Clinical spectrum of botulism.

PubMed

Cherington, M

1998-06-01

Botulism is a paralyzing disease caused by the toxin of Clostridium botulinum. The toxin produces skeletal muscle paralysis by producing a presynaptic blockade to the release of acetylcholine. Recent studies have pinpointed the site of action of the several types of botulinum neurotoxin at the nerve terminal. Since the discovery of the toxin about 100 years ago, five clinical forms of botulism have been described: 1) classic or foodborne botulism; 2) wound botulism; 3) infant botulism; 4) hidden botulism; 5) inadvertent botulism. A clinical pattern of descending weakness is characteristic of all five forms. Almost all human cases of botulism are caused by one of three serotypes (A, B, or E). Classic and wound botulism were the only two forms known until the last quarter of this century. Wound botulism was rare until the past decade. Now there are increasing numbers of cases of wound botulism in injecting drug users. Infant botulism, first described in 1976, is now the most frequently reported form. In infant botulism spores of Clostridium botulinum are ingested and germinate in the intestinal tract. Hidden botulism, the adult variant of infant botulism, occurs in adult patients who usually have an abnormality of the intestinal tract that allows colonization by Clostridium botulinum. Inadvertent botulism is the most recent form to be described. It occurs in patients who have been treated with injections of botulinum toxin for dystonic and other movement disorders. Laboratory proof of botulism is established with the detection of toxin in the patient's serum, stool, or wound. The detection of Clostridium botulinum bacteria in the stool or wound should also be considered evidence of clinical botulism. Electrophysiologic studies can provide presumptive of botulism in patients with the clinical signs of botulism. Electrophysiologic testing can be especially helpful when bioassay studies are negative. The most consistent electrophysiologic abnormality is a small evoked muscle action potential in response to a single supramaximal nerve stimulus in a clinically affected muscle. Posttetanic facilitation can be found in some affected muscles. Single-fiber EMG studies typically reveal increased jitter and blocking, which become less marked following activation. The major treatment for severe botulism is advance medical and nursing supportive care with special attention to respiratory status.

Causes and consequences of the loss of serotonergic presynapses elicited by the consumption of 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") and its congeners.

PubMed

Huether, G; Zhou, D; Rüther, E

1997-01-01

The massive and prolonged stimulation of serotonin (5-HT)-release and the increased dopaminergic activity are responsible for the acute psychomimetic and psychostimulatory effects of 3,4-methylenedioxy-methamphetamine (MDMA, "ecstasy") and its congeners. In vulnerable subjects, at high doses or repeated use, and under certain unfavorable conditions (crowding, high ambient temperature), severe, in some cases fatal, averse systemic reactions (hyperthermia, serotonin-syndrome) may occur during the first few hours. Animal experiments revealed the existence of similar differences in vulnerability and similar dose- and context-related influences on a similar sequence of acute responses. The severity of these acute systemic responses is closely related to the severity of the long-term damage to 5-HT axon terminals caused by the administration of substituted amphetamines. Attempts to identify the mechanisms involved in this selective degeneration of 5-HT presynapses brought to light a multitude of different factors and conditions which either attenuate or potentiate the loss of 5-HT terminals caused by MDMA and related amphetamine derivatives. These puzzling observations suggest that the degeneration of 5-HT presynapses represents only the final step in a sequence of events which compromise the ability of 5-HT terminals to maintain their functional and structural integrity. Substituted amphetamines selectively tax energy metabolism in 5-HT presynapses through their ability to exchange with 5-HT and to dissipate transmembrane ion gradients. The active carrier systems in the vesicular and presynaptic membrane operate at a permanently activated state. The resulting energy deficit can no longer adequately restored by the 5-HT presynapses when their availability of substrates for ATP production is additionally reduced by the hyperthermic and other energy consuming reactions which are elicited by the systemic administration of substituted amphetamines. The exhaustion of energy in 5-HT nerve terminals compromised all energy-requiring endogenous mechanisms involved in the regulation of transmembrane-ion exchange, internal Ca(++)-homeostasis, prevention of oxidative stress, detoxification, and repair. Above a critical threshold the failure of these self-protective mechanisms will lead to the degeneration of the 5-HT axon terminals. Based on the role of 5-HT as a global modulatory transmitter-system involved in the stabilization and integration of impulse flow between distributed multifocal neuronal networks, the partial loss of 5-HT presynapses must be expected to impair the ability of these networks to maintain the integrity of signal flow pattern, and increase the likelihood of switching to unstable information processing. Behavioral responding may therefore become more dominated by activities generated in individual networks, and hitherto "buffered" personality traits and predisposition may become manifested as defined psychiatric syndromes in certain predisposed subjects.

Enhancement by citral of glutamatergic spontaneous excitatory transmission in adult rat substantia gelatinosa neurons.

PubMed

Zhu, Lan; Fujita, Tsugumi; Jiang, Chang-Yu; Kumamoto, Eiichi

2016-02-10

Although citral, which is abundantly present in lemongrass, has various actions including antinociception, how citral affects synaptic transmission has not been examined as yet. Citral activates in heterologous cells transient receptor potential vanilloid-1, ankyrin-1, and melastatin-8 (TRPV1, TRPA1, and TRPM8, respectively) channels, the activation of which in the spinal lamina II [substantia gelatinosa (SG)] increases the spontaneous release of L-glutamate from nerve terminals. It remains to be examined what types of transient receptor potential channel in native neurons are activated by citral. With a focus on transient receptor potential activation, we examined the effect of citral on glutamatergic spontaneous excitatory transmission using the whole-cell patch-clamp technique to SG neurons in adult rat spinal cord slices. Bath-applied citral for 3 min increased the frequency of spontaneous excitatory postsynaptic current in a concentration-dependent manner (half-maximal effective concentration=0.58 mM), with a small increase in its amplitude. The spontaneous excitatory postsynaptic current frequency increase produced by citral was repeated at a time interval of 30 min, albeit this action recovered with a slow time course after washout. The presynaptic effect of citral was inhibited by TRPA1 antagonist HC-030031, but not by voltage-gated Na-channel blocker tetrodotoxin, TRPV1 antagonist capsazepine, and TRPM8 antagonist BCTC. It is concluded that citral increases spontaneous L-glutamate release in SG neurons by activating TRPA1 channels. Considering that the SG plays a pivotal role in modulating nociceptive transmission from the periphery, the citral activity could contribute toward at least a part of the modulation.

Regulation of Hypothalamic Presympathetic Neurons and Sympathetic Outflow by Group II Metabotropic Glutamate Receptors in Spontaneously Hypertensive Rats.

PubMed

Ye, Zeng-You; Li, De-Pei; Pan, Hui-Lin

2013-08-01

Increased glutamatergic input in the hypothalamic paraventricular nucleus (PVN) plays an important role in the development of hypertension. Group II metabotropic glutamate receptors are expressed in the PVN, but their involvement in regulating synaptic transmission and sympathetic outflow in hypertension is unclear. Here, we show that the group II metabotropic glutamate receptors agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) produced a significantly greater reduction in the frequency of spontaneous and miniature excitatory postsynaptic currents and in the amplitude of electrically evoked excitatory postsynaptic currents in retrogradely labeled spinally projecting PVN neurons in spontaneously hypertensive rats (SHRs) than in normotensive control rats. DCG-IV similarly decreased the frequency of GABAergic inhibitory postsynaptic currents of labeled PVN neurons in the 2 groups of rats. Strikingly, DCG-IV suppressed the firing of labeled PVN neurons only in SHRs. DCG-IV failed to inhibit the firing of PVN neurons of SHRs in the presence of ionotropic glutamate receptor antagonists. Lowering blood pressure with celiac ganglionectomy in SHRs normalized the DCG-IV effect on excitatory postsynaptic currents to the same level seen in control rats. Furthermore, microinjection of DCG-IV into the PVN significantly reduced blood pressure and sympathetic nerve activity in SHRs. Our findings provide new information that presynaptic group II metabotropic glutamate receptor activity at the glutamatergic terminals increases in the PVN in SHRs. Activation of group II metabotropic glutamate receptors in the PVN inhibits sympathetic vasomotor tone through attenuation of increased glutamatergic input and neuronal hyperactivity in SHRs.

M2 and M3 muscarinic receptors are involved in enteric nerve-mediated contraction of the mouse ileum: Findings obtained with muscarinic-receptor knockout mouse.

PubMed

Takeuchi, Tadayoshi; Tanaka, Keisuke; Nakajima, Hidemitsu; Matsui, Minoru; Azuma, Yasu-Taka

2007-01-01

The involvement of muscarinic receptors in neurogenic responses of the ileum was studied in wild-type and muscarinic-receptor (M-receptor) knockout (KO) mice. Electrical field stimulation to the wild-type mouse ileum induced a biphasic response, a phasic and sustained contraction that was abolished by tetrodotoxin. The sustained contraction was prolonged for an extended period after the termination of electrical field stimulation. The phasic contraction was completely inhibited by atropine. In contrast, the sustained contraction was enhanced by atropine. Ileal strips prepared from M2-receptor KO mice exhibited a phasic contraction similar to that seen in wild-type mice and a sustained contraction that was larger than that in wild-type mice. In M3-receptor KO mice, the phasic contraction was smaller than that observed in wild-type mice. Acetylcholine exogenously administrated induced concentration-dependent contractions in strips isolated from wild-type, M2- and M3-receptor KO mice. However, contractions in M3-receptor KO mice shifted to the right. The sustained contraction was inhibited by capsaicin and neurokinin NK2 receptor antagonist, suggesting that it is mediated by substance P (SP). SP-induced contraction of M2-receptor KO mice did not differ from that of wild-type mice. SP immunoreactivity was located in enteric neurons, colocalized with M2 receptor immunoreactivity. These results suggest that atropine-sensitive phasic contraction is mainly mediated via the M3 receptor, and SP-mediated sustained contraction is negatively regulated by the M2 receptor at a presynaptic level.

Activation of postsynaptic GABAB receptors modulates the bursting pattern and synaptic activity of olfactory bulb juxtaglomerular neurons.

PubMed

Karpuk, Nikolay; Hayar, Abdallah

2008-01-01

Olfactory bulb glomeruli are formed by a network of three major types of neurons collectively called juxtaglomerular (JG) cells, which include external tufted (ET), periglomerular (PG), and short axon (SA) cells. There is solid evidence that gamma-aminobutyric acid (GABA) released from PG neurons presynaptically inhibits glutamate release from olfactory nerve terminals via activation of GABA(B) receptors (GABA(B)-Rs). However, it is still unclear whether ET cells have GABA(B)-Rs. We have investigated whether ET cells have functional postsynaptic GABA(B)-Rs using extracellular and whole cell recordings in olfactory bulb slices. In the presence of fast synaptic blockers (CNQX, APV, and gabazine), the GABA(B)-R agonist baclofen either completely inhibited the bursting or reduced the bursting frequency and increased the burst duration and the number of spikes/burst in ET cells. In the presence of fast synaptic blockers and tetrodotoxin, baclofen induced an outward current in ET cells, suggesting a direct postsynaptic effect. Baclofen reduced the frequency and amplitude of spontaneous EPSCs in PG and SA cells. In the presence of sodium and potassium channel blockers, baclofen reduced the frequency of miniature EPSCs, which were inhibited by the calcium channel blocker cadmium. All baclofen effects were reversed by application of the GABA(B)-R antagonist CGP55845. We suggest that activation of GABA(B)-Rs directly inhibits ET cell bursting and decreases excitatory dendrodendritic transmission from ET to PG and SA cells. Thus the postsynaptic GABA(B)-Rs on ET cells may play an important role in shaping the activation pattern of the glomeruli during olfactory coding.

Exposure to a high fat diet during the perinatal period alters vagal motoneurone excitability, even in the absence of obesity

PubMed Central

Bhagat, Ruchi; Fortna, Samuel R; Browning, Kirsteen N

2015-01-01

The perinatal period is critically important to the development of autonomic neural circuits responsible for energy homeostasis. Vagal neurocircuits are vital to the regulation of upper gastrointestinal functions, including satiety. Diet-induced obesity modulates the excitability and responsiveness of both peripheral vagal afferents and central vagal efferents but less information is available regarding the effects of diet per se on vagal neurocircuit functions. The aims of this study were to investigate whether perinatal exposure to a high fat diet (HFD) dysregulated dorsal motor nucleus of the vagus (DMV) neurones, prior to the development of obesity. Whole cell patch clamp recordings were made from gastric-projecting DMV neurones in thin brainstem slices from rats that were exposed to either a control diet or HFD from pregnancy day 13. Our data demonstrate that following perinatal HFD: (i) DMV neurones had decreased excitability and input resistance with a reduced ability to fire action potentials; (ii) the proportion of DMV neurones excited by cholecystokinin (CCK) was unaltered but the proportion of neurones in which CCK increased excitatory glutamatergic synaptic inputs was reduced; (iii) the tonic activation of presynaptic group II metabotropic glutamate receptors on inhibitory nerve terminals was attenuated, allowing modulation of GABAergic synaptic transmission; and (iv) the size and dendritic arborization of gastric-projecting DMV neurones was increased. These results suggest that perinatal HFD exposure compromises the excitability and responsiveness of gastric-projecting DMV neurones, even in the absence of obesity, suggesting that attenuation of vago-vagal reflex signalling may precede the development of obesity. PMID:25556801

Differentiation in the angiotensin II receptor 1 blocker class on autonomic function.

PubMed

Krum, H

2001-09-01

Autonomic function is disordered in cardiovascular disease states such as chronic heart failure (CHF) and hypertension. Interactions between the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system (SNS) may potentially occur at a number of sites. These include central sites (eg, rostral ventrolateral medulla), at the level of baroreflex control, and at the sympathetic prejunctional angiotensin II receptor 1 (AT(1)) receptor, which is facilitatory for norepinephrine release from the sympathetic nerve terminal. Therefore, drugs that block the RAAS may be expected to improve autonomic dysfunction in cardiovascular disease states. In order to test the hypothesis that RAAS inhibition directly reduces SNS activity, a pithed rat model of sympathetic stimulation has been established. In this model, an increase in frequency of stimulation results in a pressor response that is sympathetically mediated and highly reproducible. This pressor response is enhanced in the presence of angiotensin II and is reduced in the presence of nonselective AIIRAs that block both AT(1) and AT(2) receptor subtypes (eg, saralasin). AT(1)-selective antagonists have also been studied in this model, at pharmacologically relevant doses. In one such study, only the AT(1) blocker eprosartan reduced sympathetically stimulated increases in blood pressure, whereas comparable doses of losartan, valsartan, and irbesartan did not. The reason(s) for the differences between eprosartan and other agents of this class on sympathetic modulation are not clear, but may relate to the chemical structure of the drug (a non- biphenyl tetrazole structure that is chemically distinct from the structure of other AIIRAs), receptor binding characteristics (competitive), or unique effects on presynaptic AT(1) receptors.

Role of alpha-synuclein in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism in mice.

PubMed

Schlüter, O M; Fornai, F; Alessandrí, M G; Takamori, S; Geppert, M; Jahn, R; Südhof, T C

2003-01-01

In humans, mutations in the alpha-synuclein gene or exposure to the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produce Parkinson's disease with loss of dopaminergic neurons and depletion of nigrostriatal dopamine. alpha-Synuclein is a vertebrate-specific component of presynaptic nerve terminals that may function in modulating synaptic transmission. To test whether MPTP toxicity involves alpha-synuclein, we generated alpha-synuclein-deficient mice by homologous recombination, and analyzed the effect of deleting alpha-synuclein on MPTP toxicity using these knockout mice. In addition, we examined commercially available mice that contain a spontaneous loss of the alpha-synuclein gene. As described previously, deletion of alpha-synuclein had no significant effects on brain structure or composition. In particular, the levels of synaptic proteins were not altered, and the concentrations of dopamine, dopamine metabolites, and dopaminergic proteins were unchanged. Upon acute MPTP challenge, alpha-synuclein knockout mice were partly protected from chronic depletion of nigrostriatal dopamine when compared with littermates of the same genetic background, whereas mice carrying the spontaneous deletion of the alpha-synuclein gene exhibited no protection. Furthermore, alpha-synuclein knockout mice but not the mice with the alpha-synuclein gene deletion were slightly more sensitive to methamphetamine than littermate control mice. These results demonstrate that alpha-synuclein is not obligatorily coupled to MPTP sensitivity, but can influence MPTP toxicity on some genetic backgrounds, and illustrate the need for extensive controls in studies aimed at describing the effects of mouse knockouts on MPTP sensitivity.

Identification of differentiation-associated brain-specific phosphate transporter as a second vesicular glutamate transporter (VGLUT2).

PubMed

Takamori, S; Rhee, J S; Rosenmund, C; Jahn, R

2001-11-15

Glutamate is the major excitatory neurotransmitter in mammalian CNS. In the presynaptic nerve terminal, glutamate is stored in synaptic vesicles and released by exocytosis. Previously, it has been shown that a transport protein originally identified as a brain-specific Na(+)-dependent inorganic phosphate transporter I (BNPI) functions as vesicular glutamate transporter and thus has been renamed VGLUT1. Recently, a protein highly homologous to VGLUT1, "differentiation-associated BNPI" (DNPI), has been discovered. Northern blot and in situ hybridization analyses indicate that DNPI mRNA is expressed in some brain regions in which VGLUT1 mRNA is not expressed. We now show that DNPI functions as vesicular glutamate transporter with properties very similar to VGLUT1 and propose to rename the protein VGLUT2. VGLUT2 is highly enriched in synaptic vesicles. Furthermore, VGLUT2 resides on a vesicle population that is distinct from vesicles containing the vesicular GABA transporter or VGLUT1, showing that the expression of VGLUT1 and VGLUT2 do not overlap. When VGLUT2 was expressed in BON cells, membrane fractions displayed ATP-dependent, carbonyl cyanide p-trifluoromethoxyphenylhydrazone-sensitive glutamate uptake. Overexpression of VGLUT2 in cultured autaptic GABAergic neurons yielded postsynaptic currents that were insensitive to the GABA(A) receptor antagonist bicuculline but blocked by the AMPA-receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfonyl-benzo[F]quinoxaline. Thus, expression of VGLUT2 suffices to cause GABAergic neurons to release glutamate in addition to GABA in a manner very similar to that reported previously for VGLUT1.

Deficient functional recovery after facial nerve crush in rats is associated with restricted rearrangements of synaptic terminals in the facial nucleus.

PubMed

Hundeshagen, G; Szameit, K; Thieme, H; Finkensieper, M; Angelov, D N; Guntinas-Lichius, O; Irintchev, A

2013-09-17

Crush injuries of peripheral nerves typically lead to axonotmesis, axonal damage without disruption of connective tissue sheaths. Generally, human patients and experimental animals recover well after axonotmesis and the favorable outcome has been attributed to precise axonal reinnervation of the original peripheral targets. Here we assessed functionally and morphologically the long-term consequences of facial nerve axonotmesis in rats. Expectedly, we found that 5 months after crush or cryogenic nerve lesion, the numbers of motoneurons with regenerated axons and their projection pattern into the main branches of the facial nerve were similar to those in control animals suggesting precise target reinnervation. Unexpectedly, however, we found that functional recovery, estimated by vibrissal motion analysis, was incomplete at 2 months after injury and did not improve thereafter. The maximum amplitude of whisking remained substantially, by more than 30% lower than control values even 5 months after axonotmesis. Morphological analyses showed that the facial motoneurons ipsilateral to injury were innervated by lower numbers of glutamatergic terminals (-15%) and cholinergic perisomatic boutons (-26%) compared with the contralateral non-injured motoneurons. The structural deficits were correlated with functional performance of individual animals and associated with microgliosis in the facial nucleus but not with polyinnervation of muscle fibers. These results support the idea that restricted CNS plasticity and insufficient afferent inputs to motoneurons may substantially contribute to functional deficits after facial nerve injuries, possibly including pathologic conditions in humans like axonotmesis in idiopathic facial nerve (Bell's) palsy. Copyright © 2013 IBRO. Published by Elsevier Ltd. All rights reserved.

Atropine and Other Anticholinergic Drugs

DTIC Science & Technology

2007-01-01

parasympathetic est concern, along with their chemical names and nerves and muscarinic and nicotinic choliner - two-letter military designations, are tabun (o...that hydrolyzes the cholin - tions, tremor, convulsions, electrical seizures and ergic neurotransmitter acetylcholine (ACh), that loss of respiratory... cholin - depress salivation, bronchial secretions and ergic synaptic nerve terminals, this leads to very sweating, increase heart rate, produce pupilary

Effects of anodal transcranial direct current stimulation over the leg motor area on lumbar spinal network excitability in healthy subjects

PubMed Central

Roche, N; Lackmy, A; Achache, V; Bussel, B; Katz, R

2011-01-01

Abstract In recent years, two techniques have become available for the non-invasive stimulation of human motor cortex: transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS). The effects of TMS and tDCS when applied over motor cortex should be considered with regard not only to cortical circuits but also to spinal motor circuits. The different modes of action and specificity of TMS and tDCS suggest that their effects on spinal network excitability may be different from that in the cortex. Until now, the effects of tDCS on lumbar spinal network excitability have never been studied. In this series of experiments, on healthy subjects, we studied the effects of anodal tDCS over the lower limb motor cortex on (i) reciprocal Ia inhibition projecting from the tibialis anterior muscle (TA) to the soleus (SOL), (ii) presynaptic inhibition of SOL Ia terminals, (iii) homonymous SOL recurrent inhibition, and (iv) SOL H-reflex recruitment curves. The results show that anodal tDCS decreases reciprocal Ia inhibition, increases recurrent inhibition and induces no modification of presynaptic inhibition of SOL Ia terminals and of SOL-H reflex recruitment curves. Our results indicate therefore that the effects of tDCS are the opposite of those previously described for TMS on spinal network excitability. They also indicate that anodal tDCS induces effects on spinal network excitability similar to those observed during co-contraction suggesting that anodal tDCS activates descending corticospinal projections mainly involved in co-contractions. PMID:21502292

Phase Advance of the Light-Dark Cycle Perturbs Diurnal Rhythms of Brain-derived Neurotrophic Factor and Neurotrophin-3 Protein Levels, Which Reduces Synaptophysin-positive Presynaptic Terminals in the Cortex of Juvenile Rats

PubMed Central

Hamatake, Michiko; Miyazaki, Noriko; Sudo, Kaori; Matsuda, Motoko; Sadakata, Tetsushi; Furuya, Asako; Ichisaka, Satoshi; Hata, Yoshio; Nakagawa, Chiaki; Nagata, Koh-ichi; Furuichi, Teiichi; Katoh-Semba, Ritsuko

2011-01-01

In adult rat brains, brain-derived neurotrophic factor (BDNF) rhythmically oscillates according to the light-dark cycle and exhibits unique functions in particular brain regions. However, little is known of this subject in juvenile rats. Here, we examined diurnal variation in BDNF and neurotrophin-3 (NT-3) levels in 14-day-old rats. BDNF levels were high in the dark phase and low in the light phase in a majority of brain regions. In contrast, NT-3 levels demonstrated an inverse phase relationship that was limited to the cerebral neocortex, including the visual cortex, and was most prominent on postnatal day 14. An 8-h phase advance of the light-dark cycle and sleep deprivation induced an increase in BDNF levels and a decrease in NT-3 levels in the neocortex, and the former treatment reduced synaptophysin expression and the numbers of synaptophysin-positive presynaptic terminals in cortical layer IV and caused abnormal BDNF and NT-3 rhythms 1 week after treatment. A similar reduction of synaptophysin expression was observed in the cortices of Bdnf gene-deficient mice and Ca2+-dependent activator protein for secretion 2 gene-deficient mice with abnormal free-running rhythm and autistic-like phenotypes. In the latter mice, no diurnal variation in BDNF levels was observed. These results indicate that regular rhythms of BDNF and NT-3 are essential for correct cortical network formation in juvenile rodents. PMID:21527636

Phase advance of the light-dark cycle perturbs diurnal rhythms of brain-derived neurotrophic factor and neurotrophin-3 protein levels, which reduces synaptophysin-positive presynaptic terminals in the cortex of juvenile rats.

PubMed

Hamatake, Michiko; Miyazaki, Noriko; Sudo, Kaori; Matsuda, Motoko; Sadakata, Tetsushi; Furuya, Asako; Ichisaka, Satoshi; Hata, Yoshio; Nakagawa, Chiaki; Nagata, Koh-ichi; Furuichi, Teiichi; Katoh-Semba, Ritsuko

2011-06-17

In adult rat brains, brain-derived neurotrophic factor (BDNF) rhythmically oscillates according to the light-dark cycle and exhibits unique functions in particular brain regions. However, little is known of this subject in juvenile rats. Here, we examined diurnal variation in BDNF and neurotrophin-3 (NT-3) levels in 14-day-old rats. BDNF levels were high in the dark phase and low in the light phase in a majority of brain regions. In contrast, NT-3 levels demonstrated an inverse phase relationship that was limited to the cerebral neocortex, including the visual cortex, and was most prominent on postnatal day 14. An 8-h phase advance of the light-dark cycle and sleep deprivation induced an increase in BDNF levels and a decrease in NT-3 levels in the neocortex, and the former treatment reduced synaptophysin expression and the numbers of synaptophysin-positive presynaptic terminals in cortical layer IV and caused abnormal BDNF and NT-3 rhythms 1 week after treatment. A similar reduction of synaptophysin expression was observed in the cortices of Bdnf gene-deficient mice and Ca(2+)-dependent activator protein for secretion 2 gene-deficient mice with abnormal free-running rhythm and autistic-like phenotypes. In the latter mice, no diurnal variation in BDNF levels was observed. These results indicate that regular rhythms of BDNF and NT-3 are essential for correct cortical network formation in juvenile rodents.

The translational regulator Cup controls NMJ presynaptic terminal morphology.

PubMed

Menon, Kaushiki P; Carrillo, Robert A; Zinn, Kai

2015-07-01

During oogenesis and early embryonic development in Drosophila, translation of proteins from maternally deposited mRNAs is tightly controlled. We and others have previously shown that translational regulatory proteins that function during oogenesis also have essential roles in the nervous system. Here we examine the role of Cup in neuromuscular system development. Maternal Cup controls translation of localized mRNAs encoding the Oskar and Nanos proteins and binds to the general translation initiation factor eIF4E. In this paper, we show that zygotic Cup protein is localized to presynaptic terminals at larval neuromuscular junctions (NMJs). cup mutant NMJs have strong phenotypes characterized by the presence of small clustered boutons called satellite boutons. They also exhibit an increase in the frequency of spontaneous glutamate release events (mEPSPs). Reduction of eIF4E expression synergizes with partial loss of Cup expression to produce satellite bouton phenotypes. The presence of satellite boutons is often associated with increases in retrograde bone morphogenetic protein (BMP) signaling, and we show that synaptic BMP signaling is elevated in cup mutants. cup genetically interacts with two genes, EndoA and Dap160, that encode proteins involved in endocytosis that are also neuronal modulators of the BMP pathway. Endophilin protein, encoded by the EndoA gene, is downregulated in a cup mutant. Our results are consistent with a model in which Cup and eIF4E work together to ensure efficient localization and translation of endocytosis proteins in motor neurons and control the strength of the retrograde BMP signal. Copyright © 2015 Elsevier Inc. All rights reserved.

The translational regulator Cup controls NMJ presynaptic terminal morphology

PubMed Central

Menon, Kaushiki P.; Carrillo, Robert A.; Zinn, Kai

2015-01-01

During oogenesis and early embryonic development in Drosophila, translation of proteins from maternally deposited mRNAs is tightly controlled. We and others have previously shown that translational regulatory proteins that function during oogenesis also have essential roles in the nervous system. Here we examine the role of Cup in neuromuscular system development. Maternal Cup controls translation of localized mRNAs encoding the Oskar and Nanos proteins and binds to the general translation initiation factor eIF4E. In this paper, we show that zygotic Cup protein is localized to presynaptic terminals at larval neuromuscular junctions (NMJs). cup mutant NMJs have strong phenotypes characterized by the presence of small clustered boutons called satellite boutons. They also exhibit an increase in the frequency of spontaneous glutamate release events (mEPSPs). Reduction of eIF4E expression synergizes with partial loss of Cup expression to produce satellite bouton phenotypes. The presence of satellite boutons is often associated with increases in retrograde bone morphogenetic protein (BMP) signaling, and we show that synaptic BMP signaling is elevated in cup mutants. cup genetically interacts with four genes (EndoA, WASp, Dap160, and Synj) encoding proteins involved in endocytosis that are also neuronal modulators of the BMP pathway. Endophilin protein, encoded by the EndoA gene, is downregulated in a cup mutant. Our results are consistent with a model in which Cup and eIF4E work together to ensure efficient localization and translation of endocytosis proteins in motor neurons and control the strength of the retrograde BMP signal. PMID:26102195

Anatomy and Neurophysiology of Cough

PubMed Central

Canning, Brendan J.; Chang, Anne B.; Bolser, Donald C.; Smith, Jaclyn A.; Mazzone, Stuart B.; Adams, Todd M.; Altman, Kenneth W.; Barker, Alan F.; Birring, Surinder S.; Blackhall, Fiona; Bolser, Donald, C.; Boulet, Louis-Philippe; Braman, Sidney S.; Brightling, Christopher; Callahan-Lyon, Priscilla; Canning, Brendan; Chang, Anne Bernadette; Coeytaux, Remy; Cowley, Terrie; Davenport, Paul; Diekemper, Rebecca L.; Ebihara, Satoru; El Solh, Ali A.; Escalante, Patricio; Feinstein, Anthony; Field, Stephen K.; Fisher, Dina; French, Cynthia T.; Gibson, Peter; Gold, Philip; Grant, Cameron; Harding, Susan M.; Harnden, Anthony; Hill, Adam T.; Irwin, Richard S.; Kahrilas, Peter J.; Keogh, Karina A.; Lane, Andrew P.; Lewis, Sandra Zelman; Lim, Kaiser; Malesker, Mark A.; Mazzone, Peter; Mazzone, Stuart; Molasiotis, Alex; Murad, M. Hassan; Newcombe, Peter; Nguyen, Huong Q.; Oppenheimer, John; Prezant, David; Pringsheim, Tamara; Restrepo, Marcos I.; Rosen, Mark; Rubin, Bruce; Ryu, Jay H.; Smith, Jaclyn; Tarlo, Susan M.; Turner, Ronald B.; Vertigan, Anne; Wang, Gang; Weir, Kelly

2014-01-01

Bronchopulmonary C-fibers and a subset of mechanically sensitive, acid-sensitive myelinated sensory nerves play essential roles in regulating cough. These vagal sensory nerves terminate primarily in the larynx, trachea, carina, and large intrapulmonary bronchi. Other bronchopulmonary sensory nerves, sensory nerves innervating other viscera, as well as somatosensory nerves innervating the chest wall, diaphragm, and abdominal musculature regulate cough patterning and cough sensitivity. The responsiveness and morphology of the airway vagal sensory nerve subtypes and the extrapulmonary sensory nerves that regulate coughing are described. The brainstem and higher brain control systems that process this sensory information are complex, but our current understanding of them is considerable and increasing. The relevance of these neural systems to clinical phenomena, such as urge to cough and psychologic methods for treatment of dystussia, is high, and modern imaging methods have revealed potential neural substrates for some features of cough in the human. PMID:25188530

Nerve Entrapment Syndromes at the Wrist and Elbow by Sonography.

PubMed

Klauser, Andrea S; Buzzegoli, Tommaso; Taljanovic, Mihra S; Strobl, Sylvia; Rauch, Stefan; Teh, James; Wanschitz, Julia; Löscher, Wolfgang; Martinoli, Carlo

2018-07-01

Nerve entrapment syndromes of the upper extremity are associated with structural abnormalities or by an intrinsic abnormality of the nerve. Nerve entrapment syndromes generally have a typical clinical presentation, and findings on physical examination and in conjunction with electrodiagnostic studies imaging is used to evaluate the cause, severity, and etiology of the entrapment. With the development of high-frequency linear array transducers (12-24 MHz), ultrasound (US) is incomparable in terms of spatial resolution to depict morphological aspects and changes in nerves. US can identify the abnormalities causing entrapment, such as fibrous bands, ganglia, anomalous muscles, and osseous deformities, with the advantage of dynamic assessment under active and passive examination. US is a unique diagnostic modality that allows superb visualization of both large and small peripheral terminal nerve branches of the upper extremity and enables the correct diagnosis of various nerve entrapment syndromes. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

Light microscopic image analysis system to quantify immunoreactive terminal area apposed to nerve cells.

PubMed

Wu, L C; D'Amelio, F; Fox, R A; Polyakov, I; Daunton, N G

1997-06-06

The present report describes a desktop computer-based method for the quantitative assessment of the area occupied by immunoreactive terminals in close apposition to nerve cells in relation to the perimeter of the cell soma. This method is based on Fast Fourier Transform (FFT) routines incorporated in NIH-Image public domain software. Pyramidal cells of layer V of the somatosensory cortex outlined by GABA immunolabeled terminals were chosen for our analysis. A Leitz Diaplan light microscope was employed for the visualization of the sections. A Sierra Scientific Model 4030 CCD camera was used to capture the images into a Macintosh Centris 650 computer. After preprocessing, filtering was performed on the power spectrum in the frequency domain produced by the FFT operation. An inverse FFT with filter procedure was employed to restore the images to the spatial domain. Pasting of the original image to the transformed one using a Boolean logic operation called 'AND'ing produced an image with the terminals enhanced. This procedure allowed the creation of a binary image using a well-defined threshold of 128. Thus, the terminal area appears in black against a white background. This methodology provides an objective means of measurement of area by counting the total number of pixels occupied by immunoreactive terminals in light microscopic sections in which the difficulties of labeling intensity, size, shape and numerical density of terminals are avoided.

Light microscopic image analysis system to quantify immunoreactive terminal area apposed to nerve cells

NASA Technical Reports Server (NTRS)

Wu, L. C.; D'Amelio, F.; Fox, R. A.; Polyakov, I.; Daunton, N. G.

1997-01-01

The present report describes a desktop computer-based method for the quantitative assessment of the area occupied by immunoreactive terminals in close apposition to nerve cells in relation to the perimeter of the cell soma. This method is based on Fast Fourier Transform (FFT) routines incorporated in NIH-Image public domain software. Pyramidal cells of layer V of the somatosensory cortex outlined by GABA immunolabeled terminals were chosen for our analysis. A Leitz Diaplan light microscope was employed for the visualization of the sections. A Sierra Scientific Model 4030 CCD camera was used to capture the images into a Macintosh Centris 650 computer. After preprocessing, filtering was performed on the power spectrum in the frequency domain produced by the FFT operation. An inverse FFT with filter procedure was employed to restore the images to the spatial domain. Pasting of the original image to the transformed one using a Boolean logic operation called 'AND'ing produced an image with the terminals enhanced. This procedure allowed the creation of a binary image using a well-defined threshold of 128. Thus, the terminal area appears in black against a white background. This methodology provides an objective means of measurement of area by counting the total number of pixels occupied by immunoreactive terminals in light microscopic sections in which the difficulties of labeling intensity, size, shape and numerical density of terminals are avoided.

Active zone protein Bassoon co-localizes with presynaptic calcium channel, modifies channel function, and recovers from aging related loss by exercise.

PubMed

Nishimune, Hiroshi; Numata, Tomohiro; Chen, Jie; Aoki, Yudai; Wang, Yonghong; Starr, Miranda P; Mori, Yasuo; Stanford, John A

2012-01-01

The P/Q-type voltage-dependent calcium channels (VDCCs) are essential for synaptic transmission at adult mammalian neuromuscular junctions (NMJs); however, the subsynaptic location of VDCCs relative to active zones in rodent NMJs, and the functional modification of VDCCs by the interaction with active zone protein Bassoon remain unknown. Here, we show that P/Q-type VDCCs distribute in a punctate pattern within the NMJ presynaptic terminals and align in three dimensions with Bassoon. This distribution pattern of P/Q-type VDCCs and Bassoon in NMJs is consistent with our previous study demonstrating the binding of VDCCs and Bassoon. In addition, we now show that the interaction between P/Q-type VDCCs and Bassoon significantly suppressed the inactivation property of P/Q-type VDCCs, suggesting that the Ca(2+) influx may be augmented by Bassoon for efficient synaptic transmission at NMJs. However, presynaptic Bassoon level was significantly attenuated in aged rat NMJs, which suggests an attenuation of VDCC function due to a lack of this interaction between VDCC and Bassoon. Importantly, the decreased Bassoon level in aged NMJs was ameliorated by isometric strength training of muscles for two months. The training increased Bassoon immunoreactivity in NMJs without affecting synapse size. These results demonstrated that the P/Q-type VDCCs preferentially accumulate at NMJ active zones and play essential role in synaptic transmission in conjunction with the active zone protein Bassoon. This molecular mechanism becomes impaired by aging, which suggests altered synaptic function in aged NMJs. However, Bassoon level in aged NMJs can be improved by muscle exercise.

Structural evidence that botulinum toxin blocks neuromuscular transmission by impairing the calcium influx that normally accompanies nerve depolarization

PubMed Central

1981-01-01

Taking advantage of the fact that nerve terminal mitochondria swell and sequester calcium during repetitive nerve stimulation, we here confirm that this change is caused by calcium influx into the nerve and use this fact to show that botulinum toxin abolishes such calcium influx. The optimal paradigm for producing the mitochondrial changes in normal nerves worked out to be 5 min of stimulation at 25 Hz in frog Ringer's solution containing five time more calcium than normal. Applying this same stimulation paradigm to botulinum-intoxicated nerves produced no mitochondrial changes at all. Only when intoxicated nerves were stimulated in 4-aminopyridine (which grossly exaggerates calcium currents in normal nerves) or when they were soaked in black widow spider venom (which is a nerve-specific calcium ionophore) could nerve mitochondria be induced to swell and accumulate calcium. These results indicate that nerve mitochondria are not damaged directly by the toxin and point instead to a primary inhibition of the normal depolarization- evoked calcium currents that accompany nerve activity. Because these currents normally provide the calcium that triggers transmitter secretion from the nerve, this demonstration of their inhibition helps to explain how botulinum toxin paralyzes. PMID:6259176

Handlebar palsy--a compression syndrome of the deep terminal (motor) branch of the ulnar nerve in biking.

PubMed

Capitani, Daniel; Beer, Serafin

2002-10-01

We describe 3 patients who developed a severe palsy of the intrinsic ulnar supplied hand muscles after bicycle riding. Clinically and electrophysiologically all showed an isolated lesion of the deep terminal motor branch of the ulnar nerve leaving the hypothenar muscle and the distal sensory branch intact. This type of lesion at the canal of Guyon is quite unusual, caused in the majority of cases by chronic external pressure over the ulnar palm. In earlier reports describing this lesion in bicycle riders, most patients experienced this lesion after a long distance ride. Due to the change of riding position and shape of handlebars (horn handle) in recent years, however, even a single bicycle ride may be sufficient to cause a lesion of this ulnar branch. Especially in downhill riding, a large part of the body weight is supported by the hand on the corner of the handlebar leading to a high load at Guyon's canal. As no sensory fibres are affected, the patients are not aware of the ongoing nerve compression until a severe lesion develops. Individual adaptation of the handlebar and riding position seems to be crucial for prevention of this type of nerve lesion.

Effect of endogenous tachykinins on neuro-effector transmission of vagal nerve in guinea-pig tracheal tissue.

PubMed

Aizawa, H; Miyazaki, N; Inoue, H; Ikeda, T; Shigematsu, N

1990-01-01

To elucidate the effect of endogenous tachykinins on neuro-effector transmission of vagal nerves, we performed in vitro experiments using guinea-pig tracheal smooth muscle. The subthreshold dose (the highest dose which did not induce any smooth muscle contraction) of capsaicin (10(-8) to 10(-7) M) increased the amplitudes of contractions evoked by electrical field stimulation (EFS) significantly, but not those by acetylcholine (ACh). The inhibitor of neutral endopeptidase, phosphoramidon (10(-7) to 10(-6) M), increased the contractions evoked by EFS significantly. The inhibitor of cholinesterase, physostigmine (10(-6) to 10(-5) M), induced smooth muscle contractions, but such contractions were inhibited by atropine, suggesting the spontaneous release of ACh from the vagal nerve terminals. The subthreshold dose of substance P or capsaicin increased the contractions evoked by physostigmine. These results indicated that endogenous tachykinins increase the spontaneous ACh release as well as the ACh release in response to vagal stimulation from the nerve terminals. Furthermore, it is suggested that the excitatory effects of the tachykinins on the vagal neuro-effector transmission may be modulated by neutral endopeptidase in the guinea pig.

A comparison of epithalamic, hypothalamic and spinal neurosecretory terminals.

PubMed

Vigh-Teichmann, I; Vigh, B

1979-01-01

Nerve endings of epithalamic, hypothalamic and spinal neurosecretory areas were studied by light and electron microscopy in various vertebrates (from fishes up to mammals) including the lancelet. Areas investigated were the pineal organ, the pulvinar corporis pinealis, the neurohypophysis, the median eminence, the urophysis, the terminal filum and the medullo-spinal neurosecretory zones. We found that in all these areas the neurosecretory endings have common structures, which we call synaptic hemidesmosomes or neurohormonal terminals. These are characterized by accumulation of vesicles, and dense projections in a terminal on the basal lamina of the surface of the nervous tissue. A critical review of the literature suggests that a considerble neuroendocrine activity is associated with synaptic hemidesmosomes as special neurohormonal effector structures of the nerve cells. The cell-to-cell synapses formed by neurosecretory cells are discussed in connection with the dual capacity of these cells to function as both endocrine and "ordinary# neuronal elements. The importance of the external cerebrospinal fluid (CSF) space for the transport of materials released in the so-called neurohemal areas, is stressed.

Selective Deletion of Sodium Salt Taste during Development Leads to Expanded Terminal Fields of Gustatory Nerves in the Adult Mouse Nucleus of the Solitary Tract.

PubMed

Sun, Chengsan; Hummler, Edith; Hill, David L

2017-01-18

Neuronal activity plays a key role in the development of sensory circuits in the mammalian brain. In the gustatory system, experimental manipulations now exist, through genetic manipulations of specific taste transduction processes, to examine how specific taste qualities (i.e., basic tastes) impact the functional and structural development of gustatory circuits. Here, we used a mouse knock-out model in which the transduction component used to discriminate sodium salts from other taste stimuli was deleted in taste bud cells throughout development. We used this model to test the hypothesis that the lack of activity elicited by sodium salt taste impacts the terminal field organization of nerves that carry taste information from taste buds to the nucleus of the solitary tract (NST) in the medulla. The glossopharyngeal, chorda tympani, and greater superficial petrosal nerves were labeled to examine their terminal fields in adult control mice and in adult mice in which the α-subunit of the epithelial sodium channel was conditionally deleted in taste buds (αENaC knockout). The terminal fields of all three nerves in the NST were up to 2.7 times greater in αENaC knock-out mice compared with the respective field volumes in control mice. The shapes of the fields were similar between the two groups; however, the density and spread of labels were greater in αENaC knock-out mice. Overall, our results show that disruption of the afferent taste signal to sodium salts disrupts the normal age-dependent "pruning" of all terminal fields, which could lead to alterations in sensory coding and taste-related behaviors. Neural activity plays a major role in the development of sensory circuits in the mammalian brain. To date, there has been no direct test of whether taste-elicited neural activity has a role in shaping central gustatory circuits. However, recently developed genetic tools now allow an assessment of how specific taste stimuli, in this case sodium salt taste, play a role in the maturation of the terminal fields in the mouse brainstem. We found that the specific deletion of sodium salt taste during development produced terminal fields in adults that were dramatically larger than in control mice, demonstrating for the first time that sodium salt taste-elicited activity is necessary for the normal maturation of gustatory inputs into the brain. Copyright © 2017 the authors 0270-6474/17/370660-13$15.00/0.

Selective Deletion of Sodium Salt Taste during Development Leads to Expanded Terminal Fields of Gustatory Nerves in the Adult Mouse Nucleus of the Solitary Tract

PubMed Central

Sun, Chengsan; Hummler, Edith

2017-01-01

Neuronal activity plays a key role in the development of sensory circuits in the mammalian brain. In the gustatory system, experimental manipulations now exist, through genetic manipulations of specific taste transduction processes, to examine how specific taste qualities (i.e., basic tastes) impact the functional and structural development of gustatory circuits. Here, we used a mouse knock-out model in which the transduction component used to discriminate sodium salts from other taste stimuli was deleted in taste bud cells throughout development. We used this model to test the hypothesis that the lack of activity elicited by sodium salt taste impacts the terminal field organization of nerves that carry taste information from taste buds to the nucleus of the solitary tract (NST) in the medulla. The glossopharyngeal, chorda tympani, and greater superficial petrosal nerves were labeled to examine their terminal fields in adult control mice and in adult mice in which the α-subunit of the epithelial sodium channel was conditionally deleted in taste buds (αENaC knockout). The terminal fields of all three nerves in the NST were up to 2.7 times greater in αENaC knock-out mice compared with the respective field volumes in control mice. The shapes of the fields were similar between the two groups; however, the density and spread of labels were greater in αENaC knock-out mice. Overall, our results show that disruption of the afferent taste signal to sodium salts disrupts the normal age-dependent “pruning” of all terminal fields, which could lead to alterations in sensory coding and taste-related behaviors. SIGNIFICANCE STATEMENT Neural activity plays a major role in the development of sensory circuits in the mammalian brain. To date, there has been no direct test of whether taste-elicited neural activity has a role in shaping central gustatory circuits. However, recently developed genetic tools now allow an assessment of how specific taste stimuli, in this case sodium salt taste, play a role in the maturation of the terminal fields in the mouse brainstem. We found that the specific deletion of sodium salt taste during development produced terminal fields in adults that were dramatically larger than in control mice, demonstrating for the first time that sodium salt taste-elicited activity is necessary for the normal maturation of gustatory inputs into the brain. PMID:28100747

Inorganic proton conducting electrolyte coupled oxide-based dendritic transistors for synaptic electronics.

PubMed

Wan, Chang Jin; Zhu, Li Qiang; Zhou, Ju Mei; Shi, Yi; Wan, Qing

2014-05-07

Ionic/electronic hybrid devices with synaptic functions are considered to be the essential building blocks for neuromorphic systems and brain-inspired computing. Here, artificial synapses based on indium-zinc-oxide (IZO) transistors gated by nanogranular SiO2 proton-conducting electrolyte films are fabricated on glass substrates. Spike-timing dependent plasticity and paired-pulse facilitation are successfully mimicked in an individual bottom-gate transistor. Most importantly, dynamic logic and dendritic integration established by spatiotemporally correlated spikes are also mimicked in dendritic transistors with two in-plane gates as the presynaptic input terminals.

The Synaptic Function of α-Synuclein

PubMed Central

Burré, Jacqueline

2015-01-01

α-Synuclein is an abundant neuronal protein which localizes predominantly to presynaptic terminals, and is strongly linked genetically and pathologically to Parkinson’s disease and other neurodegenerative diseases. While the accumulation of α-synuclein in the form of misfolded oligomers and large aggregates defines multiple neurodegenerative diseases called “synucleinopathies”, its cellular function has remained largely unclear, and is the subject of intense investigation. In this review, I focus on the structural characteristics of α-synuclein, its cellular and subcellular localization, and discuss how this relates to its function in neurons, in particular at the neuronal synapse. PMID:26407041

RIC-7 Promotes Neuropeptide Secretion

PubMed Central

Hao, Yingsong; Hu, Zhitao; Sieburth, Derek; Kaplan, Joshua M.

2012-01-01

Secretion of neurotransmitters and neuropeptides is mediated by exocytosis of distinct secretory organelles, synaptic vesicles (SVs) and dense core vesicles (DCVs) respectively. Relatively little is known about factors that differentially regulate SV and DCV secretion. Here we identify a novel protein RIC-7 that is required for neuropeptide secretion in Caenorhabditis elegans. The RIC-7 protein is expressed in all neurons and is localized to presynaptic terminals. Imaging, electrophysiology, and behavioral analysis of ric-7 mutants indicates that acetylcholine release occurs normally, while neuropeptide release is significantly decreased. These results suggest that RIC-7 promotes DCV–mediated secretion. PMID:22275875

Co-administration of betulinic acid and methamphetamine causes toxicity to dopaminergic and serotonergic nerve terminals in the striatum of late adolescent rats

PubMed Central

Killinger, Bryan; Shah, Mrudang; Moszczynska, Anna

2013-01-01

Psychostimulant methamphetamine (METH) is toxic to dopaminergic and serotonergic striatal nerve terminals in adult, but not in adolescent, brain. Betulinic acid (BA) and its derivatives are promising anti-HIV agents with some toxic properties. Many METH users, particularly young men, are HIV-positive; therefore, they might be treated with BA or its derivative for HIV infection. It is not known whether BA, or any of its derivatives, is neurotoxic in combination with METH in adolescent brain. The present study investigated the effects of BA and binge METH in the striatum in late adolescent rats. BA or METH alone did not decrease the levels of dopaminergic or serotonergic markers in the striatum whereas BA and METH together decreased these markers in a BA dose-dependent manner. BA and METH combination also caused decreases in the levels of mitochondrial complex I in the same manner; BA alone only slightly decreased the levels of the enzyme in striatal synaptosomes. BA or METH alone increased cytochrome c. METH alone decreased parkin, increased complex II and striatal BA levels. These results suggest that METH in combination with BA can be neurotoxic to dopaminergic and serotonergic striatal nerve terminals in late adolescent brain via mitochondrial dysfunction and parkin deficit. PMID:24151877

Effect of peripheral nerve injury on receptive fields of cells in the cat spinal cord.

PubMed

Devor, M; Wall, P D

1981-06-20

When the sciatic and saphenous nerves are cut and ligated in adult cats, the immediate effect is the production of a completely anesthetic foot and a region in medial lumbar dorsal horn where almost all cells have lost their natural receptive fields (RFs). Beginning at about 1 week and maturing by 4 weeks, some 40% of cells in the medial dorsal horn gain a novel RF on proximal skin, that is, upper and lower leg, thigh, lower back, or perineum. This new RF is supplied by intact proximal nerves and not by sciatic and saphenous nerve fibers that sprouted in the periphery. During the period of switching of RFs from distal to proximal skin there was no gross atrophy of dorsal horn grey matter and no Fink-Heimer stainable degeneration of central arbors and terminals of peripherally axotomized afferents. In intact animals medial dorsal horn cells showed no sign of response to mechanical stimulation of proximal skin. RFs of some of the cells had spontaneous variations in size and sensitivity, but these were not nearly sufficient to explain the large shifts observed after chronic nerve section. Tetanic electrical stimulation of skin or peripheral nerves often caused RFs to shrink, but never to expand. Although natural stimuli of proximal skin would not excite medial dorsal horn cells in intact or acutely deafferented animals, it was found that electrical stimulation of proximal nerves did excite many of these cells, often at short latencies. In the discussion we justify our working hypothesis that the appearance of novel RFs is due to the strengthening or unmasking of normally present but ineffective afferent terminals, rather than to long-distance sprouting of new afferent arbors within the spinal cord.

Intralaryngeal neuroanatomy of the recurrent laryngeal nerve of the rabbit

PubMed Central

Ryan, Stephen; McNicholas, Walter T; O'Regan, Ronan G; Nolan, Philip

2003-01-01

We undertook this study to determine the detailed neuroanatomy of the terminal branches of the recurrent laryngeal nerve (RLN) in the rabbit to facilitate future neurophysiological recordings from identified branches of this nerve. The whole larynx was isolated post mortem in 17 adult New Zealand White rabbits and prepared using a modified Sihler's technique, which stains axons and renders other tissues transparent so that nerve branches can be seen in whole mount preparations. Of the 34 hemi-laryngeal preparations processed, 28 stained well and these were dissected and used to characterize the neuroanatomy of the RLN. In most cases (23/28) the posterior cricoarytenoid muscle (PCA) was supplied by a single branch arising from the RLN, though in five PCA specimens there were two or three separate branches to the PCA. The interarytenoid muscle (IA) was supplied by two parallel filaments arising from the main trunk of the RLN rostral to the branch(es) to the PCA. The lateral cricoarytenoid muscle (LCA) commonly received innervation from two fine twigs branching from the RLN main trunk and travelling laterally towards the LCA. The remaining fibres of the RLN innervated the thyroarytenoid muscle (TA) and comprised two distinct branches, one supplying the pars vocalis and the other branching extensively to supply the remainder of the TA. No communicating anastomosis between the RLN and superior laryngeal nerve within the larynx was found. Our results suggest it is feasible to make electrophysiological recordings from identified terminal branches of the RLN supplying laryngeal adductor muscles separate from the branch or branches to the PCA. However, the very small size of the motor nerves to the IA and LCA suggests that it would be very difficult to record selectively from the nerve supply to individual laryngeal adductor muscles. PMID:12739619

The Effects of Renal Denervation on Renal Hemodynamics and Renal Vasculature in a Porcine Model

PubMed Central

Verloop, Willemien L.; Hubens, Lisette E. G.; Spiering, Wilko; Doevendans, Pieter A.; Goldschmeding, Roel; Bleys, Ronald L. A. W.; Voskuil, Michiel

2015-01-01

Rationale Recently, the efficacy of renal denervation (RDN) has been debated. It is discussed whether RDN is able to adequately target the renal nerves. Objective We aimed to investigate how effective RDN was by means of functional hemodynamic measurements and nerve damage on histology. Methods and Results We performed hemodynamic measurements in both renal arteries of healthy pigs using a Doppler flow and pressure wire. Subsequently unilateral denervation was performed, followed by repeated bilateral hemodynamic measurements. Pigs were terminated directly after RDN or were followed for 3 weeks or 3 months after the procedure. After termination, both treated and control arteries were prepared for histology to evaluate vascular damage and nerve damage. Directly after RDN, resting renal blood flow tended to increase by 29±67% (P = 0.01). In contrast, renal resistance reserve increased from 1.74 (1.28) to 1.88 (1.17) (P = 0.02) during follow-up. Vascular histopathology showed that most nerves around the treated arteries were located outside the lesion areas (8±7 out of 55±25 (14%) nerves per pig were observed within a lesion area). Subsequently, a correlation was noted between a more impaired adventitia and a reduction in renal resistance reserve (β: -0.33; P = 0.05) at three weeks of follow-up. Conclusion Only a small minority of renal nerves was targeted after RDN. Furthermore, more severe adventitial damage was related to a reduction in renal resistance in the treated arteries at follow-up. These hemodynamic and histological observations may indicate that RDN did not sufficiently target the renal nerves. Potentially, this may explain the significant spread in the response after RDN. PMID:26587981

Altered vesicular glutamate transporter distributions in the mouse cochlear nucleus following cochlear insult

PubMed Central

Heeringa, Amarins N.; Stefanescu, Roxana A.; Raphael, Yehoash; Shore, Susan E.

2015-01-01

Vesicular glutamate transporters 1 and 2 (VGLUT1 and VGLUT2) have distinct distributions in the cochlear nucleus that correspond to the sources of the labeled terminals. VGLUT1 is mainly associated with terminals of auditory nerve fibers, whereas VGLUT2 is mainly associated with glutamatergic terminals deriving from other sources that project to the cochlear nucleus (CN), including somatosensory and vestibular terminals. Previous studies in guinea pig have shown that cochlear damage results in a decrease of VGLUT1-labeled puncta and an increase in VGLUT2-labeled puncta. This indicates cross-modal compensation that is of potential importance in somatic tinnitus. To examine whether this effect is consistent across species and to provide a background for future studies, using transgenesis, the current study examines VGLUT expression profiles upon cochlear insult by intracochlear kanamycin injections in the mouse. Intracochlear kanamycin injections abolished ipsilateral ABR responses in all animals and reduced ipsilateral spiral ganglion neuron densities in animals that were sacrificed after four weeks, but not in animals that were sacrificed after three weeks. In all unilaterally deafened animals, VGLUT1 density was decreased in CN regions that receive auditory nerve fiber terminals, i.e. in the deep layer of the dorsal cochlear nucleus (DCN), in the interstitial region where the auditory nerve enters the CN, and in the magnocellular region of the antero- and posteroventral CN. In contrast, density of VGLUT2 expression was upregulated in the fusiform cell layer of the DCN and in the granule cell lamina, which are known to receive somatosensory and vestibular terminals. These results show that a cochlear insult induces cross-modal compensation in the cochlear nucleus of the mouse, confirming previous findings in guinea pig, and that these changes are not dependent on the occurrence of spiral ganglion neuron degeneration. PMID:26705736

Altered vesicular glutamate transporter distributions in the mouse cochlear nucleus following cochlear insult.

PubMed

Heeringa, A N; Stefanescu, R A; Raphael, Y; Shore, S E

2016-02-19

Vesicular glutamate transporters 1 and 2 (VGLUT1 and VGLUT2) have distinct distributions in the cochlear nucleus that correspond to sources of the labeled terminals. VGLUT1 is mainly associated with terminals of auditory nerve fibers, whereas VGLUT2 is mainly associated with glutamatergic terminals deriving from other sources that project to the cochlear nucleus (CN), including somatosensory and vestibular terminals. Previous studies in guinea pig have shown that cochlear damage results in a decrease of VGLUT1-labeled puncta and an increase in VGLUT2-labeled puncta. This indicates cross-modal compensation that is of potential importance in somatic tinnitus. To examine whether this effect is consistent across species and to provide a background for future studies, using transgenesis, the current study examines VGLUT expression profiles upon cochlear insult by intracochlear kanamycin injections in the mouse. Intracochlear kanamycin injections abolished ipsilateral ABR responses in all animals and reduced ipsilateral spiral ganglion neuron densities in animals that were sacrificed after four weeks, but not in animals that were sacrificed after three weeks. In all unilaterally deafened animals, VGLUT1 density was decreased in CN regions that receive auditory nerve fiber terminals, i.e., in the deep layer of the dorsal cochlear nucleus (DCN), in the interstitial region where the auditory nerve enters the CN, and in the magnocellular region of the antero- and posteroventral CN. In contrast, density of VGLUT2 expression was upregulated in the fusiform cell layer of the DCN and in the granule cell lamina, which are known to receive somatosensory and vestibular terminals. These results show that a cochlear insult induces cross-modal compensation in the cochlear nucleus of the mouse, confirming previous findings in guinea pig, and that these changes are not dependent on the occurrence of spiral ganglion neuron degeneration. Copyright © 2015 IBRO. Published by Elsevier Ltd. All rights reserved.

Communication networks in the brain: neurons, receptors, neurotransmitters, and alcohol.

PubMed

Lovinger, David M

2008-01-01

Nerve cells (i.e., neurons) communicate via a combination of electrical and chemical signals. Within the neuron, electrical signals driven by charged particles allow rapid conduction from one end of the cell to the other. Communication between neurons occurs at tiny gaps called synapses, where specialized parts of the two cells (i.e., the presynaptic and postsynaptic neurons) come within nanometers of one another to allow for chemical transmission. The presynaptic neuron releases a chemical (i.e., a neurotransmitter) that is received by the postsynaptic neuron's specialized proteins called neurotransmitter receptors. The neurotransmitter molecules bind to the receptor proteins and alter postsynaptic neuronal function. Two types of neurotransmitter receptors exist-ligand-gated ion channels, which permit rapid ion flow directly across the outer cell membrane, and G-protein-coupled receptors, which set into motion chemical signaling events within the cell. Hundreds of molecules are known to act as neurotransmitters in the brain. Neuronal development and function also are affected by peptides known as neurotrophins and by steroid hormones. This article reviews the chemical nature, neuronal actions, receptor subtypes, and therapeutic roles of several transmitters, neurotrophins, and hormones. It focuses on neurotransmitters with important roles in acute and chronic alcohol effects on the brain, such as those that contribute to intoxication, tolerance, dependence, and neurotoxicity, as well as maintained alcohol drinking and addiction.

Structure-Function Relationship of Transporters in the Glutamate-Glutamine Cycle of the Central Nervous System.

PubMed

Hayashi, Mariko Kato

2018-04-12

Many kinds of transporters contribute to glutamatergic excitatory synaptic transmission. Glutamate is loaded into synaptic vesicles by vesicular glutamate transporters to be released from presynaptic terminals. After synaptic vesicle release, glutamate is taken up by neurons or astrocytes to terminate the signal and to prepare for the next signal. Glutamate transporters on the plasma membrane are responsible for transporting glutamate from extracellular fluid to cytoplasm. Glutamate taken up by astrocyte is converted to glutamine by glutamine synthetase and transported back to neurons through glutamine transporters on the plasma membranes of the astrocytes and then on neurons. Glutamine is converted back to glutamate by glutaminase in the neuronal cytoplasm and then loaded into synaptic vesicles again. Here, the structures of glutamate transporters and glutamine transporters, their conformational changes, and how they use electrochemical gradients of various ions for substrate transport are summarized. Pharmacological regulations of these transporters are also discussed.

The role of microglia in synaptic stripping and synaptic degeneration: a revised perspective

PubMed Central

Hugh Perry, V; O'Connor, Vincent

2010-01-01

Chronic neurodegenerative diseases of the CNS (central nervous system) are characterized by the loss of neurons. There is, however, growing evidence to show that an early stage of this process involves degeneration of presynaptic terminals prior to the loss of the cell body. Synaptic plasticity in CNS pathology has been associated with microglia and the phenomenon of synaptic stripping. We review here the evidence for the involvement of microglia in synaptic stripping and synapse degeneration and we conclude that this is a case of guilt by association. In disease models of chronic neurodegeneration, there is no evidence that microglia play an active role in either synaptic stripping or synapse degeneration, but the degeneration of the synapse and the envelopment of a degenerating terminal appears to be a neuron autonomous event. We highlight here some of the gaps in our understanding of synapse degeneration in chronic neurodegenerative disease. PMID:20967131