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Sample records for acid ampa receptors

  1. Seizure control by decanoic acid through direct AMPA receptor inhibition.

    PubMed

    Chang, Pishan; Augustin, Katrin; Boddum, Kim; Williams, Sophie; Sun, Min; Terschak, John A; Hardege, Jörg D; Chen, Philip E; Walker, Matthew C; Williams, Robin S B

    2016-02-01

    The medium chain triglyceride ketogenic diet is an established treatment for drug-resistant epilepsy that increases plasma levels of decanoic acid and ketones. Recently, decanoic acid has been shown to provide seizure control in vivo, yet its mechanism of action remains unclear. Here we show that decanoic acid, but not the ketones β-hydroxybutryate or acetone, shows antiseizure activity in two acute ex vivo rat hippocampal slice models of epileptiform activity. To search for a mechanism of decanoic acid, we show it has a strong inhibitory effect on excitatory, but not inhibitory, neurotransmission in hippocampal slices. Using heterologous expression of excitatory ionotropic glutamate receptor AMPA subunits in Xenopus oocytes, we show that this effect is through direct AMPA receptor inhibition, a target shared by a recently introduced epilepsy treatment perampanel. Decanoic acid acts as a non-competitive antagonist at therapeutically relevant concentrations, in a voltage- and subunit-dependent manner, and this is sufficient to explain its antiseizure effects. This inhibitory effect is likely to be caused by binding to sites on the M3 helix of the AMPA-GluA2 transmembrane domain; independent from the binding site of perampanel. Together our results indicate that the direct inhibition of excitatory neurotransmission by decanoic acid in the brain contributes to the anti-convulsant effect of the medium chain triglyceride ketogenic diet. PMID:26608744

  2. Seizure control by decanoic acid through direct AMPA receptor inhibition

    PubMed Central

    Chang, Pishan; Augustin, Katrin; Boddum, Kim; Williams, Sophie; Sun, Min; Terschak, John A.; Hardege, Jörg D.; Chen, Philip E.

    2016-01-01

    See Rogawski (doi:10.1093/awv369) for a scientific commentary on this article.  The medium chain triglyceride ketogenic diet is an established treatment for drug-resistant epilepsy that increases plasma levels of decanoic acid and ketones. Recently, decanoic acid has been shown to provide seizure control in vivo, yet its mechanism of action remains unclear. Here we show that decanoic acid, but not the ketones β-hydroxybutryate or acetone, shows antiseizure activity in two acute ex vivo rat hippocampal slice models of epileptiform activity. To search for a mechanism of decanoic acid, we show it has a strong inhibitory effect on excitatory, but not inhibitory, neurotransmission in hippocampal slices. Using heterologous expression of excitatory ionotropic glutamate receptor AMPA subunits in Xenopus oocytes, we show that this effect is through direct AMPA receptor inhibition, a target shared by a recently introduced epilepsy treatment perampanel. Decanoic acid acts as a non-competitive antagonist at therapeutically relevant concentrations, in a voltage- and subunit-dependent manner, and this is sufficient to explain its antiseizure effects. This inhibitory effect is likely to be caused by binding to sites on the M3 helix of the AMPA-GluA2 transmembrane domain; independent from the binding site of perampanel. Together our results indicate that the direct inhibition of excitatory neurotransmission by decanoic acid in the brain contributes to the anti-convulsant effect of the medium chain triglyceride ketogenic diet. PMID:26608744

  3. Stargazin is an AMPA receptor auxiliary subunit.

    PubMed

    Vandenberghe, Wim; Nicoll, Roger A; Bredt, David S

    2005-01-11

    AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors mediate fast excitatory synaptic transmission in brain and underlie aspects of synaptic plasticity. Numerous AMPA receptor-binding proteins have been implicated in AMPA receptor trafficking and anchoring. However, the relative contributions of these proteins to the composition of native AMPA receptor complexes in brain remain uncertain. Here, we use blue native gel electrophoresis to analyze the composition of native AMPA receptor complexes in cerebellar extracts. We identify two receptor populations: a functional form that contains the transmembrane AMPA receptor-regulatory protein stargazin and an apo-form that lacks stargazin. Limited proteolysis confirms assembly of stargazin with a large proportion of native AMPA receptors. In contrast, other AMPA receptor-interacting proteins, such as synapse-associated protein 97, glutamate receptor-interacting protein 1, protein kinase Calpha binding protein, N-ethylmaleimide-sensitive fusion protein, AP2, and protein 4.1N, do not show significant association with AMPA receptor complexes on native gels. These data identify stargazin as an auxiliary subunit for a neurotransmitter-gated ion channel. PMID:15630087

  4. Discovery of the First α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Antagonist Dependent upon Transmembrane AMPA Receptor Regulatory Protein (TARP) γ-8.

    PubMed

    Gardinier, Kevin M; Gernert, Douglas L; Porter, Warren J; Reel, Jon K; Ornstein, Paul L; Spinazze, Patrick; Stevens, F Craig; Hahn, Patric; Hollinshead, Sean P; Mayhugh, Daniel; Schkeryantz, Jeff; Khilevich, Albert; De Frutos, Oscar; Gleason, Scott D; Kato, Akihiko S; Luffer-Atlas, Debra; Desai, Prashant V; Swanson, Steven; Burris, Kevin D; Ding, Chunjin; Heinz, Beverly A; Need, Anne B; Barth, Vanessa N; Stephenson, Gregory A; Diseroad, Benjamin A; Woods, Tim A; Yu, Hong; Bredt, David; Witkin, Jeffrey M

    2016-05-26

    Transmembrane AMPA receptor regulatory proteins (TARPs) are a family of scaffolding proteins that regulate AMPA receptor trafficking and function. TARP γ-8 is one member of this family and is highly expressed within the hippocampus relative to the cerebellum. A selective TARP γ-8-dependent AMPA receptor antagonist (TDAA) is an innovative approach to modulate AMPA receptors in specific brain regions to potentially increase the therapeutic index relative to known non-TARP-dependent AMPA antagonists. We describe here, for the first time, the discovery of a noncompetitive AMPA receptor antagonist that is dependent on the presence of TARP γ-8. Three major iteration cycles were employed to improve upon potency, CYP1A2-dependent challenges, and in vivo clearance. An optimized molecule, compound (-)-25 (LY3130481), was fully protective against pentylenetetrazole-induced convulsions in rats without the motor impairment associated with non-TARP-dependent AMPA receptor antagonists. Compound (-)-25 could be utilized to provide proof of concept for antiepileptic efficacy with reduced motor side effects in patients. PMID:27067148

  5. Tweaking Subtype Selectivity and Agonist Efficacy at (S)-2-Amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propionic acid (AMPA) Receptors in a Small Series of BnTetAMPA Analogues.

    PubMed

    Wang, Shuang-Yan; Larsen, Younes; Navarrete, Cristina Vara; Jensen, Anders A; Nielsen, Birgitte; Al-Musaed, Ali; Frydenvang, Karla; Kastrup, Jette Sandholm; Pickering, Darryl S; Clausen, Rasmus Prætorius

    2016-03-10

    A series of analogues of the (S)-2-Amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propionic acid (AMPA) receptor agonist BnTetAMPA (5b) were synthesized and characterized pharmacologically in radioligand binding assays at native and cloned AMPA receptors and functionally by two-electrode voltage clamp electrophysiology at the four homomeric AMPA receptors expressed in Xenopus laevis oocytes. The analogues 6 and 7 exhibit very different pharmacological profiles with binding affinity preference for the subtypes GluA1 and GluA3, respectively. X-ray crystal structures of three ligands (6, 7, and 8) in complex with the agonist binding domain (ABD) of GluA2 show that they induce full domain closure despite their low agonist efficacies. Trp767 in GluA2 ABD could be an important determinant for partial agonism of this compound series at AMPA receptors, since agonist efficacy also correlated with the location of the Trp767 side chain. PMID:26862980

  6. AMPA receptor desensitization is the determinant of AMPA receptor mediated excitotoxicity in purified retinal ganglion cells.

    PubMed

    Park, Yong H; Mueller, Brett H; McGrady, Nolan R; Ma, Hai-Ying; Yorio, Thomas

    2015-03-01

    The ionotropic glutamate receptors (iGLuR) have been hypothesized to play a role in neuronal pathogenesis by mediating excitotoxic death. Previous studies on iGluR in the retina have focused on two broad classes of receptors: NMDA and non-NMDA receptors including the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor (AMPAR) and kainate receptor. In this study, we examined the role of receptor desensitization on the specific excitotoxic effects of AMPAR activation on primary retinal ganglion cells (RGCs). Purified rat RGCs were isolated from postnatal day 4-7 Sprague-Dawley rats. Calcium imaging was used to identify the functionality of the AMPARs and selectivity of the s-AMPA agonist. Phosphorylated CREB and ERK1/2 expression were performed following s-AMPA treatment. s-AMPA excitotoxicity was determined by JC-1 mitochondrial membrane depolarization assay, caspase 3/7 luciferase activity assay, immunoblot analysis for α-fodrin, and Live (calcein AM)/Dead (ethidium homodimer-1) assay. RGC cultures of 98% purity, lacking Iba1 and GFAP expression were used for the present studies. Isolated prenatal RGCs expressed calcium permeable AMPAR and s-AMPA (100 μM) treatment of cultured RGCs significantly increased phosphorylation of CREB but not that of ERK1/2. A prolonged (6 h) AMPAR activation in purified RGCs using s-AMPA (100 μM) did not depolarize the RGC mitochondrial membrane potential. In addition, treatment of cultured RGCs with s-AMPA, both in the presence and absence of trophic factors (BDNF and CNTF), did not increase caspase 3/7 activities or the cleavage of α-fodrin (neuronal apoptosis marker), as compared to untreated controls. Lastly, a significant increase in cell survival of RGCs was observed after s-AMPA treatment as compared to control untreated RGCs. However, preventing the desensitization of AMPAR with the treatment with either kainic acid (100 μM) or the combination of s-AMPA and cyclothiazide (50 μM) significantly reduced cell

  7. Posttranslational regulation of AMPA receptor trafficking and function

    PubMed Central

    Lu, Wei; Roche, Katherine W.

    2011-01-01

    In the mammalian central nervous system, the majority of fast excitatory synaptic transmission is mediated by glutamate acting on AMPA-type ionotropic glutamate receptors. The abundance of AMPA receptors at the synapse can be modulated through receptor trafficking, which dynamically regulates many fundamental brain functions, including learning and memory. Reversible posttranslational modifications, including phosphorylation, palmitoylation and ubiquitination of AMPA receptor subunits are important regulatory mechanisms for controlling synaptic AMPA receptor expression and function. In this review, we highlight recent advances in the study of AMPA receptor posttranslational modifications and discuss how these modifications regulate AMPA receptor trafficking and function at synapses. PMID:22000952

  8. AMPA receptors in cerebellar granule cells during development in culture.

    PubMed

    Hack, N J; Sluiter, A A; Balázs, R

    1995-06-27

    The survival and maturation of differentiating cerebellar granule cells in culture are known to be promoted by excitatory amino acids (EAAs) which, however, compromise the survival of mature cells. In contrast to the trophic effect, the toxic effect of alpha-amino-3-hydroxy-5-methyl-4-isoxasolepropiate (AMPA) could only be elicited when the desensitisation of AMPA receptors was blocked, cyclothiazide being used in this study. Nevertheless, even under these conditions, toxicity induced by AMPA in contrast to kainate was, at 9 DIV, only half of the maximal toxicity attained by 13-16 DIV. Since cellular responses to AMPA depend so dramatically on the maturational stage of granule cells, we examined here whether this characteristic is related to developmental changes in AMPA receptor properties, which may result from changes in the subunit composition of the receptor. In contrast to toxicity, AMPA-induced 45Ca2+ influx (determined in the presence of cyclothiazide and the NMDA receptor blocker MK-801) reached a maximum already at 9 DIV. This also applied to a fraction of the 45Ca2+ uptake which persisted either after Cd2+ application or under Na(+)-free conditions and therefore presumably was mediated directly through AMPA receptor channels. Quantitative analysis of Western blots showed that the amounts of GluR4 and to a lesser extent GluR2/3/4c are substantial already at 2 DIV, remaining fairly constant until 9 DIV, followed by an increase by 16 DIV. However GluR1, which is hardly detectable in granule cells in vivo and is also low early in vitro, increased almost linearly with cultivation time.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7554232

  9. Protein tyrosine kinase regulates α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor trafficking induced by acute hypoxia in cultured brainstem neurons.

    PubMed

    Wang, H; Yu, L C; Li, Y C

    2016-01-01

    This study was performed to investigate the modulation effect of protein tyrosine kinase on postsynaptic a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor trafficking induced by acute hypoxia in cultured brainstem neurons. The cultured neurons were exposed to 1% O2 and the expression of AMPA receptor subunit GluR2 on the cell surface was significantly increased, while total GluR2 was not markedly changed. Furthermore, the hypoxia-induced increase in GluR2 expression on the cell surface was partially blocked by the protein tyrosine kinase membrane-permeable inhibitor genistein. In contrast, both the protein tyrosine kinase agonist nerve growth factor and protein tyrosine phosphatase inhibitor vanadate promoted the hypoxia-induced increase of GluR2 expression on cell surface. Moreover, GluR2 could be phosphorylated by tyrosine under normoxia and hypoxia conditions in vitro on brainstem neurons, and tyrosine phosphorylation of GluR2 was significantly stronger under hypoxia conditions. Our results indicate that acute hypoxia induces the AMPA receptor subunit GluR2 to rapidly migrate to the cell membrane to modify the strength of the synapse. This study indicates that tyrosine phosphorylation of the receptor is an important pathway regulating the rapid migration of GluR2 in the postsynaptic domain induced by hypoxia. PMID:27525851

  10. Superactivation of AMPA receptors by auxiliary proteins

    PubMed Central

    Carbone, Anna L.; Plested, Andrew J. R.

    2016-01-01

    Glutamate receptors form complexes in the brain with auxiliary proteins, which control their activity during fast synaptic transmission through a seemingly bewildering array of effects. Here we devise a way to isolate the activation of complexes using polyamines, which enables us to show that transmembrane AMPA receptor regulatory proteins (TARPs) exert their effects principally on the channel opening reaction. A thermodynamic argument suggests that because TARPs promote channel opening, receptor activation promotes AMPAR-TARP complexes into a superactive state with high open probability. A simple model based on this idea predicts all known effects of TARPs on AMPA receptor function. This model also predicts unexpected phenomena including massive potentiation in the absence of desensitization and supramaximal recovery that we subsequently detected in electrophysiological recordings. This transient positive feedback mechanism has implications for information processing in the brain, because it should allow activity-dependent facilitation of excitatory synaptic transmission through a postsynaptic mechanism. PMID:26744192

  11. Are AMPA receptor positive allosteric modulators potential pharmacotherapeutics for addiction?

    PubMed

    Watterson, Lucas R; Olive, M Foster

    2013-01-01

    Positive allosteric modulators (PAMs) of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are a diverse class of compounds that increase fast excitatory transmission in the brain. AMPA PAMs have been shown to facilitate long-term potentiation, strengthen communication between various cortical and subcortical regions, and some of these compounds increase the production and release of brain-derived neurotrophic factor (BDNF) in an activity-dependent manner. Through these mechanisms, AMPA PAMs have shown promise as broad spectrum pharmacotherapeutics in preclinical and clinical studies for various neurodegenerative and psychiatric disorders. In recent years, a small collection of preclinical animal studies has also shown that AMPA PAMs may have potential as pharmacotherapeutic adjuncts to extinction-based or cue-exposure therapies for the treatment of drug addiction. The present paper will review this preclinical literature, discuss novel data collected in our laboratory, and recommend future research directions for the possible development of AMPA PAMs as anti-addiction medications. PMID:24380895

  12. Are AMPA Receptor Positive Allosteric Modulators Potential Pharmacotherapeutics for Addiction?

    PubMed Central

    Watterson, Lucas R.; Olive, M. Foster

    2013-01-01

    Positive allosteric modulators (PAMs) of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are a diverse class of compounds that increase fast excitatory transmission in the brain. AMPA PAMs have been shown to facilitate long-term potentiation, strengthen communication between various cortical and subcortical regions, and some of these compounds increase the production and release of brain-derived neurotrophic factor (BDNF) in an activity-dependent manner. Through these mechanisms, AMPA PAMs have shown promise as broad spectrum pharmacotherapeutics in preclinical and clinical studies for various neurodegenerative and psychiatric disorders. In recent years, a small collection of preclinical animal studies has also shown that AMPA PAMs may have potential as pharmacotherapeutic adjuncts to extinction-based or cue-exposure therapies for the treatment of drug addiction. The present paper will review this preclinical literature, discuss novel data collected in our laboratory, and recommend future research directions for the possible development of AMPA PAMs as anti-addiction medications. PMID:24380895

  13. Perampanel Inhibition of AMPA Receptor Currents in Cultured Hippocampal Neurons

    PubMed Central

    Chen, Chao-Yin; Matt, Lucas; Hell, Johannes Wilhelm; Rogawski, Michael A.

    2014-01-01

    Perampanel is an aryl substituted 2-pyridone AMPA receptor antagonist that was recently approved as a treatment for epilepsy. The drug potently inhibits AMPA receptor responses but the mode of block has not been characterized. Here the action of perampanel on AMPA receptors was investigated by whole-cell voltage-clamp recording in cultured rat hippocampal neurons. Perampanel caused a slow (τ∼1 s at 3 µM), concentration-dependent inhibition of AMPA receptor currents evoked by AMPA and kainate. The rates of block and unblock of AMPA receptor currents were 1.5×105 M−1 s−1 and 0.58 s−1, respectively. Perampanel did not affect NMDA receptor currents. The extent of block of non-desensitizing kainate-evoked currents (IC50, 0.56 µM) was similar at all kainate concentrations (3–100 µM), demonstrating a noncompetitive blocking action. Parampanel did not alter the trajectory of AMPA evoked currents indicating that it does not influence AMPA receptor desensitization. Perampanel is a selective negative allosteric AMPA receptor antagonist of high-affinity and slow blocking kinetics. PMID:25229608

  14. AMPA Receptors as Therapeutic Targets for Neurological Disorders.

    PubMed

    Lee, Kevin; Goodman, Lucy; Fourie, Chantelle; Schenk, Susan; Leitch, Beulah; Montgomery, Johanna M

    2016-01-01

    Almost every neurological disease directly or indirectly affects synapse function in the brain. However, these diseases alter synapses through different mechanisms, ultimately resulting in altered synaptic transmission and/or plasticity. Glutamate is the major neurotransmitter that mediates excitatory synaptic transmission in the brain through activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) receptors. These receptors have therefore been identified as a target for the development of therapeutic treatments for neurological disorders including epilepsy, neurodegenerative diseases, autism, and drug addiction. The fact that AMPA receptors play a dominant role throughout the brain raises the significant challenge of selectively targeting only those regions affected by disease, and clinical trials have raised doubt regarding the feasibility of specifically targeting AMPA receptors for new therapeutic options. Benzamide compounds that act as positive allosteric AMPA receptor modulators, known as AMPAkines, can act on specific brain regions and were initially proposed to revolutionize the treatment of cognitive deficits associated with neurological disorders. Their therapeutic potential has since declined due to inconsistent results in clinical trials. However, recent advances in basic biomedical research are significantly increasing our knowledge of AMPA receptor structure, binding sites, and interactions with auxiliary proteins. In particular, the large complex of postsynaptic proteins that interact with AMPA receptor subunits have been shown to control AMPA receptor insertion, location, pharmacology, synaptic transmission, and plasticity. These proteins are now being considered as alternative therapeutic target sites for modulating AMPA receptors in neurological disorders. PMID:26920691

  15. TARP phosphorylation regulates synaptic AMPA receptors through lipid bilayers

    PubMed Central

    Sumioka, Akio; Yan, Dan; Tomita, Susumu

    2010-01-01

    Summary Neurons use neurotransmitters to communicate across synapses, constructing neural circuits in the brain. AMPA-type glutamate receptors are the predominant excitatory neurotransmitter receptors mediating fast synaptic transmission. AMPA receptors localize at synapses by forming protein complexes with transmembrane AMPA receptor regulatory proteins (TARPs) and PSD-95-like MAGUKs. Among the three classes of ionotropic glutamate receptors (AMPA-, NMDA, kainate-type), AMPA receptor activity is most regulatable by neuronal activity to adjust synaptic strength. Here, we mutated the prototypical TARP, stargazin, and found that TARP phosphorylation regulates synaptic AMPA receptor activity in vivo. We also found that stargazin interacts with negatively-charged lipid bilayers in its phosphorylation dependent manner, and that the lipid interaction inhibited stargazin binding to PSD-95. Cationic lipids dissociated stargazin from lipid bilayers and enhanced synaptic AMPA receptor activity in a stargazin phosphorylation-dependent manner. Thus, TARP phosphorylation plays a critical role in regulating AMPA receptor-mediated synaptic transmission via a lipid bilayer interaction. PMID:20547132

  16. Transferrin Receptor Controls AMPA Receptor Trafficking Efficiency and Synaptic Plasticity

    PubMed Central

    Liu, Ke; Lei, Run; Li, Qiong; Wang, Xin-Xin; Wu, Qian; An, Peng; Zhang, Jianchao; Zhu, Minyan; Xu, Zhiheng; Hong, Yang; Wang, Fudi; Shen, Ying; Li, Hongchang; Li, Huashun

    2016-01-01

    Transferrin receptor (TFR) is an important iron transporter regulating iron homeostasis and has long been used as a marker for clathrin mediated endocytosis. However, little is known about its additional function other than iron transport in the development of central nervous system (CNS). Here we demonstrate that TFR functions as a regulator to control AMPA receptor trafficking efficiency and synaptic plasticity. The conditional knockout (KO) of TFR in neural progenitor cells causes mice to develop progressive epileptic seizure, and dramatically reduces basal synaptic transmission and long-term potentiation (LTP). We further demonstrate that TFR KO remarkably reduces the binding efficiency of GluR2 to AP2 and subsequently decreases AMPA receptor endocytosis and recycling. Thus, our study reveals that TFR functions as a novel regulator to control AMPA trafficking efficiency and synaptic plasticity. PMID:26880306

  17. Dynamic Interaction of Stargazin-like TARPs with Cycling AMPA Receptors at Synapses

    NASA Astrophysics Data System (ADS)

    Tomita, Susumu; Fukata, Masaki; Nicoll, Roger A.; Bredt, David S.

    2004-03-01

    Activity-dependent plasticity in the brain arises in part from changes in the number of synaptic AMPA receptors. Synaptic trafficking of AMPA receptors is controlled by stargazin and homologous transmembrane AMPA receptor regulatory proteins (TARPs). We found that TARPs were stable at the plasma membrane, whereas AMPA receptors were internalized in a glutamate-regulated manner. Interaction with AMPA receptors involved both extra- and intracellular determinants of TARPs. Upon binding to glutamate, AMPA receptors detached from TARPs. This did not require ion flux or intracellular second messengers. This allosteric mechanism for AMPA receptor dissociation from TARPs may participate in glutamate-mediated internalization of receptors in synaptic plasticity.

  18. Assembly of AMPA receptors: mechanisms and regulation

    PubMed Central

    Gan, Quan; Salussolia, Catherine L; Wollmuth, Lonnie P

    2015-01-01

    AMPA receptors (AMPARs) play a critical role in excitatory glutamatergic neurotransmission. The number and subunit composition of AMPARs at synapses determines the dynamics of fast glutamatergic signalling. Functional AMPARs on the cell surface are tetramers. Thus tetrameric assembly of AMPARs represents a promising target for modulating AMPAR-mediated signalling in health and disease. Multiple structural domains within the receptor influence AMPAR assembly. In a proposed model for AMPAR assembly, the amino-terminal domain underlies the formation of a dimer pool. The transmembrane domain facilitates the formation and enhances the stability of the tetramer. The ligand-binding domain influences assembly through a process referred to as ‘domain swapping’. We propose that this core AMPAR assembly process could be regulated by neuronal signals and speculate on possible mechanisms for such regulation. PMID:25556786

  19. [Molecular mechanisms for AMPA receptor trafficking].

    PubMed

    Fukata, Masaki; Fukata, Yuko

    2008-06-01

    Finely tuned synaptic transmission in the brain provides the molecular basis for learning and memory. The misregulation of synaptic transmission is involved in the pathogenesis of various neurological disorders like epilepsy. AMPA-typed glutamate receptors (AMPARs) mediate the most prominent form of excitatory neurotransmission in the brain. Dynamic regulation of AMPARs is thought to be a primary mechanism for controlling synaptic strength. We have analyzed the molecular mechanism for AMPAR-trafficking and function by focusing on PSD-95, a major postsynaptic scaffolding protein. Here, we review the novel regulatory mechanisms of AMPARs by 1) the PSD-95 palmitoylating enzyme, which determines the position of PSD-95 at postsynapses, and 2) the epilepsy related ligand/receptor, LGI1/ADAM22, identified as the PSD-95-interacting protein. PMID:18646599

  20. Clathrin-Independent Trafficking of AMPA Receptors

    PubMed Central

    Tigaret, Cezar M.; Mellor, Jack R.

    2015-01-01

    Membrane trafficking of AMPA receptors (AMPARs) is critical for neuronal function and plasticity. Although rapid forms of AMPAR internalization during long-term depression (LTD) require clathrin and dynamin, the mechanisms governing constitutive AMPAR turnover and internalization of AMPARs during slow homeostatic forms of synaptic plasticity remain unexplored. Here, we show that, in contrast to LTD, constitutive AMPAR internalization and homeostatic AMPAR downscaling in rat neurons do not require dynamin or clathrin function. Instead, constitutive AMPAR trafficking is blocked by a Rac1 inhibitor and is regulated by a dynamic nonstructural pool of F-actin. Our findings reveal a novel role for neuronal clathrin-independent endocytosis controlled by actin dynamics and suggest that the interplay between different modes of receptor endocytosis provides for segregation between distinct modes of neuronal plasticity. PMID:25810514

  1. Calcium permeable AMPA receptors and autoreceptors in external tufted cells of rat olfactory bulb

    PubMed Central

    Ma, Jie; Lowe, Graeme

    2007-01-01

    Glomeruli are functional units of the olfactory bulb responsible for early processing of odor information encoded by single olfactory receptor genes. Glomerular neural circuitry includes numerous external tufted (ET) cells whose rhythmic burst firing may mediate synchronization of bulbar activity with the inhalation cycle. Bursting is entrained by glutamatergic input from olfactory nerve terminals, so specific properties of ionotropic glutamate receptors on ET cells are likely to be important determinants of olfactory processing. Particularly intriguing is recent evidence that α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors of juxta-glomerular neurons may permeate calcium. This could provide a novel pathway for regulating ET cell signaling. We tested the hypothesis that ET cells express functional calcium-permeable AMPA receptors. In rat olfactory bulb slices, excitatory postsynaptic currents (EPSCs) in ET cells were evoked by olfactory nerve shock, and by uncaging glutamate. We found attenuation of AMPA/kainate EPSCs by 1-naphthyl acetyl-spermine (NAS), an open-channel blocker specific for calcium permeable AMPA receptors. Cyclothiazide strongly potentiated EPSCs, indicating a major contribution from AMPA receptors. The current-voltage (I-V) relation of uncaging EPSCs showed weak inward rectification which was lost after > ~ 10 min of whole-cell dialysis, and was absent in NAS. In kainate-stimulated slices, Co2+ ions permeated cells of the glomerular layer. Large AMPA EPSCs were accompanied by fluorescence signals in fluo-4 loaded cells, suggesting calcium permeation. Depolarizing pulses evoked slow tail currents with pharmacology consistent with involvement of calcium permeable AMPA autoreceptors. Tail currents were abolished by Cd2+ and NBQX, and were sensitive to NAS block. Glutamate autoreceptors were confirmed by uncaging intracellular calcium to evoke a large inward current. Our results provide evidence that calcium permeable AMPA

  2. Cytosolic PLA2(alpha) activation in Purkinje neurons and its role in AMPA-receptor trafficking.

    PubMed

    Mashimo, Masato; Hirabayashi, Tetsuya; Murayama, Toshihiko; Shimizu, Takao

    2008-09-15

    Cytosolic phospholipase A(2)alpha (cPLA(2)alpha) selectively releases arachidonic acid from membrane phospholipids and has been proposed to be involved in the induction of long-term depression (LTD), a form of synaptic plasticity in the cerebellum. This enzyme requires two events for its full activation: Ca(2+)-dependent translocation from the cytosol to organelle membranes in order to access phospholipids as substrates, and phosphorylation by several kinases. However, the subcellular distribution and activation of cPLA(2)alpha in Purkinje cells and the role of arachidonic acid in cerebellar LTD have not been fully elucidated. In cultured Purkinje cells, stimulation of AMPA receptors, but not metabotropic glutamate receptors, triggered translocation of cPLA(2)alpha to the somatic and dendritic Golgi compartments. This translocation required Ca(2+) influx through P-type Ca(2+) channels. AMPA plus PMA, a chemical method for inducing LTD, released arachidonic acid via phosphorylation of cPLA(2)alpha. AMPA plus PMA induced a decrease in surface GluR2 for more than 2 hours. Interestingly, this reduction was occluded by a cPLA(2)alpha-specific inhibitor. Furthermore, PMA plus arachidonic acid caused the prolonged internalization of GluR2 without activating AMPA receptors. These results suggest that cPLA(2)alpha regulates the persistent decrease in the expression of AMPA receptors, underscoring the role of cPLA(2)alpha in cerebellar LTD. PMID:18713832

  3. Differential vesicular sorting of AMPA and GABAA receptors

    PubMed Central

    Gu, Yi; Chiu, Shu-Ling; Liu, Bian; Wu, Pei-Hsun; Delannoy, Michael; Lin, Da-Ting; Wirtz, Denis; Huganir, Richard L.

    2016-01-01

    In mature neurons AMPA receptors cluster at excitatory synapses primarily on dendritic spines, whereas GABAA receptors cluster at inhibitory synapses mainly on the soma and dendritic shafts. The molecular mechanisms underlying the precise sorting of these receptors remain unclear. By directly studying the constitutive exocytic vesicles of AMPA and GABAA receptors in vitro and in vivo, we demonstrate that they are initially sorted into different vesicles in the Golgi apparatus and inserted into distinct domains of the plasma membrane. These insertions are dependent on distinct Rab GTPases and SNARE complexes. The insertion of AMPA receptors requires SNAP25–syntaxin1A/B–VAMP2 complexes, whereas insertion of GABAA receptors relies on SNAP23–syntaxin1A/B–VAMP2 complexes. These SNARE complexes affect surface targeting of AMPA or GABAA receptors and synaptic transmission. Our studies reveal vesicular sorting mechanisms controlling the constitutive exocytosis of AMPA and GABAA receptors, which are critical for the regulation of excitatory and inhibitory responses in neurons. PMID:26839408

  4. Cellular Plasticity Induced by Anti–α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid (AMPA) Receptor Encephalitis Antibodies

    PubMed Central

    Peng, Xiaoyu; Hughes, Ethan G; Moscato, Emilia H; Parsons, Thomas D; Dalmau, Josep; Balice-Gordon, Rita J

    2015-01-01

    Objective Autoimmune-mediated anti–α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) encephalitis is a severe but treatment-responsive disorder with prominent short-term memory loss and seizures. The mechanisms by which patient antibodies affect synapses and neurons leading to symptoms are poorly understood. Methods The effects of patient antibodies on cultures of live rat hippocampal neurons were determined with immunostaining, Western blot, and electrophysiological analyses. Results We show that patient antibodies cause a selective decrease in the total surface amount and synaptic localization of GluA1- and GluA2-containing AMPARs, regardless of receptor subunit binding specificity, through increased internalization and degradation of surface AMPAR clusters. In contrast, patient antibodies do not alter the density of excitatory synapses, N-methyl-D-aspartate receptor (NMDAR) clusters, or cell viability. Commercially available AMPAR antibodies directed against extracellular epitopes do not result in a loss of surface and synaptic receptor clusters, suggesting specific effects of patient antibodies. Whole-cell patch clamp recordings of spontaneous miniature postsynaptic currents show that patient antibodies decrease AMPAR-mediated currents, but not NMDAR-mediated currents. Interestingly, several functional properties of neurons are also altered: inhibitory synaptic currents and vesicular γ-aminobutyric acid transporter (vGAT) staining intensity decrease, whereas the intrinsic excitability of neurons and short-interval firing increase. Interpretation These results establish that antibodies from patients with anti-AMPAR encephalitis selectively eliminate surface and synaptic AMPARs, resulting in a homeostatic decrease in inhibitory synaptic transmission and increased intrinsic excitability, which may contribute to the memory deficits and epilepsy that are prominent in patients with this disorder. PMID:25369168

  5. Mechanism of Positive Allosteric Modulators Acting on AMPA Receptors

    SciTech Connect

    Jin,R.; Clark, S.; Weeks, A.; Dudman, J.; Gouaux, E.; Partin, K.

    2005-01-01

    Ligand-gated ion channels involved in the modulation of synaptic strength are the AMPA, kainate, and NMDA glutamate receptors. Small molecules that potentiate AMPA receptor currents relieve cognitive deficits caused by neurodegenerative diseases such as Alzheimer's disease and show promise in the treatment of depression. Previously, there has been limited understanding of the molecular mechanism of action for AMPA receptor potentiators. Here we present cocrystal structures of the glutamate receptor GluR2 S1S2 ligand-binding domain in complex with aniracetam [1-(4-methoxybenzoyl)-2-pyrrolidinone] or CX614 (pyrrolidino-1, 3-oxazino benzo-1, 4-dioxan-10-one), two AMPA receptor potentiators that preferentially slow AMPA receptor deactivation. Both potentiators bind within the dimer interface of the nondesensitized receptor at a common site located on the twofold axis of molecular symmetry. Importantly, the potentiator binding site is adjacent to the 'hinge' in the ligand-binding core 'clamshell' that undergoes conformational rearrangement after glutamate binding. Using rapid solution exchange, patch-clamp electrophysiology experiments, we show that point mutations of residues that interact with potentiators in the cocrystal disrupt potentiator function. We suggest that the potentiators slow deactivation by stabilizing the clamshell in its closed-cleft, glutamate-bound conformation.

  6. Dynamic Regulation of N-Methyl-d-aspartate (NMDA) and α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors by Posttranslational Modifications.

    PubMed

    Lussier, Marc P; Sanz-Clemente, Antonio; Roche, Katherine W

    2015-11-27

    Many molecular mechanisms underlie the changes in synaptic glutamate receptor content that are required by neuronal networks to generate cellular correlates of learning and memory. During the last decade, posttranslational modifications have emerged as critical regulators of synaptic transmission and plasticity. Notably, phosphorylation, ubiquitination, and palmitoylation control the stability, trafficking, and synaptic expression of glutamate receptors in the central nervous system. In the current review, we will summarize some of the progress made by the neuroscience community regarding our understanding of phosphorylation, ubiquitination, and palmitoylation of the NMDA and AMPA subtypes of glutamate receptors. PMID:26453298

  7. Extensive phosphorylation of AMPA receptors in neurons.

    PubMed

    Diering, Graham H; Heo, Seok; Hussain, Natasha K; Liu, Bian; Huganir, Richard L

    2016-08-16

    Regulation of AMPA receptor (AMPAR) function is a fundamental mechanism controlling synaptic strength during long-term potentiation/depression and homeostatic scaling. AMPAR function and membrane trafficking is controlled by protein-protein interactions, as well as by posttranslational modifications. Phosphorylation of the GluA1 AMPAR subunit at S845 and S831 play especially important roles during synaptic plasticity. Recent controversy has emerged regarding the extent to which GluA1 phosphorylation may contribute to synaptic plasticity. Here we used a variety of methods to measure the population of phosphorylated GluA1-containing AMPARs in cultured primary neurons and mouse forebrain. Phosphorylated GluA1 represents large fractions from 12% to 50% of the total population under basal and stimulated conditions in vitro and in vivo. Furthermore, a large fraction of synapses are positive for phospho-GluA1-containing AMPARs. Our results support the large body of research indicating a prominent role of GluA1 phosphorylation in synaptic plasticity. PMID:27482106

  8. Ganglioside Regulation of AMPA Receptor Trafficking

    PubMed Central

    Prendergast, Jillian; Umanah, George K.E.; Yoo, Seung-Wan; Lagerlöf, Olof; Motari, Mary G.; Cole, Robert N.; Huganir, Richard L.; Dawson, Ted M.; Dawson, Valina L.

    2014-01-01

    Gangliosides are major cell-surface determinants on all vertebrate neurons. Human congenital disorders of ganglioside biosynthesis invariably result in intellectual disability and are often associated with intractable seizures. To probe the mechanisms of ganglioside functions, affinity-captured ganglioside-binding proteins from rat cerebellar granule neurons were identified by quantitative proteomic mass spectrometry. Of the six proteins that bound selectively to the major brain ganglioside GT1b (GT1b:GM1 > 4; p < 10−4), three regulate neurotransmitter receptor trafficking: Thorase (ATPase family AAA domain-containing protein 1), soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (γ-SNAP), and the transmembrane protein Nicalin. Thorase facilitates endocytosis of GluR2 subunit-containing AMPA-type glutamate receptors (AMPARs) in an ATPase-dependent manner; its deletion in mice results in learning and memory deficits (J. Zhang et al., 2011b). GluR2-containing AMPARs did not bind GT1b, but bound specifically to another ganglioside, GM1. Addition of noncleavable ATP (ATPγS) significantly disrupted ganglioside binding, whereas it enhanced AMPAR association with Thorase, NSF, and Nicalin. Mutant mice lacking GT1b expressed markedly higher brain Thorase, whereas Thorase-null mice expressed higher GT1b. Treatment of cultured hippocampal neurons with sialidase, which cleaves GT1b (and other sialoglycans), resulted in a significant reduction in the size of surface GluR2 puncta. These data support a model in which GM1-bound GluR2-containing AMPARs are functionally segregated from GT1b-bound AMPAR-trafficking complexes. Release of ganglioside binding may enhance GluR2-containing AMPAR association with its trafficking complexes, increasing endocytosis. Disrupting ganglioside biosynthesis may result in reduced synaptic expression of GluR2-contianing AMPARs resulting in intellectual deficits and seizure susceptibility in mice and humans. PMID:25253868

  9. Synthesis and biological evaluation of novel 9-heteroaryl substituted 7-chloro-4,5-dihydro-4-oxo-1,2,4-triazolo[1,5-a]quinoxaline-2-carboxylates (TQX) as (R,S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptor antagonists.

    PubMed

    Catarzi, Daniela; Colotta, Vittoria; Varano, Flavia; Filacchioni, Guido; Gratteri, Paola; Sgrignani, Jacopo; Galli, Alessandro; Costagli, Chiara

    2008-08-01

    In this paper, we report a study on some new 4,5-dihydro-4-oxo-1,2,4-triazolo[1,5-a]quinoxaline-2-carboxylate derivatives (TQXs), bearing a nitrogen-containing heterocycle at position-9, and designed as (R,S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptor antagonists. These compounds ensue from the structural modification of previously reported 8-heteroaryl-TQXs which were endowed with high affinity and selectivity for the AMPA receptor. All the newly synthesized compounds were biologically evaluated for their binding at the AMPA receptor. Gly/N-methyl-D-aspartic acid (NMDA) and kainic acid (KA) high-affinity binding assays were performed to assess the selectivity of the reported derivatives toward the AMPA receptor. This study produced some new TQXs which are less potent than the reference compounds, and endowed with a mixed AMPA and Gly/NMDA receptor binding affinity. To rationalize the experimental findings, a molecular modeling study was performed by docking some TQX derivatives to the AMPA receptor model. PMID:18670107

  10. Mechanism-based design of 2,3-benzodiazepine inhibitors for AMPA receptors

    PubMed Central

    Niu, Li

    2015-01-01

    2,3-Benzodiazepine (2,3-BDZ) compounds represent a group of structurally diverse, small-molecule antagonists of (R, S)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) receptors. Antagonists of AMPA receptors are drug candidates for potential treatment of a number of neurological disorders such as epilepsy, stroke and amyotrophic lateral sclerosis (ALS). How to make better inhibitors, such as 2,3-BDZs, has been an enduring quest in drug discovery. Among a few available tools to address this specific question for making better 2,3-BDZs, perhaps the best one is to use mechanistic clues from studies of the existing antagonists to design and discover more selective and more potent antagonists. Here I review recent work in this area, and propose some ideas in the continuing effort of developing newer 2,3-BDZs for tighter control of AMPA receptor activities in vivo. PMID:26713266

  11. Differential regulation of AMPA receptor subunit trafficking by palmitoylation of two distinct sites.

    PubMed

    Hayashi, Takashi; Rumbaugh, Gavin; Huganir, Richard L

    2005-09-01

    Modification of AMPA receptor function is a major mechanism for the regulation of synaptic transmission and underlies several forms of synaptic plasticity. Post-translational palmitoylation is a reversible modification that regulates localization of many proteins. Here, we report that palmitoylation of the AMPA receptor regulates receptor trafficking. All AMPA receptor subunits are palmitoylated on two cysteine residues in their transmembrane domain (TMD) 2 and in their C-terminal region. Palmitoylation on TMD 2 is upregulated by the palmitoyl acyl transferase GODZ and leads to an accumulation of the receptor in the Golgi and a reduction of receptor surface expression. C-terminal palmitoylation decreases interaction of the AMPA receptor with the 4.1N protein and regulates AMPA- and NMDA-induced AMPA receptor internalization. Moreover, depalmitoylation of the receptor is regulated by activation of glutamate receptors. These data suggest that regulated palmitoylation of AMPA receptor subunits modulates receptor trafficking and may be important for synaptic plasticity. PMID:16129400

  12. S-palmitoylation regulates AMPA receptors trafficking and function: a novel insight into synaptic regulation and therapeutics

    PubMed Central

    Han, Jun; Wu, Pengfei; Wang, Fang; Chen, Jianguo

    2014-01-01

    Glutamate acting on AMPA-type ionotropic glutamate receptor (AMPAR) mediates the majority of fast excitatory synaptic transmission in the mammalian central nervous system. Dynamic regulation of AMPAR by post-translational modifications is one of the key elements that allow the nervous system to adapt to environment stimulations. S-palmitoylation, an important lipid modification by post-translational addition of a long-chain fatty acid to a cysteine residue, regulates AMPA receptor trafficking, which dynamically affects multiple fundamental brain functions, such as learning and memory. In vivo, S-palmitoylation is controlled by palmitoyl acyl transferases and palmitoyl thioesterases. In this review, we highlight advances in the mechanisms for dynamic AMPA receptors palmitoylation, and discuss how palmitoylation affects AMPA receptors function at synapses in recent years. Pharmacological regulation of S-palmitoylation may serve as a novel therapeutic strategy for neurobiological diseases. PMID:26579419

  13. Diabetic hyperglycemia reduces Ca2+ permeability of extrasynaptic AMPA receptors in AII amacrine cells.

    PubMed

    Castilho, Áurea; Madsen, Eirik; Ambrósio, António F; Veruki, Margaret L; Hartveit, Espen

    2015-09-01

    There is increasing evidence that diabetic retinopathy is a primary neuropathological disorder that precedes the microvascular pathology associated with later stages of the disease. Recently, we found evidence for altered functional properties of synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in A17, but not AII, amacrine cells in the mammalian retina, and the observed changes were consistent with an upregulation of the GluA2 subunit, a key determinant of functional properties of AMPA receptors, including Ca(2+) permeability and current-voltage (I-V) rectification properties. Here, we have investigated functional changes of extrasynaptic AMPA receptors in AII amacrine cells evoked by diabetes. With patch-clamp recording of nucleated patches from retinal slices, we measured Ca(2+) permeability and I-V rectification in rats with ∼3 wk of streptozotocin-induced diabetes and age-matched, noninjected controls. Under bi-ionic conditions (extracellular Ca(2+) concentration = 30 mM, intracellular Cs(+) concentration = 171 mM), the reversal potential (Erev) of AMPA-evoked currents indicated a significant reduction of Ca(2+) permeability in diabetic animals [Erev = -17.7 mV, relative permeability of Ca(2+) compared with Cs(+) (PCa/PCs) = 1.39] compared with normal animals (Erev = -7.7 mV, PCa/PCs = 2.35). Insulin treatment prevented the reduction of Ca(2+) permeability. I-V rectification was examined by calculating a rectification index (RI) as the ratio of the AMPA-evoked conductance at +40 and -60 mV. The degree of inward rectification in patches from diabetic animals (RI = 0.48) was significantly reduced compared with that in normal animals (RI = 0.30). These results suggest that diabetes evokes a change in the functional properties of extrasynaptic AMPA receptors of AII amacrine cells. These changes could be representative for extrasynaptic AMPA receptors elsewhere in AII amacrine cells and suggest that synaptic and extrasynaptic AMPA

  14. Challenges for and current status of research into positive modulators of AMPA receptors

    PubMed Central

    Ward, Simon E; Bax, Benjamin D; Harries, Mark

    2010-01-01

    AMPA receptors consist of a family of hetero-oligomeric (tetrameric) receptors arising from four genes, each of which encodes a distinct receptor subunit (GluA1-4). Recombinant homo-tetrameric AMPA receptors, comprising four identical subunits, are functionally active and have been used in in vitro assays. However, the many different subunit permutations make possible the functional and anatomical diversity of AMPA receptors throughout the CNS. Furthermore, AMPA receptor subunit stoichiometry influences the biophysical and functional properties of the receptor. A number of chemically diverse positive modulators of AMPA receptor have been identified which potentiate AMPA receptor-mediated activity in vitro as well as improving cognitive performance in rodents and non-human primates with several being taken further in the clinic. This review article summarizes the current status in the research on positive allosteric modulation of AMPA receptors and outlines the challenges involved in identifying a chemically distinct series of AMPA receptor positive modulators, addressing the challenges created by the heterogeneity of the AMPA receptor populations and the development of structure-activity relationships driven by homomeric, recombinant systems on high-throughput platforms. We also review the role of X-ray crystallography in the selection and prioritization of targets for lead optimization for AMPA receptor positive modulators. PMID:20423333

  15. The essential role of AMPA receptor GluR2 subunit RNA editing in the normal and diseased brain.

    PubMed

    Wright, Amanda; Vissel, Bryce

    2012-01-01

    α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are comprised of different combinations of GluA1-GluA4 (also known asGluR1-GluR4 and GluR-A to GluR-D) subunits. The GluA2 subunit is subject to RNA editing by the ADAR2 enzyme, which converts a codon for glutamine (Gln; Q), present in the GluA2 gene, to a codon for arginine (Arg; R) found in the mRNA. AMPA receptors are calcium (Ca(2+))-permeable if they contain the unedited GluA2(Q) subunit or if they lack the GluA2 subunit. While most AMPA receptors in the brain contain the edited GluA2(R) subunit and are therefore Ca(2+)-impermeable, recent evidence suggests that Ca(2+)-permeable AMPA receptors are important in synaptic plasticity, learning, and disease. Strong evidence supports the notion that Ca(2+)-permeable AMPA receptors are usually GluA2-lacking AMPA receptors, with little evidence to date for a significant role of unedited GluA2 in normal brain function. However, recent detailed studies suggest that Ca(2+)-permeable AMPA receptors containing unedited GluA2 do in fact occur in neurons and can contribute to excitotoxic cell loss, even where it was previously thought that there was no unedited GluA2.This review provides an update on the role of GluA2 RNA editing in the healthy and diseased brain and summarizes recent insights into the mechanisms that control this process. We suggest that further studies of the role of unedited GluA2 in normal brain function and disease are warranted, and that GluA2 editing should be considered as a possible contributing factor when Ca(2+)-permeable AMPA receptors are observed. PMID:22514516

  16. Involvement of AMPA receptors in the antidepressant-like effects of dextromethorphan in mice.

    PubMed

    Nguyen, Linda; Matsumoto, Rae R

    2015-12-15

    Dextromethorphan (DM) is an antitussive with rapid acting antidepressant potential based on pharmacodynamic similarities to ketamine. Building upon our previous finding that DM produces antidepressant-like effects in the mouse forced swim test (FST), the present study aimed to establish the antidepressant-like actions of DM in the tail suspension test (TST), another well-established model predictive of antidepressant efficacy. Additionally, using the TST and FST, we investigated the role of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors in the antidepressant-like properties of DM because accumulating evidence suggests that AMPA receptors play an important role in the pathophysiology of depression and may contribute to the efficacy of antidepressant medications, including that of ketamine. We found that DM displays antidepressant-like effects in the TST similar to the conventional and fast acting antidepressants characterized by imipramine and ketamine, respectively. Moreover, decreasing the first-pass metabolism of DM by concomitant administration of quinidine (CYP2D6 inhibitor) potentiated antidepressant-like actions, implying DM itself has antidepressant efficacy. Finally, in both the TST and FST, pretreatment with the AMPA receptor antagonist NBQX (2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide) significantly attenuated the antidepressant-like behavior elicited by DM. Together, the data show that DM exerts antidepressant-like actions through AMPA receptors, further suggesting DM may act as a safe and effective fast acting antidepressant drug. PMID:25804358

  17. Amyloid-β-Induced Dysregulation of AMPA Receptor Trafficking

    PubMed Central

    Guntupalli, Sumasri; Widagdo, Jocelyn; Anggono, Victor

    2016-01-01

    Evidence from neuropathological, genetic, animal model, and biochemical studies has indicated that the accumulation of amyloid-beta (Aβ) is associated with, and probably induces, profound neuronal changes in brain regions critical for memory and cognition in the development of Alzheimer's disease (AD). There is considerable evidence that synapses are particularly vulnerable to AD, establishing synaptic dysfunction as one of the earliest events in pathogenesis, prior to neuronal loss. It is clear that excessive Aβ levels can disrupt excitatory synaptic transmission and plasticity, mainly due to dysregulation of the AMPA and NMDA glutamate receptors in the brain. Importantly, AMPA receptors are the principal glutamate receptors that mediate fast excitatory neurotransmission. This is essential for synaptic plasticity, a cellular correlate of learning and memory, which are the cognitive functions that are most disrupted in AD. Here we review recent advances in the field and provide insights into the molecular mechanisms that underlie Aβ-induced dysfunction of AMPA receptor trafficking. This review focuses primarily on NMDA receptor- and metabotropic glutamate receptor-mediated signaling. In particular, we highlight several mechanisms that underlie synaptic long-term depression as common signaling pathways that are hijacked by the neurotoxic effects of Aβ. PMID:27073700

  18. Amyloid-β-Induced Dysregulation of AMPA Receptor Trafficking.

    PubMed

    Guntupalli, Sumasri; Widagdo, Jocelyn; Anggono, Victor

    2016-01-01

    Evidence from neuropathological, genetic, animal model, and biochemical studies has indicated that the accumulation of amyloid-beta (Aβ) is associated with, and probably induces, profound neuronal changes in brain regions critical for memory and cognition in the development of Alzheimer's disease (AD). There is considerable evidence that synapses are particularly vulnerable to AD, establishing synaptic dysfunction as one of the earliest events in pathogenesis, prior to neuronal loss. It is clear that excessive Aβ levels can disrupt excitatory synaptic transmission and plasticity, mainly due to dysregulation of the AMPA and NMDA glutamate receptors in the brain. Importantly, AMPA receptors are the principal glutamate receptors that mediate fast excitatory neurotransmission. This is essential for synaptic plasticity, a cellular correlate of learning and memory, which are the cognitive functions that are most disrupted in AD. Here we review recent advances in the field and provide insights into the molecular mechanisms that underlie Aβ-induced dysfunction of AMPA receptor trafficking. This review focuses primarily on NMDA receptor- and metabotropic glutamate receptor-mediated signaling. In particular, we highlight several mechanisms that underlie synaptic long-term depression as common signaling pathways that are hijacked by the neurotoxic effects of Aβ. PMID:27073700

  19. Differential effects of chronic hyperammonemia on modulation of the glutamate-nitric oxide-cGMP pathway by metabotropic glutamate receptor 5 and low and high affinity AMPA receptors in cerebellum in vivo.

    PubMed

    Cabrera-Pastor, Andrea; Llansola, Marta; Reznikov, Vitaliy; Boix, Jordi; Felipo, Vicente

    2012-07-01

    Previous studies show that chronic hyperammonemia impairs learning ability of rats by impairing the glutamate-nitric oxide (NO)-cyclic guanosine mono-phosphate (cGMP) pathway in cerebellum. Three types of glutamate receptors cooperate in modulating the NO-cGMP pathway: metabotropic glutamate receptor 5 (mGluR5), (RS)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartic acid (NMDA) receptors. The aim of this work was to assess whether hyperammonemia alters the modulation of this pathway by mGluR5 and AMPA receptors in cerebellum in vivo. The results support that in control rats: (1) low AMPA concentrations (0.1mM) activate nearly completely Ca(2+)-permeable (glutamate receptor subunit 2 (GluR2)-lacking) AMPA receptors and the NO-cGMP pathway; (2) higher AMPA concentrations (0.3 mM) also activate Ca(2+)-impermeable (GluR2-containing) AMPA receptors, leading to activation of NMDA receptors and of NO-cGMP pathway. Moreover, the data support that chronic hyperammonemia: (1) reduces glutamate release and activation of the glutamate-NO-cGMP pathway by activation of mGluR5; (2) strongly reduces the direct activation by AMPA receptors of the NO-cGMP pathway, likely due to reduced entry of Ca(2+) through GluR2-lacking, high affinity AMPA receptors; (3) strongly increases the indirect activation of the NO-cGMP pathway by high affinity AMPA receptors, likely due to increased entry of Na(+) through GluR2-lacking AMPA receptors and NMDA receptors activation; (4) reduces the indirect activation of the NO-cGMP pathway by low affinity AMPA receptors, likely due to reduced activation of NMDA receptors. PMID:22521775

  20. FUNCTIONAL ANALYSIS OF A NOVEL POSITIVE ALLOSTERIC MODULATOR OF AMPA RECEPTORS DERIVED FROM A STRUCTURE-BASED DRUG DESIGN STRATEGY

    PubMed Central

    Harms, Jonathan E.; Benveniste, Morris; Maclean, John K. F.; Partin, Kathryn M.; Jamieson, Craig

    2012-01-01

    Positive allosteric modulators of α-amino-3-hydroxy-5-methyl-isoxazole-propionic acid (AMPA) receptors facilitate synaptic plasticity and can improve various forms of learning and memory. These modulators show promise as therapeutic agents for the treatment of neurological disorders such as schizophrenia, ADHD, and mental depression. Three classes of positive modulator, the benzamides, the thiadiazides, and the biarylsulfonamides differentially occupy a solvent accessible binding pocket at the interface between the two subunits that form the AMPA receptor ligand-binding pocket. Here, we describe the electrophysiological properties of a new chemotype derived from a structure-based drug design strategy (SBDD), which makes similar receptor interactions compared to previously reported classes of modulator. This pyrazole amide derivative, JAMI1001A, with a promising developability profile, efficaciously modulates AMPA receptor deactivation and desensitization of both flip and flop receptor isoforms. PMID:22735771

  1. Targeting of GLUR4-containing AMPA receptors to synaptic sites during in vitro classical conditioning.

    PubMed

    Mokin, M; Keifer, J

    2004-01-01

    The synaptic delivery of GluR4-containing AMPA receptors during in vitro classical conditioning of a neural correlate of an eyeblink response was examined by fluorescence imaging of punctate staining for glutamate receptor subunits and the presynaptic marker synaptophysin. There was a significant increase in GluR4-containing AMPA receptors to synaptic sites after conditioning as determined by colocalization of GluR4 subunit puncta with synaptophysin. Moreover, the trafficking of these receptor subunits requires NMDA receptor activation as it was blocked by D,L-2-amino-5-phosphonovaleric acid (AP-5). In contrast, colocalization of NR1 subunits with synaptophysin was stable regardless of whether the preparations had undergone conditioning or had been treated by AP-5. The enhanced colocalization of GluR4 and synaptophysin was accompanied by an increase in both the total number and size of puncta for both proteins, suggesting greater synthesis and aggregation during conditioning. Western blot analysis confirmed upregulation of synaptophysin and GluR4 following conditioning. These data support the hypothesis that GluR4-containing AMPA receptors are delivered to synaptic sites during conditioning. Further, they suggest coordinate presynaptic and postsynaptic modifications during in vitro classical conditioning. PMID:15350635

  2. Stress Induces Pain Transition by Potentiation of AMPA Receptor Phosphorylation

    PubMed Central

    Li, Changsheng; Yang, Ya; Liu, Sufang; Fang, Huaqiang; Zhang, Yong; Furmanski, Orion; Skinner, John; Xing, Ying; Johns, Roger A.

    2014-01-01

    Chronic postsurgical pain is a serious issue in clinical practice. After surgery, patients experience ongoing pain or become sensitive to incident, normally nonpainful stimulation. The intensity and duration of postsurgical pain vary. However, it is unclear how the transition from acute to chronic pain occurs. Here we showed that social defeat stress enhanced plantar incision-induced AMPA receptor GluA1 phosphorylation at the Ser831 site in the spinal cord and greatly prolonged plantar incision-induced pain. Interestingly, targeted mutation of the GluA1 phosphorylation site Ser831 significantly inhibited stress-induced prolongation of incisional pain. In addition, stress hormones enhanced GluA1 phosphorylation and AMPA receptor-mediated electrical activity in the spinal cord. Subthreshold stimulation induced spinal long-term potentiation in GluA1 phosphomimetic mutant mice, but not in wild-type mice. Therefore, spinal AMPA receptor phosphorylation contributes to the mechanisms underlying stress-induced pain transition. PMID:25297100

  3. Signalling mechanism for somatostatin receptor 5-mediated suppression of AMPA responses in rat retinal ganglion cells.

    PubMed

    Deng, Qin-Qin; Sheng, Wen-Long; Zhang, Gong; Weng, Shi-Jun; Yang, Xiong-Li; Zhong, Yong-Mei

    2016-08-01

    Somatostatin (SRIF) is involved in a variety of physiological functions via the activation of five subtypes of specific receptors (sst1-5). Here, we investigated the effects of SRIF on AMPA receptor (AMPAR)-mediated currents (AMPA currents) in isolated rat retinal ganglion cells (GCs) using patch-clamp techniques. Immunofluorescence double labelling demonstrated the expression of sst5 in rat GCs. Consistent to this, whole cell AMPA currents of GCs were dose-dependently suppressed by SRIF, and the effect was reversed by the sst5 antagonist BIM-23056. Intracellular dialysis of GDP-β-S or pre-incubation with the Gi/o inhibitor pertussis toxin (PTX) abolished the SRIF effect. The SRIF effect was mimicked by the administration of either 8-Br-cAMP or forskolin, but was eliminated by the protein kinase A (PKA) antagonists H-89/KT5720/Rp-cAMP. Moreover, SRIF increased intracellular Ca(2+) levels and did not suppress the AMPA currents when GCs were infused with an intracellular Ca(2+)-free solution or in the presence of ryanodine receptor modulators caffeine/ryanodine. Furthermore, the SRIF effect was eliminated when the activity of calmodulin (CaM), calcineurin and protein phosphatase 1 (PP1) was blocked with W-7, FK-506 and okadaic acid, respectively. SRIF persisted to suppress the AMPA currents when cGMP-protein kinase G (PKG) and phosphatidylinositol (PI)-/phosphatidylcholine (PC)-phospholipase C (PLC) signalling pathways were blocked. In rat flat-mount retinas, SRIF suppressed AMPAR-mediated light-evoked excitatory postsynaptic currents (L-EPSCs) in GCs. We conclude that a distinct Gi/o/cAMP-PKA/ryanodine/Ca(2+)/CaM/calcineurin/PP1 signalling pathway comes into play due to the activation of sst5 to mediate the SRIF effect on GCs. PMID:26969240

  4. Discovery and Characterization of AMPA Receptor Modulators Selective for TARP-γ8.

    PubMed

    Maher, Michael P; Wu, Nyantsz; Ravula, Suchitra; Ameriks, Michael K; Savall, Brad M; Liu, Changlu; Lord, Brian; Wyatt, Ryan M; Matta, Jose A; Dugovic, Christine; Yun, Sujin; Ver Donck, Luc; Steckler, Thomas; Wickenden, Alan D; Carruthers, Nicholas I; Lovenberg, Timothy W

    2016-05-01

    Members of the α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionic acid (AMPA) subtype of ionotropic glutamate receptors mediate the majority of fast synaptic transmission within the mammalian brain and spinal cord, representing attractive targets for therapeutic intervention. Here, we describe novel AMPA receptor modulators that require the presence of the accessory protein CACNG8, also known as transmembrane AMPA receptor regulatory protein γ8 (TARP-γ8). Using calcium flux, radioligand binding, and electrophysiological assays of wild-type and mutant forms of TARP-γ8, we demonstrate that these compounds possess a novel mechanism of action consistent with a partial disruption of the interaction between the TARP and the pore-forming subunit of the channel. One of the molecules, 5-[2-chloro-6-(trifluoromethoxy)phenyl]-1,3-dihydrobenzimidazol-2-one (JNJ-55511118), had excellent pharmacokinetic properties and achieved high receptor occupancy following oral administration. This molecule showed strong, dose-dependent inhibition of neurotransmission within the hippocampus, and a strong anticonvulsant effect. At high levels of receptor occupancy in rodent in vivo models, JNJ-55511118 showed a strong reduction in certain bands on electroencephalogram, transient hyperlocomotion, no motor impairment on rotarod, and a mild impairment in learning and memory. JNJ-55511118 is a novel tool for reversible AMPA receptor inhibition, particularly within the hippocampus, with potential therapeutic utility as an anticonvulsant or neuroprotectant. The existence of a molecule with this mechanism of action demonstrates the possibility of pharmacological targeting of accessory proteins, increasing the potential number of druggable targets. PMID:26989142

  5. Specificity protein 4 (Sp4) regulates the transcription of AMPA receptor subunit GluA2 (Gria2).

    PubMed

    Priya, Anusha; Johar, Kaid; Nair, Bindu; Wong-Riley, Margaret T T

    2014-06-01

    The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are important glutamatergic receptors mediating fast excitatory synaptic transmission in the brain. The regulation of the four subunits of AMPA receptors, GluA1-4, is poorly understood. Excitatory synaptic transmission is highly energy-demanding, and this energy is derived mainly from the oxidative pathway. Recently, we found that specificity factor regulates all subunits of cytochrome c oxidase (COX), a critical energy-generating enzyme. COX is also regulated by nuclear respiratory factor 1 (NRF-1), which transcriptionally controls the Gria2 (GluA2) gene of AMPA receptors. The goal of the present study was to test our hypothesis that Sp-factors (Sp1, Sp3, and/or Sp4) also regulate AMPA subunit genes. If so, we wish to determine if Sp-factors and NRF-1 function via a complementary, concurrent and parallel, or a combination of complementary and concurrent/parallel mechanism. By means of multiple approaches, including electrophoretic mobility shift and supershift assays, chromatin immunoprecipitation, promoter mutations, real-time quantitative PCR, and western blot analysis, we found that Sp4, but not Sp1 or Sp3, regulates the Gria2, but not Gria1, 3, or 4, subunit gene of the AMPA receptor in a concurrent and parallel manner with NRF-1. Thus, Sp4 and NRF-1 both mediate the tight coupling between neuronal activity and energy metabolism at the transcriptional level. PMID:24576410

  6. AMPA receptor antibodies in limbic encephalitis alter synaptic receptor location

    PubMed Central

    Lai, Meizan; Hughes, Ethan G.; Peng, Xiaoyu; Zhou, Lei; Gleichman, Amy J.; Shu, Huidy; Matà, Sabrina; Kremens, Daniel; Vitaliani, Roberta; Geschwind, Michael D.; Bataller, Luis; Kalb, Robert G.; Davis, Rebecca; Graus, Francesc; Lynch, David R.; Balice-Gordon, Rita; Dalmau, Josep

    2009-01-01

    Background Limbic encephalitis (LE) frequently associates with antibodies to cell surface antigens. Characterization of these antigens is important because it facilitates the diagnosis of those disorders that are treatment-responsive. We report a novel antigen of LE and the effect of patients' antibodies on neuronal cultures. Methods Clinical analysis of 10 patients with LE. Immunoprecipitation and mass spectrometry were used to identify the antigens. HEK293 cells expressing the antigens were used in immunocytochemistry and ELISA. The effect of patients' antibodies on cultures of live rat hippocampal neurons was determined with confocal microscopy. Results Median age was 60 years (38-87); 9 were women. Seven had tumors of the lung, breast or thymus. Nine patients responded to immunotherapy or oncological therapy but neurologic relapses, without tumor recurrence, were frequent and influenced the long-term outcome. One untreated patient died of LE. All patients had antibodies against neuronal cell surface antigens that by immunoprecipitation were found to be the GluR1 and GluR2 subunits of the AMPA receptor (AMPAR). HEK293 cells expressing GluR1/2 reacted with all patients' sera or CSF, providing a diagnostic test for the disorder. Application of antibodies to cultures of neurons significantly decreased the number of GluR2-containing AMPAR clusters at synapses with a smaller decrease in overall AMPAR cluster density; these effects were reversed after antibody removal. Conclusions Antibodies to GluR1/2 associate with LE that is often paraneoplastic, treatment-responsive, and has a tendency to relapse. Our findings support an antibody-mediated pathogenesis in which patients' antibodies alter the synaptic localization and number of AMPAR. PMID:19338055

  7. Synaptic AMPA receptor composition in development, plasticity and disease.

    PubMed

    Henley, Jeremy M; Wilkinson, Kevin A

    2016-06-01

    AMPA receptors (AMPARs) are assemblies of four core subunits, GluA1-4, that mediate most fast excitatory neurotransmission. The component subunits determine the functional properties of AMPARs, and the prevailing view is that the subunit composition also determines AMPAR trafficking, which is dynamically regulated during development, synaptic plasticity and in response to neuronal stress in disease. Recently, the subunit dependence of AMPAR trafficking has been questioned, leading to a reappraisal of this field. In this Review, we discuss what is known, uncertain, conjectured and unknown about the roles of the individual subunits, and how they affect AMPAR assembly, trafficking and function under both normal and pathological conditions. PMID:27080385

  8. Regulation of AMPA Receptor Trafficking and Synaptic Plasticity

    PubMed Central

    Anggono, Victor; Huganir, Richard L.

    2012-01-01

    AMPA receptors (AMPARs) mediate the majority of fast excitatory synaptic transmission in the brain. Dynamic changes in neuronal synaptic efficacy, termed synaptic plasticity, are thought to underlie information coding and storage in learning and memory. One major mechanism that regulates synaptic strength involves the tightly regulated trafficking of AMPARs into and out of synapses. The life cycle of AMPARs from their biosynthesis, membrane trafficking and synaptic targeting to their degradation are controlled by a series of orchestrated interactions with numerous intracellular regulatory proteins. Here we review recent progress made towards the understanding the regulation of AMPAR trafficking, focusing on the roles of several key intracellular AMPAR interacting proteins. PMID:22217700

  9. Routes, destinations and delays: recent advances in AMPA receptor trafficking

    PubMed Central

    Henley, Jeremy M.; Barker, Ellen A.; Glebov, Oleg O.

    2012-01-01

    Postsynaptic AMPA-type glutamate receptors (AMPARs) mediate most fast excitatory synaptic transmission and are crucial for many aspects of brain function, including learning, memory and cognition. The number, synaptic localization and subunit composition of synaptic AMPARs are tightly regulated by network activity and by the history of activity at individual synapses. Furthermore, aberrant AMPAR trafficking is implicated in neurodegenerative diseases. AMPARs therefore represent a prime target for drug development and the mechanisms that control their synaptic delivery, retention and removal are the subject of extensive research. Here, we review recent findings that have provided new insights into AMPAR trafficking and that might lead to the development of novel therapeutic strategies. PMID:21420743

  10. Novel AMPA and kainate receptor antagonists containing the pyrazolo[1,5-c]quinazoline ring system: Synthesis and structure-activity relationships.

    PubMed

    Varano, Flavia; Catarzi, Daniela; Colotta, Vittoria; Lenzi, Ombretta; Filacchioni, Guido; Galli, Alessandro; Costagli, Chiara

    2008-03-01

    This paper reports the synthesis and AMPA, Gly/NMDA, and KA receptor binding affinities of a new set of 1,9-disubstituted-8-chloro-pyrazolo[1,5-c]quinazoline-2-carboxylates 2-34. Binding data show that, in general, compounds 2-34 bind to the AMPA receptor with good affinity and selectivity. In particular, the obtained results indicate that the contemporary presence of a 1,2-dicarboxylic acid moiety and suitable benzo-substituents on the PQZ system is important to gain selective AMPA receptor antagonists. Moreover, this study shows that the presence of a 2-carboxybenzoylamino substituent at position-9 (compounds 33-34) is important for obtaining selective KA receptor antagonists. Some selected compounds were also tested for their functional antagonistic activity at both AMPA and NMDA receptor-ion channels. PMID:18063372

  11. Calcium-Permeable AMPA Receptors in the Retina

    PubMed Central

    Diamond, Jeffrey S.

    2011-01-01

    The retina transforms light entering the eye into a sophisticated neural representation of our visual world. Specialized synapses, cells, and circuits in the retina have evolved to encode luminance, contrast, motion, and other complex visual features. Although a great deal has been learned about the cellular morphology and circuitry that underlies this image processing, many of the synapses in the retina remain incompletely understood. For example, excitatory synapses in the retina feature the full panoply of glutamate receptors, but in most cases specific roles for different receptor subtypes are unclear. In this brief review, I will discuss recent progress toward understanding how Ca2+-permeable AMPA receptors (CP-GluARs) contribute to synaptic transmission and newly discovered forms of synaptic plasticity in the retina. PMID:21991245

  12. The AMPA receptor subunit GluR1 regulates dendritic architecture of motor neurons

    NASA Technical Reports Server (NTRS)

    Inglis, Fiona M.; Crockett, Richard; Korada, Sailaja; Abraham, Wickliffe C.; Hollmann, Michael; Kalb, Robert G.

    2002-01-01

    The morphology of the mature motor neuron dendritic arbor is determined by activity-dependent processes occurring during a critical period in early postnatal life. The abundance of the AMPA receptor subunit GluR1 in motor neurons is very high during this period and subsequently falls to a negligible level. To test the role of GluR1 in dendrite morphogenesis, we reintroduced GluR1 into rat motor neurons at the end of the critical period and quantitatively studied the effects on dendrite architecture. Two versions of GluR1 were studied that differed by the amino acid in the "Q/R" editing site. The amino acid occupying this site determines single-channel conductance, ionic permeability, and other essential electrophysiologic properties of the resulting receptor channels. We found large-scale remodeling of dendritic architectures in a manner depending on the amino acid occupying the Q/R editing site. Alterations in the distribution of dendritic arbor were not prevented by blocking NMDA receptors. These observations suggest that the expression of GluR1 in motor neurons modulates a component of the molecular substrate of activity-dependent dendrite morphogenesis. The control of these events relies on subunit-specific properties of AMPA receptors.

  13. Cisplatin induces neuronal activation and increases central AMPA and NMDA receptor subunit gene expression in mice.

    PubMed

    Holland, Ruby A; Leonard, John J; Kensey, Nicholas A; Hannikainen, Paavali A; De Jonghe, Bart C

    2014-09-01

    Although rats and mice do not vomit, these species are widely studied as models of energy balance and sickness behavior. Previous work has shown that rats exhibit similar neuroanatomical activation of brain and visceral afferent pathways following cisplatin chemotherapy compared to vomiting species. However, the neural response to cisplatin in mice is understudied. Here, food intake, body weight, and central c-Fos immunofluorescence were analyzed in the hindbrains of male C57BL/6 mice following IP saline or cisplatin (5mg/kg, and 20mg/kg doses). As glutamate receptor signaling is classically linked to inhibitory feeding pathways in the rodent, gene expression of selected α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartic acid (NMDA) receptor subunits were assessed in the dorsal vagal complex (DVC), parabrachial nucleus (PBN), amygdala, and bed nucleus of the stria terminalis (BNST). Our results show dose-dependent reductions in food intake and body weight following cisplatin treatment, as well as increases in cisplatin-induced c-Fos in the PBN and throughout the DVC. Quantitative PCR analysis shows cisplatin-induced increases in NMDA receptor subunit expression, particularly NR2B, in the DVC, PBN, BNST, and amygdala. In addition, upregulation of AMPA receptor subunits (GluA1 and/or GluA2) were observed in all regions examined except the amygdala. Taken together, these results suggest similar neural pathways mediating cisplatin effects in mice compared to other well-studied species, which are likely mediated by central upregulation of AMPA and NMDA receptors. PMID:24582677

  14. Interaction with the unfolded protein response reveals a role for stargazin in biosynthetic AMPA receptor transport.

    PubMed

    Vandenberghe, Wim; Nicoll, Roger A; Bredt, David S

    2005-02-01

    The transmembrane protein stargazin enhances levels of functional AMPA receptors at the neuronal plasma membrane and at synapses. To clarify the mechanism for this effect, we studied trafficking of the AMPA receptor subunit glutamate receptor 1 (GluR1) in transfected COS7 cells. GluR1 expressed poorly on the surface of these cells and was primarily retained in the endoplasmic reticulum (ER). Stargazin expression strongly increased the surface fraction of GluR1. This effect was not reduced by a dominant-negative dynamin mutant, suggesting that stargazin does not inhibit AMPA receptor endocytosis. Interestingly, upregulation of ER chaperones as part of the unfolded protein response (UPR) both mimicked and occluded the effect of stargazin, suggesting a role for stargazin in ER processing of AMPA receptors. Consistent with this idea, we detected UPR induction in cerebellar granule cells lacking stargazin. Finally, residual AMPA receptor currents in stargazin-deficient neurons were suppressed by inhibition of the UPR. These findings uncover a role for stargazin in AMPA receptor trafficking through the early compartments of the biosynthetic pathway. Furthermore, they provide evidence for modulation of AMPA receptor trafficking by the UPR. PMID:15689545

  15. AMPA RECEPTOR POTENTIATORS: FROM DRUG DESIGN TO COGNITIVE ENHANCEMENT

    PubMed Central

    PARTIN, KATHRYN M.

    2014-01-01

    Positive allosteric modulators of ionotropic glutamate receptors have emerged as a target for treating cognitive impairment and neurodegeneration, but also mental illnesses such as major depressive disorder. The possibility of creating a new class of pharmaceutical agent to treat refractive mental health issues has compelled researchers to redouble their efforts to develop a safe, effective treatment for memory and cognition impairments. Coupled with the more robust research methodologies that have emerged, including more sophisticated high-throughput-screens, higher resolution structural biology techniques, and more focused assessment on pharmacokinetics, the development of positive modulators of AMPA receptors holds great promise. We describe recent approaches that improve our understanding of the basic physiology underlying memory and cognition, and their application towards promoting human health. PMID:25462292

  16. Glutamate Stimulates Local Protein Synthesis in the Axons of Rat Cortical Neurons by Activating α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors and Metabotropic Glutamate Receptors*

    PubMed Central

    Hsu, Wei-Lun; Chung, Hui-Wen; Wu, Chih-Yueh; Wu, Huei-Ing; Lee, Yu-Tao; Chen, En-Chan; Fang, Weilun; Chang, Yen-Chung

    2015-01-01

    Glutamate is the principal excitatory neurotransmitter in the mammalian CNS. By analyzing the metabolic incorporation of azidohomoalanine, a methionine analogue, in newly synthesized proteins, we find that glutamate treatments up-regulate protein translation not only in intact rat cortical neurons in culture but also in the axons emitting from cortical neurons before making synapses with target cells. The process by which glutamate stimulates local translation in axons begins with the binding of glutamate to the ionotropic AMPA receptors and metabotropic glutamate receptor 1 and members of group 2 metabotropic glutamate receptors on the plasma membrane. Subsequently, the activated mammalian target of rapamycin (mTOR) signaling pathway and the rise in Ca2+, resulting from Ca2+ influxes through calcium-permeable AMPA receptors, voltage-gated Ca2+ channels, and transient receptor potential canonical channels, in axons stimulate the local translation machinery. For comparison, the enhancement effects of brain-derived neurotrophic factor (BDNF) on the local protein synthesis in cortical axons were also studied. The results indicate that Ca2+ influxes via transient receptor potential canonical channels and activated the mTOR pathway in axons also mediate BDNF stimulation to local protein synthesis. However, glutamate- and BDNF-induced enhancements of translation in axons exhibit different kinetics. Moreover, Ca2+ and mTOR signaling appear to play roles carrying different weights, respectively, in transducing glutamate- and BDNF-induced enhancements of axonal translation. Thus, our results indicate that exposure to transient increases of glutamate and more lasting increases of BDNF would stimulate local protein synthesis in migrating axons en route to their targets in the developing brain. PMID:26134564

  17. Restoring Light Sensitivity in Blind Retinae Using a Photochromic AMPA Receptor Agonist

    PubMed Central

    2015-01-01

    Retinal degenerative diseases can have many possible causes and are currently difficult to treat. As an alternative to therapies that require genetic manipulation or the implantation of electronic devices, photopharmacology has emerged as a viable approach to restore visual responses. Here, we present a new photopharmacological strategy that relies on a photoswitchable excitatory amino acid, ATA. This freely diffusible molecule selectively activates AMPA receptors in a light-dependent fashion. It primarily acts on amacrine and retinal ganglion cells, although a minor effect on bipolar cells has been observed. As such, it complements previous pharmacological approaches based on photochromic channel blockers and increases the potential of photopharmacology in vision restoration. PMID:26495755

  18. Activity Level-Dependent Synapse-Specific AMPA Receptor Trafficking Regulates Transmission Kinetics

    PubMed Central

    Zhu, J. Julius

    2009-01-01

    Central glutamatergic synapses may express AMPA-sensitive glutamate receptors (AMPA-Rs) with distinct gating properties and exhibit different transmission dynamics, which are important for computing various synaptic inputs received at different populations of synapses. However, how glutamatergic synapses acquire AMPA-Rs with distinct kinetics to influence synaptic integration remains poorly understood. Here I report synapse-specific trafficking of distinct AMPA-Rs in rat cortical layer 4 stellate and layer 5 pyramidal neurons. The analysis indicates that in single layer 4 stellate neurons thalamocortical synapses generate faster synaptic responses than intracortical synapses. Moreover, GluR1-containing AMPA-Rs traffic selectively into intracortical synapses, and this process requires sensory experience-dependent activity and slows down transmission kinetics. GluR4-containing AMPA-Rs traffic more heavily into thalamocortical synapses than intracortical synapses, and this process requires spontaneous synaptic activity and speeds up transmission kinetics. GluR2-containing AMPA-Rs traffic equally into both thalamocortical and intracortical synapses, and this process requires no synaptic activity and resets transmission kinetics. Notably, synaptic trafficking of distinct AMPA-Rs differentially regulates synaptic integration. Thus, synapse-specific AMPA-R trafficking coarsely sets and synaptic activity finely tunes transmission kinetics and integration properties at different synapses in central neurons. PMID:19439609

  19. A eukaryotic specific transmembrane segment is required for tetramerization in AMPA receptors.

    PubMed

    Salussolia, Catherine L; Gan, Quan; Kazi, Rashek; Singh, Puja; Allopenna, Janet; Furukawa, Hiro; Wollmuth, Lonnie P

    2013-06-01

    Most fast excitatory synaptic transmission in the nervous system is mediated by glutamate acting through ionotropic glutamate receptors (iGluRs). iGluRs (AMPA, kainate, and NMDA receptor subtypes) are tetrameric assemblies, formed as a dimer of dimers. Still, the mechanism underlying tetramerization--the necessary step for the formation of functional receptors that can be inserted into the plasma membrane--is unknown. All eukaryotic compared to prokaryotic iGluR subunits have an additional transmembrane segment, the M4 segment, which positions the physiologically critical C-terminal domain on the cytoplasmic side of the membrane. AMPA receptor (AMPAR) subunits lacking M4 do not express on the plasma membrane. Here, we show that these constructs are retained in the endoplasmic reticulum, the major cellular compartment mediating protein oligomerization. Using approaches to assay the native oligomeric state of AMPAR subunits, we find that subunits lacking M4 or containing single amino acid substitutions along an "interacting" face of the M4 helix that block surface expression no longer tetramerize in either homomeric or heteromeric assemblies. In contrast, subunit dimerization appears to be largely intact. These experiments define the M4 segment as a unique functional unit in AMPARs that is required for the critical dimer-to-tetramer transition. PMID:23739980

  20. Structure and organization of heteromeric AMPA-type glutamate receptors.

    PubMed

    Herguedas, Beatriz; García-Nafría, Javier; Cais, Ondrej; Fernández-Leiro, Rafael; Krieger, James; Ho, Hinze; Greger, Ingo H

    2016-04-29

    AMPA-type glutamate receptors (AMPARs), which are central mediators of rapid neurotransmission and synaptic plasticity, predominantly exist as heteromers of the subunits GluA1 to GluA4. Here we report the first AMPAR heteromer structures, which deviate substantially from existing GluA2 homomer structures. Crystal structures of the GluA2/3 and GluA2/4 N-terminal domains reveal a novel compact conformation with an alternating arrangement of the four subunits around a central axis. This organization is confirmed by cysteine cross-linking in full-length receptors, and it permitted us to determine the structure of an intact GluA2/3 receptor by cryogenic electron microscopy. Two models in the ligand-free state, at resolutions of 8.25 and 10.3 angstroms, exhibit substantial vertical compression and close associations between domain layers, reminiscent of N-methyl-D-aspartate receptors. Model 1 resembles a resting state and model 2 a desensitized state, thus providing snapshots of gating transitions in the nominal absence of ligand. Our data reveal organizational features of heteromeric AMPARs and provide a framework to decipher AMPAR architecture and signaling. PMID:26966189

  1. Cyclin Y inhibits plasticity-induced AMPA receptor exocytosis and LTP

    PubMed Central

    Cho, Eunsil; Kim, Dong-Hyun; Hur, Young-Na; Whitcomb, Daniel J.; Regan, Philip; Hong, Jung-Hwa; Kim, Hanna; Ho Suh, Young; Cho, Kwangwook; Park, Mikyoung

    2015-01-01

    Cyclin Y (CCNY) is a member of the cyclin protein family, known to regulate cell division in proliferating cells. Interestingly, CCNY is expressed in neurons that do not undergo cell division. Here, we report that CCNY negatively regulates long-term potentiation (LTP) of synaptic strength through inhibition of AMPA receptor trafficking. CCNY is enriched in postsynaptic fractions from rat forebrain and is localized adjacent to postsynaptic sites in dendritic spines in rat hippocampal neurons. Using live-cell imaging of a pH-sensitive AMPA receptor, we found that during LTP-inducing stimulation, CCNY inhibits AMPA receptor exocytosis in dendritic spines. Furthermore, CCNY abolishes LTP in hippocampal slices. Taken together, our findings demonstrate that CCNY inhibits plasticity-induced AMPA receptor delivery to synapses and thereby blocks LTP, identifying a novel function for CCNY in post-mitotic cells. PMID:26220330

  2. Synaptic activity regulates AMPA receptor trafficking through different recycling pathways.

    PubMed

    Zheng, Ning; Jeyifous, Okunola; Munro, Charlotte; Montgomery, Johanna M; Green, William N

    2015-01-01

    Changes in glutamatergic synaptic strength in brain are dependent on AMPA-type glutamate receptor (AMPAR) recycling, which is assumed to occur through a single local pathway. In this study, we present evidence that AMPAR recycling occurs through different pathways regulated by synaptic activity. Without synaptic stimulation, most AMPARs recycled in dynamin-independent endosomes containing the GTPase, Arf6. Few AMPARs recycled in dynamin-dependent endosomes labeled by transferrin receptors (TfRs). AMPAR recycling was blocked by alterations in the GTPase, TC10, which co-localized with Arf6 endosomes. TC10 mutants that reduced AMPAR recycling had no effect on increased AMPAR levels with long-term potentiation (LTP) and little effect on decreased AMPAR levels with long-term depression. However, internalized AMPAR levels in TfR-containing recycling endosomes increased after LTP, indicating increased AMPAR recycling through the dynamin-dependent pathway with synaptic plasticity. LTP-induced AMPAR endocytosis is inconsistent with local recycling as a source of increased surface receptors, suggesting AMPARs are trafficked from other sites. PMID:25970033

  3. DCP-LA stimulates AMPA receptor exocytosis through CaMKII activation due to PP-1 inhibition.

    PubMed

    Kanno, Takeshi; Yaguchi, Takahiro; Nagata, Tetsu; Tanaka, Akito; Nishizaki, Tomoyuki

    2009-10-01

    The linoleic acid derivative 8-[2-(2-pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA) activated Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) by inhibiting protein phosphatase-1 (PP-1). DCP-LA induced a transient huge facilitation of synaptic transmission monitored from the CA1 region of rat hippocampal slices, which was largely inhibited by the CaMKII inhibitor KN-93. DCP-LA potentiated kainate-evoked whole-cell membrane currents for Xenopus oocytes expressing alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors composed of the GluR1, GluR3, GluR1/GluR2, GluR1/GluR3, and GluR1/GluR2/GluR3 subunits, and the potentiation was significantly inhibited by KN-93. A similar potentiation was still found with mutant GluR1 (S831A) receptor lacking CaMKII phosphorylation site. The GluR1 and GluR2 subunits formed AMPA receptors in the rat hippocampus, and DCP-LA increased expression of both the subunits on the plasma membrane. The DCP-LA action was blocked by KN-93 and the exocytosis inhibitor botulinum toxin type A, but not by the endocytosis inhibitor phenylarsine oxide. DCP-LA, thus, appears to activate CaMKII through PP-1 inhibition, that stimulates AMPA receptor exocytosis to increase expression of the receptors on the plasma membrane, responsible for potentiate AMPA receptor responses and facilitation of hippocampal synaptic transmission. PMID:19492412

  4. PACSIN1 regulates the dynamics of AMPA receptor trafficking.

    PubMed

    Widagdo, Jocelyn; Fang, Huaqiang; Jang, Se Eun; Anggono, Victor

    2016-01-01

    Dynamic trafficking of AMPA receptors (AMPARs) into and out of synapses plays an important role in synaptic plasticity. We previously reported that the protein kinase C and casein kinase II substrate in neurons (PACSIN) forms a complex with AMPARs through its interaction with the protein interacting with C-kinase 1 (PICK1) to regulate NMDA receptor (NMDAR)-induced AMPAR endocytosis and cerebellar long-term depression. However, the molecular mechanism by which PACSIN regulates the dynamics of AMPAR trafficking remains unclear. Using a pH-sensitive green fluorescent protein, pHluorin, tagged to the extracellular domain of the GluA2 subunit of AMPARs, we demonstrate dual roles for PACSIN1 in controlling the internalization and recycling of GluA2 after NMDAR activation. Structure and function analysis reveals a requirement for the PACSIN1 F-BAR and SH3 domains in controlling these NMDAR-dependent processes. Interestingly, the variable region, which binds to PICK1, is not essential for NMDAR-dependent GluA2 internalization and is required only for the correct recycling of AMPARs. These results indicate that PACSIN is a versatile membrane deformation protein that links the endocytic and recycling machineries essential for dynamic AMPAR trafficking in neurons. PMID:27488904

  5. PACSIN1 regulates the dynamics of AMPA receptor trafficking

    PubMed Central

    Widagdo, Jocelyn; Fang, Huaqiang; Jang, Se Eun; Anggono, Victor

    2016-01-01

    Dynamic trafficking of AMPA receptors (AMPARs) into and out of synapses plays an important role in synaptic plasticity. We previously reported that the protein kinase C and casein kinase II substrate in neurons (PACSIN) forms a complex with AMPARs through its interaction with the protein interacting with C-kinase 1 (PICK1) to regulate NMDA receptor (NMDAR)-induced AMPAR endocytosis and cerebellar long-term depression. However, the molecular mechanism by which PACSIN regulates the dynamics of AMPAR trafficking remains unclear. Using a pH-sensitive green fluorescent protein, pHluorin, tagged to the extracellular domain of the GluA2 subunit of AMPARs, we demonstrate dual roles for PACSIN1 in controlling the internalization and recycling of GluA2 after NMDAR activation. Structure and function analysis reveals a requirement for the PACSIN1 F-BAR and SH3 domains in controlling these NMDAR-dependent processes. Interestingly, the variable region, which binds to PICK1, is not essential for NMDAR-dependent GluA2 internalization and is required only for the correct recycling of AMPARs. These results indicate that PACSIN is a versatile membrane deformation protein that links the endocytic and recycling machineries essential for dynamic AMPAR trafficking in neurons. PMID:27488904

  6. Redefining the classification of AMPA-selective ionotropic glutamate receptors

    PubMed Central

    Bowie, Derek

    2012-01-01

    Abstract AMPA-type ionotropic glutamate receptors (iGluRs) represent the major excitatory neurotransmitter receptor in the developing and adult vertebrate CNS. They are crucial for the normal hardwiring of glutamatergic circuits but also fine tune synaptic strength by cycling into and out of synapses during periods of sustained patterned activity or altered homeostasis. AMPARs are grouped into two functionally distinct tetrameric assemblies based on the inclusion or exclusion of the GluA2 receptor subunit. GluA2-containing receptors are thought to be the most abundant AMPAR in the CNS, typified by their small unitary events, Ca2+ impermeability and insensitivity to polyamine block. In contrast, GluA2-lacking AMPARs exhibit large unitary conductance, marked divalent permeability and nano- to micromolar polyamine affinity. Here, I review evidence for the existence of a third class of AMPAR which, though similarly Ca2+ permeable, is characterized by its near-insensitivity to internal and external channel block by polyamines. This novel class of AMPAR is most notably found at multivesicular release synapses found in the avian auditory brainstem and mammalian retina. Curiously, these synapses lack NMDA-type iGluRs, which are conventionally associated with controlling AMPAR insertion. The lack of NMDARs suggests that a different set of rules may govern AMPAR cycling at these synapses. AMPARs with similar functional profiles are also found on some glial cells suggesting they may have a more widespread distribution in the mammalian CNS. I conclude by noting that modest changes to the ion-permeation pathway might be sufficient to retain divalent permeability whilst eliminating polyamine sensitivity. Consequently, this emerging AMPAR subclass need not be assembled from novel subunits, yet to be cloned, but could simply occur by varying the stoichiometry of existing proteins. PMID:22106175

  7. Post-anesthesia AMPA receptor potentiation prevents anesthesia-induced learning and synaptic deficits.

    PubMed

    Huang, Lianyan; Cichon, Joseph; Ninan, Ipe; Yang, Guang

    2016-06-22

    Accumulating evidence has shown that repeated exposure to general anesthesia during critical stages of brain development results in long-lasting behavioral deficits later in life. To date, there has been no effective treatment to mitigate the neurotoxic effects of anesthesia on brain development. By performing calcium imaging in the mouse motor cortex, we show that ketamine anesthesia causes a marked and prolonged reduction in neuronal activity during the period of post-anesthesia recovery. Administration of the AMPAkine drug CX546 [1-(1,4-benzodioxan-6-ylcarbonyl)piperidine] to potentiate AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor activity during emergence from anesthesia in mice enhances neuronal activity and prevents long-term motor learning deficits induced by repeated neonatal anesthesia. In addition, we show that CX546 administration also ameliorates various synaptic deficits induced by anesthesia, including reductions in synaptic expression of NMDA (N-methyl-d-aspartate) and AMPA receptor subunits, motor training-evoked neuronal activity, and dendritic spine remodeling associated with motor learning. Together, our results indicate that pharmacologically enhancing neuronal activity during the post-anesthesia recovery period could effectively reduce the adverse effects of early-life anesthesia. PMID:27334260

  8. GSG1L suppresses AMPA receptor-mediated synaptic transmission and uniquely modulates AMPA receptor kinetics in hippocampal neurons

    PubMed Central

    Gu, Xinglong; Mao, Xia; Lussier, Marc P.; Hutchison, Mary Anne; Zhou, Liang; Hamra, F. Kent; Roche, Katherine W.; Lu, Wei

    2016-01-01

    Regulation of AMPA receptor (AMPAR)-mediated synaptic transmission is a key mechanism for synaptic plasticity. In the brain, AMPARs assemble with a number of auxiliary subunits, including TARPs, CNIHs and CKAMP44, which are important for AMPAR forward trafficking to synapses. Here we report that the membrane protein GSG1L negatively regulates AMPAR-mediated synaptic transmission. Overexpression of GSG1L strongly suppresses, and GSG1L knockout (KO) enhances, AMPAR-mediated synaptic transmission. GSG1L-dependent regulation of AMPAR synaptic transmission relies on the first extracellular loop domain and its carboxyl-terminus. GSG1L also speeds up AMPAR deactivation and desensitization in hippocampal CA1 neurons, in contrast to the effects of TARPs and CNIHs. Furthermore, GSG1L association with AMPARs inhibits CNIH2-induced slowing of the receptors in heterologous cells. Finally, GSG1L KO rats have deficits in LTP and show behavioural abnormalities in object recognition tests. These data demonstrate that GSG1L represents a new class of auxiliary subunit with distinct functional properties for AMPARs. PMID:26932439

  9. Mechanisms for Antagonistic Regulation of AMPA and NMDA-D1 Receptor Complexes at Postsynaptic Sites

    NASA Technical Reports Server (NTRS)

    Schumann, Johann; Scheler, Gabriele

    2004-01-01

    From the analysis of these pathways we conclude that postsynaptic processes that regulate synaptic transmission undergo significant cross-talk with respect to glutamatergic and neuromodulatory (dopamine) signals. The main hypothesis is that of a compensatory regulation, a competitive switch between the induction of increased AMPA conductance by CaMKII-dependent phosphorylation and reduced expression of PP2A, and increased D1 receptor sensitivity and expression by increased PKA, PP2A and decreased PP-1/calcineurin expression. Both types of plasticity are induced by NMDA receptor activation and increased internal calcium, they require different internal conditions to become expressed. Specifically we propose that AMPA regulation and D1 regulation are inversely coupled;The net result may be a bifurcation of synaptic state into predominantly AMPA or NMDA-D1 synapses. This could have functional consequences: stable connections for AMPA and conditional gating for NMDA-D1 synapses.

  10. Actin-dependent mechanisms in AMPA receptor trafficking

    PubMed Central

    Hanley, Jonathan G.

    2014-01-01

    The precise regulation of AMPA receptor (AMPAR) number and subtype at the synapse is crucial for the regulation of excitatory neurotransmission, synaptic plasticity and the consequent formation of appropriate neural circuits for learning and memory. AMPAR trafficking involves the dynamic processes of exocytosis, endocytosis and endosomal recycling, all of which involve the actin cytoskeleton. The actin cytoskeleton is highly dynamic and highly regulated by an abundance of actin-binding proteins and upstream signaling pathways that modulate actin polymerization and depolymerization. Actin dynamics generate forces that manipulate membranes in the process of vesicle biogenesis, and also for propelling vesicles through the cytoplasm to reach their destination. In addition, trafficking mechanisms exploit more stable aspects of the actin cytoskeleton by using actin-based motor proteins to traffic vesicular cargo along actin filaments. Numerous studies have shown that actin dynamics are critical for AMPAR localization and function. The identification of actin-binding proteins that physically interact with AMPAR subunits, and research into their mode of action is starting to shed light on the mechanisms involved. Such proteins either regulate actin dynamics to modulate mechanical forces exerted on AMPAR-containing membranes, or associate with actin filaments to target or transport AMPAR-containing vesicles to specific subcellular regions. In addition, actin-regulatory proteins that do not physically interact with AMPARs may influence AMPAR trafficking by regulating the local actin environment in the dendritic spine. PMID:25429259

  11. Unified quantitative model of AMPA receptor trafficking at synapses

    PubMed Central

    Czöndör, Katalin; Mondin, Magali; Garcia, Mikael; Heine, Martin; Frischknecht, Renato; Choquet, Daniel; Sibarita, Jean-Baptiste; Thoumine, Olivier R.

    2012-01-01

    Trafficking of AMPA receptors (AMPARs) plays a key role in synaptic transmission. However, a general framework integrating the two major mechanisms regulating AMPAR delivery at postsynapses (i.e., surface diffusion and internal recycling) is lacking. To this aim, we built a model based on numerical trajectories of individual AMPARs, including free diffusion in the extrasynaptic space, confinement in the synapse, and trapping at the postsynaptic density (PSD) through reversible interactions with scaffold proteins. The AMPAR/scaffold kinetic rates were adjusted by comparing computer simulations to single-particle tracking and fluorescence recovery after photobleaching experiments in primary neurons, in different conditions of synapse density and maturation. The model predicts that the steady-state AMPAR number at synapses is bidirectionally controlled by AMPAR/scaffold binding affinity and PSD size. To reveal the impact of recycling processes in basal conditions and upon synaptic potentiation or depression, spatially and temporally defined exocytic and endocytic events were introduced. The model predicts that local recycling of AMPARs close to the PSD, coupled to short-range surface diffusion, provides rapid control of AMPAR number at synapses. In contrast, because of long-range diffusion limitations, extrasynaptic recycling is intrinsically slower and less synapse-specific. Thus, by discriminating the relative contributions of AMPAR diffusion, trapping, and recycling events on spatial and temporal bases, this model provides unique insights on the dynamic regulation of synaptic strength. PMID:22331885

  12. Contextual learning requires synaptic AMPA receptor delivery in the hippocampus

    PubMed Central

    Mitsushima, Dai; Ishihara, Kouji; Sano, Akane; Kessels, Helmut W.; Takahashi, Takuya

    2011-01-01

    The hippocampus plays a central role in learning and memory. Although synaptic delivery of AMPA-type glutamate receptors (AMPARs) contributes to experience-dependent synaptic strengthening, its role in hippocampus-dependent learning remains elusive. By combining viral-mediated in vivo gene delivery with in vitro patch-clamp recordings, we found that the inhibitory avoidance task, a hippocampus-dependent contextual fear-learning paradigm, delivered GluR1-containing AMPARs into CA3-CA1 synapses of the dorsal hippocampus. To block the synaptic delivery of endogenous AMPARs, we expressed a fragment of the GluR1-cytoplasmic tail (the 14-aa GluR1 membrane-proximal region with two serines mutated to phospho-mimicking aspartates: MPR-DD). MPR-DD prevented learning-driven synaptic AMPAR delivery in CA1 neurons. Bilateral expression of MPR-DD in the CA1 region of the rat impaired inhibitory avoidance learning, indicating that synaptic GluR1 trafficking in the CA1 region of the hippocampus is required for encoding contextual fear memories. The fraction of CA1 neurons that underwent synaptic strengthening positively correlated with the performance in the inhibitory avoidance fear memory task. These data suggest that the robustness of a contextual memory depends on the number of hippocampal neurons that participate in the encoding of a memory trace. PMID:21746893

  13. AMPA receptor regulation during synaptic plasticity in hippocampus and neocortex

    PubMed Central

    Lee, Hey-Kyoung; Kirkwood, Alfredo

    2011-01-01

    Discovery of long-term potentiation (LTP) in the dentate gyrus of the rabbit hippocampus by Bliss and Lømo opened up a whole new field to study activity-dependent long-term synaptic modifications in the brain. Since then hippocampal synapses have been a key model system to study the mechanisms of different forms of synaptic plasticity. At least for the postsynaptic forms of LTP and long-term depression (LTD), regulation of AMPA receptors (AMPARs) has emerged as a key mechanism. While many of the synaptic plasticity mechanisms uncovered in at the hippocampal synapses apply to synapses across diverse brain regions, there are differences in the mechanisms that often reveal the specific functional requirements of the brain area under study. Here we will review AMPAR regulation underlying synaptic plasticity in hippocampus and neocortex. The main focus of this review will be placed on postsynaptic forms of synaptic plasticity that impinge on the regulation of AMPARs using hippocampal CA1 and primary sensory cortices as examples. And through the comparison, we will highlight the key similarities and functional differences between the two synapses. PMID:21856433

  14. Cornichons modify channel properties of recombinant and glial AMPA receptors

    PubMed Central

    Coombs, Ian D.; Soto, David; Zonouzi, Marzieh; Renzi, Massimiliano; Shelley, Chris; Farrant, Mark; Cull-Candy, Stuart G.

    2012-01-01

    Ionotropic glutamate receptors, which underlie a majority of excitatory synaptic transmission in the CNS, associate with transmembrane proteins that modify their intracellular trafficking and channel gating. For AMPA-type glutamate receptors (AMPARs), significant advances have been made in our understanding of their regulation by transmembrane AMPAR regulatory proteins (TARPs). Less is known about the functional influence of cornichons – unrelated AMPAR-interacting proteins, identified by proteomic analysis. Here we confirm that cornichon homologs 2 and 3 (CNIH-2 and CNIH-3), but not CNIH-1, slow the deactivation and desensitization of both GluA2-containing calcium-impermeable (CI-) and GluA2-lacking calcium-permeable (CP-) AMPARs expressed in tsA201 cells. CNIH-2 and -3 also enhanced the glutamate sensitivity, single-channel conductance and calcium permeability of CP-AMPARs, while decreasing their block by intracellular polyamines. We examined the potential effects of CNIHs on native AMPARs by recording from rat optic nerve oligodendrocyte precursor cells (OPCs), known to express a significant population of CP-AMPARs. These glial cells exhibited surface labelling with an anti-CNIH-2/3 antibody. Two features of their AMPAR-mediated currents – the relative efficacy of the partial agonist kainate (IKA/IGlu ratio 0.4), and a greater than five-fold potentiation of kainate responses by cyclothiazide – suggest AMPAR association with CNIHs. Additionally, overexpression of CNIH-3 in OPCs markedly slowed AMPAR desensitization. Together, our experiments support the view that CNIHs are capable of altering key properties of AMPARs and suggest that they may do so in glia. PMID:22815494

  15. AMPA receptor-mediated alterations of intracellular calcium homeostasis in rat cerebellar Purkinje cells in vitro: correlates to dark cell degeneration.

    PubMed

    Strahlendorf, J C; Brandon, T; Miles, R; Strahlendorf, H K

    1998-11-01

    In the rat cerebellar slice preparation in vitro, excessive DL-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA)-receptor activation elicits a characteristic type of excitotoxicity of Purkinje cells (PCs) known as dark cell degeneration (DCD). DCD models neurotoxicity of PCs and hippocampal pyramidal neurons in vivo following hyperexcitable states. The intent of this study was to: a) determine whether AMPA-induced neurotoxicity of PCs is correlated with temporally and spatially restricted rises in intracellular Ca2+ and b) whether GYKI 52466 and nominal external Ca2+, conditions that reduced expression of AMPA-elicited DCD, altered the induced Ca2+ patterns. Employing the Ca2+-sensitive dye Fluo-3 and a confocal laser scanning microscope, we evaluated changes in intracellular Ca2+ within PCs in a cerebellar slice preparation. AMPA application alone (30 microM for 30 min) caused a significant initial rise in perinuclear and cytoplasmic Ca2+ that returned to control levels during the latter part of the AMPA exposure period. Following removal of AMPA (expression period), perinuclear and cytoplasmic Ca2+ displayed a significant delayed rise peaking transiently 60 min after AMPA removal. The efficacy of GYKI 52466 and nominal external Ca2+ conditions to attenuate AMPA-induced DCD was correlated to reductions in AMPA-induced transient elevations in perinuclear and cytoplasmic Ca2+ levels during the expression phase and to a lesser extent during the exposure period. The present data suggest that during the expression phase, the delayed perinuclear and cytoplasmic Ca2+ transient may be the harbinger of impending loss of Ca2+ homeostasis and cell damage. PMID:9814545

  16. Neuroprotective and anticonvulsant effects of EGIS-8332, a non-competitive AMPA receptor antagonist, in a range of animal models

    PubMed Central

    Gigler, G; Móricz, K; ágoston, M; Simó, A; Albert, M; Benedek, A; Kapus, G; Kertész, S; Vegh, M; Barkóczy, J; Markó, B; Szabó, G; Matucz, É; Gacsályi, I; Lévay, G; Hársing, L G; Szénási, G

    2007-01-01

    Background and purpose: Blockade of AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors is a good treatment option for a variety of central nervous system disorders. The present study evaluated the neuroprotective and anticonvulsant effects of EGIS-8332, a non-competitive AMPA receptor antagonist, as a potential drug candidate. Experimental approach: AMPA antagonist effects of EGIS-8332 were measured using patch-clamp techniques. Neuroprotective and anticonvulsant effects of EGIS-8332 were evaluated in various experimental models, relative to those of GYKI 53405. Key results: EGIS-8332 inhibited AMPA currents in rat cerebellar Purkinje cells and inhibited the AMPA- and quisqualate-induced excitotoxicity in primary cultures of telencephalon neurons (IC50=5.1-9.0 μM), in vitro. Good anticonvulsant actions were obtained in maximal electroshock-, sound- and chemically-induced seizures (range of ED50=1.4-14.0 mg kg−1 i.p.) in mice. Four days after transient global cerebral ischaemia, EGIS-8332 decreased neuronal loss in the hippocampal CA1 area in gerbils and rats. EGIS-8332 dose-dependently reduced cerebral infarct size after permanent middle cerebral artery occlusion in mice and rats (minimum effective dose=3 mg kg−1 i.p.). Side effects of EGIS-8332 emerged much above its pharmacologically active doses. A tendency for better efficacy of GYKI 53405 than that of EGIS-8332 was observed in anticonvulsant tests that reached statistical significance in few cases, while the contrary was perceived in cerebral ischaemia tests. Conclusions and implications: EGIS-8332 seems suitable for further development for the treatment of epilepsy, ischaemia and stroke based on its efficacy in a variety of experimental disease models, and on its low side effect potential. PMID:17603549

  17. AMPA receptor signaling through BRAG2 and Arf6 critical for long-term synaptic depression.

    PubMed

    Scholz, Ralf; Berberich, Sven; Rathgeber, Louisa; Kolleker, Alexander; Köhr, Georg; Kornau, Hans-Christian

    2010-06-10

    Central nervous system synapses undergo activity-dependent alterations to support learning and memory. Long-term depression (LTD) reflects a sustained reduction of the synaptic AMPA receptor content based on targeted clathrin-mediated endocytosis. Here we report a current-independent form of AMPA receptor signaling, fundamental for LTD. We found that AMPA receptors directly interact via the GluA2 subunit with the synaptic protein BRAG2, which functions as a guanine-nucleotide exchange factor (GEF) for the coat-recruitment GTPase Arf6. BRAG2-mediated catalysis, controlled by ligand-binding and tyrosine phosphorylation of GluA2, activates Arf6 to internalize synaptic AMPA receptors upon LTD induction. Furthermore, acute blockade of the GluA2-BRAG2 interaction and targeted deletion of BRAG2 in mature hippocampal CA1 pyramidal neurons prevents LTD in CA3-to-CA1 cell synapses, irrespective of the induction pathway. We conclude that BRAG2-mediated Arf6 activation triggered by AMPA receptors is the convergent step of different forms of LTD, thus providing an essential mechanism for the control of vesicle formation by endocytic cargo. PMID:20547133

  18. Pathogenic mechanism of an autism-associated neuroligin mutation involves altered AMPA-receptor trafficking.

    PubMed

    Chanda, S; Aoto, J; Lee, S-J; Wernig, M; Südhof, T C

    2016-02-01

    Neuroligins are postsynaptic cell-adhesion molecules that bind to presynaptic neurexins. Although the general synaptic role of neuroligins is undisputed, their specific functions at a synapse remain unclear, even controversial. Moreover, many neuroligin gene mutations were associated with autism, but the pathophysiological relevance of these mutations is often unknown, and their mechanisms of action uninvestigated. Here, we examine the synaptic effects of an autism-associated neuroligin-4 substitution (called R704C), which mutates a cytoplasmic arginine residue that is conserved in all neuroligins. We show that the R704C mutation, when introduced into neuroligin-3, enhances the interaction between neuroligin-3 and AMPA receptors, increases AMPA-receptor internalization and decreases postsynaptic AMPA-receptor levels. When introduced into neuroligin-4, conversely, the R704C mutation unexpectedly elevated AMPA-receptor-mediated synaptic responses. These results suggest a general functional link between neuroligins and AMPA receptors, indicate that both neuroligin-3 and -4 act at excitatory synapses but perform surprisingly distinct functions, and demonstrate that the R704C mutation significantly impairs the normal function of neuroligin-4, thereby validating its pathogenicity. PMID:25778475

  19. Stargazin regulates AMPA receptor trafficking through adaptor protein complexes during long-term depression

    NASA Astrophysics Data System (ADS)

    Matsuda, Shinji; Kakegawa, Wataru; Budisantoso, Timotheus; Nomura, Toshihiro; Kohda, Kazuhisa; Yuzaki, Michisuke

    2013-11-01

    Long-term depression (LTD) underlies learning and memory in various brain regions. Although postsynaptic AMPA receptor trafficking mediates LTD, its underlying molecular mechanisms remain largely unclear. Here we show that stargazin, a transmembrane AMPA receptor regulatory protein, forms a ternary complex with adaptor proteins AP-2 and AP-3A in hippocampal neurons, depending on its phosphorylation state. Inhibiting the stargazin-AP-2 interaction disrupts NMDA-induced AMPA receptor endocytosis, and inhibiting that of stargazin-AP-3A abrogates the late endosomal/lysosomal trafficking of AMPA receptors, thereby upregulating receptor recycling to the cell surface. Similarly, stargazin’s interaction with AP-2 or AP-3A is necessary for low-frequency stimulus-evoked LTD in CA1 hippocampal neurons. Thus, stargazin has a crucial role in NMDA-dependent LTD by regulating two trafficking pathways of AMPA receptors—transport from the cell surface to early endosomes and from early endosomes to late endosomes/lysosomes—through its sequential binding to AP-2 and AP-3A.

  20. AMPA receptor trafficking in inflammation-induced dorsal horn central sensitization

    PubMed Central

    Tao, Yuan-Xiang

    2012-01-01

    Activity-dependent postsynaptic receptor trafficking is critical for long-term synaptic plasticity in brain, but it is unclear whether this mechanism actually mediates spinal cord dorsal horn central sensitization (a specific form of synaptic plasticity) that is associated with persistent pain. Recent studies have shown that peripheral inflammation drives changes in AMPA receptor subunit trafficking in dorsal horn and that such changes contribute to the hypersensitivity that underlies persistent pain. Here, we review current evidence to illustrate how spinal cord AMPA receptors participate in dorsal horn central sensitization associated with persistent pain. Understanding these mechanisms may allow development of novel therapeutic strategies for treating persistent pain. PMID:22466122

  1. mTOR Is Essential for Corticosteroid Effects on Hippocampal AMPA Receptor Function and Fear Memory

    ERIC Educational Resources Information Center

    Xiong, Hui; Casse, Frédéric; Zhou, Yang; Zhou, Ming; Xiong, Zhi-Qi; Joëls, Marian; Martin, Stéphane; Krugers, Harm J.

    2015-01-01

    Glucocorticoid hormones, via activation of their receptors, promote memory consolidation, but the exact underlying mechanisms remain elusive. We examined how corticosterone regulates AMPA receptors (AMPARs), which are crucial for synaptic plasticity and memory formation. Combining a live imaging fluorescent recovery after photobleaching approach…

  2. X-ray structure, symmetry and mechanism of an AMPA-subtype glutamate receptor

    SciTech Connect

    Sobolevsky, Alexander I.; Rosconi, Michael P.; Gouaux, Eric

    2010-02-02

    Ionotropic glutamate receptors mediate most excitatory neurotransmission in the central nervous system and function by opening a transmembrane ion channel upon binding of glutamate. Despite their crucial role in neurobiology, the architecture and atomic structure of an intact ionotropic glutamate receptor are unknown. Here we report the crystal structure of the {alpha}-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-sensitive, homotetrameric, rat GluA2 receptor at 3.6 {angstrom} resolution in complex with a competitive antagonist. The receptor harbours an overall axis of two-fold symmetry with the extracellular domains organized as pairs of local dimers and with the ion channel domain exhibiting four-fold symmetry. A symmetry mismatch between the extracellular and ion channel domains is mediated by two pairs of conformationally distinct subunits, A/C and B/D. Therefore, the stereochemical manner in which the A/C subunits are coupled to the ion channel gate is different from the B/D subunits. Guided by the GluA2 structure and site-directed cysteine mutagenesis, we suggest that GluN1 and GluN2A NMDA (N-methyl-D-aspartate) receptors have a similar architecture, with subunits arranged in a 1-2-1-2 pattern. We exploit the GluA2 structure to develop mechanisms of ion channel activation, desensitization and inhibition by non-competitive antagonists and pore blockers.

  3. Enhanced AMPA receptor activity increases operant alcohol self-administration and cue-induced reinstatement.

    PubMed

    Cannady, Reginald; Fisher, Kristen R; Durant, Brandon; Besheer, Joyce; Hodge, Clyde W

    2013-01-01

    Long-term alcohol exposure produces neuroadaptations that contribute to the progression of alcohol abuse disorders. Chronic alcohol consumption results in strengthened excitatory neurotransmission and increased α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPA) receptor signaling in animal models. However, the mechanistic role of enhanced AMPA receptor activity in alcohol-reinforcement and alcohol-seeking behavior remains unclear. This study examined the role of enhanced AMPA receptor function using the selective positive allosteric modulator, aniracetam, in modulating operant alcohol self-administration and cue-induced reinstatement. Male alcohol-preferring (P-) rats, trained to self-administer alcohol (15%, v/v) versus water were pre-treated with aniracetam to assess effects on maintenance of alcohol self-administration. To determine reinforcer specificity, P-rats were trained to self-administer sucrose (0.8%, w/v) versus water, and effects of aniracetam were tested. The role of aniracetam in modulating relapse of alcohol-seeking was assessed using a response contingent cue-induced reinstatement procedure in P-rats trained to self-administer 15% alcohol. Aniracetam pre-treatment significantly increased alcohol-reinforced responses relative to vehicle treatment. This increase was not attributed to aniracetam-induced hyperactivity as aniracetam pre-treatment did not alter locomotor activity. AMPA receptor involvement was confirmed because 6,7-dinitroquinoxaline-2,3-dione (AMPA receptor antagonist) blocked the aniracetam-induced increase in alcohol self-administration. Aniracetam did not alter sucrose-reinforced responses in sucrose-trained P-rats, suggesting that enhanced AMPA receptor activity is selective in modulating the reinforcing function of alcohol. Finally, aniracetam pre-treatment potentiated cue-induced reinstatement of alcohol-seeking behavior versus vehicle-treated P-rats. These data suggest that enhanced glutamate activity at AMPA

  4. Enhanced AMPA Receptor Function Promotes Cerebellar Long-Term Depression Rather than Potentiation

    ERIC Educational Resources Information Center

    van Beugen, Boeke J.; Qiao, Xin; Simmons, Dana H.; De Zeeuw, Chris I.; Hansel, Christian

    2014-01-01

    Ampakines are allosteric modulators of AMPA receptors that facilitate hippocampal long-term potentiation (LTP) and learning, and have been considered for the treatment of cognition and memory deficits. Here, we show that the ampakine CX546 raises the amplitude and slows the decay time of excitatory postsynaptic currents (EPSCs) at cerebellar…

  5. AMPA Receptor Endocytosis in Rat Perirhinal Cortex Underlies Retrieval of Object Memory

    ERIC Educational Resources Information Center

    Cazakoff, Brittany N.; Howland, John G.

    2011-01-01

    Mechanisms consistent with long-term depression in the perirhinal cortex (PRh) play a fundamental role in object recognition memory; however, whether AMPA receptor endocytosis is involved in distinct phases of recognition memory is not known. To address this question, we used local PRh infusions of the cell membrane-permeable Tat-GluA2[subscript…

  6. Long-term potentiation alters the modulator pharmacology of AMPA-type glutamate receptors.

    PubMed

    Lin, Bin; Brücher, Fernando A; Colgin, Laura Lee; Lynch, Gary

    2002-06-01

    Changes in the biophysical properties of AMPA-type glutamate receptors have been proposed to mediate the expression of long-term potentiation (LTP). The present study tested if, as predicted from this hypothesis, AMPA receptor modulators differentially affect potentiated versus control synaptic currents. Whole cell recordings were collected from CA1 pyramidal neurons in hippocampal slices from adult rats. Within-neuron comparisons were made of the excitatory postsynaptic currents (EPSCs) elicited by two separate groups of Schaffer-collateral/commissural synapses. LTP was induced by theta burst stimulation in one set of inputs; cyclothiazide (CTZ), a drug that acts on the desensitization kinetics of AMPA receptors, was infused 30 min later. The decay time constants of the potentiated EPSCs prior to drug infusion were slightly, but significantly, shorter than those of control EPSCs. CTZ slowed the decay of the EPSCs, as reported in prior studies, and did so to a significantly greater degree in the potentiated synapses. Additionally, infusion of CTZ resulted in significantly greater effects on amplitude in potentiated pathways as compared with control pathways. The interaction between LTP and CTZ was also obtained in a separate set of experiments in which GABA receptor antagonists were used to block inhibitory postsynaptic currents. Additionally, there was no significant change in paired-pulse facilitation in the presence of CTZ, indicating that presynaptic effects of the drug were negligible. These findings provide new evidence that LTP modifies AMPA receptor kinetics. Candidates for the changes responsible for the observed effects of LTP were evaluated using a model of AMPA receptor kinetics; a simple increase in the channel opening rate provided the most satisfactory match with the LTP data. PMID:12037181

  7. The Influence of Synaptic Size on AMPA Receptor Activation: A Monte Carlo Model

    PubMed Central

    Montes, Jesus; Peña, Jose M.; DeFelipe, Javier; Herreras, Oscar; Merchan-Perez, Angel

    2015-01-01

    Physiological and electron microscope studies have shown that synapses are functionally and morphologically heterogeneous and that variations in size of synaptic junctions are related to characteristics such as release probability and density of postsynaptic AMPA receptors. The present article focuses on how these morphological variations impact synaptic transmission. We based our study on Monte Carlo computational simulations of simplified model synapses whose morphological features have been extracted from hundreds of actual synaptic junctions reconstructed by three-dimensional electron microscopy. We have examined the effects that parameters such as synaptic size or density of AMPA receptors have on the number of receptors that open after release of a single synaptic vesicle. Our results indicate that the maximum number of receptors that will open after the release of a single synaptic vesicle may show a ten-fold variation in the whole population of synapses. When individual synapses are considered, there is also a stochastical variability that is maximal in small synapses with low numbers of receptors. The number of postsynaptic receptors and the size of the synaptic junction are the most influential parameters, while the packing density of receptors or the concentration of extrasynaptic transporters have little or no influence on the opening of AMPA receptors. PMID:26107874

  8. The influence of synaptic size on AMPA receptor activation: a Monte Carlo model.

    PubMed

    Montes, Jesus; Peña, Jose M; DeFelipe, Javier; Herreras, Oscar; Merchan-Perez, Angel

    2015-01-01

    Physiological and electron microscope studies have shown that synapses are functionally and morphologically heterogeneous and that variations in size of synaptic junctions are related to characteristics such as release probability and density of postsynaptic AMPA receptors. The present article focuses on how these morphological variations impact synaptic transmission. We based our study on Monte Carlo computational simulations of simplified model synapses whose morphological features have been extracted from hundreds of actual synaptic junctions reconstructed by three-dimensional electron microscopy. We have examined the effects that parameters such as synaptic size or density of AMPA receptors have on the number of receptors that open after release of a single synaptic vesicle. Our results indicate that the maximum number of receptors that will open after the release of a single synaptic vesicle may show a ten-fold variation in the whole population of synapses. When individual synapses are considered, there is also a stochastical variability that is maximal in small synapses with low numbers of receptors. The number of postsynaptic receptors and the size of the synaptic junction are the most influential parameters, while the packing density of receptors or the concentration of extrasynaptic transporters have little or no influence on the opening of AMPA receptors. PMID:26107874

  9. The Sorting Receptor SorCS1 Regulates Trafficking of Neurexin and AMPA Receptors

    PubMed Central

    Savas, Jeffrey N.; Ribeiro, Luís F.; Wierda, Keimpe D.; Wright, Rebecca; DeNardo, Laura A.; Rice, Heather C.; Chamma, Ingrid; Wang, Yi-Zhi; Zemla, Roland; Lavallée-Adam, Mathieu; Vennekens, Kristel M.; O'Sullivan, Matthew L.; Antonios, Joseph K.; Hall, Elizabeth A.; Thoumine, Olivier; Attie, Alan D.; Ghosh, Anirvan; Yates, John R.; de Wit, Joris

    2015-01-01

    The formation, function, and plasticity of synapses require dynamic changes in synaptic receptor composition. Here we identify the sorting receptor SorCS1 as a key regulator of synaptic receptor trafficking. Four independent proteomic analyses identify the synaptic adhesion molecule neurexin and the AMPA glutamate receptor (AMPAR) as major proteins sorted by SorCS1. SorCS1 localizes to early and recycling endosomes and regulates neurexin and AMPAR surface trafficking. Surface proteome analysis of SorCS1-deficient neurons shows decreased surface levels of these, and additional, receptors. Quantitative in vivo analysis of SorCS1 knockout synaptic proteomes identifies SorCS1 as a global trafficking regulator and reveals decreased levels of receptors regulating adhesion and neurotransmission, including neurexins and AMPARs. Consequently, glutamatergic transmission at SorCS1–deficient synapses is reduced due to impaired AMPAR surface expression. SORCS1 mutations have been associated with autism and Alzheimer's disease, suggesting that perturbed receptor trafficking contributes to defects in synaptic composition and function underlying synaptopathies. PMID:26291160

  10. Calcium Binding to PICK1 is Essential for the Intracellular Retention of AMPA Receptors Underlying LTD

    PubMed Central

    Citri, Ami; Bhattacharyya, Samarjit; Ma, Cong; Morishita, Wade; Fang, Scarlett; Rizo, Josep; Malenka, Robert C.

    2010-01-01

    NMDA receptor (NMDAR)-dependent LTD in the hippocampus is mediated primarily by the calcium-dependent removal of AMPA receptors (AMPARs) from the postsynaptic density. The AMPAR-binding, PDZ and BAR domain containing protein PICK1 has been implicated in the regulation of AMPAR trafficking underlying several forms of synaptic plasticity. Using a strategy involving shRNA-mediated knockdown of PICK1 and its replacement with recombinant PICK1, we performed a detailed structure-function analysis of the role of PICK1 in hippocampal synaptic plasticity and the underlying NMDAR-induced AMPAR trafficking. We found that PICK1 is not necessary for maintenance of the basal synaptic complement of AMPARs or expression of either mGluR-LTD or NMDAR-dependent LTP. Rather, PICK1 function is specific to NMDAR-dependent LTD and the underlying AMPAR trafficking. Furthermore, while PICK1 does not regulate the initial phase of NMDAR-induced AMPAR endocytosis, it is required for intracellular retention of internalized AMPARs. Detailed biophysical analysis of an N-terminal acidic motif indicated that it is involved in intramolecular electrostatic interactions that are disrupted by calcium. Mutations that interfered with the calcium-induced structural changes in PICK1 precluded LTD and the underlying NMDAR-induced intracellular retention of AMPARs. These findings support a model whereby calcium-induced modification of PICK1 structure is critical for its function in the retention of internalized AMPARs that underlies the expression of hippocampal NMDAR-dependent LTD. PMID:21147983

  11. Structural rearrangement of the intracellular domains during AMPA receptor activation.

    PubMed

    Zachariassen, Linda G; Katchan, Ljudmila; Jensen, Anna G; Pickering, Darryl S; Plested, Andrew J R; Kristensen, Anders S

    2016-07-01

    α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are ligand-gated ion channels that mediate the majority of fast excitatory neurotransmission in the central nervous system. Despite recent advances in structural studies of AMPARs, information about the specific conformational changes that underlie receptor function is lacking. Here, we used single and dual insertion of GFP variants at various positions in AMPAR subunits to enable measurements of conformational changes using fluorescence resonance energy transfer (FRET) in live cells. We produced dual CFP/YFP-tagged GluA2 subunit constructs that had normal activity and displayed intrareceptor FRET. We used fluorescence lifetime imaging microscopy (FLIM) in live HEK293 cells to determine distinct steady-state FRET efficiencies in the presence of different ligands, suggesting a dynamic picture of the resting state. Patch-clamp fluorometry of the double- and single-insert constructs showed that both the intracellular C-terminal domain (CTD) and the loop region between the M1 and M2 helices move during activation and the CTD is detached from the membrane. Our time-resolved measurements revealed unexpectedly complex fluorescence changes within these intracellular domains, providing clues as to how posttranslational modifications and receptor function interact. PMID:27313205

  12. Differential effects of glyphosate and aminomethylphosphonic acid (AMPA) on photosynthesis and chlorophyll metabolism in willow plants.

    PubMed

    Gomes, Marcelo Pedrosa; Le Manac'h, Sarah Gingras; Maccario, Sophie; Labrecque, Michel; Lucotte, Marc; Juneau, Philippe

    2016-06-01

    We used a willow species (Salix miyabeana cultivar SX64) to examine the differential secondary-effects of glyphosate and aminomethylphosphonic acid (AMPA), the principal glyphosate by-product, on chlorophyll metabolism and photosynthesis. Willow plants were treated with different concentrations of glyphosate (equivalent to 0, 1.4, 2.1 and 2.8kgha(-1)) and AMPA (equivalent to 0, 0.28, 1.4 and 2.8kgha(-1)) and evaluations of pigment contents, chlorophyll fluorescence, and oxidative stress markers (hydrogen peroxide content and antioxidant enzyme activities) in leaves were performed after 12h of exposure. We observed that AMPA and glyphosate trigger different mechanisms leading to decreases in chlorophyll content and photosynthesis rates in willow plants. Both chemicals induced ROS accumulation in willow leaves although only glyphosate-induced oxidative damage through lipid peroxidation. By disturbing chlorophyll biosynthesis, AMPA induced decreases in chlorophyll contents, with consequent effects on photosynthesis. With glyphosate, ROS increases were higher than the ROS-sensitive threshold, provoking chlorophyll degradation (as seen by pheophytin accumulation) and invariable decreases in photosynthesis. Peroxide accumulation in both AMPA and glyphosate-treated plants was due to the inhibition of antioxidant enzyme activities. The different effects of glyphosate on chlorophyll contents and photosynthesis as described in the literature may be due to various glyphosate:AMPA ratios in those plants. PMID:27155486

  13. in Silico investigation of the structural requirements for the AMPA receptor antagonism by quinoxaline derivatives

    PubMed Central

    Azam, Faizul; Abugrain, Ismaiel Mohamed; Sanalla, Mohamed Hussin; Elnaas, Radwan Fatahalla; Rajab, Ibrahim Abdassalam Ibn

    2013-01-01

    Glutamate receptors have been implicated in various neurological disorders and their antagonism offers a suitable approach for the treatment of such disorders. The field of drug design and discovery aims to find best medicines to prevent, treat and cure diseases quickly and efficiently. In this regard, computational tools have helped medicinal chemists modify and optimize molecules to potent drug candidates with better pharmacokinetic profiles, and guiding biologists and pharmacologists to explore new disease genes as well as novel drug targets. In the present study, to understand the structural requirements for AMPA receptor antagonism, molecular docking study was performed on 41 structurally diverse antagonists based on quinoxaline nucleus. Lamarckian genetic algorithm methodology was employed for docking simulations using AutoDock 4.2 program. The results obtained signify that the molecular docking approach is reliable and produces a good correlation coefficient (r2 = 0.6) between experimental and docking predicted AMPA receptor antagonistic activity. The aromatic moiety of quinoxaline core has been proved to be vital for hydrophobic contacts exhibiting - interactions in docked conformations. However, polar moieties such as carboxylic group and 1,2,4-triazole moieties were noted to be sites for hydrophilic interactions in terms of hydrogen bonding with the receptor. These analyses can be exploited to design and develop novel AMPA receptor antagonists for the treatment of different neurological disorders. PMID:24250113

  14. Synergy of AMPA and NMDA Receptor Currents in Dopaminergic Neurons: A Modeling Study.

    PubMed

    Zakharov, Denis; Lapish, Christopher; Gutkin, Boris; Kuznetsov, Alexey

    2016-01-01

    Dopaminergic (DA) neurons display two modes of firing: low-frequency tonic and high-frequency bursts. The high frequency firing within the bursts is attributed to NMDA, but not AMPA receptor activation. In our models of the DA neuron, both biophysical and abstract, the NMDA receptor current can significantly increase their firing frequency, whereas the AMPA receptor current is not able to evoke high-frequency activity and usually suppresses firing. However, both currents are produced by glutamate receptors and, consequently, are often co-activated. Here we consider combined influence of AMPA and NMDA synaptic input in the models of the DA neuron. Different types of neuronal activity (resting state, low frequency, or high frequency firing) are observed depending on the conductance of the AMPAR and NMDAR currents. In two models, biophysical and reduced, we show that the firing frequency increases more effectively if both receptors are co-activated for certain parameter values. In particular, in the more quantitative biophysical model, the maximal frequency is 40% greater than that with NMDAR alone. The dynamical mechanism of such frequency growth is explained in the framework of phase space evolution using the reduced model. In short, both the AMPAR and NMDAR currents flatten the voltage nullcline, providing the frequency increase, whereas only NMDA prevents complete unfolding of the nullcline, providing robust firing. Thus, we confirm a major role of the NMDAR in generating high-frequency firing and conclude that AMPAR activation further significantly increases the frequency. PMID:27252643

  15. Synergy of AMPA and NMDA Receptor Currents in Dopaminergic Neurons: A Modeling Study

    PubMed Central

    Zakharov, Denis; Lapish, Christopher; Gutkin, Boris; Kuznetsov, Alexey

    2016-01-01

    Dopaminergic (DA) neurons display two modes of firing: low-frequency tonic and high-frequency bursts. The high frequency firing within the bursts is attributed to NMDA, but not AMPA receptor activation. In our models of the DA neuron, both biophysical and abstract, the NMDA receptor current can significantly increase their firing frequency, whereas the AMPA receptor current is not able to evoke high-frequency activity and usually suppresses firing. However, both currents are produced by glutamate receptors and, consequently, are often co-activated. Here we consider combined influence of AMPA and NMDA synaptic input in the models of the DA neuron. Different types of neuronal activity (resting state, low frequency, or high frequency firing) are observed depending on the conductance of the AMPAR and NMDAR currents. In two models, biophysical and reduced, we show that the firing frequency increases more effectively if both receptors are co-activated for certain parameter values. In particular, in the more quantitative biophysical model, the maximal frequency is 40% greater than that with NMDAR alone. The dynamical mechanism of such frequency growth is explained in the framework of phase space evolution using the reduced model. In short, both the AMPAR and NMDAR currents flatten the voltage nullcline, providing the frequency increase, whereas only NMDA prevents complete unfolding of the nullcline, providing robust firing. Thus, we confirm a major role of the NMDAR in generating high-frequency firing and conclude that AMPAR activation further significantly increases the frequency. PMID:27252643

  16. Positive AMPA receptor modulation rapidly stimulates BDNF release and increases dendritic mRNA translation.

    PubMed

    Jourdi, Hussam; Hsu, Yu-Tien; Zhou, Miou; Qin, Qingyu; Bi, Xiaoning; Baudry, Michel

    2009-07-01

    Brain-derived neurotrophic factor (BDNF) stimulates local dendritic mRNA translation and is involved in formation and consolidation of memory. 2H,3H,6aH-pyrrolidino[2'',1''-3',2']1,3-oxazino[6',5'-5,4]-benzo[e]1,4-dioxan-10-one (CX614), one of the best-studied positive AMPA receptor modulators (also known as ampakines), increases BDNF mRNA and protein and facilitates long-term potentiation (LTP) induction. Several other ampakines also improve performance in various behavioral and learning tasks. Since local dendritic protein synthesis has been implicated in LTP stabilization and in memory consolidation, this study investigated whether CX614 could influence synaptic plasticity by upregulating dendritic protein translation. CX614 treatment of primary neuronal cultures and acute hippocampal slices rapidly activated the translation machinery and increased local dendritic protein synthesis. CX614-induced activation of translation was blocked by K252a [(9S,10R,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid methyl ester], CNQX, APV, and TTX, and was inhibited in the presence of an extracellular BDNF scavenger, TrkB-Fc. The acute effect of CX614 on translation was mediated by increased BDNF release as demonstrated with a BDNF scavenging assay using TrkB-Fc during CX614 treatment of cultured primary neurons and was blocked by nifedipine, ryanodine, and lack of extracellular Ca(2+) in acute hippocampal slices. Finally, CX614, like BDNF, rapidly increased dendritic translation of an exogenous translation reporter. Together, our results demonstrate that positive modulation of AMPA receptors rapidly stimulates dendritic translation, an effect mediated by BDNF secretion and TrkB receptor activation. They also suggest that increased BDNF secretion and stimulation of local protein synthesis contribute to the effects of ampakines on synaptic plasticity. PMID:19587275

  17. Antioxidant NAC and AMPA/KA receptor antagonist DNQX inhibited JNK3 activation following global ischemia in rat hippocampus.

    PubMed

    Tian, Hui; Zhang, Guangyi; Li, Hongchun; Zhang, Quanguang

    2003-06-01

    c-Jun N-terminal kinase-3 (JNK3), the only neural-specific isoform, may play an important role in excitotoxicity and neuronal injury. To analyze the variation of JNK3 activation, levels of phospho-JNK3 were measured at various time points of ischemia and selected time points of reperfusion, respectively. Our study illustrated that JNK3 was rapidly activated and translocated from cytosol to nucleus during ischemia. During reperfusion, two peaks of JNK3 activation occurred at 30 min and 3 days, respectively. To further define the mechanism of JNK3 activation, antioxidant N-acetylcysteine (NAC), alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate (KA) receptor antagonist 6,7-dinitro-quinoxaline-2,3(1H,4H)-dione (DNQX), N-methyl-D-aspartate (NMDA) receptor antagonist ketamine and L-type voltage-gated Ca(2+) channel (L-VGCC) antagonist nifedipine were given to the rats 20 min prior to ischemia. The results showed that NAC obviously inhibited JNK3 activation during the early reperfusion, whereas DNQX preferably attenuated JNK3 activation during the latter reperfusion. Ketamine and nifedipine had no significant effects on JNK3 activation during reperfusion. Consequently, reactive oxygen species (ROS) and AMPA/KA receptor were closely associated with JNK3 activation following global ischemia. PMID:12767482

  18. Cochlear nucleus neurons redistribute synaptic AMPA and glycine receptors in response to monaural conductive hearing loss

    PubMed Central

    Whiting, Brittany; Moiseff, Andrew; Rubio, María E.

    2009-01-01

    Neurons restore their function in response to external or internal perturbations and maintain neuronal or network stability through a homeostatic scaling mechanism. Homeostatic responses at synapses along the auditory system would be important for adaptation to normal and abnormal fluctuations in the sensory environment. We investigated at the electron microscopic level and after postembedding immunogold labeling whether projection neurons in the cochlear nucleus responded to modifications of auditory nerve activity. After unilaterally reducing the level of auditory inputs by ~ 20 dB by monaural earplugging, auditory nerve synapses on bushy cells somata and basal dendrites of fusiform cells of the ventral and dorsal cochlear nucleus, respectively, upregulated GluR3 AMPA receptor subunit, while inhibitory synapses decreased the expression of GlyRα1 subunit. These changes in expression levels were fully reversible once the earplug was removed, indicating that activity affects the trafficking of receptors at synapses. Excitatory synapses on apical dendrites of fusiform cells (parallel fibers) with different synaptic AMPA receptor subunit composition, were not affected by sound attenuation, as the expression levels of AMPA receptor subunits were the same as in normal hearing littermates. GlyRα1 subunit expression at inhibitory synapses on apical dendrites of fusiform cells was also found unaffected. Furthermore, fusiform and bushy cells of the contralateral side to the earplugging upregulated the GluR3 subunit at auditory nerve synapses. These results show that cochlear nucleus neurons innervated by the auditory nerve, are able to respond to small changes in sound levels by redistributing specific AMPA and glycine receptor subunits. PMID:19646510

  19. Abnormally increased surface expression of AMPA receptors in the cerebellum, cortex and striatum of Cln3(-/-) mice.

    PubMed

    Kovács, Attila D; Hof, Caitlin; Pearce, David A

    2015-10-21

    Mutations in the CLN3 gene cause a fatal neurodegenerative disorder, juvenile CLN3 disease. Exploring the cause of the motor coordination deficit in the Cln3(-/-) mouse model of the disease we have previously found that attenuation of AMPA receptor activity in 1-month-old Cln3(-/-) mice significantly improves their motor coordination [20]. To elucidate the mechanism of the abnormally increased AMPA receptor function in Cln3(-/-) mice, we examined the surface expression of AMPA receptors using surface cross-linking in brain slices from 1-month-old wild type (WT) and Cln3(-/-) mice. In surface cross-linked brain samples, Western blotting for AMPA receptor subunits revealed significantly increased surface levels of GluA1 and GluA2 in the cerebellum, and of GluA2 in the cortex and striatum of Cln3(-/-) mice as compared to WT mice. Expression levels of the GluA4 subunit were similar in the cerebellum of WT and Cln3(-/-) mice. While intracellular GluA1 levels in the WT and Cln3(-/-) cerebellum or cortex were similar, the intracellular expression of GluA1 in the Cln3(-/-) striatum was decreased to 56% of the WT level. Our results show a prominent increase in AMPA receptor surface expression in the brain of Cln3(-/-) mice and suggest that CLN3 is involved in the regulation of AMPA receptor surface expression. PMID:26375929

  20. Developmental Regulation of the Toxin Sensitivity of Ca2+ -Permeable AMPA Receptors in Cortical Glia

    PubMed Central

    Meucci, Olimpia; Fatatis, Alessandro; Holzwarth, James A.; Miller, Richard J.

    2009-01-01

    We examined the properties of glutamate agonist-induced Ca2+ fluxes in cultured CG-4 and O-2A progenitor cells from rat cortex. Kainate-induced Ca2+ fluxes in these cells were found to be attributable to the activation of AMPA receptors. Thus, these fluxes were enhanced by cyclothiazide but not by concanavalin A and were blocked completely by GYKI-53655. We simultaneously examined kainate-induced Ca2+ entry and Na+ currents in these cells under voltage-clamp conditions. Both of these parameters were blocked by Joro spider toxin (JSTx) in undifferentiated cells. However, neither JSTx nor Argiotoxin 636 effectively blocked either parameter in cells differentiated into type II astrocytes. This change in toxin sensitivity occurred slowly over a period of several days. Similar results were obtained in Ca2+ -imaging studies. When cells were differentiated into oligodendrocytes, they showed an intermediate sensitivity to block by JSTx as assessed using imaging and voltage-clamp studies. Analysis of the expression of AMPA-receptor subunits showed an increase in the concentration of glutamate receptor-2 (GluR2) in CG-4 cells as they differentiated into type II astrocytes and oligodendrocytes. These results demonstrate that the AMPA receptors in cells of the O-2A lineage flux appreciable amounts of Ca2+ but may contain variable amounts of edited GluR2 subunits. PMID:8551336

  1. Deficiency of Lipoprotein Lipase in Neurons Decreases AMPA Receptor Phosphorylation and Leads to Neurobehavioral Abnormalities in Mice

    PubMed Central

    Yu, Tian; Taussig, Matthew D.; DiPatrizio, Nicholas V.; Astarita, Giuseppe; Piomelli, Daniele; Bergman, Bryan C.; Dell’Acqua, Mark L.; Eckel, Robert H.; Wang, Hong

    2015-01-01

    Alterations in lipid metabolism have been found in several neurodegenerative disorders, including Alzheimer’s disease. Lipoprotein lipase (LPL) hydrolyzes triacylglycerides in lipoproteins and regulates lipid metabolism in multiple organs and tissues, including the central nervous system (CNS). Though many brain regions express LPL, the functions of this lipase in the CNS remain largely unknown. We developed mice with neuron-specific LPL deficiency that became obese on chow by 16 wks in homozygous mutant mice (NEXLPL-/-) and 10 mo in heterozygous mice (NEXLPL+/-). In the present study, we show that 21 mo NEXLPL+/- mice display substantial cognitive function decline including poorer learning and memory, and increased anxiety with no difference in general motor activities and exploratory behavior. These neurobehavioral abnormalities are associated with a reduction in the 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl) propanoic acid (AMPA) receptor subunit GluA1 and its phosphorylation, without any alterations in amyloid β accumulation. Importantly, a marked deficit in omega-3 and omega-6 polyunsaturated fatty acids (PUFA) in the hippocampus precedes the development of the neurobehavioral phenotype of NEXLPL+/- mice. And, a diet supplemented with n-3 PUFA can improve the learning and memory of NEXLPL+/- mice at both 10 mo and 21 mo of age. We interpret these findings to indicate that LPL regulates the availability of PUFA in the CNS and, this in turn, impacts the strength of synaptic plasticity in the brain of aging mice through the modification of AMPA receptor and its phosphorylation. PMID:26263173

  2. AMPA receptors undergo channel arrest in the anoxic turtle cortex.

    PubMed

    Pamenter, Matthew Edward; Shin, Damian Seung-Ho; Buck, Leslie Thomas

    2008-02-01

    Without oxygen, all mammals suffer neuronal injury and excitotoxic cell death mediated by overactivation of the glutamatergic N-methyl-D-aspartate receptor (NMDAR). The western painted turtle can survive anoxia for months, and downregulation of NMDAR activity is thought to be neuroprotective during anoxia. NMDAR activity is related to the activity of another glutamate receptor, the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR). AMPAR blockade is neuroprotective against anoxic insult in mammals, but the role of AMPARs in the turtle's anoxia tolerance has not been investigated. To determine whether AMPAR activity changes during hypoxia or anoxia in the turtle cortex, whole cell AMPAR currents, AMPAR-mediated excitatory postsynaptic potentials (EPSPs), and excitatory postsynaptic currents (EPSCs) were measured. The effect of AMPAR blockade on normoxic and anoxic NMDAR currents was also examined. During 60 min of normoxia, evoked peak AMPAR currents and the frequencies and amplitudes of EPSPs and EPSCs did not change. During anoxic perfusion, evoked AMPAR peak currents decreased 59.2 +/- 5.5 and 60.2 +/- 3.5% at 20 and 40 min, respectively. EPSP frequency (EPSP(f)) and amplitude decreased 28.7 +/- 6.4% and 13.2 +/- 1.7%, respectively, and EPSC(f) and amplitude decreased 50.7 +/- 5.1% and 51.3 +/- 4.7%, respectively. In contrast, hypoxic (Po(2) = 5%) AMPAR peak currents were potentiated 56.6 +/- 20.5 and 54.6 +/- 15.8% at 20 and 40 min, respectively. All changes were reversed by reoxygenation. AMPAR currents and EPSPs were abolished by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). In neurons pretreated with CNQX, anoxic NMDAR currents were reversibly depressed by 49.8 +/- 7.9%. These data suggest that AMPARs may undergo channel arrest in the anoxic turtle cortex. PMID:18056983

  3. Architecture of fully occupied GluA2 AMPA receptor-TARP complex elucidated by cryo-EM.

    PubMed

    Zhao, Yan; Chen, Shanshuang; Yoshioka, Craig; Baconguis, Isabelle; Gouaux, Eric

    2016-08-01

    Fast excitatory neurotransmission in the mammalian central nervous system is largely carried out by AMPA-sensitive ionotropic glutamate receptors. Localized within the postsynaptic density of glutamatergic spines, AMPA receptors are composed of heterotetrameric receptor assemblies associated with auxiliary subunits, the most common of which are transmembrane AMPA receptor regulatory proteins (TARPs). The association of TARPs with AMPA receptors modulates receptor trafficking and the kinetics of receptor gating and pharmacology. Here we report the cryo-electron microscopy (cryo-EM) structure of the homomeric rat GluA2 AMPA receptor saturated with TARP γ2 subunits, which shows how the TARPs are arranged with four-fold symmetry around the ion channel domain and make extensive interactions with the M1, M2 and M4 transmembrane helices. Poised like partially opened ‘hands’ underneath the two-fold symmetric ligand-binding domain (LBD) 'clamshells', one pair of TARPs is juxtaposed near the LBD dimer interface, whereas the other pair is near the LBD dimer-dimer interface. The extracellular ‘domains’ of TARP are positioned to not only modulate LBD clamshell closure, but also affect conformational rearrangements of the LBD layer associated with receptor activation and desensitization, while the TARP transmembrane domains buttress the ion channel pore. PMID:27368053

  4. X-ray structures of AMPA receptor-cone snail toxin complexes illuminate activation mechanism.

    PubMed

    Chen, Lei; Dürr, Katharina L; Gouaux, Eric

    2014-08-29

    AMPA-sensitive glutamate receptors are crucial to the structural and dynamic properties of the brain, to the development and function of the central nervous system, and to the treatment of neurological conditions from depression to cognitive impairment. However, the molecular principles underlying AMPA receptor activation have remained elusive. We determined multiple x-ray crystal structures of the GluA2 AMPA receptor in complex with a Conus striatus cone snail toxin, a positive allosteric modulator, and orthosteric agonists, at 3.8 to 4.1 angstrom resolution. We show how the toxin acts like a straightjacket on the ligand-binding domain (LBD) "gating ring," restraining the domains via both intra- and interdimer cross-links such that agonist-induced closure of the LBD "clamshells" is transduced into an irislike expansion of the gating ring. By structural analysis of activation-enhancing mutants, we show how the expansion of the LBD gating ring results in pulling forces on the M3 helices that, in turn, are coupled to ion channel gating. PMID:25103405

  5. 7-Chloro-5-(furan-3-yl)-3-methyl-4H-benzo[e][1,2,4]thiadiazine 1,1-Dioxide as Positive Allosteric Modulator of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor. The End of the Unsaturated-Inactive Paradigm?

    PubMed

    Citti, Cinzia; Battisti, Umberto M; Cannazza, Giuseppe; Jozwiak, Krzysztof; Stasiak, Natalia; Puja, Giulia; Ravazzini, Federica; Ciccarella, Giuseppe; Braghiroli, Daniela; Parenti, Carlo; Troisi, Luigino; Zoli, Michele

    2016-02-17

    5-Arylbenzothiadiazine type compounds acting as positive allosteric modulators of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA-PAMs) have received particular attention in the past decade for their nootropic activity and lack of the excitotoxic side effects of direct agonists. Recently, our research group has published the synthesis and biological activity of 7-chloro-5-(3-furanyl)-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide (1), one of the most active benzothiadiazine-derived AMPA-PAMs in vitro to date. However, 1 exists as two stereolabile enantiomers, which rapidly racemize in physiological conditions, and only one isomer is responsible for the pharmacological activity. In the present work, experiments carried out with rat liver microsomes show that 1 is converted by hepatic cytochrome P450 to the corresponding unsaturated derivative 2 and to the corresponding pharmacologically inactive benzenesulfonamide 3. Surprisingly, patch-clamp experiments reveal that 2 displays an activity comparable to that of the parent compound. Molecular modeling studies were performed to rationalize these results. Furthermore, mice cerebral microdialysis studies suggest that 2 is able to cross the blood-brain barrier and increases acetylcholine and serotonin levels in the hippocampus. The experimental data disclose that the achiral hepatic metabolite 2 possesses the same pharmacological activity of its parent compound 1 but with an enhanced chemical and stereochemical stability, as well as an improved pharmacokinetic profile compared with 1. PMID:26580317

  6. Glyphosate-Resistant and Conventional Canola (Brassica napus L.) Responses to Glyphosate and Aminomethylphosphonic Acid (AMPA) Treatment.

    PubMed

    Corrêa, Elza Alves; Dayan, Franck E; Owens, Daniel K; Rimando, Agnes M; Duke, Stephen O

    2016-05-11

    Glyphosate-resistant (GR) canola contains two transgenes that impart resistance to the herbicide glyphosate: (1) the microbial glyphosate oxidase gene (gox) encoding the glyphosate oxidase enzyme (GOX) that metabolizes glyphosate to aminomethylphosphonic acid (AMPA) and (2) cp4 that encodes a GR form of the glyphosate target enzyme 5-enolpyruvylshikimic acid-3-phosphate synthase. The objectives of this research were to determine the phytotoxicity of AMPA to canola, the relative metabolism of glyphosate to AMPA in GR and conventional non-GR (NGR) canola, and AMPA pool sizes in glyphosate-treated GR canola. AMPA applied at 1.0 kg ha(-1) was not phytotoxic to GR or NGR. At this AMPA application rate, NGR canola accumulated a higher concentration of AMPA in its tissues than GR canola. At rates of 1 and 3.33 kg ae ha(-1) of glyphosate, GR canola growth was stimulated. This stimulatory effect is similar to that of much lower doses of glyphosate on NGR canola. Both shikimate and AMPA accumulated in tissues of these glyphosate-treated plants. In a separate experiment in which young GR and NGR canola plants were treated with non-phytotoxic levels of [(14)C]-glyphosate, very little glyphosate was metabolized in NGR plants, whereas most of the glyphosate was metabolized to AMPA in GR plants at 7 days after application. Untreated leaves of GR plants accumulated only metabolites (mostly AMPA) of glyphosate, indicating that GOX activity is very high in the youngest leaves. These data indicate that more glyphosate is transformed to AMPA rapidly in GR canola and that the accumulated AMPA is not toxic to the canola plant. PMID:27092715

  7. 3’-Deoxyadenosine (Cordycepin) Produces a Rapid and Robust Antidepressant Effect via Enhancing Prefrontal AMPA Receptor Signaling Pathway

    PubMed Central

    Li, Bai; Hou, Yangyang; Zhu, Ming; Bao, Hongkun; Nie, Jun; Zhang, Grace Y.; Shan, Liping; Yao, Yao; Du, Kai; Yang, Hongju; Li, Meizhang; Zheng, Bingrong; Xu, Xiufeng; Xiao, Chunjie; Du, Jing

    2016-01-01

    Background: The development of rapid and safe antidepressants for the treatment of major depression is in urgent demand. Converging evidence suggests that glutamatergic signaling seems to play important roles in the pathophysiology of depression. Methods: We studied the antidepressant effects of 3’-deoxyadenosine (3’-dA, Cordycepin) and the critical role of the α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor in male CD-1 mice via behavioral and biochemical experiments. After 3’-dA treatment, the phosphorylation and synaptic localization of the AMPA receptors GluR1 and GluR2 were determined in the prefrontal cortex (PFC) and hippocampus (HIP). The traditional antidepressant imipramine was applied as a positive control. Results: We found that an injection of 3’-dA led to a rapid and robust antidepressant effect, which was significantly faster and stronger than imipramine, after 45min in tail suspension and forced swim tests. This antidepressant effect remained after 5 days of treatment with 3’-dA. Unlike the psycho-stimulants, 3’-dA did not show a hyperactive effect in the open field test. After 45min or 5 days of treatment, 3’-dA enhanced GluR1 S845 phosphorylation in both the PFC and HIP. In addition, after 45min of treatment, 3’-dA significantly up-regulated GluR1 S845 phosphorylation and GluR1, but not GluR2 levels, at the synapses in the PFC. After 5 days of treatment, 3’-dA significantly enhanced GluR1 S845 phosphorylation and GluR1, but not GluR2, at the synapses in the PFC and HIP. Moreover, the AMPA-specific antagonist GYKI 52466 was able to block the rapid antidepressant effects of 3’-dA. Conclusion: This study identified 3’-dA as a novel rapid antidepressant with clinical potential and multiple beneficial mechanisms, particularly in regulating the prefrontal AMPA receptor signaling pathway. PMID:26443809

  8. Ca(2+)-permeable AMPA and NMDA receptor channels in basket cells of rat hippocampal dentate gyrus.

    PubMed Central

    Koh, D S; Geiger, J R; Jonas, P; Sakmann, B

    1995-01-01

    1. Glutamate receptor (GluR) channels were studied in basket cells in the dentate gyrus of rat hippocampal slices. Basket cells were identified by their location, dendritic morphology and high frequency of action potentials generated during sustained current injection. 2. Dual-component currents were activated by fast application of glutamate to outside-out membrane patches isolated from basket cell somata (10 microM glycine, no external Mg2+). The fast component was selectively blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), the slow component by D-2-amino-5-phosphonopentanoic acid (D-AP5). This suggests that the two components were mediated by alpha-amino-3- hydroxy-5-methyl-4-isoxazolepropionate receptor (AMPAR)/kainate receptor and N-methyl-D-aspartate receptor (NMDAR) channels, respectively. The mean ratio of the peak current of the NMDAR component to that of the AMPAR/kainate receptor component was 0.22 (1 ms pulses of 10 mM glutamate). 3. The AMPAR/kainate receptor component, which was studied in isolation in the presence of D-AP5, was identified as AMPAR mediated on the basis of the preferential activation by AMPA as compared with kainate, the weak desensitization of kainate-activated currents, the cross-desensitization between AMPA and kainate, and the reduction of desensitization by cyclothiazide. 4. Deactivation of basket cell AMPARs following 1 ms pulses of glutamate occurred with a time constant (tau) of 1.2 +/- 0.1 ms (mean +/- S.E.M.). During 100 ms glutamate pulses AMPARs desensitized with a tau of 3.7 +/- 0.2ms. 5. The peak current-voltage (I-V) relation of AMPAR-mediated currents in Na(+)-rich extracellular solution showed a reversal potential of -4.0 +/- 2.6 mV and was characterized by a a doubly rectifying shape. The conductance of single AMPAR channels was estimated as 22.6 +/- 1.6 pS using non-stationary fluctuation analysis. AMPARs expressed in hippocampal basket cells were highly Ca2+ permeable (PCa/PK = 1.79). 6. NMDARs in

  9. Synapse-associated protein-97 isoform-specific regulation of surface AMPA receptors and synaptic function in cultured neurons.

    PubMed

    Rumbaugh, Gavin; Sia, Gek-Ming; Garner, Craig C; Huganir, Richard L

    2003-06-01

    Members of the synapse-associated protein-97 (SAP97) family of scaffold proteins have been implicated as central organizers of synaptic junctions to build macromolecular signaling complexes around specific postsynaptic neurotransmitter receptors. In this regard, SAP97 has been suggested to regulate the synaptic localization of glutamate receptor type 1 subunits of the AMPA-type glutamate receptors. To test this hypothesis directly, we assessed the effects of SAP97 overexpression on surface expression of synaptic AMPA receptors. We find that recombinant SAP97 not only becomes concentrated at synaptic junctions but also leads to an increase in synaptic AMPA receptors, spine enlargement, and an increase in miniature EPSC (mEPSC) frequency, indicating that SAP97 has both postsynaptic and presynaptic effects on synaptic transmission. Synaptic targeting of SAP97, increased surface AMPA receptors, and increased mEPSC frequency are dependent on the presence of specific alternatively spliced sequences in SAP97 that encode a protein 4.1 binding site. These results suggest that SAP97 can affect the synaptic recruitment of AMPA receptors and spine morphology and that these effects may be regulated by alternative splicing. PMID:12805297

  10. Group II Metabotropic Glutamate Receptor Agonist LY379268 Regulates AMPA Receptor Trafficking in Prefrontal Cortical Neurons

    PubMed Central

    Wang, Min-Juan; Li, Yan-Chun; Snyder, Melissa A.; Wang, Huaixing; Li, Feng; Gao, Wen-Jun

    2013-01-01

    Group II metabotropic glutamate receptor (mGluR) agonists have emerged as potential treatment drugs for schizophrenia and other neurological disorders, whereas the mechanisms involved remain elusive. Here we examined the effects of LY379268 (LY37) on the expression and trafficking of the α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor subunits GluA1 and GluA2 in prefrontal neurons. We show that LY37 significantly increased the surface and total expression of both GluA1 and GluA2 subunits in cultured prefrontal neurons and in vivo. This effect was mimicked by the selective mGluR2 agonist LY395756 and was blocked by mGluR2/3 antagonist LY341495. Moreover, we found that both GluA1 and GluA2 subunits were colocalized with PSD95 but not synapsin I, suggesting a postsynaptic localization. Consistently, treatment with LY37 significantly increased the amplitude, but not frequency, of miniature excitatory postsynaptic currents. Further, actinomycin-D blocked LY37's effects, suggesting a transcriptional regulation. In addition, application of glycogen synthase kinase-3beta (GSK-3β) inhibitor completely blocked LY37's effect on GluA2 surface expression, whereas GSK-3β inhibitor itself induced decreases in the surface and total protein levels of GluA1, but not GluA2 subunits. This suggests that GSK-3β differentially mediates GluA1 and GluA2 trafficking. Further, LY37 significantly increased the phosphorylation, but not total protein, of extracellular signal-regulated kinase 1/2 (ERK1/2). Neither ERK1/2 inhibitor PD98059 alone nor PD98059 combined with LY37 treatment induced changes in GluA1 or GluA2 surface expression or total protein levels. Our data thus suggest that mGluR2/3 agonist regulates postsynaptic AMPA receptors by affecting the synaptic trafficking of both GluA1 and GluA2 subunits and that the regulation is likely through ERK1/2 signaling in GluA1 and/or both ERK1/2 and GSK-3β signaling pathways in the GluA2 subunit. PMID:23593498

  11. Agmatine produces antidepressant-like effects by activating AMPA receptors and mTOR signaling.

    PubMed

    Neis, Vivian Binder; Moretti, Morgana; Bettio, Luis Eduardo B; Ribeiro, Camille M; Rosa, Priscila Batista; Gonçalves, Filipe Marques; Lopes, Mark William; Leal, Rodrigo Bainy; Rodrigues, Ana Lúcia S

    2016-06-01

    The activation of AMPA receptors and mTOR signaling has been reported as mechanisms underlying the antidepressant effects of fast-acting agents, specially the NMDA receptor antagonist ketamine. In the present study, oral administration of agmatine (0.1mg/kg), a neuromodulator that has been reported to modulate NMDA receptors, caused a significant reduction in the immobility time of mice submitted to the tail suspension test (TST), an effect prevented by the administration of DNQX (AMPA receptor antagonist, 2.5μg/site, i.c.v.), BDNF antibody (1μg/site, i.c.v.), K-252a (TrkB receptor antagonist, 1μg/site, i.c.v.), LY294002 (PI3K inhibitor, 10nmol/site, i.c.v.) or rapamycin (selective mTOR inhibitor, 0.2nmol/site, i.c.v.). Moreover, the administration of lithium chloride (non-selective GSK-3β inhibitor, 10mg/kg, p.o.) or AR-A014418 (selective GSK-3β inhibitor, 0.01μg/site, i.c.v.) in combination with a sub-effective dose of agmatine (0.0001mg/kg, p.o.) reduced the immobility time in the TST when compared with either drug alone. Furthermore, increased immunocontents of BDNF, PSD-95 and GluA1 were found in the prefrontal cortex of mice just 1h after agmatine administration. These results indicate that the antidepressant-like effect of agmatine in the TST may be dependent on the activation of AMPA and TrkB receptors, PI3K and mTOR signaling as well as inhibition of GSK-3β, and increase in synaptic proteins. The results contribute to elucidate the complex signaling pathways involved in the antidepressant effect of agmatine and reinforce the pivotal role of these molecular targets for antidepressant responses. PMID:27061850

  12. Membrane-tethered AKT kinase regulates basal synaptic transmission and early phase LTP expression by modulation of post-synaptic AMPA receptor level.

    PubMed

    Pen, Y; Borovok, N; Reichenstein, M; Sheinin, A; Michaelevski, I

    2016-09-01

    The serine/threonine kinase AKT/PKB plays a fundamental role in a wide variety of neuronal functions, including neuronal cell development, axonal growth, and synaptic plasticity. Multiple evidence link AKT signaling pathways to regulation of late phase long-term synaptic plasticity, synaptogenesis, and spinogenesis, as well as long-term memory formation. Nevertheless, the downstream effectors mediating the effects of AKT on early phase long-term potentiation (eLTP) are currently unknown. Here we report that using different regimes of pharmacological activation and inhibition of AKT activity in acute hippocampal slices, we found that AKT regulates the post-synaptic expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA) receptors affecting solely the expression of eLTP, with no effect on its induction and maintenance. We further show that both maintenance of basal synaptic activity and expression of eLTP require plasma membrane tethering by activated AKT and that basal synaptic activity may be regulated via the direct effects of AKT1 on the expression level of post-synaptic AMPA receptors bypassing the canonical AKT signaling. Finally, we establish that eLTP expression requires the involvement of both the canonical AKT signaling pathways and the direct effect of AKT1 on AMPA receptor activity/expression in the post-synaptic membrane. © 2016 Wiley Periodicals, Inc. PMID:27068236

  13. Novel Regulation of the Synthesis of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Subunit GluA1 by Carnitine Palmitoyltransferase 1C (CPT1C) in the Hippocampus.

    PubMed

    Fadó, Rut; Soto, David; Miñano-Molina, Alfredo J; Pozo, Macarena; Carrasco, Patricia; Yefimenko, Natalia; Rodríguez-Álvarez, José; Casals, Núria

    2015-10-16

    The regulation of AMPA-type receptor (AMPAR) abundance in the postsynaptic membrane is an important mechanism involved in learning and memory formation. Recent data suggest that one of the constituents of the AMPAR complex is carnitine palmitoyltransferase 1C (CPT1C), a brain-specific isoform located in the endoplasmic reticulum of neurons. Previous results had demonstrated that CPT1C deficiency disrupted spine maturation in hippocampal neurons and impaired spatial learning, but the role of CPT1C in AMPAR physiology had remained mostly unknown. In the present study, we show that CPT1C binds GluA1 and GluA2 and that the three proteins have the same expression profile during neuronal maturation. Moreover, in hippocampal neurons of CPT1C KO mice, AMPAR-mediated miniature excitatory postsynaptic currents and synaptic levels of AMPAR subunits GluA1 and GluA2 are significantly reduced. We show that AMPAR expression is dependent on CPT1C levels because total protein levels of GluA1 and GluA2 are decreased in CPT1C KO neurons and are increased in CPT1C-overexpressing neurons, whereas other synaptic proteins remain unaltered. Notably, mRNA levels of AMPARs remained unchanged in those cultures, indicating that CPT1C is post-transcriptionally involved. We demonstrate that CPT1C is directly involved in the de novo synthesis of GluA1 and not in protein degradation. Moreover, in CPT1C KO cultured neurons, GluA1 synthesis after chemical long term depression was clearly diminished, and brain-derived neurotrophic factor treatment was unable to phosphorylate the mammalian target of rapamycin (mTOR) and stimulate GluA1 protein synthesis. These data newly identify CPT1C as a regulator of AMPAR translation efficiency and therefore also synaptic function in the hippocampus. PMID:26338711

  14. Late-onset motoneuron disease caused by a functionally modified AMPA receptor subunit.

    PubMed

    Kuner, Rohini; Groom, Anthony J; Bresink, Iris; Kornau, Hans-Christian; Stefovska, Vanya; Müller, Gerald; Hartmann, Bettina; Tschauner, Karsten; Waibel, Stefan; Ludolph, Albert C; Ikonomidou, Chrysanthy; Seeburg, Peter H; Turski, Lechoslaw

    2005-04-19

    Amyotrophic lateral sclerosis (ALS) is a devastating disorder of the central nervous system in middle and old age that leads to progressive loss of spinal motoneurons. Transgenic mice overexpressing mutated human Cu(2+)/Zn(2+) superoxide dismutase 1 (SOD1) reproduce clinical features of the familial form of ALS. However, changes in SOD1 activity do not correlate with severity of motor decline in sporadic cases, indicating that targets unrelated to superoxide metabolism contribute to the pathogenesis of the disease. We show here that transgenic expression in mice of GluR-B(N)-containing L-alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionate (AMPA) receptors with increased Ca(2+) permeability leads to late-onset degeneration of neurons in the spinal cord and decline of motor functions. Neuronal death progresses over the entire lifespan but manifests clinically in late adulthood, resembling the course of a slow neurodegenerative disorder. Additional transgenic expression of mutated human SOD1 accelerates disease progression, aggravates the severity of motor decline, and decreases survival. These observations link persistently elevated Ca(2+) influx through AMPA channels with progressive motor decline and late-onset degeneration of spinal motoneurons, indicating that functionally altered AMPA channels may be causally related to pathogenesis of sporadic ALS in humans. PMID:15827116

  15. Late-onset motoneuron disease caused by a functionally modified AMPA receptor subunit

    PubMed Central

    Kuner, Rohini; Groom, Anthony J.; Bresink, Iris; Kornau, Hans-Christian; Stefovska, Vanya; Müller, Gerald; Hartmann, Bettina; Tschauner, Karsten; Waibel, Stefan; Ludolph, Albert C.; Ikonomidou, Chrysanthy; Seeburg, Peter H.; Turski, Lechoslaw

    2005-01-01

    Amyotrophic lateral sclerosis (ALS) is a devastating disorder of the central nervous system in middle and old age that leads to progressive loss of spinal motoneurons. Transgenic mice overexpressing mutated human Cu2+/Zn2+ superoxide dismutase 1 (SOD1) reproduce clinical features of the familial form of ALS. However, changes in SOD1 activity do not correlate with severity of motor decline in sporadic cases, indicating that targets unrelated to superoxide metabolism contribute to the pathogenesis of the disease. We show here that transgenic expression in mice of GluR-B(N)-containing l-α-amino-3-hydroxy-5-methylisoxazole-4-proprionate (AMPA) receptors with increased Ca2+ permeability leads to late-onset degeneration of neurons in the spinal cord and decline of motor functions. Neuronal death progresses over the entire lifespan but manifests clinically in late adulthood, resembling the course of a slow neurodegenerative disorder. Additional transgenic expression of mutated human SOD1 accelerates disease progression, aggravates the severity of motor decline, and decreases survival. These observations link persistently elevated Ca2+ influx through AMPA channels with progressive motor decline and late-onset degeneration of spinal motoneurons, indicating that functionally altered AMPA channels may be causally related to pathogenesis of sporadic ALS in humans. PMID:15827116

  16. Mechanisms of disease: motoneuron disease aggravated by transgenic expression of a functionally modified AMPA receptor subunit.

    PubMed

    Kuner, Rohini; Groom, Anthony J; Müller, Gerald; Kornau, Hans-Christian; Stefovska, Vanya; Bresink, Iris; Hartmann, Bettina; Tschauner, Karsten; Waibel, Stefan; Ludolph, Albert C; Ikonomidou, Chrysanthy; Seeburg, Peter H; Turski, Lechoslaw

    2005-08-01

    To reveal whether increased Ca2+ permeability of glutamate AMPA channels triggered by the transgene for GluR-B(N) induces decline in motor functions and neurodegeneration in the spinal cord, we evaluated growth, motor coordination, and spinal reflexes in transgenic GluR-B(N) and wild-type (wt) mice. To reveal whether the transgenic GluR-B(N) expression aggravates the course of motoneuron disease in SOD1 mice, we mated heterozygous GluR-B(N) and SOD1 [C57BL6Ico-TgN(hSOD1-G93A)1Gur] mice to generate double-transgenic progeny. The phenotypic sequelae in mice carrying mutations were evaluated by monitoring growth, motor coordination, and survival. Neuronal degeneration was assessed by morphological and stereological analysis of spinal cord and brain. We found that transgenic expression in mice of GluR-B(N)-containing glutamate AMPA receptors with increased Ca2+ permeability leads to a late-onset degeneration of neurons in the spinal cord and decline of motor functions. Neuronal death progressed over the entire life span, but manifested clinically in late adulthood, resembling the course of a slow neurodegenerative disorder. Additional transgenic expression of mutated human SOD1 accelerated disease progression, aggravated severity of motor decline, and decreased survival. These observations reveal that moderate, but persistently elevated Ca2+ influx via glutamate AMPA channels causes degeneration of spinal motoneurons and motor decline over the span of life. These features resemble the course of sporadic amyotrophic lateral sclerosis (ALS) in humans and suggest that modified function of glutamate AMPA channels may be causally linked to pathogenesis of ALS. PMID:16179532

  17. The Fate and Transport of Glyphosate and its Degradation Product, Aminomethylphosphonic Acid (AMPA), in Water

    NASA Astrophysics Data System (ADS)

    Scribner, E.; Meyer, M. T.

    2006-05-01

    Since 2001, the U.S. Geological Survey (USGS) has investigated the fate and transport of glyphosate and its degradation product, aminomethylphosphonic acid (AMPA), in surface water, and more recently in tile-drain flow, soil, and wet deposition. According to U.S. Environmental Protection Agency sources, glyphosate is among the world's most widely used herbicides. In 2004, glyphosate usage estimates indicated that between 103 and 113 million pounds were applied annually to crops in the United States. The use of glyphosate over a wide geographic area suggests that this herbicide might be a potential concern for air, water, and soil quality as well as measured in high concentrations in streams; therefore, it is important to monitor its fate and transport in ground-water/surface-water systems. National, regional, and field-scale studies conducted by the USGS National Water-Quality Assessment and Toxic Substance Hydrology Programs have studied the fate and transport of glyphosate in overland flow, tile- drain flow, surface water, soil, and wet-deposition samples. The samples were analyzed for glyphosate and AMPA by using derivatization and online solid-phase extraction with liquid chromatography/mass spectrometry (LC/MS) and LC/MS/MS methods developed by the USGS Organic Geochemistry Research Laboratory in Lawrence, Kansas. During spring, summer, and fall 2002 runoff periods in 50 Midwestern streams, glyphosate was detected at or above the 0.10 micrograms per liter detection limit in 35, 41, and 31 percent of samples, respectively. AMPA was detected in 53, 82, and 75 percent of samples, respectively. Results of 128 samples from a field study showed that glyphosate was transported as a narrow high- concentration pulse during the first period of runoff after application and that the concentration of glyphosate in runoff was greater than the concentration of AMPA. In tile-drain flow, glyphosate and AMPA were transported in a broad low-concentration pulse during these same

  18. Delayed antagonism of AMPA/kainate receptors reduces long-term functional deficits resulting from spinal cord trauma.

    PubMed

    Wrathall, J R; Teng, Y D; Marriott, R

    1997-06-01

    Excitatory amino acid (EAA) receptors play a significant role in delayed neuronal death after ischemic and traumatic injury to the CNS. Focal microinjection experiments have demonstrated that 2,3-dihydro-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX), a highly selective and potent antagonist of non-N-methyl-D-aspartate ionotropic EAA receptors, i.e., those preferring alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) or kainate, can reduce histopathology and functional deficits when administered at 15 min after traumatic spinal cord injury (SCI). Similarly, intravenous infusion of NBQX, beginning at 15 min postinjury (p.i.), results in a significant amelioration of the functional deficits produced by experimental SCI. However, if antagonists of AMPA/kainate receptors were to be used therapeutically for patients with SCI, administration would likely be delayed for several hours after injury. We therefore examined the effects of NBQX administered at 4 h after SCI on functional deficits and histopathology in a standardized rat model of contusive SCI. An incomplete SCI was produced in Sprague-Dawley rats at T8 with a weight-drop device (10 g x 2.5 cm). NBQX (15 nmol), or vehicle alone, was microinjected into the injury site 4 h later. Recovery of hind limb reflexes, postural control, and locomotor function was determined by a battery of behavioral tests performed for 8 weeks. Spinal cord tissue was then fixed by perfusion and used for morphometric and immunocytochemical analyses. Previous studies with acute NBQX treatment showed significant functional improvement by 1 week; the effects of delayed NBQX treatment on functional deficits were not discernible until 3-4 weeks after SCI. Thereafter, significant reductions in hindlimb deficits were demonstrated in two independent studies. The nature and magnitude of the reductions in chronic deficits were similar to those observed previously when NBQX was administered acutely at 15 min after SCI. Morphometric

  19. Basal Levels of AMPA Receptor GluA1 Subunit Phosphorylation at Threonine 840 and Serine 845 in Hippocampal Neurons

    ERIC Educational Resources Information Center

    Babiec, Walter E.; Guglietta, Ryan; O'Dell, Thomas J.

    2016-01-01

    Dephosphorylation of AMPA receptor (AMPAR) GluA1 subunits at two sites, serine 845 (S845) and threonine 840 (T840), is thought to be involved in NMDA receptor-dependent forms of long-term depression (LTD). Importantly, the notion that dephosphorylation of these sites contributes to LTD assumes that a significant fraction of GluA1 subunits are…

  20. Anti-AMPA-Receptor Encephalitis Presenting as a Rapid-Cycling Bipolar Disorder in a Young Woman with Turner Syndrome

    PubMed Central

    Quaranta, Giuseppe; Maremmani, Angelo Giovanni Icro; Perugi, Giulio

    2015-01-01

    Background. Autoimmune encephalitis is a disorder characterised by the subacute onset of seizures, short-term memory loss, and psychiatric and behavioural symptoms. Initially, it was recognised as a paraneoplastic disorder, but recently a subgroup of patients without systemic cancer was identified. Case Description. We describe a 20-year-old woman with Turner syndrome presenting with a treatment-resistant rapid cycling bipolar disorder with cognitive impairment. She was diagnosed with anti-AMPA-receptor encephalitis. She showed marked improvement after starting memantine and valproic acid. Conclusion. This case description emphasises the importance of timely recognition of autoimmune limbic encephalitis in patients with psychiatric manifestations and a possible predisposition to autoimmune conditions, in order to rule out malignancy and to quickly initiate treatment. PMID:26495149

  1. Odor Preference Learning and Memory Modify GluA1 Phosphorylation and GluA1 Distribution in the Neonate Rat Olfactory Bulb: Testing the AMPA Receptor Hypothesis in an Appetitive Learning Model

    ERIC Educational Resources Information Center

    Cui, Wen; Darby-King, Andrea; Grimes, Matthew T.; Howland, John G.; Wang, Yu Tian; McLean, John H.; Harley, Carolyn W.

    2011-01-01

    An increase in synaptic AMPA receptors is hypothesized to mediate learning and memory. AMPA receptor increases have been reported in aversive learning models, although it is not clear if they are seen with memory maintenance. Here we examine AMPA receptor changes in a cAMP/PKA/CREB-dependent appetitive learning model: odor preference learning in…

  2. Facilitation of AMPA Receptor Synaptic Delivery as a Molecular Mechanism for Cognitive Enhancement

    PubMed Central

    Sánchez-Puelles, Cristina; Pereda-Peréz, Inmaculada; Franco, Ana; Sandi, Carmen; Suárez, Luz M.; Solís, José M.; Alonso-Nanclares, Lidia; Martín, Eduardo D.; Merino-Serrais, Paula; Borcel, Erika; Li, Shizhong; Chen, Yongshuo; Gonzalez-Soriano, Juncal; Berezin, Vladimir; Bock, Elisabeth; DeFelipe, Javier; Esteban, José A.

    2012-01-01

    Cell adhesion molecules and downstream growth factor-dependent signaling are critical for brain development and synaptic plasticity, and they have been linked to cognitive function in adult animals. We have previously developed a mimetic peptide (FGL) from the neural cell adhesion molecule (NCAM) that enhances spatial learning and memory in rats. We have now investigated the cellular and molecular basis of this cognitive enhancement, using biochemical, morphological, electrophysiological, and behavioral analyses. We have found that FGL triggers a long-lasting enhancement of synaptic transmission in hippocampal CA1 neurons. This effect is mediated by a facilitated synaptic delivery of AMPA receptors, which is accompanied by enhanced NMDA receptor-dependent long-term potentiation (LTP). Both LTP and cognitive enhancement are mediated by an initial PKC activation, which is followed by persistent CaMKII activation. These results provide a mechanistic link between facilitation of AMPA receptor synaptic delivery and improved hippocampal-dependent learning, induced by a pharmacological cognitive enhancer. PMID:22363206

  3. Postsynaptic Plasticity Triggered by Ca²⁺-Permeable AMPA Receptor Activation in Retinal Amacrine Cells.

    PubMed

    Kim, Mean-Hwan; von Gersdorff, Henrique

    2016-02-01

    Amacrine cells are thought to be a major locus for mechanisms of light adaptation and contrast enhancement in the retina. However, the potential for plasticity in their AMPA receptor currents remains largely unknown. Using paired patch-clamp recordings between bipolar cell terminals and amacrine cells, we have simultaneously measured presynaptic membrane capacitance changes and EPSCs. Repetitive bipolar cell depolarizations, designed to maintain the same amount of exocytosis, nevertheless significantly potentiated evoked EPSCs in a subpopulation of amacrine cells. Likewise, repetitive iontophoresis (or puffs) of glutamate (or AMPA) onto the dendrites of amacrine cells also significantly potentiated evoked currents and [Ca(2+)]i rises. However, strong postsynaptic Ca(2+) buffering with BAPTA abolished the potentiation and selective antagonists of Ca(2+)-permeable AMPA receptors also blocked the potentiation of AMPA-mediated currents. Together these results suggest that Ca(2+) influx via Ca(2+)-permeable AMPA receptors can elicit a rapid form of postsynaptic plasticity in a subgroup of amacrine cell dendrites. PMID:26804991

  4. The SOL-2/Neto auxiliary protein modulates the function of AMPA-subtype ionotropic glutamate receptors.

    PubMed

    Wang, Rui; Mellem, Jerry E; Jensen, Michael; Brockie, Penelope J; Walker, Craig S; Hoerndli, Frédéric J; Hauth, Linda; Madsen, David M; Maricq, Andres V

    2012-09-01

    The neurotransmitter glutamate mediates excitatory synaptic transmission by gating ionotropic glutamate receptors (iGluRs). AMPA receptors (AMPARs), a subtype of iGluR, are strongly implicated in synaptic plasticity, learning, and memory. We previously discovered two classes of AMPAR auxiliary proteins in C. elegans that modify receptor kinetics and thus change synaptic transmission. Here, we have identified another auxiliary protein, SOL-2, a CUB-domain protein that associates with both the related auxiliary subunit SOL-1 and with the GLR-1 AMPAR. In sol-2 mutants, behaviors dependent on glutamatergic transmission are disrupted, GLR-1-mediated currents are diminished, and GLR-1 desensitization and pharmacology are modified. Remarkably, a secreted variant of SOL-1 delivered in trans can rescue sol-1 mutants, and this rescue depends on in cis expression of SOL-2. Finally, we demonstrate that SOL-1 and SOL-2 have an ongoing role in the adult nervous system to control AMPAR-mediated currents. PMID:22958824

  5. Concomitant manipulation of murine NMDA- and AMPA-receptors to produce pro-cognitive drug effects in mice.

    PubMed

    Vignisse, Julie; Steinbusch, Harry W M; Grigoriev, Vladimir; Bolkunov, Alexei; Proshin, Alexey; Bettendorff, Lucien; Bachurin, Sergey; Strekalova, Tatyana

    2014-02-01

    Bifunctional drug therapy targeting distinct receptor signalling systems can generate increased efficacy at lower concentrations compared to monofunctional therapy. Non-competitive blockade of the NMDA receptors or the potentiation of AMPA receptors is well documented to result in memory enhancement. Here, we compared the efficacy of the low-affinity NMDA receptor blocker memantine or the positive modulator of AMPA receptor QXX (in C57BL/6J at 1 or 5mg/kg, ip) with new derivatives of isothiourea (0.5-1 mg/kg, ip) that have bifunctional efficacy. Low-affinity NMDA blockade by these derivatives was achieved by introducing greater flexibility into the molecule, and AMPA receptor stimulation was produced by a sulfamide-containing derivative of isothiourea. Contextual learning was examined in a step-down avoidance task and extinction of contextual memory was studied in a fear-conditioning paradigm. Memantine enhanced contextual learning while QXX facilitated memory extinction; both drugs were effective at 5 mg/kg. The new derivative IPAC-5 elevated memory scores in both tasks at the dose 0.5 mg/kg and exhibited the lowest IC₅₀ values of NMDA receptor blockade and highest potency of AMPA receptor stimulation. Thus, among the new drugs tested, IPAC-5 replicated the properties of memantine and QXX in one administration with increased potency. Our data suggest that a concomitant manipulation of NMDA- and AMPA-receptors results in pro-cognitive effects and supports the concept bifunctional drug therapy as a promising strategy to replace monofunctional therapies with greater efficacy and improved compliance. PMID:23993168

  6. NMDA and AMPA/kainate glutamatergic receptors in the prelimbic medial prefrontal cortex modulate the elaborated defensive behavior and innate fear-induced antinociception elicited by GABAA receptor blockade in the medial hypothalamus.

    PubMed

    de Freitas, Renato Leonardo; Salgado-Rohner, Carlos José; Biagioni, Audrey Francisco; Medeiros, Priscila; Hallak, Jaime Eduardo Cecílio; Crippa, José Alexandre S; Coimbra, Norberto Cysne

    2014-06-01

    The aim of the present study was to investigate the involvement of N-methyl-d-aspartate (NMDA) and amino-3-hydroxy-5-methyl-isoxazole-4-proprionate (AMPA)/kainate receptors of the prelimbic (PL) division of the medial prefrontal cortex (MPFC) on the panic attack-like reactions evoked by γ-aminobutyric acid-A receptor blockade in the medial hypothalamus (MH). Rats were pretreated with NaCl 0.9%, LY235959 (NMDA receptor antagonist), and NBQX (AMPA/kainate receptor antagonist) in the PL at 3 different concentrations. Ten minutes later, the MH was treated with bicuculline, and the defensive responses were recorded for 10 min. The antagonism of NMDA receptors in the PL decreased the frequency and duration of all defensive behaviors evoked by the stimulation of the MH and reduced the innate fear-induced antinociception. However, the pretreatment of the PL cortex with NBQX was able to decrease only part of defensive responses and innate fear-induced antinociception. The present findings suggest that the NMDA-glutamatergic system of the PL is critically involved in panic-like responses and innate fear-induced antinociception and those AMPA/kainate receptors are also recruited during the elaboration of fear-induced antinociception and in panic attack-related response. The activation of the glutamatergic neurotransmission of PL division of the MPFC during the elaboration of oriented behavioral reactions elicited by the chemical stimulation of the MH recruits mainly NMDA receptors in comparison with AMPA/kainate receptors. PMID:23349224

  7. Reactive oxygen species (ROS) modulate AMPA receptor phosphorylation and cell-surface localization in concert with pain-related behavior

    PubMed Central

    Lee, Daniel Z.; Chung, Jin M.; Chung, Kyungsoon; Kang, Myoung-Goo

    2012-01-01

    Sensitization of dorsal horn neurons (DHNs) in the spinal cord is dependent on pain-related synaptic plasticity and causes persistent pain. The DHN sensitization is mediated by a signal transduction pathway initiated by the activation of NMDA receptors (NMDA-Rs). Recent studies have shown that elevated levels of reactive oxygen species (ROS) and phosphorylation-dependent trafficking of GluA2 subunit of AMPA receptors (AMPA-Rs) are a part of the signaling pathway for DHN sensitization. However, the relationship between ROS and AMPA-R phosphorylation and trafficking is not known. Thus, this study investigated the effects of ROS scavengers on the phosphorylation and cell-surface localization of GluA1 and GluA2. Intrathecal NMDA- and intradermal capsaicin-induced hyperalgesic mice were used for this study since both pain models share the NMDA-R activation-dependent DHN sensitization in the spinal cord. Our behavioral, biochemical, and immunohistochemical analyses demonstrated that: 1) NMDA-R activation in vivo increased the phosphorylation of AMPA-Rs at GluA1 (S818, S831, and S845) and GluA2 (S880) subunits, 2) NMDA-R activation in vivo increased cell-surface localization of GluA1 but decreased that of GluA2, and 3) reduction of ROS levels by ROS scavengers PBN or TEMPOL reversed these changes in AMPA-Rs, as well as pain-related behavior. Given that AMPA-R trafficking to the cell surface and synapse is regulated by NMDA-R activation-dependent phosphorylation of GluA1 and GluA2, our study suggests that the ROS-dependent changes in the phosphorylation and cell-surface localization of AMPA-Rs are necessary for DHN sensitization and thus pain-related behavior. We further suggest that ROS reduction will ameliorate these molecular changes and pain. PMID:22770842

  8. Auxiliary Subunit GSG1L Acts to Suppress Calcium-Permeable AMPA Receptor Function

    PubMed Central

    McGee, Thomas P.; Bats, Cécile

    2015-01-01

    AMPA-type glutamate receptors are ligand-gated cation channels responsible for a majority of the fast excitatory synaptic transmission in the brain. Their behavior and calcium permeability depends critically on their subunit composition and the identity of associated auxiliary proteins. Calcium-permeable AMPA receptors (CP-AMPARs) contribute to various forms of synaptic plasticity, and their dysfunction underlies a number of serious neurological conditions. For CP-AMPARs, the prototypical transmembrane AMPAR regulatory protein stargazin, which acts as an auxiliary subunit, enhances receptor function by increasing single-channel conductance, slowing channel gating, increasing calcium permeability, and relieving the voltage-dependent block by endogenous intracellular polyamines. We find that, in contrast, GSG1L, a transmembrane auxiliary protein identified recently as being part of the AMPAR proteome, acts to reduce the weighted mean single-channel conductance and calcium permeability of recombinant CP-AMPARs, while increasing polyamine-dependent rectification. To examine the effects of GSG1L on native AMPARs, we manipulated its expression in cerebellar and hippocampal neurons. Transfection of GSG1L into mouse cultured cerebellar stellate cells that lack this protein increased the inward rectification of mEPSCs. Conversely, shRNA-mediated knockdown of endogenous GSG1L in rat cultured hippocampal pyramidal neurons led to an increase in mEPSC amplitude and in the underlying weighted mean single-channel conductance, revealing that GSG1L acts to suppress current flow through native CP-AMPARs. Thus, our data suggest that GSG1L extends the functional repertoire of AMPAR auxiliary subunits, which can act not only to enhance but also diminish current flow through their associated AMPARs. SIGNIFICANCE STATEMENT Calcium-permeable AMPA receptors (CP-AMPARs) are an important group of receptors for the neurotransmitter glutamate. These receptors contribute to various forms of

  9. AMPA receptor trafficking and the mechanisms underlying synaptic plasticity and cognitive aging.

    PubMed

    Henley, Jeremy M; Wilkinson, Kevin A

    2013-03-01

    Even in healthy individuals there is an inexorable agerelated decline in cognitive function. This is due, in large part, to reduced synaptic plasticity caused by changes in the molecular composition of the postsynaptic membrane. AMPA receptors (AMPARs) are glutamate-gated cation channels that mediate the overwhelming majority of fast excitatory transmission in the brain. Changes in AMPAR number and/or function are a core feature of synaptic plasticity and age-related cognitive decline, AMPARs are highly dynamic proteins that are subject to highly controlled trafficking, recycling, and/or degradation and replacement. This active regulation of AMPAR synthesis, targeting, synaptic dwell time, and degradation is fundamentally important for memory formation and storage. Further, aberrant AMPAR trafficking and consequent detrimental changes in synapses are strongly implicated in many brain diseases, which represent a vast social and economic burden. The purpose of this article is to provide an overview of the molecular and cellular AMPA receptor trafficking events that control synaptic responsiveness and plasticity, and highlight what is known currently known about how these processes change with age and disease. PMID:23576886

  10. AMPA receptor trafficking and the mechanisms underlying synaptic plasticity and cognitive aging

    PubMed Central

    Henley, Jeremy M.; Wilkinson, Kevin A.

    2013-01-01

    Even in healthy individuals there is an inexorable agerelated decline in cognitive function. This is due, in large part, to reduced synaptic plasticity caused by changes in the molecular composition of the postsynaptic membrane. AMPA receptors (AMPARs) are glutamate-gated cation channels that mediate the overwhelming majority of fast excitatory transmission in the brain. Changes in AMPAR number and/or function are a core feature of synaptic plasticity and age-related cognitive decline, AMPARs are highly dynamic proteins that are subject to highly controlled trafficking, recycling, and/or degradation and replacement. This active regulation of AMPAR synthesis, targeting, synaptic dwell time, and degradation is fundamentally important for memory formation and storage. Further, aberrant AMPAR trafficking and consequent detrimental changes in synapses are strongly implicated in many brain diseases, which represent a vast social and economic burden. The purpose of this article is to provide an overview of the molecular and cellular AMPA receptor trafficking events that control synaptic responsiveness and plasticity, and highlight what is known currently known about how these processes change with age and disease. PMID:23576886

  11. Estrous Cycle-Dependent Phasic Changes in the Stoichiometry of Hippocampal Synaptic AMPA Receptors in Rats.

    PubMed

    Tada, Hirobumi; Koide, Mayu; Ara, Wakana; Shibata, Yusuke; Funabashi, Toshiya; Suyama, Kumiko; Goto, Takahisa; Takahashi, Takuya

    2015-01-01

    Cognitive function can be affected by the estrous cycle. However, the effect of the estrous cycle on synaptic functions is poorly understood. Here we show that in female rats, inhibitory-avoidance (IA) task (hippocampus-dependent contextual fear-learning task) drives GluA2-lacking Ca2+-permeable AMPA receptors (CP-AMPARs) into the hippocampal CA3-CA1 synapses during all periods of the estrous cycle except the proestrous period, when estrogen levels are high. In addition, IA task failed to drive CP-AMPARs into the CA3-CA1 synapses of ovariectomized rats only when estrogen was present. Thus, changes in the stoichiometry of AMPA receptors during learning depend on estrogen levels. Furthermore, the induction of long-term potentiation (LTP) after IA task was prevented during the proestrous period, while intact LTP is still expressed after IA task during other period of the estrous cycle. Consistent with this finding, rats conditioned by IA training failed to acquire hippocampus-dependent Y-maze task during the proestrous period. On the other hand, during other estrous period, rats were able to learn Y-maze task after IA conditioning. These results suggest that high estrogen levels prevent the IA learning-induced delivery of CP-AMPARs into hippocampal CA3-CA1 synapses and limit synaptic plasticity after IA task, thus preventing the acquisition of additional learning. PMID:26121335

  12. Vitamin D3 supplementation increases insulin level by regulating altered IP3 and AMPA receptor expression in the pancreatic islets of streptozotocin-induced diabetic rat.

    PubMed

    Jayanarayanan, Sadanandan; Anju, Thoppil R; Smijin, Soman; Paulose, Cheramadathikudiyil Skaria

    2015-10-01

    Pancreatic islets, particularly insulin-secreting β cells, share common characteristics with neurons. Glutamate is one of the major excitatory neurotransmitter in the brain and pancreas, and its action is mediated through glutamate receptors. In the present work, we analysed the role of vitamin D3 in the modulation of AMPA receptor subunit and their functional role in insulin release. Radio receptor binding study in diabetic rats showed a significant increase in AMPA receptor density. Insulin AMPA colabelling study showed an altered AMPA GluR2 and GluR4 subunit expression in the pancreatic beta cells. We also found lowered IP3 content and decreased IP3 receptor in pancreas of diabetic rats. The alterations in AMPA and IP3 receptor resulted in reduced cytosolic calcium level concentration, which further blocks Ca(2+)-mediated insulin release. Vitamin D3 supplementation restored the alteration in vitamin D receptor expression, AMPA receptor density and AMPA and IP3 receptor expression in the pancreatic islets that helps to restore the calcium-mediated insulin secretion. Our study reveals the antidiabetic property of vitamin D3 that is suggested to have therapeutic role through regulating glutamatergic function in diabetic rats. PMID:26054778

  13. Synaptic commitment: developmentally regulated reciprocal changes in hippocampal granule cell NMDA and AMPA receptors over the lifespan.

    PubMed

    Yang, Zhiyong; Krause, Michael; Rao, Geeta; McNaughton, Bruce L; Barnes, C A

    2008-06-01

    Synaptic transmission in hippocampal field CA1 is largely N-methyl-d-aspartate receptor (NMDA(R)) dependent during the early postnatal period. It becomes increasingly mediated by alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionate (AMPA) receptors until an adult ratio of AMPA to NMDA receptors is achieved. It is shown here that increases in the AMPA receptor (AMPA(R))-mediated field potential response continue over the life span of the F-344 rat at the perforant path-granule cell synapse in the dentate gyrus. In contrast, the NMDA(R)-dependent component of the response decreases with age between 1 and 27 mo, leading to an increase of AMPA(R)/NMDA(R) ratio with age. One possible explanation of this age difference is that the AMPA(R)/NMDA(R) ratio can be modified by experience. To test the idea that the changed ratio is caused by the old rats' longer lives, an intensive 10-mo period of enrichment treatment was given to a group of animals, beginning at 3 mo of age. Compared with animals housed in standard cages, the enrichment treatment did not alter the glutamatergic response ratio measured with field potential recording methods. These data provide support for the conclusion that the observed change with age is developmentally regulated rather than experience dependent. Given the role of the NMDA(R) in synaptic plasticity, these changes suggest a progressive commitment of perforant path synapses to particular weights over the life span. One possible implication of this effect includes preservation of selected memories, ultimately at the expense of a reduced capacity to store new information. PMID:18417629

  14. Alternative splicing of AMPA receptor subunits in the 6-OHDA-lesioned rat model of Parkinson's disease and L-DOPA-induced dyskinesia.

    PubMed

    Kobylecki, Christopher; Crossman, Alan R; Ravenscroft, Paula

    2013-09-01

    Abnormal corticostriatal plasticity is a key mechanism of L-DOPA-induced dyskinesia (LID) in Parkinson's disease (PD). Antagonists at glutamatergic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, such as IEM 1460, reduce induction and expression of dyskinesia in rat and non-human primate models of PD. AMPA receptor function is regulated by post-transcriptional splicing of subunit mRNA to produce flip and flop isoforms, which may therefore influence corticostriatal plasticity. The aim of this work was to evaluate alterations in alternative splicing of striatal AMPA receptor subunits in the unilateral 6-hydroxydopamine (6-OHDA)-lesioned rat model of LID and PD. Male Sprague-Dawley rats received 12.5 μg 6-OHDA injections into the right medial forebrain bundle. In experiment 1, to assess acute dyskinesia, rats received L-DOPA/benserazide (6/15 mg/kg, i.p.) or vehicle for 21 days. In experiment 2, to assess dyskinesia priming, rats received vehicle, L-DOPA+vehicle or L-DOPA+IEM 1460 (3 mg/kg, i.p.) for 21 days. Animals were humanely killed 1h following final treatment in experiment 1, and 48 h following final treatment in experiment 2. Coronal sections of rostral striatum were processed for in situ hybridisation histochemistry, using oligonucleotide probes specific for the GluR1 and GluR2 subunits and their flip and flop isoforms. L-DOPA treatment increased GluR2-flip mRNA expression in the lesioned striatum of both groups; this was blocked by the Ca(2+)-permeable AMPA receptor antagonist IEM 1460. GluR1-flip expression was increased after 48 h drug washout but not in acute LID. There were no changes in expression of flop isoforms. Alternative splicing of AMPAR subunits contributes to abnormal striatal plasticity in the induction and expression of LID. Increases in GluR2-flip expression depend on activation of Ca(2+)-permeable AMPA receptors, which are a potential target of anti-dyskinetic therapies. PMID:23360800

  15. The AMPA receptor antagonist perampanel robustly rescues amyotrophic lateral sclerosis (ALS) pathology in sporadic ALS model mice

    PubMed Central

    Akamatsu, Megumi; Yamashita, Takenari; Hirose, Naoki; Teramoto, Sayaka; Kwak, Shin

    2016-01-01

    Both TDP-43 pathology and failure of RNA editing of AMPA receptor subunit GluA2, are etiology-linked molecular abnormalities that concomitantly occur in the motor neurons of the majority of patients with amyotrophic lateral sclerosis (ALS). AR2 mice, in which an RNA editing enzyme adenosine deaminase acting on RNA 2 (ADAR2) is conditionally knocked out in the motor neurons, exhibit a progressive ALS phenotype with TDP-43 pathology in the motor neurons through a Ca2+-permeable AMPA receptor-mediated mechanism. Therefore, amelioration of the increased Ca2+ influx by AMPA receptor antagonists may be a potential ALS therapy. Here, we showed that orally administered perampanel, a selective, non-competitive AMPA receptor antagonist significantly prevented the progression of the ALS phenotype and normalized the TDP-43 pathology-associated death of motor neurons in the AR2 mice. Given that perampanel is an approved anti-epileptic drug, perampanel is a potential candidate ALS drug worthy of a clinical trial. PMID:27350567

  16. Deletion of the GluA1 AMPA Receptor Subunit Alters the Expression of Short-Term Memory

    ERIC Educational Resources Information Center

    Sanderson, David J.; Sprengel, Rolf; Seeburg, Peter H.; Bannerman, David M.

    2011-01-01

    Deletion of the GluA1 AMPA receptor subunit selectively impairs short-term memory for spatial locations. We further investigated this deficit by examining memory for discrete nonspatial visual stimuli in an operant chamber. Unconditioned suppression of magazine responding to visual stimuli was measured in wild-type and GluA1 knockout mice.…

  17. Identification of an ionotropic glutamate receptor AMPA1/GRIA1 polymorphism in crossbred beef cows differing in fertility

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A proposed functional polymorphism in the ionotropic glutamate receptor AMPA1 (GRIA1) has been reported to influence antral follicle numbers and fertility in cows. Repeat Breeder cows that fail to produce a calf in multiple seasons have been reported to have reduced numbers of small (1-3 mm) antral ...

  18. The AMPA receptor antagonist perampanel robustly rescues amyotrophic lateral sclerosis (ALS) pathology in sporadic ALS model mice.

    PubMed

    Akamatsu, Megumi; Yamashita, Takenari; Hirose, Naoki; Teramoto, Sayaka; Kwak, Shin

    2016-01-01

    Both TDP-43 pathology and failure of RNA editing of AMPA receptor subunit GluA2, are etiology-linked molecular abnormalities that concomitantly occur in the motor neurons of the majority of patients with amyotrophic lateral sclerosis (ALS). AR2 mice, in which an RNA editing enzyme adenosine deaminase acting on RNA 2 (ADAR2) is conditionally knocked out in the motor neurons, exhibit a progressive ALS phenotype with TDP-43 pathology in the motor neurons through a Ca(2+)-permeable AMPA receptor-mediated mechanism. Therefore, amelioration of the increased Ca(2+) influx by AMPA receptor antagonists may be a potential ALS therapy. Here, we showed that orally administered perampanel, a selective, non-competitive AMPA receptor antagonist significantly prevented the progression of the ALS phenotype and normalized the TDP-43 pathology-associated death of motor neurons in the AR2 mice. Given that perampanel is an approved anti-epileptic drug, perampanel is a potential candidate ALS drug worthy of a clinical trial. PMID:27350567

  19. Myelin Proteolipid Protein Complexes with αv Integrin and AMPA Receptors In Vivo and Regulates AMPA-Dependent Oligodendrocyte Progenitor Cell Migration through the Modulation of Cell-Surface GluR2 Expression

    PubMed Central

    Harlow, Danielle E.; Saul, Katherine E.; Komuro, Hitoshi

    2015-01-01

    In previous studies, stimulation of ionotropic AMPA/kainate glutamate receptors on cultured oligodendrocyte cells induced the formation of a signaling complex that includes the AMPA receptor, integrins, calcium-binding proteins, and, surprisingly, the myelin proteolipid protein (PLP). AMPA stimulation of cultured oligodendrocyte progenitor cells (OPCs) also caused an increase in OPC migration. The current studies focused primarily on the formation of the PLP–αv integrin–AMPA receptor complex in vivo and whether complex formation impacts OPC migration in the brain. We found that in wild-type cerebellum, PLP associates with αv integrin and the calcium-impermeable GluR2 subunit of the AMPA receptor, but in mice lacking PLP, αv integrin did not associate with GluR2. Live imaging studies of OPC migration in ex vivo cerebellar slices demonstrated altered OPC migratory responses to neurotransmitter stimulation in the absence of PLP and GluR2 or when αv integrin levels were reduced. Chemotaxis assays of purified OPCs revealed that AMPA stimulation was neither attractive nor repulsive but clearly increased the migration rate of wild-type but not PLP null OPCs. AMPA receptor stimulation of wild-type OPCs caused decreased cell-surface expression of the GluR2 AMPA receptor subunit and increased intracellular Ca2+ signaling, whereas PLP null OPCs did not reduce GluR2 at the cell surface or increase Ca2+ signaling in response to AMPA treatment. Together, these studies demonstrate that PLP is critical for OPC responses to glutamate signaling and has important implications for OPC responses when levels of glutamate are high in the extracellular space, such as following demyelination. SIGNIFICANCE STATEMENT After demyelination, such as occurs in multiple sclerosis, remyelination of axons is often incomplete, leading to loss of neuronal function and clinical disability. Remyelination may fail because oligodendrocyte precursor cells (OPCs) do not completely migrate into

  20. Subsynaptic AMPA Receptor Distribution Is Acutely Regulated by Actin-Driven Reorganization of the Postsynaptic Density

    PubMed Central

    Kerr, Justin M.; Blanpied, Thomas A.

    2012-01-01

    AMPA receptors (AMPARs) mediate synaptic transmission and plasticity during learning, development, and disease. Mechanisms determining subsynaptic receptor position are poorly understood but are key determinants of quantal size. We used a series of live-cell, high-resolution imaging approaches to measure protein organization within single postsynaptic densities in rat hippocampal neurons. By photobleaching receptors in synapse subdomains, we found that most AMPARs do not freely diffuse within the synapse, indicating they are embedded in a matrix that determines their subsynaptic position. However, time lapse analysis revealed that synaptic AMPARs are continuously repositioned in concert with plasticity of this scaffold matrix rather than simply by free diffusion. Using a fluorescence correlation analysis, we found that across the lateral extent of single PSDs, component proteins were differentially distributed, and this distribution was continually adjusted by actin treadmilling. The C-terminal PDZ ligand of GluA1 did not regulate its mobility or distribution in the synapse. However, glutamate receptor activation promoted subsynaptic mobility. Strikingly, subsynaptic immobility of both AMPARs and scaffold molecules remained essentially intact even after loss of actin filaments. We conclude that receptors are actively repositioned at the synapse by treadmilling of the actin cytoskeleton, an influence which is transmitted only indirectly to receptors via the pliable and surprisingly dynamic internal structure of the PSD. PMID:22238102

  1. Bipolar disorder: involvement of signaling cascades and AMPA receptor trafficking at synapses

    PubMed Central

    DU, JING; QUIROZ, JORGE; YUAN, PEIXIONG; ZARATE, CARLOS; MANJI, HUSSEINI K.

    2009-01-01

    There is increasing evidence that severe mood disorders are associated with impairment of structural plasticity and cellular resilience. Cumulative data demonstrate that mood stabilizers regulate intracellular signaling cascades, including protein kinase C (PKC), PKA, mitogen-activated protein (MAP) kinase, glycogen synthase kinase 3-β (GSK3-β) and intracellular calcium, which are signaling pathways that regulate synaptic plasticity. In this context, it is noteworthy that a growing body of data indicates that the glutamatergic system, has a major role in neuronal plasticity and cellular resilience, might be involved in the pathophysiology and treatment of mood disorders. AMPA glutamate-receptor trafficking is important in synaptic plasticity and might play crucial roles in maintaining critical neuronal circuits associated with mood. Two clinically effective, structurally dissimilar, antimanic agents, lithium and valproate (VPA), down-regulate synaptic expression of AMPA receptor subunit GluR1 in hippocampus in chronically treated rats. This reduction in synaptic GluR1 by lithium and VPA is due to attenuated phosphorylation of GluR1 at a specific PKA site (residue 845 of GluR1), which is crucial for AMPA receptor insertion. By contrast, imipramine, which can provoke mania, increases synaptic expression of GluR1 in the hippocampus in vivo. Furthermore, there is ample evidence from preclinical and clinical research that the glutamatergic system is involved in the pathophysiology of mood disorders and that many of the somatic treatments used for mood disorders including antidepressants, mood stabilizers, atypical antipsychotic drugs and electroconvulsive therapy have both direct and indirect effects on the glutamatergic system. Given these findings, further research with medications that specifically affect the glutamatergic system is warranted. Recent studies in our lab have shown that riluzole, a FDA approved medicine that regulates the glutamatergic system, shows

  2. Domain Architecture of a Calcium-Permeable AMPA Receptor in a Ligand-Free Conformation

    PubMed Central

    Midgett, Charles R.; Gill, Avinash; Madden, Dean R.

    2012-01-01

    Ligand-gated ion channels couple the free energy of agonist binding to the gating of selective transmembrane ion pores, permitting cells to regulate ion flux in response to external chemical stimuli. However, the stereochemical mechanisms responsible for this coupling remain obscure. In the case of the ionotropic glutamate receptors (iGluRs), the modular nature of receptor subunits has facilitated structural analysis of the N-terminal domain (NTD), and of multiple conformations of the ligand-binding domain (LBD). Recently, the crystallographic structure of an antagonist-bound form of the receptor was determined. However, disulfide trapping of this conformation blocks channel opening, suggesting that channel activation involves additional quaternary packing arrangements. To explore the conformational space available to iGluR channels, we report here a second, clearly distinct domain architecture of homotetrameric, calcium-permeable AMPA receptors, determined by single-particle electron microscopy of untagged and fluorescently tagged constructs in a ligand-free state. It reveals a novel packing of NTD dimers, and a separation of LBD dimers across a central vestibule. In this arrangement, which reconciles diverse functional observations, agonist-induced cleft closure across LBD dimers can be converted into a twisting motion that provides a basis for receptor activation. PMID:22232575

  3. Roles of the NMDA Receptor and EAAC1 Transporter in the Modulation of Extracellular Glutamate by Low and High Affinity AMPA Receptors in the Cerebellum in Vivo: Differential Alteration in Chronic Hyperammonemia.

    PubMed

    Cabrera-Pastor, Andrea; Taoro, Lucas; Llansola, Marta; Felipo, Vicente

    2015-12-16

    The roles of high- and low-affinity AMPA receptors in modulating extracellular glutamate in the cerebellum remain unclear. Altered glutamatergic neurotransmission is involved in neurological alterations in hyperammonemia, which differently affects high- and low-affinity AMPA receptors. The aims were to assess by in vivo microdialysis (a) the effects of high- and low-affinity AMPA receptor activation on extracellular glutamate in the cerebellum; (b) whether chronic hyperammonemia alters extracellular glutamate modulation by high- and/or low-affinity AMPA receptors; and (c) the contribution of NMDA receptors and EAAC1 transporter to AMPA-induced changes in extracellular glutamate. In control rats, high affinity receptor activation does not affect extracellular glutamate but increases glutamate if NMDA receptors are blocked. Low affinity AMPA receptor activation increases transiently extracellular glutamate followed by reduction below basal levels and return to basal values. The reduction is associated with transient increased membrane expression of EAAC1 and is prevented by blocking NMDA receptors. Blocking NMDA receptors with MK-801 induces a transient increase in extracellular glutamate which is associated with reduced membrane expression of EAAC1 followed by increased membrane expression of the glutamate transporter GLT-1. Chronic hyperammonemia does not affect responses to activation of low affinity AMPA receptors. Activation of high affinity AMPA receptors increases extracellular glutamate in hyperammonemic rats by an NMDA receptor-dependent mechanism. In conclusion, these results show that there is a tightly controlled interplay between AMPA and NMDA receptors and an EAAC1 transporter in controlling extracellular glutamate. Hyperammonemia alters high- but not low-affinity AMPA receptors. PMID:26428532

  4. The inhibitory input to mouse cerebellar Purkinje cells is reciprocally modulated by Bergmann glial P2Y1 and AMPA receptor signaling.

    PubMed

    Rudolph, Ramona; Jahn, Hannah M; Courjaret, Raphael; Messemer, Nanette; Kirchhoff, Frank; Deitmer, Joachim W

    2016-07-01

    Synaptic transmission has been shown to be modulated by glial functions, but the modes of specific glial action may vary in different neural circuits. We have tested the hypothesis, if Bergmann GLIA (BG) are involved in shaping neuronal communication in the mouse cerebellar cortex, using acutely isolated cerebellar slices of wild-type (WT) and of glia-specific receptor knockout mice. Activation of P2Y1 receptors by ADP (100 µM) or glutamatergic receptors by AMPA (0.3 µM) resulted in a robust, reversible and repeatable rise of evoked inhibitory input in Purkinje cells by 80% and 150%, respectively. The ADP-induced response was suppressed by prior application of AMPA, and the AMPA-induced response was suppressed by prior application of ADP. Genetic deletion or pharmacological blockade of either receptor restored the response to the other receptor agonist. Both ADP and AMPA responses were sensitive to Rose Bengal, which blocks vesicular glutamate uptake, and to the NMDA receptor antagonist D-AP5. Our results provide strong evidence that activation of both ADP and AMPA receptors, located on BGs, results in the release of glutamate, which in turn activates inhibitory interneurons via NMDA-type glutamate receptors. This infers that BG cells, by means of metabotropic signaling via their AMPA and P2Y1 receptors, which mutually suppress each other, would interdependently contribute to the fine-tuning of Purkinje cell activity in the cerebellar cortex. GLIA 2016. GLIA 2016;64:1265-1280. PMID:27144942

  5. Reversible Palmitoylation Regulates Surface Stability of AMPA Receptors in the Nucleus Accumbens in Response to Cocaine in vivo

    PubMed Central

    Van Dolah, Dustin K.; Mao, Li-Min; Shaffer, Christopher; Guo, Ming-Lei; Fibuch, Eugene E.; Chu, Xiang-Ping; Buch, Shilpa; Wang, John Q.

    2010-01-01

    Background Palmitoylation is emerging as one of the most important posttranslational modifications of excitatory synaptic proteins in mammalian brain cells. As a reversible and regulatable modification sensitive to changing synaptic inputs, palmitoylation of ionotropic glutamate receptors contributes to not only the modulation of normal receptor and synaptic activities, but also the pathogenesis of various neuropsychiatric disorders. Here, we report that palmitoylation of the AMPA receptor is regulated by the psychostimulant, cocaine, and such regulation is involved in cocaine action. Methods We tested palmitoylation and surface expression of AMPA receptors in striatal neurons and psychomotor behavior in responses to cocaine in rats. Results All four AMPA receptor subunits (GluA1-4 or GluR1-4) are palmitoylated in the nucleus accumbens (NAc) of adult rats. Among them, GluA1 and GluA3 are preferentially upregulated in their palmitoylation levels by a systemic injection of cocaine. The upregulated GluA1 and 3 palmitoylation is a transient and reversible event. Consequently, it increases the susceptibility of surface-expressed GluA1 and 3 to internalization trafficking, leading to a temporal loss of surface receptor expression. Blockade of the regulated GluA1/3 palmitoylation with a palmitoylation inhibitor in the local NAc reverses the loss of surface GluA1/3. The inhibition of palmitoylation also concurrently sustains behavioral responsivity to cocaine. Conclusions Our data identify a novel drug-palmitoylation coupling in the center of limbic reward circuits. Through palmitoylating selective AMPA receptor subunits, cocaine activity-dependently regulates trafficking and subcellular localization of the receptor in NAc neurons and dynamically controls psychomotor sensitivity to the psychoactive drug in vivo. PMID:21216391

  6. KCC2 Gates Activity-Driven AMPA Receptor Traffic through Cofilin Phosphorylation.

    PubMed

    Chevy, Quentin; Heubl, Martin; Goutierre, Marie; Backer, Stéphanie; Moutkine, Imane; Eugène, Emmanuel; Bloch-Gallego, Evelyne; Lévi, Sabine; Poncer, Jean Christophe

    2015-12-01

    Expression of the neuronal K/Cl transporter KCC2 is tightly regulated throughout development and by both normal and pathological neuronal activity. Changes in KCC2 expression have often been associated with altered chloride homeostasis and GABA signaling. However, recent evidence supports a role of KCC2 in the development and function of glutamatergic synapses through mechanisms that remain poorly understood. Here we show that suppressing KCC2 expression in rat hippocampal neurons precludes long-term potentiation of glutamatergic synapses specifically by preventing activity-driven membrane delivery of AMPA receptors. This effect is independent of KCC2 transporter function and can be accounted for by increased Rac1/PAK- and LIMK-dependent cofilin phosphorylation and actin polymerization in dendritic spines. Our results demonstrate that KCC2 plays a critical role in the regulation of spine actin cytoskeleton and gates long-term plasticity at excitatory synapses in cortical neurons. PMID:26631461

  7. Elucidation of AMPA receptor-stargazin complexes by cryo-electron microscopy.

    PubMed

    Twomey, Edward C; Yelshanskaya, Maria V; Grassucci, Robert A; Frank, Joachim; Sobolevsky, Alexander I

    2016-07-01

    AMPA-subtype ionotropic glutamate receptors (AMPARs) mediate fast excitatory neurotransmission and contribute to high cognitive processes such as learning and memory. In the brain, AMPAR trafficking, gating, and pharmacology is tightly controlled by transmembrane AMPAR regulatory proteins (TARPs). Here, we used cryo-electron microscopy to elucidate the structural basis of AMPAR regulation by one of these auxiliary proteins, TARP γ2, or stargazin (STZ). Our structures illuminate the variable interaction stoichiometry of the AMPAR-TARP complex, with one or two TARP molecules binding one tetrameric AMPAR. Analysis of the AMPAR-STZ binding interfaces suggests that electrostatic interactions between the extracellular domains of AMPAR and STZ play an important role in modulating AMPAR function through contact surfaces that are conserved across AMPARs and TARPs. We propose a model explaining how TARPs stabilize the activated state of AMPARs and how the interactions between AMPARs and their auxiliary proteins control fast excitatory synaptic transmission. PMID:27365450

  8. Transport of AMPA receptors during long-term potentiation is impaired in rats with hepatic encephalopathy.

    PubMed

    Monfort, Pilar; Piedrafita, Blanca; Felipo, Vicente

    2009-12-01

    Cognitive function is impaired in patients with hepatic encephalopathy. Learning ability is also impaired in rats with hepatic encephalopathy due to portacaval shunts. Long-term potentiation (LTP) in hippocampus, considered the basis of some forms of learning and memory, is impaired in rats with portacaval shunt. We analyzed the mechanisms by which LTP is impaired in these rats. In control rats, application of the tetanus to induce LTP increases phosphorylation of Thr286 of calcium-calmodulin dependent protein kinase II. This activates the kinase which phosphorylates the GluR1 subunit of AMPA receptors in Ser831 and induces its translocation to the post-synaptic densities. All these steps are completely prevented in rats with hepatic encephalopathy in which the tetanus does not induce phosphorylation of CaMKII or GluR1 nor translocation of this subunit to the post-synaptic membrane. This would explain the impairment in LTP in these rats. PMID:19450629

  9. AMPA receptor synaptic plasticity induced by psychostimulants: the past, present, and therapeutic future

    PubMed Central

    Bowers, M. Scott; Chen, Billy T.; Bonci, Antonello

    2010-01-01

    Experience-dependent plasticity at excitatory synapses of the mesocorticolimbic system is a fundamental brain mechanism that enables adaptation to an ever-changing environment. These synaptic responses are critical for the planning and execution of adaptive behaviors that maximize survival. The mesocorticolimbic system mediates procurement of positive reinforcers such as food and sex; however, drugs of abuse re-sculpt this crucial circuitry to promote compulsive drug-seeking behavior. This review will discuss the long-term changes in glutamatergic neurotransmission that occur within the mesolimbic system following cocaine exposure. In addition, we will examine how these long-lasting neuroadaptations may drive the pathology of psychostimulant addiction. Finally, we review clinical trials that highlight antagonists at excitatory AMPA receptors as promising targets against cocaine abuse. PMID:20624588

  10. Gestational nicotine exposure regulates expression of AMPA and NMDA receptors and their signaling apparatus in developing and adult rat hippocampus

    PubMed Central

    Wang, Hong; Dávila-García, Martha I.; Yarl, Weonpo; Gondré-Lewis, Marjorie C.

    2011-01-01

    Untimely activation of nicotinic acetylcholine receptor (nAChR) by nicotine results in short- and long-term consequences on learning and behavior. In this study, the aim was to determine how prenatal nicotine exposure affects components of glutamatergic signaling in the hippocampus during postnatal development. We investigated regulation of both nAChRs and glutamate receptors for α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and N-methyl-D-aspartate (NMDA), from postnatal day (P) 1 to P63 after a temporally restricted exposure to saline or nicotine for 14 days in utero. We analyzed postsynaptic density components associated with AMPAR and NMDAR signaling: Calcium/calmodulin-dependent protein kinase II α (CaMKIIα), Calmodulin (CaM), and postsynaptic density-95 (PSD95), as well as presynaptically localized synaptosomal-associated protein 25 (SNAP25). At P1, there was significantly heightened expression of AMPAR subunit GluR1 but not GluR2, and of NMDAR subunits NR1, NR2a and NR2d but not NR2b. NR2c was not detectable. At P1, the postsynaptic proteins CaMKIIα, CaM, and PSD95 were also significantly upregulated, together with presynaptic SNAP25. This enhanced expression of glutamate receptors and signaling proteins was concomitant with elevated levels of [3H] Epibatidine (EB) binding in prenatal nicotine-exposed hippocampus, indicating that α4β2 nAChR may influence glutamatergic function in the hippocampus at P1. By P14, neither [3H]EB binding nor the expression levels of subunits GluR1, GluR2, NR1, NR2a, NR2b, NR2c, or NR2d seemed changed with prenatal nicotine. However, CaMKIIα was significantly upregulated with nicotine treatment while CaM showed downregulation at P14. The effects of nicotine persisted in young adult brains at P63. They exhibited significantly downregulated GluR2, NR1, and NR2c expression levels in hippocampal homogenates and a considerably muted overall distribution of [3H]AMPA binding in areas CA1, CA2, CA3, and the dentate

  11. The effect of AMPA receptor blockade on spatial information acquisition, consolidation and expression in juvenile rats.

    PubMed

    Tzakis, Nikolaos; Bosnic, Tim; Ritchie, Thomas; Dixon, Kaylyn; Holahan, Matthew R

    2016-09-01

    Improvement on spatial tasks in rats is observed during a late, postnatal developmental period (post-natal day (PND) 18 - PND 20). The developmental emergence of this spatial function occurs in conjunction with hippocampal connectivity changes and enhanced hippocampal-AMPA receptor-mediated synaptic responses. The current work investigated the effect of AMPAr blockade on the emergence and long-term storage of spatial information in juvenile rats and associated neural activity patterns in the dorsal hippocampus CA1 region. Male, Long Evans rats between the ages of PND 18 and PND 20 were systemically (i.p.) administered the AMPAr antagonist, NBQX, (0, 5 or 10mg/kg) every day prior to hidden platform water maze training (PND 18, 19 and 20), every day immediately post-training or immediately before the probe test (PND 41). NBQX administration prior to training prolonged latencies, pathlength and increased thigmotaxis during the acquisition phase. Administration of NBQX immediately posttraining had no effect on the day-to-day performance. When given a probe test 3weeks later, the saline group across all conditions spent more time in the target quadrant. Rats treated with pretraining 5mg NBQX dose showed a preference for the target quadrant while the posttraining and pretesting 5mg NBQX doses impaired the target quadrant preference. Groups injected with 10mg of NBQX pretraining, posttraining or pretesting did not show a preference for the target quadrant. c-Fos labeling in the CA1 reflected these differences in probe performance in that groups showing greater than chance dwell time in the target quadrant showed more c-Fos labeling in the CA1 region than groups that did not show a target quadrant preference. These findings provide support for the critical role of AMPA receptor-mediated function in the organization and long-term storage of spatial memories acquired during the juvenile period. PMID:27353718

  12. Modeling of slow glutamate diffusion and AMPA receptor activation in the cerebellar glomerulus.

    PubMed

    Saftenku, E E

    2005-06-01

    Synaptic conductances are influenced markedly by the geometry of the space surrounding the synapse since the transient glutamate concentration in the synaptic cleft is determined by this geometry. Our paper is an attempt to understand the reasons for slow glutamate diffusion in the cerebellar glomerulus, a structure situated around the enlarged mossy fiber terminal in the cerebellum and surrounded by a glial sheath. For this purpose, analytical expressions for glutamate diffusion in the glomerulus were considered in models with two-, three-, and fractional two-three-dimensional (2D-3D) geometry with an absorbing boundary. The time course of average glutamate concentration in the synaptic cleft of the mossy fiber-granule cell connection was calculated for both direct release of glutamate from the same synaptic unit, and for cumulative spillover of glutamate from neighboring release sites. Several kinetic schemes were examined, and the parameters of the diffusion models were estimated by identifying theoretical activation of AMPA receptors with direct release and spillover components of published experimental AMPA receptor-mediated EPSCs. For model selection, the correspondence of simulated paired-pulse ratio and EPSC increase after prevention of desensitization to experimental values were also taken into consideration. Our results suggest at least a 7- to 10-fold lower apparent diffusion coefficient of glutamate in the porous medium of the glomerulus than in water. The modeling of glutamate diffusion in the 2D-3D geometry gives the best fit of experimental EPSCs. We show that it could be only partly explained by normal diffusion of glutamate in the complex geometry of the glomerulus. We assume that anomalous diffusion of glutamate occurs in the glomerulus. A good match of experimental estimations and theoretical parameters, obtained in the simulations that use an approximation of anomalous diffusion by a solution for fractional Brownian motion, confirms our

  13. Involvement of AMPA/kainate and GABAA receptors in topiramate neuroprotective effects against methylphenidate abuse sequels involving oxidative stress and inflammation in rat isolated hippocampus.

    PubMed

    Motaghinejad, Majid; Motevalian, Manijeh

    2016-08-01

    Abuses of methylphenidate (MPH) as psychostimulant cause neural damage of brain cells. Neuroprotective properties of topiramate (TPM) have been indicated in several studies but its exact mechanism of action remains unclear. The current study evaluates protective role of various doses of TPM and its mechanism of action in MPH induced oxidative stress and inflammation. The neuroprotective effects of various doses of TPM against MPH induced oxidative stress and inflammation were evaluated and then the action of TPM was studied in presence of domoic acid (DOM), as AMPA/kainate receptor agonist and bicuculline (BIC) as GABAA receptor antagonist, in isolated rat hippocampus. Open Field Test (OFT) was used to investigate motor activity changes. Oxidative, antioxidant and inflammatory factors were measured in isolated hippocampus. TPM (70 and 100mg/kg) decreased MPH induced motor activity disturbances and inhibit MPH induced oxidative stress and inflammation. On the other hand pretreatment of animals with DOM or BIC, inhibit this effect of TPM and potentiate MPH induced motor activity disturbances and increased lipid peroxidation, mitochondrial oxidized form of glutathione (GSSG) level, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in isolated hippocampal cells and decreased reduced form of glutathione (GSH) level, superoxide dismutase, glutathione peroxidase and glutathione reductase activity. It seems that TPM can protect cells of hippocampus from oxidative stress and neuroinflammation and it could be partly by activation of GABAA receptor and inhibition of AMPA/kainite receptor. PMID:27105819

  14. Involvement of adrenoceptors, dopamine receptors and AMPA receptors in antidepressant-like action of 7-O-ethylfangchinoline in mice

    PubMed Central

    Sheng, Zhao-fu; Cui, Xiang-yu; Cui, Su-ying; Yu, Bin; Zhang, Xue-qiong; Li, Sheng-jie; Cao, Qing; Huang, Yuan-li; Xu, Ya-ping; Song, Jin-zhi; Ding, Hui; Lin, Zhi-ge; Yang, Guang; Zhang, Yong-he

    2015-01-01

    Aim: 7-O-ethylfangchinoline (YH-200) is a bisbenzylisoquinoline derivative. The aim of this study was to investigate the antidepressant-like action and underlying mechanisms of YH-200 in mice. Methods: Mice were treated with YH-200 (15, 30, and 60 mg/kg, ig) or tetrandrine (30 and 60 mg/kg, ig) before conducting forced swimming test (FST), tail suspension test (TST), or open field test (OFT). Results: YH-200 (60 mg/kg) significantly decreased the immobility time in both FST and TST, and prolonged the latency to immobility in FST. YH-200 (60 mg/kg) was more potent than the natural bisbenzylisoquinoline alkaloid tetrandrine (60 mg/kg) in FST. Pretreatment with α1-adrenoceptor antagonist prazosin (1 mg/kg), β-adrenoceptor antagonist propranolol (2 mg/kg), dopamine D1/D5 receptor antagonist SCH23390 (0.05 mg/kg), dopamine D2/D3 receptor antagonist haloperidol (0.2 mg/kg) or AMPA receptor antagonist NBQX (10 mg/kg) prevented the antidepressant-like action of YH-200 (60 mg/kg) in FST. In contrast, pretreatment with α2 adrenoceptor antagonist yohimbine (1 mg/kg) augmented the antidepressant-like action of YH-200 (30 mg/kg) in FST. Chronic administration of YH-200 (30 and 60 mg/kg for 14 d) did not produce drug tolerance; instead its antidepressant-like action was strengthened. Chronic administration of YH-200 did not affect the body weight of mice compared to control mice. Conclusion: YH-200 exerts its antidepressant-like action in mice via acting at multi-targets, including α1, α2 and β-adrenoceptors, D1/D5 and D2 /D3 receptors, as well as AMPA receptors. PMID:26238289

  15. The role of the AMPA receptor and 5-HT(3) receptor on aggressive behavior and depressive-like symptoms in chronic social isolation-reared mice.

    PubMed

    Shimizu, Koh; Kurosawa, Natsuki; Seki, Kenjiro

    2016-01-01

    Chronic social isolation (SI)-reared mice exhibit aggressive and depressive-like behaviors. However, the pathophysiological changes caused by chronic SI remain unclear. The hypothalamus and amygdala have been suggested to be associated with the stress of SI. In addition to serotonin 3 (5-HT3) receptors, AMPA receptors have also been suggested to be involved in aggressive behavior and depressive-like symptoms in animals. Therefore, we examined whether chronic SI affects AMPA and 5-HT3 receptor expression levels in these regions. A Western blot analysis revealed that after four weeks of SI, mice exhibited up-regulated AMPA receptor subunit (GluR1, GluR2) protein levels in the amygdala and down-regulated hypothalamic 5-HT3 receptor protein levels. The AMPA/kainate receptor antagonist NBQX (10 mg/kg; i.p.) attenuated SI-induced depressive-like symptoms but not aggressive behavior. Intra-amygdalar infusions of the selective AMPA receptor agonist (S)-AMPA (10 μM) induced despair-like behavior, but not sucrose preference or aggressive behavior, in mice not reared in SI (naïve mice). Alternatively, treatment with the 5-HT3 receptor agonist SR57227A (3.0 mg/kg; i.p.) decreased aggression levels. In addition, intra-hypothalamic infusions of the 5-HT3 receptor antagonist ondansetron (3 μM) did not trigger aggressive behavior in naïve mice; however, the administration of ondansetron (0.3 mg/kg; i.p.) increased aggression levels in two-week SI mice, which rarely exhibited the aggressive behavior. Moreover, ondansetron did not affect the depressive-like symptoms of the SI mice. These results suggest that SI-induced up-regulation of GluR1 and GluR2 subunits protein levels in the amygdalar region and down-regulation of 5-HT3 receptor proteins level in the hypothalamic region are associated with the effect of AMPA receptor agonist and 5-HT3 receptor antagonist -induced aggressive behavior and depressive-like symptoms. PMID:26522741

  16. Reinforcement-Related Regulation of AMPA Glutamate Receptor Subunits in the Ventral Tegmental Area Enhances Motivation for Cocaine

    PubMed Central

    Choi, Kwang Ho; Edwards, Scott; Graham, Danielle L.; Larson, Erin B.; Whisler, Kimberly N.; Simmons, Diana; Friedman, Allyson K.; Walsh, Jessica J.; Rahman, Zia; Monteggia, Lisa M.; Eisch, Amelia J.; Neve, Rachael L.; Nestler, Eric J.; Han, Ming-Hu; Self, David W.

    2011-01-01

    Chronic cocaine use produces numerous biological changes in brain, but relatively few are functionally associated with cocaine reinforcement. Here we show that daily intravenous cocaine self-administration, but not passive cocaine administration, induces dynamic up-regulation of the AMPA glutamate receptor subunits GluR1 and GluR2 in the ventral tegmental area (VTA) of rats. Increases in GluR1 protein and GluR1S845 phosphorylation are associated with increased GluR1 mRNA in self-administering animals, while increased GluR2 protein levels occurred despite substantial decreases in GluR2 mRNA. We investigated the functional significance of GluR1 up-regulation in the VTA on cocaine self-administration using localized viral-mediated gene transfer. Over-expression of GluR1WT in rat VTA primarily infected dopamine neurons (75%), and increased AMPA receptor-mediated membrane rectification in these neurons with AMPA application. Similar GluR1WT over-expression potentiated locomotor responses to intra-VTA AMPA, but not NMDA, infusions. In cocaine self-administering animals, over-expression of GluR1WT in the VTA markedly increased the motivation for cocaine injections on a progressive ratio schedule of cocaine reinforcement. In contrast, over-expression of protein kinase A-resistant GluR1S845A in the VTA reduced peak rates of cocaine self-administration on a fixed ratio reinforcement schedule. Neither viral vector altered sucrose self-administration, and over-expression of GluR1WT or GluR1S845A in the adjacent substantia nigra had no effect on cocaine self-administration. Taken together, these results suggest that dynamic regulation of AMPA receptors in the VTA during cocaine self-administration contributes to cocaine addiction by acting to facilitate subsequent cocaine use. PMID:21613507

  17. AMPA receptors serum-dependently mediate GABAA receptor alpha1 and alpha6 subunit down-regulation in cultured mouse cerebellar granule cells.

    PubMed

    Uusi-Oukari, Mikko; Kontturi, Leena-Stiina; Kallinen, Sampsa A; Salonen, Virpi

    2010-04-01

    Depolarization of cultured mouse cerebellar granule cells with potassium or kainate results in developmentally arrested state that includes down-regulation of GABA(A) receptor alpha1, alpha6 and beta2 subunit expression. These subunits are normally strongly expressed in cerebellar granule cells from second postnatal week throughout the adulthood. In the present study we demonstrate that selective activation of AMPA subtype of glutamate receptors down-regulates alpha1 and alpha6 subunit mRNA expression. Removal of AMPA agonist from culture medium restores expression of these subunits indicating reversibility of the down-regulation. In serum-free culture medium AMPA receptor activation did not down-regulate alpha1 or alpha6 subunit expression. Furthermore, the down-regulation was strongly attenuated when the cells were cultured in the presence of dialysed fetal calf serum. The results indicate that down-regulation of GABA(A) receptor alpha1 and alpha6 subunits by AMPA receptor activation is dependent on the presence of low molecular weight compounds present in fetal calf serum. In order to study mouse cerebellar granule cell maturation and/or regulation of GABA(A) receptor subunit expression in culture, the experiments should be performed in the absence of fetal calf serum. PMID:20170697

  18. Metabotropic glutamate receptor 5 modulates the nitric oxide-cGMP pathway in cerebellum in vivo through activation of AMPA receptors.

    PubMed

    Boix, Jordi; Llansola, Marta; Cabrera-Pastor, Andrea; Felipo, Vicente

    2011-04-01

    Metabotropic glutamate receptors (mGluRs) modulate important processes in cerebellum including long-term depression, which also requires formation of nitric oxide (NO) and cGMP. Some reports suggest that mGluRs could modulate the NO-cGMP pathway in cerebellum. However this modulation has not been studied in detail. The aim of this work was to assess by microdialysis in freely moving rats whether activation of mGluR5 modulates the NO-cGMP pathway in cerebellum in vivo and to analyze the underlying mechanisms. We show that mGluR5 activation increases extracellular glutamate, citrulline and cGMP in cerebellum. Blocking NMDA receptors with MK-801 does not prevent any of these effects, indicating that NMDA receptors activation is not required. However in the presence of MK-801 the effects are more transient, returning faster to basal levels. Blocking AMPA receptors prevents the increase in citrulline and cGMP induced by mGluR5 activation, but not the increase in glutamate. The release of glutamate is prevented by tetrodotoxin but not by fluoroacetate, indicating that glutamate is released from neurons and not from astrocytes. Activation of AMPA receptors increases citrulline and cGMP. These data indicate that activation of mGluR5 induces an increase of extracellular glutamate which activates AMPA receptors, leading to activation of nitric oxide synthase and increased NO, which activates guanylate cyclase, increasing cGMP. The response mediated by AMPA receptors desensitize rapidly. Activation of AMPA receptors also induces a mild depolarization, allowing activation of NMDA receptors which prolongs the duration of the effect initiated by activation of AMPA receptors. These data support that the three types of glutamate receptors: mGluR5, AMPA and NMDA cooperate in the modulation of the grade and duration of activation of the NO-cGMP pathway in cerebellum in vivo. This pathway would modulate cerebellar processes such as long-term depression. PMID:21300123

  19. Nuclear respiratory factor 2 regulates the transcription of AMPA receptor subunit GluA2 (Gria2).

    PubMed

    Priya, Anusha; Johar, Kaid; Nair, Bindu; Wong-Riley, Margaret T T

    2014-12-01

    Neuronal activity is highly dependent on energy metabolism. Nuclear respiratory factor 2 (NRF-2) tightly couples neuronal activity and energy metabolism by transcriptionally co-regulating all 13 subunits of an important energy-generating enzyme, cytochrome c oxidase (COX), as well as critical subunits of excitatory NMDA receptors. AMPA receptors are another major class of excitatory glutamatergic receptors that mediate most of the fast excitatory synaptic transmission in the brain. They are heterotetrameric proteins composed of various combinations of GluA1-4 subunits, with GluA2 being the most common one. We have previously shown that GluA2 (Gria2) is transcriptionally regulated by nuclear respiratory factor 1 (NRF-1) and specificity protein 4 (Sp4), which also regulate all subunits of COX. However, it was not known if NRF-2 also couples neuronal activity and energy metabolism by regulating subunits of the AMPA receptors. By means of multiple approaches, including electrophoretic mobility shift and supershift assays, chromatin immunoprecipitation, promoter mutations, real-time quantitative PCR, and western blot analysis, NRF-2 was found to functionally regulate the expression of Gria2, but not of Gria1, Gria3, or Gria4 genes in neurons. By regulating the GluA2 subunit of the AMPA receptor, NRF-2 couples energy metabolism and neuronal activity at the transcriptional level through a concurrent and parallel mechanism with NRF-1 and Sp4. PMID:25245478

  20. Regulation of AMPA receptor GluR1 subunit surface expression by a 4. 1N-linked actin cytoskeletal association.

    PubMed

    Shen, L; Liang, F; Walensky, L D; Huganir, R L

    2000-11-01

    The synaptic localization, clustering, and immobilization of neurotransmitter receptors and ion channels play important roles in synapse formation and synaptic transmission. Although several proteins have been identified that interact with AMPA receptors and that may regulate their synaptic targeting, little is known about the interaction of AMPA receptors with the cytoskeleton. In studies examining the interaction of the AMPA receptor GluR1 subunit with neuronal proteins, we determined that GluR1 interacts with the 4.1G and 4.1N proteins, homologs of the erythrocyte membrane cytoskeletal protein 4.1. Using the yeast two-hybrid system and a heterologous cell system, we demonstrated that both 4.1G and 4.1N bind to a membrane proximal region of the GluR1 C terminus, and that a region within the C-terminal domain of 4.1G or 4.1N is sufficient to mediate the interaction. We also found that 4.1N can associate with GluR1 in vivo and colocalizes with AMPA receptors at excitatory synapses. Disruption of the interaction of GluR1 with 4.1N or disruption of actin filaments decreased the surface expression of GluR1 in heterologous cells. Moreover, disruption of actin filaments in cultured cortical neurons dramatically reduced the level of surface AMPA receptors. These results suggest that protein 4.1N may link AMPA receptors to the actin cytoskeleton. PMID:11050113

  1. HPLC with fluorescence detection assay of perampanel, a novel AMPA receptor antagonist, in human plasma for clinical pharmacokinetic studies.

    PubMed

    Mano, Yuji; Takenaka, Osamu; Kusano, Kazutomi

    2015-10-01

    Perampanel (Fycompa®), a novel α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, is registered for the adjunctive treatment of patients (aged ≥12 years) with refractory partial-onset seizures. To support therapeutic drug monitoring, a simple high-performance liquid chromatography (HPLC) assay with fluorescence detection was developed to determine perampanel concentrations in human plasma and validated to support clinical trials. Human plasma samples (1.0 mL) were processed by liquid extraction using diethyl ether, followed by chromatographic separation on a YMC Pack Pro C18 column (150 × 4.6 mm i.d., 5 µm) with isocratic elution of acetonitrile-water-acetic acid-sodium acetate (840:560:3:1.8, v/v/v/w) at a flow rate of 1.0 mL/min. Column eluent was monitored at excitation and emission wavelengths of 290 and 430 nm, respectively. The assay was linear (range 1.0-500 ng/mL) and this could be extended to 25 µg/mL by 50-fold dilution integrity. No endogenous peaks were detected in the elution of analytes in drug-free blank human plasma from six individuals and no interference was observed with co-medications tested. Intra- and inter-batch reproducibility studies demonstrated accuracy and precision within the acceptance criteria of bioanalytical guidelines. Validation data demonstrated that our assay is simple, selective, reproducible and suitable for therapeutic drug monitoring of perampanel. PMID:25828925

  2. Differential reelin-induced enhancement of NMDA and AMPA receptor activity in the adult hippocampus.

    PubMed

    Qiu, Shenfeng; Zhao, Lisa F; Korwek, Kimberly M; Weeber, Edwin J

    2006-12-13

    The developmental lamination of the hippocampus and other cortical structures requires a signaling cascade initiated by reelin and its receptors, apoER2 (apolipoprotein E receptor 2) and VLDLR (very-low-density lipoprotein receptor). However, the functional significance of continued reelin expression in the postnatal brain remains poorly understood. Here, we show that reelin application to adult mice hippocampal slices leads to enhanced glutamatergic transmission mediated by NMDA receptors (NMDARs) and AMPA receptors (AMPARs) through distinct mechanisms. Application of recombinant reelin enhanced NMDAR-mediated currents through postsynaptic mechanisms, as revealed by the variance-mean analysis of synaptic NMDAR currents, assessment of spontaneous miniature events, and the levels of NMDAR subunits at synaptic surface. In comparison, nonstationary fluctuation analysis of miniature AMPAR currents and quantification of synaptic surface proteins revealed that reelin-induced enhancement of AMPAR responses was mediated by increased AMPAR numbers. Reelin enhancement of synaptic NMDAR currents was abolished when receptor-associated protein (RAP) or the Src inhibitor 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]-pyrimidine (PP1) was bath applied and was abrogated by including PP1 in the recording electrodes. In comparison, including RAP or an inactive PP1 analog PP3 in the recording electrode was without effect. Interestingly, the increased AMPAR response after reelin application was not blocked by PP1 but was blocked by the phosphoinositide-3' kinase (PI3K) inhibitors wortmannin and LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride]. Furthermore, reelin-induced, PI3K-dependent AMPAR surface insertion was also observed in cultured hippocampal neurons. Together, these results reveal a differential functional coupling of reelin signaling with NMDAR and AMPAR function and define a novel mechanism for controlling synaptic strength and plasticity

  3. Impaired Associative Fear Learning in Mice with Complete Loss or Haploinsufficiency of AMPA GluR1 Receptors

    PubMed Central

    Feyder, Michael; Wiedholz, Lisa; Sprengel, Rolf; Holmes, Andrew

    2007-01-01

    There is compelling evidence that l-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) glutamate receptors containing the GluR1 subunit contribute to the molecular mechanisms associated with learning. AMPA GluR1 glutamate receptor knockout mice (KO) exhibit abnormal hippocampal and amygdala plasticity, and deficits on various assays for cognition including Pavlovian fear conditioning. Here we examined associative fear learning in mice with complete absence (KO) or partial loss (heterozygous mutant, HET) of GluR1 on multiple fear conditioning paradigms. After multi-trial delay or trace conditioning, KO displayed impaired tone and context fear recall relative to WT, whereas HET were normal. After one-trial delay conditioning, both KO and HET showed impaired tone and context recall. HET and KO showed normal nociceptive sensitivity in the hot plate and tail flick tests. These data demonstrate that the complete absence of GluR1 subunit-containing receptors prevents the formation of associative fear memories, while GluR1 haploinsufficiency is sufficient to impair one-trial fear learning. These findings support growing evidence of a major role for GluR1-containing AMPA receptors in amygdala-mediated forms of learning and memory. PMID:18958186

  4. GluN2B-containing NMDA receptors and AMPA receptors in medial prefrontal cortex are necessary for odor span in rats

    PubMed Central

    Davies, Don A.; Greba, Quentin; Howland, John G.

    2013-01-01

    Working memory is a type of short-term memory involved in the maintenance and manipulation of information essential for complex cognition. While memory span capacity has been extensively studied in humans as a measure of working memory, it has received considerably less attention in rodents. Our aim was to examine the role of the N-methyl-D-aspartate (NMDA) and α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors in odor span capacity using systemic injections or infusions of receptor antagonists into the medial prefrontal cortex (mPFC). Long Evans rats were trained on a well-characterized odor span task (OST). Initially, rats were trained to dig for a food reward in sand followed by training on a non-match to sample discrimination using sand scented with household spices. The rats were then required to perform a serial delayed non-match to sample procedure which was their odor span. Systemic injection of the broad spectrum NMDA receptor antagonist 3-(2-Carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) (10 mg/kg) or the GluN2B-selective antagonist Ro 25-6981 (10 mg/kg but not 6 mg/kg) significantly reduced odor span capacity. Infusions of the GluN2B- selective antagonist Ro 25-6981 (2.5 μg/hemisphere) into mPFC reduced span capacity, an effect that was nearly significant (p = 0.069). Infusions of the AMPA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (1.25 μg/hemisphere) into mPFC reduced span capacity and latency for the rats to make a choice in the task. These results demonstrate span capacity in rats depends on ionotropic glutamate receptor activation in the mPFC. Further understanding of the circuitry underlying span capacity may aid in the novel therapeutic drug development for persons with working memory impairments as a result of disorders such as schizophrenia and Alzheimer’s disease. PMID:24348356

  5. Expression of ionotropic glutamate receptors, AMPA, kainite and NMDA, in the pigeon retina.

    PubMed

    Atoji, Yasuro

    2015-07-01

    Glutamate is an excitatory neurotransmitter in the vertebrate retina. A previous study found vesicular glutamate transporter 2 (vGluT2) mRNA in the pigeon retina, suggesting that bipolar and ganglion cells are glutamatergic. The present study examined the localization of ionotropic glutamate receptors to identify receptor cells in the pigeon retina using in situ hybridization histochemistry. Nine subunits of AMPA receptor (GluA1, GluA2, GluA3, and GluA4), kainate receptor (GluK1, GluK2, and GluK4), and NMDA receptor (GluN1 and GluN2A) were found to be expressed in the inner nuclear layer (INL) and ganglion cell layers. GluA1, GluA2, GluA3, and GluA4 were primarily expressed in the inner half of INL, and the signal intensity was strong for GluA2, GluA3, and GluA4. GluK1 was intensely expressed in the outer half of INL, whereas GluK2 and GluK4 were mainly localized in the inner half of INL. GluN1 and GluN2A were moderately expressed in the inner half of INL. Horizontal cells expressed GluA3 and GluA4, and ganglion cells expressed all subunits examined. These results suggest that the glutamatergic neurotransmission in the pigeon retina is similar to that in mammals. PMID:25983186

  6. Regulation of AMPA receptor subunit GluA1 surface expression by PAK3 phosphorylation

    PubMed Central

    Hussain, Natasha K.; Thomas, Gareth M.; Luo, Junjie; Huganir, Richard L.

    2015-01-01

    AMPA receptors (AMPARs) are the major excitatory receptors of the brain and are fundamental to synaptic plasticity, memory, and cognition. Dynamic recycling of AMPARs in neurons is regulated through several types of posttranslational modification, including phosphorylation. Here, we identify a previously unidentified signal transduction cascade that modulates phosphorylation of serine residue 863 (S863) in the GluA1 AMPAR subunit and controls surface trafficking of GluA1 in neurons. Activation of the EphR–Ephrin signal transduction pathway enhances S863 phosphorylation. Further, EphB2 can interact with Zizimin1, a guanine–nucleotide exchange factor that activates Cdc42 and stimulates S863 phosphorylation in neurons. Among the numerous targets downstream of Cdc42, we determined that the p21-activated kinase-3 (PAK3) phosphorylates S863 in vitro. Moreover, specific loss of PAK3 expression and pharmacological inhibition of PAK both disrupt activity-dependent phosphorylation of S863 in cortical neurons. EphB2, Cdc42, and PAKs are broadly capable of controlling dendritic spine formation and synaptic plasticity and are implicated in multiple cognitive disorders. Collectively, these data delineate a novel signal cascade regulating AMPAR trafficking that may contribute to the molecular mechanisms that govern learning and cognition. PMID:26460013

  7. Developmental origin dictates interneuron AMPA and NMDA receptor subunit composition and plasticity

    PubMed Central

    Matta, Jose A; Pelkey, Kenneth A; Craig, Michael T; Chittajallu, Ramesh; Jeffries, Brian W; McBain, Chris J

    2014-01-01

    Disrupted excitatory synapse maturation in GABAergic interneurons may promote neuropsychiatric disorders such as schizophrenia. However, establishing developmental programs for nascent synapses in GABAergic cells is confounded by their sparsity, heterogeneity and late acquisition of subtype-defining characteristics. We investigated synaptic development in mouse interneurons targeting cells by lineage from medial ganglionic eminence (MGE) or caudal ganglionic eminence (CGE) progenitors. MGE-derived interneuron synapses were dominated by GluA2-lacking AMPA-type glutamate receptors (AMPARs), with little contribution from NMDA-type receptors (NMDARs) throughout development. In contrast, CGE-derived cell synapses had large NMDAR components and used GluA2-containing AMPARs. In neonates, both MGE- and CGE-derived interneurons expressed primarily GluN2B subunit–containing NMDARs, which most CGE-derived interneurons retained into adulthood. However, MGE-derived interneuron NMDARs underwent a GluN2B-to-GluN2A switch that could be triggered acutely with repetitive synaptic activity. Our findings establish ganglionic eminence–dependent rules for early synaptic integration programs of distinct interneuron cohorts, including parvalbumin- and cholecystokinin-expressing basket cells. PMID:23852113

  8. Reversal of aging-related emotional memory deficits by norepinephrine via regulating the stability of surface AMPA receptors.

    PubMed

    Luo, Yi; Zhou, Jun; Li, Ming-Xing; Wu, Peng-Fei; Hu, Zhuang-Li; Ni, Lan; Jin, You; Chen, Jian-Guo; Wang, Fang

    2015-04-01

    Aging-related emotional memory deficit is a well-known complication in Alzheimer's disease and normal aging. However, little is known about its molecular mechanism. To address this issue, we examined the role of norepinephrine (NE) and its relevant drug desipramine in the regulation of hippocampal long-term potentiation (LTP), surface expression of AMPA receptor, and associative fear memory in rats. We found that there was a defective regulation of NE content and AMPA receptor trafficking during fear conditioning, which were accompanied by impaired emotional memory and LTP in aged rats. Furthermore, we also found that the exogenous upregulation of NE ameliorated the impairment of LTP and emotional memory via enhancing AMPA receptor trafficking in aged rats, and the downregulation of NE impaired LTP in adult rats. Finally, acute treatment with NE or desipramine rescued the impaired emotional memory in aged rats. These results imply a pivotal role for NE in synaptic plasticity and associative fear memory in aging rats and suggest that desipramine is a potential candidate for treating aging-related emotional memory deficit. PMID:25564942

  9. The AMPA receptor antagonist perampanel in the adjunctive treatment of partial-onset seizures: clinical trial evidence and experience

    PubMed Central

    2015-01-01

    More than 20 antiepileptic drugs (AEDs) are currently available for the medical treatment of epilepsies. However, still about 30% of all epilepsies have a drug-resistant course. Even worse, in the case of some epilepsy syndromes, freedom from seizures is almost never achieved. Therefore, new treatment options are still necessary, especially if theoretical concepts such as a new mode of action offer new horizons. Perampanel is the first-in-class orally active, selective, noncompetitive antagonist of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. The pharmacokinetic profile offers once-daily dosing in the evening as the best route of administration. According to the results of three pivotal placebo-controlled, double-blind phase III trials that investigated perampanel as an adjunctive AED in adult and adolescent patients from age 12 years who had ongoing focal epileptic seizures despite receiving one to three AEDs, perampanel has been widely licensed and introduced. Phase III trials showed superiority of adjunctive perampanel over placebo consistently in the range between 4 and 12 mg. Dizziness and somnolence were by far the leading adverse events. This review covers the clinical trial evidence but also clinical experience with perampanel after launch according to observational studies. PMID:25941541

  10. Activation of AMPA Receptors Mediates the Antidepressant Action of Deep Brain Stimulation of the Infralimbic Prefrontal Cortex.

    PubMed

    Jiménez-Sánchez, Laura; Castañé, Anna; Pérez-Caballero, Laura; Grifoll-Escoda, Marc; López-Gil, Xavier; Campa, Leticia; Galofré, Mireia; Berrocoso, Esther; Adell, Albert

    2016-06-01

    Although deep brain stimulation (DBS) has been used with success in treatment-resistant depression, little is known about its mechanism of action. We examined the antidepressant-like activity of short (1 h) DBS applied to the infralimbic prefrontal cortex in the forced swim test (FST) and the novelty-suppressed feeding test (NSFT). We also used in vivo microdialysis to evaluate the release of glutamate, γ-aminobutyric acid, serotonin, dopamine, and noradrenaline in the prefrontal cortex and c-Fos immunohistochemistry to determine the brain regions activated by DBS. One hour of DBS of the infralimbic prefrontal cortex has antidepressant-like effects in FST and NSFT, and increases prefrontal efflux of glutamate, which would activate AMPA receptors (AMPARs). This effect is specific of the infralimbic area since it is not observed after DBS of the prelimbic subregion. The activation of prefrontal AMPARs would result in a stimulation of prefrontal output to the brainstem, thus increasing serotonin, dopamine, and noradrenaline in the prefrontal cortex. Further, the activation of prefrontal AMPARs is necessary and sufficient condition for the antidepressant response of 1 h DBS. PMID:26088969

  11. Glyphosate-resistant and conventional canola (Brassica napus L.)responses to glyphosate and Aminomethylphosphonic Acid (AMPA) treatment

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Glyphosate-resistant (GR) canola expresses two transgenes: 1) the microbial glyphosate oxidase gene (gox) encoding the glyphosate oxidase enzyme (GOX) that metabolizes glyphosate to aminomethylphosphonic acid (AMPA) and 2) cp4 that encodes a GR form of the glyphosate target enzyme 5-enolpyruvylshiki...

  12. Reactive oxygen species (ROS) modulate AMPA receptor phosphorylation and cell-surface localization in concert with pain-related behavior.

    PubMed

    Lee, Daniel Z; Chung, Jin M; Chung, Kyungsoon; Kang, Myoung-Goo

    2012-09-01

    Sensitization of dorsal horn neurons (DHNs) in the spinal cord is dependent on pain-related synaptic plasticity and causes persistent pain. The DHN sensitization is mediated by a signal transduction pathway initiated by the activation of N-methyl-d-aspartate receptors (NMDA-Rs). Recent studies have shown that elevated levels of reactive oxygen species (ROS) and phosphorylation-dependent trafficking of GluA2 subunit of α-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (AMPA-Rs) are a part of the signaling pathway for DHN sensitization. However, the relationship between ROS and AMPA-R phosphorylation and trafficking is not known. Thus, this study investigated the effects of ROS scavengers on the phosphorylation and cell-surface localization of GluA1 and GluA2. Intrathecal NMDA- and intradermal capsaicin-induced hyperalgesic mice were used for this study since both pain models share the NMDA-R activation-dependent DHN sensitization in the spinal cord. Our behavioral, biochemical, and immunohistochemical analyses demonstrated that: 1) NMDA-R activation in vivo increased the phosphorylation of AMPA-Rs at GluA1 (S818, S831, and S845) and GluA2 (S880) subunits; 2) NMDA-R activation in vivo increased cell-surface localization of GluA1 but decreased that of GluA2; and 3) reduction of ROS levels by ROS scavengers PBN (N-tert-butyl-α-phenylnitrone) or TEMPOL (4-hydroxy-2, 2, 6, 6-tetramethylpiperidin-1-oxyl) reversed these changes in AMPA-Rs, as well as pain-related behavior. Given that AMPA-R trafficking to the cell surface and synapse is regulated by NMDA-R activation-dependent phosphorylation of GluA1 and GluA2, our study suggests that the ROS-dependent changes in the phosphorylation and cell-surface localization of AMPA-Rs are necessary for DHN sensitization and thus, pain-related behavior. We further suggest that ROS reduction will ameliorate these molecular changes and pain. PMID:22770842

  13. Nogo Receptor Signaling Restricts Adult Neural Plasticity by Limiting Synaptic AMPA Receptor Delivery

    PubMed Central

    Jitsuki, Susumu; Nakajima, Waki; Takemoto, Kiwamu; Sano, Akane; Tada, Hirobumi; Takahashi-Jitsuki, Aoi; Takahashi, Takuya

    2016-01-01

    Experience-dependent plasticity is limited in the adult brain, and its molecular and cellular mechanisms are poorly understood. Removal of the myelin-inhibiting signaling protein, Nogo receptor (NgR1), restores adult neural plasticity. Here we found that, in NgR1-deficient mice, whisker experience-driven synaptic α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) insertion in the barrel cortex, which is normally complete by 2 weeks after birth, lasts into adulthood. In vivo live imaging by two-photon microscopy revealed more AMPAR on the surface of spines in the adult barrel cortex of NgR1-deficient than on those of wild-type (WT) mice. Furthermore, we observed that whisker stimulation produced new spines in the adult barrel cortex of mutant but not WT mice, and that the newly synthesized spines contained surface AMPAR. These results suggest that Nogo signaling limits plasticity by restricting synaptic AMPAR delivery in coordination with anatomical plasticity. PMID:26472557

  14. Shisa6 traps AMPA receptors at postsynaptic sites and prevents their desensitization during synaptic activity

    PubMed Central

    Klaassen, Remco V.; Stroeder, Jasper; Coussen, Françoise; Hafner, Anne-Sophie; Petersen, Jennifer D.; Renancio, Cedric; Schmitz, Leanne J. M.; Normand, Elisabeth; Lodder, Johannes C.; Rotaru, Diana C.; Rao-Ruiz, Priyanka; Spijker, Sabine; Mansvelder, Huibert D.; Choquet, Daniel; Smit, August B.

    2016-01-01

    Trafficking and biophysical properties of AMPA receptors (AMPARs) in the brain depend on interactions with associated proteins. We identify Shisa6, a single transmembrane protein, as a stable and directly interacting bona fide AMPAR auxiliary subunit. Shisa6 is enriched at hippocampal postsynaptic membranes and co-localizes with AMPARs. The Shisa6 C-terminus harbours a PDZ domain ligand that binds to PSD-95, constraining mobility of AMPARs in the plasma membrane and confining them to postsynaptic densities. Shisa6 expressed in HEK293 cells alters GluA1- and GluA2-mediated currents by prolonging decay times and decreasing the extent of AMPAR desensitization, while slowing the rate of recovery from desensitization. Using gene deletion, we show that Shisa6 increases rise and decay times of hippocampal CA1 miniature excitatory postsynaptic currents (mEPSCs). Shisa6-containing AMPARs show prominent sustained currents, indicating protection from full desensitization. Accordingly, Shisa6 prevents synaptically trapped AMPARs from depression at high-frequency synaptic transmission. PMID:26931375

  15. Calcineurin Mediates Synaptic Scaling Via Synaptic Trafficking of Ca2+-Permeable AMPA Receptors

    PubMed Central

    Kim, Seonil; Ziff, Edward B.

    2014-01-01

    Homeostatic synaptic plasticity is a negative-feedback mechanism for compensating excessive excitation or inhibition of neuronal activity. When neuronal activity is chronically suppressed, neurons increase synaptic strength across all affected synapses via synaptic scaling. One mechanism for this change is alteration of synaptic AMPA receptor (AMPAR) accumulation. Although decreased intracellular Ca2+ levels caused by chronic inhibition of neuronal activity are believed to be an important trigger of synaptic scaling, the mechanism of Ca2+-mediated AMPAR-dependent synaptic scaling is not yet understood. Here, we use dissociated mouse cortical neurons and employ Ca2+ imaging, electrophysiological, cell biological, and biochemical approaches to describe a novel mechanism in which homeostasis of Ca2+ signaling modulates activity deprivation-induced synaptic scaling by three steps: (1) suppression of neuronal activity decreases somatic Ca2+ signals; (2) reduced activity of calcineurin, a Ca2+-dependent serine/threonine phosphatase, increases synaptic expression of Ca2+-permeable AMPARs (CPARs) by stabilizing GluA1 phosphorylation; and (3) Ca2+ influx via CPARs restores CREB phosphorylation as a homeostatic response by Ca2+-induced Ca2+ release from the ER. Therefore, we suggest that synaptic scaling not only maintains neuronal stability by increasing postsynaptic strength but also maintains nuclear Ca2+ signaling by synaptic expression of CPARs and ER Ca2+ propagation. PMID:24983627

  16. AMPA Receptor-Induced Local Brain-Derived Neurotrophic Factor Signaling Mediates Motor Recovery after Stroke

    PubMed Central

    Clarkson, Andrew N.; Overman, Justine J.; Zhong, Sheng; Mueller, Rudolf; Lynch, Gary; Carmichael, S. Thomas

    2015-01-01

    Stroke is the leading cause of adult disability. Recovery after stroke shares similar molecular and cellular properties with learning and memory. A main component of learning-induced plasticity involves signaling through AMPA receptors (AMPARs). We systematically tested the role of AMPAR function in motor recovery in a mouse model of focal stroke. AMPAR function controls functional recovery beginning 5 d after the stroke. Positive allosteric modulators of AMPARs enhance recovery of limb control when administered after a delay from the stroke. Conversely, AMPAR antagonists impair motor recovery. The contributions of AMPARs to recovery are mediated by release of brain-derived neurotrophic factor (BDNF) in periinfarct cortex, as blocking local BDNF function in periinfarct cortex blocks AMPAR-mediated recovery and prevents the normal pattern of motor recovery. In contrast to a delayed AMPAR role in motor recovery, early administration of AMPAR agonists after stroke increases stroke damage. These findings indicate that the role of glutamate signaling through the AMPAR changes over time in stroke: early potentiation of AMPAR signaling worsens stroke damage, whereas later potentiation of the same signaling system improves functional recovery. PMID:21389231

  17. Enhanced AMPA receptor function promotes cerebellar long-term depression rather than potentiation

    PubMed Central

    van Beugen, Boeke J.; Qiao, Xin; Simmons, Dana H.; De Zeeuw, Chris I.

    2014-01-01

    Ampakines are allosteric modulators of AMPA receptors that facilitate hippocampal long-term potentiation (LTP) and learning, and have been considered for the treatment of cognition and memory deficits. Here, we show that the ampakine CX546 raises the amplitude and slows the decay time of excitatory postsynaptic currents (EPSCs) at cerebellar parallel fiber (PF) to Purkinje cell synapses, thus resembling CX546 effects described at hippocampal synapses. Using the fluorescent calcium indicator dye Oregon Green BAPTA-2 and an ultra-high-speed CCD camera, we also monitored calcium transients in Purkinje cell dendrites. In the presence of CX546 in the bath, PF-evoked calcium transients were enhanced and prolonged, suggesting that CX546 not only enhances synaptic transmission, but also boosts dendritic calcium signaling at cerebellar synapses. In contrast to previous observations in the hippocampus, however, CX546 applied during cerebellar recordings facilitates long-term depression (LTD) rather than LTP at PF synapses. These findings show that ampakines selectively modify the LTP–LTD balance depending on the brain area and type of synapse, and may provide tools for the targeted regulation of synaptic memories. PMID:25403454

  18. Distinct Structural Pathways Coordinate the Activation of AMPA Receptor-Auxiliary Subunit Complexes

    PubMed Central

    Dawe, G. Brent; Musgaard, Maria; Aurousseau, Mark R.P.; Nayeem, Naushaba; Green, Tim; Biggin, Philip C.; Bowie, Derek

    2016-01-01

    Summary Neurotransmitter-gated ion channels adopt different gating modes to fine-tune signaling at central synapses. At glutamatergic synapses, high and low activity of AMPA receptors (AMPARs) is observed when pore-forming subunits coassemble with or without auxiliary subunits, respectively. Whether a common structural pathway accounts for these different gating modes is unclear. Here, we identify two structural motifs that determine the time course of AMPAR channel activation. A network of electrostatic interactions at the apex of the AMPAR ligand-binding domain (LBD) is essential for gating by pore-forming subunits, whereas a conserved motif on the lower, D2 lobe of the LBD prolongs channel activity when auxiliary subunits are present. Accordingly, channel activity is almost entirely abolished by elimination of the electrostatic network but restored via auxiliary protein interactions at the D2 lobe. In summary, we propose that activation of native AMPAR complexes is coordinated by distinct structural pathways, favored by the association/dissociation of auxiliary subunits. PMID:26924438

  19. Regulation of AMPA receptor extrasynaptic insertion by 4.1N, phosphorylation and palmitoylation.

    PubMed

    Lin, Da-Ting; Makino, Yuichi; Sharma, Kamal; Hayashi, Takashi; Neve, Rachael; Takamiya, Kogo; Huganir, Richard L

    2009-07-01

    The insertion of AMPA receptors (AMPARs) into the plasma membrane is an important step in the synaptic delivery of AMPARs during the expression of synaptic plasticity. However, the molecular mechanisms regulating AMPAR insertion remain elusive. By directly visualizing individual insertion events of the AMPAR subunit GluR1 in rodents, we found that the protein 4.1N was required for activity-dependent GluR1 insertion. Protein kinase C (PKC) phosphorylation of the serine 816 (S816) and S818 residues of GluR1 enhanced 4.1N binding to GluR1 and facilitated GluR1 insertion. In addition, palmitoylation of GluR1 C811 residue modulated PKC phosphorylation and GluR1 insertion. Finally, disrupting 4.1N-dependent GluR1 insertion decreased surface expression of GluR1 and the expression of long-term potentiation. Our study uncovers a previously unknown mechanism that governs activity-dependent GluR1 trafficking, reveals an interaction between AMPAR palmitoylation and phosphorylation, and underscores the functional importance of 4.1N in AMPAR trafficking and synaptic plasticity. PMID:19503082

  20. AMPA receptor plasticity in the nucleus accumbens after repeated exposure to cocaine

    PubMed Central

    Wolf, Marina E.; Ferrario, Carrie R.

    2010-01-01

    This review focuses on cocaine-induced postsynaptic plasticity in the nucleus accumbens (NAc) involving changes in AMPA receptor (AMPAR) transmission. First, fundamental properties of AMPAR in the NAc are reviewed. Then, we provide a detailed and critical analysis of literature demonstrating alterations in AMPAR transmission in association with behavioral sensitization to cocaine and cocaine self-administration. We conclude that cocaine exposure leads to changes in AMPAR transmission that depend on many factors including whether exposure is contingent or non-contingent, the duration of withdrawal, and whether extinction training has occurred. The relationship between changes in AMPAR transmission and responding to cocaine or cocaine-paired cues can also be affected by these variables. However, after prolonged withdrawal in the absence of extinction training, our findings and others lead us to propose that AMPAR transmission is enhanced, resulting in stronger responding to drug-paired cues. Finally, many results indicate that the state of synaptic transmission in the NAc after cocaine exposure is associated with impairment of AMPAR-dependent plasticity. This may contribute to a broad range of addiction-related behavioral changes. PMID:20109488

  1. Shisa6 traps AMPA receptors at postsynaptic sites and prevents their desensitization during synaptic activity.

    PubMed

    Klaassen, Remco V; Stroeder, Jasper; Coussen, Françoise; Hafner, Anne-Sophie; Petersen, Jennifer D; Renancio, Cedric; Schmitz, Leanne J M; Normand, Elisabeth; Lodder, Johannes C; Rotaru, Diana C; Rao-Ruiz, Priyanka; Spijker, Sabine; Mansvelder, Huibert D; Choquet, Daniel; Smit, August B

    2016-01-01

    Trafficking and biophysical properties of AMPA receptors (AMPARs) in the brain depend on interactions with associated proteins. We identify Shisa6, a single transmembrane protein, as a stable and directly interacting bona fide AMPAR auxiliary subunit. Shisa6 is enriched at hippocampal postsynaptic membranes and co-localizes with AMPARs. The Shisa6 C-terminus harbours a PDZ domain ligand that binds to PSD-95, constraining mobility of AMPARs in the plasma membrane and confining them to postsynaptic densities. Shisa6 expressed in HEK293 cells alters GluA1- and GluA2-mediated currents by prolonging decay times and decreasing the extent of AMPAR desensitization, while slowing the rate of recovery from desensitization. Using gene deletion, we show that Shisa6 increases rise and decay times of hippocampal CA1 miniature excitatory postsynaptic currents (mEPSCs). Shisa6-containing AMPARs show prominent sustained currents, indicating protection from full desensitization. Accordingly, Shisa6 prevents synaptically trapped AMPARs from depression at high-frequency synaptic transmission. PMID:26931375

  2. Role of TARP interaction in S-SCAM-mediated regulation of AMPA receptors.

    PubMed

    Danielson, Eric; Metallo, Jacob; Lee, Sang H

    2012-01-01

    Scaffolding proteins are involved in the incorporation, anchoring, maintenance, and removal of AMPA receptors (AMPARs) at synapses, either through a direct interaction with AMPARs or via indirect association through auxiliary subunits of transmembrane AMPAR regulatory proteins (TARPs). Synaptic scaffolding molecule (S-SCAM) is a newly characterized member of the scaffolding proteins critical for the regulation and maintenance of AMPAR levels at synapses, and directly binds to TARPs through a PDZ interaction. However, the functional significance of S-SCAM-TARP interaction in the regulation of AMPARs has not been tested. Here we show that overexpression of the C-terminal peptide of TARP-γ2 fused to EGFP abolished the S-SCAM-mediated enhancement of surface GluA2 expression. Conversely, the deletion of the PDZ-5 domain of S-SCAM that binds TARPs greatly attenuated the S-SCAM-induced increase of surface GluA2 expression. In contrast, the deletion of the guanylate kinase domain of S-SCAM did not show a significant effect on the regulation of AMPARs. Together, these results suggest that S-SCAM is regulating AMPARs through TARPs. PMID:22878254

  3. Distinct Structural Pathways Coordinate the Activation of AMPA Receptor-Auxiliary Subunit Complexes.

    PubMed

    Dawe, G Brent; Musgaard, Maria; Aurousseau, Mark R P; Nayeem, Naushaba; Green, Tim; Biggin, Philip C; Bowie, Derek

    2016-03-16

    Neurotransmitter-gated ion channels adopt different gating modes to fine-tune signaling at central synapses. At glutamatergic synapses, high and low activity of AMPA receptors (AMPARs) is observed when pore-forming subunits coassemble with or without auxiliary subunits, respectively. Whether a common structural pathway accounts for these different gating modes is unclear. Here, we identify two structural motifs that determine the time course of AMPAR channel activation. A network of electrostatic interactions at the apex of the AMPAR ligand-binding domain (LBD) is essential for gating by pore-forming subunits, whereas a conserved motif on the lower, D2 lobe of the LBD prolongs channel activity when auxiliary subunits are present. Accordingly, channel activity is almost entirely abolished by elimination of the electrostatic network but restored via auxiliary protein interactions at the D2 lobe. In summary, we propose that activation of native AMPAR complexes is coordinated by distinct structural pathways, favored by the association/dissociation of auxiliary subunits. PMID:26924438

  4. TNF-α triggers rapid membrane insertion of Ca(2+) permeable AMPA receptors into adult motor neurons and enhances their susceptibility to slow excitotoxic injury.

    PubMed

    Yin, Hong Z; Hsu, Cheng-I; Yu, Stephen; Rao, Shyam D; Sorkin, Linda S; Weiss, John H

    2012-12-01

    Excitotoxicity (caused by over-activation of glutamate receptors) and inflammation both contribute to motor neuron (MN) damage in amyotrophic lateral sclerosis (ALS) and other diseases of the spinal cord. Microglial and astrocytic activation in these conditions results in release of inflammatory mediators, including the cytokine, tumor necrosis factor-alpha (TNF-α). TNF-α has complex effects on neurons, one of which is to trigger rapid membrane insertion of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type glutamate receptors, and in some cases, specific insertion of GluA2 lacking, Ca(2+) permeable AMPA receptors (Ca-perm AMPAr). In the present study, we use a histochemical stain based upon kainate stimulated uptake of cobalt ions ("Co(2+) labeling") to provide the first direct demonstration of the presence of substantial numbers of Ca-perm AMPAr in ventral horn MNs of adult rats under basal conditions. We further find that TNF-α exposure causes a rapid increase in the numbers of these receptors, via a phosphatidylinositol 3 kinase (PI3K) and protein kinase A (PKA) dependent mechanism. Finally, to assess the relevance of TNF-α to slow excitotoxic MN injury, we made use of organotypic spinal cord slice cultures. Co(2+) labeling revealed that MNs in these cultures possess Ca-perm AMPAr. Addition of either a low level of TNF-α, or of the glutamate uptake blocker, trans-pyrrolidine-2,4-dicarboxylic acid (PDC) to the cultures for 48 h resulted in little MN injury. However, when combined, TNF-α+PDC caused considerable MN degeneration, which was blocked by the AMPA/kainate receptor blocker, 2,3-Dihydroxy-6-nitro-7-sulfamoylbenzo (F) quinoxaline (NBQX), or the Ca-perm AMPAr selective blocker, 1-naphthyl acetylspermine (NASPM). Thus, these data support the idea that prolonged TNF-α elevation, as may be induced by glial activation, acts in part by increasing the numbers of Ca-perm AMPAr on MNs to enhance injurious excitotoxic effects of deficient

  5. Molecular Dissection of the Interaction between the AMPA Receptor and Cornichon Homolog-3

    PubMed Central

    Shanks, Natalie F.; Cais, Ondrej; Maruo, Tomohiko; Savas, Jeffrey N.; Zaika, Elena I.; Azumaya, Caleigh M.; Yates, John R.; Greger, Ingo

    2014-01-01

    Cornichon homologs (CNIHs) are AMPA-type glutamate receptor (AMPAR) auxiliary subunits that modulate AMPAR ion channel function and trafficking. Mechanisms underlying this interaction and functional modulation of the receptor complex are currently unclear. Here, using proteins expressed from mouse and rat cDNA, we show that CNIH-3 forms a stable complex with tetrameric AMPARs and contributes to the transmembrane density in single-particle electron microscopy structures. Peptide array-based screening and in vitro mutagenesis identified two clusters of conserved membrane-proximal residues in CNIHs that contribute to AMPAR binding. Because CNIH-1 binds to AMPARs but modulates gating at a significantly lower magnitude compared with CNIH-3, these conserved residues mediate a direct interaction between AMPARs and CNIHs. In addition, residues in the extracellular loop of CNIH-2/3 absent in CNIH-1/4 are critical for both AMPAR interaction and gating modulation. On the AMPAR extracellular domains, the ligand-binding domain and possibly a stretch of linker, connecting the ligand-binding domain to the fourth membrane-spanning segment, is the principal contact point with the CNIH-3 extracellular loop. In contrast, the membrane-distal N-terminal domain is less involved in AMPAR gating modulation by CNIH-3 and AMPAR binding to CNIH-3. Collectively, our results identify conserved residues in the membrane-proximal region of CNIHs that contribute to AMPAR binding and an additional unique segment in the CNIH-2/3 extracellular loop required for both physical interaction and gating modulation of the AMPAR. Consistent with the dissociable properties of binding and gating modulation, we identified a mutant CNIH-3 that preserves AMPAR binding capability but has attenuated activity of gating modulation. PMID:25186755

  6. Dysregulation of AMPA receptor transmission in the nucleus accumbens in animal models of cocaine addiction

    PubMed Central

    Wolf, Marina E.

    2014-01-01

    Plasticity of glutamate transmission in neuronal circuits involving the nucleus accumbens (NAc) is now recognized to play a critical role in cocaine addiction. NAc neurons are excited primarily by AMPA-type glutamate receptors (AMPAR) and this is required for cocaine seeking. This review will briefly describe AMPAR properties and trafficking, with a focus on studies in NAc neurons, and then consider mechanisms by which cocaine may alter AMPAR transmission. Two examples will be discussed that may be important in two different stages of addiction: learning about drugs and drug-related cues during the period of drug exposure, and persistent vulnerability to craving and relapse after abstinence is achieved. The first example is drawn from studies of cultured NAc neurons. Elevation of DA levels (as would occur following cocaine exposure) facilitates activity-dependent strengthening of excitatory synapses onto medium spiny neurons, the main cell type and projection neuron of the NAc. This occurs because activation of D1-class receptors primes AMPAR for synaptic insertion, creating a temporal window in which stimuli related to cocaine-taking are more efficacious at eliciting synaptic plasticity and thus being encoded into memory. The second example involves rat models of cocaine addiction. Cell surface and synaptic expression of AMPAR on NAc neurons is persistently increased after withdrawal from repeated cocaine exposure. We hypothesize that this increases the reactivity of NAc neurons to glutamate inputs from cortex and limbic structures, facilitating the ability of these inputs to trigger cocaine seeking and thus contributing to the persistent vulnerability to relapse that characterizes addiction. PMID:20361291

  7. Inhibition by adenosine A2A receptors of NMDA but not AMPA currents in rat neostriatal neurons

    PubMed Central

    Wirkner, Kerstin; Assmann, Heike; Köles, Laszlo; Gerevich, Zoltan; Franke, Heike; Nörenberg, Wolfgang; Boehm, Rudolf; Illes, Peter

    2000-01-01

    Whole-cell patch clamp experiments were used to investigate the transduction mechanism of adenosine A2A receptors in modulating N-methyl-D-aspartate (NMDA)-induced currents in rat striatal brain slices. The A2A receptor agonist 2-p-(2-carboxyethyl)phenethylamino-5′-N-ethylcarboxamidoadenosine (CGS 21680) inhibited the NMDA, but not the (S)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) current in a subset of striatal neurons. Lucifer yellow-filled pipettes in combination with immunostaining of A2A receptors were used to identify CGS 21680-sensitive cells as typical medium spiny striatal neurons. Dibutyryl cyclic AMP and the protein kinase A activator Sp-cyclic AMPs, but not the protein kinase A inhibitors Rp-cyclic AMPS or PKI(14–24)amide abolished the inhibitory effect of CGS 21680. The phospholipase C inhibitor U-73122, but not the inactive structural analogue U-73343 also interfered with CGS 21680. The activation of protein kinase C by phorbol 12-myristate 13-acetate or the blockade of this enzyme by staurosporine did not alter the effect of CGS 21680. Heparin, an antagonist of inositol 1,4,5-trisphosphate (InsP3) and a more efficient buffering of intracellular Ca2+ by BAPTA instead of EGTA in the pipette solution, abolished the CGS 21680-induced inhibition. The calmodulin antagonist W-7 and cytochalasin B which enhances actin depolymerization also prevented the effect of CGS 21680; the calmodulin kinase II inhibitors CaM kinase II(281–309) and KN-93 but not the inactive structural analogue KN-92 were also effective. The calcineurin inhibitor deltamethrin did not interfere with CGS 21680. It is suggested that the transduction mechanism of A2A receptors to inhibit NMDA receptor channels is the phospholipase C/InsP3/calmodulin and calmodulin kinase II pathway. The adenylate cyclase/protein kinase A and phospholipase C/protein kinase C pathways do not appear to be involved. PMID:10807662

  8. NMDA and AMPA receptors contribute similarly to temporal processing in mammalian retinal ganglion cells

    PubMed Central

    Stafford, Benjamin K; Manookin, Michael B; Singer, Joshua H; Demb, Jonathan B

    2014-01-01

    Postsynaptic AMPA- and NMDA-type glutamate receptors (AMPARs, NMDARs) are commonly expressed at the same synapses. AMPARs are thought to mediate the majority of fast excitatory neurotransmission whereas NMDARs, with their relatively slower kinetics and higher Ca2+ permeability, are thought to mediate synaptic plasticity, especially in neural circuits devoted to learning and memory. In sensory neurons, however, the roles of AMPARs and NMDARs are less well understood. Here, we tested in the in vitro guinea pig retina whether AMPARs and NMDARs differentially support temporal contrast encoding by two ganglion cell types. In both OFF Alpha and Delta ganglion cells, contrast stimulation evoked an NMDAR-mediated response with a characteristic J-shaped I–V relationship. In OFF Delta cells, AMPAR- and NMDAR-mediated responses could be modulated at low frequencies but were suppressed during 10 Hz stimulation, when responses were instead shaped by synaptic inhibition. With inhibition blocked, both AMPAR- and NMDAR-mediated responses could be modulated at 10 Hz, indicating that NMDAR kinetics do not limit temporal encoding. In OFF Alpha cells, NMDAR-mediated responses followed stimuli at frequencies up to ∼18 Hz. In both cell types, NMDAR-mediated responses to contrast modulation at 9–18 Hz showed delays of <10 ms relative to AMPAR-mediated responses. Thus, NMDARs combine with AMPARs to encode rapidly modulated glutamate release, and NMDAR kinetics do not limit temporal coding by OFF Alpha and Delta ganglion cells substantially. Furthermore, glutamatergic transmission is differentially regulated across bipolar cell pathways: in some, release is suppressed at high temporal frequencies by presynaptic inhibition. PMID:25217374

  9. MAGI-1 modulates AMPA receptor synaptic localization and behavioral plasticity in response to prior experience.

    PubMed

    Emtage, Lesley; Chang, Howard; Tiver, Rebecca; Rongo, Christopher

    2009-01-01

    It is well established that the efficacy of synaptic connections can be rapidly modified by neural activity, yet how the environment and prior experience modulate such synaptic and behavioral plasticity is only beginning to be understood. Here we show in C. elegans that the broadly conserved scaffolding molecule MAGI-1 is required for the plasticity observed in a glutamatergic circuit. This mechanosensory circuit mediates reversals in locomotion in response to touch stimulation, and the AMPA-type receptor (AMPAR) subunits GLR-1 and GLR-2, which are required for reversal behavior, are localized to ventral cord synapses in this circuit. We find that animals modulate GLR-1 and GLR-2 localization in response to prior mechanosensory stimulation; a specific isoform of MAGI-1 (MAGI-1L) is critical for this modulation. We show that MAGI-1L interacts with AMPARs through the intracellular domain of the GLR-2 subunit, which is required for the modulation of AMPAR synaptic localization by mechanical stimulation. In addition, mutations that prevent the ubiquitination of GLR-1 prevent the decrease in AMPAR localization observed in previously stimulated magi-1 mutants. Finally, we find that previously-stimulated animals later habituate to subsequent mechanostimulation more rapidly compared to animals initially reared without mechanical stimulation; MAGI-1L, GLR-1, and GLR-2 are required for this change in habituation kinetics. Our findings demonstrate that prior experience can cause long-term alterations in both behavioral plasticity and AMPAR localization at synapses in an intact animal, and indicate a new, direct role for MAGI/S-SCAM proteins in modulating AMPAR localization and function in the wake of variable sensory experience. PMID:19242552

  10. ANTIDEPRESSANT-LIKE EFFECTS OF LOW KETAMINE DOSE IS ASSOCIATED WITH INCREASED HIPPOCAMPAL AMPA/NMDA RECEPTOR DENSITY RATIO IN FEMALE WISTAR-KYOTO RATS

    PubMed Central

    Tizabi, Yousef; Bhatti, Babur H; Manaye, Kebreten F; Das, Jharna R; Akinfiresoye, Luli

    2012-01-01

    Preclinical as well as limited clinical studies indicate that ketamine, a non-competitive glutamate NMDA receptor antagonist, may exert a quick and prolonged antidepressant effect. It has been postulated that ketamine action is due to inhibition of NMDA and stimulation of AMPA receptors. Here, we sought to determine whether ketamine would exert antidepressant effects in Wistar-Kyoto (WKY) rats, a putative animal model of depression and whether this effect would be associated with changes in AMPA/NMDA receptor densities in the hippocampus. Adult female WKY rats and their control Wistar rats were subjected to acute and chronic ketamine doses and their locomotor activity (LMA) and immobility in the forced swim test (FST) were evaluated. Hippocampal AMPA and NMDA receptor densities were also measured following a chronic ketamine dose. Ketamine, both acutely (0.5–5.0 mg/kg ip) and chronically (0.5–2.5 mg/kg daily for 10 days) resulted in a dose-dependent and prolonged decrease in immobility in the FST in WKY rats only, suggesting an antidepressant-like effect in this model. Chronic treatment with an effective dose of ketamine also resulted in an increase in AMPA/NMDA receptor density ratio in the hippocampus of WKY rats. LMA was not affected by any ketamine treatment in either strain. These results indicate a rapid and lasting antidepressant-like effect of a low ketamine dose in WKY rat model of depression. Moreover, the increase in AMPA/NMDA receptor density in hippocampus could be a contributory factor to behavioral effects of ketamine. These findings suggest potential therapeutic benefit in simultaneous reduction of central NMDA and elevation of AMPA receptor function in treatment of depression. PMID:22521815

  11. Development of calcium-permeable AMPA receptors and their correlation with NMDA receptors in fast-spiking interneurons of rat prefrontal cortex

    PubMed Central

    Wang, Huai-Xing; Gao, Wen-Jun

    2010-01-01

    Abnormal influx of Ca2+ is thought to contribute to the neuronal injury associated with a number of brain disorders, and Ca2+-permeable AMPA receptors (CP-AMPARs) play a critical role in the pathological process. Despite the apparent vulnerability of fast-spiking (FS) interneurons in neurological disorders, little is known about the CP-AMPARs expressed by functionally identified FS interneurons in the developing prefrontal cortex (PFC). We investigated the development of inwardly rectifying AMPA receptor-mediated currents and their correlation with NMDA receptor-mediated currents in FS interneurons in the rat PFC. We found that 78% of the FS interneurons expressed a low rectification index, presumably Ca2+-permeable AMPARs, with only 22% exhibiting AMPARs with a high rectification index, probably Ca2+ impermeable (CI). FS interneurons with CP-AMPARs exhibited properties distinct from those expressing CI-AMPARs, although both displayed similar morphologies, passive membrane properties and AMPA currents at resting membrane potentials. The AMPA receptors also exhibited dramatic changes during cortical development with significantly more FS interneurons with CP-AMPARs and a clearly decreased rectification index during adolescence. In addition, FS interneurons with CP-AMPARs exhibited few or no NMDA currents, distinct frequency-dependent synaptic facilitation, and protracted maturation in short-term plasticity. These data suggest that CP-AMPARs in FS interneurons may play a critical role in neuronal integration and that their characteristic properties may make these cells particularly vulnerable to disruptive influences in the PFC, thus contributing to the onset of many psychiatric disorders. PMID:20547673

  12. Facilitation of AMPA receptor-mediated steady-state current by extrasynaptic NMDA receptors in supraoptic magnocellular neurosecretory cells.

    PubMed

    Pai, Yoon Hyoung; Lim, Chae Seong; Park, Kyung-Ah; Cho, Hyun Sil; Lee, Gyu-Seung; Shin, Yong Sup; Kim, Hyun-Woo; Jeon, Byeong Hwa; Yoon, Seok Hwa; Park, Jin Bong

    2016-07-01

    In addition to classical synaptic transmission, information is transmitted between cells via the activation of extrasynaptic receptors that generate persistent tonic current in the brain. While growing evidence supports the presence of tonic NMDA current (INMDA) generated by extrasynaptic NMDA receptors (eNMDARs), the functional significance of tonic INMDA in various brain regions remains poorly understood. Here, we demonstrate that activation of eNMDARs that generate INMDA facilitates the α-amino-3-hydroxy-5-methylisoxazole-4-proprionate receptor (AMPAR)-mediated steady-state current in supraoptic nucleus (SON) magnocellular neurosecretory cells (MNCs). In low-Mg(2+) artificial cerebrospinal fluid (aCSF), glutamate induced an inward shift in Iho lding (IGLU) at a holding potential (Vholding) of -70 mV which was partly blocked by an AMPAR antagonist, NBQX. NBQX-sensitive IGLU was observed even in normal aCSF at Vholding of -40 mV or -20 mV. IGLU was completely abolished by pretreatment with an NMDAR blocker, AP5, under all tested conditions. AMPA induced a reproducible inward shift in Iholding (IAMPA) in SON MNCs. Pretreatment with AP5 attenuated IAMPA amplitudes to ~60% of the control levels in low-Mg(2+) aCSF, but not in normal aCSF at Vholding of -70 mV. IAMPA attenuation by AP5 was also prominent in normal aCSF at depolarized holding potentials. Memantine, an eNMDAR blocker, mimicked the AP5-induced IAMPA attenuation in SON MNCs. Finally, chronic dehydration did not affect IAMPA attenuation by AP5 in the neurons. These results suggest that tonic INMDA, mediated by eNMDAR, facilitates AMPAR function, changing the postsynaptic response to its agonists in normal and osmotically challenged SON MNCs. PMID:27382359

  13. Facilitation of AMPA receptor-mediated steady-state current by extrasynaptic NMDA receptors in supraoptic magnocellular neurosecretory cells

    PubMed Central

    Pai, Yoon Hyoung; Lim, Chae Seong; Park, Kyung-Ah; Cho, Hyun Sil; Lee, Gyu-Seung; Shin, Yong Sup; Kim, Hyun-Woo; Jeon, Byeong Hwa

    2016-01-01

    In addition to classical synaptic transmission, information is transmitted between cells via the activation of extrasynaptic receptors that generate persistent tonic current in the brain. While growing evidence supports the presence of tonic NMDA current (INMDA) generated by extrasynaptic NMDA receptors (eNMDARs), the functional significance of tonic INMDA in various brain regions remains poorly understood. Here, we demonstrate that activation of eNMDARs that generate INMDA facilitates the α-amino-3-hydroxy-5-methylisoxazole-4-proprionate receptor (AMPAR)-mediated steady-state current in supraoptic nucleus (SON) magnocellular neurosecretory cells (MNCs). In low-Mg2+ artificial cerebrospinal fluid (aCSF), glutamate induced an inward shift in Iholding (IGLU) at a holding potential (Vholding) of –70 mV which was partly blocked by an AMPAR antagonist, NBQX. NBQX-sensitive IGLU was observed even in normal aCSF at Vholding of –40 mV or –20 mV. IGLU was completely abolished by pretreatment with an NMDAR blocker, AP5, under all tested conditions. AMPA induced a reproducible inward shift in Iholding (IAMPA) in SON MNCs. Pretreatment with AP5 attenuated IAMPA amplitudes to ~60% of the control levels in low-Mg2+ aCSF, but not in normal aCSF at Vholding of –70 mV. IAMPA attenuation by AP5 was also prominent in normal aCSF at depolarized holding potentials. Memantine, an eNMDAR blocker, mimicked the AP5-induced IAMPA attenuation in SON MNCs. Finally, chronic dehydration did not affect IAMPA attenuation by AP5 in the neurons. These results suggest that tonic INMDA, mediated by eNMDAR, facilitates AMPAR function, changing the postsynaptic response to its agonists in normal and osmotically challenged SON MNCs. PMID:27382359

  14. Inflammation alters trafficking of extrasynaptic AMPA receptors in tonically firing lamina II neurons of the rat spinal dorsal horn

    PubMed Central

    Kopach, Olga; Kao, Sheng-Chin; Petralia, Ronald S.; Belan, Pavel; Tao, Yuan-Xiang; Voitenko, Nana

    2011-01-01

    Peripheral inflammation alters AMPA receptor (AMPAR) subunit trafficking and increases AMPAR Ca2+ permeability at synapses of spinal dorsal horn neurons. However, it is unclear whether AMPAR trafficking at extrasynaptic sites of these neurons also changes under persistent inflammatory pain conditions. Using patch-clamp recording combined with Ca2+ imaging and cobalt staining, we found that, under normal conditions, an extrasynaptic pool of AMPARs in rat substantia gelatinosa (SG) neurons of spinal dorsal horn predominantly consists of GluR2-containing Ca2+-impermeable receptors. Maintenance of complete Freund’s adjuvant (CFA)-induced inflammation was associated with a marked enhancement of AMPA-induced currents and [Ca2+]i transients in SG neurons, while, as we previously showed, the amplitude of synaptically evoked AMPAR-mediated currents was not changed 24 h after CFA. These findings indicate that extrasynaptic AMPARs are upregulated and their Ca2+ permeability increases dramatically. This increase occurred in SG neurons characterized by intrinsic tonic firing properties, but not in those exhibited strong adaptation. This increase was also accompanied by an inward rectification of AMPA-induced currents and enhancement of sensitivity to a highly selective Ca2+-permeable AMPAR blocker, IEM-1460. Electron microcopy and biochemical assays additionally showed an increase in the amount of GluR1 at extrasynaptic membranes in dorsal horn neurons 24 h post-CFA. Taken together, our findings suggest that CFA-induced inflammation increases functional expression and proportion of extrasynaptic GluR1-containing Ca2+-permeable AMPARs in tonically firing excitatory dorsal horn neurons. We suggest that the altered extrasynaptic AMPAR trafficking might participate in the maintenance of persistent inflammatory pain. PMID:21282008

  15. Inflammation alters trafficking of extrasynaptic AMPA receptors in tonically firing lamina II neurons of the rat spinal dorsal horn.

    PubMed

    Kopach, Olga; Kao, Sheng-Chin; Petralia, Ronald S; Belan, Pavel; Tao, Yuan-Xiang; Voitenko, Nana

    2011-04-01

    Peripheral inflammation alters AMPA receptor (AMPAR) subunit trafficking and increases AMPAR Ca(2+) permeability at synapses of spinal dorsal horn neurons. However, it is unclear whether AMPAR trafficking at extrasynaptic sites of these neurons also changes under persistent inflammatory pain conditions. Using patch-clamp recording combined with Ca(2+) imaging and cobalt staining, we found that, under normal conditions, an extrasynaptic pool of AMPARs in rat substantia gelatinosa (SG) neurons of spinal dorsal horn predominantly consists of GluR2-containing Ca(2+)-impermeable receptors. Maintenance of complete Freund's adjuvant (CFA)-induced inflammation was associated with a marked enhancement of AMPA-induced currents and [Ca(2+)](i) transients in SG neurons, while, as we previously showed, the amplitude of synaptically evoked AMPAR-mediated currents was not changed 24 h after CFA. These findings indicate that extrasynaptic AMPARs are upregulated and their Ca(2+) permeability increases dramatically. This increase occurred in SG neurons characterized by intrinsic tonic firing properties, but not in those exhibited strong adaptation. This increase was also accompanied by an inward rectification of AMPA-induced currents and enhancement of sensitivity to a highly selective Ca(2+)-permeable AMPAR blocker, IEM-1460. Electron microcopy and biochemical assays additionally showed an increase in the amount of GluR1 at extrasynaptic membranes in dorsal horn neurons 24h post-CFA. Taken together, our findings indicate that CFA-induced inflammation increases functional expression and proportion of extrasynaptic GluR1-containing Ca(2+)-permeable AMPARs in tonically firing excitatory dorsal horn neurons, suggesting that the altered extrasynaptic AMPAR trafficking might participate in the maintenance of persistent inflammatory pain. PMID:21282008

  16. NMDA receptors in preBötzinger complex neurons can drive respiratory rhythm independent of AMPA receptors

    PubMed Central

    Morgado-Valle, Consuelo; Feldman, Jack L

    2007-01-01

    The role of AMPA receptors (AMPARs) in generation and propagation of respiratory rhythm is well documented both in vivo and in vitro, whereas the functional significance of NMDA receptors (NMDARs) in preBötzinger complex (preBötC) neurons has not been explored. Here we examined the interactions between AMPARs and NMDARs during spontaneous respiratory rhythm generation in slices from neonatal rats in vitro. We tested the hypothesis that activation of NMDARs can drive respiratory rhythm in the absence of other excitatory drives. Blockade of NMDARs with dizocilpine hydrogen maleate (MK-801, 20 μm) had a negligible effect on respiratory rhythm and pattern under standard conditions in vitro, whereas blockade of AMPARs with NBQX (0.5 μm) completely abolished respiratory activity. Removal of extracellular Mg2+ to relieve the voltage-dependent block of NMDARs maintained respiratory rhythm without a significant effect on period, even in the presence of high NBQX concentrations (≤ 100 μm). Removal of Mg2+ increased inspiratory-modulated inward current peak (II) and charge (QI) in preBötC neurons voltage-clamped at −60 mV by 245% and 309%, respectively, with respect to basal values. We conclude that the normal AMPAR-mediated postsynaptic current underlying respiratory drive can be replaced by NMDAR-mediated postsynaptic current when the voltage-dependent Mg2+ block is removed. Under this condition, respiratory-related frequency is unaffected by changes in II, suggesting that the two can be independently regulated. PMID:17446224

  17. The neuronal K-Cl cotransporter KCC2 influences postsynaptic AMPA receptor content and lateral diffusion in dendritic spines

    PubMed Central

    Gauvain, Grégory; Chamma, Ingrid; Chevy, Quentin; Cabezas, Carolina; Irinopoulou, Theano; Bodrug, Natalia; Carnaud, Michèle; Lévi, Sabine; Poncer, Jean Christophe

    2011-01-01

    The K-Cl cotransporter KCC2 plays an essential role in neuronal chloride homeostasis, and thereby influences the efficacy and polarity of GABA signaling. Although KCC2 is expressed throughout the somatodendritic membrane, it is remarkably enriched in dendritic spines, which host most glutamatergic synapses in cortical neurons. KCC2 has been shown to influence spine morphogenesis and functional maturation in developing neurons, but its function in mature dendritic spines remains unknown. Here, we report that suppressing KCC2 expression decreases the efficacy of excitatory synapses in mature hippocampal neurons. This effect correlates with a reduced postsynaptic aggregation of GluR1-containing AMPA receptors and is mimicked by a dominant negative mutant of KCC2 interaction with cytoskeleton but not by pharmacological suppression of KCC2 function. Single-particle tracking experiments reveal that suppressing KCC2 increases lateral diffusion of the mobile fraction of AMPA receptor subunit GluR1 in spines but not in adjacent dendritic shafts. Increased diffusion was also observed for transmembrane but not membrane-anchored recombinant neuronal cell adhesion molecules. We suggest that KCC2, likely through interactions with the actin cytoskeleton, hinders transmembrane protein diffusion, and thereby contributes to their confinement within dendritic spines. PMID:21878564

  18. α7 Nicotinic Acetylcholine Receptors Occur at Postsynaptic Densities of AMPA Receptor-Positive and -Negative Excitatory Synapses in Rat Sensory Cortex

    PubMed Central

    Levy, Robert B.; Aoki, Chiye

    2010-01-01

    NMDA receptor (NMDAR) activation requires concurrent membrane depolarization, and glutamatergic synapses lacking AMPA receptors (AMPARs) are often considered “silent” in the absence of another source of membrane depolarization. During the second postnatal week, NMDA currents can be enhanced in rat auditory cortex through activation of the α7 nicotinic acetylcholine receptor (α7nAChR). Electrophysiological results support a mainly presynaptic role for α7nAChR at these synapses. However, immunocytochemical evidence that α7nAChR is prevalent at postsynaptic sites of glutamatergic synapses in hippocampus and neocortex, along with emerging electrophysiological evidence for postsynaptic nicotinic currents in neocortex and hippocampus, has prompted speculation that α7nAChR allows for activation of NMDAR postsynaptically at synapses lacking AMPAR. Here we used dual immunolabeling and electron microscopy to examine the distribution of α7nAChR relative to AMPAR (GluR1, GluR2, and GluR3 subunits combined) at excitatory synapses in somatosensory cortex of adult and 1-week-old rats. α7nAChR occurred discretely over most of the thick postsynaptic densities in all cortical layers of both age groups. AMPAR immunoreactivity was also detectable at most synapses; its distribution was independent of that of α7nAChR. In both age groups, approximately one-quarter of asymmetrical synapses were α7nAChR positive and AMPAR negative. The variability of postsynaptic α7nAChR labeling density was greater at postnatal day (PD) 7 than in adulthood, and PD 7 neuropil contained a subset of small AMPA receptor-negative synapses with a high density of α7nAChR immunoreactivity. These observations support the idea that acetylcholine receptors can aid in activating glutamatergic synapses and work together with AMPA receptors to mediate postsynaptic excitation throughout life. PMID:12077196

  19. α/β-Hydrolase domain-containing 6 (ABHD6) negatively regulates the surface delivery and synaptic function of AMPA receptors

    PubMed Central

    Wei, Mengping; Zhang, Jian; Jia, Moye; Yang, Chaojuan; Pan, Yunlong; Li, Shuaiqi; Luo, Yiwen; Zheng, Junyuan; Ji, Jianguo; Chen, Jianguo; Hu, Xinli; Xiong, Jingwei; Shi, Yun; Zhang, Chen

    2016-01-01

    In the brain, AMPA-type glutamate receptors are major postsynaptic receptors at excitatory synapses that mediate fast neurotransmission and synaptic plasticity. α/β-Hydrolase domain-containing 6 (ABHD6), a monoacylglycerol lipase, was previously found to be a component of AMPA receptor macromolecular complexes, but its physiological significance in the function of AMPA receptors (AMPARs) has remained unclear. The present study shows that overexpression of ABHD6 in neurons drastically reduced excitatory neurotransmission mediated by AMPA but not by NMDA receptors at excitatory synapses. Inactivation of ABHD6 expression in neurons by either CRISPR/Cas9 or shRNA knockdown methods significantly increased excitatory neurotransmission at excitatory synapses. Interestingly, overexpression of ABHD6 reduced glutamate-induced currents and the surface expression of GluA1 in HEK293T cells expressing GluA1 and stargazin, suggesting a direct functional interaction between these two proteins. The C-terminal tail of GluA1 was required for the binding between of ABHD6 and GluA1. Mutagenesis analysis revealed a GFCLIPQ sequence in the GluA1 C terminus that was essential for the inhibitory effect of ABHD6. The hydrolase activity of ABHD6 was not required for the effects of ABHD6 on AMPAR function in either neurons or transfected HEK293T cells. Thus, these findings reveal a novel and unexpected mechanism governing AMPAR trafficking at synapses through ABHD6. PMID:27114538

  20. α/β-Hydrolase domain-containing 6 (ABHD6) negatively regulates the surface delivery and synaptic function of AMPA receptors.

    PubMed

    Wei, Mengping; Zhang, Jian; Jia, Moye; Yang, Chaojuan; Pan, Yunlong; Li, Shuaiqi; Luo, Yiwen; Zheng, Junyuan; Ji, Jianguo; Chen, Jianguo; Hu, Xinli; Xiong, Jingwei; Shi, Yun; Zhang, Chen

    2016-05-10

    In the brain, AMPA-type glutamate receptors are major postsynaptic receptors at excitatory synapses that mediate fast neurotransmission and synaptic plasticity. α/β-Hydrolase domain-containing 6 (ABHD6), a monoacylglycerol lipase, was previously found to be a component of AMPA receptor macromolecular complexes, but its physiological significance in the function of AMPA receptors (AMPARs) has remained unclear. The present study shows that overexpression of ABHD6 in neurons drastically reduced excitatory neurotransmission mediated by AMPA but not by NMDA receptors at excitatory synapses. Inactivation of ABHD6 expression in neurons by either CRISPR/Cas9 or shRNA knockdown methods significantly increased excitatory neurotransmission at excitatory synapses. Interestingly, overexpression of ABHD6 reduced glutamate-induced currents and the surface expression of GluA1 in HEK293T cells expressing GluA1 and stargazin, suggesting a direct functional interaction between these two proteins. The C-terminal tail of GluA1 was required for the binding between of ABHD6 and GluA1. Mutagenesis analysis revealed a GFCLIPQ sequence in the GluA1 C terminus that was essential for the inhibitory effect of ABHD6. The hydrolase activity of ABHD6 was not required for the effects of ABHD6 on AMPAR function in either neurons or transfected HEK293T cells. Thus, these findings reveal a novel and unexpected mechanism governing AMPAR trafficking at synapses through ABHD6. PMID:27114538

  1. Autoantibodies to epilepsy-related LGI1 in limbic encephalitis neutralize LGI1-ADAM22 interaction and reduce synaptic AMPA receptors.

    PubMed

    Ohkawa, Toshika; Fukata, Yuko; Yamasaki, Miwako; Miyazaki, Taisuke; Yokoi, Norihiko; Takashima, Hiroshi; Watanabe, Masahiko; Watanabe, Osamu; Fukata, Masaki

    2013-11-13

    More than 30 mutations in LGI1, a secreted neuronal protein, have been reported with autosomal dominant lateral temporal lobe epilepsy (ADLTE). Although LGI1 haploinsufficiency is thought to cause ADLTE, the underlying molecular mechanism that results in abnormal brain excitability remains mysterious. Here, we focused on a mode of action of LGI1 autoantibodies associated with limbic encephalitis (LE), which is one of acquired epileptic disorders characterized by subacute onset of amnesia and seizures. We comprehensively screened human sera from patients with immune-mediated neurological disorders for LGI1 autoantibodies, which also uncovered novel autoantibodies against six cell surface antigens including DCC, DPP10, and ADAM23. Our developed ELISA arrays revealed a specific role for LGI1 antibodies in LE and concomitant involvement of multiple antibodies, including LGI1 antibodies in neuromyotonia, a peripheral nerve disorder. LGI1 antibodies associated with LE specifically inhibited the ligand-receptor interaction between LGI1 and ADAM22/23 by targeting the EPTP repeat domain of LGI1 and reversibly reduced synaptic AMPA receptor clusters in rat hippocampal neurons. Furthermore, we found that disruption of LGI1-ADAM22 interaction by soluble extracellular domain of ADAM22 was sufficient to reduce synaptic AMPA receptors in rat hippocampal neurons and that levels of AMPA receptor were greatly reduced in the hippocampal dentate gyrus in the epileptic LGI1 knock-out mouse. Therefore, either genetic or acquired loss of the LGI1-ADAM22 interaction reduces the AMPA receptor function, causing epileptic disorders. These results suggest that by finely regulating the synaptic AMPA receptors, the LGI1-ADAM22 interaction maintains physiological brain excitability throughout life. PMID:24227725

  2. Autoantibodies to Epilepsy-Related LGI1 in Limbic Encephalitis Neutralize LGI1-ADAM22 Interaction and Reduce Synaptic AMPA Receptors

    PubMed Central

    Ohkawa, Toshika; Fukata, Yuko; Yamasaki, Miwako; Miyazaki, Taisuke; Yokoi, Norihiko; Takashima, Hiroshi; Watanabe, Masahiko; Watanabe, Osamu

    2013-01-01

    More than 30 mutations in LGI1, a secreted neuronal protein, have been reported with autosomal dominant lateral temporal lobe epilepsy (ADLTE). Although LGI1 haploinsufficiency is thought to cause ADLTE, the underlying molecular mechanism that results in abnormal brain excitability remains mysterious. Here, we focused on a mode of action of LGI1 autoantibodies associated with limbic encephalitis (LE), which is one of acquired epileptic disorders characterized by subacute onset of amnesia and seizures. We comprehensively screened human sera from patients with immune-mediated neurological disorders for LGI1 autoantibodies, which also uncovered novel autoantibodies against six cell surface antigens including DCC, DPP10, and ADAM23. Our developed ELISA arrays revealed a specific role for LGI1 antibodies in LE and concomitant involvement of multiple antibodies, including LGI1 antibodies in neuromyotonia, a peripheral nerve disorder. LGI1 antibodies associated with LE specifically inhibited the ligand-receptor interaction between LGI1 and ADAM22/23 by targeting the EPTP repeat domain of LGI1 and reversibly reduced synaptic AMPA receptor clusters in rat hippocampal neurons. Furthermore, we found that disruption of LGI1-ADAM22 interaction by soluble extracellular domain of ADAM22 was sufficient to reduce synaptic AMPA receptors in rat hippocampal neurons and that levels of AMPA receptor were greatly reduced in the hippocampal dentate gyrus in the epileptic LGI1 knock-out mouse. Therefore, either genetic or acquired loss of the LGI1-ADAM22 interaction reduces the AMPA receptor function, causing epileptic disorders. These results suggest that by finely regulating the synaptic AMPA receptors, the LGI1-ADAM22 interaction maintains physiological brain excitability throughout life. PMID:24227725

  3. Histone Modification of Nedd4 Ubiquitin Ligase Controls the Loss of AMPA Receptors and Cognitive Impairment Induced by Repeated Stress

    PubMed Central

    Wei, Jing; Xiong, Zhe; Lee, Janine B.; Cheng, Jia; Duffney, Lara J.; Matas, Emmanuel

    2016-01-01

    Stress and the major stress hormone corticosterone induce profound influences in the brain. Altered histone modification and transcriptional dysfunction have been implicated in stress-related mental disorders. We previously found that repeated stress caused an impairment of prefrontal cortex (PFC)-mediated cognitive functions by increasing the ubiquitination and degradation of AMPA-type glutamate receptors via a mechanism depending on the E3 ubiquitin ligase Nedd4. Here, we demonstrated that in PFC of repeatedly stressed rats, active glucocorticoid receptor had the increased binding to the glucocorticoid response element of histone deacetylase 2 (HDAC2) promoter, resulting in the upregulation of HDAC2. Inhibition or knock-down of HDAC2 blocked the stress-induced impairment of synaptic transmission, AMPAR expression, and recognition memory. Furthermore, we found that, in stressed animals, the HDAC2-dependent downregulation of histone methyltransferase Ehmt2 (G9a) led to the loss of repressive histone methylation at the Nedd4-1 promoter and the transcriptional activation of Nedd4. These results have provided an epigenetic mechanism and a potential treatment strategy for the detrimental effects of chronic stress. SIGNIFICANCE STATEMENT Prolonged stress exposure can induce altered histone modification and transcriptional dysfunction, which may underlie the profound influence of stress in regulating brain functions. We report an important finding about the epigenetic mechanism controlling the detrimental effects of repeated stress on synaptic transmission and cognitive function. First, it has revealed the stress-induced alteration of key epigenetic regulators HDAC2 and Ehmt2, which determines the synaptic and behavioral effects of repeated stress. Second, it has uncovered the stress-induced histone modification of the target gene Nedd4, an E3 ligase that is critically involved in the ubiquitination and degradation of AMPA receptors and cognition. Third, it has provided

  4. Alterations in AMPA receptor subunits and TARPs in the rat nucleus accumbens related to the formation of Ca²⁺-permeable AMPA receptors during the incubation of cocaine craving.

    PubMed

    Ferrario, Carrie R; Loweth, Jessica A; Milovanovic, Mike; Ford, Kerstin A; Galiñanes, Gregorio L; Heng, Li-Jun; Tseng, Kuei Y; Wolf, Marina E

    2011-12-01

    Cue-induced cocaine seeking intensifies or incubates after withdrawal from extended access cocaine self-administration, a phenomenon termed incubation of cocaine craving. The expression of incubated craving is mediated by Ca²⁺-permeable AMPA receptors (CP-AMPARs) in the nucleus accumbens (NAc). Thus, CP-AMPARs are a potential target for therapeutic intervention, making it important to understand mechanisms that govern their accumulation. Here we used subcellular fractionation and biotinylation of NAc tissue to examine the abundance and distribution of AMPAR subunits, and GluA1 phosphorylation, in the incubation model. We also studied two transmembrane AMPA receptor regulatory proteins (TARPs), γ-2 and γ-4. Our results, together with earlier findings, suggest that some of the new CP-AMPARs are synaptic. These are probably associated with γ-2, but they are loosely tethered to the PSD. Levels of GluA1 phosphorylated at serine 845 (pS845 GluA1) were significantly increased in biotinylated tissue and in an extrasynaptic membrane-enriched fraction. These results suggest that increased synaptic levels of CP-AMPARs may result in part from an increase in pS845 GluA1 in extrasynaptic membranes, given that S845 phosphorylation primes GluA1-containing AMPARs for synaptic insertion and extrasynaptic AMPARs supply the synapse. Some of the new extrasynaptic CP-AMPARs are likely associated with γ-4, rather than γ-2. The maintenance of CP-AMPARs in NAc synapses during withdrawal is accompanied by activation of CaMKII and ERK2 but not CaMKI. Overall, AMPAR plasticity in the incubation model shares some features with better described forms of synaptic plasticity, although the timing of the phenomenon and the persistence of related neuroadaptations are significantly different. PMID:21276808

  5. TARP-associated AMPA receptors display an increased maximum channel conductance and multiple kinetically distinct open states

    PubMed Central

    Shelley, Chris; Farrant, Mark; Cull-Candy, Stuart G

    2012-01-01

    Fast excitatory synaptic transmission in the CNS is mediated mainly by AMPA-type glutamate receptors (AMPARs), whose biophysical properties are dramatically modulated by the presence of transmembrane AMPAR regulatory proteins (TARPs). To help construct a kinetic model that will realistically describe native AMPAR/TARP function, we have examined the single-channel properties of homomeric GluA1 AMPARs in combination with the TARPs, γ-2, γ-4 and γ-5. In a saturating concentration of agonist, each of these AMPAR/TARP combinations gave rise to single-channel currents with multiple conductance levels that appeared intrinsic to the receptor-channel complex, and showed long-lived subconductance states. The open time and burst length distributions of the receptor complexes displayed multiple dwell-time components. In the case of γ-2- and γ-4-associated receptors, these distributions included a long-lived component lasting tens of milliseconds that was absent from both GluA1 alone and γ-5-associated receptors. The open time distributions for each conductance level required two dwell-time components, indicating that at each conductance level the channel occupies a minimum of two kinetically distinct open states. We have explored how these data place novel constraints on possible kinetic models of TARP-associated AMPARs that may be used to define AMPAR-mediated synaptic transmission. PMID:22988139

  6. Surface expression of GluR-D AMPA receptor is dependent on an interaction between its C-terminal domain and a 4.1 protein.

    PubMed

    Coleman, Sarah K; Cai, Chunlin; Mottershead, David G; Haapalahti, Jukka-Pekka; Keinänen, Kari

    2003-02-01

    Dynamic regulation of the number and activity of AMPA receptors is believed to underlie many forms of synaptic plasticity and is presumably mediated by specific protein-protein interactions involving the C-terminal domain of the receptor. Several proteins interacting with the C-terminal tails of the glutamate receptor (GluR)-A and GluR-B subunits have been identified and implicated in the regulation of endocytosis and exocytosis, clustering, and anchoring of AMPA receptors to the cytoskeleton. In contrast, little is known of the molecular interactions of the GluR-D subunit, or of the mechanisms regulating the traffic of GluR-D-containing AMPA receptors. We analyzed the subcellular localization of homomeric GluR-D receptors carrying C-terminal deletions in transfected human embryonic kidney (HEK) 293 cells and in primary neurons by immunofluorescence microscopy and ELISA. A minimal requirement for a 14-residue cytoplasmic segment for the surface expression of homomeric GluR-D receptors was identified. Previously, a similar region in the GluR-A subunit was implicated in an interaction with 4.1 family proteins. Coimmunoprecipitation demonstrated that GluR-D associated with 4.1 protein(s) in both HEK293 cells and rat brain. Moreover, glutathione S-transferase pull-down experiments showed that the same 14-residue segment is critical for 4.1 binding to GluR-A and GluR-D. Point mutations within this segment dramatically decreased the surface expression of GluR-D in HEK293 cells, with a concomitant loss of the 4.1 interaction. Our findings demonstrate a novel molecular interaction for the GluR-D subunit and suggest that the association with the 4.1 family protein(s) plays an essential role in the transport to and stabilization of GluR-D-containing AMPA receptors at the cell surface. PMID:12574408

  7. GluA2-Containing AMPA Receptors Distinguish Ribbon-Associated from Ribbonless Afferent Contacts on Rat Cochlear Hair Cells.

    PubMed

    Martinez-Monedero, Rodrigo; Liu, Chang; Weisz, Catherine; Vyas, Pankhuri; Fuchs, Paul Albert; Glowatzki, Elisabeth

    2016-01-01

    Mechanosensory hair cells release glutamate at ribbon synapses to excite postsynaptic afferent neurons, via AMPA-type ionotropic glutamate receptors (AMPARs). However, type II afferent neurons contacting outer hair cells in the mammalian cochlea were thought to differ in this respect, failing to show GluA immunolabeling and with many "ribbonless" afferent contacts. Here it is shown that antibodies to the AMPAR subunit GluA2 labeled afferent contacts below inner and outer hair cells in the rat cochlea, and that synaptic currents in type II afferents had AMPAR-specific pharmacology. Only half the postsynaptic densities of type II afferents that labeled for PSD-95, Shank, or Homer were associated with GluA2 immunopuncta or presynaptic ribbons, the "empty slots" corresponding to ribbonless contacts described previously. These results extend the universality of AMPAergic transmission by hair cells, and support the existence of silent afferent contacts. PMID:27257620

  8. Antidepressant Effects of AMPA and Ketamine Combination: Role of Hippocampal BDNF, Synapsin, and mTOR

    PubMed Central

    Akinfiresoye, Luli; Tizabi, Yousef

    2013-01-01

    Rationale A number of preclinical and clinical studies suggest ketamine, a glutamate NMDA (N-methyl-D-aspartate) receptor antagonist, has a rapid and lasting antidepressant effect when administered either acutely or chronically. It has been postulated that this effect is due to stimulation of AMPA (alpha-amino-3-hydroxy-5-methyl–4-isoxazolepropionic acid) receptors. Objective In this study, we tested whether AMPA alone has an antidepressant effect and if the combination of AMPA and ketamine provides added benefit in Wistar-Kyoto (WKY) rats, a putative animal model of depression. Results Chronic AMPA treatment resulted in a dose dependent antidepressant effect in both the forced swim test (FST) and sucrose preference test. Moreover, chronic administration (10–11d) of combinations of AMPA and ketamine, at doses that were ineffective on their own, resulted in a significant antidepressant effect. The behavioral effects were associated with increases in hippocampal brain derived neurotrophic factor (BDNF), synapsin, and mammalian target of rapamycin (mTOR). Conclusion These findings are the first to provide evidence for an antidepressant effect of AMPA, and suggest the usefulness of AMPA-ketamine combination in treatment of depression. Furthermore, these effects appear to be associated with increases in markers of hippocampal neurogenesis and synaptogenesis, suggesting a mechanism of their action. PMID:23732839

  9. Dynamic changes of excitatory amino acid receptors in the rat hippocampus following transient cerebral ischemia

    SciTech Connect

    Westerberg, E.; Monaghan, D.T.; Kalimo, H.; Cotman, C.W.; Wieloch, T.W.

    1989-03-01

    The changes in excitatory amino acid receptor ligand binding induced by transient cerebral ischemia were studied in the rat hippocampal subfields. Ten minutes of ischemia was induced by common carotid artery occlusion combined with hypotension, and the animals were allowed variable periods of recovery ranging from 1 day to 4 weeks. The binding of 3H-AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) to quisqualate receptors, 3H-kainic acid (KA) to kainate receptors, and 3H-glutamate to N-methyl-D-aspartate (NMDA) receptors as determined by quantitative autoradiography. One week following ischemia the CA1 region of the hippocampus displayed a severe (90%) dendrosomatic lesion with preservation of presynaptic terminals. This was associated with a 60% decrease in AMPA binding and a 25% decrease in glutamate binding to NMDA receptors. At 4 weeks postischemia, both AMPA and NMDA sites were greatly reduced. Although the dentate gyrus granule cells are resistant to an ischemic insult of this magnitude, this region showed marked changes in receptor binding. One week following ischemia, the AMPA and NMDA binding decreased by approximately 40 and 20%, respectively. Following 2 weeks of recovery, the NMDA binding was not significantly different from control level, while the AMPA binding remained depressed up to 4 weeks postischemia. The high density of KA binding sites in the inner molecular layer of the dentate gyrus was unaffected by the ischemic insult, despite an extensive degeneration of cells in the hilus of dentate gyrus which projects glutamatergic afferents to this area.

  10. The Prefrontal Dectin-1/AMPA Receptor Signaling Pathway Mediates The Robust and Prolonged Antidepressant Effect of Proteo-β-Glucan from Maitake.

    PubMed

    Bao, Hongkun; Ran, Pengzhan; Zhu, Ming; Sun, Lijuan; Li, Bai; Hou, Yangyang; Nie, Jun; Shan, Liping; Li, Hongliang; Zheng, Shangyong; Xu, Xiufeng; Xiao, Chunjie; Du, Jing

    2016-01-01

    Proteo-β-glucan from Maitake (PGM) is a strong immune regulator, and its receptor is called Dectin-1. Cumulative evidence suggests that AMPA receptors are important for the treatment of depression. Here, we report that PGM treatment leads to a significant antidepressant effect in the tail suspension test and forced swim test after sixty minutes of treatment in mice. After five consecutive days of PGM treatment, this antidepressant effect remained. PGM treatment did not show a hyperactive effect in the open field test. PGM significantly enhanced the expression of its receptor Dectin-1, as well as p-GluA1(S845) and GluA1, but not GluA2 or GluA3 in the prefrontal cortex (PFC) after five days of treatment. The Dectin-1 inhibitor Laminarin was able to block the antidepressant effect of PGM. At the synapses of PFC, PGM treatment significantly up-regulated the p-GluA1(S845), GluA1, GluA2, and GluA3 levels. Moreover, PGM's antidepressant effects and the increase of p-GluA1(S845)/GluA1 lasted for 3 days after stopping treatment. The AMPA-specific antagonist GYKI 52466 was able to block the antidepressant effect of PGM. This study identified PGM as a novel antidepressant with clinical potential and a new antidepressant mechanism for regulating prefrontal Dectin-1/AMPA receptor signalling. PMID:27329257

  11. The Prefrontal Dectin-1/AMPA Receptor Signaling Pathway Mediates The Robust and Prolonged Antidepressant Effect of Proteo-β-Glucan from Maitake

    PubMed Central

    Bao, Hongkun; Ran, Pengzhan; Zhu, Ming; Sun, Lijuan; Li, Bai; Hou, Yangyang; Nie, Jun; Shan, Liping; Li, Hongliang; Zheng, Shangyong; Xu, Xiufeng; Xiao, Chunjie; Du, Jing

    2016-01-01

    Proteo-β-glucan from Maitake (PGM) is a strong immune regulator, and its receptor is called Dectin-1. Cumulative evidence suggests that AMPA receptors are important for the treatment of depression. Here, we report that PGM treatment leads to a significant antidepressant effect in the tail suspension test and forced swim test after sixty minutes of treatment in mice. After five consecutive days of PGM treatment, this antidepressant effect remained. PGM treatment did not show a hyperactive effect in the open field test. PGM significantly enhanced the expression of its receptor Dectin-1, as well as p-GluA1(S845) and GluA1, but not GluA2 or GluA3 in the prefrontal cortex (PFC) after five days of treatment. The Dectin-1 inhibitor Laminarin was able to block the antidepressant effect of PGM. At the synapses of PFC, PGM treatment significantly up-regulated the p-GluA1(S845), GluA1, GluA2, and GluA3 levels. Moreover, PGM’s antidepressant effects and the increase of p-GluA1(S845)/GluA1 lasted for 3 days after stopping treatment. The AMPA-specific antagonist GYKI 52466 was able to block the antidepressant effect of PGM. This study identified PGM as a novel antidepressant with clinical potential and a new antidepressant mechanism for regulating prefrontal Dectin-1/AMPA receptor signalling. PMID:27329257

  12. The role of AMPA receptors in postsynaptic mechanisms of synaptic plasticity

    PubMed Central

    Chater, Thomas E.; Goda, Yukiko

    2014-01-01

    In the mammalian central nervous system, excitatory glutamatergic synapses harness neurotransmission that is mediated by ion flow through α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). AMPARs, which are enriched in the postsynaptic membrane on dendritic spines, are highly dynamic, and shuttle in and out of synapses in an activity-dependent manner. Changes in their number, subunit composition, phosphorylation state, and accessory proteins can all regulate AMPARs and thus modify synaptic strength and support cellular forms of learning. Furthermore, dysregulation of AMPAR plasticity has been implicated in various pathological states and has important consequences for mental health. Here we focus on the mechanisms that control AMPAR plasticity, drawing particularly from the extensive studies on hippocampal synapses, and highlight recent advances in the field along with considerations for future directions. PMID:25505875

  13. A Computational Model for the AMPA Receptor Phosphorylation Master Switch Regulating Cerebellar Long-Term Depression

    PubMed Central

    Gallimore, Andrew R.; Aricescu, A. Radu; Yuzaki, Michisuke; Calinescu, Radu

    2016-01-01

    The expression of long-term depression (LTD) in cerebellar Purkinje cells results from the internalisation of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs) from the postsynaptic membrane. This process is regulated by a complex signalling pathway involving sustained protein kinase C (PKC) activation, inhibition of serine/threonine phosphatase, and an active protein tyrosine phosphatase, PTPMEG. In addition, two AMPAR-interacting proteins–glutamate receptor-interacting protein (GRIP) and protein interacting with C kinase 1 (PICK1)–regulate the availability of AMPARs for trafficking between the postsynaptic membrane and the endosome. Here we present a new computational model of these overlapping signalling pathways. The model reveals how PTPMEG cooperates with PKC to drive LTD expression by facilitating the effect of PKC on the dissociation of AMPARs from GRIP and thus their availability for trafficking. Model simulations show that LTD expression is increased by serine/threonine phosphatase inhibition, and negatively regulated by Src-family tyrosine kinase activity, which restricts the dissociation of AMPARs from GRIP under basal conditions. We use the model to expose the dynamic balance between AMPAR internalisation and reinsertion, and the phosphorylation switch responsible for the perturbation of this balance and for the rapid plasticity initiation and regulation. Our model advances the understanding of PF-PC LTD regulation and induction, and provides a validated extensible platform for more detailed studies of this fundamental synaptic process. PMID:26807999

  14. A Computational Model for the AMPA Receptor Phosphorylation Master Switch Regulating Cerebellar Long-Term Depression.

    PubMed

    Gallimore, Andrew R; Aricescu, A Radu; Yuzaki, Michisuke; Calinescu, Radu

    2016-01-01

    The expression of long-term depression (LTD) in cerebellar Purkinje cells results from the internalisation of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs) from the postsynaptic membrane. This process is regulated by a complex signalling pathway involving sustained protein kinase C (PKC) activation, inhibition of serine/threonine phosphatase, and an active protein tyrosine phosphatase, PTPMEG. In addition, two AMPAR-interacting proteins-glutamate receptor-interacting protein (GRIP) and protein interacting with C kinase 1 (PICK1)-regulate the availability of AMPARs for trafficking between the postsynaptic membrane and the endosome. Here we present a new computational model of these overlapping signalling pathways. The model reveals how PTPMEG cooperates with PKC to drive LTD expression by facilitating the effect of PKC on the dissociation of AMPARs from GRIP and thus their availability for trafficking. Model simulations show that LTD expression is increased by serine/threonine phosphatase inhibition, and negatively regulated by Src-family tyrosine kinase activity, which restricts the dissociation of AMPARs from GRIP under basal conditions. We use the model to expose the dynamic balance between AMPAR internalisation and reinsertion, and the phosphorylation switch responsible for the perturbation of this balance and for the rapid plasticity initiation and regulation. Our model advances the understanding of PF-PC LTD regulation and induction, and provides a validated extensible platform for more detailed studies of this fundamental synaptic process. PMID:26807999

  15. In vivo synaptic scaling is mediated by GluA2-lacking AMPA receptors in the embryonic spinal cord

    PubMed Central

    Garcia-Bereguiain, Miguel Angel; Gonzalez-Islas, Carlos; Lindsly, Casie; Butler, Ellie; Hill, Atlantis Wilkins; Wenner, Peter

    2013-01-01

    When spiking activity within a network is perturbed for hours to days, compensatory changes in synaptic strength are triggered that are thought to be important for the homeostatic maintenance of network or cellular spiking activity. In one form of this homeostatic plasticity, called synaptic scaling, all of a cell’s AMPAergic miniature postsynaptic currents (mEPSCs) are increased or decreased by some scaling factor. While synaptic scaling has been observed in a variety of systems, the mechanisms that underlie AMPAergic scaling have been controversial. Certain studies find that synaptic scaling is mediated by GluA2-lacking calcium permeable receptors (CP-AMPARs), while others have found that scaling is mediated by GluA2-containing calcium impermeable receptors (CI-AMPARs). Spontaneous network activity is observed in most developing circuits, and in the spinal cord this activity drives embryonic movements. Blocking spontaneous network activity in the chick embryo by infusing lidocaine in vivo triggers synaptic scaling in spinal motoneurons; here we show that AMPAergic scaling occurs through increases in mEPSC conductance that appear to be mediated by the insertion of GluA2-lacking AMPA receptors at the expense of GluA2-containing receptors. We have previously reported that in vivo blockade of GABAA transmission, at a developmental stage when GABA is excitatory, also triggered AMPAergic synaptic scaling. Here, we show that this form of AMPAergic scaling is also mediated by CP-AMPARs. These findings suggest that AMPAergic scaling triggered by blocking spiking activity or GABAA receptor transmission represent similar phenomenon, supporting the idea that activity-blockade triggers scaling by reducing GABAA transmission. PMID:23595738

  16. Discriminative stimulus effects of NMDA, AMPA and mGluR5 glutamate receptor ligands in methamphetamine-trained rats

    PubMed Central

    Wooters, Thomas E.; Dwoskin, Linda P.; Bardo, Michael T.

    2011-01-01

    Glutamate contributes to the reinforcing and stimulant effects of methamphetamine, yet its potential role in the interoceptive stimulus properties of methamphetamine is unknown. In the current study, adult male Sprague-Dawley rats were trained to discriminate methamphetamine (1.0 mg/kg, i.p.) from saline in a standard operant discrimination task. The effects of methamphetamine (0.1-1.0 mg/kg, i.p.), the N-methyl-D-aspartate (NMDA) receptor channel blockers MK-801 (0.03-0.3 mg/kg, i.p.) and ketamine (1.0-10.0 mg/kg, i.p.), the low-affinity NMDA antagonist memantine (1.0-10 mg/kg, i.p.), the polyamine site NMDA receptor antagonist ifenprodil (1-10 mg/kg), the α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 1-10 mg/kg, i.p.), and the metabotropic 5 (mGluR5) receptor antagonist 6-methyl-2-(phenylethynyl)pyridine (MPEP; 1-10 mg/kg) given alone were determined in substitution tests. The effects of MK-801 (0.03 and 0.1 mg/kg), ketamine (1.0 and 3.0 mg/kg), ifenprodil (5.6 mg/kg), CNQX (5.6 mg/kg) and MPEP (5.6 mg/kg) were also tested in combination with methamphetamine to assess for alterations in the methamphetamine cue. In substitution tests, none of the test drugs generalized to the methamphetamine cue. However, ketamine and ifenprodil produced significant leftward shifts in the methamphetamine dose-response curve; pretreatment with 3 mg/kg of ketamine, for example, decreased the ED50 value for methamphetamine by half. These results suggest that blockade of the NMDA receptor augments the interoceptive stimulus properties of methamphetamine. PMID:21836462

  17. Amyloid-β impairs, and ibuprofen restores, the cGMP pathway, synaptic expression of AMPA receptors and long-term potentiation in the hippocampus.

    PubMed

    Monfort, Pilar; Felipo, Vicente

    2010-01-01

    Amyloid-β (Aβ) rapidly impairs hippocampal long-term potentiation (LTP) and cognitive function in rats. We hypothesized that: a) Aβ-induced impairment of LTP would be due to impairment of the nitric oxide (NO)-cGMP pathway and AMPA receptor translocation; and b) treatment with the anti-inflammatory drug ibuprofen would restore the NO-cGMP pathway and LTP. The aims of this work were to assess whether ibuprofen prevents and/or rescues Aβ-induced LTP impairments in hippocampal slices and to analyze the role of the altered NO-cGMP-protein kinase G pathway and AMPA receptor phosphorylation and synaptic expression in the mechanisms by which Aβ impairs and ibuprofen restores LTP. Aβ impairs tetanus-induced activation of guanylate cyclase and cGMP increase, preventing protein kinase G activation, phosphorylation of GluR1 in Ser845 and AMPA receptors translocation to synaptic membranes, which is responsible for LTP impairment by Aβ. Ibuprofen prevents LTP impairment by Aβ by restoring guanylate cyclase activation and increase in cGMP and, subsequently, activation of protein kinase G, phosphorylation of GluR1 in Ser845 and synaptic expression of AMPA receptors. Restoration of cGMP levels is enough to restore all this process as indicated by the fact that the cGMP analog 8-Br-cGMP also normalizes the function of this pathway and restores LTP in the presence of Aβ. These results indicate that Aβ impairs LTP by impairing the NO-cGMP pathway and that ibuprofen restores LTP by restoring this pathway. These data suggest that restoring cGMP levels may have therapeutic utility to improve cognitive function impaired by Aβ. PMID:20858955

  18. NBQX, a highly selective competitive antagonist of AMPA and KA ionotropic glutamate receptors, increases seizures and mortality following picornavirus infection.

    PubMed

    Libbey, Jane E; Hanak, Tyler J; Doty, Daniel J; Wilcox, Karen S; Fujinami, Robert S

    2016-06-01

    Seizures occur due to an imbalance between excitation and inhibition, with the balance tipping towards excitation, and glutamate is the predominant excitatory neurotransmitter in the central nervous system of mammals. Since upregulation of expression and/or function of glutamate receptors can contribute to seizures we determined the effects of three antagonists, NBQX, GYKI-52466 and MK 801, of the various ionotropic glutamate receptors, AMPA, NMDA and KA, on acute seizure development in the Theiler's murine encephalomyelitis virus (TMEV)-induced seizure model. We found that only NBQX had an effect on acute seizure development, resulting in a significantly higher number of mice experiencing seizures, an increase in the number of seizures per mouse, a greater cumulative seizure score per mouse and a significantly higher mortality rate among the mice. Although NBQX has previously been shown to be a potent anticonvulsant in animal seizure models, seizures induced by electrical stimulation, drug administration or as a result of genetic predisposition may differ greatly in terms of mechanism of seizure development from our virus-induced seizure model, which could explain the opposite, proconvulsant effect of NBQX observed in the TMEV-induced seizure model. PMID:27072529

  19. Alteration of AMPA Receptor-Mediated Synaptic Transmission by Alexa Fluor 488 and 594 in Cerebellar Stellate Cells.

    PubMed

    Maroteaux, Matthieu; Liu, Siqiong June

    2016-01-01

    The fluorescent dyes, Alexa Fluor 488 and 594 are commonly used to visualize dendritic structures and the localization of synapses, both of which are critical for the spatial and temporal integration of synaptic inputs. However, the effect of the dyes on synaptic transmission is not known. Here we investigated whether Alexa Fluor dyes alter the properties of synaptic currents mediated by two subtypes of AMPA receptors (AMPARs) at cerebellar stellate cell synapses. In naive mice, GluA2-lacking AMPAR-mediated synaptic currents displayed an inwardly rectifying current-voltage (I-V) relationship due to blockade by cytoplasmic spermine at depolarized potentials. We found that the inclusion of 100 µm Alexa Fluor dye, but not 10 µm, in the pipette solution led to a gradual increase in the amplitude of EPSCs at +40 mV and a change in the I-V relationship from inwardly rectifying to more linear. In mice exposed to an acute stress, AMPARs switched to GluA2-containing receptors, and 100 µm Alexa Fluor 594 did not alter the I-V relationship of synaptic currents. Therefore, a high concentration of Alexa Fluor dye changed the I-V relationship of EPSCs at GluA2-lacking AMPAR synapses. PMID:27280156

  20. Alteration of AMPA Receptor-Mediated Synaptic Transmission by Alexa Fluor 488 and 594 in Cerebellar Stellate Cells123

    PubMed Central

    2016-01-01

    Abstract The fluorescent dyes, Alexa Fluor 488 and 594 are commonly used to visualize dendritic structures and the localization of synapses, both of which are critical for the spatial and temporal integration of synaptic inputs. However, the effect of the dyes on synaptic transmission is not known. Here we investigated whether Alexa Fluor dyes alter the properties of synaptic currents mediated by two subtypes of AMPA receptors (AMPARs) at cerebellar stellate cell synapses. In naive mice, GluA2-lacking AMPAR-mediated synaptic currents displayed an inwardly rectifying current–voltage (I–V) relationship due to blockade by cytoplasmic spermine at depolarized potentials. We found that the inclusion of 100 µm Alexa Fluor dye, but not 10 µm, in the pipette solution led to a gradual increase in the amplitude of EPSCs at +40 mV and a change in the I–V relationship from inwardly rectifying to more linear. In mice exposed to an acute stress, AMPARs switched to GluA2-containing receptors, and 100 µm Alexa Fluor 594 did not alter the I–V relationship of synaptic currents. Therefore, a high concentration of Alexa Fluor dye changed the I–V relationship of EPSCs at GluA2-lacking AMPAR synapses. PMID:27280156

  1. Nuclear respiratory factor 1 co-regulates AMPA glutamate receptor subunit 2 and cytochrome c oxidase : Tight coupling of glutamatergic transmission and energy metabolism in neurons

    PubMed Central

    Dhar, Shilpa S.; Liang, Huan Ling; Wong-Riley, Margaret T. T.

    2013-01-01

    Neuronal activity, especially of the excitatory glutamatergic type, is highly dependent on energy from the oxidative pathway. We hypothesized that the coupling existed at the transcriptional level by having the same transcription factor to regulate a marker of energy metabolism, cytochrome c oxidase (COX) and an important subunit of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors, GluR2 (Gria2). Nuclear respiratory factor 1 (NRF-1) was a viable candidate because it regulates all COX subunits and potentially activates Gria2. By means of in silico analysis, electrophoretic mobility shift and supershift, chromatin immunoprecipitation, and promoter mutational assays, we found that NRF-1 functionally bound to Gria2 promoter. Silencing of NRF-1 with small interference RNA prevented the depolarization-stimulated up-regulation of Gria2 and COX, and over-expression of NRF-1 rescued neurons from TTX-induced down-regulation of Gria2 and COX transcripts. Thus, neuronal activity and energy metabolism are tightly coupled at the molecular level, and NRF-1 is a critical agent in this process. PMID:19166514

  2. β-Amyloid Impairs AMPA Receptor Trafficking and Function by Reducing Ca2+/Calmodulin-dependent Protein Kinase II Synaptic Distribution*

    PubMed Central

    Gu, Zhenglin; Liu, Wenhua; Yan, Zhen

    2009-01-01

    A fundamental feature of Alzheimer disease (AD) is the accumulation of β-amyloid (Aβ), a peptide generated from the amyloid precursor protein (APP). Emerging evidence suggests that soluble Aβ oligomers adversely affect synaptic function, which leads to cognitive failure associated with AD. The Aβ-induced synaptic dysfunction has been attributed to the synaptic removal of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors (AMPARs); however, it is unclear how Aβ induces the loss of AMPARs at the synapses. In this study we have examined the potential involvement of Ca2+/calmodulin-dependent protein kinase II (CaMKII), a signaling molecule critical for AMPAR trafficking and function. We found that the synaptic pool of CaMKII was significantly decreased in cortical neurons from APP transgenic mice, and the density of CaMKII clusters at synapses was significantly reduced by Aβ oligomer treatment. In parallel, the surface expression of GluR1 subunit as well as AMPAR-mediated synaptic response and ionic current was selectively decreased in APP transgenic mice and Aβ-treated cultures. Moreover, the reducing effect of Aβ on AMPAR current density was mimicked and occluded by knockdown of CaMKII and blocked by overexpression of CaMKII. These results suggest that the Aβ-induced change in CaMKII subcellular distribution may underlie the removal of AMPARs from synaptic membrane by Aβ. PMID:19240035

  3. Activation of AMPA receptor promotes TNF-α release via the ROS-cSrc-NFκB signaling cascade in RAW264.7 macrophages

    SciTech Connect

    Cheng, Xiu-Li; Ding, Fan; Li, Hui; Tan, Xiao-Qiu; Liu, Xiao; Cao, Ji-Min; Gao, Xue

    2015-05-29

    The relationship between glutamate signaling and inflammation has not been well defined. This study aimed to investigate the role of AMPA receptor (AMPAR) in the expression and release of tumor necrosis factor-alpha (TNF-α) from macrophages and the underlying mechanisms. A series of approaches, including confocal microscopy, immunofluorescency, flow cytometry, ELISA and Western blotting, were used to estimate the expression of AMPAR and downstream signaling molecules, TNF-α release and reactive oxygen species (ROS) generation in the macrophage-like RAW264.7 cells. The results demonstrated that AMPAR was expressed in RAW264.7 cells. AMPA significantly enhanced TNF-α release from RAW264.7 cells, and this effect was abolished by CNQX (AMPAR antagonist). AMPA also induced elevation of ROS production, phosphorylation of c-Src and activation of nuclear factor (NF)-κB in RAW264.7 cells. Blocking c-Src by PP2, scavenging ROS by glutathione (GSH) or inhibiting NF-κB activation by pyrrolidine dithiocarbamate (PDTC) decreased TNF-α production from RAW264.7 cells. We concluded that AMPA promotes TNF-α release in RAW264.7 macrophages likely through the following signaling cascade: AMPAR activation → ROS generation → c-Src phosphorylation → NF-κB activation → TNF-α elevation. The study suggests that AMPAR may participate in macrophage activation and inflammation. - Highlights: • AMPAR is expressed in RAW264.7 macrophages and is upregulated by AMPA stimulation. • Activation of AMPAR stimulates TNF-α release in macrophages through the ROS-cSrc-NFκB signaling cascade. • Macrophage AMPAR signaling may play an important role in inflammation.

  4. Dopamine alters AMPA receptor synaptic expression and subunit composition in dopamine neurons of the ventral tegmental area cultured with prefrontal cortex neurons.

    PubMed

    Gao, Can; Wolf, Marina E

    2007-12-26

    Excitatory synapses onto dopamine (DA) neurons of the ventral tegmental area (VTA) represent a critical site of psychostimulant-induced synaptic plasticity. This plasticity involves alterations in synaptic strength through AMPA receptor (AMPAR) redistribution. Here, we report an in vitro model for studying regulation of AMPAR trafficking in DA neurons under control conditions and after elevation of DA levels, mimicking cocaine exposure. We used cocultures containing rat VTA neurons and prefrontal cortex (PFC) neurons from enhanced cyan fluorescent protein-expressing mice. In VTA-PFC cocultures, D1 receptor activation (10 min) increased synaptic and nonsynaptic glutamate receptor subunit 1 (GluR1) and GluR2 surface expression on DA neurons. NMDA or AMPA receptor antagonists blocked this effect, and it was not observed in pure VTA cultures, suggesting that DA agonists acted on D1 receptors on PFC neurons, altering their excitatory transmission onto VTA DA neurons and, thus, influencing AMPARs. To mimic the longer elevation in extracellular DA levels produced by systemic cocaine, cocultures were incubated with DA for 1 h. Synaptic GluR1 was increased 24 h later, reminiscent of the increased AMPA/NMDA ratio at excitatory synapses onto VTA DA neurons 24 h after cocaine injection (Ungless et al., 2001). In contrast, GluR2 was unchanged. Analysis of colocalization of surface GluR1-3 labeling suggested that control DA neurons express a substantial number of GluR1/2, GluR2/3, and homomeric GluR1 receptors and that the increase in surface AMPARs 24 h after DA exposure may in part reflect increased GluR1/3-containing receptors. These results help define the cellular basis for plasticity underlying the development of behavioral sensitization. PMID:18160635

  5. Direct interactions between PSD-95 and stargazin control synaptic AMPA receptor number

    PubMed Central

    Schnell, Eric; Sizemore, Max; Karimzadegan, Siavash; Chen, Lu; Bredt, David S.; Nicoll, Roger A.

    2002-01-01

    Excitatory synapses in the brain exhibit a remarkable degree of functional plasticity, which largely reflects changes in the number of synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). However, mechanisms involved in recruiting AMPARs to synapses are unknown. Here we use hippocampal slice cultures and biolistic gene transfections to study the targeting of AMPARs to synapses. We show that AMPARs are localized to synapses through direct binding of the first two PDZ domains of synaptic PSD-95 (postsynaptic density protein of 95 kDa) to the AMPAR-associated protein, stargazin. Increasing the level of synaptic PSD-95 recruits new AMPARs to synapses without changing the number of surface AMPARs. At the same time, we show that stargazin overexpression drastically increases the number of extra-synaptic AMPARs, but fails to alter synaptic currents if synaptic PSD-95 levels are kept constant. Finally, we make compensatory mutations to both PSD-95 and stargazin to demonstrate the central role of direct interactions between them in determining the number of synaptic AMPARs. PMID:12359873

  6. Regulation of AMPA receptor extrasynaptic insertion by 4.1N, phosphorylation and palmitoylation

    PubMed Central

    Lin, Da–Ting; Makino, Yuichi; Sharma, Kamal; Hayashi, Takashi; Neve, Rachael; Takamiya, Kogo; Huganir, Richard L.

    2009-01-01

    The insertion of alpha–amino–3–hydroxy–5–methyl–4–isoxazolepropionic acid receptors (AMPARs) into the plasma membrane is a key step in synaptic delivery of AMPARs during the expression of synaptic plasticity. However, the molecular mechanisms regulating AMPAR insertion remain elusive. By directly visualizing individual insertion events of the AMPAR subunit GluR1, we demonstrate that Protein 4.1N is required for activity dependent GluR1 insertion. PKC phosphorylation of GluR1 S816 and S818 residues enhances 4.1N binding to GluR1, and facilitates GluR1 insertion. In addition, palmitoylation of GluR1 C811 residue modulates PKC phosphorylation and GluR1 insertion. Finally, disrupting 4.1N dependent GluR1 insertion decreases surface expression of GluR1 and the expression of long–term potentiation (LTP). Our study uncovers a novel mechanism that governs activity dependent GluR1 trafficking, reveals an interesting interplay between AMPAR palmitoylation and phosphorylation, and underscores the functional significance of the 4.1N protein in AMPAR trafficking and synaptic plasticity. PMID:19503082

  7. Structural and Single-Channel Results Indicate that the Rates of Ligand Binding Domain Closing and Opening Directly Impact AMPA Receptor Gating

    SciTech Connect

    Zhang,W.; Cho, Y.; Lolis, E.; Howe, J.

    2008-01-01

    At most excitatory central synapses, glutamate is released from presynaptic terminals and binds to postsynaptic AMPA receptors, initiating a series of conformational changes that result in ion channel opening. Efficient transmission at these synapses requires that glutamate binding to AMPA receptors results in rapid and near-synchronous opening of postsynaptic receptor channels. In addition, if the information encoded in the frequency of action potential discharge is to be transmitted faithfully, glutamate must dissociate from the receptor quickly, enabling the synapse to discriminate presynaptic action potentials that are spaced closely in time. The current view is that the efficacy of agonists is directly related to the extent to which ligand binding results in closure of the binding domain. For glutamate to dissociate from the receptor, however, the binding domain must open. Previously, we showed that mutations in glutamate receptor subunit 2 that should destabilize the closed conformation not only sped deactivation but also altered the relative efficacy of glutamate and quisqualate. Here we present x-ray crystallographic and single-channel data that support the conclusions that binding domain closing necessarily precedes channel opening and that the kinetics of conformational changes at the level of the binding domain importantly influence ion channel gating. Our findings suggest that the stability of the closed-cleft conformation has been tuned during evolution so that glutamate dissociates from the receptor as rapidly as possible but remains an efficacious agonist.

  8. α4α6β2* Nicotinic Acetylcholine Receptor Activation on Ventral Tegmental Area Dopamine Neurons Is Sufficient to Stimulate a Depolarizing Conductance and Enhance Surface AMPA Receptor Function

    PubMed Central

    Engle, Staci E.; Shih, Pei-Yu; McIntosh, J. Michael

    2013-01-01

    Tobacco addiction is a serious threat to public health in the United States and abroad, and development of new therapeutic approaches is a major priority. Nicotine activates and/or desensitizes nicotinic acetylcholine receptors (nAChRs) throughout the brain. nAChRs in ventral tegmental area (VTA) dopamine (DA) neurons are crucial for the rewarding and reinforcing properties of nicotine in rodents, suggesting that they may be key mediators of nicotine’s action in humans. However, it is unknown which nAChR subtypes are sufficient to activate these neurons. To test the hypothesis that nAChRs containing α6 subunits are sufficient to activate VTA DA neurons, we studied mice expressing hypersensitive, gain-of-function α6 nAChRs (α6L9′S mice). In voltage-clamp recordings in brain slices from adult mice, 100 nM nicotine was sufficient to elicit inward currents in VTA DA neurons via α6β2* nAChRs. In addition, we found that low concentrations of nicotine could act selectively through α6β2* nAChRs to enhance the function of 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid (AMPA) receptors on the surface of these cells. In contrast, α6β2* activation did not enhance N-methyl-d-aspartic acid receptor function. Finally, AMPA receptor (AMPAR) function was not similarly enhanced in brain slices from α6L9′S mice lacking α4 nAChR subunits, suggesting that α4α6β2* nAChRs are important for enhancing AMPAR function in VTA DA neurons. Together, these data suggest that activation of α4α6β2* nAChRs in VTA DA neurons is sufficient to support the initiation of cellular changes that play a role in addiction to nicotine. α4α6β2* nAChRs may be a promising target for future smoking cessation pharmacotherapy. PMID:23788655

  9. Involvement of AMPA receptor desensitization in short-term synaptic depression at the calyx of Held in developing rats

    PubMed Central

    Koike-Tani, Maki; Kanda, Takeshi; Saitoh, Naoto; Yamashita, Takayuki; Takahashi, Tomoyuki

    2008-01-01

    Paired-pulse facilitation (PPF) and depression (PPD) are forms of short-term plasticity that are generally thought to reflect changes in transmitter release probability. However, desensitization of postsynaptic AMPA receptors (AMPARs) significantly contributes to PPD at many glutamatergic synapses. To clarify the involvement of AMPAR desensitization in synaptic PPD, we compared PPD with AMPAR desensitization, induced by paired-pulse glutamate application in patches excised from postsynaptic cells at the calyx of Held synapse of developing rats. We found that AMPAR desensitization contributed significantly to PPD before the onset of hearing (P10–12), but that its contribution became negligible after hearing onset. During postnatal development (P7–21) the recovery of AMPARs from desensitization became faster. Concomitantly, glutamate sensitivity of AMPAR desensitization declined. Single-cell reverse transcription-polymerase chain reaction (RT-PCR) analysis indicated a developmental decline of GluR1 expression that correlated with speeding of the recovery of AMPARs from desensitization. Transmitter release probability declined during the second postnatal week (P7–14). Manipulation of the extracellular Ca2+/Mg2+ ratio, to match release probability at P7–8 and P13–15 synapses, revealed that the release probability is also an important factor determining the involvement of AMPAR desensitization in PPD. We conclude that the extent of involvement of AMPAR desensitization in short-term synaptic depression is determined by both pre- and postsynaptic mechanisms. PMID:18339695

  10. FUS regulates AMPA receptor function and FTLD/ALS-associated behaviour via GluA1 mRNA stabilization

    PubMed Central

    Udagawa, Tsuyoshi; Fujioka, Yusuke; Tanaka, Motoki; Honda, Daiyu; Yokoi, Satoshi; Riku, Yuichi; Ibi, Daisuke; Nagai, Taku; Yamada, Kiyofumi; Watanabe, Hirohisa; Katsuno, Masahisa; Inada, Toshifumi; Ohno, Kinji; Sokabe, Masahiro; Okado, Haruo; Ishigaki, Shinsuke; Sobue, Gen

    2015-01-01

    FUS is an RNA/DNA-binding protein involved in multiple steps of gene expression and is associated with amyotrophic lateral sclerosis (ALS) and fronto-temporal lobar degeneration (FTLD). However, the specific disease-causing and/or modifying mechanism mediated by FUS is largely unknown. Here we evaluate intrinsic roles of FUS on synaptic functions and animal behaviours. We find that FUS depletion downregulates GluA1, a subunit of AMPA receptor. FUS binds GluA1 mRNA in the vicinity of the 3′ terminus and controls poly (A) tail maintenance, thus regulating stability. GluA1 reduction upon FUS knockdown reduces miniature EPSC amplitude both in cultured neurons and in vivo. FUS knockdown in hippocampus attenuates dendritic spine maturation and causes behavioural aberrations including hyperactivity, disinhibition and social interaction defects, which are partly ameliorated by GluA1 reintroduction. These results highlight the pivotal role of FUS in regulating GluA1 mRNA stability, post-synaptic function and FTLD-like animal behaviours. PMID:25968143

  11. Activation of AMPA receptor in the infralimbic cortex facilitates extinction and attenuates the heroin-seeking behavior in rats.

    PubMed

    Chen, Weisheng; Wang, Yiqi; Sun, Anna; Zhou, Linyi; Xu, Wenjin; Zhu, Huaqiang; Zhuang, Dingding; Lai, Miaojun; Zhang, Fuqiang; Zhou, Wenhua; Liu, Huifen

    2016-01-26

    Infralimbic cortex (IL) is proposed to suppress cocaine seeking after extinction, but whether the IL regulates the extinction and reinstatement of heroin-seeking behavior is unknown. To address this issue, the male SD rats were trained to self-administer heroin under a FR1 schedule for consecutive 14 days, then the rats underwent 7 daily 2h extinction session in the operant chamber. The activation of IL by microinjection PEPA, an allosteric AMPA receptor potentiator into IL before each of extinction session facilitated the extinction responding after heroin self-administration, but did not alter the locomotor activity in an open field testing environment. Other rats were first trained under a FR1 schedule for heroin self-administration for 14 days, followed by 14 days of extinction training, and reinstatement of heroin-seeking induced by cues was measured for 2h. Intra-IL microinjecting of PEPA at 15min prior to test inhibited the reinstatement of heroin-seeking induced by cues. Moreover, the expression of GluR1 in the IL and NAc remarkably increased after treatment with PEPA during the reinstatement. These finding suggested that activation of glutamatergic projection from IL to NAc shell may be involved in the extinction and reinstatement of heroin-seeking. PMID:26639425

  12. Differential expression of postsynaptic NMDA and AMPA receptor subunits in the hippocampus and prefrontal cortex of the flinders sensitive line rat model of depression.

    PubMed

    Treccani, Giulia; Gaarn du Jardin, Kristian; Wegener, Gregers; Müller, Heidi Kaastrup

    2016-11-01

    Glutamatergic abnormalities have recently been implicated in the pathophysiology of depression, and the ionotropic glutamate receptors in particular have been suggested as possible underlying molecular determinants. The Flinders Sensitive Line (FSL) rats constitute a validated model of depression with dysfunctional regulation of glutamate transmission relatively to their control strain Flinders Resistant Line (FRL). To gain insight into how signaling through glutamate receptors may be altered in the FSL rats, we investigated the expression and phosphorylation of AMPA and NMDA receptor subunits in an enriched postsynaptic fraction of the hippocampus and prefrontal cortex. Compared to the hippocampal postsynaptic fractions of FRL rats, FSL rats exhibited decreased and increased levels of the NMDA receptor subunits GluN2A and GluN2B, respectively, causing a lower ratio of GluN2A/GluN2B. The GluA2/GluA3 AMPA receptor subunit ratio was significantly decreased while the expression of the individual GluA1, GluA2, and GluA3 subunits were unaltered including phosphorylation levels of GluA1 at S831 and S845. There were no changes in the prefrontal cortex. These results support altered expression of postsynaptic glutamate receptors in the hippocampus of FSL rats, which may contribute to the depressive-like phenotype of these rats. PMID:27262028

  13. Target- and input-dependent organization of AMPA and NMDA receptors in synaptic connections of the cochlear nucleus

    PubMed Central

    Rubio, María E.; Fukazawa, Yugo; Kamasawa, Naomi; Clarkson, Cheryl; Molnár, Elek; Shigemoto, Ryuichi

    2014-01-01

    We examined the synaptic structure, quantity and distribution of AMPA- and NMDA-type glutamate receptors (AMPARs and NMDARs, respectively) in rat cochlear nuclei by a highly sensitive freeze-fracture replica labeling technique. Four excitatory synapses formed by two distinct inputs, auditory nerve (AN) and parallel fibers (PF), on different cell types were analyzed. These excitatory synapse types included AN synapses on bushy cells (AN-BC synapses) and fusiform cells (AN-FC synapses) and PF synapses on FC (PF-FC synapses) and cartwheel cell spines (PF-CwC synapses). Immunogold labeling revealed differences in synaptic structure as well as AMPAR and NMDAR number and/or density in both AN and PF synapses, indicating a target-dependent organization. The immunogold receptor labeling also identified differences in the synaptic organization of FCs based on AN or PF connections, indicating an input-dependent organization in FCs. Among the four excitatory synapse types, the AN-BC synapses were the smallest and had the most densely packed IMPs, whereas the PF-CwC synapses were the largest and had sparsely-packed IMPs. All four synapse types showed positive correlations between the IMP-cluster area and the AMPAR number, indicating a common intra-synapse-type relationship for glutamatergic synapses. Immunogold particles for AMPARs were distributed over the entire area of individual AN synapses, PF synapses often showed synaptic areas devoid of labeling. The gold-labeling for NMDARs occurred in a mosaic fashion, with less positive correlations between the IMP-cluster area and the NMDAR number. Our observations reveal target- and input-dependent features in the structure, number, and organization of AMPARs and NMDARs in AN and PF synapses. PMID:25041792

  14. Calcium-Permeable AMPA Receptors Mediate the Induction of the Protein Kinase A-Dependent Component of Long-Term Potentiation in the Hippocampus

    PubMed Central

    Park, Pojeong; Sanderson, Thomas M.; Amici, Mascia; Choi, Sun-Lim; Bortolotto, Zuner A.; Zhuo, Min

    2016-01-01

    Two forms of NMDA receptor (NMDAR)-dependent long-term potentiation (LTP) at hippocampal CA1 synapses can be distinguished based on their sensitivity to inhibitors of protein kinase A (PKA). The PKA-dependent form requires multiple episodes of high-frequency stimulation (HFS) or theta burst stimuli (TBS) with a spacing between episodes in the order of minutes. To investigate the mechanism by which spaced episodes induce the PKA-dependent form of LTP, we have compared, in interleaved experiments, spaced (s) and compressed (c) TBS protocols in the rat CA1 synapses. We find that LTP induced by sTBS, but not that induced by cTBS, involves the insertion of calcium-permeable (CP) AMPARs, as assessed using pharmacological and electrophysiological criteria. Furthermore, a single TBS when paired with rolipram [4-(3-(cyclopentyloxy)-4-methoxyphenyl)pyrrolidin-2-one], to activate PKA, generates an LTP that also involves the insertion of CP-AMPARs. These data demonstrate that the involvement of CP-AMPARs in LTP is critically determined by the timing of the induction trigger and is associated specifically with the PKA-dependent form of LTP. SIGNIFICANCE STATEMENT Long-term potentiation is a family of synaptic mechanisms that are believed to be important for learning and memory. Two of the most extensively studied forms are triggered by the synaptic activation of NMDA receptors and expressed by changes in AMPA receptor function. They can be distinguished on the basis of their requirement for activation of a protein kinase, PKA. We show that the PKA-dependent form also involves the transient insertion of calcium-permeable AMPA receptors. These results have implications for relating synaptic plasticity to learning and memory and suggest a specific linkage between PKA activation and the rapid synaptic insertion of calcium-permeable AMPA receptors during long-term potentiation. PMID:26758849

  15. Differential role of AMPA receptors in mouse tests of antidepressant and anxiolytic action.

    PubMed

    Andreasen, Jesper T; Fitzpatrick, Ciaran M; Larsen, Maria; Skovgaard, Lars; Nielsen, Simon D; Clausen, Rasmus P; Troelsen, Karin; Pickering, Darryl S

    2015-03-19

    Depression and anxiety often co-occur, and conventional monoamine-facilitating antidepressants show efficacy against symptoms in both disorders. Rodent studies indicate that antidepressant effects of monoamine-based antidepressants involve increased α-amino-3-hydroxy-5- methyl-4-isoxazolepropionic acid glutamate receptor (AMPAR) neurotransmission, and positive allosteric modulators (PAMs) at AMPARs produced antidepressant-like effects in rodents. While this suggests that increased AMPAR-mediated neurotransmission is beneficial in depression management, preclinical studies addressing AMPARs in relation to anxiety have given ambiguous results with both anxiolytic-like and anxiogenic-like effects observed after AMPAR blockade. This study systematically compared the effects of the AMPAR potentiator LY451646 and the AMPAR antagonist GYKI-53655 on depression-related behaviour using the mouse forced swim (FST) and tail suspension tests (TST), and anxiety-related behaviour using the elevated zero maze (EZM), marble burying (MB) and novelty-induced hypophagia (NIH) tests. The serotonin-selective antidepressant citalopram was included for comparison. Due to the importance of AMPARs in learning and memory we also tested if GYKI-53655 disrupted performance in the V-maze test for attention-dependent behaviour, and the social transmission of food preference (STFP) test of long-term memory. LY451646 (3 mg/kg) showed an antidepressant-like profile in the FST and TST, and GYKI-53655 (≥ 5 mg/kg) had a depressogenic-like effect in the TST but no effect in the FST. Conversely, GYKI-53655 produced marked anxiolytic-like effects in the EZM (≥ 2.5 mg/kg), MBT (≥ 2.5 mg/kg), and NIH tests (≥ 5 mg/kg), while LY451646 (≥ 3 mg/kg) increased anxiety-like behaviour in the EZM. Citalopram showed an antidepressant-like effect in the FST (≥ 10 mg/kg), but not TST, an anxiolytic-like effect in the EZM (≥ 3 mg/kg) and MB test (≥ 2.5 mg/kg), and an anxiogenic-like effect in the NIH

  16. A study of the oligomeric state of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-preferring glutamate receptors in the synaptic junctions of porcine brain.

    PubMed

    Wu, T Y; Liu, C I; Chang, Y C

    1996-11-01

    The number of the subunits in an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-preferring L-glutamate receptor in the synaptic junctions of porcine brain was investigated in this study. Upon incubation of the synaptic junctions with three cross-linking regents, dimethyl adipimidate (DMA), dimethyl suberimidate (DMS) and N-succinimidyl-(4-azidophenyl)-1,3'-dithiopropionate (SADP), AMPA receptor subunits in higher-molecular-mass aggregates were detected by immunoblotting. These aggregates migrated as proteins of approx. 200, 300 and 400 kDa. The number and identity of the subunits in a solubilized AMPA receptor were also investigated here. Two samples, W1 and W2, enriched in AMPA receptors were prepared from synaptic junctions by a combination of detergent-solubilization, anion-exchange chromatography and wheatgerm agglutinin affinity chromatography. Hydrodynamic behaviour analyses revealed that the majority of the AMPA receptors in either one of these samples were asymmetrical detergent-surrounded particles with a protein mass around 350 kDa. SDS/PAGE analysis revealed that the majority of AMPA receptors in the W1 sample were comprised of dimers of 106 kDa subunits which were covalently linked by disulphide bonds. Cross-linking these receptors with SADP yielded a new band of approx. 400 kDa. The results obtained here, either from the studies of AMPA receptors embedding in synaptic junctions or from those of detergent-solubilized and partially purified receptors, suggest that AMPA receptors contain a basic core structure comprising of four 106 kDa subunits. PMID:8920974

  17. A study of the oligomeric state of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-preferring glutamate receptors in the synaptic junctions of porcine brain.

    PubMed Central

    Wu, T Y; Liu, C I; Chang, Y C

    1996-01-01

    The number of the subunits in an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-preferring L-glutamate receptor in the synaptic junctions of porcine brain was investigated in this study. Upon incubation of the synaptic junctions with three cross-linking regents, dimethyl adipimidate (DMA), dimethyl suberimidate (DMS) and N-succinimidyl-(4-azidophenyl)-1,3'-dithiopropionate (SADP), AMPA receptor subunits in higher-molecular-mass aggregates were detected by immunoblotting. These aggregates migrated as proteins of approx. 200, 300 and 400 kDa. The number and identity of the subunits in a solubilized AMPA receptor were also investigated here. Two samples, W1 and W2, enriched in AMPA receptors were prepared from synaptic junctions by a combination of detergent-solubilization, anion-exchange chromatography and wheatgerm agglutinin affinity chromatography. Hydrodynamic behaviour analyses revealed that the majority of the AMPA receptors in either one of these samples were asymmetrical detergent-surrounded particles with a protein mass around 350 kDa. SDS/PAGE analysis revealed that the majority of AMPA receptors in the W1 sample were comprised of dimers of 106 kDa subunits which were covalently linked by disulphide bonds. Cross-linking these receptors with SADP yielded a new band of approx. 400 kDa. The results obtained here, either from the studies of AMPA receptors embedding in synaptic junctions or from those of detergent-solubilized and partially purified receptors, suggest that AMPA receptors contain a basic core structure comprising of four 106 kDa subunits. PMID:8920974

  18. Regulation of AMPA Receptor Function by the Human Memory-Associated Gene KIBRA

    PubMed Central

    Makuch, Lauren; Volk, Lenora; Anggono, Victor; Johnson, Richard C.; Yu, Yilin; Duning, Kerstin; Kremerskothen, Joachim; Xia, Jun; Takamiya, Kogo; Huganir, Richard L.

    2011-01-01

    KIBRA has recently been identified as a gene associated with human memory performance. Despite the elucidation of the role of KIBRA in several diverse processes in non-neuronal cells, the molecular function of KIBRA in neurons is unknown. We found that KIBRA directly binds to the protein interacting with C-kinase 1 (PICK1) and forms a complex with α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPARs), the major excitatory neurotransmitter receptors in the brain. KIBRA knockdown accelerates the rate of AMPAR recycling following N-methyl-D-aspartate receptor induced internalization. Genetic deletion of KIBRA in mice impairs both long-term depression and long-term potentiation at hippocampal Schaffer collateral-CA1 synapses. Moreover, KIBRA knockout mice have severe deficits in contextual fear learning and memory. These results indicate that KIBRA regulates higher brain function by regulating AMPAR trafficking and synaptic plasticity. PMID:21943600

  19. AMPA and GABA(A/B) receptor subunit expression in the cuneate nucleus of adult squirrel monkeys during peripheral nerve regeneration.

    PubMed

    Mowery, Todd M; Kostylev, Polina V; Garraghty, Preston E

    2014-01-24

    The primate somatosensory neuroaxis provides an excellent model system with which to investigate adult neural plasticity. Here, we report immunohistochemical staining data for AMPA and GABAA/B receptor subunits in the cuneate nucleus of adult squirrel monkeys 1 and 5 months after median nerve compression. This method of nerve injury allowed the investigation of the way in which patterns of receptor correlates change during peripheral nerve regeneration. These results are compared to cortical data collected within the same animals. As observed in the cortex, the pattern of subunit staining in the brainstem 1 month after nerve compression suggests that the sensory deprived nucleus enters a state of reorganization. That is, the expression of GluR2/3 AMPA receptor subunits is significantly increased, while GABA α1 and GABABR1b receptor subunits are significantly decreased. Five months after nerve injury, the pattern of subunit expression is again very similar to that observed in the infragranular layers of cortex. At this later time we observe a significant increase in GluR2/3 and GABABR1a, with no change in GABAAα1, and a significant decrease in GABABR1b. Together these results suggest that during reorganization and recovery from injury the brainstem and cortex are governed by homogeneous mechanisms of plasticity. PMID:24315976

  20. Dynamics of the Ligand Binding Domain Layer during AMPA Receptor Activation.

    PubMed

    Baranovic, Jelena; Chebli, Miriam; Salazar, Hector; Carbone, Anna L; Faelber, Katja; Lau, Albert Y; Daumke, Oliver; Plested, Andrew J R

    2016-02-23

    Ionotropic glutamate receptors are postsynaptic tetrameric ligand-gated channels whose activity mediates fast excitatory transmission. Glutamate binding to clamshell-shaped ligand binding domains (LBDs) triggers opening of the integral ion channel, but how the four LBDs orchestrate receptor activation is unknown. Here, we present a high-resolution x-ray crystal structure displaying two tetrameric LBD arrangements fully bound to glutamate. Using a series of engineered metal ion trapping mutants, we showed that the more compact of the two assemblies corresponds to an arrangement populated during activation of full-length receptors. State-dependent cross-linking of the mutants identified zinc bridges between the canonical active LBD dimers that formed when the tetramer was either fully or partially bound by glutamate. These bridges also stabilized the resting state, consistent with the recently published full-length apo structure. Our results provide insight into the activation mechanism of glutamate receptors and the complex conformational space that the LBD layer can sample. PMID:26910426

  1. Molecular Mechanisms Contributing to TARP Regulation of Channel Conductance and Polyamine Block of Calcium-Permeable AMPA Receptors

    PubMed Central

    Coombs, Ian D.; Gratacòs-Batlle, Esther

    2014-01-01

    Many properties of fast synaptic transmission in the brain are influenced by transmembrane AMPAR regulatory proteins (TARPs) that modulate the pharmacology and gating of AMPA-type glutamate receptors (AMPARs). Although much is known about TARP influence on AMPAR pharmacology and kinetics through their modulation of the extracellular ligand-binding domain (LBD), less is known about their regulation of the ion channel region. TARP-induced modifications in AMPAR channel behavior include increased single-channel conductance and weakened block of calcium-permeable AMPARs (CP-AMPARs) by endogenous intracellular polyamines. To investigate how TARPs modify ion flux and channel block, we examined the action of γ-2 (stargazin) on GluA1 and GluA4 CP-AMPARs. First, we compared the permeation of organic cations of different sizes. We found that γ-2 increased the permeability of several cations but not the estimated AMPAR pore size, suggesting that TARP-induced relief of polyamine block does not reflect altered pore diameter. Second, to determine whether residues in the TARP intracellular C-tail regulate polyamine block and channel conductance, we examined various γ-2 C-tail mutants. We identified the membrane proximal region of the C terminus as crucial for full TARP-attenuation of polyamine block, whereas complete deletion of the C-tail markedly enhanced the TARP-induced increase in channel conductance; thus, the TARP C-tail influences ion permeation. Third, we identified a site in the pore-lining region of the AMPAR, close to its Q/R site, that is crucial in determining the TARP-induced changes in single-channel conductance. This conserved residue represents a site of TARP action, independent of the AMPAR LBD. PMID:25164663

  2. AMPA receptor upregulation in the nucleus accumbens shell of cocaine-sensitized rats depends upon S-nitrosylation of stargazin

    PubMed Central

    Milovanovic, Mike; Park, Diana J.; West, Anthony R.; Snyder, Solomon H.; Wolf, Marina E.

    2014-01-01

    Behavioral sensitization to cocaine is associated with increased AMPA receptor (AMPAR) surface expression in the nucleus accumbens (NAc). This upregulation is withdrawal-dependent, as it is not detected on withdrawal day (WD) 1, but is observed on WD7–21. Its underlying mechanisms have not been clearly established. Nitric oxide (NO) regulates AMPAR trafficking in the brain by S-nitrosylation of the AMPAR auxiliary subunit, stargazin, leading to increased AMPAR surface expression. Our goal was to determine if stargazin S-nitrosylation contributes to AMPAR upregulation during sensitization. First, we measured stargazin S-nitrosylation in NAc core and shell subregions on WD14 after 8 daily injections of saline or 15mg/kg cocaine. Stargazin S-nitrosylation was markedly increased in NAc shell but not core. To determine if this is associated with AMPAR upregulation, rats received 8 cocaine or saline injections followed by twice-daily treatments with vehicle or the nitric oxide synthase inhibitor L-NAME (50mg/kg) on WD1–6, the time when AMPAR upregulation is developing in cocaine-exposed rats. Cocaine/vehicle rats showed elevated stargazin and GluA1 surface expression on WD7 compared to saline/vehicle rats; the GluA1 increase was more robust in core, while stargazin increased more robustly in shell. These effects of cocaine were attenuated in shell but not core when cocaine injections were followed by L-NAME treatment on WD1–6. Together, these results indicate that elevated S-nitrosylation of stargazin contributes to AMPAR upregulation during sensitization selectively in the NAc shell. It is possible that AMPAR upregulation in core involves a different TARP, γ4, which also upregulates in the NAc of sensitized rats. PMID:24035918

  3. BDNF contributes to both rapid and homeostatic alterations in AMPA receptor surface expression in nucleus accumbens medium spiny neurons

    PubMed Central

    Reimers, Jeremy M.; Loweth, Jessica A.; Wolf, Marina E.

    2015-01-01

    Brain-derived neurotrophic factor (BDNF) plays a critical role in plasticity at glutamate synapses and the effects of repeated cocaine exposure. We recently showed that intracranial injection of BDNF into the rat nucleus accumbens (NAc), a key region for cocaine addiction, rapidly increases AMPA receptor (AMPAR) surface expression. To further characterize BDNF’s role in both rapid AMPAR trafficking and slower, homeostatic changes in AMPAR surface expression, we investigated the effects of acute (30 min) and long-term (24 h) treatment with BDNF on AMPAR distribution in NAc medium spiny neurons from postnatal rats co-cultured with mouse prefrontal cortex (PFC) neurons to restore excitatory inputs. Immunocytochemical studies showed that acute BDNF treatment increased cell surface GluA1 and GluA2 levels, as well as their co-localization, on NAc neurons. This effect of BDNF, confirmed using a protein crosslinking assay, was dependent on ERK but not AKT signaling. In contrast, long-term BDNF treatment decreased AMPAR surface expression on NAc neurons. Based on this latter result, we tested the hypothesis that BDNF plays a role in AMPAR “scaling down” in response to a prolonged increase in neuronal activity produced by bicuculline (24 h). Supporting this hypothesis, decreasing BDNF signaling with the extracellular BDNF scavenger TrkB-Fc prevented the scaling down of GluA1 and GluA2 surface levels in NAc neurons normally produced by bicuculline. In conclusion, BDNF exerts bidirectional effects on NAc AMPAR surface expression, depending on duration of exposure. Furthermore, BDNF’s involvement in synaptic scaling in the NAc differs from its previously described role in the visual cortex. PMID:24712995

  4. Inhibition of Spinal Ca2+-Permeable AMPA Receptors with Dicationic Compounds Alleviates Persistent Inflammatory Pain without Adverse Effects

    PubMed Central

    Kopach, Olga; Krotov, Volodymyr; Goncharenko, Julia; Voitenko, Nana

    2016-01-01

    Upregulation of Ca2+-permeable AMPA receptors (CP-AMPARs) in the dorsal horn (DH) neurons of the spinal cord has been causally linked to the maintenance of persistent inflammatory pain. Therefore, inhibition of CP-AMPARs could potentially alleviate an, otherwise, poorly treatable chronic pain. However, a loss of CP-AMPARs could produce considerable side effects because of the crucial role of CP-AMPARs in synaptic plasticity. Here we have tested whether the inhibition of spinal CP-AMPARs with dicationic compounds, the open-channel antagonists acting in an activity-dependent manner, can relieve inflammatory pain without adverse effects being developed. Dicationic compounds, N1-(1-phenylcyclohexyl)pentane-1,5-diaminium bromide (IEM-1925) and 1-trimethylammonio-5-1-adamantane-methyl-ammoniopentane dibromide (IEM-1460) were applied intrathecally (i.t.) as a post-treatment for inflammatory pain in the model of complete Freund’s adjuvant (CFA)-induced long-lasting peripheral inflammation. The capability of dicationic compounds to ameliorate inflammatory pain was tested in rats in vivo using the Hargreaves, the von Frey and the open-field tests. Treatment with IEM-1460 or IEM-1925 resulted in profound alleviation of inflammatory pain. The pain relief appeared shortly after compound administration. The effects were concentration-dependent, displaying a high potency of dicationic compounds for alleviation of inflammatory hyperalgesia in the micromolar range, for both acute and long-lasting responses. The period of pain maintenance was shortened following treatment. Treatment with IEM-1460 or IEM-1925 changed neither thermal and mechanical basal sensitivities nor animal locomotion, suggesting that inhibition of CP-AMPARs with dicationic compounds does not give rise to detectable side effects. Thus, the ability of dicationic compounds to alleviate persistent inflammatory pain may provide new routes in the treatment of chronic pain. PMID:26973464

  5. Inhibition of Spinal Ca(2+)-Permeable AMPA Receptors with Dicationic Compounds Alleviates Persistent Inflammatory Pain without Adverse Effects.

    PubMed

    Kopach, Olga; Krotov, Volodymyr; Goncharenko, Julia; Voitenko, Nana

    2016-01-01

    Upregulation of Ca(2+)-permeable AMPA receptors (CP-AMPARs) in the dorsal horn (DH) neurons of the spinal cord has been causally linked to the maintenance of persistent inflammatory pain. Therefore, inhibition of CP-AMPARs could potentially alleviate an, otherwise, poorly treatable chronic pain. However, a loss of CP-AMPARs could produce considerable side effects because of the crucial role of CP-AMPARs in synaptic plasticity. Here we have tested whether the inhibition of spinal CP-AMPARs with dicationic compounds, the open-channel antagonists acting in an activity-dependent manner, can relieve inflammatory pain without adverse effects being developed. Dicationic compounds, N1-(1-phenylcyclohexyl)pentane-1,5-diaminium bromide (IEM-1925) and 1-trimethylammonio-5-1-adamantane-methyl-ammoniopentane dibromide (IEM-1460) were applied intrathecally (i.t.) as a post-treatment for inflammatory pain in the model of complete Freund's adjuvant (CFA)-induced long-lasting peripheral inflammation. The capability of dicationic compounds to ameliorate inflammatory pain was tested in rats in vivo using the Hargreaves, the von Frey and the open-field tests. Treatment with IEM-1460 or IEM-1925 resulted in profound alleviation of inflammatory pain. The pain relief appeared shortly after compound administration. The effects were concentration-dependent, displaying a high potency of dicationic compounds for alleviation of inflammatory hyperalgesia in the micromolar range, for both acute and long-lasting responses. The period of pain maintenance was shortened following treatment. Treatment with IEM-1460 or IEM-1925 changed neither thermal and mechanical basal sensitivities nor animal locomotion, suggesting that inhibition of CP-AMPARs with dicationic compounds does not give rise to detectable side effects. Thus, the ability of dicationic compounds to alleviate persistent inflammatory pain may provide new routes in the treatment of chronic pain. PMID:26973464

  6. Loss of Ca(2+)-permeable AMPA receptors in synapses of tonic firing substantia gelatinosa neurons in the chronic constriction injury model of neuropathic pain.

    PubMed

    Chen, Yishen; Derkach, Victor A; Smith, Peter A

    2016-05-01

    Synapses transmitting nociceptive information in the spinal dorsal horn undergo enduring changes following peripheral nerve injury. Indeed, such injury alters the expression of the GluA2 subunit of glutamatergic AMPA receptors (AMPARs) in the substantia gelatinosa and this predicts altered channel conductance and calcium permeability, leading to an altered function of excitatory synapses. We therefore investigated the functional properties of synaptic AMPA receptors in rat substantia gelatinosa neurons following 10-20d chronic constriction injury (CCI) of the sciatic nerve; a model of neuropathic pain. We measured their single-channel conductance and sensitivity to a blocker of calcium permeable AMPA receptors (CP-AMPARs), IEM1460 (50μM). In putative inhibitory, tonic firing neurons, CCI reduced the average single-channel conductance of synaptic AMPAR from 14.4±3.5pS (n=12) to 9.2±1.0pS (n=10, p<0.05). IEM1460 also more effectively antagonized evoked, spontaneous and miniature EPSCs in tonic neurons from sham operated animals than in those from animals that had been subjected to CCI. By contrast, CCI did not change the effectiveness of IEM1460 in delay firing neurons although average single channel conductance was increased from 7.6±1.2pS (n=11) to 12.2±1.5pS (n=10, p<0.01). CCI thus elicits plastic changes in a specific set of glutamatergic synapses of substantia gelatinosa due to subunit recomposition and loss of GluA2-lacking CP-AMPAR. These insights reveal a molecular mechanism of nerve injury acting at synapses of inhibitory neurons to reduce their drive and therefore inhibitory tone in the spinal cord, therefore contributing to the central sensitization associated with neuropathic pain. PMID:26948545

  7. The antidepressant-like effects of glutamatergic drugs ketamine and AMPA receptor potentiator LY 451646 are preserved in bdnf⁺/⁻ heterozygous null mice.

    PubMed

    Lindholm, Jesse S O; Autio, Henri; Vesa, Liisa; Antila, Hanna; Lindemann, Lothar; Hoener, Marius C; Skolnick, Phil; Rantamäki, Tomi; Castrén, Eero

    2012-01-01

    Accumulating evidence suggests that biogenic amine-based antidepressants act, at least in part, via regulation of brain-derived neurotrophic factor (BDNF) signaling. Biogenic amine-based antidepressants increase BDNF synthesis and activate its signaling pathway through TrkB receptors. Moreover, the antidepressant-like effects of these molecules are abolished in BDNF deficient mice. Glutamate-based drugs, including the NMDA antagonist ketamine, and the AMPA receptor potentiator LY 451646, mimic the effects of antidepressants in preclinical tests with high predictive validity. In humans, a single intravenous dose of ketamine produces an antidepressant effect that is rapid, robust and persistent. In this study, we examined the role of BDNF in expression of the antidepressant-like effects of ketamine and an AMPA receptor potentiator (LY 451646) in the forced swim test (FST). Ketamine and LY 451646 produced antidepressant-like effects in the FST in mice at 45 min after a single injection, but no effects were observed one week after a single ketamine injection. As previously reported, the effects of imipramine in the forced swim test were blunted in heterozygous BDNF knockout (bdnf(+/-)) mice. However ketamine and LY 451646 produced similar antidepressant-like responses in wildtype and bdnf(+/-) mice. Neither ketamine nor LY 451646 significantly influenced the levels BDNF or TrkB phosphorylation in the hippocampus when assessed at 45 min or 7 days after the drug administration. These data demonstrate that under the conditions tested, neither ketamine nor the AMPA-potentiator LY 451656 activate BDNF signaling, but produce a characteristic antidepressant-like response in heterozygous bdnf(+/-) mice. These data indicate that unlike biogenic amine-based agents, BDNF signaling does not play a pivotal role in the antidepressant effects of glutamate-based compounds. This article is part of a Special Issue entitled 'Anxiety and Depression'. PMID:21867718

  8. Differential neuronal and glial expression of GluR1 AMPA receptor subunit and the scaffolding proteins SAP97 and 4.1N during rat cerebellar development.

    PubMed

    Douyard, Jessica; Shen, Lei; Huganir, Richard L; Rubio, Maria E

    2007-05-01

    In neurons, AMPA glutamate receptors are developmentally regulated and selectively targeted to synaptic sites. Astroglial cells also express AMPA receptors, but their developmental pattern of expression and targeting mechanisms are unknown. In this study we investigated by immunocytochemistry at the light and electron microscopy level the expression of GluR1 and its scaffolding proteins SAP97 (synapse-associated protein) and 4.1N during cerebellar development. In cerebellar cortex the GluR1 AMPA receptor subunit is expressed exclusively in Bergmann glia in the adult rodent. Interestingly, we observed that GluR1 was expressed postsynaptically at the climbing fibers (CF) synapse at early ages during Purkinje cell dendritic growth and before the complete ensheathment of CF/Purkinje cell synapses by Bergmann glia. However, its expression changed from neurons to Bergmann glia once these glial cells had completed their enwrapping process. In contrast, GluR2/3 and GluR4 AMPAR subunits were stably expressed in both Purkinje cells (GluR2/3) and Bergmann glia (GluR4) throughout postnatal development. Our data indicate that GluR1 expression undergoes a developmental switch from neurons to glia and that this appears to correlate with the degree of Purkinje cell dendritic growth and their enwrapping by Bergmann glia. SAP97 and 4.1N were developmentally regulated in the same pattern as GluR1. Therefore, SAP97 and 4.1N may play a role in the transport and insertion of GluR1 at CF/Purkinje cell synapses during early ages and at Bergmann glia plasma membrane in the adult. The parallel fiber (PF)/Purkinje cell synapse contained GluR2/3 but lacked GluR1, SAP97, and 4.1N at the time of PF synaptogenesis. PMID:17335044

  9. Brain-derived neurotrophic factor acutely enhances tyrosine phosphorylation of the AMPA receptor subunit GluR1 via NMDA receptor-dependent mechanisms.

    PubMed

    Wu, Kuo; Len, Guo-Wei; McAuliffe, Geoff; Ma, Chia; Tai, Jessica P; Xu, Fei; Black, Ira B

    2004-11-01

    Brain-derived growth factor (BDNF) acutely regulates synaptic transmission and modulates hippocampal long-term potentiation (LTP) and long-term depression (LTD), cellular models of plasticity associated with learning and memory. Our previous studies revealed that BDNF rapidly increases phosphorylation of NMDA receptor subunits NR1 and NR2B in the postsynaptic density (PSD), potentially linking receptor phosphorylation to synaptic plasticity. To further define molecular mechanisms governing BDNF actions, we examined tyrosine phosphorylation of GluR1, the most well-characterized subunit of AMPA receptors. Initially, we investigated synaptoneurosomes that contain intact pre- and postsynaptic elements. Incubation of synaptoneurosomes with BDNF for 5 min increased tyrosine phosphorylation of GluR1 in a dose-dependent manner, with a maximal, 4-fold enhancement at 10 ng/ml BDNF. NGF had no effects, suggesting the specificity of BDNF actions. Subsequently, we found that BDNF elicited a maximal, 2.5-fold increase in GluR1 phosphorylation in the PSD at 250 ng/ml BDNF within 5 min, suggesting that BDNF enhances the phosphorylation through postsynaptic mechanisms. Activation of trkB receptors was critical as k252-a, an inhibitor of trk receptor tyrosine kinase, blocked the BDNF-activated GluR1 phosphorylation. In addition, AP-5 and MK 801, NMDA receptor antagonists, blocked BDNF enhancement of phosphorylation in synaptoneurosomes or PSDs. Conversely, NMDA, the specific receptor agonist, evoked respective 3.8- and 2-fold increases in phosphorylation in synaptoneurosomes and PSDs within 5 min, mimicking the effects of BDNF. These findings raise the possibility that BDNF modulates GluR1 activity via changes in NMDA receptor function. Moreover, incubation of synaptoneurosomes or PSDs with BDNF and ifenprodil, a specific NR2B antagonist, reproduced the results of AP-5 and MK-801. Finally, coexposure of synaptoneurosomes or PSDs to BDNF and NMDA was not additive, suggesting that

  10. Evidence for a Specific Integrative Mechanism for Episodic Memory Mediated by AMPA/kainate Receptors in a Circuit Involving Medial Prefrontal Cortex and Hippocampal CA3 Region.

    PubMed

    de Souza Silva, Maria A; Huston, Joseph P; Wang, An-Li; Petri, David; Chao, Owen Yuan-Hsin

    2016-07-01

    We asked whether episodic-like memory requires neural mechanisms independent of those that mediate its component memories for "what," "when," and "where," and if neuronal connectivity between the medial prefrontal cortex (mPFC) and the hippocampus (HPC) CA3 subregion is essential for episodic-like memory. Unilateral lesion of the mPFC was combined with unilateral lesion of the CA3 in the ipsi- or contralateral hemispheres in rats. Episodic-like memory was tested using a task, which assesses the integration of memories for "what, where, and when" concomitantly. Tests for novel object recognition (what), object place (where), and temporal order memory (when) were also applied. Bilateral disconnection of the mPFC-CA3 circuit by N-methyl-d-aspartate (NMDA) lesions disrupted episodic-like memory, but left the component memories for object, place, and temporal order, per se, intact. Furthermore, unilateral NMDA lesion of the CA3 plus injection of (6-cyano-7-nitroquinoxaline-2,3-dione) (CNQX) (AMPA/kainate receptor antagonist), but not AP-5 (NMDA receptor antagonist), into the contralateral mPFC also disrupted episodic-like memory, indicating the mPFC AMPA/kainate receptors as critical for this circuit. These results argue for a selective neural system that specifically subserves episodic memory, as it is not critically involved in the control of its component memories for object, place, and time. PMID:26048953

  11. Subthreshold receptive fields and baseline excitability of "silent" S1 callosal neurons in awake rabbits: contributions of AMPA/kainate and NMDA receptors.

    PubMed

    Swadlow, H A; Hicks, T P

    1997-07-01

    The contribution of NMDA and non-NMDA receptors to excitatory subthreshold receptive fields was examined in callosal efferent neurons (CC neurons) in primary somatosensory cortex of the fully awake rabbit. Only neurons showing no traditional (suprathreshold) receptive fields were examined. Subthreshold responses were examined by monitoring the thresholds of efferent neurons to juxtasomal current pulses (JSCPs) delivered through the recording microelectrode. Changes in threshold following a peripheral conditioning stimulus signify a subthreshold response. Using this method, excitatory postsynaptic potentials and inhibitory postsynaptic potentials are manifested as decreases and increases in JSCP threshold, respectively. NMDA and non-NMDA agonists and antagonists were administered iontophoretically via a multibarrel micropipette assembly attached to the recording/stimulating microelectrode. Receptor-selective doses of both AMPA/kainate and NMDA antagonists decreased the excitability of CC neurons in the absence of any peripheral stimulation. Threshold to JSCPs rose by a mean of 20% for both classes of antagonist. Despite the similar effects of NMDA and non-NMDA antagonists on baseline excitability, these antagonists had dramatically different effects on the subthreshold excitatory response to activation of the receptive field. Whereas receptor-selective doses of AMPA/kainate antagonists either eliminated or severely attenuated the subthreshold excitatory responses to peripheral stimulation, NMDA antagonists had little or no effect on the subthreshold evoked response. PMID:9262195

  12. Identification of an ionotropic glutamate receptor AMPA1/GRIA1 polymorphism in crossbred beef cows differing in fertility.

    PubMed

    Cushman, R A; Miles, J R; Rempel, L A; McDaneld, T G; Kuehn, L A; Chitko-McKown, C G; Nonneman, D; Echternkamp, S E

    2013-06-01

    A proposed functional polymorphism in the ionotropic glutamate receptor AMPA1 (GRIA1) has been reported to influence antral follicle numbers and fertility in cows. Repeat breeder cows that fail to produce a calf in multiple seasons have been reported to have reduced numbers of small (1 to 3 mm) antral follicles in their ovaries. Therefore, we tested the hypothesis that this GRIA1 polymorphism was affecting antral follicle numbers in repeat breeder cows. Repeat breeder cows (n = 64) and control cows (n = 72) that had always produced a calf were housed in a dry lot and observed twice daily for behavioral estrus. Blood samples were collected, and cows were genotyped for this GRIA1 polymorphism and for a polymorphism in the GnRH receptor (GnRHR) that was proposed to influence age at puberty. On d 3 to 8 after estrus cows were slaughtered, and reproductive organs were collected to determine antral follicle count, ovary size, and uterine horn diameter. Repeat breeder cows were older at first calving than control cows (P = 0.006). The length (P = 0.03) and height (P = 0.02) of the ovary contralateral to the corpus luteum (CL) were greater in control cows than repeat breeder cows. The endometrial diameter in the horn ipsilateral to the CL was greater in the control cows than the repeat breeder cows. Repeat breeder cows had fewer small (1 to 5 mm) antral follicles than control cows (P = 0.003); however, there was no association between GRIA1 genotype and antral follicle number. The GnRHR polymorphism was associated with age at first calving because cows that were homozygous for the C allele had a greater age at first calving than heterozygous cows or cows that were homozygous for the T allele (P = 0.01). In the granulosa cells from small (1 to 5 mm) antral follicles, mRNA abundances of 2 markers of oocyte quality, anti-Müllerian hormone and pentraxin 3, did not differ between fertility groups (P ≥ 0.12). We conclude that this GRIA1 polymorphism exists in beef cows but

  13. Editing for an AMPA receptor subunit RNA in prefrontal cortex and striatum in Alzheimer's disease, Huntington's disease and schizophrenia

    NASA Technical Reports Server (NTRS)

    Akbarian, S.; Smith, M. A.; Jones, E. G.; Bloom, F. E. (Principal Investigator)

    1995-01-01

    Animal studies and cell culture experiments demonstrated that posttranscriptional editing of the transcript of the GluR-2 gene, resulting in substitution of an arginine for glutamine in the second transmembrane region (TM II) of the expressed protein, is associated with a reduction in Ca2+ permeability of the receptor channel. Thus, disturbances in GluR-2 RNA editing with alteration of intracellular Ca2+ homeostasis could lead to neuronal dysfunction and even neuronal degeneration. The present study determined the proportions of edited and unedited GluR-2 RNA in the prefrontal cortex of brains from patients with Alzheimer's disease, in the striatum of brains from patients with Huntington's disease, and in the same areas of brains from age-matched schizophrenics and controls, by using reverse transcriptase-polymerase chain reaction, restriction endonuclease digestion, gel electrophoresis and scintillation radiometry. In the prefrontal cortex of controls, < 0.1% of all GluR-2 RNA molecules were unedited and > 99.9% were edited; in the prefrontal cortex both of schizophrenics and of Alzheimer's patients approximately 1.0% of all GluR-2 RNA molecules were unedited and 99% were edited. In the striatum of controls and of schizophrenics, approximately 0.5% of GluR-2 RNA molecules were unedited and 99.5% were edited; in the striatum of Huntington's patients nearly 5.0% of GluR-2 RNA was unedited. In the prefrontal white matter of controls, approximately 7.0% of GluR-2 RNA was unedited. In the normal human prefrontal cortex and striatum, the large majority of GluR-2 RNA molecules contains a CGG codon for arginine in the TMII coding region; this implies that the corresponding AMPA receptors have a low Ca2+ permeability, as previously demonstrated for the rat brain. The process of GluR-2 RNA editing is compromised in a region-specific manner in schizophrenia, in Alzheimer's disease and Huntington's Chorea although in each of these disorders there is still a large excess of

  14. Adenosine A1 Receptor-Mediated Endocytosis of AMPA Receptors Contributes to Impairments in Long-Term Potentiation (LTP) in the Middle-Aged Rat Hippocampus.

    PubMed

    Chen, Zhicheng; Stockwell, Jocelyn; Cayabyab, Francisco S

    2016-05-01

    Aging causes multiple changes in the mammalian brain, including changes in synaptic signaling. Previous reports have shown increased extracellular adenosine in the aging brain, and we recently reported that activation of adenosine A1 receptors (A1Rs) induces AMPA receptor (AMPAR) internalization in rat hippocampus. This study investigated whether aging-related changes in the rat hippocampus include altered surface expression of adenosine A1 and A2A receptors, and whether these changes correspond to changes in AMPAR surface expression and altered synaptic plasticity. We found reduced A1R surface expression in middle-aged rat hippocampus, and also reduced GluA1 and GluA2 AMPAR subunit surface expression. Using a chemically-induced LTP (cLTP) experimental protocol, we recorded fEPSPs in young (1 month old) and middle-aged (7-12 month old) rat hippocampal slices. There were significant impairments in cLTP in middle-aged slices, suggesting impaired synaptic plasticity. Since we previously showed that the A1R agonist N(6)-cyclopentyladenosine (CPA) reduced both A1Rs and GluA2/GluA1 AMPARs, we hypothesized that the observed impaired synaptic plasticity in middle-aged brains is regulated by A1R-mediated AMPAR internalization by clathrin-mediated endocytosis. Following cLTP, we found a significant increase in GluA1 and GluA2 surface expression in young rats, which was blunted in middle-aged brains or in young brains pretreated with CPA. Blocking A1Rs with 8-cyclopentyl-1,3-dipropylxanthine or AMPAR endocytosis with either Tat-GluA2-3Y peptide or dynasore (dynamin inhibitor) similarly enhanced AMPAR surface expression following cLTP. These data suggest that age-dependent alteration in adenosine receptor expression contributes to increased AMPAR endocytosis and impaired synaptic plasticity in aged brains. PMID:26700433

  15. Activation of the sigma receptor 1 modulates AMPA receptor-mediated light-evoked excitatory postsynaptic currents in rat retinal ganglion cells.

    PubMed

    Liu, Lei-Lei; Deng, Qin-Qin; Weng, Shi-Jun; Yang, Xiong-Li; Zhong, Yong-Mei

    2016-09-22

    Sigma receptor (σR), a unique receptor family, is classified into three subtypes: σR1, σR2 and σR3. It was previously shown that σR1 activation induced by 1μM SKF10047 (SKF) suppressed N-methyl-d-aspartate (NMDA) receptor-mediated responses of rat retinal ganglion cells (GCs) and the suppression was mediated by a distinct Ca(2+)-dependent phospholipase C (PLC)-protein kinase C (PKC) pathway. In the present work, using whole-cell patch-clamp techniques in rat retinal slice preparations, we further demonstrate that SKF of higher dosage (50μM) significantly suppressed AMPA receptor (AMPAR)-mediated light-evoked excitatory postsynaptic currents (L-EPSCs) of retinal ON-type GCs (ON GCs), and the effect was reversed by the σR1 antagonist BD1047, suggesting the involvement of σR1. The SKF (50μM) effect was unlikely due to a change in glutamate release from bipolar cells, as suggested by the unaltered paired-pulse ratio (PPR) of AMPAR-mediated EPSCs of ON GCs. SKF (50μM) did not change L-EPSCs of ON GCs when the G protein inhibitor GDP-β-S or the protein kinase G (PKG) inhibitor KT5823 was intracellularly infused. Calcium imaging further revealed that SKF (50μM) did not change intracellular calcium concentration in GCs and persisted to suppress L-EPSCs when intracellular calcium was chelated by BAPTA. The SKF (50μM) effect was intact when protein kinase A (PKA) and phosphatidylinostiol (PI)-PLC signaling pathways were both blocked. We conclude that the SKF (50μM) effect is Ca(2+)-independent, PKG-dependent, but not involving PKA, PI-PLC pathways. PMID:27373906

  16. "Silent" Priming of Translation-Dependent LTP by [Beta]-Adrenergic Receptors Involves Phosphorylation and Recruitment of AMPA Receptors

    ERIC Educational Resources Information Center

    Tenorio, Gustavo; Connor, Steven A.; Guevremont, Diane; Abraham, Wickliffe C.; Williams, Joanna; O'Dell, Thomas J.; Nguyen, Peter V.

    2010-01-01

    The capacity for long-term changes in synaptic efficacy can be altered by prior synaptic activity, a process known as "metaplasticity." Activation of receptors for modulatory neurotransmitters can trigger downstream signaling cascades that persist beyond initial receptor activation and may thus have metaplastic effects. Because activation of…

  17. Enhanced Odor Discrimination and Impaired Olfactory Memory by Spatially Controlled Switch of AMPA Receptors

    PubMed Central

    2005-01-01

    Genetic perturbations of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPARs) are widely used to dissect molecular mechanisms of sensory coding, learning, and memory. In this study, we investigated the role of Ca2+-permeable AMPARs in olfactory behavior. AMPAR modification was obtained by depletion of the GluR-B subunit or expression of unedited GluR-B(Q), both leading to increased Ca2+ permeability of AMPARs. Mice with this functional AMPAR switch, specifically in forebrain, showed enhanced olfactory discrimination and more rapid learning in a go/no-go operant conditioning task. Olfactory memory, however, was dramatically impaired. GluR-B depletion in forebrain was ectopically variable (“mosaic”) among individuals and strongly correlated with decreased olfactory memory in hippocampus and cortex. Accordingly, memory was rescued by transgenic GluR-B expression restricted to piriform cortex and hippocampus, while enhanced odor discrimination was independent of both GluR-B variability and transgenic GluR-B expression. Thus, correlated differences in behavior and levels of GluR-B expression allowed a mechanistic and spatial dissection of olfactory learning, discrimination, and memory capabilities. PMID:16216087

  18. A Role for Calcium-Permeable AMPA Receptors in Synaptic Plasticity and Learning

    PubMed Central

    Gray, Erin E.; Abdipranoto, Andrea; Thangthaeng, Nopporn; Jacobs, Nate; Saab, Faysal; Tonegawa, Susumu; Heinemann, Stephen F.; O'Dell, Thomas J.; Fanselow, Michael S.; Vissel, Bryce

    2010-01-01

    A central concept in the field of learning and memory is that NMDARs are essential for synaptic plasticity and memory formation. Surprisingly then, multiple studies have found that behavioral experience can reduce or eliminate the contribution of these receptors to learning. The cellular mechanisms that mediate learning in the absence of NMDAR activation are currently unknown. To address this issue, we examined the contribution of Ca2+-permeable AMPARs to learning and plasticity in the hippocampus. Mutant mice were engineered with a conditional genetic deletion of GluR2 in the CA1 region of the hippocampus (GluR2-cKO mice). Electrophysiology experiments in these animals revealed a novel form of long-term potentiation (LTP) that was independent of NMDARs and mediated by GluR2-lacking Ca2+-permeable AMPARs. Behavioral analyses found that GluR2-cKO mice were impaired on multiple hippocampus-dependent learning tasks that required NMDAR activation. This suggests that AMPAR-mediated LTP interferes with NMDAR-dependent plasticity. In contrast, NMDAR-independent learning was normal in knockout mice and required the activation of Ca2+-permeable AMPARs. These results suggest that GluR2-lacking AMPARs play a functional and previously unidentified role in learning; they appear to mediate changes in synaptic strength that occur after plasticity has been established by NMDARs. PMID:20927382

  19. Developmental switch in the kinase dependency of long-term potentiation depends on expression of GluA4 subunit-containing AMPA receptors

    PubMed Central

    Luchkina, Natalia V.; Huupponen, Johanna; Clarke, Vernon R. J.; Coleman, Sarah K.; Keinänen, Kari; Taira, Tomi; Lauri, Sari E.

    2014-01-01

    The AMPA-receptor subunit GluA4 is expressed transiently in CA1 pyramidal neurons at the time synaptic connectivity is forming, but its physiological significance is unknown. Here we show that GluA4 expression is sufficient to alter the signaling requirements of long-term potentiation (LTP) and can fully explain the switch in the LTP kinase dependency from PKA to Ca2+/calmodulin-dependent protein kinase II during synapse maturation. At immature synapses, activation of PKA leads to a robust potentiation of AMPA-receptor function via the mobilization of GluA4. Analysis of GluA4-deficient mice indicates that this mechanism is critical for neonatal PKA-dependent LTP. Furthermore, lentiviral expression of GluA4 in CA1 neurons conferred a PKA-dependent synaptic potentiation and LTP regardless of the developmental stage. Thus, GluA4 defines the signaling requirements for LTP and silent synapse activation during a critical period of synapse development. PMID:24599589

  20. Mapping the Interaction Sites between AMPA Receptors and TARPs Reveals a Role for the Receptor N-Terminal Domain in Channel Gating

    PubMed Central

    Cais, Ondrej; Herguedas, Beatriz; Krol, Karolina; Cull-Candy, Stuart G.; Farrant, Mark; Greger, Ingo H.

    2014-01-01

    Summary AMPA-type glutamate receptors (AMPARs) mediate fast neurotransmission at excitatory synapses. The extent and fidelity of postsynaptic depolarization triggered by AMPAR activation are shaped by AMPAR auxiliary subunits, including the transmembrane AMPAR regulatory proteins (TARPs). TARPs profoundly influence gating, an effect thought to be mediated by an interaction with the AMPAR ion channel and ligand binding domain (LBD). Here, we show that the distal N-terminal domain (NTD) contributes to TARP modulation. Alterations in the NTD-LBD linker result in TARP-dependent and TARP-selective changes in AMPAR gating. Using peptide arrays, we identify a TARP interaction region on the NTD and define the path of TARP contacts along the LBD surface. Moreover, we map key binding sites on the TARP itself and show that mutation of these residues mediates gating modulation. Our data reveal a TARP-dependent allosteric role for the AMPAR NTD and suggest that TARP binding triggers a drastic reorganization of the AMPAR complex. PMID:25373908

  1. Changes of AMPA receptor properties in the neocortex and hippocampus following pilocarpine-induced status epilepticus in rats.

    PubMed

    Malkin, Sergey L; Amakhin, Dmitry V; Veniaminova, Ekaterina A; Kim, Kira Kh; Zubareva, Olga E; Magazanik, Lev G; Zaitsev, Aleksey V

    2016-07-01

    Temporal lobe epilepsy (TLE) is the most common type of epilepsy in humans. The lithium-pilocarpine model in rodents reproduces some of the main features of human TLE. Three-week-old Wistar rats were used in this study. The changes in AMPA receptor subunit composition were investigated in several brain areas, including the medial prefrontal cortex (mPFC), the temporal cortex (TC), and the dorsal (DH) and ventral hippocampus (VH) during the first week following pilocarpine-induced status epilepticus (PILO-induced SE). In the hippocampus, GluA1 and GluA2 mRNA expression slightly decreased after PILO-induced SE and returned to the initial level on the seventh day. We did not detect any significant changes in mRNA expression of the GluA1 and GluA2 subunits in the TC, whereas in the mPFC we observed a significant increase of GluA1 mRNA expression on the third day and a decrease in GluA2 mRNA expression during the entire first week. Accordingly, the GluA1/GluA2 expression ratio increased in the mPFC, and the functional properties of the pyramidal cell excitatory synapses were disturbed. Using whole-cell voltage-clamp recordings, we found that on the third day following PILO-induced SE, isolated mPFC pyramidal neurons showed an inwardly rectifying current-voltage relation of kainate-evoked currents, suggesting the presence of GluA2-lacking calcium-permeable AMPARs (CP-AMPARs). IEM-1460, a selective antagonist of CP-AMPARs, significantly reduced the amplitude of evoked EPSC in pyramidal neurons from mPFC slices on the first and third days, but not on the seventh day. The antagonist had no effects on EPSC amplitude in slices from control animals. Thus, our data demonstrate that PILO-induced SE affects subunit composition of AMPARs in different brain areas, including the mPFC. SE induces transient (up to few days) incorporation of CP-AMPARs in the excitatory synapses of mPFC pyramidal neurons, which may disrupt normal circuitry functions. PMID:27109923

  2. Methylphenidate amplifies long-term potentiation in rat hippocampus CA1 area involving the insertion of AMPA receptors by activation of β-adrenergic and D1/D5 receptors.

    PubMed

    Rozas, C; Carvallo, C; Contreras, D; Carreño, M; Ugarte, G; Delgado, R; Zeise, M L; Morales, B

    2015-12-01

    Methylphenidate (MPH, Ritalin©) is widely used in the treatment of Attention Deficit Hyperactivity Disorder and recently as a drug of abuse. Although the effect of MPH has been studied in brain regions such as striatum and prefrontal cortex (PFC), the hippocampus has received relatively little attention. It is known that MPH increases the TBS-dependent Long Term Potentiation (LTP) in the CA1 area. However, the cellular and molecular mechanisms involved in this process are still unknown. Using field potential recordings and western blot analysis in rat hippocampal slices of young rats, we found that acute application of MPH enhances LTP in CA3-CA1 synapses in a dose-dependent manner with an EC50 of 73.44±6.32 nM. Using specific antagonists and paired-pulse facilitation protocols, we observed that the MPH-dependent increase of LTP involves not only β-adrenergic receptors activation but also post-synaptic D1/D5 dopamine receptors. The inhibition of PKA with PKI, suppressed the facilitation of LTP induced by MPH consistent with an involvement of the adenyl cyclase-cAMP-PKA dependent cascade downstream of the activation of D1/D5 receptors. In addition, samples of CA1 areas taken from slices potentiated with MPH presented an increase in the phosphorylation of the Ser845 residue of the GluA1 subunit of AMPA receptors compared to control slices. This effect was reverted by SCH23390, antagonist of D1/D5 receptors, and PKI. Moreover, we found an increase of surface-associated functional AMPA receptors. We propose that MPH increases TBS-dependent LTP in CA3-CA1 synapses through a polysynaptic mechanism involving activation of β-adrenergic and D1/D5 dopaminergic receptors and promoting the trafficking and insertion of functional AMPA receptors to the plasma membrane. PMID:26165920

  3. Structural investigation of the 7-chloro-3-hydroxy-1H-quinazoline-2,4-dione scaffold to obtain AMPA and kainate receptor selective antagonists. Synthesis, pharmacological, and molecular modeling studies.

    PubMed

    Colotta, Vittoria; Catarzi, Daniela; Varano, Flavia; Lenzi, Ombretta; Filacchioni, Guido; Costagli, Chiara; Galli, Alessandro; Ghelardini, Carla; Galeotti, Nicoletta; Gratteri, Paola; Sgrignani, Jacopo; Deflorian, Francesca; Moro, Stefano

    2006-10-01

    In this paper, the study of new 7-chloro-3-hydroxy-1H-quinazoline-2,4-dione derivatives, designed as AMPA and kainate (KA) receptor antagonists, is reported. Some derivatives bear different carboxy-containing alkyl chains on the 3-hydroxy group, while various heterocyclic rings or amide moieties are present at the 6-position of other compounds. Binding data at Gly/NMDA, AMPA, and high-affinity KA receptors showed that the presence of the free 3-hydroxy group is of paramount importance for a good affinity at all three investigated receptors, while introduction of some 6-heterocyclic moieties yielded AMPA-selective antagonists. The most significant result was the finding of the 6-(2-carboxybenzoylamino)-3-hydroxy-1H-quinazolin-2,4-dione 12, which possesses good affinity for high-affinity and low-affinity KA receptors (Ki=0.62 microM and 1.6 microM, respectively), as well as good selectivity. To rationalize the trend of affinities of the reported derivatives, an intensive molecular modeling study was carried out by docking compounds to models of the Gly/NMDA, AMPA, and KA receptors. PMID:17004715

  4. Interactions between N-Ethylmaleimide-sensitive factor and GluA2 contribute to effects of glucocorticoid hormones on AMPA receptor function in the rodent hippocampus.

    PubMed

    Xiong, Hui; Cassé, Frédéric; Zhou, Ming; Xiong, Zhi-Qi; Joels, Marian; Martin, Stéphane; Krugers, Harm J

    2016-07-01

    Glucocorticoid hormones, via activation of their receptors, promote memory consolidation, but the exact underlying mechanisms remain elusive. We examined how corticosterone regulates AMPA receptor (AMPAR) availability in the synapse, which is important for synaptic plasticity and memory formation. Peptides which specifically block the interaction between N-Ethylmaleimide-Sensitive Factor (NSF) and the AMPAR-subunit GluA2 prevented the increase in synaptic transmission and surface expression of AMPARs known to occur after corticosterone application to hippocampal neurons. Combining a live imaging Fluorescence Recovery After Photobleaching (FRAP) approach with the use of the pH-sensitive GFP-AMPAR tagging revealed that this NSF/GluA2 interaction was also essential for the increase of the mobile fraction and reduction of the diffusion of AMPARs after treating hippocampal neurons with corticosterone. We conclude that the interaction between NSF and GluA2 contributes to the effects of corticosterone on AMPAR function. © 2016 Wiley Periodicals, Inc. PMID:26766634

  5. Enhanced Long-Term and Impaired Short-Term Spatial Memory in GluA1 AMPA Receptor Subunit Knockout Mice: Evidence for a Dual-Process Memory Model

    ERIC Educational Resources Information Center

    Sanderson, David J.; Good, Mark A.; Skelton, Kathryn; Sprengel, Rolf; Seeburg, Peter H.; Rawlins, J. Nicholas P.; Bannerman, David M.

    2009-01-01

    The GluA1 AMPA receptor subunit is a key mediator of hippocampal synaptic plasticity and is especially important for a rapidly-induced, short-lasting form of potentiation. GluA1 gene deletion impairs hippocampus-dependent, spatial working memory, but spares hippocampus-dependent spatial reference memory. These findings may reflect the necessity of…

  6. PKCα is required for inflammation-induced trafficking of extrasynaptic AMPA receptors in tonically firing lamina II dorsal horn neurons during the maintenance of persistent inflammatory pain

    PubMed Central

    Kopach, Olga; Viatchenko-Karpinski, Viacheslav; Atianjoh, Fidelis E.; Belan, Pavel; Tao, Yuan-Xiang; Voitenko, Nana

    2012-01-01

    Persistent inflammation promotes internalization of synaptic GluR2-containing Ca2+-impermeable AMPA receptors (AMPARs) and insertion of GluR1-containing Ca2+-permeable AMPARs at extrasynaptic sites in dorsal horn neurons. Previously we have shown that internalization of synaptic GluR2-containing AMPARs requires an activation of spinal cord protein kinase C alpha (PKCα), but molecular mechanisms that underlie altered trafficking of extrasynaptic AMPARs are still unclear. By utilizing the antisence oligodeoxynucleotides that specifically knockdown PKCα, we have found that a decrease in dorsal horn PKCα expression prevents complete Freund’s adjuvant (CFA)-induced increase in a functional expression of extrasynaptic Ca2+-permeable AMPARs in substantia gelatinosa (SG) neurons of the rat spinal cord. This was manifested as an abolishment of augmented AMPA-induced currents and associated [Ca2+]i transients, and as a reverse of the current rectification 1 d post-CFA. These changes were observed specifically in SG neurons characterized by intrinsic tonic firing properties, but not in those exhibiting strong adaptation. Finally, dorsal horn PKCα knockdown produced anti-nociceptive effect on CFA-induced thermal and mechanical hypersensitivity during the maintenance period of inflammatory pain, indicating a role for PKCα in persistent inflammatory pain maintenance. Altogether, our results indicate that inflammation-induced trafficking of extrasynaptic Ca2+-permeable AMPARs in tonically firing SG neurons depends on PKCα, and suggest that this PKCα-dependent trafficking may contribute to the persistent inflammatory pain maintenance. PMID:23374940

  7. Sources of aminomethylphosphonic acid (AMPA) in urban and rural catchments in Ontario, Canada: Glyphosate or phosphonates in wastewater?

    PubMed

    Struger, J; Van Stempvoort, D R; Brown, S J

    2015-09-01

    Correlation analysis suggests that occurrences of AMPA in streams of southern Ontario are linked mainly to glyphosate in both urban and rural settings, rather than to wastewater sources, as some previous studies have suggested. For this analysis the artificial sweetener acesulfame was analyzed as a wastewater indicator in surface water samples collected from urban and rural settings in southern Ontario, Canada. This interpretation is supported by the concurrence of seasonal fluctuations of glyphosate and AMPA concentrations. Herbicide applications in larger urban centres and along major transportation corridors appear to be important sources of glyphosate and AMPA in surface water, in addition to uses of this herbicide in rural and mixed use areas. Fluctuations in concentrations of acesulfame and glyphosate residues were found to be related to hydrologic events. PMID:26187493

  8. Episodic sucrose intake during food restriction increases synaptic abundance of AMPA receptors in nucleus accumbens and augments intake of sucrose following restoration of ad libitum feeding.

    PubMed

    Peng, X-X; Lister, A; Rabinowitsch, A; Kolaric, R; Cabeza de Vaca, S; Ziff, E B; Carr, K D

    2015-06-01

    Weight-loss dieting often leads to loss of control, rebound weight gain, and is a risk factor for binge pathology. Based on findings that food restriction (FR) upregulates sucrose-induced trafficking of glutamatergic AMPA receptors to the nucleus accumbens (NAc) postsynaptic density (PSD), this study was an initial test of the hypothesis that episodic "breakthrough" intake of forbidden food during dieting interacts with upregulated mechanisms of synaptic plasticity to increase reward-driven feeding. Ad libitum (AL) fed and FR subjects consumed a limited amount of 10% sucrose, or had access to water, every other day for 10 occasions. Beginning three weeks after return of FR rats to AL feeding, when 24-h chow intake and rate of body weight gain had normalized, subjects with a history of sucrose intake during FR consumed more sucrose during a four week intermittent access protocol than the two AL groups and the group that had access to water during FR. In an experiment that substituted noncontingent administration of d-amphetamine for sucrose, FR subjects displayed an enhanced locomotor response during active FR but a blunted response, relative to AL subjects, during recovery from FR. This result suggests that the enduring increase in sucrose consumption is unlikely to be explained by residual enhancing effects of FR on dopamine signaling. In a biochemical experiment which paralleled the sucrose behavioral experiment, rats with a history of sucrose intake during FR displayed increased abundance of pSer845-GluA1, GluA2, and GluA3 in the NAc PSD relative to rats with a history of FR without sucrose access and rats that had been AL throughout, whether they had a history of episodic sucrose intake or not. A history of FR, with or without a history of sucrose intake, was associated with increased abundance of GluA1. A terminal 15-min bout of sucrose intake produced a further increase in pSer845-GluA1 and GluA2 in subjects with a history of sucrose intake during FR

  9. The density of AMPA receptors activated by a transmitter quantum at the climbing fibre-Purkinje cell synapse in immature rats

    PubMed Central

    Momiyama, Akiko; Silver, R Angus; Häusser, Michael; Notomi, Takuya; Wu, Yue; Shigemoto, Ryuichi; Cull-Candy, Stuart G

    2003-01-01

    We aimed to estimate the number of AMPA receptors (AMPARs) bound by the quantal transmitter packet, their single-channel conductance and their density in the postsynaptic membrane at cerebellar Purkinje cell synapses. The synaptic and extrasynaptic AMPARs were examined in Purkinje cells in 2- to 4-day-old rats, when they receive synaptic inputs solely from climbing fibres (CFs). Evoked CF EPSCs and whole-cell AMPA currents displayed roughly linear current-voltage relationships, consistent with the presence of GluR2 subunits in synaptic and extrasynaptic AMPARs. The mean quantal size, estimated from the miniature EPSCs (MEPSCs), was ∼300 pS. Peak-scaled non-stationary fluctuation analysis of spontaneous EPSCs and MEPSCs gave a weighted-mean synaptic channel conductance of ∼5 pS (∼7 pS when corrected for filtering). By applying non-stationary fluctuation analysis to extrasynaptic currents activated by brief glutamate pulses (5 mm), we also obtained a small single-channel conductance estimate for extrasynaptic AMPARs (∼11 pS). This approach allowed us to obtain a maximum open probability (Po,max) value for the extrasynaptic receptors (Po,max = 0.72). Directly resolved extrasynaptic channel openings in the continued presence of glutamate exhibited clear multiple-conductance levels. The mean area of the postsynaptic density (PSD) of these synapses was 0.074 μm2, measured by reconstructing electron-microscopic (EM) serial sections. Postembedding immunogold labelling by anti-GluR2/3 antibody revealed that AMPARs are localised in PSDs. From these data and by simulating error factors, we estimate that at least 66 AMPARs are bound by a quantal transmitter packet at CF-Purkinje cell synapses, and the receptors are packed at a minimum density of ∼900 μm−2 in the postsynaptic membrane. PMID:12665613

  10. Mechanism of Inhibition of the GluA2 AMPA Receptor Channel Opening by Talampanel and Its Enantiomer: The Stereochemistry of the 4-Methyl Group on the Diazepine Ring of 2,3-Benzodiazepine Derivatives

    PubMed Central

    2013-01-01

    Stereoselectivity of 2,3-benzodiazepine compounds provides a unique way for the design of stereoisomers as more selective and more potent inhibitors as drug candidates for treatment of the neurological diseases involving excessive activity of AMPA receptors. Here we investigate a pair of enantiomers known as Talampanel and its (+) counterpart about their mechanism of inhibition and selectivity toward four AMPA receptor subunits or GluA1–4. We show that Talampanel is the eutomer with the endismic ratio being 14 for the closed-channel and 10 for the open-channel state of GluA2. Kinetic evidence supports that Talampanel is a noncompetitive inhibitor and it binds to the same site for those 2,3-benzodiazepine compounds with the C-4 methyl group on the diazepine ring. This site, which we term as the “M” site, recognizes preferentially those 2,3-benzodiazepine compounds with the C-4 methyl group being in the R configuration, as in the chemical structure of Talampanel. Given that Talampanel inhibits GluA1 and GluA2, but is virtually ineffective on the GluA3 and GluA4 AMPA receptor subunits, we hypothesize that the “M” site(s) on GluA1 and GluA2 to which Talampanel binds is different from that on GluA3 and GluA4. If the molecular properties of the AMPA receptors and Talampanel are used for selecting an inhibitor as a single drug candidate for controlling the activity of all AMPA receptors in vivo, Talampanel is not ideal. Our results further suggest that addition of longer acyl groups to the N-3 position should produce more potent 2,3-benzodiazepine inhibitors for the “M” site. PMID:23402301

  11. GluA2-Containing AMPA Receptors Distinguish Ribbon-Associated from Ribbonless Afferent Contacts on Rat Cochlear Hair Cells123

    PubMed Central

    Martinez-Monedero, Rodrigo

    2016-01-01

    Abstract Mechanosensory hair cells release glutamate at ribbon synapses to excite postsynaptic afferent neurons, via AMPA-type ionotropic glutamate receptors (AMPARs). However, type II afferent neurons contacting outer hair cells in the mammalian cochlea were thought to differ in this respect, failing to show GluA immunolabeling and with many “ribbonless” afferent contacts. Here it is shown that antibodies to the AMPAR subunit GluA2 labeled afferent contacts below inner and outer hair cells in the rat cochlea, and that synaptic currents in type II afferents had AMPAR-specific pharmacology. Only half the postsynaptic densities of type II afferents that labeled for PSD-95, Shank, or Homer were associated with GluA2 immunopuncta or presynaptic ribbons, the “empty slots” corresponding to ribbonless contacts described previously. These results extend the universality of AMPAergic transmission by hair cells, and support the existence of silent afferent contacts. PMID:27257620

  12. Role of bed nucleus of the stria terminalis and amygdala AMPA receptors in the development and expression of context conditioning and sensitization of startle by prior shock

    PubMed Central

    Davis, Michael

    2013-01-01

    A core symptom of post-traumatic stress disorder is hyper-arousal—manifest in part by increases in the amplitude of the acoustic startle reflex. Gewirtz et al. (Prog Neuropsychopharmacol Biol Psychiatry 22:625–648, 1998) found that, in rats, persistent shock-induced startle increases were prevented by pre-test electrolytic lesions of the bed nucleus of the stria terminalis (BNST). We used reversible inactivation to determine if similar effects reflect actions on (a) BNST neurons themselves versus fibers-of-passage, (b) the development versus expression of such increases, and (c) associative fear versus non-associative sensitization. Twenty-four hours after the last of three shock sessions, startle was markedly enhanced when rats were tested in a non-shock context. These increases decayed over the course of several days. Decay was unaffected by context exposure, and elevated startle was restored when rats were tested for the first time in the original shock context. Thus, both associative and non-associative components could be measured under different conditions. Pre-test intra-BNST infusions of the AMPA receptor antagonist NBQX (3 μg/side) blocked the non-associative (as did infusions into the basolateral amygdala) but not the associative component, whereas pre-shock infusions disrupted both. NBQX did not affect baseline startle or shock reactivity. These results indicate that AMPA receptors in or very near to the BNST are critical for the expression and development of non-associative shock-induced startle sensitization, and also for context fear conditioning, but not context fear expression. More generally, they suggest that treatments targeting the BNST may be clinically useful for treating trauma-related hyper-arousal and perhaps for retarding its development. PMID:23934654

  13. Differential glutamate AMPA-receptor plasticity in subpopulations of VTA neurons in the presence or absence of residual cocaine: Implications for the development of addiction

    PubMed Central

    Lane, D.A.; Reed, B.; Kreek, M.J.; Pickel, V.M.

    2011-01-01

    Cocaine-induced plasticity of mesocorticolimbic dopamine (DA) neurons, originating in the ventral tegmental area (VTA), persists in the absence of cocaine and may contribute to both drug-craving and relapse. Glutamate AMPA receptors (AMPARs) in these neurons are implicated in this plasticity. However, there is no ultrastructural evidence that the absence of cocaine following repeated administrations affects the critical surface/synaptic availability of AMPAR GluR1 subunits in either DA or non-DA, putative GABAergic neurons within the VTA. To assess this, we used electron microscopic immunolabeling in the VTA of adult male mice sacrificed at 30 minutes or 72 hours after receiving the final of six (15 mg/kg) cocaine injections, a dosing paradigm that resulted in development of locomotor sensitization. At each time point, both cocaine- and saline-injected mice showed AMPAR GluR1 immunogold labeling in somatodendritic profiles, many of which contained immunoperoxidase labeling for the DA-synthesizing enzyme, tyrosine hydroxylase (TH). At 30 minutes after the last injection, when cocaine was systemically present, only the non-TH labeled dendrites showed a significant increase in the synaptic/plasmalemmal density of GluR1 immunogold particles. At 72 hours, when systemic cocaine was depleted, synaptic GluR1 labeling was greatly enhanced in TH-containing dendrites throughout the VTA and in non-TH dendrites of the limbic-associated paranigral VTA. Our results demonstrate that systemic cocaine produces GluR1 trafficking specifically in non-DA neurons of the VTA, which may subsequently contribute to the abstinent-induced enhancement of AMPA receptor synaptic transmission in mesocorticolimbic DA neurons leading to heightened drug seeking behavior. PMID:21215761

  14. Cannabinoid-glutamate interactions in the regulation of food intake in neonatal layer- type chicks: role of glutamate NMDA and AMPA receptors.

    PubMed

    Keyshams, Negar; Zendehdel, Morteza; Babapour, Vahab; Baghbanzadeh, Ali

    2016-06-01

    The involvement of the endocannabinoid system in the brain functions is likely the conclusion of its capability to interact with specific neurotransmitters in several brain regions. The present study was designed to examine the role of the glutamatergic system on cannabinoid-induced hyperphagia in chicken. In this survey 10 experiments designed to investigate interaction of cannabinoidergic and glutamatergic systems on feeding behavior in neonatal chickens. In experiment 1, chicken were intracerebroventricular (ICV) injected with saline, 2-AG (2-Arachidonoylglycerol, 5.28 nmol, CB1 receptors agonist), MK-801(NMDA receptor antagonist, 15 nmol) and co-administration of 2-AG + MK-801. In experiment 2, injection of saline, 2-AG (5.28 nmol), CNQX) AMPA/kainate receptor antagonist, 390 nmol) and their combination (2-AG + CNQX) was done. In Experiment 3, injections were saline, 2-AG (5.28 nmol), AIDA)mGluR1 antagonist, 2 nmol) and 2-AG + AIDA. Experiments 4 and 5 were similar to experiment 3, except birds injected with LY341495 (mGLUR2 glutamate antagonist, 150 nmol) and UBP1112 (mGLUR3 glutamate antagonist, 2 nmol) instead of AIDA. Experiments 6-10 followed the procedure similar to experiments 1-5, except chickens received ICV injection of CB65 (CB2 receptor agonist, 3 nmol), instead of 2-AG. Then the cumulative food intake measured until 120 min post injection. According to the results, ICV injection of 2-AG and CB65 significantly increased food intake (P < 0.001). Co-injection of 2-AG and MK-801 significantly amplified hyperphagic effect of CB1 receptors agonist(P < 0.001). Moreover, co-administration of CB65 plus CNQX significantly increased CB65- induced hyperphagia in FD3 neonatal layer-type chickens (P < 0.001). These results suggest there is an interaction between endocannabinoids and glutamatergic systems via NMDA and AMPA receptors in feeding behavior of neonatal layer-type chickens. PMID:27000110

  15. Modulation of DL-. alpha. -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/quisqualate receptors by phospholipase A sub 2 : A necessary step in long-term potentiation

    SciTech Connect

    Massicotte, G.; Baudry, M. ); Vanderklish, P.; Lynch, G. )

    1991-03-01

    The effects of kainate (KA)-induced epileptic seizures on the binding properites of hippocampal glutamate receptors, on the modulation of DL-{alpha}-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/quisqualate receptor by phospholipase A{sub 2} (PLA{sub 2}), and on the formation of long-term potentiation (LTP) were studied in hippocampal membranes and hippocampal slices. Systemic administration of KA produced specific changes in the binding properties of the AMPA/quisqualate receptors and its regulation. Whereas the binding of various ligands to the N-methyl-D-aspartate receptors was not modified by KA treatment, there was a singificant decrease in the maximal number of binding sites for ({sup 3}H)AMPA. The loss of LTP was not due to changes in postsynaptic responses elicited by the bursts that trigger the potentiation effect, thus suggesting that KA treatment disrupts processes that follow N-methyl-D-aspartate receptor activation. Systemic administration of KA was associated with calpain activation as the amount of spectrin breakdown products was increased severalfold in hippocampus but not in cerebellum. Pretreatment of telencephalic membranes with calpain greatly reduced the PLA{sub 2}-induced increase in ({sup 3}H)AMPA binding. The results provide evidence in favor of an essential role of PLA{sub 2} in the development of LTP and suggest that the order of activation of different calcium-dependent processes is critical for producing the final changes underlying LTP.

  16. Synaptic targeting of AMPA receptors is regulated by a CaMKII site in the first intracellular loop of GluA1

    PubMed Central

    Lu, Wei; Isozaki, Kaname; Roche, Katherine W.; Nicoll, Roger A.

    2010-01-01

    The accumulation of AMPA receptors (AMPARs) at synapses is essential for excitatory synaptic transmission. However, the mechanisms underlying synaptic targeting of AMPARs remain elusive. We have now used a molecular replacement approach on an AMPAR-null background to investigate the targeting mechanisms necessary for regulating AMPAR trafficking in the hippocampus. Although there is an extensive literature on the role of the GluA1 C-tail in AMPAR trafficking, there is no effect of overexpressing the C-tail on basal transmission. Instead, we found that the first intracellular loop domain (Loop1) of GluA1, a previously overlooked region within AMPARs, is critical for receptor targeting to synapses, but not for delivery of receptors to the plasma membrane. We also identified a CaMKII phosphorylation site (S567) in the GluA1 Loop1, which is phosphorylated in vitro and in vivo. Furthermore, we show that S567 is a key residue that regulates Loop1-mediated AMPAR trafficking. Thus, our study reveals a unique mechanism for targeting AMPARs to synapses to mediate synaptic transmission. PMID:21135237

  17. A case of autism with an interstitial deletion on 4q leading to hemizygosity for genes encoding for glutamine and glycine neurotransmitter receptor sub-units (AMPA 2, GLRA3, GLRB) and neuropeptide receptors NPY1R, NPY5R

    PubMed Central

    Ramanathan, Subhadra; Woodroffe, Abigail; Flodman, Pamela L; Mays, Lee Z; Hanouni, Mona; Modahl, Charlotte B; Steinberg-Epstein, Robin; Bocian, Maureen E; Spence, M Anne; Smith, Moyra

    2004-01-01

    Background Autism is a pervasive developmental disorder characterized by a triad of deficits: qualitative impairments in social interactions, communication deficits, and repetitive and stereotyped patterns of behavior. Although autism is etiologically heterogeneous, family and twin studies have established a definite genetic basis. The inheritance of idiopathic autism is presumed to be complex, with many genes involved; environmental factors are also possibly contributory. The analysis of chromosome abnormalities associated with autism contributes greatly to the identification of autism candidate genes. Case presentation We describe a child with autistic disorder and an interstitial deletion on chromosome 4q. This child first presented at 12 months of age with developmental delay and minor dysmorphic features. At 4 years of age a diagnosis of Pervasive Developmental Disorder was made. At 11 years of age he met diagnostic criteria for autism. Cytogenetic studies revealed a chromosome 4q deletion. The karyotype was 46, XY del 4 (q31.3-q33). Here we report the clinical phenotype of the child and the molecular characterization of the deletion using molecular cytogenetic techniques and analysis of polymorphic markers. These studies revealed a 19 megabase deletion spanning 4q32 to 4q34. Analysis of existing polymorphic markers and new markers developed in this study revealed that the deletion arose on a paternally derived chromosome. To date 33 genes of known or inferred function are deleted as a consequence of the deletion. Among these are the AMPA 2 gene that encodes the glutamate receptor GluR2 sub-unit, GLRA3 and GLRB genes that encode glycine receptor subunits and neuropeptide Y receptor genes NPY1R and NPY5R. Conclusions The deletion in this autistic subject serves to highlight specific autism candidate genes. He is hemizygous for AMPA 2, GLRA3, GLRB, NPY1R and NPY5R. GluR2 is the major determinant of AMPA receptor structure. Glutamate receptors maintain structural

  18. Pharmacological properties and H+ sensitivity of excitatory amino acid receptor channels in rat cerebellar granule neurones.

    PubMed Central

    Traynelis, S F; Cull-Candy, S G

    1991-01-01

    1. N-Methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), and kainate receptor channels have been examined in rat cerebellar granule neurones with whole-cell and single-channel patch-clamp methods. The whole-cell peak and steady-state aspartate and NMDA currents were reversibly inhibited by extracellular protons; the IC50 (concentration producing half-maximal inhibition) for the full H+ inhibition curve for NMDA receptors corresponded to pH 7.3, near to physiological pH. (S)-AMPA and kainate whole-cell currents were inhibited by protons with IC50 values that corresponded to pH 6.3 and 5.7, respectively; these receptors were, however, insensitive to H+ concentrations that inhibited NMDA receptor responses. 2. Proton inhibition of the NMDA, AMPA and kainate receptor-mediated responses was voltage insensitive, and did not involve a shift in reversal potential. 3. The EC50 (concentration producing half-maximal effect) for aspartate calculated from the whole-cell dose-response curve was similar at pH 6.8 and 7.6 (mean 11.2 microM). Although the EC50 for glycine potentiation of the aspartate response was marginally increased from 273 nM at pH 7.6 to 373 nM at pH 6.8, H+ inhibition was not overcome by up to 1 mM-external glycine. Inhibiting concentrations of H+ appropriate for AMPA and kainate receptors did not markedly alter the EC50 values determined for (S)-AMPA (3.4 microM) and kainate (114 microM) at pH 7.2. 4. Treatment of neurones with N-ethylmaleimide, iodoacetic acid, dithiothretiol or diethyl pyrocarbonate did not influence proton inhibition of NMDA receptor responses. However, treatment with diethyl pyrocarbonate, which potentiated aspartate responses, appeared to reduce the effectiveness of Zn2+ inhibition of NMDA receptors. 5. Desensitization of whole-cell NMDA and (S)-AMPA currents was studied with ionophoretic application of agonist to the cell soma. Whole-cell aspartate currents desensitized rapidly, irrespective of the

  19. O-GlcNAcylation of AMPA Receptor GluA2 Is Associated with a Novel Form of Long-Term Depression at Hippocampal Synapses

    PubMed Central

    Taylor, Erica W.; Wang, Kai; Nelson, Amy R.; Bredemann, Teruko M.; Fraser, Kyle B.; Clinton, Sarah M.; Puckett, Rosemary; Marchase, Richard B.; Chatham, John C.

    2014-01-01

    Serine phosphorylation of AMPA receptor (AMPAR) subunits GluA1 and GluA2 modulates AMPAR trafficking during long-term changes in strength of hippocampal excitatory transmission required for normal learning and memory. The post-translational addition and removal of O-linked β-N-acetylglucosamine (O-GlcNAc) also occurs on serine residues. This, together with the high expression of the enzymes O-GlcNAc transferase (OGT) and β-N-acetylglucosamindase (O-GlcNAcase), suggests a potential role for O-GlcNAcylation in modifying synaptic efficacy and cognition. Furthermore, because key synaptic proteins are O-GlcNAcylated, this modification may be as important to brain function as phosphorylation, yet its physiological significance remains unknown. We report that acutely increasing O-GlcNAcylation in Sprague Dawley rat hippocampal slices induces an NMDA receptor and protein kinase C-independent long-term depression (LTD) at hippocampal CA3–CA1 synapses (O-GcNAc LTD). This LTD requires AMPAR GluA2 subunits, which we demonstrate are O-GlcNAcylated. Increasing O-GlcNAcylation interferes with long-term potentiation, and in hippocampal behavioral assays, it prevents novel object recognition and placement without affecting contextual fear conditioning. Our findings provide evidence that O-GlcNAcylation dynamically modulates hippocampal synaptic function and learning and memory, and suggest that altered O-GlcNAc levels could underlie cognitive dysfunction in neurological diseases. PMID:24381264

  20. What causes aberrant salience in schizophrenia? A role for impaired short-term habituation and the GRIA1 (GluA1) AMPA receptor subunit

    PubMed Central

    Barkus, C; Sanderson, DJ; Rawlins, JNP; Walton, ME; Harrison, PJ; Bannerman, DM

    2014-01-01

    The GRIA1 locus, encoding the GluA1 (also known as GluRA or GluR1) AMPA glutamate receptor subunit, shows genome-wide association to schizophrenia. As well as extending the evidence that glutamatergic abnormalities play a key role in the disorder, this finding draws attention to the behavioural phenotype of Gria1 knockout mice. These mice show deficits in short-term habituation. Importantly, under some conditions the attention being paid to a recently presented neutral stimulus can actually increase rather than decrease (sensitization). We propose that this mouse phenotype represents a cause of aberrant salience and, in turn, that aberrant salience (and the resulting positive symptoms) in schizophrenia may arise, at least in part, from a glutamatergic genetic predisposition and a deficit in short-term habituation. This proposal links an established risk gene with a psychological process central to psychosis, and is supported by findings of comparable deficits in short-term habituation in mice lacking the NMDAR receptor subunit Grin2a (which also shows association to schizophrenia). Since aberrant salience is primarily a dopaminergic phenomenon, the model supports the view that the dopaminergic abnormalities can be downstream of a glutamatergic aetiology. Finally, we suggest that, as illustrated here, the real value of genetically modified mice is not as ‘models of schizophrenia’, but as experimental tools which can link genomic discoveries with psychological processes, and help elucidate the underlying neural mechanisms. PMID:25224260

  1. Excitatory synapses are stronger in the hippocampus of Rett syndrome mice due to altered synaptic trafficking of AMPA-type glutamate receptors.

    PubMed

    Li, Wei; Xu, Xin; Pozzo-Miller, Lucas

    2016-03-15

    Deficits in long-term potentiation (LTP) at central excitatory synapses are thought to contribute to cognitive impairments in neurodevelopmental disorders associated with intellectual disability and autism. Using the methyl-CpG-binding protein 2 (Mecp2) knockout (KO) mouse model of Rett syndrome, we show that naïve excitatory synapses onto hippocampal pyramidal neurons of symptomatic mice have all of the hallmarks of potentiated synapses. Stronger Mecp2 KO synapses failed to undergo LTP after either theta-burst afferent stimulation or pairing afferent stimulation with postsynaptic depolarization. On the other hand, basal synaptic strength and LTP were not affected in slices from younger presymptomatic Mecp2 KO mice. Furthermore, spine synapses in pyramidal neurons from symptomatic Mecp2 KO are larger and do not grow in size or incorporate GluA1 subunits after electrical or chemical LTP. Our data suggest that LTP is occluded in Mecp2 KO mice by already potentiated synapses. The higher surface levels of GluA1-containing receptors are consistent with altered expression levels of proteins involved in AMPA receptor trafficking, suggesting previously unidentified targets for therapeutic intervention for Rett syndrome and other MECP2-related disorders. PMID:26929363

  2. Radiosynthesis and preliminary PET evaluation of (18)F-labeled 2-(1-(3-fluorophenyl)-2-oxo-5-(pyrimidin-2-yl)-1,2-dihydropyridin-3-yl)benzonitrile for imaging AMPA receptors.

    PubMed

    Yuan, Gengyang; Jones, Graham B; Vasdev, Neil; Liang, Steven H

    2016-10-01

    To prompt the development of (18)F-labeled positron emission tomography (PET) tracers for the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor, we have prepared (18)F-labeled 2-(1-(3-fluorophenyl)-2-oxo-5-(pyrimidin-2-yl)-1,2-dihydropyridin-3-yl)benzonitrile ([(18)F]8). The radiosynthesis was achieved by a one-pot two-step method that utilized a spirocyclic hypervalent iodine(III) mediated radiofluorination to prepare the (18)F-labeled 1-bromo-3-fluorobenzene ([(18)F]15) intermediate with K(18)F. A subsequent copper(I) iodide mediated coupling reaction was carried out with 2-(2-oxo-5-(pyrimidin-2-yl)-1,2-dihydropyridin-3-yl)benzonitrile (10) to [(18)F]8 in 10±2% uncorrected radiochemical yield relative to starting (18)F-fluoride with >99% radiochemical purity and 29.6±7.4Gbq/μmol specific activity at the time of injection. PET imaging studies with the title radiotracer in normal mice demonstrated good brain uptake (peak standardized uptake value (SUV)=2.3±0.1) and warrants further in vivo validation. PMID:27546294

  3. Synthesis and Pharmacology of Mono-, Di-, and Trialkyl-Substituted 7-Chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-Dioxides Combined with X-ray Structure Analysis to Understand the Unexpected Structure-Activity Relationship at AMPA Receptors.

    PubMed

    Larsen, Anja Probst; Francotte, Pierre; Frydenvang, Karla; Tapken, Daniel; Goffin, Eric; Fraikin, Pierre; Caignard, Daniel-Henri; Lestage, Pierre; Danober, Laurence; Pirotte, Bernard; Kastrup, Jette Sandholm

    2016-03-16

    Positive allosteric modulators of 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA)-type ionotropic glutamate receptors are promising compounds for treatment of neurological disorders, for example, Alzheimer's disease. Here, we report synthesis and pharmacological evaluation of a series of mono-, di-, or trialkyl-substituted 7-chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides, comprising in total 16 new modulators. The trisubstituted compounds 7b, 7d, and 7e revealed potent activity (EC2× = 2.7-4.3 μM; concentration of compound responsible for a 2-fold increase of the AMPA mediated response) as AMPA receptor potentiators in an in vitro cellular fluorescence assay (FLIPR). The 4-cyclopropyl compound 7f was found to be considerably less potent (EC2× = 60 μM), in contrast to previously described 4-monoalkyl-substituted benzothiadiazine dioxides for which the cyclopropyl group constitutes the best choice of substituent. 7b was subjected to X-ray structural analysis in complex with the GluA2 ligand-binding domain. We propose an explanation of the unexpected structure-activity relationship of this new series of mono-, di-, and trialkyl-substituted 1,2,4-benzothiadiazine 1,1-dioxide compounds. The methyl substituent in the 3-position directs the binding mode of the 1,2,4-benzothiadiazine 1,1-dioxide (BTD) scaffold. When a methyl substituent is present in the 3-position of the BTD, additional methyl substituents in both the 2- and 4-positions increase potency, whereas introduction of a 4-cyclopropyl group does not enhance potency of 2,3,4-alkyl-substituted BTDs. A hydrogen bond donor in the 2-position of the BTD is not necessary for modulator potency. PMID:26771108

  4. Joint CP-AMPA and group I mGlu receptor activation is required for synaptic plasticity in dentate gyrus fast-spiking interneurons

    PubMed Central

    Hainmüller, Thomas; Krieglstein, Kerstin; Kulik, Akos; Bartos, Marlene

    2014-01-01

    Hippocampal principal cell (PC) assemblies provide the brain with a mnemonic representation of space. It is assumed that the formation of cell assemblies is supported by long-lasting modification of glutamatergic synapses onto perisomatic inhibitory interneurons (PIIs), which provide powerful feedback inhibition to neuronal networks. Repetitive activation of dentate gyrus PIIs by excitatory mossy fiber (MF) inputs induces Hebbian long-term potentiation (LTP). In contrast, long-term depression (LTD) emerges in the absence of PII activity. However, little is known about the molecular mechanisms underlying synaptic plasticity in PIIs. Here, we examined the role of group I metabotropic glutamate receptors 1 and 5 (mGluRs1/5) in inducing plastic changes at MF-PII synapses. We found that mGluRs1/5 are located perisynaptically and that pharmacological block of mGluR1 or mGluR5 abolished MF-LTP. In contrast, their exogenous activation was insufficient to induce MF-LTP but cleared MF-LTD. No LTP could be elicited in PIIs loaded with blockers of G protein signaling and Ca2+-dependent PKC. Two-photon imaging revealed that the intracellular Ca2+ rise necessary for MF-LTP was largely mediated by Ca2+-permeable AMPA receptors (CP-AMPARs), but less by NMDA receptors or mGluRs1/5. Thus, our data indicate that fast Ca2+ signaling via CP-AMPARs and slow G protein-mediated signaling via mGluRs1/5 converge to a PKC-dependent molecular pathway to induce Hebbian MF-LTP. We further propose that Hebbian activation of mGluRs1/5 gates PIIs into a “readiness mode” to promote MF-LTP, which, in turn, will support timed PII recruitment, thereby assisting in PC assembly formation. PMID:25161282

  5. S-SCAM/MAGI-2 is an essential synaptic scaffolding molecule for the GluA2-containing maintenance pool of AMPA receptors.

    PubMed

    Danielson, Eric; Zhang, Nanyan; Metallo, Jacob; Kaleka, Kanwardeep; Shin, Seung Min; Gerges, Nashaat; Lee, Sang H

    2012-05-16

    Synaptic plasticity, the cellular basis of learning and memory, involves the dynamic trafficking of AMPA receptors (AMPARs) into and out of synapses. One of the remaining key unanswered aspects of AMPAR trafficking is the mechanism by which synaptic strength is preserved despite protein turnover. In particular, the identity of AMPAR scaffolding molecule(s) involved in the maintenance of GluA2-containing AMPARs is completely unknown. Here we report that the synaptic scaffolding molecule (S-SCAM; also called membrane-associated guanylate kinase inverted-2 and atrophin interacting protein-1) plays the critical role of maintaining synaptic strength. Increasing S-SCAM levels in rat hippocampal neurons led to specific increases in the surface AMPAR levels, enhanced AMPAR-mediated synaptic transmission, and enlargement of dendritic spines, without significantly effecting GluN levels or NMDA receptor (NMDAR) EPSC. Conversely, decreasing S-SCAM levels by RNA interference-mediated knockdown caused the loss of synaptic AMPARs, which was followed by a severe reduction in the dendritic spine density. Importantly, S-SCAM regulated synaptic AMPAR levels in a manner, dependent on GluA2 not GluA1, sensitive to N-ethylmaleimide-sensitive fusion protein interaction, and independent of activity. Further, S-SCAM increased surface AMPAR levels in the absence of PSD-95, while PSD-95 was dependent on S-SCAM to increase surface AMPAR levels. Finally, S-SCAM overexpression hampered NMDA-induced internalization of AMPARs and prevented the induction of long term-depression, while S-SCAM knockdown did not. Together, these results suggest that S-SCAM is an essential AMPAR scaffolding molecule for the GluA2-containing pool of AMPARs, which are involved in the constitutive pathway of maintaining synaptic strength. PMID:22593065

  6. Altered mRNA editing and expression of ionotropic glutamate receptors after kainic acid exposure in cyclooxygenase-2 deficient mice.

    PubMed

    Caracciolo, Luca; Barbon, Alessandro; Palumbo, Sara; Mora, Cristina; Toscano, Christopher D; Bosetti, Francesca; Barlati, Sergio

    2011-01-01

    Kainic acid (KA) binds to the AMPA/KA receptors and induces seizures that result in inflammation, oxidative damage and neuronal death. We previously showed that cyclooxygenase-2 deficient (COX-2(-/-)) mice are more vulnerable to KA-induced excitotoxicity. Here, we investigated whether the increased susceptibility of COX-2(-/-) mice to KA is associated with altered mRNA expression and editing of glutamate receptors. The expression of AMPA GluR2, GluR3 and KA GluR6 was increased in vehicle-injected COX-2(-/-) mice compared to wild type (WT) mice in hippocampus and cortex, whereas gene expression of NMDA receptors was decreased. KA treatment decreased the expression of AMPA, KA and NMDA receptors in the hippocampus, with a significant effect in COX-2(-/-) mice. Furthermore, we analyzed RNA editing levels and found that the level of GluR3 R/G editing site was selectively increased in the hippocampus and decreased in the cortex in COX-2(-/-) compared with WT mice. After KA, GluR4 R/G editing site, flip form, was increased in the hippocampus of COX-2(-/-) mice. Treatment of WT mice with the COX-2 inhibitor celecoxib for two weeks decreased the expression of AMPA/KA and NMDAR subunits after KA, as observed in COX-2(-/-) mice. After KA exposure, COX-2(-/-) mice showed increased mRNA expression of markers of inflammation and oxidative stress, such as cytokines (TNF-α, IL-1β and IL-6), inducible nitric oxide synthase (iNOS), microglia (CD11b) and astrocyte (GFAP). Thus, COX-2 gene deletion can exacerbate the inflammatory response to KA. We suggest that COX-2 plays a role in attenuating glutamate excitotoxicity by modulating RNA editing of AMPA/KA and mRNA expression of all ionotropic glutamate receptor subunits and, in turn, neuronal excitability. These changes may contribute to the increased vulnerability of COX-2(-/-) mice to KA. The overstimulation of glutamate receptors as a consequence of COX-2 gene deletion suggests a functional coupling between COX-2 and the

  7. PSD-95 family MAGUKs are essential for anchoring AMPA and NMDA receptor complexes at the postsynaptic density

    PubMed Central

    Chen, Xiaobing; Levy, Jonathan M.; Hou, Austin; Winters, Christine; Azzam, Rita; Sousa, Alioscka A.; Leapman, Richard D.; Nicoll, Roger A.; Reese, Thomas S.

    2015-01-01

    The postsynaptic density (PSD)-95 family of membrane-associated guanylate kinases (MAGUKs) are major scaffolding proteins at the PSD in glutamatergic excitatory synapses, where they maintain and modulate synaptic strength. How MAGUKs underlie synaptic strength at the molecular level is still not well understood. Here, we explore the structural and functional roles of MAGUKs at hippocampal excitatory synapses by simultaneous knocking down PSD-95, PSD-93, and synapse-associated protein (SAP)102 and combining electrophysiology and transmission electron microscopic (TEM) tomography imaging to analyze the resulting changes. Acute MAGUK knockdown greatly reduces synaptic transmission mediated by α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPARs) and N-methyl-d-aspartate receptors (NMDARs). This knockdown leads to a significant rise in the number of silent synapses, diminishes the size of PSDs without changes in pre- or postsynaptic membrane, and depletes the number of membrane-associated PSD-95–like vertical filaments and transmembrane structures, identified as AMPARs and NMDARs by EM tomography. The differential distribution of these receptor-like structures and dependence of their abundance on PSD size matches that of AMPARs and NMDARs in the hippocampal synapses. The loss of these structures following MAGUK knockdown tracks the reduction in postsynaptic AMPAR and NMDAR transmission, confirming the structural identities of these two types of receptors. These results demonstrate that MAGUKs are required for anchoring both types of glutamate receptors at the PSD and are consistent with a structural model where MAGUKs, corresponding to membrane-associated vertical filaments, are the essential structural proteins that anchor and organize both types of glutamate receptors and govern the overall molecular organization of the PSD. PMID:26604311

  8. AMPA Receptor Phosphorylation and Synaptic Colocalization on Motor Neurons Drive Maladaptive Plasticity below Complete Spinal Cord Injury1,2,3

    PubMed Central

    Stuck, Ellen D.; Irvine, Karen-Amanda; Bresnahan, Jacqueline C.

    2015-01-01

    Abstract Clinical spinal cord injury (SCI) is accompanied by comorbid peripheral injury in 47% of patients. Human and animal modeling data have shown that painful peripheral injuries undermine long-term recovery of locomotion through unknown mechanisms. Peripheral nociceptive stimuli induce maladaptive synaptic plasticity in dorsal horn sensory systems through AMPA receptor (AMPAR) phosphorylation and trafficking to synapses. Here we test whether ventral horn motor neurons in rats demonstrate similar experience-dependent maladaptive plasticity below a complete SCI in vivo. Quantitative biochemistry demonstrated that intermittent nociceptive stimulation (INS) rapidly and selectively increases AMPAR subunit GluA1 serine 831 phosphorylation and localization to synapses in the injured spinal cord, while reducing synaptic GluA2. These changes predict motor dysfunction in the absence of cell death signaling, suggesting an opportunity for therapeutic reversal. Automated confocal time-course analysis of lumbar ventral horn motor neurons confirmed a time-dependent increase in synaptic GluA1 with concurrent decrease in synaptic GluA2. Optical fractionation of neuronal plasma membranes revealed GluA2 removal from extrasynaptic sites on motor neurons early after INS followed by removal from synapses 2 h later. As GluA2-lacking AMPARs are canonical calcium-permeable AMPARs (CP-AMPARs), their stimulus- and time-dependent insertion provides a therapeutic target for limiting calcium-dependent dynamic maladaptive plasticity after SCI. Confirming this, a selective CP-AMPAR antagonist protected against INS-induced maladaptive spinal plasticity, restoring adaptive motor responses on a sensorimotor spinal training task. These findings highlight the critical involvement of AMPARs in experience-dependent spinal cord plasticity after injury and provide a pharmacologically targetable synaptic mechanism by which early postinjury experience shapes motor plasticity. PMID:26668821

  9. Calcium permeable AMPA receptor-dependent long lasting plasticity of intrinsic excitability in fast spiking interneurons of the dentate gyrus decreases inhibition in the granule cell layer.

    PubMed

    Dasgupta, Debanjan; Sikdar, Sujit Kumar

    2015-03-01

    The local fast-spiking interneurons (FSINs) are considered to be crucial for the generation, maintenance, and modulation of neuronal network oscillations especially in the gamma frequency band. Gamma frequency oscillations have been associated with different aspects of behavior. But the prolonged effects of gamma frequency synaptic activity on the FSINs remain elusive. Using whole cell current clamp patch recordings, we observed a sustained decrease of intrinsic excitability in the FSINs of the dentate gyrus (DG) following repetitive stimulations of the mossy fibers at 30 Hz (gamma bursts). Surprisingly, the granule cells (GCs) did not express intrinsic plastic changes upon similar synaptic excitation of their apical dendritic inputs. Interestingly, pairing the gamma bursts with membrane hyperpolarization accentuated the plasticity in FSINs following the induction protocol, while the plasticity attenuated following gamma bursts paired with membrane depolarization. Paired pulse ratio measurement of the synaptic responses did not show significant changes during the experiments. However, the induction protocols were accompanied with postsynaptic calcium rise in FSINs. Interestingly, the maximum and the minimum increase occurred during gamma bursts with membrane hyperpolarization and depolarization respectively. Including a selective blocker of calcium-permeable AMPA receptors (CP-AMPARs) in the bath; significantly attenuated the calcium rise and blocked the membrane potential dependence of the calcium rise in the FSINs, suggesting their involvement in the observed phenomenon. Chelation of intracellular calcium, blocking HCN channel conductance or blocking CP-AMPARs during the experiment forbade the long lasting expression of the plasticity. Simultaneous dual patch recordings from FSINs and synaptically connected putative GCs confirmed the decreased inhibition in the GCs accompanying the decreased intrinsic excitability in the FSINs. Experimentally constrained network

  10. Differences in AMPA and GABAA/B receptor subunit expression between the chronically reorganized cortex and brainstem of adult squirrel monkeys

    PubMed Central

    Mowery, Todd M.; Sarin, Rohini M.; Kostylev, Polina V; Garraghty, Preston E.

    2015-01-01

    The primate somatosensory neuraxis provides a highly translational model system with which to investigate adult neural plasticity. Here, we report immunohistochemical staining data for AMPA and GABAA/B receptor subunits of area 3b cortex and cuneate nucleus of adult squirrel monkeys one to five years after median and ulnar nerve transection. In Area 3B cortex, the expression of GluR1 AMPAR subunits in reorganized regions are significantly increased, while the expression of GluR2/3 AMPAR subunits are not. GABAA α1 subunit expression in the reorganized region is not significantly different from control regions. Presynaptic GABABR1a subunit expression was also not significantly different between reorganized and control regions, while postsynaptic GABABR1b subunit expression was significantly decreased. In the cuneate nucleus of the brainstem, the expression of GluR1 AMPAR subunits in reorganized regions was not significantly different, while GluR2/3 AMPAR subunit expression was significantly elevated. GABAA α1 subunit expression in the reorganized region was significantly decreased. Presynaptic GABABR1a subunit expression was not significantly different, while postsynaptic GABABR1b subunit expression was significantly decreased. When subunit expression is compared, brainstem and cortical patterns diverge over longer periods of recovery. Persistent patterns of change in the cortex are stable by 1 year. Alternatively, subunit expression in the cuneate nucleus one to five years after nerve injury is similar to that seen 1 month after a reorganizing injury. This suggests that cortical plasticity continues to change over many months as receptive field reorganization occurs, while brainstem plasticity obtains a level of stable persistence by one month. PMID:25791620

  11. Integrated Multiscale Modeling of the Nervous System: Predicting Changes in Hippocampal Network Activity by a Positive AMPA Receptor Modulator

    PubMed Central

    Allam, Sushmita L.; Hu, Eric Y.; Greget, Renaud; Ambert, Nicolas; Keller, Anne Florence; Bischoff, Serge; Baudry, Michel; Berger, Theodore W.

    2012-01-01

    One of the fundamental characteristics of the brain is its hierarchical organization. Scales in both space and time that must be considered when integrating across hierarchies of the nervous system are sufficiently great as to have impeded the development of routine multilevel modeling methodologies. Complex molecular interactions at the level of receptors and channels regulate activity at the level of neurons; interactions between multiple populations of neurons ultimately give rise to complex neural systems function and behavior. This spatial complexity takes place in the context of a composite temporal integration of multiple, different events unfolding at the millisecond, second, minute, hour, and longer time scales. In this study, we present a multiscale modeling methodology that integrates synaptic models into single neuron, and multineuron, network models. We have applied this approach to the specific problem of how changes at the level of kinetic parameters of a receptor-channel model are translated into changes in the temporal firing pattern of a single neuron, and ultimately, changes in the spatiotemporal activity of a network of neurons. These results demonstrate how this powerful methodology can be applied to understand the effects of a given local process within multiple hierarchical levels of the nervous system. PMID:21642035

  12. Dimensions and ion selectivity of recombinant AMPA and kainate receptor channels and their dependence on Q/R site residues.

    PubMed Central

    Burnashev, N; Villarroel, A; Sakmann, B

    1996-01-01

    1. Recombinant alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor (AMPAR) subunits (GluR-A or GluR-B) and kainate receptor (KAR) subunit (GluR-6) in their unedited (Q)- and edited (R)-forms were expressed in HEK 293 cells. To estimate the dimensions of the narrow portion of these channels, biionic reversal potentials for organic cations of different mean diameters were determined with Cs+ as the internal reference ion. 2. Homomeric channels assembled from Q-form subunits were cation selective. The relation between the relative permeability and the mean size of different organic cations suggests that the diameter of the narrow portion of Q-form channels is approximately 0.78 nm for AMPAR and 0.75 nm for KAR channels. 3. Homomeric channels assembled from R-form subunits were permeant for anions and cations. When probed with CsC1 gradients the relative chloride permeability (PC1/PCs) was estimated as 0.14 for GluR-B(R) and 0.74 for GluR-6(R)-subunit channels. The permeability versus mean size relation for large cations measured with the weakly permeant F- as anion, indicates that for the R-form KAR channels the apparent pore diameter is close to 0.76 nm. 4. Heteromeric AMPAR and KAR channels co-assembled from Q- and R-form subunits were cation selective. The diameter of the narrow portion of these channels is estimated to be in the range between 0.70 and 0.74 nm. 5. The results indicated that the diameters of the narrow portion of AMPAR and KAR channels of different subunit composition and of widely different ion selectivity are comparable. Therefore, the differences in the anion versus cation selectivity, in Ca2+ permeability and in channel conductance are likely to be determined by the difference in charge density of the channel. PMID:8910205

  13. Ischemia-induced synaptic plasticity drives sustained expression of calcium-permeable AMPA receptors in the hippocampus.

    PubMed

    Dias, Raquel B; Rombo, Diogo M; Ribeiro, Joaquim A; Sebastião, Ana M

    2013-02-01

    Long lasting enhancement of synaptic transmission can be triggered by brief bursts of afferent stimulation, underlying long-term potentiation (LTP), and also by brief ischemia in a process known as i-LTP. The extent to which LTP and i-LTP rely on comparable cellular mechanisms remains unclear. Under physiological conditions, LTP induction drives transient expression of calcium-permeable AMPARs (CP-AMPARs) at synapses, whose ability to undergo plasticity is primed by endogenous activation of adenosine A(2A) receptors (A(2A)Rs). The present work thus addressed the contribution of CP-AMPARs and A(2A)Rs to i-LTP, which was induced in rat hippocampal slices by brief (10 min) oxygen/glucose deprivation (OGD). The amplitude of afferent-evoked excitatory postsynaptic currents (EPSCs) recorded from CA1 pyramidal neurons was decreased during OGD but gradually recovered toward values significantly above (157 ± 17%) the baseline (100%) 40-50 min after re-oxygenation. This i-LTP was precluded by CP-AMPAR blockade (internal spermine (500 μM) or extracellular NASPM (20 μM) application) as well as by A(2A)R blockade with a selective antagonist (SCH 58261, 100 nM). OGD prompted sustained (>70 min) facilitation of mEPSC amplitude and frequency, and decreased mEPSC decay time, all of which were prevented by SCH 58261 (100 nM). The ability of NASPM (20 μM) to acutely inhibit EPSCs 1 h after OGD, but not in control conditions nor in OGD-challenged slices when in the presence of SCH 58261 (100 nM), further supports sustained CP-AMPAR recruitment by i-LTP in an A(2A)R-dependent way. We propose that although i-LTP may initially mimic LTP, failure of auto-regulated CP-AMPAR removal from synapses could constitute an early divergent event between these forms of plasticity. PMID:23041538

  14. Nuclear receptors in bile acid metabolism

    PubMed Central

    Li, Tiangang; Chiang, John Y. L.

    2013-01-01

    Bile acids are signaling molecules that activate nuclear receptors, such as farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, and vitamin D receptor, and play a critical role in the regulation of lipid, glucose, energy, and drug metabolism. These xenobiotic/endobiotic-sensing nuclear receptors regulate phase I oxidation, phase II conjugation, and phase III transport in bile acid and drug metabolism in the digestive system. Integration of bile acid metabolism with drug metabolism controls absorption, transport, and metabolism of nutrients and drugs to maintain metabolic homeostasis and also protects against liver injury, inflammation, and related metabolic diseases, such as nonalcoholic fatty liver disease, diabetes, and obesity. Bile-acid–based drugs targeting nuclear receptors are in clinical trials for treating cholestatic liver diseases and fatty liver disease. PMID:23330546

  15. AMPA Receptor–mTOR Activation is Required for the Antidepressant-Like Effects of Sarcosine during the Forced Swim Test in Rats: Insertion of AMPA Receptor may Play a Role

    PubMed Central

    Chen, Kuang-Ti; Tsai, Mang-Hung; Wu, Ching-Hsiang; Jou, Ming-Jia; Wei, I-Hua; Huang, Chih-Chia

    2015-01-01

    Sarcosine, an endogenous amino acid, is a competitive inhibitor of the type I glycine transporter and an N-methyl-d-aspartate receptor (NMDAR) coagonist. Recently, we found that sarcosine, an NMDAR enhancer, can improve depression-related behaviors in rodents and humans. This result differs from previous studies, which have reported antidepressant effects of NMDAR antagonists. The mechanisms underlying the therapeutic response of sarcosine remain unknown. This study examines the role of mammalian target of rapamycin (mTOR) signaling and α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor (AMPAR) activation, which are involved in the antidepressant-like effects of several glutamatergic system modulators. The effects of sarcosine in a forced swim test (FST) and the expression levels of phosphorylated mTOR signaling proteins were examined in the absence or presence of mTOR and AMPAR inhibitors. In addition, the influence of sarcosine on AMPAR trafficking was determined by analyzing the phosphorylation of AMPAR subunit GluR1 at the PKA site (often considered an indicator for GluR1 membrane insertion in neurons). A single injection of sarcosine exhibited antidepressant-like effects in rats in the FST and rapidly activated the mTOR signaling pathway, which were significantly blocked by mTOR inhibitor rapamycin or the AMPAR inhibitor 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX) pretreatment. Moreover, NBQX pretreatment eliminated the ability of sarcosine to stimulate the phosphorylated mTOR signaling proteins. Furthermore, GluR1 phosphorylation at its PKA site was significantly increased after an acute in vivo sarcosine treatment. The results demonstrated that sarcosine exerts antidepressant-like effects by enhancing AMPAR–mTOR signaling pathway activity and facilitating AMPAR membrane insertion. Highlights – A single injection of sarcosine rapidly exerted antidepressant-like effects with a concomitant increase in the activation of the mammalian

  16. Regulation of GluA1 α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Receptor Function by Protein Kinase C at Serine-818 and Threonine-840

    PubMed Central

    Jenkins, Meagan A.; Wells, Gordon; Bachman, Julia; Snyder, James P.; Jenkins, Andrew; Huganir, Richard L.; Oswald, Robert E.

    2014-01-01

    Three residues within the AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor subunit GluA1 C terminus (Ser818, Ser831, Thr840) can be phosphorylated by Ca2+/phospholipid-dependent protein kinase (PKC). Here, we show that PKC phosphorylation of GluA1 Ser818 or Thr840 enhances the weighted mean channel conductance without altering the response time course or agonist potency. These data support the idea that these residues constitute a hyper-regulatory domain for the AMPA receptor. Introduction of phosphomimetic mutations increases conductance only at these three sites within the proximal C terminus, consistent with a structural model with a flexible linker connecting the distal C-terminal domain to the more proximal domain containing a helix bracketed by Ser831 and Thr840. NMR spectra support this model and raise the possibility that phosphorylation can alter the configuration of this domain. Our findings provide insight into the structure and function of the C-terminal domain of GluA1, which controls AMPA receptor function and trafficking during synaptic plasticity in the central nervous system. PMID:24452473

  17. Ethanol directly depresses AMPA and NMDA glutamate currents in spinal cord motor neurons independent of actions on GABAA or glycine receptors.

    PubMed

    Wang, M Y; Rampil, I J; Kendig, J J

    1999-07-01

    Ethanol is a general anesthetic agent as defined by abolition of movement in response to noxious stimulation. This anesthetic endpoint is due to spinal anesthetic actions. This study was designed to test the hypothesis that ethanol acts directly on motor neurons to inhibit excitatory synaptic transmission at glutamate receptors. Whole cell recordings were made in visually identified motor neurons in spinal cord slices from 14- to 23-day-old rats. Currents were evoked by stimulating a dorsal root fragment or by brief pulses of glutamate. Ethanol at general anesthetic concentrations (50-200 mM) depressed both responses. Ethanol also depressed glutamate-evoked responses in the presence of tetrodotoxin (300 nM), showing that its actions are postsynaptic. Block of inhibitory gamma-aminobutyric acidA and glycine receptors by bicuculline (50 microM) and strychnine (5 microM), respectively, did not significantly reduce the effects of ethanol on glutamate currents. Ethanol also depressed glutamate-evoked currents when the inhibitory receptors were blocked and either D, L-2-amino-5-phosphonopentanoic acid (40 microM) or 6-cyano-7-nitroquinoxaline-2,3-dione disodium (10 microM) were applied to block N-methyl-D-aspartate or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate receptors, respectively. The results show that ethanol exerts direct depressant effects on both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and N-methyl-D-aspartate glutamate currents in motor neurons. Enhancement of gamma-aminobutyric acidA and glycine inhibition is not required for this effect. Direct depression of glutamatergic excitatory transmission by a postsynaptic action on motor neurons thus may contribute to general anesthesia as defined by immobility in response to a noxious stimulus. PMID:10381800

  18. Influence of early life status epilepticus on the developmental expression profile of the GluA2 subunit of AMPA receptors.

    PubMed

    Szczurowska, E; Ergang, P; Kubová, H; Druga, R; Salaj, M; Mareš, P

    2016-09-01

    AMPA receptors (AMPARs) are responsible for fast excitatory neurotransmission, and their prolonged activation can result in the generation and spread of epileptic seizures. At early stages of postnatal development, the majority of AMPARs are permeable to both Na(+) and Ca(2+) ions. This permeability, which increases neuronal excitability, is due to the lack of the GluA2 subunit, encoded by the GRIA2A gene, and/or the presence of an unedited GluA2 subunit Q/R site (glutamine instead of arginine). Lithium chloride- and pilocarpine-induced status epilepticus (LiCl/Pilo-SE) in rodents represents a model of severe seizures that result in development of temporal lobe epilepsy (TLE). The aim of this study was to determine how LiCl/Pilo-SE induced early in life (at postnatal day 12; P12) alters normal expression of the GRIA2A gene and GluA2 protein. SE was interrupted by an injection of paraldehyde (Para). Control groups were 1) naïve animals, and 2) siblings of SE rats receiving only LiCl and paraldehyde (LiCl/Para). The expression profile of GRIA2A mRNA was determined via qPCR, and GluA2 protein levels were measured by western blotting. The analysis was performed at 3h (protein levels), and then 3-, 6-, 13-, and 60days, following LiCl/Pilo-SE or LiCl/Para injection (i.e. at P12, P15, P18, P25, P72 respectively). Six different brain regions were analyzed: frontal (CXFR), parietal (CXPAR), and occipital (CXOC) cortex, dorsal (HD) and ventral (HV) hippocampus, and thalamus (TH). There was a significant increase in GRIA2A mRNA expression in the CXFR, CXPAR, and CXOC of P18 SE animals. In CXFR and HD, increased expression of GluA2 AMPAR subunit protein was detected, as well as a surge in GRIA2A mRNA and GluA2 protein expression especially at P18. In HD the surge was detected not only during development (P18), but also later in life (P72). Since high levels of GluA2 can be neuroprotective (by decreasing Ca(2+) permeability), our data suggest that the neocortex and dorsal

  19. AMPA/NMDA cooperativity and integration during a single synaptic event.

    PubMed

    Di Maio, Vito; Ventriglia, Francesco; Santillo, Silvia

    2016-10-01

    Coexistence of AMPA and NMDA receptors in glutamatergic synapses leads to a cooperative effect that can be very complex. This effect is dependent on many parameters including the relative and absolute number of the two types of receptors and biophysical parameters that can vary among synapses of the same cell. Herein we simulate the AMPA/NMDA cooperativity by using different number of the two types of receptors and considering the effect of the spine resistance on the EPSC production. Our results show that the relative number of NMDA with respect to AMPA produces a different degree of cooperation which depends also on the spine resistance. PMID:27299885

  20. Brain-derived neurotrophic factor activation of CaM-kinase kinase via transient receptor potential canonical channels induces the translation and synaptic incorporation of GluA1-containing calcium-permeable AMPA receptors.

    PubMed

    Fortin, Dale A; Srivastava, Taasin; Dwarakanath, Diya; Pierre, Philippe; Nygaard, Sean; Derkach, Victor A; Soderling, Thomas R

    2012-06-13

    Glutamatergic synapses in early postnatal development transiently express calcium-permeable AMPA receptors (CP-AMPARs). Although these GluA2-lacking receptors are essential and are elevated in response to brain-derived neurotrophic factor (BDNF), little is known regarding molecular mechanisms that govern their expression and synaptic insertion. Here we show that BDNF-induced GluA1 translation in rat primary hippocampal neurons requires the activation of mammalian target of rapamycin (mTOR) via calcium calmodulin-dependent protein kinase kinase (CaMKK). Specifically, BDNF-mediated phosphorylation of threonine 308 (T308) in AKT, a known substrate of CaMKK and an upstream activator of mTOR-dependent translation, was prevented by (1) pharmacological inhibition of CaMKK with STO-609, (2) overexpression of a dominant-negative CaMKK, or (3) short hairpin-mediated knockdown of CaMKK. GluA1 surface expression induced by BDNF, as assessed by immunocytochemistry using an extracellular N-terminal GluA1 antibody or by surface biotinylation, was impaired following knockdown of CaMKK or treatment with STO-609. Activation of CaMKK by BDNF requires transient receptor potential canonical (TRPC) channels as SKF-96365, but not the NMDA receptor antagonist d-APV, prevented BDNF-induced GluA1 surface expression as well as phosphorylation of CaMKI, AKT(T308), and mTOR. Using siRNA we confirmed the involvement of TRPC5 and TRPC6 subunits in BDNF-induced AKT(T308) phosphorylation. The BDNF-induced increase in mEPSC was blocked by IEM-1460, a selected antagonist of CP-AMPARs, as well as by the specific repression of acute GluA1 translation via siRNA to GluA1 but not GluA2. Together these data support the conclusion that newly synthesized GluA1 subunits, induced by BDNF, are readily incorporated into synapses where they enhance the expression of CP-AMPARs and synaptic strength. PMID:22699894

  1. Acid-sensitive ion channels and receptors.

    PubMed

    Holzer, Peter

    2009-01-01

    Acidosis is a noxious condition associated with inflammation, ischaemia or defective acid containment. As a consequence, acid sensing has evolved as an important property of afferent neurons with unmyelinated and thinly myelinated nerve fibres. Protons evoke multiple currents in primary afferent neurons, which are carried by several acid-sensitive ion channels. Among these, acid-sensing ion channels (ASICs) and transient receptor potential (TRP) vanilloid-1 (TRPV1) ion channels have been most thoroughly studied. ASICs survey moderate decreases in extracellular pH, whereas TRPV1 is activated only by severe acidosis resulting in pH values below 6. Two-pore-domain K(+) (K(2P)) channels are differentially regulated by small deviations of extra- or intracellular pH from physiological levels. Other acid-sensitive channels include TRPV4, TRPC4, TRPC5, TRPP2 (PKD2L1), ionotropic purinoceptors (P2X), inward rectifier K(+) channels, voltage-activated K(+) channels, L-type Ca(2+) channels, hyperpolarization-activated cyclic nucleotide gated channels, gap junction channels, and Cl(-) channels. In addition, acid-sensitive G protein coupled receptors have also been identified. Most of these molecular acid sensors are expressed by primary sensory neurons, although to different degrees and in various combinations. Emerging evidence indicates that many of the acid-sensitive ion channels and receptors play a role in acid sensing, acid-induced pain and acid-evoked feedback regulation of homeostatic reactions. The existence and apparent redundancy of multiple pH surveillance systems attests to the concept that acid-base regulation is a vital issue for cell and tissue homeostasis. Since upregulation and overactivity of acid sensors appear to contribute to various forms of chronic pain, acid-sensitive ion channels and receptors are considered as targets for novel analgesic drugs. This approach will only be successful if the pathological implications of acid sensors can be differentiated

  2. Acid-sensitive ion channels and receptors

    PubMed Central

    Holzer, Peter

    2015-01-01

    Acidosis is a noxious condition associated with inflammation, ischaemia or defective acid containment. As a consequence, acid sensing has evolved as an important property of afferent neurons with unmyelinated and thinly myelinated nerve fibres. Protons evoke multiple currents in primary afferent neurons, which are carried by several acid-sensitive ion channels. Among these, acid-sensing ion channels (ASICs) and transient receptor potential (TRP) vanilloid-1 (TRPV1) ion channels have been most thoroughly studied. ASICs survey moderate decreases in extracellular pH whereas TRPV1 is activated only by severe acidosis resulting in pH values below 6. Two-pore domain K+ (K2P) channels are differentially regulated by small deviations of extra- or intracellular pH from physiological levels. Other acid-sensitive channels comprise TRPV4, TRPC4, TRPC5, TRPP2 (PKD2L1), ionotropic purinoceptors (P2X), inward rectifier K+ channels, voltage-activated K+ channels, L-type Ca2+ channels, hyperpolarization-activated cyclic nucleotide-gated channels, gap junction channels, and Cl− channels. In addition, acid-sensitive G protein-coupled receptors have also been identified. Most of these molecular acid sensors are expressed by primary sensory neurons, although to different degrees and in various combinations. Emerging evidence indicates that many of the acid-sensitive ion channels and receptors play a role in acid sensing, acid-induced pain and acid-evoked feedback regulation of homeostatic reactions. The existence and apparent redundancy of multiple pH surveillance systems attests to the concept that acid-base regulation is a vital issue for cell and tissue homeostasis. Since upregulation and overactivity of acid sensors appear to contribute to various forms of chronic pain, acid-sensitive ion channels and receptors are considered as targets for novel analgesic drugs. This approach will only be successful if the pathological implications of acid sensors can be differentiated

  3. Synthesis and biological evaluation of a new set of pyrazolo[1,5-c]quinazolines as glycine/N-methyl-D-aspartic acid receptor antagonists.

    PubMed

    Varano, Flavia; Catarzi, Daniela; Colotta, Vittoria; Poli, Daniela; Filacchioni, Guido; Galli, Alessandro; Costagli, Chiara

    2009-08-01

    Previous studies have shown that 8-chloro-5,6-dihydro-5-oxo-pyrazolo[1,5-c]quinazoline-2-carboxylates (PQZ series) represent a family of glycine/N-methyl-D-aspartic acid (NMDA) and/or (R,S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) and/or kainic acid (KA) receptor antagonists. Moreover, some groups have been identified that introduced in suitable positions of the PQZ 2-carboxylate framework shift affinity and selectivity toward glycine/NMDA receptor. These substituents are a carboxylate function at position-1 and/or a chlorine atom at position-9. In this paper we report a study on some new 5,6-dihydro-5-oxo-pyrazolo[1,5-c]quinazoline-1-carboxylates bearing at position-2 a lipophilic amide group or lacking substituent at this same position. All the newly synthesised compounds were evaluated for their binding at glycine/NMDA, AMPA and KA receptors. These studies led to the identification of some new PQZ derivatives endowed with good glycine/NMDA receptor affinity and selectivity and to better definition of the structure-activity relationship (SAR) of this class of compounds. PMID:19652407

  4. Hydrodynamic and pharmacological characterization of putative alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate-sensitive L-glutamate receptors solubilized from pig brain.

    PubMed Central

    Wu, T Y; Chang, Y C

    1994-01-01

    L-[3H]Glutamate binding sites with characteristics resembling that of membrane-bound alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate-subtype L-glutamate receptors have been solubilized from pig brain synaptic junctions by Triton X-114. Binding of [3H]AMPA to these soluble sites in the presence of KSCN results in a curvilinear Scatchard plot that can be resolved into a high-affinity component and a low-affinity component. These Triton-X-114-solubilized sites can be further separated into two species of binding sites by gel-filtration chromatography or sucrose-density-gradient centrifugation. The pharmacological profiles of these two species of binding site are almost identical, and the rank orders of potency for glutamatergic drugs in displacing L-[3H]glutamate binding to these sites are quisqualate > 6,7-dinitroquinoxaline-2,3-dione > 6-cyano-7-nitroquinoxaline-2,3-dione > AMPA > L-glutamate > kainate >> N-methyl-D-aspartate = L-2-amino-4-phosphonobutyrate. Both sites are found to bind [3H]AMPA, and in the presence of KSCN the binding activities are significantly enhanced. Analysis of the hydrodynamic behaviour of these binding sites by sucrose-density-gradient centrifugation in H2O- and 2H2O-based solvents and gel-filtration chromatography has revealed that one of these sites (Stokes radius 8.3 nm, sedimentation coefficient 18.5 S) consists of 562 kDa protein and 281 kDa detergent, and the other site (Stokes radius 9.6 nm, sedimentation coefficient 13.4 S) consists of 352 kDa protein and 569 kDa detergent. Frictional coefficients of these sites indicate that these receptor-detergent complexes are asymmetrical in structure, consistent with large transmembrane proteins. PMID:7516151

  5. Hydrodynamic and pharmacological characterization of putative alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate-sensitive L-glutamate receptors solubilized from pig brain.

    PubMed

    Wu, T Y; Chang, Y C

    1994-06-01

    L-[3H]Glutamate binding sites with characteristics resembling that of membrane-bound alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate-subtype L-glutamate receptors have been solubilized from pig brain synaptic junctions by Triton X-114. Binding of [3H]AMPA to these soluble sites in the presence of KSCN results in a curvilinear Scatchard plot that can be resolved into a high-affinity component and a low-affinity component. These Triton-X-114-solubilized sites can be further separated into two species of binding sites by gel-filtration chromatography or sucrose-density-gradient centrifugation. The pharmacological profiles of these two species of binding site are almost identical, and the rank orders of potency for glutamatergic drugs in displacing L-[3H]glutamate binding to these sites are quisqualate > 6,7-dinitroquinoxaline-2,3-dione > 6-cyano-7-nitroquinoxaline-2,3-dione > AMPA > L-glutamate > kainate > N-methyl-D-aspartate = L-2-amino-4-phosphonobutyrate. Both sites are found to bind [3H]AMPA, and in the presence of KSCN the binding activities are significantly enhanced. Analysis of the hydrodynamic behaviour of these binding sites by sucrose-density-gradient centrifugation in H2O- and 2H2O-based solvents and gel-filtration chromatography has revealed that one of these sites (Stokes radius 8.3 nm, sedimentation coefficient 18.5 S) consists of 562 kDa protein and 281 kDa detergent, and the other site (Stokes radius 9.6 nm, sedimentation coefficient 13.4 S) consists of 352 kDa protein and 569 kDa detergent. Frictional coefficients of these sites indicate that these receptor-detergent complexes are asymmetrical in structure, consistent with large transmembrane proteins. PMID:7516151

  6. AMPA experimental communications systems

    NASA Technical Reports Server (NTRS)

    Beckerman, D.; Fass, S.; Keon, T.; Sielman, P.

    1982-01-01

    The program was conducted to demonstrate the satellite communication advantages of Adaptive Phased Array Technology. A laboratory based experiment was designed and implemented to demonstrate a low earth orbit satellite communications system. Using a 32 element, L-band phased array augmented with 4 sets of weights (2 for reception and 2 for transmission) a high speed digital processing system and operating against multiple user terminals and interferers, the AMPA system demonstrated: communications with austere user terminals, frequency reuse, communications in the face of interference, and geolocation. The program and experiment objectives are described, the system hardware and software/firmware are defined, and the test performed and the resultant test data are presented.

  7. How Ca2+-permeable AMPA receptors, the kinase PKA, and the phosphatase PP2B are intertwined in synaptic LTP and LTD.

    PubMed

    Hell, Johannes W

    2016-01-01

    Both synaptic long-term potentiation (LTP) and long-term depression (LTD) are thought to be critical for memory formation. Dell'Acqua and co-workers now demonstrate that transient postsynaptic incorporation of Ca(2+)-permeable (CP) α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) is required for LTD in the exemplary hippocampal CA1 region in 2-week-old mice. Mechanistically, LTD depends on AKAP150-anchored protein kinase A (PKA) to promote the initial functional recruitment of CP-AMPARs during LTD induction and on AKAP150-anchored protein phosphatase 2B (PP2B) to trigger their subsequent removal as part of the lasting depression of synaptic transmission. PMID:27117250

  8. Enhanced long term potentiation and decreased AMPA receptor desensitization in the acute period following a single kainate induced early life seizure.

    PubMed

    O'Leary, Heather; Bernard, Paul B; Castano, Anna M; Benke, Tim A

    2016-03-01

    Neonatal seizures are associated with long term disabilities including epilepsy and cognitive deficits. Using a neonatal seizure rat model that does not develop epilepsy, but develops a phenotype consistent with other models of intellectual disability (ID) and autism spectrum disorders (ASD), we sought to isolate the acute effects of a single episode of early life seizure on hippocampal CA1 synaptic development and plasticity. We have previously shown chronic changes in glutamatergic synapses, loss of long term potentiation (LTP) and enhanced long term depression (LTD), in the adult male rat ~50days following kainic acid (KA) induced early life seizure (KA-ELS) in post-natal (P) 7day old male Sprague-Dawley rats. In the present work, we examined the electrophysiological properties and expression levels of glutamate receptors in the acute period, 2 and 7days, post KA-ELS. Our results show for the first time enhanced LTP 7days after KA-ELS, but no change 2days post KA-ELS. Additionally, we report that ionotropic α-amino-3-hydroxy-5-methyl-isoxazole-propionic acid type glutamate receptor (AMPAR) desensitization is decreased in the same time frame, with no changes in AMPAR expression, phosphorylation, or membrane insertion. Inappropriate enhancement of the synaptic connections in the acute period after the seizure could alter the normal patterning of synaptic development in the hippocampus during this critical period and contribute to learning deficits. Thus, this study demonstrates a novel mechanism by which KA-ELS alters early network properties that potentially lead to adverse outcomes. PMID:26706598

  9. The Effect of Glutamate Receptor Agonists on Mouse Retinal Astrocyte [Ca2+]i

    PubMed Central

    Blandford, Stephanie N.

    2016-01-01

    Calcium-imaging techniques were used to determine if mouse retinal astrocytes in situ respond to agonists of ionotropic (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, AMPA; N-methyl-D-aspartate, NMDA) and metabotropic (S-3,5-dihydroxyphenylglycine, DHPG; trans-1-amino-1,3-cyclopentanedicarboxylic acid, ACPD) glutamate receptors. In most cases we found no evidence that retinal astrocyte intracellular calcium ion concentration ([Ca2+]i) increased in response to these glutamate agonists. The one exception was AMPA that increased [Ca2+]i in some, but not all, mouse retinal astrocytes in situ. However, AMPA did not increase [Ca2+]i in mouse retinal astrocytes in vitro, suggesting that the effect of AMPA in situ may be indirect. PMID:27413752

  10. Developmental expression of retinoic acid receptors (RARs)

    PubMed Central

    Dollé, Pascal

    2009-01-01

    Here, I review the developmental expression features of genes encoding the retinoic acid receptors (RARs) and the 'retinoid X' or rexinoid receptors (RXRs). The first detailed expression studies were performed in the mouse over two decades ago, following the cloning of the murine Rar genes. These studies revealed complex expression features at all stages of post-implantation development, one receptor gene (Rara) showing widespread expression, the two others (Rarb and Rarg) with highly regionalized and/or cell type-specific expression in both neural and non-neural tissues. Rxr genes also have either widespread (Rxra, Rxrb), or highly-restricted (Rxrg) expression patterns. Studies performed in zebrafish and Xenopus demonstrated expression of Rar and Rxr genes (both maternal and zygotic), at early pre-gastrulation stages. The eventual characterization of specific enzymes involved in the synthesis of retinoic acid (retinol/retinaldehyde dehydrogenases), or the triggering of its catabolism (CYP26 cytochrome P450s), all of them showing differential expression patterns, led to a clearer understanding of the phenomenons regulated by retinoic acid signaling during development. Functional studies involving targeted gene disruptions in the mouse, and additional approaches such as dominant negative receptor expression in other models, have pinpointed the specific, versus partly redundant, roles of the RARs and RXRs in many developing organ systems. These pleiotropic roles are summarized hereafter in relationship to the receptors’ expression patterns. PMID:19471585

  11. Interactions of methoxyacetic acid with androgen receptor

    SciTech Connect

    Bagchi, Gargi; Hurst, Christopher H.; Waxman, David J.

    2009-07-15

    Endocrine disruptive compounds (EDC) alter hormone-stimulated, nuclear receptor-dependent physiological and developmental processes by a variety of mechanisms. One recently identified mode of endocrine disruption is through hormone sensitization, where the EDC modulates intracellular signaling pathways that control nuclear receptor function, thereby regulating receptor transcriptional activity indirectly. Methoxyacetic acid (MAA), the primary, active metabolite of the industrial solvent ethylene glycol monomethyl ether and a testicular toxicant, belongs to this EDC class. Modulation of nuclear receptor activity by MAA could contribute to the testicular toxicity associated with MAA exposure. In the present study, we evaluated the impact of MAA on the transcriptional activity of several nuclear receptors including the androgen receptor (AR), which plays a pivotal role in the development and maturation of spermatocytes. AR transcriptional activity is shown to be increased by MAA through a tyrosine kinase signaling pathway that involves PI3-kinase. In a combinatorial setting with AR antagonists, MAA potentiated the AR response without significantly altering the EC{sub 50} for androgen responsiveness, partially alleviating the antagonistic effect of the anti-androgens. Finally, MAA treatment of TM3 mouse testicular Leydig cells markedly increased the expression of Cyp17a1 and Shbg while suppressing Igfbp3 expression by {approx} 90%. Deregulation of these genes may alter androgen synthesis and action in a manner that contributes to MAA-induced testicular toxicity.

  12. Alterations in Hippocampal Oxidative Stress, Expression of AMPA Receptor GluR2 Subunit and Associated Spatial Memory Loss by Bacopa monnieri Extract (CDRI-08) in Streptozotocin-Induced Diabetes Mellitus Type 2 Mice

    PubMed Central

    Pandey, Surya P.; Singh, Hemant K.; Prasad, S.

    2015-01-01

    Bacopa monnieri extract has been implicated in the recovery of memory impairments due to various neurological disorders in animal models and humans. However, the precise molecular mechanism of the role of CDRI-08, a well characterized fraction of Bacopa monnieri extract, in recovery of the diabetes mellitus-induced memory impairments is not known. Here, we demonstrate that DM2 mice treated orally with lower dose of CDRI-08 (50- or 100 mg/kg BW) is able to significantly enhance spatial memory in STZ-DM2 mice and this is correlated with a significant decline in oxidative stress and up regulation of the AMPA receptor GluR2 subunit gene expression in the hippocampus. Treatment of DM2 mice with its higher dose (150 mg/kg BW or above) shows anti-diabetic effect in addition to its ability to recover the spatial memory impairment by reversing the DM2-induced elevated oxidative stress and decreased GluR2 subunit expression near to their values in normal and CDRI-08 treated control mice. Our results provide evidences towards molecular basis of the memory enhancing and anti diabetic role of the Bacopa monnieri extract in STZ-induced DM2 mice, which may have therapeutic implications. PMID:26161865

  13. A patch clamp study of the effects of ciprofloxacin and biphenyl acetic acid on rat hippocampal neurone GABAA and ionotropic glutamate receptors.

    PubMed

    Halliwell, R F; Davey, P G; Lambert, J J

    1995-12-01

    The neurotoxic effects of 4-quinolones alone and in combination with certain non-steroidal anti-inflammatory drugs (NSAIDs) may be related to an interaction at GABAA and/or ionotropic glutamate receptors. In the present study, the effects of the fluoroquinolone, ciprofloxacin, alone and in combination with the NSAID, biphenyl acetic acid (BPAA), were examined on GABAA-, NMDA-, AMPA-, and kainate-evoked current responses recorded from cultured rat hippocampal neurones, using the whole cell patch clamp technique. GABA-evoked currents were reversibly inhibited by bicuculline (3 microM) and ciprofloxacin (100 microM) to 11 +/- 5 and 38 +/- 7% of control, respectively. BPAA (100 microM) had little affect on the GABA current (the response was 82 +/- 4% of control) but enhanced the inhibitory potency of ciprofloxacin by approx. 3000-fold. The antagonist effects of ciprofloxacin (30 microM) and ciprofloxacin (0.03 microM) together with BPAA (100 microM) on the GABA-evoked current were not voltage-dependent. Whole cell currents evoked by NMDA, AMPA or kainate were little influenced by ciprofloxacin (100 microM), BPAA (100 microM), or ciprofloxacin plus BPAA (both at 100 microM); the responses being > or = 90% of control in all cases. These data suggest that the proconvulsant effects of quinolones when combined with BPAA may be related to antagonism of central GABAA receptors but not to an interaction at ionotropic glutamate receptors. PMID:8788959

  14. Evolution of retinoic acid receptors and retinoic acid signaling.

    PubMed

    Gutierrez-Mazariegos, Juliana; Schubert, Michael; Laudet, Vincent

    2014-01-01

    Retinoic acid (RA) is a vitamin A-derived morphogen controlling important developmental processes in vertebrates, and more generally in chordates, including axial patterning and tissue formation and differentiation. In the embryo, endogenous RA levels are controlled by RA synthesizing and degrading enzymes and the RA signal is transduced by two retinoid receptors: the retinoic acid receptor (RAR) and the retinoid X receptor (RXR). Both RAR and RXR are members of the nuclear receptor superfamily of ligand-activated transcription factors and mainly act as heterodimers to activate the transcription of target genes in the presence of their ligand, all-trans RA. This signaling pathway was long thought to be a chordate innovation, however, recent findings of gene homologs involved in RA signaling in the genomes of a wide variety of non-chordate animals, including ambulacrarians (sea urchins and acorn worms) and lophotrochozoans (annelids and mollusks), challenged this traditional view and suggested that the RA signaling pathway might have a more ancient evolutionary origin than previously thought. In this chapter, we discuss the evolutionary history of the RA signaling pathway, and more particularly of the RARs, which might have experienced independent gene losses and duplications in different animal lineages. In sum, the available data reveal novel insights into the origin of the RA signaling pathway as well as into the evolutionary history of the RARs. PMID:24962881

  15. Paradoxical proepileptic response to NMDA receptor blockade linked to cortical interneuron defect in stargazer mice.

    PubMed

    Maheshwari, Atul; Nahm, Walter K; Noebels, Jeffrey L

    2013-01-01

    Paradoxical seizure exacerbation by anti-epileptic medication is a well-known clinical phenomenon in epilepsy, but the cellular mechanisms remain unclear. One possibility is enhanced network disinhibition by unintended suppression of inhibitory interneurons. We investigated this hypothesis in the stargazer mouse model of absence epilepsy, which bears a mutation in stargazin, an AMPA receptor trafficking protein. If AMPA signaling onto inhibitory GABAergic neurons is impaired, their activation by glutamate depends critically upon NMDA receptors. Indeed, we find that stargazer seizures are exacerbated by NMDA receptor blockade with CPP (3-[(R)-2-carboxypiperazin-4-yl]-prop-2-enyl-1-phosphonic acid) and MK-801, whereas other genetic absence epilepsy models are sensitive to these antagonists. To determine how an AMPA receptor trafficking defect could lead to paradoxical network activation, we analyzed stargazin and AMPA receptor localization and found that stargazin is detected exclusively in parvalbumin-positive (PV (+)) fast-spiking interneurons in somatosensory cortex, where it is co-expressed with the AMPA receptor subunit GluA4. PV (+) cortical interneurons in stargazer show a near twofold decrease in the dendrite:soma GluA4 expression ratio compared to wild-type (WT) littermates. We explored the functional consequence of this trafficking defect on network excitability in neocortical slices. Both NMDA receptor antagonists suppressed 0 Mg (2) (+)-induced network discharges in WT but augmented bursting in stargazer cortex. Interneurons mediate this paradoxical response, since the difference between genotypes was masked by GABA receptor blockade. Our findings provide a cellular locus for AMPA receptor-dependent signaling defects in stargazer cortex and define an interneuron-dependent mechanism for paradoxical seizure exacerbation in absence epilepsy. PMID:24065886

  16. Age-Dependent Modifications of AMPA Receptor Subunit Expression Levels and Related Cognitive Effects in 3xTg-AD Mice.

    PubMed

    Cantanelli, Pamela; Sperduti, Samantha; Ciavardelli, Domenico; Stuppia, Liborio; Gatta, Valentina; Sensi, Stefano Luca

    2014-01-01

    GluA1, GluA2, GluA3, and GluA4 are the constitutive subunits of amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), the major mediators of fast excitatory transmission in the mammalian central nervous system. Most AMPARs are Ca(2+)-impermeable because of the presence of the GluA2 subunit. GluA2 mRNA undergoes an editing process that results in a Q-R substitution, a key factor in the regulation of AMPAR Ca(2+)-permeability. AMPARs lacking GluA2 or containing the unedited subunit are permeable to Ca(2+) and Zn(2+). The phenomenon physiologically modulates synaptic plasticity while, in pathologic conditions, leads to increased vulnerability to excitotoxic neuronal death. Given the importance of these subunits, we have therefore evaluated possible associations between changes in expression levels of AMPAR subunits and development of cognitive deficits in 3xTg-AD mice, a widely investigated transgenic mouse model of Alzheimer's disease (AD). With quantitative real-time PCR analysis, we assayed hippocampal mRNA expression levels of GluA1-4 subunits occurring in young [3 months of age (m.o.a.)] and old (12 m.o.a) Tg-AD mice and made comparisons with levels found in age-matched wild type (WT) mice. Efficiency of GluA2 RNA editing was also analyzed. All animals were cognitively tested for learning short- and long-term spatial memory with the Morris Water Maze (MWM) navigation task. 3xTg-AD mice showed age-dependent decreases of mRNA levels for all the AMPAR subunits, with the exception of GluA2. Editing remained fully efficient with aging in 3xTg-AD and WT mice. A one-to-one correlation analysis between MWM performances and GluA1-4 mRNA expression profiles showed negative correlations between GluA2 levels and MWM performances in young 3xTg-AD mice. On the contrary, positive correlations between GluA2 mRNA and MWM performances were found in young WT mice. Our data suggest that increases of AMPARs that contain GluA1, GluA3, and GluA4 subunits may help in

  17. Age-Dependent Modifications of AMPA Receptor Subunit Expression Levels and Related Cognitive Effects in 3xTg-AD Mice

    PubMed Central

    Cantanelli, Pamela; Sperduti, Samantha; Ciavardelli, Domenico; Stuppia, Liborio; Gatta, Valentina; Sensi, Stefano Luca

    2014-01-01

    GluA1, GluA2, GluA3, and GluA4 are the constitutive subunits of amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), the major mediators of fast excitatory transmission in the mammalian central nervous system. Most AMPARs are Ca2+-impermeable because of the presence of the GluA2 subunit. GluA2 mRNA undergoes an editing process that results in a Q–R substitution, a key factor in the regulation of AMPAR Ca2+-permeability. AMPARs lacking GluA2 or containing the unedited subunit are permeable to Ca2+ and Zn2+. The phenomenon physiologically modulates synaptic plasticity while, in pathologic conditions, leads to increased vulnerability to excitotoxic neuronal death. Given the importance of these subunits, we have therefore evaluated possible associations between changes in expression levels of AMPAR subunits and development of cognitive deficits in 3xTg-AD mice, a widely investigated transgenic mouse model of Alzheimer’s disease (AD). With quantitative real-time PCR analysis, we assayed hippocampal mRNA expression levels of GluA1–4 subunits occurring in young [3 months of age (m.o.a.)] and old (12 m.o.a) Tg-AD mice and made comparisons with levels found in age-matched wild type (WT) mice. Efficiency of GluA2 RNA editing was also analyzed. All animals were cognitively tested for learning short- and long-term spatial memory with the Morris Water Maze (MWM) navigation task. 3xTg-AD mice showed age-dependent decreases of mRNA levels for all the AMPAR subunits, with the exception of GluA2. Editing remained fully efficient with aging in 3xTg-AD and WT mice. A one-to-one correlation analysis between MWM performances and GluA1–4 mRNA expression profiles showed negative correlations between GluA2 levels and MWM performances in young 3xTg-AD mice. On the contrary, positive correlations between GluA2 mRNA and MWM performances were found in young WT mice. Our data suggest that increases of AMPARs that contain GluA1, GluA3, and GluA4 subunits may help in

  18. A role of ADAR2 and RNA editing of glutamate receptors in mood disorders and schizophrenia

    PubMed Central

    2014-01-01

    Background Pre-mRNAs of 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)-propanoic acid (AMPA)/kainate glutamate receptors undergo post-transcriptional modification known as RNA editing that is mediated by adenosine deaminase acting on RNA type 2 (ADAR2). This modification alters the amino acid sequence and function of the receptor. Glutamatergic signaling has been suggested to have a role in mood disorders and schizophrenia, but it is unknown whether altered RNA editing of AMPA/kainate receptors has pathophysiological significance in these mental disorders. In this study, we found that ADAR2 expression tended to be decreased in the postmortem brains of patients with schizophrenia and bipolar disorder. Results Decreased ADAR2 expression was significantly correlated with decreased editing of the R/G sites of AMPA receptors. In heterozygous Adar2 knockout mice (Adar2+/− mice), editing of the R/G sites of AMPA receptors was decreased. Adar2+/− mice showed a tendency of increased activity in the open-field test and a tendency of resistance to immobility in the forced swimming test. They also showed enhanced amphetamine-induced hyperactivity. There was no significant difference in amphetamine-induced hyperactivity between Adar2+/− and wild type mice after the treatment with an AMPA/kainate receptor antagonist, 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline. Conclusions These findings collectively suggest that altered RNA editing efficiency of AMPA receptors due to down-regulation of ADAR2 has a possible role in the pathophysiology of mental disorders. PMID:24443933

  19. Urban contributions of glyphosate and its degradate AMPA to streams in the United States

    USGS Publications Warehouse

    Kolpin, D.W.; Thurman, E.M.; Lee, E.A.; Meyer, M.T.; Furlong, E.T.; Glassmeyer, S.T.

    2006-01-01

    Glyphosate is the most widely used herbicide in the world, being routinely applied to control weeds in both agricultural and urban settings. Microbial degradation of glyphosate produces aminomethyl phosphonic acid (AMPA). The high polarity and water-solubility of glyphosate and AMPA has, until recently, made their analysis in water samples problematic. Thus, compared to other herbicides (e.g. atrazine) there are relatively few studies on the environmental occurrence of glyphosate and AMPA. In 2002, treated effluent samples were collected from 10 wastewater treatment plants (WWTPs) to study the occurrence of glyphosate and AMPA. Stream samples were collected upstream and downstream of the 10 WWTPs. Two reference streams were also sampled. The results document the apparent contribution of WWTP effluent to stream concentrations of glyphosate and AMPA, with roughly a two-fold increase in their frequencies of detection between stream samples collected upstream and those collected downstream of the WWTPs. Thus, urban use of glyphosate contributes to glyphosate and AMPA concentrations in streams in the United States. Overall, AMPA was detected much more frequently (67.5%) compared to glyphosate (17.5%).

  20. A retinoic acid receptor-specific element controls the retinoic acid receptor-beta promoter.

    PubMed

    Hoffmann, B; Lehmann, J M; Zhang, X K; Hermann, T; Husmann, M; Graupner, G; Pfahl, M

    1990-11-01

    The morphogen retinoic acid (RA) regulates gene transcription by interacting with specific nuclear receptors that recognize DNA sequences near responsive promoters. While much has recently been learned about the nuclear receptor proteins, little is known about the genes that are directly regulated by RA and their cis-acting response elements recognized by these receptors. Here we have analyzed the RA receptor-beta (RAR beta) gene promoter that is controlled by RA. We find that a RA-responsive element (RARE) is located adjacent to the TATA box. The RARE shows a direct repeat symmetry which is essential for its function. While thyroid hormone-responsive elements can also function as RAR response elements, we show here that this RARE is activated by endogenous RARs and RAR beta, but cannot be regulated by thyroid hormone receptors and other known nuclear receptors. In addition, we find that RAR gamma is a poor activator of this RARE. However, the response element is bound with high affinity by both RAR beta and RAR gamma as well as by thyroid hormone receptors. Thus, interaction between specific response elements and receptors is insufficient for gene activation. PMID:2177841

  1. AMPA/Kainate, NMDA, and Dopamine D1 Receptor Function in the Nucleus Accumbens Core: A Context-Limited Role in the Encoding and Consolidation of Instrumental Memory

    ERIC Educational Resources Information Center

    Hernandez, Pepe J.; Andrzejewski, Matthew E.; Sadeghian, Kenneth; Panksepp, Jules B.; Kelley, Ann E.

    2005-01-01

    Neural integration of glutamate- and dopamine-coded signals within the nucleus accumbens (NAc) is a fundamental process governing cellular plasticity underlying reward-related learning. Intra-NAc core blockade of NMDA or D1 receptors in rats impairs instrumental learning (lever-pressing for sugar pellets), but it is not known during which phase of…

  2. Nutritional Signaling via Free Fatty Acid Receptors.

    PubMed

    Miyamoto, Junki; Hasegawa, Sae; Kasubuchi, Mayu; Ichimura, Atsuhiko; Nakajima, Akira; Kimura, Ikuo

    2016-01-01

    Excess energy is stored primarily as triglycerides, which are mobilized when demand for energy arises. Dysfunction of energy balance by excess food intake leads to metabolic diseases, such as obesity and diabetes. Free fatty acids (FFAs) provided by dietary fat are not only important nutrients, but also contribute key physiological functions via FFA receptor (FFAR)-mediated signaling molecules, which depend on FFAs' carbon chain length and the ligand specificity of the receptors. Functional analyses have revealed that FFARs are critical for metabolic functions, such as peptide hormone secretion and inflammation, and contribute to energy homeostasis. In particular, recent studies have shown that the administration of selective agonists of G protein-coupled receptor (GPR) 40 and GPR120 improved glucose metabolism and systemic metabolic disorders. Furthermore, the anti-inflammation and energy metabolism effects of short chain FAs have been linked to the activation of GPR41 and GPR43. In this review, we summarize recent progress in research on FFAs and their physiological roles in the regulation of energy metabolism. PMID:27023530

  3. Nutritional Signaling via Free Fatty Acid Receptors

    PubMed Central

    Miyamoto, Junki; Hasegawa, Sae; Kasubuchi, Mayu; Ichimura, Atsuhiko; Nakajima, Akira; Kimura, Ikuo

    2016-01-01

    Excess energy is stored primarily as triglycerides, which are mobilized when demand for energy arises. Dysfunction of energy balance by excess food intake leads to metabolic diseases, such as obesity and diabetes. Free fatty acids (FFAs) provided by dietary fat are not only important nutrients, but also contribute key physiological functions via FFA receptor (FFAR)-mediated signaling molecules, which depend on FFAs’ carbon chain length and the ligand specificity of the receptors. Functional analyses have revealed that FFARs are critical for metabolic functions, such as peptide hormone secretion and inflammation, and contribute to energy homeostasis. In particular, recent studies have shown that the administration of selective agonists of G protein-coupled receptor (GPR) 40 and GPR120 improved glucose metabolism and systemic metabolic disorders. Furthermore, the anti-inflammation and energy metabolism effects of short chain FAs have been linked to the activation of GPR41 and GPR43. In this review, we summarize recent progress in research on FFAs and their physiological roles in the regulation of energy metabolism. PMID:27023530

  4. Impact of subanesthetic doses of ketamine on AMPA-mediated responses in rats: An in vivo electrophysiological study on monoaminergic and glutamatergic neurons

    PubMed Central

    El Iskandrani, Kareem S; Oosterhof, Chris A; Blier, Pierre

    2015-01-01

    The rapid antidepressant action of a subanesthetic dose of ketamine in treatment-resistant patients represents the most striking recent breakthrough in the understanding of the antidepressant response. Evidence demonstrates tight interactions between the glutamatergic and monoaminergic systems. It is thus hypothesized that monoamine systems may play a role in the immediate/rapid effects of ketamine. In vivo electrophysiological recordings were carried in male rats following ketamine administration (10 and 25 mg/kg, i.p.) to first assess its effects on monoaminergic neuron firing. In a second series of experiments, the effects of ketamine administration on α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)- and N-methyl-D-aspartate receptor (NMDA)-evoked responses in hippocampus CA3 pyramidal neurons were also investigated using micro-iontophoretic applications. Although acute (~2 hours) ketamine administration did not affect the mean firing activity of dorsal raphe serotonin and ventral tegmental area dopamine neurons, it did increase that of locus coeruleus norepinephrine neurons. In the latter brain region, while ketamine also enhanced bursting activity, it did increase population activity of dopamine neurons in the ventral tegmental area. These effects of ketamine were prevented by the prior administration of the AMPA receptor antagonist 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide. An increase in AMPA-evoked response of CA3 pyramidal neurons was also observed 30 minutes following acute ketamine administration. The present findings suggest that acute ketamine administration produces a rapid enhancement of catecholaminergic neurons firing activity through an amplification of AMPA transmission. These effects may play a crucial role in the antidepressant effects of ketamine observed shortly following its infusion in depressed patients. PMID:25759403

  5. Differential Expression of AMPA Subunits Induced by NMDA Intrahippocampal Injection in Rats

    PubMed Central

    Fachim, Helene A.; Pereira, Adriana C.; Iyomasa-Pilon, Melina M.; Rosa, Maria L. N. M.

    2016-01-01

    Glutamate is involved in excitotoxic mechanisms by interacting with different receptors. Such interactions result in neuronal death associated with several neurodegenerative disorders of the central nervous system (CNS). The aim of this work was to study the time course of changes in the expression of GluR1 and GluR2 subunits of glutamate amino-acid-3-hydroxy-5-methyl-isoxazol-4-propionic acid (AMPA) receptors in rat hippocampus induced by NMDA intrahippocampal injection. Rats were submitted to stereotaxic surgery for NMDA or saline (control) microinjection into dorsal hippocampus and the parameters were evaluated 24 h, 1, 2, and 4 weeks after injection. The extension and efficacy of the NMDA-induced injury were evaluated by Morris water maze (MWM) behavioral test and Nissl staining. The expression of GluR1 and GluR2 receptors, glial fibrillary acidic protein (GFAP), and neuronal marker (NeuN) was analyzed by immunohistochemistry. It was observed the impairment of learning and memory functions, loss of neuronal cells, and glial proliferation in CA1 area of NMDA compared with control groups, confirming the injury efficacy. In addition, NMDA injection induced distinct changes in GluR1 and GluR2 expression over the time. In conclusion, such changes may be related to the complex mechanism triggered in response to NMDA injection resulting in a local injury and in the activation of neuronal plasticity. PMID:26912994

  6. Postsynaptic VAMP/Synaptobrevin Facilitates Differential Vesicle Trafficking of GluA1 and GluA2 AMPA Receptor Subunits

    PubMed Central

    Hussain, Suleman; Davanger, Svend

    2015-01-01

    Vertebrate organisms adapt to a continuously changing environment by regulating the strength of synaptic connections between brain cells. Excitatory synapses are believed to increase their strength by vesicular insertion of transmitter glutamate receptors into the postsynaptic plasma membrane. These vesicles, however, have never been demonstrated or characterized. For the first time, we show the presence of small vesicles in postsynaptic spines, often closely adjacent to the plasma membrane and PSD (postsynaptic density). We demonstrate that they harbor vesicle-associated membrane protein 2 (VAMP2/synaptobrevin-2) and glutamate receptor subunit 1 (GluA1). Disrupting VAMP2 by tetanus toxin treatment reduces the concentration of GluA1 in the postsynaptic plasma membrane. GluA1/VAMP2-containing vesicles, but not GluA2/VAMP2-vesicles, are concentrated in postsynaptic spines relative to dendrites. Our results indicate that small postsynaptic vesicles containing GluA1 are inserted directly into the spine plasma membrane through a VAMP2-dependent mechanism. PMID:26488171

  7. L-glutamate Receptor In Paramecium

    NASA Astrophysics Data System (ADS)

    Bernal-Martínez, Juan; Ortega-Soto, Arturo

    2004-09-01

    Behavioral, electrophysiological and biochemical experiments were performed in order to establish the presence of a glutamate receptor in the ciliate Paramecium. It was found that an AMPA/KA receptor is functionally expressed in Paramecium and that this receptor is immunologically and fillogenetically related to the AMPA/KA receptor present in vertebrates.

  8. Region- and age-dependent reductions of hippocampal long-term potentiation and NMDA to AMPA ratio in a genetic model of Alzheimer's disease.

    PubMed

    Tozzi, Alessandro; Sclip, Alessandra; Tantucci, Michela; de Iure, Antonio; Ghiglieri, Veronica; Costa, Cinzia; Di Filippo, Massimiliano; Borsello, Tiziana; Calabresi, Paolo

    2015-01-01

    To characterize the mechanisms underlying region- and age-dependent hippocampal synaptic dysfunction in Alzheimer's disease, we used transgenic CRND8 mice, expressing the Swedish-Indiana APP mutation. In 2-month-old mice, no β-amyloid plaques deposition, but the presence of soluble oligomers, were found in CA1 area but not in dentate gyrus (DG). At this age, long-term potentiation (LTP) was reduced selectively in CA1. In 6-month-old mice, the presence of soluble oligomers was accompanied by accumulation of β-amyloid plaques and decreased LTP in CA1 and DG regions. In both regions, the loss of LTP was linked to reduced N-methyl-D-aspartate (NMDA) to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) current ratio. The acetylcholine-esterase inhibitor, neostigmine rescued LTP in CA1 area at early stage of the disease but not after plaques deposition. Conversely, the NMDA receptor antagonist memantine restored LTP selectively in DG at later stages of the disease. Both these effects were associated with a normalization of the NMDA to AMPA ratio. The association between the recovery of LTP and the normalization of the NMDA to AMPA ratio provides information on new possible therapeutic strategies in Alzheimer's disease. PMID:25104560

  9. Water quality of the main tributaries of the Paraná Basin: glyphosate and AMPA in surface water and bottom sediments.

    PubMed

    Ronco, A E; Marino, D J G; Abelando, M; Almada, P; Apartin, C D

    2016-08-01

    The Paraná River, the sixth largest in the world, is the receptor of pollution loads from tributaries traversing urban and industrialized areas plus agricultural expanses, particularly so in the river's middle and lower reaches along the Argentine sector. In the present study, we analyzed and discussed the main water quality parameters, sediment compositions, and content of the herbicide glyphosate plus its metabolite aminomethylphosphonic acid (AMPA) in water and sediments. Samples were obtained from distal positions in the principal tributaries of the Paraná and the main watercourse during surveys conducted in 2011 and 2012 to monitor the basin. Only 15 % of the water samples contained detectable concentrations of glyphosate at an average concentration of 0.60 μg/L, while no detectable levels of AMPA were observed. The herbicide and metabolite were primarily present in sediments of the middle and lower stretch's tributaries, there occurring at a respective average of 37 and 17 % in samples. The mean detectable concentrations measured were 742 and 521 μg/kg at mean, maximum, and minimum glyphosate/AMPA ratios of 2.76, 7.80, and 0.06, respectively. The detection of both compounds was correlated with the presence of sulfides and copper in the sediment matrix. PMID:27395359

  10. Pharmacology of bile acid receptors: Evolution of bile acids from simple detergents to complex signaling molecules.

    PubMed

    Copple, Bryan L; Li, Tiangang

    2016-02-01

    For many years, bile acids were thought to only function as detergents which solubilize fats and facilitate the uptake of fat-soluble vitamins in the intestine. Many early observations; however, demonstrated that bile acids regulate more complex processes, such as bile acids synthesis and immune cell function through activation of signal transduction pathways. These studies were the first to suggest that receptors may exist for bile acids. Ultimately, seminal studies by many investigators led to the discovery of several bile acid-activated receptors including the farnesoid X receptor, the vitamin D receptor, the pregnane X receptor, TGR5, α5 β1 integrin, and sphingosine-1-phosphate receptor 2. Several of these receptors are expressed outside of the gastrointestinal system, indicating that bile acids may have diverse functions throughout the body. Characterization of the functions of these receptors over the last two decades has identified many important roles for these receptors in regulation of bile acid synthesis, transport, and detoxification; regulation of glucose utilization; regulation of fatty acid synthesis and oxidation; regulation of immune cell function; regulation of energy expenditure; and regulation of neural processes such as gastric motility. Through these many functions, bile acids regulate many aspects of digestion ranging from uptake of essential vitamins to proper utilization of nutrients. Accordingly, within a short time period, bile acids moved beyond simple detergents and into the realm of complex signaling molecules. Because of the important processes that bile acids regulate through activation of receptors, drugs that target these receptors are under development for the treatment of several diseases, including cholestatic liver disease and metabolic syndrome. In this review, we will describe the various bile acid receptors, the signal transduction pathways activated by these receptors, and briefly discuss the physiological processes that

  11. P2X-mediated AMPA receptor internalization and synaptic depression is controlled by two CaMKII phosphorylation sites on GluA1 in hippocampal neurons.

    PubMed

    Pougnet, Johan-Till; Compans, Benjamin; Martinez, Audrey; Choquet, Daniel; Hosy, Eric; Boué-Grabot, Eric

    2016-01-01

    Plasticity at excitatory synapses can be induced either by synaptic release of glutamate or the release of gliotransmitters such as ATP. Recently, we showed that postsynaptic P2X2 receptors activated by ATP released from astrocytes downregulate synaptic AMPAR, providing a novel mechanism by which glial cells modulate synaptic activity. ATP- and lNMDA-induced depression in the CA1 region of the hippocampus are additive, suggesting distinct molecular pathways. AMPARs are homo-or hetero-tetramers composed of GluA1-A4. Here, we first show that P2X2-mediated AMPAR inhibition is dependent on the subunit composition of AMPAR. GluA3 homomers are insensitive and their presence in heteromers alters P2X-mediated inhibition. Using a mutational approach, we demonstrate that the two CaMKII phosphorylation sites S567 and S831 located in the cytoplasmic Loop1 and C-terminal tail of GluA1 subunits, respectively, are critical for P2X2-mediated AMPAR inhibition recorded from co-expressing Xenopus oocytes and removal of surface AMPAR at synapses of hippocampal neurons imaged by the super-resolution dSTORM technique. Finally, using phosphorylation site-specific antibodies, we show that P2X-induced depression in hippocampal slices produces a dephosphorylation of the GluA1 subunit at S567, contrary to NMDAR-mediated LTD. These findings indicate that GluA1 phosphorylation of S567 and S831 is critical for P2X2-mediated AMPAR internalization and ATP-driven synaptic depression. PMID:27624155

  12. Toxicity of AMPA to the earthworm Eisenia andrei Bouché, 1972 in tropical artificial soil.

    PubMed

    Domínguez, Anahí; Brown, George Gardner; Sautter, Klaus Dieter; de Oliveira, Cintia Mara Ribas; de Vasconcelos, Eliane Carvalho; Niva, Cintia Carla; Bartz, Marie Luise Carolina; Bedano, José Camilo

    2016-01-01

    Aminomethylphosphonic acid (AMPA) - one of glyphosate's main metabolites - has been classified as persistent in soils, raising concern regarding the widespread use of glyphosate in agriculture and forestry. Glyphosate may have negative or neutral effects on soil biota, but no information is available on the toxicity of AMPA to soil invertebrates. Therefore our aim was to study the effect of AMPA on mortality and reproduction of the earthworm species Eisenia andrei using standard soil ecotoxicological methods (ISO). Field-relevant concentrations of AMPA had no significant effects on mortality in acute or chronic assays. Except at the highest concentration tested, a significant biomass loss was observed compared to controls in the chronic assay. The number of juveniles and cocoons increased with higher concentrations of AMPA applied, but their mean weights decreased. This mass loss indicates higher sensitivity of juveniles than adults to AMPA. Our results suggest that earthworms coming from parents grown in contaminated soils may have reduced growth, limiting their beneficial roles in key soil ecosystem functions. Nevertheless, further research is needed to better understand the mechanisms underlying the sublethal effects observed here. PMID:26792548

  13. Toxicity of AMPA to the earthworm Eisenia andrei Bouché, 1972 in tropical artificial soil

    PubMed Central

    Domínguez, Anahí; Brown, George Gardner; Sautter, Klaus Dieter; Ribas de Oliveira, Cintia Mara; de Vasconcelos, Eliane Carvalho; Niva, Cintia Carla; Bartz, Marie Luise Carolina; Bedano, José Camilo

    2016-01-01

    Aminomethylphosphonic acid (AMPA) - one of glyphosate’s main metabolites - has been classified as persistent in soils, raising concern regarding the widespread use of glyphosate in agriculture and forestry. Glyphosate may have negative or neutral effects on soil biota, but no information is available on the toxicity of AMPA to soil invertebrates. Therefore our aim was to study the effect of AMPA on mortality and reproduction of the earthworm species Eisenia andrei using standard soil ecotoxicological methods (ISO). Field-relevant concentrations of AMPA had no significant effects on mortality in acute or chronic assays. Except at the highest concentration tested, a significant biomass loss was observed compared to controls in the chronic assay. The number of juveniles and cocoons increased with higher concentrations of AMPA applied, but their mean weights decreased. This mass loss indicates higher sensitivity of juveniles than adults to AMPA. Our results suggest that earthworms coming from parents grown in contaminated soils may have reduced growth, limiting their beneficial roles in key soil ecosystem functions. Nevertheless, further research is needed to better understand the mechanisms underlying the sublethal effects observed here. PMID:26792548

  14. Allosteric modulation of retinal GABA receptors by ascorbic acid

    PubMed Central

    Calero, Cecilia I.; Vickers, Evan; Moraga Cid, Gustavo; Aguayo, Luis G.; von Gersdorff, Henrique; Calvo, Daniel J.

    2011-01-01

    Summary Ionotropic γ-aminobutyric acid receptors (GABAA and GABAC) belong to the cys-loop receptor family of ligand-gated ion channels. GABAC receptors are highly expressed in the retina, mainly localized at the axon terminals of bipolar cells. Ascorbic acid, an endogenous redox agent, modulates the function of diverse proteins, and basal levels of ascorbic acid in the retina are very high. However, the effect of ascorbic acid on retinal GABA receptors has not been studied. Here we show that the function of GABAC and GABAA receptors is regulated by ascorbic acid. Patch-clamp recordings from bipolar cell terminals in goldfish retinal slices revealed that GABAC receptor-mediated currents activated by tonic background levels of extracellular GABA, and GABAC currents elicited by local GABA puffs, are both significantly enhanced by ascorbic acid. In addition, a significant rundown of GABA-puff evoked currents was observed in the absence of ascorbic acid. GABA-evoked Cl- currents mediated by homomeric ρ1 GABAC receptors expressed in Xenopus laevis oocytes were also potentiated by ascorbic acid in a concentration-dependent, stereospecific, reversible, and voltage-independent manner. Studies involving the chemical modification of sulfhydryl groups showed that the two cys-loop cysteines and histidine 141, all located in the ρ1 subunit extracellular domain, each play a key role in the modulation of GABAC receptors by ascorbic acid. Additionally, we show that retinal GABAA IPSCs and heterologously expressed GABAA receptor currents are similarly augmented by ascorbic acid. Our results suggest that ascorbic acid may act as an endogenous agent capable of potentiating GABAergic neurotransmission in the CNS. PMID:21715633

  15. Comparative analyses of lysophosphatidic acid receptor-mediated signaling.

    PubMed

    Fukushima, Nobuyuki; Ishii, Shoichi; Tsujiuchi, Toshifumi; Kagawa, Nao; Katoh, Kazutaka

    2015-06-01

    Lysophosphatidic acid (LPA) is a bioactive lipid mediator that activates G protein-coupled LPA receptors to exert fundamental cellular functions. Six LPA receptor genes have been identified in vertebrates and are classified into two subfamilies, the endothelial differentiation genes (edg) and the non-edg family. Studies using genetically engineered mice, frogs, and zebrafish have demonstrated that LPA receptor-mediated signaling has biological, developmental, and pathophysiological functions. Computational analyses have also identified several amino acids (aa) critical for LPA recognition by human LPA receptors. This review focuses on the evolutionary aspects of LPA receptor-mediated signaling by comparing the aa sequences of vertebrate LPA receptors and LPA-producing enzymes; it also summarizes the LPA receptor-dependent effects commonly observed in mouse, frog, and fish. PMID:25732591

  16. ABA renewal involves enhancements in both GluA2-lacking AMPA receptor activity and GluA1 phosphorylation in the lateral amygdala.

    PubMed

    Park, Kyungjoon; Song, Beomjong; Kim, Jeongyeon; Hong, Ingie; Song, Sangho; Lee, Junuk; Park, Sungmo; Kim, Jihye; An, Bobae; Lee, Hyun Woo; Lee, Seungbok; Kim, Hyun; Lee, Justin C; Lee, Sukwon; Choi, Sukwoo

    2014-01-01

    Fear renewal, the context-specific relapse of fear following fear extinction, is a leading animal model of post-traumatic stress disorders (PTSD) and fear-related disorders. Although fear extinction can diminish fear responses, this effect is restricted to the context where the extinction is carried out, and the extinguished fear strongly relapses when assessed in the original acquisition context (ABA renewal) or in a context distinct from the conditioning and extinction contexts (ABC renewal). We have previously identified Ser831 phosphorylation of GluA1 subunit in the lateral amygdala (LA) as a key molecular mechanism for ABC renewal. However, molecular mechanisms underlying ABA renewal remain to be elucidated. Here, we found that both the excitatory synaptic efficacy and GluA2-lacking AMPAR activity at thalamic input synapses onto the LA (T-LA synapses) were enhanced upon ABA renewal. GluA2-lacking AMPAR activity was also increased during low-threshold potentiation, a potential cellular substrate of renewal, at T-LA synapses. The microinjection of 1-naphtylacetyl-spermine (NASPM), a selective blocker of GluA2-lacking AMPARs, into the LA attenuated ABA renewal, suggesting a critical role of GluA2-lacking AMPARs in ABA renewal. We also found that Ser831 phosphorylation of GluA1 in the LA was increased upon ABA renewal. We developed a short peptide mimicking the Ser831-containing C-tail region of GluA1, which can be phosphorylated upon renewal (GluA1S); thus, the phosphorylated GluA1S may compete with Ser831-phosphorylated GluA1. This GluA1S peptide blocked the low-threshold potentiation when dialyzed into a recorded neuron. The microinjection of a cell-permeable form of GluA1S peptide into the LA attenuated ABA renewal. In support of the GluA1S experiments, a GluA1D peptide (in which the serine at 831 is replaced with a phosphomimetic amino acid, aspartate) attenuated ABA renewal when microinjected into the LA. These findings suggest that enhancements in both the

  17. Acid rain: the relationship between sources and receptors

    SciTech Connect

    Calvert, J.G.

    1988-01-01

    Acid Rain: The Relationship Between Sources and Receptors consists of a collection of papers and discussions from the third annual conference sponsored by the Acid Rain Information Clearinghouse. The conference, held in December 1986, was supported by the Electric Power Research Institute (EPRI), the Gas Research Institute, and the National Acid Precipitation Assessment Program (NAPAP).

  18. Cell-type Specific Development of NMDA Receptors in the Interneurons of Rat Prefrontal Cortex

    PubMed Central

    Wang, Huai-Xing; Gao, Wen-Jun

    2009-01-01

    In the prefrontal cortex, N-methyl-D-aspartic acid (NMDA) receptors are critical not only for normal prefrontal functions but also for the pathological processes of schizophrenia. Little is known, however, about the developmental properties of NMDA receptors in the functionally diverse subpopulations of interneurons. We investigated the developmental changes of NMDA receptors in rat prefrontal interneurons using patch clamp recording in cortical slices. We found that fast-spiking (FS) interneurons exhibited properties of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and NMDA currents distinct from those in regular spiking (RS) and low-threshold spiking (LTS) interneurons, particularly during the adolescent period. In juvenile animals, most (73%) of the FS cells demonstrated both AMPA and NMDA currents. The NMDA currents, however, gradually became undetectable during cortical development, with most (74%) of the FS cells exhibiting no NMDA current in adults. In contrast, AMPA and NMDA currents in RS and LTS interneurons were relatively stable, without significant changes from juveniles to adults. Moreover, even in FS cells with NMDA currents, the NMDA/AMPA ratio dramatically decreased during the adolescent period but returned to juvenile level in adults, compared to the relatively stable ratios in RS and LTS interneurons. These data suggest that FS interneurons in the PFC undergo dramatic changes in glutamatergic receptors during the adolescent period. These properties may make FS cells particularly sensitive and vulnerable to epigenetic stimulation, thus contributing to the onset of many psychiatric disorders, including schizophrenia. PMID:19242405

  19. Metabotropic glutamate receptors depress vagal and aortic baroreceptor signal transmission in the NTS.

    PubMed

    Liu, Z; Chen, C Y; Bonham, A C

    1998-11-01

    We sought to determine whether metabotropic glutamate receptors contribute to frequency-dependent depression of vagal and aortic baroreceptor signal transmission in the nucleus of the solitary tract (NTS) in vivo. In alpha-chloralose-anesthetized rabbits, we determined the number of extracellular action potentials synaptically evoked by low (1 Hz)- or high-frequency vagal (3-20 Hz) or aortic depressor nerve (ADN) (6-80 Hz) stimulation and postsynaptically evoked by the ionotropic glutamate receptor agonist alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). The metabotropic glutamate receptor agonist (2S,1'S, 2'S)-2-(carboxycyclopropyl)glycine (L-CCG-I) attenuated NTS responses monosynaptically evoked by 1-Hz vagus stimulation by 34% (n = 25; P = 0.011), while augmenting AMPA-evoked responses by 64% (n = 17; P = 0.026). The metabotropic glutamate receptor antagonist alpha-methyl-4-phosphonophenylglycine (MPPG) did not affect NTS responses to low-frequency vagal stimulation (n = 11) or AMPA (n = 10) but augmented responses to high-frequency stimulation by 50% (n = 25; P = 0.0001). MPPG also augmented NTS responses to high-frequency ADN stimulation by 35% (n = 9; P = 0.048) but did not affect responses to low-frequency stimulation (n = 9) or AMPA (n = 7). The results suggest that metabotropic glutamate receptors, presumably at presynaptic sites, contribute to frequency-dependent depression of vagal and aortic baroreceptor signal transmission in NTS. PMID:9815076

  20. Effects of Gamma Hydroxybutyric Acid on Inhibition and Excitation in Rat Neocortex

    PubMed Central

    Li, Qiang; Kuhn, Cynthia M.; Wilson, Wilkie A.; Lewis, Darrell V.

    2008-01-01

    The mechanism by which the sedative and amnestic recreational drug gamma hydroxybutyric acid (GHB) acts is controversial. Some studies indicate that it acts at its unique receptor, while others demonstrate effects mediated through the GABAB receptor. We examined the effect of GHB on evoked GABAA receptor mediated mono- and polysynaptic IPSCs as well as on NMDA and AMPA mediated EPSCs in layers II/III pyramidal cells of the frontal cortex of rat brain. One millimolar (mM) GHB suppressed monosynaptic IPSCs by 20%, whereas polysynaptic IPSCs were reduced by 56%. GHB (1mM) also produced a significant suppression of NMDA-mediated EPSCs by 53% compared to 27% suppression of AMPA-mediated EPSCs. All effects of GHB on IPSCs and EPSCs were reversed by the specific GABAB antagonist CGP62349, but not by the GHB receptor antagonist NCS 382. Consistent with a presynaptic site of action, GHB reduced the frequency but not the amplitude of AMPA receptor mediated mEPSCs and had no effect on postsynaptic currents evoked by direct application of NMDA. Finally, even though GHB appeared to be acting at presynaptic GABAB receptors, GHB and the GABAB agonist baclofen appeared to have opposite potencies for depression of NMDA vs AMPA mediated EPSCs. GHB showed a preference for depressing NMDA responses while baclofen more potently suppressed AMPA responses. The suppression of NMDA more than AMPA responses by GHB at intoxicating doses may make it attractive as a recreational drug and may explain why GHB is abused and baclofen is not. PMID:17904295

  1. A Boronic Acid Porphyrin Receptor for Ginsenoside Sensing

    PubMed Central

    Hargrove, Amanda E.; Reyes, Ryan N.; Riddington, Ian; Anslyn, Eric V.; Sessler, Jonathan L.

    2010-01-01

    Ginsenoside detection was pursued through the design of a porphyrin receptor containing two boronic acid units. This receptor was found to undergo different degrees of fluorescence quenching with five ginsenoside guests and an acylated derivative. The trends in the 1:1 binding constants, as well as ESI-HRMS analysis, support a binding mode in which the ginsenoside sugar units are bound to the boronic acid groups while the steroid core and porphyrin ring participate in hydrophobic interactions. PMID:20860384

  2. Distribution of immunoreactive GABA and glutamate receptors in the gustatory portion of the nucleus of the solitary tract in rat.

    PubMed

    King, Michael S

    2003-05-15

    The distribution of glutamate (GLU) and gamma-aminobutyric acid (GABA) receptors within the gustatory portion of the rat nucleus of the solitary tract (gNST) was investigated using immunohistochemical, histological and neural tract tracing techniques. Numerous somata throughout the gNST were immunoreactive for alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and N-methyl-D-aspartate (NMDA) receptors, while few were labeled for kainate receptors. AMPA and NMDA receptors were particularly abundant in the rostral central (RC) subdivision of the gNST, which receives most of the primary afferent input from the oral cavity and contains most of the gNST neurons that project to the parabrachial nuclei (PBN). This finding supports electrophysiological evidence that AMPA and NMDA receptors are involved in responses to orosensory input and indicates that their action may influence ascending taste signals as well. Compared to the ionotropic GLU receptors, few cell bodies were immunoreactive for metabotropic GLU receptors. Somata immunoreactive for GABA(A) and GABA(B) receptors were located throughout the nucleus. The densest neuropil labeling was for GABA(A) receptors in the ventral (V) subnucleus, the gNST subdivision that sends output to brainstem oromotor centers. The distributions of immunolabeling for GLU and GABA receptors imply that different functional roles may exist for specific receptors within this nucleus. PMID:12754086

  3. Proteomic Analysis of α-Amino-3-hydroxy-5-methyl-4-isoxazole Propionate Receptor Complexes*

    PubMed Central

    Kang, Myoung-Goo; Nuriya, Mutsuo; Guo, Yurong; Martindale, Kevin D.; Lee, Daniel Z.; Huganir, Richard L.

    2012-01-01

    The AMPA receptor (AMPA-R) is a major excitatory neurotransmitter receptor in the brain. Identifying and characterizing the neuronal proteins interacting with AMPA-Rs have provided important information about the molecular mechanisms underlying synaptic transmission and plasticity. In this study, to identify more AMPA-R interactors in vivo, we performed proteomic analyses of AMPA-R complexes from the brain. AMPA-R complexes were isolated from the brain through various combinations of biochemical techniques for solubilization, enrichment, and immunoprecipitation. Mass spectrometry analyses of these isolated complexes identified several novel components of the AMPA-R complexes as well as some previously identified components. The identification of these novel components helps to further define the complex mechanisms involved in the regulation of AMPA receptor function and synaptic plasticity. PMID:22753414

  4. Fatty acid activation of peroxisome proliferator-activated receptor (PPAR).

    PubMed

    Bocos, C; Göttlicher, M; Gearing, K; Banner, C; Enmark, E; Teboul, M; Crickmore, A; Gustafsson, J A

    1995-06-01

    Peroxisome proliferators such as clofibric acid, nafenopin, and WY-14,643 have been shown to activate peroxisome proliferator-activated receptor (PPAR), a member of the steroid nuclear receptor superfamily. We have cloned the cDNA from rat that is homologous to that from mouse, which encodes a 97% similar protein. To search for physiologically occurring activators, we established a transcriptional transactivation assay by stably expressing in CHO cells a chimera of rat PPAR and the human glucocorticoid receptor that activates expression of the placental alkaline phosphatase reporter gene under the control of the mouse mammary tumor virus promoter. 150 microM concentrations of arachidonic or linoleic acid but not of dehydroepiandrosterone, cholesterol, or 25-hydroxy-cholesterol, activated the receptor chimera. In addition, saturated fatty acids induced the reporter gene. Shortening the chain length to n = 6 or introduction of an omega-terminal carboxylic group abolished the activation potential of the fatty acid. To test whether a common PPAR binding metabolite might be formed from free fatty acids we tested the effects of differentially beta-oxidizable fatty acids and inhibitors of fatty acid metabolism. The peroxisomal proliferation-inducing, non-beta-oxidizable, tetradecylthioacetic acid activated PPAR to the same extent as the strong peroxisomal proliferator WY-14,643, whereas the homologous beta-oxidizable tetradecylthiopropionic acid was only as potent as a non-substituted fatty acid. Cyclooxygenase inhibitors, radical scavengers or cytochrome P450 inhibitors did not affect activation of PPAR. In conclusion, beta-oxidation is apparently not required for the formation of the PPAR-activating molecule and this moiety might be a fatty acid, its ester with CoA, or a further derivative of the activated fatty acid prior to beta-oxidation of the acyl-CoA ester. PMID:7626496

  5. Bile acid derivatives as ligands of the farnesoid x receptor: molecular determinants for bile acid binding and receptor modulation.

    PubMed

    Gioiello, Antimo; Cerra, Bruno; Mostarda, Serena; Guercini, Chiara; Pellicciari, Roberto; Macchiarulo, Antonio

    2014-01-01

    Bile acids are a peculiar class of steroidal compounds that never cease to amaze. From being simple detergents with a primary role in aiding the absorption of fats and fat-soluble vitamins, bile acids are now widely considered as crucial hormones endowed with genomic and non-genomic functions that are mediated by their interaction with several proteins including the nuclear receptor Farnesoid X Receptor (FXR). Taking advantages of the peculiar properties of bile acids in interacting with the FXR receptor, several biliary derivatives have been synthesized and tested as FXR ligands. The availability of these compounds has contributed to characterize the receptor from a structural, patho-physiological and therapeutic standpoint. Among these, obeticholic acid is a first-in-class FXR agonist that is demonstrating hepatoprotective effects upon FXR activation in patients with liver diseases such as primary biliary cirrhosis and nonalcoholic steatohepatitis. This review provides an historical overview of the rationale behind the discovery of obeticholic acid and chemical tools generated to depict the molecular features and bio-pharmacological relevance of the FXR receptor, as well as to summarize structure-activity relationships of bile acid-based FXR ligands so far reported. PMID:25388535

  6. URBAN CONTRIBUTIONS OF GLYSPHOSATE AND ITS DEGRADATE AMPA TO STREAMS IN THE UNITED STATES

    EPA Science Inventory

    Glyphosate is the most widely used herbicide in the world, being routinely applied to control weeds in both agricultural and urban settings. Microbial degradation of glyphosate produces aminomethyl phosphonic acid (AMPA). The high polarity and water-solubility of glyphosate and A...

  7. Glyphosate-resistant and conventional canola (Brassica napus L.)responses to glyphosate and AMPA treatment

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Glyphosate-resistant (GR) canola expresses two transgenes: 1) the microbial glyphosate oxidase gene (gox) encoding the glyphosate oxidase enzyme (GOX) that metabolizes glyphosate to aminomethylphosphonic acid (AMPA) and 2) cp4 that encodes a GR form of the glyphosate target enzyme 5-enolpyruvylshiki...

  8. [Interactions between dopamine receptor and NMDA/type A γ-aminobutyric acid receptors].

    PubMed

    Chen, Hui-Ying; Wei, Ting-Jia; Weng, Jing-Jin; Qin, Jiang-Yuan; Huang, Xi; Su, Ji-Ping

    2016-04-25

    Type A γ-aminobutyric acid receptors (GABAAR) and N-methyl-D-aspartate receptors (NMDAR) are the major inhibitory and excitatory receptors in the central nervous system, respectively. Co-expression of the receptors in the synapse may lead to functional influence between receptors, namely receptor interaction. The interactions between GABAAR and NMDAR can be either positive or negative. However, the mechanisms of interaction between the two receptors remain poorly understood, and potential mechanisms include (1) through a second messenger; (2) by receptors trafficking; (3) by direct interaction; (4) by a third receptor-mediation. Dopamine is the most abundant catecholamine neurotransmitter in the brain, and its receptors, dopamine receptors (DR) can activate multiple signaling pathways. Earlier studies on the interaction between DR and GABAAR/NMDAR have shown some underlying mechanisms, suggesting that DR could mediate the interaction between GABAAR and NMDAR. This paper summarized some recent progresses in the studies of the interaction between DR and NMDAR/GABAAR, providing a further understanding on the interaction between NMDAR and GABAAR mediated by DR. PMID:27108906

  9. NASA Adaptive Multibeam Phased Array (AMPA): An application study

    NASA Technical Reports Server (NTRS)

    Mittra, R.; Lee, S. W.; Gee, W.

    1982-01-01

    The proposed orbital geometry for the adaptive multibeam phased array (AMPA) communication system is reviewed and some of the system's capabilities and preliminary specifications are highlighted. Typical AMPA user link models and calculations are presented, the principal AMPA features are described, and the implementation of the system is demonstrated. System tradeoffs and requirements are discussed. Recommendations are included.

  10. Bile acid receptors and nonalcoholic fatty liver disease

    PubMed Central

    Yuan, Liyun; Bambha, Kiran

    2015-01-01

    With the high prevalence of obesity, diabetes, and other features of the metabolic syndrome in United States, nonalcoholic fatty liver disease (NAFLD) has inevitably become a very prevalent chronic liver disease and is now emerging as one of the leading indications for liver transplantation. Insulin resistance and derangement of lipid metabolism, accompanied by activation of the pro-inflammatory response and fibrogenesis, are essential pathways in the development of the more clinically significant form of NAFLD, known as nonalcoholic steatohepatitis (NASH). Recent advances in the functional characterization of bile acid receptors, such as farnesoid X receptor (FXR) and transmembrane G protein-coupled receptor (TGR) 5, have provided further insight in the pathophysiology of NASH and have led to the development of potential therapeutic targets for NAFLD and NASH. Beyond maintaining bile acid metabolism, FXR and TGR5 also regulate lipid metabolism, maintain glucose homeostasis, increase energy expenditure, and ameliorate hepatic inflammation. These intriguing features have been exploited to develop bile acid analogues to target pathways in NAFLD and NASH pathogenesis. This review provides a brief overview of the pathogenesis of NAFLD and NASH, and then delves into the biological functions of bile acid receptors, particularly with respect to NASH pathogenesis, with a description of the associated experimental data, and, finally, we discuss the prospects of bile acid analogues in the treatment of NAFLD and NASH. PMID:26668692

  11. TrkB activation by 7, 8-dihydroxyflavone increases synapse AMPA subunits and ameliorates spatial memory deficits in a mouse model of Alzheimer's disease.

    PubMed

    Gao, Lei; Tian, Mi; Zhao, Hong-Yun; Xu, Qian-Qian; Huang, Yu-Ming; Si, Qun-Cao; Tian, Qing; Wu, Qing-Ming; Hu, Xia-Min; Sun, Li-Bo; McClintock, Shawn M; Zeng, Yan

    2016-02-01

    We recently demonstrated that activation of tyrosine receptor kinase B (TrkB) by 7, 8-dihydroxyflavone (7, 8-DHF), the selective TrkB agonist, increased surface alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptors (AMPARs) AMPA receptor subunit GluR1 (GluA1) subunit expression at the synapses of Fragile X Syndrome mutant mice. This present study investigated the effects of 7, 8-DHF on both memory function and synapse structure in relation to the synapse protein level of AMPARs in the Tg2576 Alzheimer's disease (AD) mouse model. The study found that chronic oral administration of 7, 8-DHF significantly improved spatial memory and minimized dendrite loss in the hippocampus of Tg2576 mice. A key feature of 7, 8-DHF action was the increased expression of both GluA1 and GluA2 at synapses. Interestingly, 7, 8-DHF had no effect on the attenuation of amyloid precursor protein or Aβ exhibiting in the Tg2576 AD brains, yet it activated the phosphorylation of TrkB receptors and its downstream signals including CaMKII, Akt, Erk1/2, and cAMP-response element-binding protein. Importantly, cyclotraxin B (a TrkB inhibitor), U0126 (a Ras-ERK pathway inhibitor), Wortmannin (an Akt phosphorylation inhibitor), and KN-93 (a CaMKII inhibitor) counteracted the enhanced expression and phosphorylation of AMPAR subunits induced by 7, 8-DHF. Collectively, our results demonstrated that 7, 8-DHF acted on TrkB and resolved learning and memory impairments in the absence of reduced amyloid in amyloid precursor protein transgenic mice partially through improved synaptic structure and enhanced synaptic AMPARs. The findings suggest that the application of 7, 8-DHF may be a promising new approach to improve cognitive abilities in AD. We provided extensive data demonstrating that 7, 8-dihydroflavone, the TrkB agonist, improved Tg2576 mice spatial memory. This improvement is correlated with a reversion to normal values of GluA1 and GluA2 AMPA receptor subunits and dendritic

  12. 2-Cycloalkyl phenoxyacetic acid CRTh2 receptor antagonists.

    PubMed

    Sandham, David A; Aldcroft, Clive; Baettig, Urs; Barker, Lucy; Beer, David; Bhalay, Gurdip; Brown, Zarin; Dubois, Gerald; Budd, David; Bidlake, Louise; Campbell, Emma; Cox, Brian; Everatt, Brian; Harrison, David; Leblanc, Catherine J; Manini, Jodie; Profit, Rachael; Stringer, Rowan; Thompson, Katy S; Turner, Katharine L; Tweed, Morris F; Walker, Christoph; Watson, Simon J; Whitebread, Steven; Willis, Jennifer; Williams, Gareth; Wilson, Caroline

    2007-08-01

    High throughput screening identified a phenoxyacetic acid scaffold as a novel CRTh2 receptor antagonist chemotype, which could be optimised to furnish a compound with functional potency for inhibition of human eosinophil shape change and oral bioavailability in the rat. PMID:17531480

  13. Retinoic Acid-mediated Nuclear Receptor Activation and Hepatocyte Proliferation

    PubMed Central

    Bushue, Nathan; Wan, Yu-Jui Yvonne

    2016-01-01

    Due to their well-known differentiation and apoptosis-inducing abilities, retinoic acid (RA) and its analogs have strong anti-cancer efficacy in human cancers. However, in vivo RA is a liver mitogen. While speculation has persisted that RA-mediated signaling is likely involved in hepatocyte proliferation during liver regeneration, direct evidence is still required. Findings in support of this proposition include observations that a release of retinyl palmitate (the precursor of RA) occurs in liver stellate cells following liver injury. Nevertheless, the biological action of this released vitamin A is virtually unknown. More likely is that the released vitamin A is converted to RA, the biological form, and then bound to a specific receptor (retinoid x receptor; RXRα), which is most abundantly expressed in the liver. Considering the mitogenic effects of RA, the RA-activated RXRα would likely then influence hepatocyte proliferation and liver tissue repair. At present, the mechanism by which RA stimulates hepatocyte proliferation is largely unknown. This review summarizes the activation of nuclear receptors (peroxisome proliferator activated receptor-α, pregnane x receptor, constitutive androstane receptor, and farnesoid x receptor) in an RXRα dependent manner to induce hepatocyte proliferation, providing a link between RA and its proliferative role.

  14. The effects of AMPA blockade on the spectral profile of human early visual cortex recordings studied with non-invasive MEG.

    PubMed

    Muthukumaraswamy, Suresh D; Routley, Bethany; Droog, Wouter; Singh, Krish D; Hamandi, Khalid

    2016-08-01

    The generation of gamma-band (>30 Hz) cortical activity is thought to depend on the reciprocal connections of excitatory glutamatergic principal cells with inhibitory GABAergic interneurons. Both in vitro and in vivo animal studies have shown that blockade of glutamatergic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors reduces the amplitude of gamma-band activity. In this registered report, we hypothesised that similar effects would be observed in humans following administration of perampanel, a first in class AMPA antagonist, used in the treatment of epilepsy. In a single-blind placebo-controlled crossover study, 20 healthy male participants completed two study days. On one day participants were given a 6 mg dose of perampanel and on the other an inactive placebo. magnetoencephalography (MEG) recordings of brain activity were taken before and two hours after drug administration, with activity in the visual cortex probed using a stimulation protocol known to induce gamma-band activity in the primary visual cortex. As hypothesised, our results indicated a decrease in gamma-band amplitudes following perampanel administration. The decreases in gamma-band amplitudes observed were temporally restricted to the early time-period of stimulus presentation (up to 400 msec) with no significant effects observed on early evoked responses or alpha rhythms. This suggests that the early time-window of induced visual gamma-band activity, thought to reflect input to the visual cortex from the lateral geniculate nucleus, is most sensitive to AMPA blocking drugs. PMID:27209006

  15. Bile acid nuclear receptor FXR and digestive system diseases

    PubMed Central

    Ding, Lili; Yang, Li; Wang, Zhengtao; Huang, Wendong

    2015-01-01

    Bile acids (BAs) are not only digestive surfactants but also important cell signaling molecules, which stimulate several signaling pathways to regulate some important biological processes. The bile-acid-activated nuclear receptor, farnesoid X receptor (FXR), plays a pivotal role in regulating bile acid, lipid and glucose homeostasis as well as in regulating the inflammatory responses, barrier function and prevention of bacterial translocation in the intestinal tract. As expected, FXR is involved in the pathophysiology of a wide range of diseases of gastrointestinal tract, including inflammatory bowel disease, colorectal cancer and type 2 diabetes. In this review, we discuss current knowledge of the roles of FXR in physiology of the digestive system and the related diseases. Better understanding of the roles of FXR in digestive system will accelerate the development of FXR ligands/modulators for the treatment of digestive system diseases. PMID:26579439

  16. Bile acid nuclear receptor FXR and digestive system diseases.

    PubMed

    Ding, Lili; Yang, Li; Wang, Zhengtao; Huang, Wendong

    2015-03-01

    Bile acids (BAs) are not only digestive surfactants but also important cell signaling molecules, which stimulate several signaling pathways to regulate some important biological processes. The bile-acid-activated nuclear receptor, farnesoid X receptor (FXR), plays a pivotal role in regulating bile acid, lipid and glucose homeostasis as well as in regulating the inflammatory responses, barrier function and prevention of bacterial translocation in the intestinal tract. As expected, FXR is involved in the pathophysiology of a wide range of diseases of gastrointestinal tract, including inflammatory bowel disease, colorectal cancer and type 2 diabetes. In this review, we discuss current knowledge of the roles of FXR in physiology of the digestive system and the related diseases. Better understanding of the roles of FXR in digestive system will accelerate the development of FXR ligands/modulators for the treatment of digestive system diseases. PMID:26579439

  17. Binding mode of an α-amino acid-linked quinoxaline-2,3-dione analogue at glutamate receptor subtype GluK1.

    PubMed

    Demmer, Charles S; Møller, Charlotte; Brown, Patricia M G E; Han, Liwei; Pickering, Darryl S; Nielsen, Birgitte; Bowie, Derek; Frydenvang, Karla; Kastrup, Jette S; Bunch, Lennart

    2015-06-17

    Two α-amino acid-functionalized quinoxalines, 1a (CNG-10301) and 1b (CNG-10300), of a quinoxaline moiety coupled to an amino acid moiety were designed, synthesized, and characterized pharmacologically. While 1a displayed low affinity at native AMPA, KA, and NMDA receptors, and at homomeric GluK1,3 receptors, the affinity for GluK2 was in the midmicromolar range (Ki = 136 μM), 1b displayed low to midmicromolar range binding affinity at all the iGluRs (Ki = 9-126 μM). In functional experiments (outside-out patches excised from transfected HEK293T cells), 100 μM 1a partially blocked GluK1 (33% peak response), while GluK2 was unaffected (96% peak response). Furthermore, 1a was shown not to be an agonist at GluK1 and GluK2 at 100 μM. On the other hand, 100 μM 1b fully antagonized GluK1 (8% peak response) but only partially blocked GluK2 (33% peak response). An X-ray structure at 2.3 Å resolution of 1b in the GluK1-LBD (ligand-binding domain) disclosed an unexpected binding mode compared to the predictions made during the design phase; the quinoxaline moiety remains to act as an amino acid bioisostere, but the amino acid moiety is oriented into a new area within the GluK1 receptor. The structure of the GluK1-LBD with 1b showed a large variation in domain openings of the three molecules from 25° to 49°, demonstrating that the GluK1-LBD is capable of undergoing major domain movements. PMID:25856736

  18. Brain-derived neurotrophic factor acutely inhibits AMPA-mediated currents in developing sensory relay neurons.

    PubMed

    Balkowiec, A; Kunze, D L; Katz, D M

    2000-03-01

    Brain-derived neurotrophic factor (BDNF) is expressed by many primary sensory neurons that no longer require neurotrophins for survival, indicating that BDNF may be used as a signaling molecule by the afferents themselves. Because many primary afferents also express glutamate, we investigated the possibility that BDNF modulates glutamatergic AMPA responses of newborn second-order sensory relay neurons. Perforated-patch, voltage-clamp recordings were made from dissociated neurons of the brainstem nucleus tractus solitarius (nTS), a region that receives massive primary afferent input from BDNF-containing neurons in the nodose and petrosal cranial sensory ganglia. Electrophysiological analysis was combined in some experiments with anterograde labeling of primary afferent terminals to specifically analyze responses of identified second-order neurons. Our data demonstrate that BDNF strongly inhibits AMPA-mediated currents in a large subset of nTS cells. Specifically, AMPA responses were either completely abolished or markedly inhibited by BDNF in 73% of postnatal day (P0) cells and in 82% of identified P5 second-order sensory relay neurons. This effect of BDNF is mimicked by NT-4, but not NGF, and blocked by the Trk tyrosine kinase inhibitor K252a, consistent with a requirement for TrkB receptor activation. Moreover, analysis of TrkB expression in culture revealed a close correlation between the percentage of nTS neurons in which BDNF inhibits AMPA currents and the percentage of neurons that exhibit TrkB immunoreactivity. These data document a previously undefined mechanism of acute modulation of AMPA responses by BDNF and indicate that BDNF may regulate glutamatergic transmission at primary afferent synapses. PMID:10684891

  19. Ligand regulation of retinoic acid receptor-related orphan receptors: implications for development of novel therapeutics

    PubMed Central

    Solt, Laura A.; Griffin, Patrick R.; Burris, Thomas P.

    2016-01-01

    Purpose of review In the late 1980s, the cloning of several nuclear receptors led to the intense search and isolation of new members of this superfamily. Despite their identification, many of these receptors were dubbed ‘orphan’ receptors, as their physiological ligands remained unknown. Recent reports have presented evidence for one family of orphan receptors, the retinoic acid receptor-related orphan receptors (RORs), in several pathologies, including osteoporosis, several autoimmune diseases, asthma, cancer, diabetes and obesity. The present review summarizes the studies identifying ligands for the RORs and evaluates their role as targets for potential therapeutics. Recent findings Significant progress was made in the initial identification of ligands for the RORs when X-ray crystallographic studies identified several molecules within the ligand-binding pockets of RORα and RORβ. Recently, we identified endogenous and synthetic ligands for RORα and RORγ, thereby solidifying their function as ligand-dependent transcription factors. Summary Recent studies have established roles for the RORs in physiological development and the advent of disease. Identification of ligands for the RORs, both endogenous and synthetic, has established these receptors as attractive new therapeutic targets for the treatment of ROR-related diseases. PMID:20463469

  20. Glyphosate and AMPA adsorption in soils: laboratory experiments and pedotransfer rules.

    PubMed

    Sidoli, Pauline; Baran, Nicole; Angulo-Jaramillo, Rafael

    2016-03-01

    Adsorption of the herbicide glyphosate and its main metabolite AMPA (aminomethylphosphonic acid) was investigated on 17 different agricultural soils. Batch equilibration adsorption data are shown by Freundlich adsorption isotherms. Glyphosate adsorption is clearly affected by equilibration concentrations, but the nonlinear AMPA adsorption isotherms indicate saturation of the adsorption sites with increasing equilibrium concentrations. pHCaCl2 (i.e. experimental pH) is the major parameter governing glyphosate and AMPA adsorption in soils. However, considering pHCaCl2 values, available phosphate amount, and amorphous iron and aluminium oxide contents by using a nonlinear multiple regression equation, obtains the most accurate and powerful pedotransfer rule for predicting the adsorption constants for these two molecules. As amorphous iron and aluminium oxide contents in soil are not systematically determined, we also propose a pedotransfer rule with two variables-pHCaCl2 values and available phosphate amount-that remains acceptable for both molecules. Moreover, the use of the commonly measured pHwater or pHKCl values gives less accurate results compared to pHCaCl2 measurements. To our knowledge, this study is the first AMPA adsorption characterization for a significant number of temperate climate soils. PMID:26581693

  1. Anti-inflammatory effects of the hydroxycarboxylic acid receptor 2.

    PubMed

    Graff, Emily C; Fang, Han; Wanders, Desiree; Judd, Robert L

    2016-02-01

    The hydroxycarboxylic acid receptors (HCA1-3) are a family of G-protein-coupled receptors that are critical for sensing endogenous intermediates of metabolism. All three receptors are predominantly expressed on adipocytes and mediate anti-lipolytic effects. In addition to adipocytes, HCA2 is highly expressed on immune cells, including macrophages, monocytes, neutrophils and dermal dendritic cells, among other cell types. The endogenous ligand for HCA2 is beta-hydroxybutyrate (β-OHB), a ketone body produced by the liver through β-oxidation when an individual is in a negative energy balance. Recent studies demonstrate that HCA2 mediates profound anti-inflammatory effects in a variety of tissues, indicating that HCA2 may be an important therapeutic target for treating inflammatory disease processes. This review summarizes the roles of HCA2 on inflammation in a number of tissues and clinical states. PMID:26773933

  2. Lysophosphatidic acid receptor (LPAR) modulators: The current pharmacological toolbox.

    PubMed

    Llona-Minguez, Sabin; Ghassemian, Artin; Helleday, Thomas

    2015-04-01

    Lysophosphatidic acids (LPA) are key lipid-signalling molecules that regulate a remarkably diverse set of cellular events, such as motility, chemotaxis, cell cycle progression, viability, and wound healing. The physiological and pathophysiological consequences of LPA signalling are evident and misregulation of LPA signalling can lead to pathologies like cancer, atherosclerosis, ischaemia, and fibrosis. LPA exerts its biological actions mainly through several types of G protein-coupled receptors, some of which display opposing or redundant effects. For this reason, selective LPA receptor small-molecule ligands can shine light on LPA biology and present an exciting opportunity for drug discovery endeavours. This review provides insights into the detailed chemical nature and pharmacological profile of the small-molecules thus far developed as LPA receptor modulators, as well as information on the preparation of key pharmaceuticals. This summary will facilitate future research efforts and nurture collaboration between chemists and biologists working in this emerging field. PMID:25704399

  3. Crystal Structure of Antagonist Bound Human Lysophosphatidic Acid Receptor 1

    PubMed Central

    Chrencik, Jill E.; Roth, Christopher B.; Terakado, Masahiko; Kurata, Haruto; Omi, Rie; Kihara, Yasuyuki; Warshaviak, Dora; Nakade, Shinji; Asmar-Rovira, Guillermo; Mileni, Mauro; Mizuno, Hirotaka; Griffith, Mark T.; Rodgers, Caroline; Han, Gye Won; Velasquez, Jeffrey; Chun, Jerold; Stevens, Raymond C.

    2015-01-01

    Summary Lipid biology continues to emerge as an area of significant therapeutic interest, particularly as the result of an enhanced understanding of the wealth of signaling molecules with diverse physiological properties. This growth in knowledge is epitomized by lysophosphatidic acid (LPA), which functions through interactions with six cognate G protein-coupled receptors. Herein we present three crystal structures of LPA1 in complex with antagonist tool compounds selected and designed through structural and stability analysis. Structural analysis combined with molecular dynamics identified a basis for ligand access to the LPA1 binding pocket from the extracellular space contrasting with the proposed access for the sphingosine 1-phosphate receptor. Characteristics of the LPA1 binding pocket raise the possibility of promiscuous ligand recognition of phosphorylated endocannabinoids. Cell-based assays confirmed this hypothesis, linking the distinct receptor systems through metabolically related ligands with potential functional and therapeutic implications for treatment of disease. PMID:26091040

  4. Nuclear bile acid signaling through the farnesoid X receptor.

    PubMed

    Mazuy, Claire; Helleboid, Audrey; Staels, Bart; Lefebvre, Philippe

    2015-05-01

    Bile acids (BAs) are amphipathic molecules produced from cholesterol by the liver. Expelled from the gallbladder upon meal ingestion, BAs serve as fat solubilizers in the intestine. BAs are reabsorbed in the ileum and return via the portal vein to the liver where, together with nutrients, they provide signals to coordinate metabolic responses. BAs act on energy and metabolic homeostasis through the activation of membrane and nuclear receptors, among which the nuclear receptor farnesoid X receptor (FXR) is an important regulator of several metabolic pathways. Highly expressed in the liver and the small intestine, FXR contributes to BA effects on metabolism, inflammation and cell cycle control. The pharmacological modulation of its activity has emerged as a potential therapeutic strategy for liver and metabolic diseases. This review highlights recent advances regarding the mechanisms by which the BA sensor FXR contributes to global signaling effects of BAs, and how FXR activity may be regulated by nutrient-sensitive signaling pathways. PMID:25511198

  5. Identification of COUP-TFII Orphan Nuclear Receptor as a Retinoic Acid-Activated Receptor

    SciTech Connect

    Kruse, Schoen W; Suino-Powell, Kelly; Zhou, X Edward; Kretschman, Jennifer E; Reynolds, Ross; Vonrhein, Clemens; Xu, Yong; Wang, Liliang; Tsai, Sophia Y; Tsai, Ming-Jer; Xu, H Eric

    2010-01-12

    The chicken ovalbumin upstream promoter-transcription factors (COUP-TFI and II) make up the most conserved subfamily of nuclear receptors that play key roles in angiogenesis, neuronal development, organogenesis, cell fate determination, and metabolic homeostasis. Although the biological functions of COUP-TFs have been studied extensively, little is known of their structural features or aspects of ligand regulation. Here we report the ligand-free 1.48 {angstrom} crystal structure of the human COUP-TFII ligand-binding domain. The structure reveals an autorepressed conformation of the receptor, where helix {alpha}10 is bent into the ligand-binding pocket and the activation function-2 helix is folded into the cofactor binding site, thus preventing the recruitment of coactivators. In contrast, in multiple cell lines, COUP-TFII exhibits constitutive transcriptional activity, which can be further potentiated by nuclear receptor coactivators. Mutations designed to disrupt cofactor binding, dimerization, and ligand binding, substantially reduce the COUP-TFII transcriptional activity. Importantly, retinoid acids are able to promote COUP-TFII to recruit coactivators and activate a COUP-TF reporter construct. Although the concentration needed is higher than the physiological levels of retinoic acids, these findings demonstrate that COUP-TFII is a ligand-regulated nuclear receptor, in which ligands activate the receptor by releasing it from the autorepressed conformation.

  6. A third human retinoic acid receptor, hRAR-. gamma

    SciTech Connect

    Krust, A.; Kastner, Ph.; Petkovich, M.; Zelent, A.; Chambon, P. )

    1989-07-01

    Retinoic acid receptors (RARs) are retinoic acid (RA)-inducible enhancer factors belonging to the superfamily of steroid/thyroid nuclear receptors. The authors have previously characterized two human RAR (hRAR-{alpha} and hRAR-{beta}) cDNAs and have recently cloned their murine cognates (mRAR-{alpha} and mRAR-{beta}) together with a third RAR (mRAR-{gamma}) whose RNA was detected predominantly in skin, a well-known target for RA. mRAR-{gamma} cDNA was used here to clone its human counterpart (hRAR-{gamma}) from a T47D breast cancer cell cDNA library. Using a transient transfection assay in HeLa cells and a reporter gene harboring a synthetic RA responsive element, they demonstrate that hRAR-{gamma} cDNA indeed encodes a RA-inducible transcriptional trans-activator. Interestingly, comparisons of the amino acid sequences of all six human and mouse RARs indicate that the interspecies conservation of a given member of the RAR subfamily (either {alpha}, {beta}, or {gamma}) is much higher than the conservation of all three receptors within a given species. These observations indicate that RAR-{alpha}, -{beta}, and -{gamma} may perform specific functions. They show also that hRAR-{gamma} RNA is the predominant RAR RNA species in human skin, which suggests that hRAR-{gamma} mediates some of the retinoid effects in this tissue.

  7. Selective potentiation of alpha 1 glycine receptors by ginkgolic acid

    PubMed Central

    Maleeva, Galyna; Buldakova, Svetlana; Bregestovski, Piotr

    2015-01-01

    Glycine receptors (GlyRs) belong to the superfamily of pentameric cys-loop receptor-operated channels and are involved in numerous physiological functions, including movement, vision, and pain. In search for compounds performing subunit-specific modulation of GlyRs we studied action of ginkgolic acid, an abundant Ginkgo biloba product. Using patch-clamp recordings, we analyzed the effects of ginkgolic acid in concentrations from 30 nM to 25 μM on α1–α3 and α1/β, α2/β configurations of GlyR and on GABAARs expressed in cultured CHO-K1 cells and mouse neuroblastoma (N2a) cells. Ginkgolic acid caused an increase in the amplitude of currents mediated by homomeric α1 and heteromeric α1/β GlyRs and provoked a left-shift of the concentration-dependent curves for glycine. Even at high concentrations (10–25 μM) ginkgolic acid was not able to augment ionic currents mediated by α2, α2/β, and α3 GlyRs, or by GABAAR consisting of α1/β2/γ2 subunits. Mutation of three residues (T59A/A261G/A303S) in the α2 GlyR subunit to the corresponding ones from the α1 converted the action of ginkgolic acid to potentiation with a distinct decrease in EC50 for glycine, suggesting an important role for these residues in modulation by ginkgolic acid. Our results suggest that ginkgolic acid is a novel selective enhancer of α1 GlyRs. PMID:26578878

  8. Novel retinoic acid receptor ligands in Xenopus embryos.

    PubMed Central

    Blumberg, B; Bolado, J; Derguini, F; Craig, A G; Moreno, T A; Chakravarti, D; Heyman, R A; Buck, J; Evans, R M

    1996-01-01

    Retinoids are a large family of natural and synthetic compounds related to vitamin A that have pleiotropic effects on body physiology, reproduction, immunity, and embryonic development. The diverse activities of retinoids are primarily mediated by two families of nuclear retinoic acid receptors, the RARs and RXRs. Retinoic acids are thought to be the only natural ligands for these receptors and are widely assumed to be the active principle of vitamin A. However, during an unbiased, bioactivity-guided fractionation of Xenopus embryos, we were unable to detect significant levels of all-trans or 9-cis retinoic acids. Instead, we found that the major bioactive retinoid in the Xenopus egg and early embryo is 4-oxoretinaldehyde, which is capable of binding to and transactivating RARs. In addition to its inherent activity, 4-oxoretinaldehyde appears to be a metabolic precursor of two other RAR ligands, 4-oxoretinoic acid and 4-oxoretinol. The remarkable increase in activity of retinaldehyde and retinol as a consequence of 4-oxo derivatization suggests that this metabolic step could serve a critical regulatory function during embryogenesis. Images Fig. 1 Fig. 4 PMID:8643496

  9. 7, 8-Dihydroxyflavone induces synapse expression of AMPA GluA1 and ameliorates cognitive and spine abnormalities in a mouse model of fragile X syndrome.

    PubMed

    Tian, Mi; Zeng, Yan; Hu, Yilan; Yuan, Xiuxue; Liu, Shumin; Li, Jie; Lu, Pan; Sun, Yao; Gao, Lei; Fu, Daan; Li, Yi; Wang, Shasha; McClintock, Shawn M

    2015-02-01

    Fragile X syndrome (FXS) is characterized by immature dendritic spine architectures and cognitive impairment. 7, 8-Dihydroxyflavone (7, 8-DHF) has recently been identified as a high affinity tropomyosin receptor kinase B (TrkB) agonist. The purpose of this paper was to examine the utility of 7, 8-DHF as an effective pharmacotherapeutic agent that targets dendritic pathology and cognitive impairments in FXS mutant. We synthesized pharmacologic, behavioral, and biochemical approaches to examine the effects of 7, 8-DHF on spatial and fear memory functions, and morphological spine abnormalities in fragile X mental retardation 1 (Fmr1) gene knock-out mice. The study found that 4 weeks of treatment with 7, 8-DHF improved spatial and fear memory, and ameliorated morphological spine abnormalities including the number and elongation of spines in the hippocampus and amygdala. Further mechanism analysis revealed that 7, 8-DHF enhanced the expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) GluA1 receptor, but reduced the normal levels of GluA2 at the synapses in Fmr1. Potentially related to drug-induced changes in AMPA receptor subunits, 7, 8-DHF at the synapses led to phosphorylation of specific serine sites on subunits Ser818 and Ser813 of GluA1, and Ser880 of GluA2, as well as phosphorylation of TrkB, calcium/calmodulin-dependent protein kinase II, and protein kinase C. However, 7, 8-DHF neither affected behavioral performance nor increased TrkB phosphorylation in WT mice, which suggested that it had FXS-specific correcting effect. Altogether, these results demonstrated that 7, 8-DHF improved learning and memory, and reduced abnormalities in spine morphology, thus providing a potential pharmacotherapeutic strategy for FXS. PMID:25229717

  10. Palmitoylation-dependent regulation of glutamate receptors and their PDZ domain-containing partners

    PubMed Central

    Thomas, Gareth M.; Huganir, Richard L.

    2013-01-01

    In recent years, it has become clear that both AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid)- and NMDA (N-methyl-D-aspartate)-type glutamate receptors, and many of their interacting partners, are palmitoylated proteins. Interfering with palmitoylation dramatically affects receptor trafficking and distribution and, in turn, can profoundly alter synaptic transmission. Increased knowledge of synaptic palmitoylation not only will aid our understanding of physiological neuronal regulation, but also may provide insights into, and even novel treatments for, neuropathological conditions. In the present paper, we review recent advances regarding the regulation of ionotropic glutamate receptor trafficking and function by palmitoylation. PMID:23356261

  11. Electrophysiological evidence for acidic, basic, and neutral amino acid olfactory receptor sites in the catfish.

    PubMed

    Caprio, J; Byrd, R P

    1984-09-01

    Electrophysiological experiments indicate that olfactory receptors of the channel catfish, Ictalurus punctatus, contain different receptor sites for the acidic (A), basic (B), and neutral amino acids; further, at least two partially interacting neutral sites exist, one for the hydrophilic neutral amino acids containing short side chains (SCN), and the second for the hydrophobic amino acids containing long side chains (LCN). The extent of cross-adaptation was determined by comparing the electro-olfactogram (EOG) responses to 20 "test" amino acids during continuous bathing of the olfactory mucosa with water only (control) to those during each of the eight "adapting" amino acid regimes. Both the adapting and test amino acids were adjusted in concentrations to provide approximately equal response magnitudes in the unadapted state. Under all eight adapting regimes, the test EOG responses were reduced from those obtained in the unadapted state, but substantial quantitative differences resulted, depending upon the molecular structure of the adapting stimulus. Analyses of the patterns of EOG responses to the test stimuli identified and characterized the respective "transduction processes," a term used to describe membrane events initiated by a particular subset of amino acid stimuli that are intricately linked to the origin of the olfactory receptor potential. Only when the stimulus compounds interact with different transduction processes are the stimuli assumed to bind to different membrane "sites." Four relatively independent L-alpha-amino acid transduction processes (and thus at least four binding sites) identified in this report include: (a) the A process for aspartic and glutamic acids; (b) the B process for arginine and lysine; (c) the SCN process for glycine, alanine, serine, glutamine, and possibly cysteine; (d) the LCN process for methionine, ethionine, valine, norvaline, leucine, norleucine, glutamic acid-gamma-methyl ester, histidine, phenylalanine, and also

  12. Receptor for protons: First observations on Acid Sensing Ion Channels.

    PubMed

    Krishtal, Oleg

    2015-07-01

    The history of ASICs began in 1980 with unexpected observation. The concept of highly selective Na(+) current gated by specific receptors for protons was not easily accepted. It took 16 years to get these receptor/channels cloned and start a new stage in their investigation. "The receptor for protons" became ASIC comprising under this name a family of receptor/channels ubiquitous for mammalian nervous system, both peripheral and central. The role of ASICs as putative nociceptors was suggested almost immediately after their discovery. This role subsequently was proven in many forms of pain-related phenomena. Many other functions of ASICs have been also found or primed for speculations both in physiology and in disease. Despite the width of field and strength of efforts, numerous basic questions are to be answered before we understand how the local changes in pH in the nervous tissue transform into electric and messenger signaling via ASICs as transducers. This article is part of the Special Issue entitled 'Acid-Sensing Ion Channels in the Nervous System'. PMID:25582296

  13. Expression of bile acid receptor TGR5 in gastric adenocarcinoma.

    PubMed

    Cao, Weibiao; Tian, Wei; Hong, Jie; Li, Dan; Tavares, Rosemarie; Noble, Lelia; Moss, Steven F; Resnick, Murray B

    2013-02-15

    Bile reflux is a risk factor in the development of intestinal metaplasia in the stomach and is believed to function as an initiator of gastric carcinogenesis. However, whether the G protein-coupled bile acid receptor TGR5 is expressed in this tumor is not known. In this study, we determined the expression of TGR5 in gastric adenocarcinoma and examined the role of TGR5 in cell proliferation. Strong TGR5 staining was present in 12% of cases of intestinal metaplasia but in no cases of normal gastric epithelium (P < 0.01). Moderate to strong TGR5 membranous and cytoplasmic staining was present in 52% of the intestinal but in only 25% of the diffuse subtype of adenocarcinomas (P < 0.001). Kaplan-Meier univariate survival analysis revealed that moderate to strong TGR5 staining was associated with decreased patient survival (P < 0.05). Treatment with taurodeoxycholic acid (TDCA, a bile acid) significantly increased thymidine incorporation in the AGS gastric adenocarcinoma cell line, suggesting that bile acids may increase cell proliferation. This increase was significantly decreased by knockdown of TGR5 with TGR5 small-interfering RNA (siRNA). In addition, overexpression of TGR5 significantly enhanced TDCA-induced increases in thymidine incorporation. TGR5 is coupled with G(q)α and Gα(i-3) proteins. TDCA-induced increase in thymidine incorporation was significantly decreased by knockdown of G(q)α and Gα(i-3) with their siRNAs. We conclude that TGR5 is overexpressed in most gastric intestinal-type adenocarcinomas, and moderate to strong TGR5 staining is associated with decreased patient survival in all gastric adenocarcinomas. Bile acids increase cell proliferation via activation of TGR5 receptors and G(q)α and Gα(i-3) proteins. PMID:23238937

  14. Nicotinic modulation of glutamate receptor function at nerve terminal level: a fine-tuning of synaptic signals.

    PubMed

    Marchi, Mario; Grilli, Massimo; Pittaluga, Anna M

    2015-01-01

    This review focuses on a specific interaction occurring between the nicotinic cholinergic receptors (nAChRs) and the glutamatergic receptors (GluRs) at the nerve endings level. We have employed synaptosomes in superfusion and supplemented and integrated our findings with data obtained using techniques from molecular biology and immuno-cytochemistry, and the assessment of receptor trafficking. In particular, we characterize the following: (1) the direct and unequivocal localization of native α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) glutamatergic receptors on specific nerve terminals, (2) their pharmacological characterization and functional co-localization with nAChRs on the same nerve endings, and (3) the existence of synergistic or antagonistic interactions among them. Indeed, in the rat nucleus accumbens (NAc), the function of some AMPA and NMDA receptors present on the dopaminergic and glutamatergic nerve terminals can be regulated negatively or positively in response to a brief activation of nAChRs. This effect occurs rapidly and involves the trafficking of AMPA and NMDA receptors. The event takes place also at very low concentrations of nicotine and involves the activation of several nAChRs subtypes. This dynamic control by cholinergic nicotinic system of glutamatergic NMDA and AMPA receptors might therefore represent an important neuronal presynaptic adaptation associated with nicotine administration. The understanding of the role of these nicotine-induced functional changes might open new and interesting perspectives both in terms of explaining the mechanisms that underlie some of the effects of nicotine addiction and in the development of new drugs for smoking cessation. PMID:25972809

  15. The genuine ligand of a jasmonic acid receptor

    PubMed Central

    Xie, Daoxin

    2010-01-01

    Jasmonic acid (JA), its metabolites, such as the methyl ester or amino acid conjugates as well as its precursor 12-oxophytodienoic acid (OPDA) are lipid-derived signals. JA, OPDA and JA-amino acid conjugates are known to function as signals in plant stress responses and development. More recently, formation of JA-amino acid conjugates and high biological activity of JA-Isoleucine (JA-Ile) were found to be essential in JA signaling. A breakthrough was the identification of JAZ proteins which interact with the F-box protein COI1 if JA-Ile is bound. This interaction leads to proteasomal degradation of JAZs being negative regulators of JA-induced transcription. Surprisingly, a distinct stereoisomer of JA-Ile, the (+)-7-iso-JA-Ile [(3R,7S) form] is most active. Coronatine, a bacterial phytotoxine with an identical stereochemistry at the cyclopentanone ring, has a similar bioactivity. This was explained by the recent identification of COI1 as the JA receptor and accords well with molecular modeling studies. Whereas over the last two decades JA was quantified to describe any JA dependent process, now we have to take into account a distinct stereoisomer of JA-Ile. Until recently a quantitative analysis of (+)-7-iso-JA-Ile was missing presumable due to its equilibration to (−)-JA-Ile. Now such an analysis was achieved. These aspects will be discussed based on our new knowledge on JA perception and signaling. PMID:20404483

  16. Roles of subunit phosphorylation in regulating glutamate receptor function

    PubMed Central

    Wang, John Q.; Guo, Ming-Lei; Jin, Dao-Zhong; Xue, Bing; Fibuch, Eugene E.; Mao, Li-Min

    2014-01-01

    Protein phosphorylation is an important mechanism for regulating ionotropic glutamate receptors (iGluRs). Early studies have established that major iGluR subtypes, including α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors and N-methyl-D-aspartate (NMDA) receptors, are subject to phosphorylation. Multiple serine, threonine, and tyrosine residues predominantly within the C-terminal regions of AMPA receptor and NMDA receptor subunits have been identified as sensitive phosphorylation sites. These distinct sites undergo either constitutive phosphorylation or activity-dependent phosphorylation induced by changing cellular and synaptic inputs as reversible events. An increasing number of synapse-enriched protein kinases have been found to phosphorylate iGluR. The common kinases include protein kinase A, protein kinase C, Ca2+/calmodulin-dependent protein kinase II, Src/Fyn non-receptor tyrosine kinases, and cyclin dependent kinase-5. Regulated phosphorylation plays a well-documented role in modulating the biochemical, biophysical, and functional properties of the receptor. In the future, identifying the precise mechanisms how phosphorylation regulates iGluR activities and finding the link between iGluR phosphorylation and the pathogenesis of various brain diseases, including psychiatric and neurodegenerative diseases, chronic pain, stroke, Alzheimer’s disease and substance addiction, will be hot topics and could contribute to the development of novel pharmacotherapies, by targeting the defined phosphorylation process, for suppressing iGluR-related disorders. PMID:24291102

  17. Structural mechanism of glutamate receptor activation and desensitization.

    PubMed

    Meyerson, Joel R; Kumar, Janesh; Chittori, Sagar; Rao, Prashant; Pierson, Jason; Bartesaghi, Alberto; Mayer, Mark L; Subramaniam, Sriram

    2014-10-16

    Ionotropic glutamate receptors are ligand-gated ion channels that mediate excitatory synaptic transmission in the vertebrate brain. To gain a better understanding of how structural changes gate ion flux across the membrane, we trapped rat AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) and kainate receptor subtypes in their major functional states and analysed the resulting structures using cryo-electron microscopy. We show that transition to the active state involves a 'corkscrew' motion of the receptor assembly, driven by closure of the ligand-binding domain. Desensitization is accompanied by disruption of the amino-terminal domain tetramer in AMPA, but not kainate, receptors with a two-fold to four-fold symmetry transition in the ligand-binding domains in both subtypes. The 7.6 Å structure of a desensitized kainate receptor shows how these changes accommodate channel closing. These findings integrate previous physiological, biochemical and structural analyses of glutamate receptors and provide a molecular explanation for key steps in receptor gating. PMID:25119039

  18. Effects of blockade of ionotropic glutamate receptors on blood-brain barrier disruption in focal cerebral ischemia.

    PubMed

    Liu, Xia; Hunter, Christine; Weiss, Harvey R; Chi, Oak Z

    2010-12-01

    To determine whether blockade of ionotropic glutamate receptors such as NMDA or AMPA receptors would attenuate blood-brain barrier (BBB) disruption in focal cerebral ischemia, 15 min before middle cerebral artery (MCA) occlusion, CGS-19755 or NBQX was injected intraperitoneally in rats. At 1 h after MCA occlusion, BBB permeability was determined by measuring the transfer coefficient (K(i)) of (14)C-α-aminoisobutyric acid and the volume of dextran distribution. With MCA occlusion, K(i) was increased in the ischemic cortex (IC) (316%). CGS-19755 attenuated the increase in K(i) in the IC (-46%), but NBQX did not significantly decrease it. The difference in the volume of dextran distribution between the IC and the contralateral cortex became insignificant with the blockade of NMDA or AMPA receptors. Our data demonstrated that blockade of NMDA or AMPA receptors could attenuate the BBB disruption in focal cerebral ischemia and suggest that ionotropic glutamate receptors are involved in part in BBB disruption. PMID:20217443

  19. The repertoire of olfactory C family G protein-coupled receptors in zebrafish: candidate chemosensory receptors for amino acids

    PubMed Central

    Alioto, Tyler S; Ngai, John

    2006-01-01

    Background Vertebrate odorant receptors comprise at least three types of G protein-coupled receptors (GPCRs): the OR, V1R, and V2R/V2R-like receptors, the latter group belonging to the C family of GPCRs. These receptor families are thought to receive chemosensory information from a wide spectrum of odorant and pheromonal cues that influence critical animal behaviors such as feeding, reproduction and other social interactions. Results Using genome database mining and other informatics approaches, we identified and characterized the repertoire of 54 intact "V2R-like" olfactory C family GPCRs in the zebrafish. Phylogenetic analysis – which also included a set of 34 C family GPCRs from fugu – places the fish olfactory receptors in three major groups, which are related to but clearly distinct from other C family GPCRs, including the calcium sensing receptor, metabotropic glutamate receptors, GABA-B receptor, T1R taste receptors, and the major group of V2R vomeronasal receptor families. Interestingly, an analysis of sequence conservation and selective pressure in the zebrafish receptors revealed the retention of a conserved sequence motif previously shown to be required for ligand binding in other amino acid receptors. Conclusion Based on our findings, we propose that the repertoire of zebrafish olfactory C family GPCRs has evolved to allow the detection and discrimination of a spectrum of amino acid and/or amino acid-based compounds, which are potent olfactory cues in fish. Furthermore, as the major groups of fish receptors and mammalian V2R receptors appear to have diverged significantly from a common ancestral gene(s), these receptors likely mediate chemosensation of different classes of chemical structures by their respective organisms. PMID:17156446

  20. BILE ACIDS REGULATE THE ONTOGENIC EXPRESSION OF ILEAL BILE ACID BINDING PROTEIN IN THE RAT VIA THE FARNESOID X RECEPTOR

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In the rat, an increase in ileal bile acid binding protein (IBABP) expression occurs during the third postnatal week. In vitro studies suggest that bile acids (BAs) increase IBABP transcription by activating the BA receptor, farnesoid X receptor (FXR). Thus, we investigated the role of BAs on the on...

  1. Possible intermolecular interaction between quinolones and biphenylacetic acid inhibits gamma-aminobutyric acid receptor sites.

    PubMed

    Akahane, K; Kimura, Y; Tsutomi, Y; Hayakawa, I

    1994-10-01

    The combination of some new quinolone antibacterial agents with 4-biphenylacetic acid (BPAA), a metabolite of fenbufen, is known to specifically induce functional blockade of the gamma-aminobutyric acid (GABA) receptors. The mechanisms of these drug interactions were further examined. Scatchard analysis of [3H]muscimol binding to rat brain plasma membranes in the presence of enoxacin and BPAA revealed that a significant decrease in the number of muscimol binding sites was produced without affecting the affinity of binding to the receptors. In the presence of norfloxacin, BPAA inhibited muscimol binding the most potently of the six BPAA-related compounds tested. Fenbufen and 9,10-dihydro-gamma-oxo-2-phenanthrenebutyric acid also inhibited the binding, and 4-biphenylcarboxylic acid and methyl 4-biphenylacetate inhibited it slightly, but 3-benzoylpropionic acid exhibited no competitive inhibition. Accordingly, hybrid molecules of norfloxacin and BPAA were synthesized for stereochemical analysis of these drug interactions. A hybrid with a -CONH(CH2)3- chain between norfloxacin and BPAA (flexible structure) inhibited muscimol binding, and intracisternal injection of this hybrid caused clonic convulsions in mice more potently than the combination of norfloxacin and BPAA did. In contrast, a hybrid linked by -CONH- (stretched structure) showed almost no such inhibitory effect. 1H NMR analysis indicated the presence of intramolecular attraction at the quinoline ring of the hybrid exhibiting the antagonistic activity. These results suggest the possibility that quinolones and BPAA interact with the GABA receptor at nearby sites and that the binding affinity of quinolones to the GABA receptors is largely enhanced by the intermolecular interaction with BPAA. PMID:7840564

  2. Possible intermolecular interaction between quinolones and biphenylacetic acid inhibits gamma-aminobutyric acid receptor sites.

    PubMed Central

    Akahane, K; Kimura, Y; Tsutomi, Y; Hayakawa, I

    1994-01-01

    The combination of some new quinolone antibacterial agents with 4-biphenylacetic acid (BPAA), a metabolite of fenbufen, is known to specifically induce functional blockade of the gamma-aminobutyric acid (GABA) receptors. The mechanisms of these drug interactions were further examined. Scatchard analysis of [3H]muscimol binding to rat brain plasma membranes in the presence of enoxacin and BPAA revealed that a significant decrease in the number of muscimol binding sites was produced without affecting the affinity of binding to the receptors. In the presence of norfloxacin, BPAA inhibited muscimol binding the most potently of the six BPAA-related compounds tested. Fenbufen and 9,10-dihydro-gamma-oxo-2-phenanthrenebutyric acid also inhibited the binding, and 4-biphenylcarboxylic acid and methyl 4-biphenylacetate inhibited it slightly, but 3-benzoylpropionic acid exhibited no competitive inhibition. Accordingly, hybrid molecules of norfloxacin and BPAA were synthesized for stereochemical analysis of these drug interactions. A hybrid with a -CONH(CH2)3- chain between norfloxacin and BPAA (flexible structure) inhibited muscimol binding, and intracisternal injection of this hybrid caused clonic convulsions in mice more potently than the combination of norfloxacin and BPAA did. In contrast, a hybrid linked by -CONH- (stretched structure) showed almost no such inhibitory effect. 1H NMR analysis indicated the presence of intramolecular attraction at the quinoline ring of the hybrid exhibiting the antagonistic activity. These results suggest the possibility that quinolones and BPAA interact with the GABA receptor at nearby sites and that the binding affinity of quinolones to the GABA receptors is largely enhanced by the intermolecular interaction with BPAA. PMID:7840564

  3. Pharmacological activation of lysophosphatidic acid receptors regulates erythropoiesis

    PubMed Central

    Lin, Kuan-Hung; Ho, Ya-Hsuan; Chiang, Jui-Chung; Li, Meng-Wei; Lin, Shi-Hung; Chen, Wei-Min; Chiang, Chi-Ling; Lin, Yu-Nung; Yang, Ya-Jan; Chen, Chiung-Nien; Lu, Jenher; Huang, Chang-Jen; Tigyi, Gabor; Yao, Chao-Ling; Lee, Hsinyu

    2016-01-01

    Lysophosphatidic acid (LPA), a growth factor-like phospholipid, regulates numerous physiological functions, including cell proliferation and differentiation. In a previous study, we have demonstrated that LPA activates erythropoiesis by activating the LPA 3 receptor subtype (LPA3) under erythropoietin (EPO) induction. In the present study, we applied a pharmacological approach to further elucidate the functions of LPA receptors during red blood cell (RBC) differentiation. In K562 human erythroleukemia cells, knockdown of LPA2 enhanced erythropoiesis, whereas knockdown of LPA3 inhibited RBC differentiation. In CD34+ human hematopoietic stem cells (hHSC) and K526 cells, the LPA3 agonist 1-oleoyl-2-methyl-sn-glycero-3-phosphothionate (2S-OMPT) promoted erythropoiesis, whereas the LPA2 agonist dodecyl monophosphate (DMP) and the nonlipid specific agonist GRI977143 (GRI) suppressed this process. In zebrafish embryos, hemoglobin expression was significantly increased by 2S-OMPT treatment but was inhibited by GRI. Furthermore, GRI treatment decreased, whereas 2S-OMPT treatment increased RBC counts and amount of hemoglobin level in adult BALB/c mice. These results indicate that LPA2 and LPA3 play opposing roles during RBC differentiation. The pharmacological activation of LPA receptor subtypes represent a novel strategies for augmenting or inhibiting erythropoiesis. PMID:27244685

  4. Pharmacological activation of lysophosphatidic acid receptors regulates erythropoiesis.

    PubMed

    Lin, Kuan-Hung; Ho, Ya-Hsuan; Chiang, Jui-Chung; Li, Meng-Wei; Lin, Shi-Hung; Chen, Wei-Min; Chiang, Chi-Ling; Lin, Yu-Nung; Yang, Ya-Jan; Chen, Chiung-Nien; Lu, Jenher; Huang, Chang-Jen; Tigyi, Gabor; Yao, Chao-Ling; Lee, Hsinyu

    2016-01-01

    Lysophosphatidic acid (LPA), a growth factor-like phospholipid, regulates numerous physiological functions, including cell proliferation and differentiation. In a previous study, we have demonstrated that LPA activates erythropoiesis by activating the LPA 3 receptor subtype (LPA3) under erythropoietin (EPO) induction. In the present study, we applied a pharmacological approach to further elucidate the functions of LPA receptors during red blood cell (RBC) differentiation. In K562 human erythroleukemia cells, knockdown of LPA2 enhanced erythropoiesis, whereas knockdown of LPA3 inhibited RBC differentiation. In CD34(+) human hematopoietic stem cells (hHSC) and K526 cells, the LPA3 agonist 1-oleoyl-2-methyl-sn-glycero-3-phosphothionate (2S-OMPT) promoted erythropoiesis, whereas the LPA2 agonist dodecyl monophosphate (DMP) and the nonlipid specific agonist GRI977143 (GRI) suppressed this process. In zebrafish embryos, hemoglobin expression was significantly increased by 2S-OMPT treatment but was inhibited by GRI. Furthermore, GRI treatment decreased, whereas 2S-OMPT treatment increased RBC counts and amount of hemoglobin level in adult BALB/c mice. These results indicate that LPA2 and LPA3 play opposing roles during RBC differentiation. The pharmacological activation of LPA receptor subtypes represent a novel strategies for augmenting or inhibiting erythropoiesis. PMID:27244685

  5. Deciphering the nuclear bile acid receptor FXR paradigm

    PubMed Central

    Modica, Salvatore; Gadaleta, Raffaella M.; Moschetta, Antonio

    2010-01-01

    Originally called retinoid X receptor interacting protein 14 (RIP14), the farnesoid X receptor (FXR) was renamed after the ability of its rat form to bind supra-physiological concentrations of farnesol. In 1999 FXR was de-orphanized since primary bile acids were identified as natural ligands. Strongly expressed in the liver and intestine, FXR has been shown to be the master transcriptional regulator of several entero-hepatic metabolic pathways with relevance to the pathophysiology of conditions such as cholestasis, fatty liver disease, cholesterol gallstone disease, intestinal inflammation and tumors. Furthermore, given the importance of FXR in the gut-liver axis feedbacks regulating lipid and glucose homeostasis, FXR modulation appears to have great input in diseases such as metabolic syndrome and diabetes. Exciting results from several cellular and animal models have provided the impetus to develop synthetic FXR ligands as novel pharmacological agents. Fourteen years from its discovery, FXR has gone from bench to bedside; a novel nuclear receptor ligand is going into clinical use. PMID:21383957

  6. Interaction of the C-terminal acidic domain of the insulin receptor with histone modulates the receptor kinase activity.

    PubMed

    Baron, V; Kaliman, P; Alengrin, F; Van Obberghen, E

    1995-04-01

    In this study, we investigated the role of the insulin receptor domain 1270-1280, an acid-rich sequence located in the receptor C-terminus. Antipeptide IgG raised against this sequence were obtained and used to analyze their effect on receptor function. Antipeptide IgG inhibited receptor autophosphorylation at Tyr1146, Tyr1150 and Tyr1151. These sites are known to be key modulators of the receptor activity. Autophosphorylation at other sites may also have been inhibited. The antipeptide antibody decreased the receptor kinase activity measured with poly(Glu80Tyr20) and a synthetic peptide corresponding to the proreceptor sequence 1142-1158. We provide evidence that the effect of the antibody on substrate phosphorylation may result from the control of the phosphorylation level of the receptor. Concerning the action of the antipeptide IgG on the receptor kinase activity, histone did not behave similarly to poly(Glu80Tyr20). The antibody recognizing sequence 1270-1280 competed with histone for an overlapping binding site. Histone also modulated insulin receptor autophosphorylation, supporting the idea that interference with domain 1270-1280 alters the receptor kinase. Our data suggest that the acidic region including residues 1270-1280 of the insulin receptor C-terminus is involved in the following events: (a) receptor binding with histone, an exogenous substrate of the receptor kinase, and (b) the regulation of receptor autophosphorylation and kinase activity. Based on these observations, we would like to propose that this insulin receptor domain could interact with cellular proteins modulating the receptor kinase. PMID:7744039

  7. Molecular basis for amino acid sensing by family C G-protein-coupled receptors

    PubMed Central

    Wellendorph, P; Bräuner-Osborne, H

    2009-01-01

    Family C of human G-protein-coupled receptors (GPCRs) is constituted by eight metabotropic glutamate receptors, two γ-aminobutyric acid type B (GABAB1–2) subunits forming the heterodimeric GABAB receptor, the calcium-sensing receptor, three taste1 receptors (T1R1–3), a promiscuous L-α-amino acid receptor G-protein-coupled receptor family C, group 6, subtype A (GPRC6A) and seven orphan receptors. Aside from the orphan receptors, the family C GPCRs are dimeric receptors characterized by a large extracellular Venus flytrap domain which bind the endogenous agonists. Except from the GABAB1–2 and T1R2–3 receptor, all receptors are either activated or positively modulated by amino acids. In this review, we outline mutational, biophysical and structural studies which have elucidated the interaction of the amino acids with the Venus flytrap domains, molecular mechanisms of receptor selectivity and the initial steps in receptor activation. PMID:19298394

  8. Retinoic acid receptors: from molecular mechanisms to cancer therapy.

    PubMed

    di Masi, Alessandra; Leboffe, Loris; De Marinis, Elisabetta; Pagano, Francesca; Cicconi, Laura; Rochette-Egly, Cécile; Lo-Coco, Francesco; Ascenzi, Paolo; Nervi, Clara

    2015-02-01

    Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported. PMID:25543955

  9. Leveraging abscisic acid receptors for efficient water use in Arabidopsis

    PubMed Central

    Yang, Zhenyu; Liu, Jinghui; Tischer, Stefanie V.; Christmann, Alexander; Windisch, Wilhelm; Schnyder, Hans; Grill, Erwin

    2016-01-01

    Plant growth requires the influx of atmospheric CO2 through stomatal pores, and this carbon uptake for photosynthesis is inherently associated with a large efflux of water vapor. Under water deficit, plants reduce transpiration and are able to improve carbon for water exchange leading to higher water use efficiency (WUE). Whether increased WUE can be achieved without trade-offs in plant growth is debated. The signals mediating the WUE response under water deficit are not fully elucidated but involve the phytohormone abscisic acid (ABA). ABA is perceived by a family of related receptors known to mediate acclimation responses and to reduce transpiration. We now show that enhanced stimulation of ABA signaling via distinct ABA receptors can result in plants constitutively growing at high WUE in the model species Arabidopsis. WUE was assessed by three independent approaches involving gravimetric analyses, 13C discrimination studies of shoots and derived cellulose fractions, and by gas exchange measurements of whole plants and individual leaves. Plants expressing the ABA receptors RCAR6/PYL12 combined up to 40% increased WUE with high growth rates, i.e., are water productive. Water productivity was associated with maintenance of net carbon assimilation by compensatory increases of leaf CO2 gradients, thereby sustaining biomass acquisition. Leaf surface temperatures and growth potentials of plants growing under well-watered conditions were found to be reliable indicators for water productivity. The study shows that ABA receptors can be explored to generate more plant biomass per water transpired, which is a prime goal for a more sustainable water use in agriculture. PMID:27247417

  10. Leveraging abscisic acid receptors for efficient water use in Arabidopsis.

    PubMed

    Yang, Zhenyu; Liu, Jinghui; Tischer, Stefanie V; Christmann, Alexander; Windisch, Wilhelm; Schnyder, Hans; Grill, Erwin

    2016-06-14

    Plant growth requires the influx of atmospheric CO2 through stomatal pores, and this carbon uptake for photosynthesis is inherently associated with a large efflux of water vapor. Under water deficit, plants reduce transpiration and are able to improve carbon for water exchange leading to higher water use efficiency (WUE). Whether increased WUE can be achieved without trade-offs in plant growth is debated. The signals mediating the WUE response under water deficit are not fully elucidated but involve the phytohormone abscisic acid (ABA). ABA is perceived by a family of related receptors known to mediate acclimation responses and to reduce transpiration. We now show that enhanced stimulation of ABA signaling via distinct ABA receptors can result in plants constitutively growing at high WUE in the model species Arabidopsis WUE was assessed by three independent approaches involving gravimetric analyses, (13)C discrimination studies of shoots and derived cellulose fractions, and by gas exchange measurements of whole plants and individual leaves. Plants expressing the ABA receptors RCAR6/PYL12 combined up to 40% increased WUE with high growth rates, i.e., are water productive. Water productivity was associated with maintenance of net carbon assimilation by compensatory increases of leaf CO2 gradients, thereby sustaining biomass acquisition. Leaf surface temperatures and growth potentials of plants growing under well-watered conditions were found to be reliable indicators for water productivity. The study shows that ABA receptors can be explored to generate more plant biomass per water transpired, which is a prime goal for a more sustainable water use in agriculture. PMID:27247417

  11. [Role of excitatory amino acids in neuropathology].

    PubMed

    Wikinski, S I; Acosta, G B

    1995-01-01

    Excitatory amino acids (EAA) became known as neurotransmitters of the central nervous system (CNS) in the last decade. The most studied EAA are glutamate and aspartate. Both are synthetized by the same mechanism as gamaaminobutyric acid. (Fig. 1). Glutamate is widely distributed in the CNS and the spinal cord, being the areas of higher concentration the cerebral cortex, the hypocampus and the cerebellum. There have been identified two type of receptors for glutamate: ionotropic and metabotropic. The former includes three different types: NMDA, AMPA and KA. NMDA receptor is coupled to a Na+ and Ca2+ channel being the second ion the most important one. This receptor has several sites of binding for various substances. Along with the site for N-methyl-D-aspartate, which binds glutamate and/or aspartate, there have been identified a site for the binding of glycine (which is different from the strychnine sensitive one), a site for poliamines such as spermine and spermidine, and a site for the binding of Zn2+ (Table 1). AMPA receptor is associated to a Ca(2+)-Na+ channel, being in this case the Na+ the most important ion. There are two metabotropic type receptors: L-AP4 and trans-ACPD. Both are coupled to a G protein and agonists exert their action increasing phospholipase C activity which in turn induces an increment of IP3 and diacyl-glicerol, and a consecutive releasing of Ca2+ from intracellular stores. EAA play a role in some physiological processes. One of them is long-term potentiation (LTP), an electrochemical phenomenon involved in memory consolidation. Antagonists of NMDA and AMPA receptor prevent the development of LTP, and conversely, the agonist of glycine site of NMDA receptor--D-cycloserine--facilitates memory consolidation. Since 1957, EAA are considered neurotoxic substances and there are many indirect evidences to support this statement. Pathogenesis of neuronal damage elicited by EAA involves the events shown in Fig. 3. Prevention of the cascade of

  12. Thyroid hormone receptor can modulate retinoic acid-mediated axis formation in frog embryogenesis.

    PubMed Central

    Banker, D E; Eisenman, R N

    1993-01-01

    Thyroid hormone receptor acts as a hormone-dependent transcriptional transactivator and as a transcriptional repressor in the absence of thyroid hormone. Specifically, thyroid hormone receptor can repress retinoic acid-induced gene expression through interactions with retinoic acid receptor. (Retinoic acid is a potent teratogen in the frog Xenopus laevis, acting at early embryonic stages to interfere with the formation of anterior structures. Endogenous retinoic acid is thought to act in normal anterior-posterior axis formation.) We have previously shown that thyroid hormone receptor RNA (alpha isotype) is expressed and polysome-associated during Xenopus embryogenesis preceding thyroid gland maturation and endogenous thyroid hormone production (D. E. Banker, J. Bigler, and R. N. Eisenman, Mol. Cell. Biol. 11:5079-5089, 1991). To determine whether thyroid hormone receptor might influence the effects of retinoic acid in early frog development, we have examined the results of ectopic thyroid hormone receptor expression on retinoic acid teratogenesis. We demonstrate that microinjections of full-length thyroid hormone receptor RNA protect injected embryos from retinoic acid teratogenesis. DNA binding is apparently essential to this protective function, as truncated thyroid hormone receptors, lacking DNA-binding domains but including hormone-binding and dimerization domains, do not protect from retinoic acid. We have shown that microinjections of these dominant-interfering thyroid hormone receptors, as well as anti-thyroid hormone receptor antibodies, increase retinoic acid teratogenesis in injected embryos, presumably by inactivating endogenous thyroid hormone receptor. This finding suggests that endogenous thyroid hormone receptors may act to limit retinoic acid sensitivity. On the other hand, after thyroid hormone treatment, ectopic thyroid hormone receptor mediates teratogenesis that is indistinguishable from the dorsoanterior deficiencies produced in retinoic acid

  13. Bile Acid-Activated Receptors, Intestinal Microbiota, and the Treatment of Metabolic Disorders.

    PubMed

    Fiorucci, Stefano; Distrutti, Eleonora

    2015-11-01

    The composition of the bile acid pool is a function of the microbial metabolism of bile acids in the intestine. Perturbations of the microbiota shape the bile acid pool and modulate the activity of bile acid-activated receptors (BARs) even beyond the gastrointestinal tract, triggering various metabolic axes and altering host metabolism. Bile acids, in turn, can also regulate the composition of the gut microbiome at the highest taxonomic levels. Primary bile acids from the host are preferential ligands for the farnesoid X receptor (FXR), while secondary bile acids from the microbiota are ligands for G-protein-coupled bile acid receptor 1 (GPBAR1). In this review, we examine the role of bile acid signaling in the regulation of intestinal microbiota and how changes in bile acid composition affect human metabolism. Bile acids may offer novel therapeutic modalities in inflammation, obesity, and diabetes. PMID:26481828

  14. EMBO Retinoids 2011: mechanisms, biology and pathology of signaling by retinoic acid and retinoic acid receptors

    PubMed Central

    McKenna, Neil J.

    2012-01-01

    Retinoic acid (RA) is one of the principal active metabolites of vitamin A (retinol) which mediates a spectrum of critical physiological and developmental processes. Transcriptional regulation by RA is mediated primarily by members of the retinoic acid receptor (RAR) subfamily of the nuclear receptor (NR) superfamily of transcription factors. NRs bind specific genomic DNA sequence motifs and engage coregulators and components of the basal transcription machinery to effect transcriptional regulation at target gene promoters. Disruption of signaling by retinoic acid is thought to underlie the etiology of a number of inflammatory and neoplastic diseases including breast cancer and haematological malignancies. A meeting of international researchers in retinoid signaling was convened in Strasbourg in September 2011 under the auspices of the European Molecular Biology Organization (EMBO). Retinoids 2011 encompassed myriad mechanistic, biological and pathological aspects of these hormones and their cognate receptors, as well as setting these advances in the context of wider current questions on signaling by members of the NR superfamily. PMID:22438793

  15. A Single Amino Acid Substitution in 1918 Influenza Virus Hemagglutinin Changes Receptor Binding Specificity

    PubMed Central

    Glaser, Laurel; Stevens, James; Zamarin, Dmitriy; Wilson, Ian A.; García-Sastre, Adolfo; Tumpey, Terrence M.; Basler, Christopher F.; Taubenberger, Jeffery K.; Palese, Peter

    2005-01-01

    The receptor binding specificity of influenza viruses may be important for host restriction of human and avian viruses. Here, we show that the hemagglutinin (HA) of the virus that caused the 1918 influenza pandemic has strain-specific differences in its receptor binding specificity. The A/South Carolina/1/18 HA preferentially binds the α2,6 sialic acid (human) cellular receptor, whereas the A/New York/1/18 HA, which differs by only one amino acid, binds both the α2,6 and the α2,3 sialic acid (avian) cellular receptors. Compared to the conserved consensus sequence in the receptor binding site of avian HAs, only a single amino acid at position 190 was changed in the A/New York/1/18 HA. Mutation of this single amino acid back to the avian consensus resulted in a preference for the avian receptor. PMID:16103207

  16. Expression of gastric antisecretory and prostaglandin E receptor binding activity of misoprostol by misoprostol free acid.

    PubMed

    Tsai, B S; Kessler, L K; Stolzenbach, J; Schoenhard, G; Bauer, R F

    1991-05-01

    In enriched canine parietal cell preparations, misoprostol, an analog of prostaglandin E1 methyl ester, was rapidly deesterified to misoprostol free acid. Under this circumstance, misoprostol and misoprostol free acid exhibited equal antisecretory potency against histamine-stimulated acid secretion and bound equally well to prostaglandin E receptors. When the deesterification of misoprostol was inhibited by paraoxon, an esterase inhibitor, the antisecretory and receptor binding activity of misoprostol was markedly reduced, with potency much less than misoprostol free acid. These results indicate that misoprostol free acid is the active biological form of misoprostol that binds to prostaglandin E receptors and mediates the antisecretory action of misoprostol. PMID:1850690

  17. Obeticholic acid, a synthetic bile acid agonist of the farnesoid X receptor, attenuates experimental autoimmune encephalomyelitis.

    PubMed

    Ho, Peggy P; Steinman, Lawrence

    2016-02-01

    Bile acids are ligands for the nuclear hormone receptor, farnesoid X receptor (FXR). The bile acid-FXR interaction regulates bile acid synthesis, transport, and cholesterol metabolism. Recently, bile acid-FXR regulation has been reported to play an integral role in both hepatic and intestinal inflammation, and in atherosclerosis. In this study, we found that FXR knockout mice had more disease severity in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Obeticholic acid (6α-ethyl-chenodeoxycholic acid, 6-ECDCA), a synthetic FXR agonist, is an orally available drug that is currently in clinical trials for the treatment of inflammatory diseases such as alcoholic hepatitis, nonalcoholic steatohepatitis, and primary biliary cirrhosis. When we treated mice exhibiting established EAE with 6-ECDCA, or the natural FXR ligand chenodeoxycholic acid (CDCA), clinical disease was ameliorated by (i) suppressing lymphocyte activation and proinflammatory cytokine production; (ii) reducing CD4(+) T cells and CD19(+) B cell populations and their expression of negative checkpoint regulators programmed cell death protein 1 (PD1), programmed death-ligand 1 (PD-L1), and B and T lymphocyte attenuator (BTLA); (iii) increasing CD8(+) T cells and PD1, PDl-1, and BTLA expression; and (iv) reducing VLA-4 expression in both the T- and B-cell populations. Moreover, adoptive transfer of 6-ECDCA- or CDCA-treated donor cells failed to transfer disease in naive recipients. Thus, we show that FXR functions as a negative regulator in neuroinflammation and we highlight that FXR agonists represent a potential previously unidentified therapy for MS. PMID:26811456

  18. Regulation of vitamin D receptor expression by retinoic acid receptor alpha in acute myeloid leukemia cells.

    PubMed

    Marchwicka, Aleksandra; Cebrat, Małgorzata; Łaszkiewicz, Agnieszka; Śnieżewski, Łukasz; Brown, Geoffrey; Marcinkowska, Ewa

    2016-05-01

    Acute myeloid leukemia (AML) is the predominant acute leukemia among adults, characterized by an accumulation of malignant immature myeloid precursors. A very promising way to treat AML is differentiation therapy using either all-trans-retinoic acid (ATRA) or 1,25-dihydroxyvitamin D3 (1,25D), or the use of both these differentiation-inducing agents. However, the effect of combination treatment varies in different AML cell lines, and this is due to ATRA either down- or up-regulating transcription of vitamin D receptor (VDR) in the cells examined. The mechanism of transcriptional regulation of VDR in response to ATRA has not been fully elucidated. Here, we show that the retinoic acid receptor α (RARα) is responsible for regulating VDR transcription in AML cells. We have shown that a VDR transcriptional variant, originating in exon 1a, is regulated by RARα agonists in AML cells. Moreover, in cells with a high basal level of RARα protein, the VDR gene is transcriptionally repressed as long as RARα agonist is absent. In these cells down-regulation of the level of RARα leads to increased expression of VDR. We consider that our findings provide a mechanistic background to explain the different outcomes from treating AML cell lines with a combination of ATRA and 1,25D. PMID:26969398

  19. Expression of human epileptic temporal lobe neurotransmitter receptors in Xenopus oocytes: An innovative approach to study epilepsy.

    PubMed

    Palma, Eleonora; Esposito, Vincenzo; Mileo, Anna Maria; Di Gennaro, Giancarlo; Quarato, Pierpaolo; Giangaspero, Felice; Scoppetta, Ciriaco; Onorati, Paolo; Trettel, Flavia; Miledi, Ricardo; Eusebi, Fabrizio

    2002-11-12

    Poly(A(+)) RNA was extracted from the temporal lobe (TL) of medically intractable epileptic patients which underwent surgical TL resection. Injection of this mRNA into Xenopus oocytes led to the expression of ionotropic receptors for gamma-aminobutyric acid (GABA), kainate (KAI) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). Membrane currents elicited by GABA inverted polarity at -15 mV, close to the oocyte's chloride equilibrium potential, were inhibited by bicuculline, and were potentiated by pentobarbital and flunitrazepam. These basic characteristics were also displayed by GABA currents elicited in oocytes injected with mRNAs isolated from human TL glioma (TLG) or from mouse TL. However, the GABA receptors expressed by the epileptic TL mRNA exhibited some unusual properties, consisting in a rapid current run-down after repetitive GABA applications and a large EC(50) (125 microM). AMPA alone evoked very small or nil currents, whereas KAI induced larger currents. Nevertheless, upon cyclothiazide treatment, AMPA elicited substantial currents that, like the KAI currents, were inhibited by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Furthermore, the glutamate receptor 5 (GluR5) agonist, ATPA, failed to evoke an obvious current although both RT-PCR and Western blot analyses showed GluR5 expression in the epileptic TL. Oocytes injected with mouse TL or human TLG mRNAs generated KAI and AMPA currents similar to those evoked in oocytes injected with epileptic TL mRNA but, in contrast to these, the mouse TL and human TLG oocytes were also responsive to ATPA. Our findings are in accord with the concept that both a depression of GABA inhibition and a dysfunction of the KAI-receptor system maintain a high neuronal excitability that results in epileptic seizures. PMID:12409614

  20. Expression of human epileptic temporal lobe neurotransmitter receptors in Xenopus oocytes: An innovative approach to study epilepsy

    PubMed Central

    Palma, Eleonora; Esposito, Vincenzo; Mileo, Anna Maria; Di Gennaro, Giancarlo; Quarato, Pierpaolo; Giangaspero, Felice; Scoppetta, Ciriaco; Onorati, Paolo; Trettel, Flavia; Miledi, Ricardo; Eusebi, Fabrizio

    2002-01-01

    Poly(A+) RNA was extracted from the temporal lobe (TL) of medically intractable epileptic patients which underwent surgical TL resection. Injection of this mRNA into Xenopus oocytes led to the expression of ionotropic receptors for γ-aminobutyric acid (GABA), kainate (KAI) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). Membrane currents elicited by GABA inverted polarity at −15 mV, close to the oocyte's chloride equilibrium potential, were inhibited by bicuculline, and were potentiated by pentobarbital and flunitrazepam. These basic characteristics were also displayed by GABA currents elicited in oocytes injected with mRNAs isolated from human TL glioma (TLG) or from mouse TL. However, the GABA receptors expressed by the epileptic TL mRNA exhibited some unusual properties, consisting in a rapid current run-down after repetitive GABA applications and a large EC50 (125 μM). AMPA alone evoked very small or nil currents, whereas KAI induced larger currents. Nevertheless, upon cyclothiazide treatment, AMPA elicited substantial currents that, like the KAI currents, were inhibited by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Furthermore, the glutamate receptor 5 (GluR5) agonist, ATPA, failed to evoke an obvious current although both RT-PCR and Western blot analyses showed GluR5 expression in the epileptic TL. Oocytes injected with mouse TL or human TLG mRNAs generated KAI and AMPA currents similar to those evoked in oocytes injected with epileptic TL mRNA but, in contrast to these, the mouse TL and human TLG oocytes were also responsive to ATPA. Our findings are in accord with the concept that both a depression of GABA inhibition and a dysfunction of the KAI-receptor system maintain a high neuronal excitability that results in epileptic seizures. PMID:12409614

  1. Tulane virus recognizes sialic acids as cellular receptors.

    PubMed

    Tan, Ming; Wei, Chao; Huang, Pengwei; Fan, Qiang; Quigley, Christina; Xia, Ming; Fang, Hao; Zhang, Xufu; Zhong, Weiming; Klassen, John S; Jiang, Xi

    2015-01-01

    The recent discovery that human noroviruses (huNoVs) recognize sialic acids (SAs) in addition to histo-blood group antigens (HBGAs) pointed to a new direction in studying virus-host interactions during calicivirus infection. HuNoVs remain difficult to study due to the lack of an effective cell culture model. In this study, we demonstrated that Tulane virus (TV), a cultivable primate calicivirus, also recognizes SAs in addition to the previously known TV-HBGA interactions. Evidence supporting this discovery includes that TV virions bound synthetic sialoglycoconjugates (SGCs) and that treatment of TV permissive LLC-MK2 cells with either neuraminidases or SA-binding lectins inhibited TV infectivity. In addition, we found that Maackia amurensis leukoagglutinin (MAL), a lectin that recognizes the α-2,3 linked SAs, bound LLC-MK2 cells, as well as TV, by which MAL promoted TV infectivity in cell culture. Our findings further highlight TV as a valuable surrogate for huNoVs, particularly in studying virus-host interactions that may involve two host carbohydrate receptors or co-receptors for infection. PMID:26146020

  2. Neurosteroid Agonist at GABAA Receptor Induces Persistent Neuroplasticity in VTA Dopamine Neurons

    PubMed Central

    Vashchinkina, Elena; Manner, Aino K; Vekovischeva, Olga; Hollander, Bjørnar den; Uusi-Oukari, Mikko; Aitta-aho, Teemu; Korpi, Esa R

    2014-01-01

    The main fast-acting inhibitory receptors in the mammalian brain are γ-aminobutyric acid type-A (GABAA) receptors for which neurosteroids, a subclass of steroids synthesized de novo in the brain, constitute a group of endogenous ligands with the most potent positive modulatory actions known. Neurosteroids can act on all subtypes of GABAA receptors, with a preference for δ-subunit-containing receptors that mediate extrasynaptic tonic inhibition. Pathological conditions characterized by emotional and motivational disturbances are often associated with perturbation in the levels of endogenous neurosteroids. We studied the effects of ganaxolone (GAN)—a synthetic analog of endogenous allopregnanolone that lacks activity on nuclear steroid receptors—on the mesolimbic dopamine (DA) system involved in emotions and motivation. A single dose of GAN in young mice induced a dose-dependent, long-lasting neuroplasticity of glutamate synapses of DA neurons ex vivo in the ventral tegmental area (VTA). Increased α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/N-methyl-D-aspartate ratio and rectification of AMPA receptor responses even at 6 days after GAN administration suggested persistent synaptic targeting of GluA2-lacking AMPA receptors. This glutamate neuroplasticity was not observed in GABAA receptor δ-subunit-knockout (δ-KO) mice. GAN (500 nM) applied locally to VTA selectively increased tonic inhibition of GABA interneurons and triggered potentiation of DA neurons within 4 h in vitro. Place-conditioning experiments in adult wild-type C57BL/6J and δ-KO mice revealed aversive properties of repeated GAN administration that were dependent on the δ-subunits. Prolonged neuroadaptation to neurosteroids in the VTA might contribute to both the physiology and pathophysiology underlying processes and changes in motivation, mood, cognition, and drug addiction. PMID:24077066

  3. Synthesis and biological evaluation of phenoxyacetic acid derivatives as novel free fatty acid receptor 1 agonists.

    PubMed

    Wang, Xuekun; Zhao, Tianxiao; Yang, Baowei; Li, Zheng; Cui, Jian; Dai, Yuxuan; Qiu, Qianqian; Qiang, Hao; Huang, Wenlong; Qian, Hai

    2015-01-01

    Free fatty acid receptor 1 (FFA1) is a new potential drug target for the treatment of type 2 diabetes because of its role in amplifying glucose-stimulated insulin secretion in pancreatic β-cell. In the present studies, we identified phenoxyacetic acid derivative (18b) as a potent FFA1 agonist (EC50=62.3 nM) based on the structure of phenylpropanoic acid derivative 4p. Moreover, compound 18b could significantly improve oral glucose tolerance in ICR mice and dose-dependently reduced glucose levels in type 2 diabetic C57BL/6 mice without observation of hypoglycemic side effect. Additionally, compound 18b exhibited acceptable PK profiles. In summary, compound 18b with ideal PK profiles exhibited good activity in vitro and in vivo, and might be a promising drug candidate for the treatment of diabetes mellitus. PMID:25481394

  4. Identification of the orphan GPCR, P2Y(10) receptor as the sphingosine-1-phosphate and lysophosphatidic acid receptor.

    PubMed

    Murakami, Masanori; Shiraishi, Akira; Tabata, Kenichi; Fujita, Norihisa

    2008-07-11

    Phylogenetic analysis of transmembrane regions of GPCRs using PHYLIP indicated that the orphan receptor P2Y(10) receptor was classified into the cluster consisting nucleotide and lipid receptors. Based on the results, we studied the abilities of nucleotides and lipids to activate the P2Y(10) receptors. As a result, sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA) evoked intracellular Ca(2+) increases in the CHO cells stably expressing the P2Y(10) fused with a G(16alpha) protein. These Ca(2+) responses were inhibited by S1P receptor and LPA receptor antagonists. The introduction of siRNA designed for P2Y(10) receptor into the P2Y(10)-CHO cells effectively blocked both S1P- and LPA-induced Ca(2+) increases. RT-PCR analysis showed that the mouse P2Y(10) was expressed in reproductive organs, brain, lung and skeletal muscle, suggesting the receptor plays physiological roles throughout the whole body. In conclusion, the P2Y(10) receptor is the first receptor identified as a dual lysophospholipid receptor. PMID:18466763

  5. Non-fibrillar amyloid-{beta} peptide reduces NMDA-induced neurotoxicity, but not AMPA-induced neurotoxicity

    SciTech Connect

    Niidome, Tetsuhiro; Goto, Yasuaki; Kato, Masaru; Wang, Pi-Lin; Goh, Saori; Tanaka, Naoki; Akaike, Akinori; Kihara, Takeshi; Sugimoto, Hachiro

    2009-09-04

    Amyloid-{beta} peptide (A{beta}) is thought to be linked to the pathogenesis of Alzheimer's disease. Recent studies suggest that A{beta} has important physiological roles in addition to its pathological roles. We recently demonstrated that A{beta}42 protects hippocampal neurons from glutamate-induced neurotoxicity, but the relationship between A{beta}42 assemblies and their neuroprotective effects remains largely unknown. In this study, we prepared non-fibrillar and fibrillar A{beta}42 based on the results of the thioflavin T assay, Western blot analysis, and atomic force microscopy, and examined the effects of non-fibrillar and fibrillar A{beta}42 on glutamate-induced neurotoxicity. Non-fibrillar A{beta}42, but not fibrillar A{beta}42, protected hippocampal neurons from glutamate-induced neurotoxicity. Furthermore, non-fibrillar A{beta}42 decreased both neurotoxicity and increases in the intracellular Ca{sup 2+} concentration induced by N-methyl-D-aspartate (NMDA), but not by {alpha}-amino-3-hydrozy-5-methyl-4-isoxazole propionic acid (AMPA). Our results suggest that non-fibrillar A{beta}42 protects hippocampal neurons from glutamate-induced neurotoxicity through regulation of the NMDA receptor.

  6. Developmental Nicotine Exposure Alters AMPA Neurotransmission in the Hypoglossal Motor Nucleus and Pre-Bötzinger Complex of Neonatal Rats

    PubMed Central

    Jaiswal, Stuti J.; Pilarski, Jason Q.; Harrison, Caitlyn M.; Fregosi, Ralph F.

    2014-01-01

    Developmental nicotine exposure (DNE) impacts central respiratory control in neonates born to smoking mothers. We previously showed that DNE enhances the respiratory motor response to bath application of AMPA to the brainstem, although it was unclear which brainstem respiratory neurons mediated these effects (Pilarski and Fregosi, 2009). Here we examine how DNE influences AMPA-type glutamatergic neurotransmission in the pre-Bötzinger complex (pre-BötC) and the hypoglossal motor nucleus (XIIMN), which are neuronal populations located in the medulla that are necessary for normal breathing. Using rhythmic brainstem slices from neonatal rats, we microinjected AMPA into the pre-BötC or the XIIMN while recording from XII nerve rootlets (XIIn) as an index of respiratory motor output. DNE increased the duration of tonic activity and reduced rhythmic burst amplitude after AMPA microinjection into the XIIMN. Also, DNE led to an increase in respiratory burst frequency after AMPA injection into the pre-BötC. Whole-cell patch-clamp recordings of XII motoneurons showed that DNE increased motoneuron excitability but did not change inward currents. Immunohistochemical studies indicate that DNE reduced the expression of glutamate receptor subunits 2 and 3 (GluR2/3) in the XIIMN and the pre-BötC. Our data show that DNE alters AMPAergic synaptic transmission in both the XIIMN and pre-BötC, although the mechanism by which this occurs is unclear. We suggest that the DNE-induced reduction in GluR2/3 may represent an attempt to compensate for increased cell excitability, consistent with mechanisms underlying homeostatic plasticity. PMID:23392689

  7. Modelling fate and transport of glyphosate and AMPA in the Meuse catchment to assess the contribution of different pollution sources

    NASA Astrophysics Data System (ADS)

    Desmet, Nele; Seuntjens, Piet

    2013-04-01

    Large river basins have multiple sources of pesticides and usually the pollution sources are spread over the entire catchment. The cumulative effect of pesticides entering the river system in upstream areas and the formation of persistent degradation products can compromise downstream water use e.g. raw water quality for drinking water abstractions. For assessments at catchment scale pesticide fluxes coming from different sources and sub basins need to be taken into account. To improve management strategies, a sound understanding of the sources, emission routes, transport, environmental fate and conversion of pesticides is needed. In the Netherlands, the Meuse river basin is an important source for drinking water production. The river suffers from elevated concentrations of glyphosate and aminomethylphosphonic acid (AMPA). For AMPA it is rather unclear to what extent the pollution is related to glyphosate degradation and what is the contribution of other sources, especial phosphonates in domestic and industrial waste water. Based on the available monitoring data only it is difficult to distinguish between AMPA sources in such a large river basin. This hampers interpretation and decision making for water quality management in the Meuse catchment. Here, application of water quality models is very useful to obtain complementary information and insights. Modelling allows accounting for temporal and spatial variability in discharge and concentrations as well as distinguishing the contribution from conversion processes. In this study, a model for the river Meuse was developed and applied to assess the contribution of tributary and transnational influxes, glyphosate degradation and other sources to the AMPA pollution.

  8. Enhancement of arachidonic acid signaling pathway by nicotinic acid receptor HM74A

    SciTech Connect

    Tang, Yuting . E-mail: ytang@prdus.jnj.com; Zhou, Lubing; Gunnet, Joseph W.; Wines, Pamela G.; Cryan, Ellen V.; Demarest, Keith T.

    2006-06-23

    HM74A is a G protein-coupled receptor for nicotinic acid (niacin), which has been used clinically to treat dyslipidemia for decades. The molecular mechanisms whereby niacin exerts its pleiotropic effects on lipid metabolism remain largely unknown. In addition, the most common side effect in niacin therapy is skin flushing that is caused by prostaglandin release, suggesting that the phospholipase A{sub 2} (PLA{sub 2})/arachidonic acid (AA) pathway is involved. Various eicosanoids have been shown to activate peroxisome-proliferator activated receptors (PPAR) that play a diverse array of roles in lipid metabolism. To further elucidate the potential roles of HM74A in mediating the therapeutic effects and/or side effects of niacin, we sought to explore the signaling events upon HM74A activation. Here we demonstrated that HM74A synergistically enhanced UTP- and bradykinin-mediated AA release in a pertussis toxin-sensitive manner in A431 cells. Activation of HM74A also led to Ca{sup 2+}-mobilization and enhanced bradykinin-promoted Ca{sup 2+}-mobilization through Gi protein. While HM74A increased ERK1/2 activation by the bradykinin receptor, it had no effects on UTP-promoted ERK1/2 activation.Furthermore, UTP- and bradykinin-mediated AA release was significantly decreased in the presence of both MAPK kinase inhibitor PD 098059 and PKC inhibitor GF 109203X. However, the synergistic effects of HM74A were not dramatically affected by co-treatment with both inhibitors, indicating the cross-talk occurred at the receptor level. Finally, stimulation of A431 cells transiently transfected with PPRE-luciferase with AA significantly induced luciferase activity, mimicking the effects of PPAR{gamma} agonist rosiglitazone, suggesting that alteration of AA signaling pathway can regulate gene expression via endogenous PPARs.

  9. Obeticholic acid, a synthetic bile acid agonist of the farnesoid X receptor, attenuates experimental autoimmune encephalomyelitis

    PubMed Central

    Ho, Peggy P.; Steinman, Lawrence

    2016-01-01

    Bile acids are ligands for the nuclear hormone receptor, farnesoid X receptor (FXR). The bile acid–FXR interaction regulates bile acid synthesis, transport, and cholesterol metabolism. Recently, bile acid–FXR regulation has been reported to play an integral role in both hepatic and intestinal inflammation, and in atherosclerosis. In this study, we found that FXR knockout mice had more disease severity in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Obeticholic acid (6α-ethyl-chenodeoxycholic acid, 6-ECDCA), a synthetic FXR agonist, is an orally available drug that is currently in clinical trials for the treatment of inflammatory diseases such as alcoholic hepatitis, nonalcoholic steatohepatitis, and primary biliary cirrhosis. When we treated mice exhibiting established EAE with 6-ECDCA, or the natural FXR ligand chenodeoxycholic acid (CDCA), clinical disease was ameliorated by (i) suppressing lymphocyte activation and proinflammatory cytokine production; (ii) reducing CD4+ T cells and CD19+ B cell populations and their expression of negative checkpoint regulators programmed cell death protein 1 (PD1), programmed death-ligand 1 (PD-L1), and B and T lymphocyte attenuator (BTLA); (iii) increasing CD8+ T cells and PD1, PDl-1, and BTLA expression; and (iv) reducing VLA-4 expression in both the T- and B-cell populations. Moreover, adoptive transfer of 6-ECDCA– or CDCA-treated donor cells failed to transfer disease in naive recipients. Thus, we show that FXR functions as a negative regulator in neuroinflammation and we highlight that FXR agonists represent a potential previously unidentified therapy for MS. PMID:26811456

  10. Endocytic Adaptor Epidermal Growth Factor Receptor Substrate 15 (Eps15) Is Involved in the Trafficking of Ubiquitinated α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid Receptors*

    PubMed Central

    Lin, Amy; Man, Heng-Ye

    2014-01-01

    AMPA-type glutamate receptors (AMPARs) play a critical role in mediating fast excitatory synaptic transmission in the brain. Alterations in receptor expression, distribution, and trafficking have been shown to underlie synaptic plasticity and higher brain functions, including learning and memory, as well as brain dysfunctions such as drug addiction and psychological disorders. Therefore, it is essential to elucidate the molecular mechanisms that regulate AMPAR dynamics. We have shown previously that mammalian AMPARs are subject to posttranslational modification by ubiquitin, with AMPAR ubiquitination enhancing receptor internalization and reducing AMPAR cell surface expression. Here we report a crucial role for epidermal growth factor receptor substrate 15 (Eps15), an endocytic adaptor, in ubiquitination-dependent AMPAR internalization. We find that suppression or overexpression of Eps15 results in changes in AMPAR surface expression. Eps15 interacts with AMPARs, which requires Nedd4-mediated GluA1 ubiquitination and the ubiquitin-interacting motif of Eps15. Importantly, we find that Eps15 plays an important role in AMPAR internalization. Knockdown of Eps15 suppresses the internalization of GluA1 but not the mutant GluA1 that lacks ubiquitination sites, indicating a role of Eps15 for the internalization of ubiquitinated AMPARs. These results reveal a novel molecular mechanism employed specifically for the trafficking of the ubiquitin-modified AMPARs. PMID:25023288

  11. Direct activation of GABAA receptors by substances in the organic acid fraction of Japanese sake.

    PubMed

    Izu, Hanae; Shigemori, Kensuke; Eguchi, Masaya; Kawane, Shuhei; Fujii, Shouko; Kitamura, Yuji; Aoshima, Hitoshi; Yamada, Yasue

    2017-01-01

    We investigated the effect of substances present in Japanese sake on the response of ionotropic γ-aminobutyric acid (GABA)A receptors expressed in Xenopus oocytes. Sake was fractionated by ion-exchange chromatography. The fraction containing organic acids (OA fraction) showed agonist activities on the GABAA receptor. OA fractions from sake were analyzed by capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS). Of the 64 compounds identified, 13 compounds showed GABAA receptor agonist activities. Especially, l-lactic acid showed high agonist activity and its EC50 value was 37μM. Intraperitoneal injections of l-lactic acid, gluconic acid, and pyruvic acid (10, 10, and 5mg/kg BW, respectively), which showed agonistic activity on the GABAA receptor, led to significant anxiolytic effects during an elevated plus-maze test in mice. PMID:27507485

  12. Farnesoid X receptor, the bile acid sensing nuclear receptor, in liver regeneration

    PubMed Central

    Li, Guodong; L. Guo, Grace

    2015-01-01

    The liver is unique in regenerative potential, which could recover the lost mass and function after injury from ischemia and resection. The underlying molecular mechanisms of liver regeneration have been extensively studied in the past using the partial hepatectomy (PH) model in rodents, where 2/3 PH is carried out by removing two lobes. The whole process of liver regeneration is complicated, orchestrated event involving a network of connected interactions, which still remain fully elusive. Bile acids (BAs) are ligands of farnesoid X receptor (FXR), a nuclear receptor of ligand-activated transcription factor. FXR has been shown to be highly involved in liver regeneration. BAs and FXR not only interact with each other but also regulate various downstream targets independently during liver regeneration. Moreover, recent findings suggest that tissue-specific FXR also contributes to liver regeneration significantly. These novel findings suggest that FXR has much broader role than regulating BA, cholesterol, lipid and glucose metabolism. Therefore, these researches highlight FXR as an important pharmaceutical target for potential use of FXR ligands to regulate liver regeneration in clinic. This review focuses on the roles of BAs and FXR in liver regeneration and the current underlying molecular mechanisms which contribute to liver regeneration. PMID:26579433

  13. Lysophosphatidic Acid (LPA) Receptor 5 Inhibits B Cell Antigen Receptor Signaling and Antibody Response1

    PubMed Central

    Shotts, Kristin; Donovan, Erin E.; Strauch, Pamela; Pujanauski, Lindsey M.; Victorino, Francisco; Al-Shami, Amin; Fujiwara, Yuko; Tigyi, Gabor; Oravecz, Tamas; Pelanda, Roberta; Torres, Raul M.

    2014-01-01

    Lysophospholipids have emerged as biologically important chemoattractants capable of directing lymphocyte development, trafficking and localization. Lysophosphatidic acid (LPA) is a major lysophospholipid found systemically and whose levels are elevated in certain pathological settings such as cancer and infections. Here, we demonstrate that BCR signal transduction by mature murine B cells is inhibited upon LPA engagement of the LPA5 (GPR92) receptor via a Gα12/13 – Arhgef1 pathway. The inhibition of BCR signaling by LPA5 manifests by impaired intracellular calcium store release and most likely by interfering with inositol 1,4,5-trisphosphate receptor activity. We further show that LPA5 also limits antigen-specific induction of CD69 and CD86 expression and that LPA5-deficient B cells display enhanced antibody responses. Thus, these data show that LPA5 negatively regulates BCR signaling, B cell activation and immune response. Our findings extend the influence of lysophospholipids on immune function and suggest that alterations in LPA levels likely influence adaptive humoral immunity. PMID:24890721

  14. Silent, fluorescent labeling of native neuronal receptors.

    PubMed

    Vytla, Devaiah; Combs-Bachmann, Rosamund E; Hussey, Amanda M; Hafez, Ismail; Chambers, James J

    2011-10-21

    We have developed a minimally-perturbing strategy that enables labeling and subcellular visualization of endogenous dendritic receptors on live, wild-type neurons. Specifically, calcium-permeable non-NMDA glutamate receptors expressed in hippocampal neurons can be targeted with this novel synthetic tri-functional molecule. This ligand-directed probe was targeted towards AMPA receptors and bears an electrophilic group for covalent bond formation with an amino acid side chain on the extracellular side of the ion channel. This molecule was designed in such a way that the use-dependent, polyamine-based ligand accumulates the chemically-reactive group at the extracellular side of these polyamine-sensitive receptors, thereby allowing covalent bond formation between an electrophilic moiety on the nanoprobe and a nucleophilic amino acid sidechain on the receptor. Bioconjugation of this molecule results in a stable covalent bond between the nanoprobe and the target receptor. Subsequent photolysis of a portion of the nanoprobe may then be employed to effect ligand release allowing the receptor to re-enter the non-liganded state, all the while retaining the fluorescent beacon for visualization. This technology allows for rapid fluorescent labeling of native polyamine-sensitive receptors and further advances the field of fluorescent labeling of native biological molecules. PMID:21897969

  15. NMDA receptor contributions to visual contrast coding

    PubMed Central

    Manookin, Michael B.; Weick, Michael; Stafford, Benjamin K.; Demb, Jonathan B.

    2010-01-01

    Summary In the retina, it is not well understood how visual processing depends on AMPA- and NMDA-type glutamate receptors. Here, we investigated how these receptors contribute to contrast coding in identified guinea pig ganglion cell types, in vitro. NMDA-mediated responses were negligible in ON α cells but substantial in OFF α and δ cells. OFF δ cell NMDA receptors were composed of GluN2B subunits. Using a novel deconvolution method, we determined the individual contributions of AMPA, NMDA and inhibitory currents to light responses of each cell type. OFF α and δ cells used NMDA receptors for encoding either the full contrast range (α), including near-threshold responses, or only a high range (δ). However, contrast sensitivity depended substantially on NMDA receptors only in OFF α cells. NMDA receptors contribute to visual contrast coding in a cell-type specific manner. Certain cell types generate excitatory responses using primarily AMPA receptors or disinhibition. PMID:20670835

  16. Amino acid conjugates of lithocholic acid as antagonists of the EphA2 receptor

    PubMed Central

    Incerti, Matteo; Tognolini, Massimiliano; Russo, Simonetta; Pala, Daniele; Giorgio, Carmine; Hassan-Mohamed, Iftiin; Noberini, Roberta; Pasquale, Elena B.; Vicini, Paola; Piersanti, Silvia; Rivara, Silvia; Barocelli, Elisabetta; Mor, Marco; Lodola, Alessio

    2013-01-01

    The Eph receptor–ephrin system is an emerging target for the development of novel antiangiogenetic agents. We recently identified lithocholic acid (LCA) as a small molecule able to block EphA2-dependent signals in cancer cells, suggesting that its (5β)-cholan-24-oic acid scaffold can be used as a template to design a new generation of improved EphA2 antagonists. Here, we report the design and synthesis of an extended set of LCA derivatives obtained by conjugation of its carboxyl group with different α-amino acids. Structure-activity relationships indicate that the presence of a lipophilic amino acid side chain is fundamental to achieve good potencies. The L-Trp derivative (20, PCM126) was the most potent antagonist of the series disrupting EphA2-ephrinA1 interaction and blocking EphA2 phosphorylation in prostate cancer cells at low μM concentrations, thus being significantly more potent than LCA. Compound 20 is among the most potent small molecule antagonists of the EphA2 receptor. PMID:23489211

  17. Characterization of DNA Binding and Retinoic Acid Binding Properties of Retinoic Acid Receptor

    NASA Astrophysics Data System (ADS)

    Yang, Na; Schule, Roland; Mangelsdorf, David J.; Evans, Ronald M.

    1991-05-01

    High-level expression of the full-length human retinoic acid receptor (RAR) α and the DNA binding domain of the RAR in Escherichia coli was achieved by using a T7 RNA polymerase-directed expression system. After induction, full-length RAR protein was produced at an estimated level of 20% of the total bacterial proteins. Both intact RAR molecules and the DNA binding domain bind to the cognate DNA response element with high specificity in the absence of retinoic acid. However, this binding is enhanced to a great extent upon the addition of eukaryotic cell extracts. The factor responsible for this enhancement is heat-sensitive and forms a complex with RAR that binds to DNA and exhibits a distinct migration pattern in the gel-mobility-shift assay. The interaction site of the factor with RAR is localized in the 70-amino acid DNA binding region of RAR. The hormone binding ability of the RARα protein was assayed by a charcoal absorption assay and the RAR protein was found to bind to retinoic acid with a K_d of 2.1 x 10-10 M.

  18. Structural basis and functions of abscisic acid receptors PYLs

    PubMed Central

    Zhang, Xing L.; Jiang, Lun; Xin, Qi; Liu, Yang; Tan, Jian X.; Chen, Zhong Z.

    2015-01-01

    Abscisic acid (ABA) plays a key role in many developmental processes and responses to adaptive stresses in plants. Recently, a new family of nucleocytoplasmic PYR/PYL/RCAR (PYLs) has been identified as bona fide ABA receptors. PYLs together with protein phosphatases type-2C (PP2Cs), Snf1 (Sucrose-non-fermentation 1)-related kinases subfamily 2 (SnRK2s) and downstream substrates constitute the core ABA signaling network. Generally, PP2Cs inactivate SnRK2s kinases by physical interaction and direct dephosphorylation. Upon ABA binding, PYLs change their conformations and then contact and inhibit PP2Cs, thus activating SnRK2s. Here, we reviewed the recent progress in research regarding the structures of the core signaling pathways of ABA, including the (+)-ABA, (−)-ABA and ABA analogs pyrabactin as well as 6AS perception by PYLs, SnRK2s mimicking PYLs in binding PP2Cs. PYLs inhibited PP2Cs in both the presence and absence of ABA and activated SnRK2s. The present review elucidates multiple ABA signal perception and transduction by PYLs, which might shed light on how to design small chemical compounds for improving plant performance in the future. PMID:25745428

  19. Action of Natural Abscisic Acid Precursors and Catabolites on Abscisic Acid Receptor Complexes1[W

    PubMed Central

    Kepka, Michal; Benson, Chantel L.; Gonugunta, Vijay K.; Nelson, Ken M.; Christmann, Alexander; Grill, Erwin; Abrams, Suzanne R.

    2011-01-01

    The phytohormone abscisic acid (ABA) regulates stress responses and controls numerous aspects of plant growth and development. Biosynthetic precursors and catabolites of ABA have been shown to trigger ABA responses in physiological assays, but it is not clear whether these are intrinsically active or whether they are converted into ABA in planta. In this study, we analyzed the effect of ABA precursors, conjugates, and catabolites on hormone signaling in Arabidopsis (Arabidopsis thaliana). The compounds were also tested in vitro for their ability to regulate the phosphatase moiety of ABA receptor complexes consisting of the protein phosphatase 2C ABI2 and the coreceptors RCAR1/PYL9, RCAR3/PYL8, and RCAR11/PYR1. Using mutants defective in ABA biosynthesis, we show that the physiological activity associated with ABA precursors derives predominantly from their bioconversion to ABA. The ABA glucose ester conjugate, which is the most widespread storage form of ABA, showed weak ABA-like activity in germination assays and in triggering ABA signaling in protoplasts. The ABA conjugate and precursors showed negligible activity as a regulatory ligand of the ABI2/RCAR receptor complexes. The majority of ABA catabolites were inactive in our assays. To analyze the chemically unstable 8′- and 9′-hydroxylated ABA catabolites, we used stable tetralone derivatives of these compounds, which did trigger selective ABA responses. ABA synthetic analogs exhibited differential activity as regulatory ligands of different ABA receptor complexes in vitro. The data show that ABA precursors, catabolites, and conjugates have limited intrinsic bioactivity and that both natural and synthetic ABA-related compounds can be used to probe the structural requirements of ABA ligand-receptor interactions. PMID:21976481

  20. Interaction of mechanisms involving epoxyeicosatrienoic acids, adenosine receptors, and metabotropic glutamate receptors in neurovascular coupling in rat whisker barrel cortex

    PubMed Central

    Shi, Yanrong; Liu, Xiaoguang; Gebremedhin, Debebe; Falck, John R; Harder, David R; Koehler, Raymond C

    2008-01-01

    Adenosine, astrocyte metabotropic glutamate receptors (mGluRs), and epoxyeicosatrienoic acids (EETs) have been implicated in neurovascular coupling. Although A2A and A2B receptors mediate cerebral vasodilation to adenosine, the role of each receptor in the cerebral blood flow (CBF) response to neural activation remains to be fully elucidated. In addition, adenosine can amplify astrocyte calcium, which may increase arachidonic acid metabolites such as EETs. The interaction of these pathways was investigated by determining if combined treatment with antagonists exerted an additive inhibitory effect on the CBF response. During whisker stimulation of anesthetized rats, the increase in cortical CBF was reduced by approximately half after individual administration of A2B, mGluR and EET antagonists and EET synthesis inhibitors. Combining treatment of either a mGluR antagonist, an EET antagonist, or an EET synthesis inhibitor with an A2B receptor antagonist did not produce an additional decrement in the CBF response. Likewise, the CBF response also remained reduced by ~50% when an EET antagonist was combined with an mGluR antagonist or an mGluR antagonist plus an A2B receptor antagonist. In contrast, A2A and A3 receptor antagonists had no effect on the CBF response to whisker stimulation. We conclude that (1) adenosine A2B receptors, rather than A2A or A3 receptors, play a significant role in coupling cortical CBF to neuronal activity, and (2) the adenosine A2B receptor, mGluR, and EETs signaling pathways are not functionally additive, consistent with the possibility of astrocytic mGluR and adenosine A2B receptor linkage to the synthesis and release of vasodilatory EETs. PMID:17519974

  1. Nitric oxide modulates blood pressure through NMDA receptors in the rostral ventrolateral medulla of conscious rats.

    PubMed

    Machado, Natalia L S; Silva, Fernanda C S; Chianca, Deoclecio A; de Menezes, Rodrigo C

    2016-07-15

    The rostral ventrolateral medulla (RVLM) is an important site of cardiovascular control related to the tonic excitation and regulating the sympathetic vasomotor tone through local presympathetic neurons. Nitric oxide (NO) has been implicated in the modulation of neurotransmission by several areas of the central nervous system including the RVLM. However the pathways driving NO affects and the correlation between NO and glutamate-induced mechanisms are not well established. Here, we investigate the influence of NO on the cardiovascular response evoked by the activation of NMDA and non-NMDA glutamatergic receptors in the RVLM in conscious rats. For that, we examined the influence of acute inhibition of the NO production within the RVLM, by injecting the nonselective constitutive NOS inhibitor, l-NAME, on responses evoked by the microinjection of excitatory amino acids l-glutamate, NMDA or AMPA agonists into RVLM. Our results show that the injection of l-glutamate, NMDA or AMPA agonists into RVLM, unilaterally, induced a marked increase in the mean arterial pressure (MAP). Pretreatment with l-NAME reduced the hypertensive response evoked by the glutamate injection, and also abolished the pressor response induced by the injection of NMDA into the RVLM. However, blocking the NO synthesis did not alter the response produced by the injection of AMPA agonist. These data provide evidence that the glutamatergic neurotransmission within the RVLM depends on excitatory effects exerted by NO on NMDA receptors, and that this mechanism might be essential to regulate systemic blood pressure. PMID:27150817

  2. Reduction in Dietary Omega-6 Polyunsaturated Fatty Acids: Eicosapentaenoic Acid plus Docosahexaenoic Acid Ratio Minimizes Atherosclerotic Lesion Formation and Inflammatory Response in the LDL Receptor Null Mouse

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dietary very long chain omega-3 polyunsaturated fatty acids (PUFA) have been associated with reduced CVD risk. LDL receptor null mice (LDLr-/-) were used to assess different dietary ratios of omega-6 PUFA to eicosapentaenoic acid plus docosahexaenoic acid (omega-6:EPA+DHA) on atherogenesis and infl...

  3. Hrs recognizes a hydrophobic amino acid cluster in cytokine receptors during ubiquitin-independent endosomal sorting.

    PubMed

    Amano, Yuji; Yamashita, Yuki; Kojima, Katsuhiko; Yoshino, Kazuhisa; Tanaka, Nobuyuki; Sugamura, Kazuo; Takeshita, Toshikazu

    2011-04-29

    Hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) is a component of the ESCRT-0 protein complex that captures ubiquitylated cargo proteins and sorts them to the lysosomal pathway. Although Hrs acts as a key transporter for ubiquitin-dependent endosomal sorting, we previously reported that Hrs is also involved in ubiquitin-independent endosomal sorting of interleukin-2 receptor β (IL-2Rβ). Here, we show direct interactions between bacterially expressed Hrs and interleukin-4 receptor α (IL-4Rα), indicating that their binding is not required for ubiquitylation of the receptors, similar to the case for IL-2Rβ. Examinations of the Hrs binding regions of the receptors reveal that a hydrophobic amino acid cluster in both IL-2Rβ and IL-4Rα is essential for the binding. Whereas the wild-type receptors are delivered to LAMP1-positive late endosomes, mutant receptors lacking the hydrophobic amino acid cluster are sorted to lysobisphosphatidic acid-positive late endosomes rather than LAMP1-positive late endosomes. We also show that the degradation of these mutant receptors is attenuated. Accordingly, Hrs functions during ubiquitin-independent endosomal sorting of the receptors by recognizing the hydrophobic amino acid cluster. These findings suggest the existence of a group of cargo proteins that have this hydrophobic amino acid cluster as a ubiquitin-independent sorting signal. PMID:21362618

  4. Amino acid receptors mediate calcium permeability in synaptosomes from rat brain

    SciTech Connect

    Pastuszko, A.; Wilson, D.F.

    1986-05-01

    Selected acidic amino acids and amino acid analogues were shown to increase the Ca/sup 2 +/ permeability of the plasma membrane of synaptosomes isolated from rat brain. Increased synaptosomal Ca/sup 2 +/ content was measured by uptake of /sup 45/Ca/sup 2 +/. Increased intrasynaptosomal free calcium was measured by the fluorescent calcium indicators indo 1 and quin 2. The increase in calcium permeability was maximal within 0.5 seconds (the limit of resolution of the methods used). The calcium permeability system(s) being modulated by the receptors appears to be Ca/sup 2 +/ channels but has properties different from the voltage dependent Ca/sup 2 +/ channels. Four different types of receptors have been observed; a kainate receptor antagonized by quisqualate, an L-cysteine sulfinate receptor, a 2-amino-2-phosphono-valerate receptor and an N-methyl-D-aspartate receptor. Each type of receptor is highly specific in ligand binding and none were activated or antagonized by aspartate or glutamate at concentrations up to 10 mM. Currently available data indicate substantial differences in ligand specificity between these presynaptic receptors and the postsynaptic receptors which have been classified by electrophysiological and radio-ligand binding studies. The neurotoxicity of kainate, L-cysteine sulfinate and N-methyl-D-aspartate may be due in part to metabolic and electrophysiological disturbances resulting from increased calcium in neurons having these receptors.

  5. Vitamin D receptor regulation of the steroid/bile acid sulfotransferase SULT2A1.

    PubMed

    Chatterjee, Bandana; Echchgadda, Ibtissam; Song, Chung Seog

    2005-01-01

    SULT2A1 is a sulfo-conjugating phase II enzyme expressed at very high levels in the liver and intestine, the two major first-pass metabolic tissues, and in the steroidogenic adrenal tissue. SULT2A1 acts preferentially on the hydroxysteroids dehydroepiandrosterone, testosterone/dihydrotestosterone, and pregnenolone and on cholesterol-derived amphipathic sterol bile acids. Several therapeutic drugs and other xenobiotics, which include xenoestrogens, are also sulfonated by this cytosolic steroid/bile acid sulfotransferase. Nonsteroid nuclear receptors with key roles in the metabolism and detoxification of endobiotics and xenobiotics, such as bile acid-activated farnesoid X receptor, xenobiotic-activated pregnane X receptor and constitutive androstane receptor, and lipid-activated peroxisome proliferator-activated receptor-alpha, mediate transcription induction of SULT2A1 in the enterohepatic system. The ligand-activated vitamin D receptor (VDR) is another nuclear receptor that stimulates SULT2A1 transcription, and the regulatory elements in human, mouse, and rat promoters directing this induction have been characterized. Given that bile acid sulfonation is catalyzed exclusively by SULT2A1 and that the 3alpha-sulfate of the highly toxic lithocholic acid is a major excretory metabolite in humans, we speculate that a role for the VDR pathway in SULT2A1 expression may have emerged to shield first-pass tissues from the cytotoxic effects of a bile acid overload arising from disrupted sterol homeostasis triggered by endogenous and exogenous factors. PMID:16399349

  6. Work plan for determining the occurrence of glyphosate, its transformation product AMPA, other herbicide compounds, and antibiotics in midwestern United States streams, 2002

    USGS Publications Warehouse

    Battaglin, W.A.; Thurman, E.M.; Kolpin, D.W.; Scribner, E.A.; Sandstrom, M.W.; Kuivila, K.M.

    2003-01-01

    The objective of this study is to determine the distribution of glyphosate and its primary transformation product aminomethylphosphonic acid (AMPA) in midwestern streams during post-application and harvest-season runoff events. Water samples will be collected in 2002 during two post-herbicide-application runoff events and one harvest-season runoff event from 53 sites on streams in the Midwestern United States. All samples will be analyzed at the U.S. Geological Survey Organic Geochemistry Research Laboratory in Lawrence, Kansas, for glyphosate and 20 other herbicides. Samples will also be analyzed for a glyphosate transformation product (AMPA) and 26 other herbicide transformation products, using GC/MS or HPLC/MS. Selected samples will be analyzed for 36 antibiotics or antibiotic transformational products. Results from this study will represent the first broad-scale investigation of glyphosate and AMPA in U.S. water resources.

  7. Interaction between retinoid acid receptor-related orphan receptor alpha (RORA) and neuropeptide S receptor 1 (NPSR1) in asthma.

    PubMed

    Acevedo, Nathalie; Sääf, Annika; Söderhäll, Cilla; Melén, Erik; Mandelin, Jami; Pietras, Christina Orsmark; Ezer, Sini; Karisola, Piia; Vendelin, Johanna; Gennäs, Gustav Boije af; Yli-Kauhaluoma, Jari; Alenius, Harri; von Mutius, Erika; Doekes, Gert; Braun-Fahrländer, Charlotte; Riedler, Josef; van Hage, Marianne; D'Amato, Mauro; Scheynius, Annika; Pershagen, Göran; Kere, Juha; Pulkkinen, Ville

    2013-01-01

    Retinoid acid receptor-related Orphan Receptor Alpha (RORA) was recently identified as a susceptibility gene for asthma in a genome-wide association study. To investigate the impact of RORA on asthma susceptibility, we performed a genetic association study between RORA single nucleotide polymorphisms (SNPs) in the vicinity of the asthma-associated SNP (rs11071559) and asthma-related traits. Because the regulatory region of a previously implicated asthma susceptibility gene, Neuropeptide S receptor 1 (NPSR1), has predicted elements for RORA binding, we hypothesized that RORA may interact biologically and genetically with NPSR1. 37 RORA SNPs and eight NPSR1 SNPs were genotyped in the Swedish birth cohort BAMSE (2033 children) and the European cross-sectional PARSIFAL study (1120 children). Seven RORA SNPs confined into a 49 kb region were significantly associated with physician-diagnosed childhood asthma. The most significant association with rs7164773 (T/C) was driven by the CC genotype in asthma cases (OR = 2.0, 95%CI 1.36-2.93, p = 0.0003 in BAMSE; and 1.61, 1.18-2.19, p = 0.002 in the combined BAMSE-PARSIFAL datasets, respectively), and strikingly, the risk effect was dependent on the Gln344Arg mutation in NPSR1. In cell models, stimulation of NPSR1 activated a pathway including RORA and other circadian clock genes. Over-expression of RORA decreased NPSR1 promoter activity further suggesting a regulatory loop between these genes. In addition, Rora mRNA expression was lower in the lung tissue of Npsr1 deficient mice compared to wildtype littermates during the early hours of the light period. We conclude that RORA SNPs are associated with childhood asthma and show epistasis with NPSR1, and the interaction between RORA and NPSR1 may be of biological relevance. Combinations of common susceptibility alleles and less common functional polymorphisms may modify the joint risk effects on asthma susceptibility. PMID:23565190

  8. Kynurenic acid amides as novel NR2B selective NMDA receptor antagonists.

    PubMed

    Borza, István; Kolok, Sándor; Galgóczy, Kornél; Gere, Anikó; Horváth, Csilla; Farkas, Sándor; Greiner, István; Domány, György

    2007-01-15

    A novel series of kynurenic acid amides, ring-enlarged derivatives of indole-2-carboxamides, was prepared and identified as in vivo active NR2B subtype selective NMDA receptor antagonists. The synthesis and SAR studies are discussed. PMID:17074483

  9. Data for amino acid alignment of Japanese stingray melanocortin receptors with other gnathostome melanocortin receptor sequences, and the ligand selectivity of Japanese stingray melanocortin receptors.

    PubMed

    Takahashi, Akiyoshi; Davis, Perry; Reinick, Christina; Mizusawa, Kanta; Sakamoto, Tatsuya; Dores, Robert M

    2016-06-01

    This article contains structure and pharmacological characteristics of melanocortin receptors (MCRs) related to research published in "Characterization of melanocortin receptors from stingray Dasyatis akajei, a cartilaginous fish" (Takahashi et al., 2016) [1]. The amino acid sequences of the stingray, D. akajei, MC1R, MC2R, MC3R, MC4R, and MC5R were aligned with the corresponding melanocortin receptor sequences from the elephant shark, Callorhinchus milii, the dogfish, Squalus acanthias, the goldfish, Carassius auratus, and the mouse, Mus musculus. These alignments provide the basis for phylogenetic analysis of these gnathostome melanocortin receptor sequences. In addition, the Japanese stingray melanocortin receptors were separately expressed in Chinese Hamster Ovary cells, and stimulated with stingray ACTH, α-MSH, β-MSH, γ-MSH, δ-MSH, and β-endorphin. The dose response curves reveal the order of ligand selectivity for each stingray MCR. PMID:27408924

  10. Potentiation of Gamma Aminobutyric Acid Receptors (GABAAR) by Ethanol: How Are Inhibitory Receptors Affected?

    PubMed Central

    Förstera, Benjamin; Castro, Patricio A.; Moraga-Cid, Gustavo; Aguayo, Luis G.

    2016-01-01

    In recent years there has been an increase in the understanding of ethanol actions on the type A γ-aminobutyric acid chloride channel (GABAAR), a member of the pentameric ligand gated ion channels (pLGICs). However, the mechanism by which ethanol potentiates the complex is still not fully understood and a number of publications have shown contradictory results. Thus many questions still remain unresolved requiring further studies for a better comprehension of this effect. The present review concentrates on the involvement of GABAAR in the acute actions of ethanol and specifically focuses on the immediate, direct or indirect, synaptic and extra-synaptic modulatory effects. To elaborate on the immediate, direct modulation of GABAAR by acute ethanol exposure, electrophysiological studies investigating the importance of different subunits, and data from receptor mutants will be examined. We will also discuss the nature of the putative binding sites for ethanol based on structural data obtained from other members of the pLGICs family. Finally, we will briefly highlight the glycine gated chloride channel (GlyR), another member of the pLGIC family, as a suitable target for the development of new pharmacological tools. PMID:27199667

  11. Unnatural agrochemical ligands for engineered abscisic acid receptors.

    PubMed

    Rodriguez, Pedro L; Lozano-Juste, Jorge

    2015-06-01

    Existing agrochemicals can be endowed with new applications through protein engineering of plant receptors. A recent study shows an engineered PYR1 ABA receptor can be activated by mandipropamid. Plants engineered with such PYR1 variant are responsive to this agrochemical, which confers protection against drought through activation of ABA signaling. PMID:25891067

  12. Castor oil induces laxation and uterus contraction via ricinoleic acid activating prostaglandin EP3 receptors.

    PubMed

    Tunaru, Sorin; Althoff, Till F; Nüsing, Rolf M; Diener, Martin; Offermanns, Stefan

    2012-06-01

    Castor oil is one of the oldest drugs. When given orally, it has a laxative effect and induces labor in pregnant females. The effects of castor oil are mediated by ricinoleic acid, a hydroxylated fatty acid released from castor oil by intestinal lipases. Despite the wide-spread use of castor oil in conventional and folk medicine, the molecular mechanism by which ricinoleic acid acts remains unknown. Here we show that the EP(3) prostanoid receptor is specifically activated by ricinoleic acid and that it mediates the pharmacological effects of castor oil. In mice lacking EP(3) receptors, the laxative effect and the uterus contraction induced via ricinoleic acid are absent. Although a conditional deletion of the EP(3) receptor gene in intestinal epithelial cells did not affect castor oil-induced diarrhea, mice lacking EP(3) receptors only in smooth-muscle cells were unresponsive to this drug. Thus, the castor oil metabolite ricinoleic acid activates intestinal and uterine smooth-muscle cells via EP(3) prostanoid receptors. These findings identify the cellular and molecular mechanism underlying the pharmacological effects of castor oil and indicate a role of the EP(3) receptor as a target to induce laxative effects. PMID:22615395

  13. Distinct binding determinants for 9-cis retinoic acid are located within AF-2 of retinoic acid receptor alpha.

    PubMed Central

    Tate, B F; Allenby, G; Janocha, R; Kazmer, S; Speck, J; Sturzenbecker, L J; Abarzúa, P; Levin, A A; Grippo, J F

    1994-01-01

    Retinoids exert their physiological action by interacting with two families of nuclear receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs), which regulate gene expression by forming transcriptionally active heterodimeric RAR/RXR or homodimeric RXR/RXR complexes on DNA. Retinoid receptor activity resides in several regions, including the DNA and ligand binding domains, a dimerization interface, and both a ligand-independent (AF-1) and a ligand-dependent (AF-2) transactivation function. While 9-cis retinoic acid (RA) alone is the cognate ligand for the RXRs, both 9-cis RA and all-trans RA (t-RA) compete for binding with high affinity to the RARs. This latter observation suggested to us that the two isomers may interact with a common binding site. Here we report that RAR alpha has two distinct but overlapping binding sites for 9-cis RA and t-RA. Truncation of a human RAR alpha to 419 amino acids yields a receptor that binds both t-RA and 9-cis RA with high affinity, but truncation to amino acid 404 yields a mutant receptor that binds only t-RA with high affinity. Remarkably, this region also defines a C-terminal boundary for AF-2, as addition of amino acids 405 to 419 restores receptor-mediated gene activity to a truncated human RAR alpha lacking this region. It is interesting to speculate that binding of retinoid stereoisomers to unique sites within an RAR may function with AF-2 to cause differential activation of retinoid-responsive gene pathways. Images PMID:8139538

  14. Nuclear receptor-dependent bile acid signaling is required for normal liver regeneration.

    PubMed

    Huang, Wendong; Ma, Ke; Zhang, Jun; Qatanani, Mohammed; Cuvillier, James; Liu, Jun; Dong, Bingning; Huang, Xiongfei; Moore, David D

    2006-04-14

    Liver mass depends on one or more unidentified humoral signals that drive regeneration when liver functional capacity is diminished. Bile acids are important liver products, and their levels are tightly regulated. Here, we identify a role for nuclear receptor-dependent bile acid signaling in normal liver regeneration. Elevated bile acid levels accelerate regeneration, and decreased levels inhibit liver regrowth, as does the absence of the primary nuclear bile acid receptor FXR. We propose that FXR activation by increased bile acid flux is a signal of decreased functional capacity of the liver. FXR, and possibly other nuclear receptors, may promote homeostasis not only by regulating expression of appropriate metabolic target genes but also by driving homeotrophic liver growth. PMID:16614213

  15. Eicosopentaneoic Acid and Other Free Fatty Acid Receptor Agonists Inhibit Lysophosphatidic Acid- and Epidermal Growth Factor-Induced Proliferation of Human Breast Cancer Cells

    PubMed Central

    Hopkins, Mandi M.; Zhang, Zhihong; Liu, Ze; Meier, Kathryn E.

    2016-01-01

    Many key actions of ω-3 (n-3) fatty acids have recently been shown to be mediated by two G protein-coupled receptors (GPCRs) in the free fatty acid receptor (FFAR) family, FFA1 (GPR40) and FFA4 (GPR120). n-3 Fatty acids inhibit proliferation of human breast cancer cells in culture and in animals. In the current study, the roles of FFA1 and FFA4 were investigated. In addition, the role of cross-talk between GPCRs activated by lysophosphatidic acid (LPA), and the tyrosine kinase receptor activated by epidermal growth factor (EGF), was examined. In MCF-7 and MDA-MB-231 human breast cancer cell lines, both LPA and EGF stimulated proliferation, Erk activation, Akt activation, and CCN1 induction. LPA antagonists blocked effects of LPA and EGF on proliferation in MCF-7 and MDA-MB-231, and on cell migration in MCF-7. The n-3 fatty acid eicosopentaneoic acid inhibited LPA- and EGF-induced proliferation in both cell lines. Two synthetic FFAR agonists, GW9508 and TUG-891, likewise inhibited LPA- and EGF-induced proliferation. The data suggest a major role for FFA1, which was expressed by both cell lines. The results indicate that n-3 fatty acids inhibit breast cancer cell proliferation via FFARs, and suggest a mechanism involving negative cross-talk between FFARS, LPA receptors, and EGF receptor. PMID:26821052

  16. γ-Hydroxybutyric acid (GHB) is not an agonist of extrasynaptic GABAA receptors.

    PubMed

    Connelly, William M; Errington, Adam C; Crunelli, Vincenzo

    2013-01-01

    γ-Hydroxybutyric acid (GHB) is an endogenous compound and a drug used clinically to treat the symptoms of narcolepsy. GHB is known to be an agonist of GABAB receptors with millimolar affinity, but also binds with much higher affinity to another site, known as the GHB receptor. While a body of evidence has shown that GHB does not bind to GABAA receptors widely, recent evidence has suggested that the GHB receptor is in fact on extrasynaptic α4β1δ GABAA receptors, where GHB acts as an agonist with an EC50 of 140 nM. We investigated three neuronal cell types that express a tonic GABAA receptor current mediated by extrasynaptic receptors: ventrobasal (VB) thalamic neurons, dentate gyrus granule cells and striatal medium spiny neurons. Using whole-cell voltage clamp in brain slices, we found no evidence that GHB (10 µM) induced any GABAA receptor mediated current in these cell types, nor that it modulated inhibitory synaptic currents. Furthermore, a high concentration of GHB (3 mM) was able to produce a GABAB receptor mediated current, but did not induce any other currents. These results suggest either that GHB is not a high affinity agonist at native α4β1δ receptors, or that these receptors do not exist in classical areas associated with extrasynaptic currents. PMID:24244421

  17. γ-Hydroxybutyric Acid (GHB) Is Not an Agonist of Extrasynaptic GABAA Receptors

    PubMed Central

    Connelly, William M.; Errington, Adam C.; Crunelli, Vincenzo

    2013-01-01

    γ-Hydroxybutyric acid (GHB) is an endogenous compound and a drug used clinically to treat the symptoms of narcolepsy. GHB is known to be an agonist of GABAB receptors with millimolar affinity, but also binds with much higher affinity to another site, known as the GHB receptor. While a body of evidence has shown that GHB does not bind to GABAA receptors widely, recent evidence has suggested that the GHB receptor is in fact on extrasynaptic α4β1δ GABAA receptors, where GHB acts as an agonist with an EC50 of 140 nM. We investigated three neuronal cell types that express a tonic GABAA receptor current mediated by extrasynaptic receptors: ventrobasal (VB) thalamic neurons, dentate gyrus granule cells and striatal medium spiny neurons. Using whole-cell voltage clamp in brain slices, we found no evidence that GHB (10 µM) induced any GABAA receptor mediated current in these cell types, nor that it modulated inhibitory synaptic currents. Furthermore, a high concentration of GHB (3 mM) was able to produce a GABAB receptor mediated current, but did not induce any other currents. These results suggest either that GHB is not a high affinity agonist at native α4β1δ receptors, or that these receptors do not exist in classical areas associated with extrasynaptic currents. PMID:24244421

  18. Stoichiometry and phosphoisotypes of hippocampal AMPA type glutamate receptor phosphorylation

    PubMed Central

    Hosokawa, Tomohisa; Mitsushima, Dai; Kaneko, Rina; Hayashi, Yasunori

    2014-01-01

    SUMMARY It has been proposed that the AMPAR phosphorylation regulates trafficking and channel activity, thereby playing an important role in synaptic plasticity. However, the actual stoichiometry of phosphorylation, information critical to understand the role of phosphorylation, is not known because of the lack of appropriate techniques for measurement. Here, using Phos-tag SDS-PAGE, we estimated the proportion of phosphorylated AMPAR subunit GluA1. The level of phosphorylated GluA1 at S831 and S845, two major sites implicated in AMPAR regulation, is almost negligible. Less than 1% of GluA1 is phosphorylated at S831 and less than 0.1% at S845. Considering the number of AMPAR at each synapse, the majority of synapses do not contain any phosphorylated AMPAR. Also, we did not see evidence of GluA1 dually phosphorylated at S831 and S845. Neuronal stimulation and learning increased phosphorylation but the proportion was still low. Our results impel us to reconsider the mechanisms underlying synaptic plasticity. PMID:25533481

  19. Binding characteristics of gamma-hydroxybutyric acid as a weak but selective GABAB receptor agonist.

    PubMed

    Mathivet, P; Bernasconi, R; De Barry, J; Marescaux, C; Bittiger, H

    1997-02-19

    The aim of this study was to reexamine the concept that gamma-hydroxybutyric acid (GHB) is a weak but selective agonist at gamma-aminobutyric acidB (GABAB) receptors, using binding experiments with several radioligands. Ki values of GHB were similar (approximately equal to 100 microM) in three agonist radioligand assays for GABAB receptors, [3H]baclofen (beta-para-chlorophenyl-gamma-aminobutyric acid), [3H]CGP 27492 (3-aminopropyl-phosphinic acid) and [3H]GABA, in the presence of the GABAA receptor agonist isoguvacine with rat cortical, cerebellar and hippocampal membranes. In competition experiments between GHB and the GABAB receptor antagonist, [3H]CGP 54626 (3-N [1-{(S)-3,4-dichlorophenyl}-ethylamino]-2-(S)-hydroxypropyl cyclo-hexylmethyl phosphinic acid), the IC50 values were significantly increased with 300 microM of 5'-guanyl-imidodiphosphate (Gpp(NH)p), which suggested that guanine nucleotide binding proteins (G-proteins) modulate GHB binding on GABAB receptors. The inhibition by GHB of [3H]CGP 27492 binding in cortical membranes was not altered in the presence of 0.3 or 3 mM of the two GHB dehydrogenase inhibitors, valproate and ethosuximide. Thus, GHB is not reconverted into GABA by GHB dehydrogenase. Taken together, the results of this study demonstrated that GHB is an endogenous weak but selective agonist at GABAB receptors. PMID:9083788

  20. Nucleic acid recognizing Toll-like receptors and autoimmunity.

    PubMed

    von Landenberg, Philipp; Bauer, Stefan

    2007-12-01

    The understanding of autoimmune diseases experienced an impressive boost since the Toll-like receptors (TLRs) have been identified as possible key players in autoimmune pathophysiology. Although these receptors recognize a variety of structures derived from viruses, bacteria, and fungi leading to subsequent initiation of the relevant immune responses, recent data support the idea that TLRs are crucial in the induction and perpetuation of certain autoimmune diseases, especially the systemic lupus erythematosus (SLE). In this review, we will summarize recent data on involvement of TLRs in the development of autoimmune diseases. We will focus on TLRs 7, 8, and 9 that were originally identified as receptors specific for bacterial and viral RNA/DNA, but more recent in vitro and in vivo studies have linked these receptors to the detection of host RNA, DNA, and RNA-associated or DNA-associated proteins in the context of autoimmunity. PMID:18060756

  1. Targeted disruption of retinoic acid receptor alpha (RAR alpha) and RAR gamma results in receptor-specific alterations in retinoic acid-mediated differentiation and retinoic acid metabolism.

    PubMed Central

    Boylan, J F; Lufkin, T; Achkar, C C; Taneja, R; Chambon, P; Gudas, L J

    1995-01-01

    F9 embryonic teratocarcinoma stem cells differentiate into an epithelial cell type called extraembryonic endoderm when treated with retinoic acid (RA), a derivative of retinol (vitamin A). This differentiation is presumably mediated through the actions of retinoid receptors, the RARs and RXRs. To delineate the functions of each of the different retinoid receptors in this model system, we have generated F9 cell lines in which both