Oxotremorine-M potentiates NMDA receptors by muscarinic receptor dependent and independent mechanisms.

PubMed

Zwart, Ruud; Reed, Hannah; Sher, Emanuele

2018-01-01

Muscarinic acetylcholine M1 receptors play an important role in synaptic plasticity in the hippocampus and cortex. Potentiation of NMDA receptors as a consequence of muscarinic acetylcholine M1 receptor activation is a crucial event mediating the cholinergic modulation of synaptic plasticity, which is a cellular mechanism for learning and memory. In Alzheimer's disease, the cholinergic input to the hippocampus and cortex is severely degenerated, and agonists or positive allosteric modulators of M1 receptors are therefore thought to be of potential use to treat the deficits in cognitive functions in Alzheimer's disease. In this study we developed a simple system in which muscarinic modulation of NMDA receptors can be studied in vitro. Human M1 receptors and NR1/2B NMDA receptors were co-expressed in Xenopus oocytes and various muscarinic agonists were assessed for their modulatory effects on NMDA receptor-mediated responses. As expected, NMDA receptor-mediated responses were potentiated by oxotremorine-M, oxotremorine or xanomeline when the drugs were applied between subsequent NMDA responses, an effect which was fully blocked by the muscarinic receptor antagonist atropine. However, in oocytes expressing NR1/2B NMDA receptors but not muscarinic M1 receptors, oxotremorine-M co-applied with NMDA also resulted in a potentiation of NMDA currents and this effect was not blocked by atropine, demonstrating that oxotremorine-M is able to directly potentiate NMDA receptors. Oxotremorine, which is a close analogue of oxotremorine-M, and xanomeline, a chemically distinct muscarinic agonist, did not potentiate NMDA receptors by this direct mechanism. Comparing the chemical structures of the three different muscarinic agonists used in this study suggests that the tri-methyl ammonium moiety present in oxotremorine-M is important for the compound's interaction with NMDA receptors. Copyright © 2017 Elsevier Inc. All rights reserved.

D-Cycloserine for Treatment Nonresponders with Obsessive-Compulsive Disorder: A Case Report

ERIC Educational Resources Information Center

Norberg, Melissa M.; Gilliam, Christina M.; Villavicencio, Anna; Pearlson, Godfrey D.; Tolin, David F.

2012-01-01

Despite being the most effective treatment available, as many as one third of patients who receive exposure and response prevention (ERP) for obsessive-compulsive disorder (OCD) do not initially respond to treatment. Recent research suggests that the n-methyl d-aspartate (NMDA) receptor partial agonist D-Cycloserine (DCS) may speed up the course…

Modafinil: A Molecule of Military Interest

DTIC Science & Technology

2001-06-01

noradrenalin LC: locus coeruleus iR-Glu: ionotropic MCn: magnocellular nucleus glutamate receptors (NMDA and non-NMDA) DR: dorsal raphe mR-Glu: metabotropic ...21 This metabotropic receptor agonist. However, the EAA- inhibition of cortical GABA outflow is antagonized release inhibitor propentofylline has...NMDA receptor antagonist and metabotropic psychostimulant, during a sixty-hour sleep receptor agonist. deprivation experiment. Fundam Clin Pharmacol

Development of 2′-substituted (2S,1′R,2′S)-2-(carboxycyclopropyl)glycine analogues as potent N-methyl-d-aspartic acid receptor agonists

PubMed Central

Risgaard, Rune; Nielsen, Simon D.; Hansen, Kasper B.; Jensen, Christina M.; Nielsen, Birgitte; Traynelis, Stephen F.; Clausen, Rasmus P.

2013-01-01

A series of 2′-substituted analogues of the selective NMDA receptor ligand (2S,1′R,2′S)-2-(carboxycyclopropyl)glycine ((S)-CCG-IV) have been designed, synthesized and pharmacologically characterized. The design was based on a docking study hypothesizing that substituents in the 2′-position would protrude into a region where differences among the NMDA receptor GluN2 subunits exist. Various synthetic routes were explored, and two different routes provided a series of alkyl-substituted analogues. Pharmacological characterization revealed that these compounds are NMDA receptor agonists and that potency decreases with increasing size of the alkyl groups. Variations in agonist activity are observed at the different recombinant NMDA receptor subtypes. This study demonstrates that it is possible to introduce substituents in the 2′-position of (S)-CCG-IV while maintaining agonist activity and that variation among NMDA receptor subtypes may be achieved by probing this region of the receptor. PMID:23614571

Testing the effects of Δ9-THC and D-cycloserine on extinction of conditioned fear in humans

PubMed Central

Klumpers, Floris; Denys, Damiaan; Kenemans, J Leon; Grillon, Christian; van der Aart, Jasper; Baas, Johanna MP

2012-01-01

Preclinical evidence implicates several neurotransmitter systems in the extinction of conditioned fear. These results are of great interest, because the reduction of acquired fear associations is critical in therapies for anxiety disorders. We tested whether findings with respect to the N-methyl-D-aspartate (NMDA) and cannabinoid receptor (CB) systems in animals carry over to healthy human subjects. To that end, we administered selected doses of D-cycloserine (partial NMDA receptor agonist, 250 mg), delta-9-tetrahydrocannabinol (THC, CB1 receptor agonist, 10 mg), or placebo prior to the extinction session of a 3-day conditioning protocol. D-cycloserine did not affect within-session extinction, or the retention of extinction in healthy human participants, in contrast with patient data but in line with previous reports in healthy volunteers. During extinction training, Δ9-THC reduced conditioned skin conductance responses, but not fear-potentiated startle. This effect was not retained at the retention test 2 days later, suggesting it was dependent on acute effects of the drug. Our findings implicate that facilitation of the CB1 or NMDA system with the substances used in this study does not affect conditioned fear extinction lastingly in healthy humans. The apparent discrepancy between these findings and the results from (pre-) clinical trials is discussed in terms of room for improvement in these systems in healthy volunteers, and the lack of specificity of THC as a CB1 agonist. PMID:22351380

D-Cycloserine Does Not Facilitate Fear Extinction by Reducing Conditioned Stimulus Processing or Promoting Conditioned Inhibition to Contextual Cues

ERIC Educational Resources Information Center

Baker, Kathryn D.; McNally, Gavan P.; Richardson, Rick

2012-01-01

The NMDA receptor partial agonist d-cycloserine (DCS) enhances the extinction of learned fear in rats and exposure therapy in humans with anxiety disorders. Despite these benefits, little is known about the mechanisms by which DCS promotes the loss of fear. The present study examined whether DCS augments extinction retention (1) through reductions…

Rosiglitazone Suppresses In Vitro Seizures in Hippocampal Slice by Inhibiting Presynaptic Glutamate Release in a Model of Temporal Lobe Epilepsy.

PubMed

Wong, Shi-Bing; Cheng, Sin-Jhong; Hung, Wei-Chen; Lee, Wang-Tso; Min, Ming-Yuan

2015-01-01

Peroxisomal proliferator-activated receptor gamma (PPARγ) is a nuclear hormone receptor whose agonist, rosiglitazone has a neuroprotective effect to hippocampal neurons in pilocarpine-induced seizures. Hippocampal slice preparations treated in Mg2+ free medium can induce ictal and interictal-like epileptiform discharges, which is regarded as an in vitro model of N-methyl-D-aspartate (NMDA) receptor-mediated temporal lobe epilepsy (TLE). We applied rosiglitazone in hippocampal slices treated in Mg2+ free medium. The effects of rosiglitazone on hippocampal CA1-Schaffer collateral synaptic transmission were tested. We also examined the neuroprotective effect of rosiglitazone toward NMDA excitotoxicity on cultured hippocampal slices. Application of 10 μM rosiglitazone significantly suppressed amplitude and frequency of epileptiform discharges in CA1 neurons. Pretreatment with the PPARγ antagonist GW9662 did not block the effect of rosiglitazone on suppressing discharge frequency, but reverse the effect on suppressing discharge amplitude. Application of rosiglitazone suppressed synaptic transmission in the CA1-Schaffer collateral pathway. By miniature excitatory-potential synaptic current (mEPSC) analysis, rosiglitazone significantly suppressed presynaptic neurotransmitter release. This phenomenon can be reversed by pretreating PPARγ antagonist GW9662. Also, rosiglitazone protected cultured hippocampal slices from NMDA-induced excitotoxicity. The protective effect of 10 μM rosiglitazone was partially antagonized by concomitant high dose GW9662 treatment, indicating that this effect is partially mediated by PPARγ receptors. In conclusion, rosiglitazone suppressed NMDA receptor-mediated epileptiform discharges by inhibition of presynaptic neurotransmitter release. Rosiglitazone protected hippocampal slice from NMDA excitotoxicity partially by PPARγ activation. We suggest that rosiglitazone could be a potential agent to treat patients with TLE.

Ventral tegmental ionotropic glutamate receptor stimulation of nucleus accumbens tonic dopamine efflux blunts hindbrain-evoked phasic neurotransmission: implications for dopamine dysregulation disorders.

PubMed

Tye, S J; Miller, A D; Blaha, C D

2013-11-12

Activation of glutamate receptors within the ventral tegmental area (VTA) stimulates extrasynaptic (basal) dopamine release in terminal regions, including the nucleus accumbens (NAc). Hindbrain inputs from the laterodorsal tegmental nucleus (LDT) are critical for elicitation of phasic VTA dopamine cell activity and consequent transient dopamine release. This study investigated the role of VTA ionotropic glutamate receptor (iGluR) stimulation on both basal and LDT electrical stimulation-evoked dopamine efflux in the NAc using in vivo chronoamperometry and fixed potential amperometry in combination with stearate-graphite paste and carbon fiber electrodes, respectively. Intra-VTA infusion of the iGluR agonists (±)-α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA; 1 μg/μl) or N-methyl-d-aspartic acid (NMDA; 2 μg/μl) enhanced basal NAc dopamine efflux. This iGluR-mediated potentiation of basal dopamine efflux was paralleled by an attenuation of LDT-evoked transient NAc dopamine efflux, suggesting that excitation of basal activity effectively inhibited the capacity of hindbrain afferents to elicit transient dopamine efflux. In line with this, post-NMDA infusion of the dopamine D2 autoreceptor (D2R) agonist quinpirole (1 μg/μl; intra-VTA) partially recovered NMDA-mediated attenuation of LDT-evoked NAc dopamine, while concurrently attenuating NMDA-mediated potentiation of basal dopamine efflux. Post-NMDA infusion of quinpirole (1 μg/μl) alone attenuated basal and LDT-evoked dopamine efflux. Taken together, these data reveal that hyperstimulation of basal dopamine transmission can stunt hindbrain burst-like stimulation-evoked dopamine efflux. Inhibitory autoreceptor mechanisms within the VTA help to partially recover the magnitude of phasic dopamine efflux, highlighting the importance of both iGluRs and D2 autoreceptors in maintaining the functional balance of tonic and phasic dopamine neurotransmission. Dysregulation of this balance may have important implications for disorders of dopamine dysregulation such as attention deficit hyperactivity disorder. Copyright © 2013 IBRO. Published by Elsevier Ltd. All rights reserved.

New targets for rapid antidepressant action.

PubMed

Machado-Vieira, Rodrigo; Henter, Ioline D; Zarate, Carlos A

2017-05-01

Current therapeutic options for major depressive disorder (MDD) and bipolar disorder (BD) are associated with a lag of onset that can prolong distress and impairment for patients, and their antidepressant efficacy is often limited. All currently approved antidepressant medications for MDD act primarily through monoaminergic mechanisms. Glutamate is the major excitatory neurotransmitter in the central nervous system, and glutamate and its cognate receptors are implicated in the pathophysiology of MDD, and in the development of novel therapeutics for this disorder. The rapid and robust antidepressant effects of the N-methyl-d-aspartate (NMDA) antagonist ketamine were first observed in 2000. Since then, other NMDA receptor antagonists have been studied in MDD. Most have demonstrated relatively modest antidepressant effects compared to ketamine, but some have shown more favorable characteristics. This article reviews the clinical evidence supporting the use of novel glutamate receptor modulators with direct affinity for cognate receptors: (1) non-competitive NMDA receptor antagonists (ketamine, memantine, dextromethorphan, AZD6765); (2) subunit (GluN2B)-specific NMDA receptor antagonists (CP-101,606/traxoprodil, MK-0657); (3) NMDA receptor glycine-site partial agonists (GLYX-13); and (4) metabotropic glutamate receptor (mGluR) modulators (AZD2066, RO4917523/basimglurant). We also briefly discuss several other theoretical glutamate receptor targets with preclinical antidepressant-like efficacy that have yet to be studied clinically; these include α-amino-3-hydroxyl-5-methyl-4-isoxazoleproprionic acid (AMPA) agonists and mGluR2/3 negative allosteric modulators. The review also discusses other promising, non-glutamatergic targets for potential rapid antidepressant effects, including the cholinergic system (scopolamine), the opioid system (ALKS-5461), corticotropin releasing factor (CRF) receptor antagonists (CP-316,311), and others. Published by Elsevier Ltd.

New Targets for Rapid Antidepressant Action

PubMed Central

Machado-Vieira, Rodrigo; Henter, Ioline D; Zarate, Carlos A.

2016-01-01

Current therapeutic options for major depressive disorder (MDD) and bipolar disorder (BD) are associated with a lag of onset that can prolong distress and impairment for patients, and their antidepressant efficacy is often limited. All currently approved antidepressant medications for MDD act primarily through monoaminergic mechanisms. Glutamate is the major excitatory neurotransmitter in the central nervous system, and glutamate and its cognate receptors are implicated in the pathophysiology of MDD, and in the development of novel therapeutics for this disorder. The rapid and robust antidepressant effects of the N-methyl-D-aspartate (NMDA) antagonist ketamine were first observed in 2000. Since then, other NMDA receptor antagonists have been studied in MDD. Most have demonstrated relatively modest antidepressant effects compared to ketamine, but some have shown more favorable characteristics. This article reviews the clinical evidence supporting the use of novel glutamate receptor modulators with direct affinity for cognate receptors: 1) non-competitive NMDA receptor antagonists (ketamine, memantine, dextromethorphan, AZD6765); 2) subunit (GluN2B)-specific NMDA receptor antagonists (CP-101,606/traxoprodil, MK-0657); 3) NMDA receptor glycine-site partial agonists (GLYX-13); and 4) metabotropic glutamate receptor (mGluR) modulators (AZD2066, RO4917523/basimglurant). We also briefly discuss several other theoretical glutamate receptor targets with preclinical antidepressant-like efficacy that have yet to be studied clinically; these include α-amino-3-hydroxyl-5-methyl-4-isoxazoleproprionic acid (AMPA) agonists and mGluR2/3 negative allosteric modulators. The review also discusses other promising, non-glutamatergic targets for potential rapid antidepressant effects, including the cholinergic system (scopolamine), the opioid system (ALKS-5461), corticotropin releasing factor (CRF) receptor antagonists (CP-316,311), and others. PMID:26724279

Tandospirone, a 5-HT1A partial agonist, ameliorates aberrant lactate production in the prefrontal cortex of rats exposed to blockade of N-methy-D-aspartate receptors; Toward the therapeutics of cognitive impairment of schizophrenia.

PubMed

Uehara, Takashi; Matsuoka, Tadasu; Sumiyoshi, Tomiki

2014-01-01

Augmentation therapy with serotonin-1A (5-HT1A) receptor partial agonists has been suggested to improve cognitive impairment in patients with schizophrenia. Decreased activity of prefrontal cortex may provide a basis for cognitive deficits of the disease. Lactate plays a significant role in the supply of energy to the brain, and glutamatergic neurotransmission contributes to lactate production. The purposes of this study were to examine the effect of repeated administration (once a daily for 4 days) of tandospirone (0.05 or 5 mg/kg) on brain energy metabolism, as represented by extracellular lactate concentration (eLAC) in the medial prefrontal cortex (mPFC) of a rat model of schizophrenia. Four-day treatment with MK-801, an NMDA-R antagonist, prolonged eLAC elevation induced by foot-shock stress (FS). Co-administration with the high-dose tandospirone suppressed prolonged FS-induced eLAC elevation in rats receiving MK-801, whereas tandospirone by itself did not affected eLAC increment. These results suggest that stimulation of 5-HT1A receptors ameliorates abnormalities of energy metabolism in the mPFC due to blockade of NMDA receptors. These findings provide a possible mechanism, based on brain energy metabolism, by which 5-HT1A agonism improve cognitive impairment of schizophrenia and related disorders.

A NMDA receptor glycine site partial agonist, GLYX-13, simultaneously enhances LTP and reduces LTD at Schaffer collateral-CA1 synapses in hippocampus.

PubMed

Zhang, Xiao-lei; Sullivan, John A; Moskal, Joseph R; Stanton, Patric K

2008-12-01

N-methyl-D-aspartate glutamate receptors (NMDARs) are a key route for Ca2+ influx into neurons important to both activity-dependent synaptic plasticity and, when uncontrolled, triggering events that cause neuronal degeneration and death. Among regulatory binding sites on the NMDAR complex is a glycine binding site, distinct from the glutamate binding site, which must be co-activated for NMDAR channel opening. We developed a novel glycine site partial agonist, GLYX-13, which is both nootropic and neuroprotective in vivo. Here, we assessed the effects of GLYX-13 on long-term synaptic plasticity and NMDAR transmission at Schaffer collateral-CA1 synapses in hippocampal slices in vitro. GLYX-13 simultaneously enhanced the magnitude of long-term potentiation (LTP) of synaptic transmission, while reducing long-term depression (LTD). GLYX-13 reduced NMDA receptor-mediated synaptic currents in CA1 pyramidal neurons evoked by low frequency Schaffer collateral stimulation, but enhanced NMDAR currents during high frequency bursts of activity, and these actions were occluded by a saturating concentration of the glycine site agonist d-serine. Direct two-photon imaging of Schaffer collateral burst-evoked increases in [Ca2+] in individual dendritic spines revealed that GLYX-13 selectively enhanced burst-induced NMDAR-dependent spine Ca2+ influx. Examining the rate of MK-801 block of synaptic versus extrasynaptic NMDAR-gated channels revealed that GLYX-13 selectively enhanced activation of burst-driven extrasynaptic NMDARs, with an action that was blocked by the NR2B-selective NMDAR antagonist ifenprodil. Our data suggest that GLYX-13 may have unique therapeutic potential as a learning and memory enhancer because of its ability to simultaneously enhance LTP and suppress LTD.

Characterization of l-Theanine Excitatory Actions on Hippocampal Neurons: Toward the Generation of Novel N-Methyl-d-aspartate Receptor Modulators Based on Its Backbone.

PubMed

Sebih, Fatiha; Rousset, Matthieu; Bellahouel, Salima; Rolland, Marc; de Jesus Ferreira, Marie Celeste; Guiramand, Janique; Cohen-Solal, Catherine; Barbanel, Gérard; Cens, Thierry; Abouazza, Mohammed; Tassou, Adrien; Gratuze, Maud; Meusnier, Céline; Charnet, Pierre; Vignes, Michel; Rolland, Valérie

2017-08-16

l-Theanine (or l-γ-N-ethyl-glutamine) is the major amino acid found in Camellia sinensis. It has received much attention because of its pleiotropic physiological and pharmacological activities leading to health benefits in humans, especially. We describe here a new, easy, efficient, and environmentally friendly chemical synthesis of l-theanine and l-γ-N-propyl-Gln and their corresponding d-isomers. l-Theanine, and its derivatives obtained so far, exhibited partial coagonistic action at N-methyl-d-aspartate (NMDA) receptors, with no detectable agonist effect at other glutamate receptors, on cultured hippocampal neurons. This activity was retained on NMDA receptors expressed in Xenopus oocytes. In addition, both GluN2A and GluN2B containing NMDA receptors were equally modulated by l-theanine. The stereochemical change from l-theanine to d-theanine along with the substitution of the ethyl for a propyl moiety in the γ-N position of l- and d-theanine significantly enhanced the biological efficacy, as measured on cultured hippocampal neurons. l-Theanine structure thus represents an interesting backbone to develop novel NMDA receptor modulators.

Glycine Potentiates AMPA Receptor Function through Metabotropic Activation of GluN2A-Containing NMDA Receptors

PubMed Central

Li, Li-Jun; Hu, Rong; Lujan, Brendan; Chen, Juan; Zhang, Jian-Jian; Nakano, Yasuko; Cui, Tian-Yuan; Liao, Ming-Xia; Chen, Jin-Cao; Man, Heng-Ye; Feng, Hua; Wan, Qi

2016-01-01

NMDA receptors are Ca2+-permeable ion channels. The activation of NMDA receptors requires agonist glutamate and co-agonist glycine. Recent evidence indicates that NMDA receptor also has metabotropic function. Here we report that in cultured mouse hippocampal neurons, glycine increases AMPA receptor-mediated currents independent of the channel activity of NMDA receptors and the activation of glycine receptors. The potentiation of AMPA receptor function by glycine is antagonized by the inhibition of ERK1/2. In the hippocampal neurons and in the HEK293 cells transfected with different combinations of NMDA receptors, glycine preferentially acts on GluN2A-containing NMDA receptors (GluN2ARs), but not GluN2B-containing NMDA receptors (GluN2BRs), to enhance ERK1/2 phosphorylation independent of the channel activity of GluN2ARs. Without requiring the channel activity of GluN2ARs, glycine increases AMPA receptor-mediated currents through GluN2ARs. Thus, these results reveal a metabotropic function of GluN2ARs in mediating glycine-induced potentiation of AMPA receptor function via ERK1/2 activation. PMID:27807405

Complex effects of mGluR5 antagonism on sociability and stereotypic behaviors in mice: possible implications for the pharmacotherapy of autism spectrum disorders.

PubMed

Burket, Jessica A; Herndon, Amy L; Winebarger, Erin E; Jacome, Luis F; Deutsch, Stephen I

2011-10-10

Balb/c mice display deficits of sociability; for example, they show reduced locomotor activity in the presence of an enclosed or freely-moving social stimulus mouse. Transgenic mice with defective or diminished expression of NMDA receptors manifest impaired sociability, while a partial and full agonist of the obligatory glycine co-agonist binding site on the NMDA receptor improved sociability in the Balb/c mouse strain. Because 2-methyl-6-(phenylethynyl)-pyridine (MPEP), an antagonist of the mGluR5 metabotropic glutamate receptor (mGluR), reduced self-grooming behavior in BTBR T+tfJ (BTBR) mice, another inbred genetic mouse model of autism spectrum disorders (ASDs), and mGluR5 antagonism is emerging as an experimental treatment for the 'fragile X syndrome," which has a high prevalence of co-morbid ASDs, we examined the effects of MPEP on sociability and stereotypic behaviors in Balb/c and Swiss Webster mice in a standard paradigm. MPEP had complex effects on sociability, impairing some measures of sociability in both strains, while it reduced the intensity of some spontaneous measures of stereotypic behaviors emerging during free social interaction in Swiss Webster mice. Conceivably, mGluR5 antagonism exacerbates diminished endogenous tone of NMDA receptor-mediated neurotransmission in neural circuits relevant to at least some measures of sociability in Balb/c mice; the mGluR5 receptor contributes to regulation of the phosphorylation status of the NMDA receptor. In any event, although stereotypies are an important therapeutic target in ASDs, medication strategies to attenuate their severity via antagonism of mGluR5 receptors must be pursued cautiously because of their potential to worsen at least some measures of sociability. Copyright © 2011 Elsevier Inc. All rights reserved.

Mechanistic Insights into Xenon Inhibition of NMDA Receptors from MD Simulations

PubMed Central

Liu, Lu Tian; Xu, Yan; Tang, Pei

2010-01-01

Inhibition of N-methyl-D-aspartate (NMDA) receptors has been viewed as a primary cause of xenon anesthesia, yet the mechanism is unclear. Here, we investigated interactions between xenon and the ligand-binding domain (LBD) of a NMDA receptor and examined xenon-induced structural and dynamical changes that are relevant to functional changes of the NMDA receptor. Several comparative molecular dynamics simulations were performed on two X-ray structures representing the open- and closed-cleft LBD of the NMDA receptor. We identified plausible xenon action sites in the LBD, including those nearby agonist sites, in the hinge region, and at the interface between two subunits. The xenon binding energy varies from −5.3 to −0.7 kcal/mol. Xenon's effect on the NMDA receptor is conformation-dependent and is produced through both competitive and non-competitive mechanisms. Xenon can promote cleft opening in the absence of agonists and consequently stabilizes the closed channel. Xenon can also bind at the interface of two subunits, alter the inter-subunit interaction, and lead to a reduction of the distance between GT-links. This reduction corresponds to a rearrangement of the channel toward a direction of pore size decreasing, implying a closed or desensitized channel. In addition to these non-competitive actions, xenon was found to weaken the glutamate binding, which could lead to low agonist efficacy and appear as competitive inhibition. PMID:20560662

Neonatal (+)-methamphetamine exposure in rats alters adult locomotor responses to dopamine D1 and D2 agonists and to a glutamate NMDA receptor antagonist, but not to serotonin agonists

PubMed Central

Graham, Devon L.; Amos-Kroohs, Robyn M.; Braun, Amanda A.; Grace, Curtis E.; Schaefer, Tori L.; Skelton, Matthew R.; Williams, Michael T.; Vorhees, Charles V.

2015-01-01

Neonatal exposure to (+)-methamphetamine (Meth) results in long-term behavioural abnormalities but its developmental mechanisms are unknown. In a series of experiments, rats were treated from post-natal days (PD) 11–20 (stage that approximates human development from the second to third trimester) with Meth or saline and assessed using locomotor activity as the readout following pharmacological challenge doses with dopamine, serotonin and glutamate agonists or antagonists during adulthood. Exposure to Meth early in life resulted in an exaggerated adult locomotor hyperactivity response to the dopamine D1 agonist SKF-82958 at multiple doses, a high dose only under-response activating effect of the D2 agonist quinpirole, and an exaggerated under-response to the activating effect of the N-methyl-D-aspartic acid (NMDA) receptor antagonist, MK-801. No change in locomotor response was seen following challenge with the 5-HT releaser p-chloroamphetamine or the 5-HT2/3 receptor agonist, quipazine. These are the first data to show that PD 11-20 Meth exposure induces long-lasting alterations to dopamine D1, D2 and glutamate NMDA receptor function and may suggest how developmental Meth exposure leads to many of its long-term adverse effects. PMID:22391043

Failure to Recognize Novelty after Extended Methamphetamine Self-Administration Results from Loss of Long-Term Depression in the Perirhinal Cortex

PubMed Central

Scofield, Michael D; Trantham-Davidson, Heather; Schwendt, Marek; Leong, Kah-Chung; Peters, Jamie; See, Ronald E; Reichel, Carmela M

2015-01-01

Exposure to methamphetamine (meth) can produce lasting memory impairments in humans and rodents. We recently demonstrated that extended access meth self-administration results in novel object recognition (NOR) memory deficits in rats. Recognition of novelty depends upon intact perirhinal (pRh) cortex function, which is compromised by meth-induced downregulation of GluN2B-containing N-methyl-D-aspartate (NMDA) receptors. NMDA receptors containing this subunit have a critical role in pRh long-term depression (LTD), one of the primary physiological processes thought to underlie object recognition memory. We hypothesized that meth-induced downregulation of GluN2B receptors would compromise pRh LTD, leading to loss of NOR memory. We found that meth self-administration resulted in an inability to induce pRh LTD following 1 Hz stimulation, an effect that was reversed with bath application of the NMDA receptor partial agonist D-cycloserine (DCS). In addition, pRh microinfusion of DCS restored meth-induced memory deficits. Furthermore, blockade of GluN2B-containing NMDA receptors with Ro 25-6981 prevented DCS restoration of pRh LTD in meth subjects. Thus, targeting pRh LTD may be a promising strategy to treat meth-induced cognitive impairment. PMID:25865928

mGluR2/3 agonist LY379268 rescues NMDA and GABAA receptor level deficits induced in a two-hit mouse model of schizophrenia.

PubMed

Engel, Martin; Snikeris, Peta; Matosin, Natalie; Newell, Kelly Anne; Huang, Xu-Feng; Frank, Elisabeth

2016-04-01

An imbalance of excitatory and inhibitory neurotransmission underlies the glutamate hypothesis of schizophrenia. Agonists of group II metabotropic glutamate receptors, mGluR2/3, have been proposed as novel therapeutic agents to correct this imbalance. However, the influence of mGluR2/3 activity on excitatory and inhibitory neurotransmitter receptors has not been explored. We aimed to investigate the ability of a novel mGluR2/3 agonist, LY379268, to modulate the availability of the excitatory N-methyl-D-aspartate receptor (NMDA-R) and the inhibitory gamma-aminobutyrate-A receptor (GABAA-R), in a two-hit mouse model of schizophrenia. Wild type (WT) and heterozygous neuregulin 1 transmembrane domain mutant mice (NRG1 HET) were treated daily with phencyclidine (10 mg/kg ip) or saline for 14 days. After a 14-day washout, an acute dose of the mGluR2/3 agonist LY379268 (3 mg/kg), olanzapine (antipsychotic drug comparison, 1.5 mg/kg), or saline was administered. NMDA-R and GABAA-R binding densities were examined by receptor autoradiography in several schizophrenia-relevant brain regions. In both WT and NRG1 HET mice, phencyclidine treatment significantly reduced NMDA-R and GABAA-R binding density in the prefrontal cortex, hippocampus, and nucleus accumbens. Acute treatment with LY379268 restored NMDA-R and GABAA-R levels in the two-hit mouse model comparable to olanzapine. We demonstrate that the mGluR2/3 agonist LY379268 restores excitatory and inhibitory deficits with similar efficiency as olanzapine in our two-hit schizophrenia mouse model. This study significantly contributes to our understanding of the mechanisms underlying the therapeutic effects of LY379268 and supports the use of agents aimed at mGluR2/3.

NMDA receptor adjusted co-administration of ecstasy and cannabinoid receptor-1 agonist in the amygdala via stimulation of BDNF/Trk-B/CREB pathway in adult male rats.

PubMed

Ashabi, Ghorbangol; Sadat-Shirazi, Mitra-Sadat; Khalifeh, Solmaz; Elhampour, Laleh; Zarrindast, Mohammad-Reza

2017-04-01

Consumption of cannabinoid receptor-1 (CB-1) agonist such as cannabis is widely taken in 3,4- methylenedioxymethamphetamine (MDMA) or ecstasy users; it has been hypothesized that co-consumption of CB-1 agonist might protect neurons against MDMA toxicity. N-methyl-d-aspartate (NMDA) receptors regulate neuronal plasticity and firing rate in the brain through Tyrosine-kinase B (Trk-B) activation. The molecular and electrophysiological association among NMDA and MDMA/Arachidonylcyclopropylamide (ACPA, a selective CB-1 receptor agonist) co-consumption was not well-known. Here, neuronal spontaneous activity, Brain-derived neurotrophic factor (BDNF), Trk-B and cAMP response element binding protein (CREB) phosphorylation levels were recognized in ACPA and MDMA co-injected rats. Besides, we proved the role of NMDA receptor on MDMA and ACPA combination on neuronal spontaneous activity and Trk-B/BDNF pathway in the central amygdala (CeA). Male rats were anesthetized with intra-peritoneal injections of urethane; MDMA, D-2-amino-5-phosphonopentanoate (D-AP5, NMDA receptor antagonist) were injected into CeA. ACPA was administrated by intra-cerebroventricular injection. Thirty minutes following injections, neuronal firing rate was recorded from CeA. Two hours after drug injection, amygdala was collected from brain for molecular evaluations. Single administration of MDMA and/or ACPA reduced firing rates compared with sham group in the CeA dose-dependently. Injection of D-AP5, ACPA and MDMA reduced firing rate compared with sham group (P<0.001). Interestingly, injection of ACPA+MDMA enhanced BDNF, Trk-B and CREB phosphorylation compared with MDMA groups. D-AP5, ACPA and MDMA co-injection decreased BDNF, Trk-B and CREB phosphorylation levels compared with ACPA+MDMA in the amygdala (P<0.01). Probably, NMDA receptors are involved in the protective role of acute MDMA+ACPA co-injection via BDNF/Trk-B/CREB pathways. Copyright © 2017 Elsevier Inc. All rights reserved.

Dextromethorphan differentially affects opioid antinociception in rats

PubMed Central

Chen, Shiou-Lan; Huang, Eagle Yi-Kung; Chow, Lok-Hi; Tao, Pao-Luh

2005-01-01

Opioid drugs such as morphine and meperidine are widely used in clinical pain management, although they can cause some adverse effects. A number of studies indicate that N-methyl-D-aspartate (NMDA) receptors may play a role in the mechanism of morphine analgesia, tolerance and dependence. Being an antitussive with NMDA antagonist properties, dextromethorphan (DM) may have some therapeutic benefits when coadministered with morphine. In the present study, we investigated the effects of DM on the antinociceptive effects of different opioids. We also investigated the possible pharmacokinetic mechanisms involved. The antinociceptive effects of the μ-opioid receptor agonists morphine (5 mg kg−1, s.c.), meperidine (25 mg kg−1, s.c.) and codeine (25 mg kg−1, s.c.), and the κ-opioid agonists nalbuphine (8 mg kg−1, s.c.) and U-50,488H (20 mg kg−1, s.c.) were studied using the tail-flick test in male Sprague–Dawley rats. Coadministration of DM (20 mg kg−1, i.p.) with these opioids was also performed and investigated. The pharmacokinetic effects of DM on morphine and codeine were examined, and the free concentration of morphine or codeine in serum was determined by HPLC. It was found that DM potentiated the antinociceptive effects of some μ-opioid agonists but not codeine or κ-opioid agonists in rats. DM potentiated morphine's antinociceptive effect, and acutely increased the serum concentration of morphine. In contrast, DM attenuated the antinociceptive effect of codeine and decreased the serum concentration of its active metabolite (morphine). The pharmacokinetic interactions between DM and opioids may partially explain the differential effects of DM on the antinociception caused by opioids. PMID:15655510

GluN2C/GluN2D subunit-selective NMDA receptor potentiator CIQ reverses MK-801-induced impairment in prepulse inhibition and working memory in Y-maze test in mice

PubMed Central

Suryavanshi, P S; Ugale, R R; Yilmazer-Hanke, D; Stairs, D J; Dravid, S M

2014-01-01

Background and Purpose Despite ample evidence supporting the N-methyl-d-aspartate receptor (NMDAR) hypofunction hypothesis of schizophrenia, progress in the development of effective therapeutics based on this hypothesis has been limited. Facilitation of NMDA receptor function by co-agonists (d-serine or glycine) only partially alleviates the symptoms in schizophrenia; other means to facilitate NMDA receptors are required. NMDA receptor sub-types differ in their subunit composition, with varied GluN2 subunits (GluN2A-GluN2D) imparting different physiological, biochemical and pharmacological properties. CIQ is a positive allosteric modulator that is selective for GluN2C/GluN2D-containing NMDA receptors (Mullasseril et al.). Experimental Approach The effect of systemic administration of CIQ was tested on impairment in prepulse inhibition (PPI), hyperlocomotion and stereotypy induced by i.p. administration of MK-801 and methamphetamine. The effect of CIQ was also tested on MK-801-induced impairment in working memory in Y-maze spontaneous alternation test. Key Results We found that systemic administration of CIQ (20 mg·kg−1, i.p.) in mice reversed MK-801 (0.15 mg·kg−1, i.p.)-induced, but not methamphetamine (3 mg·kg−1, i.p.)-induced, deficit in PPI. MK-801 increased the startle amplitude to pulse alone, which was not reversed by CIQ. In contrast, methamphetamine reduced the startle amplitude to pulse alone, which was reversed by CIQ. CIQ also partially attenuated MK-801- and methamphetamine-induced hyperlocomotion and stereotyped behaviours. Additionally, CIQ reversed the MK-801-induced working memory deficit in spontaneous alternation in a Y-maze. Conclusion and Implications Together, these results suggest that facilitation of GluN2C/GluN2D-containing receptors may serve as an important therapeutic strategy for treating positive and cognitive symptoms in schizophrenia. PMID:24236947

Pharmacological evidence that a failure to recruit NMDA receptors contributes to impaired fear extinction retention in adolescent rats.

PubMed

Baker, Kathryn D; Richardson, Rick

2017-09-01

Adolescents, both humans and rodents, exhibit a marked impairment in extinction of fear relative to younger and older groups which could be caused by a failure to efficiently recruit NMDA receptors (NMDARs) in adolescence. It is well-established that systemic administration of NMDAR antagonists (e.g., MK801) before extinction training impairs the retention of extinction in adult and juvenile rodents, but it is unknown whether this is also the case for adolescents. Therefore, in the present study we investigated the effect of pharmacologically manipulating the NMDAR on extinction retention in adolescent rats. When extinction retention is typically impaired (i.e., after one session of extinction training) adolescent male rats given d-cycloserine (a partial NMDAR agonist) showed enhanced extinction retention relative to saline-treated animals while animals given MK801 (a non-competitive antagonist) did not exhibit any further impairment of extinction retention relative to the controls. In a further two experiments we demonstrated that when two sessions of extinction training separated by either 4 or 24h intervals were given to adolescent rats, saline-treated animals exhibited good extinction retention and the animals given MK801 before the second session exhibited impaired extinction retention. These findings suggest that extinction in adolescence does not initially involve NMDARs and this is a likely mechanism that contributes to the impaired fear inhibition observed at this age. However, NMDARs appear to be recruited with extended extinction training or after administration of a partial agonist, both of which lead to effective extinction retention. Copyright © 2016 Elsevier Inc. All rights reserved.

Characterization of methadone as a β-arrestin-biased μ-opioid receptor agonist

PubMed Central

Doi, Seira; Mori, Tomohisa; Uzawa, Naoki; Arima, Takamichi; Takahashi, Tomoyuki; Uchida, Masashi; Yawata, Ayaka; Narita, Michiko; Uezono, Yasuhito; Suzuki, Tsutomu

2016-01-01

Background Methadone is a unique µ-opioid receptor agonist. Although several researchers have insisted that the pharmacological effects of methadone are mediated through the blockade of NMDA receptor, the underlying mechanism by which methadone exerts its distinct pharmacological effects compared to those of other µ-opioid receptor agonists is still controversial. In the present study, we further investigated the pharmacological profile of methadone compared to those of fentanyl and morphine as measured mainly by the discriminative stimulus effect and in vitro assays for NMDA receptor binding, µ-opioid receptor-internalization, and µ-opioid receptor-mediated β-arrestin recruitment. Results We found that fentanyl substituted for the discriminative stimulus effects of methadone, whereas a relatively high dose of morphine was required to substitute for the discriminative stimulus effects of methadone in rats. Under these conditions, the non-competitive NMDA receptor antagonist MK-801 did not substitute for the discriminative stimulus effects of methadone. In association with its discriminative stimulus effect, methadone failed to displace the receptor binding of MK801 using mouse brain membrane. Methadone and fentanyl, but not morphine, induced potent µ-opioid receptor internalization accompanied by the strong recruitment of β-arrestin-2 in µ-opioid receptor-overexpressing cells. Conclusions These results suggest that methadone may, at least partly, produce its pharmacological effect as a β-arrestin-biased µ-opioid receptor agonist, similar to fentanyl, and NMDA receptor blockade is not the main contributor to the pharmacological profile of methadone. PMID:27317580

Fluoxetine reverses the behavioral despair induced by neurogenic stress in mice: role of N-methyl-d-aspartate and opioid receptors.

PubMed

Haj-Mirzaian, Arya; Kordjazy, Nastaran; Ostadhadi, Sattar; Amiri, Shayan; Haj-Mirzaian, Arvin; Dehpour, AhmadReza

2016-06-01

Opioid and N-methyl-d-aspartate (NMDA) receptors mediate different effects of fluoxetine. We investigated whether opioid and NMDA receptors are involved in the protective effect of fluoxetine against the behavioral despair induced by acute physical stress in male mice. We used the forced swimming test (FST), tail suspension test (TST), and open-field test (OFT) for behavioral evaluation. We used fluoxetine, naltrexone (opioid receptor antagonist), MK-801 (NMDA receptor antagonist), morphine (opioid receptor agonist), and NMDA (NMDA receptor agonist). Acute foot-shock stress (FSS) significantly induced behavioral despair (depressive-like) and anxiety-like behaviors in tests. Fluoxetine (5 mg/kg) reversed the depressant-like effect of FSS, but it did not alter the locomotion and anxiety-like behavior in animals. Acute administration of subeffective doses of naltrexone (0.3 mg/kg) or MK-801 (0.01 mg/kg) potentiated the antidepressant-like effect of fluoxetine, while subeffective doses of morphine (1 mg/kg) and NMDA (75 mg/kg) abolished this effect of fluoxetine. Also, co-administration of subeffective doses of naltrexone (0.05 mg/kg) and MK-801 (0.003 mg/kg) with fluoxetine (1 mg/kg) induced a significant decrease in the immobility time in FST and TST. Our results showed that opioid and NMDA receptors (alone or in combination) are involved in the antidepressant-like effect of fluoxetine against physical stress.

Control of Appetite and Food Preference by NMDA Receptor and Its Co-Agonist d-Serine

PubMed Central

Sasaki, Tsutomu; Matsui, Sho; Kitamura, Tadahiro

2016-01-01

Obesity causes a significant negative impact on health of human beings world-wide. The main reason for weight gain, which eventually leads to obesity, is excessive ingestion of energy above the body’s homeostatic needs. Therefore, the elucidation of detailed mechanisms for appetite control is necessary to prevent and treat obesity. N-methyl-d-aspartate (NMDA) receptor is a post-synaptic glutamate receptor and is important for excitatory neurotransmission. It is expressed throughout the nervous system, and is important for long-term potentiation. It requires both ligand (glutamate) and co-agonist (d-serine or glycine) for efficient opening of the channel to allow calcium influx. d-serine is contained in fermented foods and marine invertebrates, and brain d-serine level is maintained by synthesis in vivo and supply from food and gut microbiota. Although the NMDA receptor has been reported to take part in the central regulation of appetite, the role of d-serine had not been addressed. We recently reported that exogenous d-serine administration can suppress appetite and alter food preference. In this review, we will discuss how NMDA receptor and its co-agonist d-seine participate in the control of appetite and food preference, and elaborate on how this system could possibly be manipulated to suppress obesity. PMID:27399680

DOSE RESPONSE DEETERMINATION OF NMDA ANTAGONISTS AND GABA AGONIST ON SUSTAINED ATTENTION.

EPA Science Inventory

We have shown that acute inhalation of toluene impairs sustained attention as assessed with a visual signal detection task (SDT). In vitro studies indicate that the NMDA and GABA systems are primary targets of anesthetic agents and organic solvents such as toluene. Pharmacologica...

GLYX-13, a NMDA Receptor Glycine-Site Functional Partial Agonist, Induces Antidepressant-Like Effects Without Ketamine-Like Side Effects

PubMed Central

Burgdorf, Jeffrey; Zhang, Xiao-lei; Nicholson, Katherine L; Balster, Robert L; David Leander, J; Stanton, Patric K; Gross, Amanda L; Kroes, Roger A; Moskal, Joseph R

2013-01-01

Recent human clinical studies with the NMDA receptor (NMDAR) antagonist ketamine have revealed profound and long-lasting antidepressant effects with rapid onset in several clinical trials, but antidepressant effects were preceded by dissociative side effects. Here we show that GLYX-13, a novel NMDAR glycine-site functional partial agonist, produces an antidepressant-like effect in the Porsolt, novelty induced hypophagia, and learned helplessness tests in rats without exhibiting substance abuse-related, gating, and sedative side effects of ketamine in the drug discrimination, conditioned place preference, pre-pulse inhibition and open-field tests. Like ketamine, the GLYX-13-induced antidepressant-like effects required AMPA/kainate receptor activation, as evidenced by the ability of NBQX to abolish the antidepressant-like effect. Both GLYX-13 and ketamine persistently (24 h) enhanced the induction of long-term potentiation of synaptic transmission and the magnitude of NMDAR-NR2B conductance at rat Schaffer collateral-CA1 synapses in vitro. Cell surface biotinylation studies showed that both GLYX-13 and ketamine led to increases in both NR2B and GluR1 protein levels, as measured by Western analysis, whereas no changes were seen in mRNA expression (microarray and qRT-PCR). GLYX-13, unlike ketamine, produced its antidepressant-like effect when injected directly into the medial prefrontal cortex (MPFC). These results suggest that GLYX-13 produces an antidepressant-like effect without the side effects seen with ketamine at least in part by directly modulating NR2B-containing NMDARs in the MPFC. Furthermore, the enhancement of ‘metaplasticity' by both GLYX-13 and ketamine may help explain the long-lasting antidepressant effects of these NMDAR modulators. GLYX-13 is currently in a Phase II clinical development program for treatment-resistant depression. PMID:23303054

F15063, a compound with D2/D3 antagonist, 5-HT1A agonist and D4 partial agonist properties: (III) Activity in models of cognition and negative symptoms

PubMed Central

Depoortère, R; Auclair, A L; Bardin, L; Slot, L Bruins; Kleven, M S; Colpaert, F; Vacher, B; Newman-Tancredi, A

2007-01-01

Background and purpose: The D2/D3 receptor antagonist, D4 receptor partial agonist, and high efficacy 5-HT1A receptor agonist F15063 was shown to be highly efficacious and potent in rodent models of activity against positive symptoms of schizophrenia. However F15063 induced neither catalepsy nor the ‘serotonin syndrome'. Here, we evaluated its profile in rat models predictive of efficacy against negative symptoms/cognitive deficits of schizophrenia. Experimental approach: F15063, given i.p., was assessed in models of behavioural deficits induced by interference with the NMDA/glutamatergic (phencyclidine: PCP) or cholinergic (scopolamine) systems. Key results: Through 5-HT1A activation, F15063 partially alleviated (MED: 0.04 mg kg−1) PCP-induced social interaction deficit between two adult rats, without effect by itself, underlining its potential to combat negative symptoms. At doses above 0.16 mg kg−1, F15063 reduced interaction by itself. F15063 (0.16 mg kg−1) selectively re-established PCP-impaired ‘cognitive flexibility' in a reversal learning task, suggesting potential against adaptability deficits. F15063 (0.04–0.63 mg kg−1) also reversed scopolamine-induced amnesia in a juvenile-adult rat social recognition test, indicative of a pro-cholinergic influence. Activity in this latter test is consistent with its D4 partial agonism, as it was blocked by the D4 antagonist L745,870. Finally, F15063 up to 40 mg kg−1 did not disrupt basal prepulse inhibition of startle reflex in rats, a marker of sensorimotor gating. Conclusions and implications: The balance of D2/D3, D4 and 5-HT1A receptor interactions of F15063 yields a promising profile of activity in models of cognitive deficits and negative symptoms of schizophrenia. PMID:17375085

NMDA receptors are involved in the antidepressant-like effects of capsaicin following amphetamine withdrawal in male mice.

PubMed

Amiri, Shayan; Alijanpour, Sakineh; Tirgar, Fatemeh; Haj-Mirzaian, Arya; Amini-Khoei, Hossein; Rahimi-Balaei, Maryam; Rastegar, Mojgan; Ghaderi, Marzieh; Ghazi-Khansari, Mahmoud; Zarrindast, Mohammad-Reza

2016-08-04

Amphetamine withdrawal (AW) is accompanied by diminished pleasure and depression which plays a key role in drug relapse and addictive behaviors. There is no efficient treatment for AW-induced depression and underpinning mechanisms were not well determined. Considering both transient receptor potential cation channel, subfamily V, member 1 (TRPV1) and N-Methyl-d-aspartate (NMDA) receptors contribute to pathophysiology of mood and addictive disorders, in this study, we investigated the role of TRPV1 and NMDA receptors in mediating depressive-like behaviors following AW in male mice. Results revealed that administration of capsaicin, TRPV1 agonist, (100μg/mouse, i.c.v.) and MK-801, NMDA receptor antagonist (0.005mg/kg, i.p.) reversed AW-induced depressive-like behaviors in forced swimming test (FST) and splash test with no effect on animals' locomotion. Co-administration of sub-effective doses of MK-801 (0.001mg/kg, i.p.) and capsaicin (10μg/mouse, i.c.v) exerted antidepressant-like effects in behavioral tests. Capsazepine, TRPV1 antagonist, (100μg/mouse, i.c.v) and NMDA, NMDA receptor agonist (7.5mg/kg, i.p.) abolished the effects of capsaicin and MK-801, respectively. None of aforementioned treatments had any effect on behavior of control animals. Collectively, our findings showed that activation of TRPV1 and blockade of NMDA receptors produced antidepressant-like effects in male mice following AW, and these receptors are involved in AW-induced depressive-like behaviors. Further, we found that rapid antidepressant-like effects of capsaicin in FST and splash test are partly mediated by NMDA receptors. Copyright © 2016. Published by Elsevier Ltd.

Glutamate and GABA in lateral hypothalamic mechanisms controlling food intake.

PubMed

Stanley, B G; Urstadt, K R; Charles, J R; Kee, T

2011-07-25

By the 1990s a convergence of evidence had accumulated to suggest that neurons within the lateral hypothalamus (LH) play important roles in the stimulation of feeding behavior. However, there was little direct evidence demonstrating that neurotransmitters in the LH could, like electrical stimulation, elicit feeding in satiated animals. The present paper is a brief review in honor of Bartley Hoebel's scientific contributions, emphasizing the evidence from my lab that the excitatory neurotransmitter glutamate and the inhibitory neurotransmitter gamma aminobutyric acid (GABA) in the LH mediate feeding stimulation and feeding inhibition respectively. Specifically, we summarize evidence that LH injection of glutamate, or agonists of its N-methyl-D-aspartate (NMDA) and non-NMDA receptors, elicits feeding in satiated rats, that NMDA receptor antagonists block the eating elicited by NMDA and, more importantly, that NMDA blockade suppresses natural feeding and can reduce body weight. Conversely, GABA(A) agonists injected into the LH suppress feeding and can also reduce body weight, while GABA(A) receptor antagonists actually elicit eating when injected into the LH of satiated rats. It is suggested that natural feeding may reflect the moment-to-moment balance in the activity of glutamate and GABA within the LH. Copyright © 2011 Elsevier Inc. All rights reserved.

Characterization of the Antinociceptive Effects of the Individual Isomers of Methadone Following Acute and Chronic Administration

PubMed Central

Morgan, Richard W.; Nicholson, Katherine L.

2011-01-01

Methadone is a long-acting opioid used in the treatment of various pain states and substitution therapy in heroin addiction. Extensive behavioral characterization has been carried out utilizing the racemate, but limited investigation has been performed with the individual isomers. While the l-isomer is a potent opioid agonist, the d-isomer has weak μ opioid activity and has also been shown to possess N-methyl-d-aspartate (NMDA) antagonist properties in vitro. The acute antinociceptive effects of the isomers were evaluated in rats using a warm water tail withdrawal procedure at two stimulus intensities (50° and 55° C). Increasing dose ratios of d- to l-methadone were administered chronically to determine the ability of the d-isomer to modulate antinociceptive tolerance to the l-isomer. Acutely, both l- (0.1-5.6 mg/kg, sc) and d- (3.0-56.0 mg/kg, sc) methadone produced antinociception though the efficacy of the d-isomer was limited at 55° C. These effects were dose-dependently blocked by naltrexone (0.01-1.0 mg/kg, sc). Administered chronically, d-methadone (1.7-10 mg/kg, sc) dose-dependently blocked tolerance development to the l-isomer (1.7 mg/kg, sc). These findings support the antinociceptive effects of the isomers being opioid receptor mediated with the l-isomer functioning as a full efficacy agonist whereas the d-isomer appears to have lower efficacy. The ability of nonracemic doses of the d-isomer to prevent tolerance development to the l-isomer may be attributed to partial μ agonist activity however NMDA antagonist activity cannot be discounted. PMID:21836464

Pulmonary stretch receptor afferents activate excitatory amino acid receptors in the nucleus tractus solitarii in rats.

PubMed

Bonham, A C; Coles, S K; McCrimmon, D R

1993-05-01

1. The goal of the present study was to identify potential neurotransmitter candidates in the Breuer-Hering (BH) reflex pathway, specifically at synapses between the primary afferents and probable second-order neurones (pump cells) within the nucleus tractus solitarii (NTS). We hypothesized that if activation of specific receptors in the NTS is required for production of the BH reflex, then (1) injection of the receptor agonist(s) would mimic the reflex response (apnoea), (2) injection of appropriate antagonists would impair the apnoea produced by either lung inflation or agonist injection, and (3) second-order neurones in the pathway would be excited by either lung inflation or agonists while antagonists would prevent the response to either. 2. Studies were carried out either in spontaneously breathing or in paralysed, thoracotomized and ventilated rats in which either diaphragm EMG or phrenic nerve activity, expired CO2 concentration and arterial pressure were continuously monitored. The BH reflex was physiologically activated by inflating the lungs. 3. Pressure injections (0.03-15 pmol) of selective excitatory amino acid (EAA) receptor agonists, quisqualic acid (Quis) and N-methyl-D-aspartic acid (NMDA) into an area of the NTS shown previously to contain neurones required for production of the BH reflex produced dose-dependent apnoeas that mimicked the response to lung inflation. Injection of substance P (0.03-4 pmol) did not alter baseline respiratory pattern. 4. Injections of the EAA antagonists, kynurenic acid (Kyn; 0.6-240 pmol), 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX) or 6,7-dinitroquinoxaline-2,3-dione (DNQX) into the BH region of the NTS reversibly impaired the apnoea produced by lung inflation. All three antagonists reduced or abolished the apnoeas resulting from injection of Quis or NMDA, and slowed baseline respiratory frequency. In contrast, injections of the highly selective NMDA receptor antagonist, D-2-amino-5-phosphonovaleric acids (AP5), in doses sufficient to block the apnoeic response to NMDA, neither altered the reflex apnoea evoked by lung inflation nor the baseline respiratory pattern. 5. Pump cells located within the BH region were excited by pressure injections of the broad spectrum EAA agonist, DL-homocysteic acid (DLH). Kyn reversibly blocked the excitation of pump cells in response to either lung inflation or DLH injection. 6. These findings suggest that EAAs mediate primary afferent excitation of second-order neurones in the Breuer-Hering reflex pathway, primarily through the activation of non-NMDA EAA receptor subtypes.

Enhancing and impairing extinction of habit memory through modulation of NMDA receptors in the dorsolateral striatum.

PubMed

Goodman, Jarid; Ressler, Reed L; Packard, Mark G

2017-06-03

The present experiments investigated the involvement of N-methyl-d-aspartate (NMDA) receptors of the dorsolateral striatum (DLS) in consolidation of extinction in a habit memory task. Adult male Long-Evans rats were initially trained in a food-reinforced response learning version of a plus-maze task and were subsequently given extinction training in which the food was removed from the maze. In experiment 1, immediately after the first day of extinction training, rats received bilateral intra-DLS injections of the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP5; 2µg/side) or physiological saline. In experiment 2, immediately following the first day of extinction training, animals were given intra-DLS injections of NMDA receptor partial agonist d-cycloserine (DCS; 10 or 20µg/side) or saline. In both experiments, the number of perseverative trials (a trial in which a rat made the same previously reinforced body-turn response) and latency to reach the previously correct food well were used as measures of extinction behavior. Results indicated that post-training intra-DLS injections of AP5 impaired extinction. In contrast, post-training intra-DLS infusions of DCS (20µg) enhanced extinction. Intra-DLS administration of AP5 or DCS given two hours after extinction training did not influence extinction of response learning, indicating that immediate post-training administration of AP5 and DCS specifically influenced consolidation of the extinction memory. The present results indicate a critical role for DLS NMDA receptors in modulating extinction of habit memory and may be relevant to developing therapeutic approaches to combat the maladaptive habits observed in human psychopathologies in which DLS-dependent memory has been implicated (e.g. drug addiction and relapse and obsessive compulsive disorder). Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.

D-Cycloserine improves functional outcome after traumatic brain injury with wide therapeutic window

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

Adeleye, A.; Biegon, A.; Adeleye, A.

It has been long thought that hyperactivation of N-methyl-D-aspartate (NMDA) receptors underlies neurological decline after traumatic brain injury. However, all clinical trials with NMDA receptor antagonists failed. Since NMDA receptors are down-regulated from 4 h to 2 weeks after brain injury, activation at 24 h, rather than inhibition, of these receptors, was previously shown to be beneficial in mice. Here, we tested the therapeutic window, dose regimen and mechanism of action of the NMDA receptor partial agonist d-cycloserine (DCS) in traumatic brain injury. Male mice were subjected to trauma using a weight-drop model, and administered 10 mg/kg (i.p.) DCS ormore » vehicle once (8, 16, 24, or 72 h) twice (24 and 48 h) or three times (24, 48 and 72 h). Functional recovery was assessed for up to 60 days, using a Neurological Severity Score that measures neurobehavioral parameters. In all groups in which treatment was begun at 24 or 72 h neurobehavioral function was significantly better than in the vehicle-treated groups. Additional doses, on days 2 and 3 did not further improve recovery. Mice treated at 8 h or 16 h post injury did not differ from the vehicle-treated controls. Co-administration of the NMDA receptor antagonist MK-801 completely blocked the protective effect of DCS given at 24 h. Infarct volume measured by 2,3,5-triphenyltetrazolium chloride staining at 48 h or by cresyl violet at 28 days was not affected by DCS treatment. Since DCS is used clinically for other indications, the present study offers a novel approach for treating human traumatic brain injury with a therapeutic window of at least 24 h.« less

Non-ionotropic signaling by the NMDA receptor: controversy and opportunity.

PubMed

Gray, John A; Zito, Karen; Hell, Johannes W

2016-01-01

Provocative emerging evidence suggests that the N-methyl-d-aspartate (NMDA) receptor can signal in the absence of ion flux through the receptor. This non-ionotropic signaling is thought to be due to agonist-induced conformational changes in the receptor, independently of channel opening. Non-ionotropic NMDA receptor signaling has been proposed to be sufficient to induce synaptic long-term depression (LTD), directly challenging the decades-old model that prolonged low-level calcium influx is required to induce LTD. Here, we briefly review these recent findings, focusing primarily on the potential role of non-ionotropic signaling in NMDA receptor-mediated LTD. Further reports concerning additional roles of non-ionotropic NMDA receptor signaling are also discussed. If validated, this new view of NMDA receptor-mediated signaling will usher in an exciting new era of exploring synapse function and dysfunction.

Non-ionotropic signaling by the NMDA receptor: controversy and opportunity

PubMed Central

Gray, John A.; Zito, Karen; Hell, Johannes W.

2016-01-01

Provocative emerging evidence suggests that the N-methyl-d-aspartate (NMDA) receptor can signal in the absence of ion flux through the receptor. This non-ionotropic signaling is thought to be due to agonist-induced conformational changes in the receptor, independently of channel opening. Non-ionotropic NMDA receptor signaling has been proposed to be sufficient to induce synaptic long-term depression (LTD), directly challenging the decades-old model that prolonged low-level calcium influx is required to induce LTD. Here, we briefly review these recent findings, focusing primarily on the potential role of non-ionotropic signaling in NMDA receptor-mediated LTD. Further reports concerning additional roles of non-ionotropic NMDA receptor signaling are also discussed. If validated, this new view of NMDA receptor-mediated signaling will usher in an exciting new era of exploring synapse function and dysfunction. PMID:27303637

Neurophysiological Analysis of Circadian Rhythm Entrainment

DTIC Science & Technology

1994-05-24

on activations in response to the ionotropic agonist NMDA (25). These results point to a previously uninvestigated role for metabotropic receptors in...are selective agonists of the metabotropic type of glutamate receptor . Selective metabotropic antagonists can block these effects but do not alter...glutamate receptors on SCN cell activity. In slice preparations, our initial findings are that the selective metabotropic agonist 1S,3R-ACPD has very potent

Ethanol Inhibition of Constitutively Open N-Methyl-d-Aspartate Receptors

PubMed Central

Xu, Minfu; Smothers, C. Thetford; Trudell, James

2012-01-01

N-Methyl-d-aspartate (NMDA) receptors gate a slow and calcium-rich component of the postsynaptic glutamate response. Like all ionotropic glutamate receptors, NMDA subunits contain a highly conserved motif (SYTANLAAF) in the transmembrane (TM) 3 domain that is critically involved in channel gating. Mutation of an alanine in this domain (A7; underlined above) results in constitutively open receptors that show reduced sensitivity to several allosteric modulators. In this study, we examined the effects of ethanol, a substance that inhibits NMDA currents via an unknown mechanism, on tonically active NMDA receptors expressed in human embryonic kidney 293 cells. Ethanol (100 mM) inhibited currents from GluN1(A7R)/GluN2A and GluN1(A7R)/GluN2B receptors by approximately 50%, whereas those from GluN1/GluN2B(A7R) receptors were reduced by less than 10%. In cysteine-substituted GluN1 and GluN2 A7 mutants, estimated ethanol IC50 values for agonist-gated currents were 101, 117, 103, and 69 mM for GluN1(A7C)/GluN2A, GluN1(A7C)/GluN2B, GluN1/GluN2A(A7C), and GluN1/GluN2B(A7C) receptors, respectively. After exposure to the thiol-modifying reagent 2-(trimethylammonium)ethyl methanethiosulfonate (MTSET), A7C mutants showed robust agonist-independent currents and reduced sensitivity to ethanol (IC50 values of 371, 256, 715, and 958 mM, respectively, as above). In contrast, cysteine modification of the ligand-binding domain resulted in constitutively open receptors that showed robust ethanol inhibition. Ethanol inhibition of MTSET-treated GluN1(A7C) receptors was further reduced by TM3/TM4 mutations previously shown to reduce ethanol sensitivity of agonist-gated receptors. Overall, these results show that ethanol affects NMDA receptor function at a site distal from agonist binding and appears to exert greater effects via perturbation of GluN2 subunits. PMID:22005043

Pharmacological specificity of N-methyl-D-aspartate discrimination in rats.

PubMed

Grech, D M; Willetts, J; Balster, R L

1993-04-01

The purpose of this study was to provide further information on the usefulness of N-methyl-D-aspartate (NMDA) discrimination in rats as a behavioral model for NMDA receptor activation. The pharmacological specificity of the NMDA discriminative stimulus was examined in rats trained to discriminate 30 mg/kg, i.p. NMDA from saline using a 2-lever fixed-ratio (FR) 32 food reinforcement schedule. Pharmacologically diverse centrally-acting agents were examined for their ability to substitute for NMDA. Morphine did not substitute for NMDA; neither did the central stimulants, caffeine and (+)-amphetamine, which produced a maximum mean of only 16 and 35% NMDA-lever responding, respectively. Pentylenetetrazol and picrotoxin also did not substitute for NMDA. Compounds interacting with cholinergic neurotransmission including nicotine, physostigmine, arecoline and mecamylamine, produced at best, only intermediate levels of NMDA-lever responding (32-61%), with the highest levels of NMDA-lever responding generally occurring at doses that also reduced rates of responding. These results suggest that the discriminative stimulus properties of NMDA are dissimilar from those of a number of centrally-acting drugs. Combined with the results of studies indicating that the NMDA discriminative stimulus can be antagonized by competitive NMDA antagonists, these results provide further evidence that NMDA receptor activation is the basis of NMDA discrimination and that this model may be useful for studying site-selective NMDA agonists and antagonists.

Effects of the NMDA receptor antagonist, D-CPPene, on sensitization to the operant decrement produced by naloxone in morphine-treated rats.

PubMed

Bespalov, A Y; Medvedev, I O; Sukhotina, I A; Zvartau, E E

2001-04-01

Sensitization to the rate-decreasing effects of opioid antagonists induced by acute pretreatment with opioid agonists has been suggested to reflect initial changes in opioid systems that underlie physical dependence. Glutamate receptors are implicated in the development and expression of opioid dependence, and antagonists acting at the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors have been shown repeatedly to attenuate the severity of opioid withdrawal. The present study evaluated the ability of a competitive NMDA receptor antagonist, D-CPPene (SDZ EAA 494; 3-(2-carboxypiperazin-4-yl)-1-propenyl-1-phosphonic acid), to affect morphine-induced sensitization to naloxone in rats trained to lever-press on a multiple-trial, fixed-ratio 10 schedule of food reinforcement. D-CPPene (0.3-3 mg/kg) was administered either 4 h or 30 min prior to the test session. Morphine (10 mg/kg) or its vehicle was administered 4 h before naloxone challenge (0.3-3 mg/kg). D-CPPene failed to prevent morphine-induced potentiation of the naloxone-produced decrement in operant performance. Thus, these results suggest that agonist-induced sensitization to behavioral effects of opioid antagonists may be insensitive to NMDA receptor blockade.

High Concentrations of Tranexamic Acid Inhibit Ionotropic Glutamate Receptors.

PubMed

Lecker, Irene; Wang, Dian-Shi; Kaneshwaran, Kirusanthy; Mazer, C David; Orser, Beverley A

2017-07-01

The antifibrinolytic drug tranexamic acid is structurally similar to the amino acid glycine and may cause seizures and myoclonus by acting as a competitive antagonist of glycine receptors. Glycine is an obligatory co-agonist of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors. Thus, it is plausible that tranexamic acid inhibits NMDA receptors by acting as a competitive antagonist at the glycine binding site. The aim of this study was to determine whether tranexamic acid inhibits NMDA receptors, as well as α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and kainate subtypes of ionotropic glutamate receptors. Tranexamic acid modulation of NMDA, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, and kainate receptors was studied using whole cell voltage-clamp recordings of current from cultured mouse hippocampal neurons. Tranexamic acid rapidly and reversibly inhibited NMDA receptors (half maximal inhibitory concentration = 241 ± 45 mM, mean ± SD; 95% CI, 200 to 281; n = 5) and shifted the glycine concentration-response curve for NMDA-evoked current to the right. Tranexamic acid also inhibited α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (half maximal inhibitory concentration = 231 ± 91 mM; 95% CI, 148 to 314; n = 5 to 6) and kainate receptors (half maximal inhibitory concentration = 90 ± 24 mM; 95% CI, 68 to 112; n = 5). Tranexamic acid inhibits NMDA receptors likely by reducing the binding of the co-agonist glycine and also inhibits α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and kainate receptors. Receptor blockade occurs at high millimolar concentrations of tranexamic acid, similar to the concentrations that occur after topical application to peripheral tissues. Glutamate receptors in tissues including bone, heart, and nerves play various physiologic roles, and tranexamic acid inhibition of these receptors may contribute to adverse drug effects.

Kainate toxicity in energy-compromised rat hippocampal slices: differences between oxygen and glucose deprivation.

PubMed

Schurr, A; Rigor, B M

1993-06-18

The effects of kainate (KA) on the recovery of neuronal function in rat hippocampal slices after hypoxia or glucose deprivation (GD) were investigated and compared to those of (R,S)-alpha-amino-3-hydroxy-5-methyl-4- isoxazoleproprionate (AMPA). KA and AMPA were found to be more toxic than either N-methyl-D-aspartate (NMDA), quinolinate, or glutamate, both under normal conditions and under states of energy deprivation. Doses as low as 1 microM KA or AMPA were sufficient to significantly reduce the recovery rate of neuronal function in slices after a standardized period of hypoxia or GD. The enhancement of hypoxic neuronal damage by both agonists could be partially blocked by the antagonist kynurenate, by the NMDA competitive antagonist AP5, and by elevating [Mg2+] in or by omitting Ca2+ from the perfusion medium. The AMPA antagonist glutamic acid diethyl ester was ineffective in preventing the enhanced hypoxic neuronal damage by either KA or AMPA. The antagonist of the glycine modulatory site on the NMDA receptor, 7-chlorokynurenate, did not block the KA toxicity but was able to block the toxicity of AMPA. 2,3-Dihydroxyquinoxaline completely blocked the KA- and AMPA-enhanced hypoxic neuronal damage. The KA-enhanced, GD-induced neuronal damage was prevented by Ca2+ depletion and partially antagonized by kynurenate but not by AP5 or elevated [Mg2+]. The results of the present study indicate that the KA receptor is involved in the mechanism of neuronal damage induced by hypoxia and GD, probably allowing Ca2+ influx and subsequent intracellular Ca2+ overload.(ABSTRACT TRUNCATED AT 250 WORDS)

The 5-HT2A receptor antagonist M100907 is more effective in counteracting NMDA antagonist- than dopamine agonist-induced hyperactivity in mice.

PubMed

Carlsson, M L; Martin, P; Nilsson, M; Sorensen, S M; Carlsson, A; Waters, S; Waters, N

1999-01-01

The purpose of the present study was to compare the effectiveness of the selective 5-HT2A antagonist M100907 in different psychosis models. The classical neuroleptic haloperidol was used as reference compound. Two hyperdopaminergia and two hypoglutamatergia mouse models were used. Hyperdopaminergia was produced by the DA releaser d-amphetamine or the DA uptake inhibitor GBR 12909. Hypoglutamatergia was produced by the un-competitive NMDA receptor antagonist MK-801 or the competitive NMDA receptor antagonist D-CPPene. M100907 was found to counteract the locomotor stimulant effects of the NMDA receptor antagonists MK-801 and D-CPPene, but spontaneous locomotion, d-amphetamine- and GBR-12909-induced hyperactivity were not significantly affected. Haloperidol, on the other hand, antagonized both NMDA antagonist- and DA agonist-induced hyperactivity, as well as spontaneous locomotion in the highest dose used. Based on the present and previous results we draw the conclusion that 5-HT2A receptor antagonists are particularly effective against behavioural anomalies resulting from hypoglutamatergia of various origins. The clinical implications of our results and conclusions would be that a 5-HT2A receptor antagonist, due to i a the low side effect liability, could be the preferable treatment strategy in various disorders associated with hypoglutamatergia; such conditions might include schizophrenia, childhood autism and dementia disorders.

Non-NMDA receptor antagonist-induced drinking in rat

NASA Technical Reports Server (NTRS)

Xu, Z.; Johnson, A. K.

1998-01-01

Glutamate has been implicated in the central control of mechanisms that maintain body fluid homeostasis. The present studies demonstrate that intracerebroventricular (i.c.v.) injections of the non-N-methyl-d-aspartate (NMDA) receptor antagonists 6, 7-dinitroquinoxaline-2,3-dione (DNQX) and 6-cyano-7-nitroquinoxaline-2,3 dione (CNQX) induce drinking in rats. The dipsogenic effect of i.c.v. DNQX was antagonized by the non-NMDA receptor agonist alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). The water intake induced by DNQX was also blocked by pretreatment with a NMDA receptor antagonist, MK-801, but not by angiotensin type 1 (AT1) or acetylcholine muscarinic receptor antagonists (losartan and atropine). The results indicate that non-NMDA receptors may exert a tonic inhibitory effect within brain circuits that control dipsogenic activity and that functional integrity of NMDA receptors may be required for the non-NMDA receptor antagonists to induce water intake. Copyright 1998 Published by Elsevier Science B.V.

Mechanical stress activates NMDA receptors in the absence of agonists.

PubMed

Maneshi, Mohammad Mehdi; Maki, Bruce; Gnanasambandam, Radhakrishnan; Belin, Sophie; Popescu, Gabriela K; Sachs, Frederick; Hua, Susan Z

2017-01-03

While studying the physiological response of primary rat astrocytes to fluid shear stress in a model of traumatic brain injury (TBI), we found that shear stress induced Ca 2+ entry. The influx was inhibited by MK-801, a specific pore blocker of N-Methyl-D-aspartic acid receptor (NMDAR) channels, and this occurred in the absence of agonists. Other NMDA open channel blockers ketamine and memantine showed a similar effect. The competitive glutamate antagonists AP5 and GluN2B-selective inhibitor ifenprodil reduced NMDA-activated currents, but had no effect on the mechanically induced Ca 2+ influx. Extracellular Mg 2+ at 2 mM did not significantly affect the shear induced Ca 2+ influx, but at 10 mM it produced significant inhibition. Patch clamp experiments showed mechanical activation of NMDAR and inhibition by MK-801. The mechanical sensitivity of NMDARs may play a role in the normal physiology of fluid flow in the glymphatic system and it has obvious relevance to TBI.

Mechanical stress activates NMDA receptors in the absence of agonists

PubMed Central

Maneshi, Mohammad Mehdi; Maki, Bruce; Gnanasambandam, Radhakrishnan; Belin, Sophie; Popescu, Gabriela K.; Sachs, Frederick; Hua, Susan Z.

2017-01-01

While studying the physiological response of primary rat astrocytes to fluid shear stress in a model of traumatic brain injury (TBI), we found that shear stress induced Ca2+ entry. The influx was inhibited by MK-801, a specific pore blocker of N-Methyl-D-aspartic acid receptor (NMDAR) channels, and this occurred in the absence of agonists. Other NMDA open channel blockers ketamine and memantine showed a similar effect. The competitive glutamate antagonists AP5 and GluN2B-selective inhibitor ifenprodil reduced NMDA-activated currents, but had no effect on the mechanically induced Ca2+ influx. Extracellular Mg2+ at 2 mM did not significantly affect the shear induced Ca2+ influx, but at 10 mM it produced significant inhibition. Patch clamp experiments showed mechanical activation of NMDAR and inhibition by MK-801. The mechanical sensitivity of NMDARs may play a role in the normal physiology of fluid flow in the glymphatic system and it has obvious relevance to TBI. PMID:28045032

Structure and symmetry inform gating principles of ionotropic glutamate receptors.

PubMed

Zhu, Shujia; Gouaux, Eric

2017-01-01

Ionotropic glutamate receptors (iGluRs) transduce signals derived from release of the excitatory neurotransmitter glutamate from pre-synaptic neurons into excitation of post-synaptic neurons on a millisecond time-scale. In recent years, the elucidation of full-length iGluR structures of NMDA, AMPA and kainate receptors by X-ray crystallography and single particle cryo-electron microscopy has greatly enhanced our understanding of the interrelationships between receptor architecture and gating mechanism. Here we briefly review full-length iGluR structures and discuss the similarities and differences between NMDA receptors and non-NMDA iGluRs. We focus on distinct conformations, including ligand-free, agonist-bound active, agonist-bound desensitized and antagonist-bound conformations as well as modulator and auxiliary protein-bound states. These findings provide insights into structure-based mechanisms of iGluR gating and modulation which together shape the amplitude and time course of the excitatory postsynaptic potential. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'. Copyright © 2016 Elsevier Ltd. All rights reserved.

Cellular and synaptic effect of substance P on neonatal phrenic motoneurons.

PubMed

Ptak, K; Konrad, M; Di Pasquale, E; Tell, F; Hilaire, G; Monteau, R

2000-01-01

Experiments were carried out on the in vitro brainstem-spinal cord preparation of the newborn rat to analyse the effects of substance P (SP) on phrenic motoneuron (PMN) activity. In current-clamp mode, SP significantly depolarized PMNs, increased their input resistance, decreased the rheobase current and shifted the firing frequency-intensity relationships leftwards, but did not affect spike frequency adaptation or single spike configuration. The neurokinin receptor agonist NK1 had SP-mimetic effects, whereas the NK3 and NK2 receptor agonists were less effective and ineffective, respectively. In a tetrodotoxin-containing aCSF, only SP or the NK1 receptor agonist were still active. No depolarization was observed when the NK1 receptor agonist was applied in the presence of muscarine. In voltage-clamp mode, SP or the NK1 receptor agonist produced an inward current (ISP) which was not significantly reduced by extracellular application of tetraethylammonium, Co2+, 4-aminopyridine or Cs+. In aCSF containing tetrodotoxin, Co2+ and Cs+, ISP was blocked by muscarine. No PMN displayed any M-type potassium current but only a current showing no voltage sensitivity over the range -100 to 0 mV, reversing near the expected EK +, hence consistent with a leak current. SP application to the spinal cord only (using a partitioned chamber) significantly increased the phrenic activity. Pretreatment with the NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (AP5) decreased the C4 discharge duration and blocked the effect of SP, thus exhibiting an NMDA potentiation by SP. In conclusion, SP modulates postsynaptically the response of phrenic motoneurons to the inspiratory drive through the reduction of a leak conductance and the potentiation of the NMDA component of the synaptic input.

Potentiation of mouse vagal afferent mechanosensitivity by ionotropic and metabotropic glutamate receptors

PubMed Central

Slattery, James A; Page, Amanda J; Dorian, Camilla L; Brierley, Stuart M; Blackshaw, L Ashley

2006-01-01

Glutamate acts at central synapses via ionotropic (iGluR – NMDA, AMPA and kainate) and metabotropic glutamate receptors (mGluRs). Group I mGluRs are excitatory whilst group II and III are inhibitory. Inhibitory mGluRs also modulate peripherally the mechanosensitivity of gastro-oesophageal vagal afferents. Here we determined the potential of excitatory GluRs to play an opposing role in modulating vagal afferent mechanosensitivity, and investigated expression of receptor subunit mRNA within the nodose ganglion. The responses of mouse gastro-oesophageal vagal afferents to graded mechanical stimuli were investigated before and during application of selective GluR ligands to their peripheral endings. Two types of vagal afferents were tested: tension receptors, which respond to circumferential tension, and mucosal receptors, which respond only to mucosal stroking. The selective iGluR agonists NMDA and AMPA concentration-dependently potentiated afferent responses. Their corresponding antagonists AP-5 and NBQX alone attenuated mechanosensory responses as did the non-selective antagonist kynurenate. The kainate selective agonist SYM-2081 had minor effects on mechanosensitivity, and the antagonist UBP 302 was ineffective. The mGluR5 antagonist MTEP concentration-dependently inhibited mechanosensitivity. Efficacy of agonists and antagonists differed on mucosal and tension receptors. We conclude that excitatory modulation of afferent mechanosensitivity occurs mainly via NMDA, AMPA and mGlu5 receptors, and the role of each differs according to afferent subtypes. PCR data indicated that all NMDA, kainate and AMPA receptor subunits plus mGluR5 are expressed, and are therefore candidates for the neuromodulation we observed. PMID:16945965

Potentiation of mouse vagal afferent mechanosensitivity by ionotropic and metabotropic glutamate receptors.

PubMed

Slattery, James A; Page, Amanda J; Dorian, Camilla L; Brierley, Stuart M; Blackshaw, L Ashley

2006-11-15

Glutamate acts at central synapses via ionotropic (iGluR--NMDA, AMPA and kainate) and metabotropic glutamate receptors (mGluRs). Group I mGluRs are excitatory whilst group II and III are inhibitory. Inhibitory mGluRs also modulate peripherally the mechanosensitivity of gastro-oesophageal vagal afferents. Here we determined the potential of excitatory GluRs to play an opposing role in modulating vagal afferent mechanosensitivity, and investigated expression of receptor subunit mRNA within the nodose ganglion. The responses of mouse gastro-oesophageal vagal afferents to graded mechanical stimuli were investigated before and during application of selective GluR ligands to their peripheral endings. Two types of vagal afferents were tested: tension receptors, which respond to circumferential tension, and mucosal receptors, which respond only to mucosal stroking. The selective iGluR agonists NMDA and AMPA concentration-dependently potentiated afferent responses. Their corresponding antagonists AP-5 and NBQX alone attenuated mechanosensory responses as did the non-selective antagonist kynurenate. The kainate selective agonist SYM-2081 had minor effects on mechanosensitivity, and the antagonist UBP 302 was ineffective. The mGluR5 antagonist MTEP concentration-dependently inhibited mechanosensitivity. Efficacy of agonists and antagonists differed on mucosal and tension receptors. We conclude that excitatory modulation of afferent mechanosensitivity occurs mainly via NMDA, AMPA and mGlu5 receptors, and the role of each differs according to afferent subtypes. PCR data indicated that all NMDA, kainate and AMPA receptor subunits plus mGluR5 are expressed, and are therefore candidates for the neuromodulation we observed.

Group III mGlu receptor agonists potentiate the anticonvulsant effect of AMPA and NMDA receptor block.

PubMed

De Sarro, Giovambattista; Chimirri, Alba; Meldrum, Brian S

2002-09-06

We report the anticonvulsant action in DBA/2 mice of two mGlu Group III receptor agonists: (R,S)-4-phosphonophenylglycine, (R,S)-PPG, a compound with moderate mGlu8 selectivity, and of (1S,3R,4S)-1-aminocyclopentane-1,2,4-tricarboxylic acid, ACPT-1, a selective agonist for mGlu4alpha receptors. Both compounds, given intracerebroventricularly at doses which did not show marked anticonvulsant activity, produced a consistent shift to the left of the dose-response curves (i.e. enhanced the anticonvulsant properties) of 1-(4'-aminophenyl)-3,5-dihydro-7,8-dimethoxy-4H-2,3-benzodiazepin-4-one hydrochloride, CFM-2, a noncompetitive AMPA receptor antagonist, and 3-((+/-)-2-carboxypiperazin-4-yl)-1-phosphonic acid, CPPene, a competitive NMDA receptor antagonist, in DBA/2 mice. In addition, (R,S)-PPG and ACPT-1 administered intracerebroventricularly prolonged the time course of the anticonvulsant properties of CFM-2 (33 micromol/kg, i.p.) and CPPene (3.3 micromol/kg, i.p.) administered intraperitoneally. We conclude that modest reduction of synaptic glutamate release by activation of Group III metabotropic receptors potentiates the anticonvulsant effect of AMPA and NMDA receptor blockade. Copyright 2002 Elsevier Science B.V.

Acute D2/D3 dopaminergic agonism but chronic D2/D3 antagonism prevents NMDA antagonist neurotoxicity.

PubMed

Farber, Nuri B; Nemmers, Brian; Noguchi, Kevin K

2006-09-15

Antagonists of the N-methyl-D-aspartate (NMDA) glutamate receptor, most likely by producing disinhibtion in complex circuits, acutely produce psychosis and cognitive disturbances in humans, and neurotoxicity in rodents. Studies examining NMDA Receptor Hypofunction (NRHypo) neurotoxicity in animals, therefore, may provide insights into the pathophysiology of psychotic disorders. Dopaminergic D2 and/or D3 agents can modify psychosis over days to weeks, suggesting involvement of these transmitter system(s). We studied the ability of D2/D3 agonists and antagonists to modify NRHypo neurotoxicity both after a one-time acute exposure and after chronic daily exposure. Here we report that D2/D3 dopamine agonists, probably via D3 receptors, prevent NRHypo neurotoxicity when given acutely. The protective effect with D2/D3 agonists is not seen after chronic daily dosing. In contrast, the antipsychotic haloperidol does not affect NRHypo neurotoxicity when given acutely at D2/D3 doses. However, after chronic daily dosing of 1, 3, or 5 weeks, haloperidol does prevent NRHypo neurotoxicity with longer durations producing greater protection. Understanding the changes that occur in the NRHypo circuit after chronic exposure to dopaminergic agents could provide important clues into the pathophysiology of psychotic disorders.

A possible participation of transient receptor potential vanilloid type 1 channels in the antidepressant effect of fluoxetine.

PubMed

Manna, Shyamshree S S; Umathe, Sudhir N

2012-06-15

The present study investigated the influence of transient receptor vanilloid type 1 (TRPV1) channel agonist (capsaicin) and antagonist (capsazepine) either alone or in combination with traditional antidepressant drug, fluoxetine; or a serotonin hydroxylase inhibitor, para-chlorophenylalanine; or a glutamate N-methyl-D-aspartate (NMDA) receptor agonist, NMDA on the forced swim test and tail suspension test using male Swiss mice. Results revealed that intracerebroventricular injections of capsaicin (200 and 300 μg/mouse) and capsazepine (100 and 200 μg/mouse) reduced the immobility time, exhibiting antidepressant-like activity that was comparable to the effects of fluoxetine (2.5-10 μg/mouse) in both the tests. However, in the presence of inactive dose (10 μg/mouse) of capsazepine, capsaicin (300 μg/mouse) had no influence on the indices of both tests, signifying that the effects are TRPV1-mediated. Further, the antidepressant-like effects of both the TRPV1 ligands were neutralized in mice-pretreated with NMDA (0.1 μg/mouse), suggestive of the fact that decreased glutamatergic transmission might contribute to the antidepressant-like activity. In addition, co-administration of sub-threshold dose of capsazepine (10 μg/mouse) and fluoxetine (1.75 μg/mouse) produced a synergistic effect in both the tests. In contrast, inactive doses of capsaicin (10 and 100 μg/mouse) partially abolished the antidepressant effect of fluoxetine (10 μg/mouse), while its effect was potentiated by active dose of capsaicin (200 μg/mouse). Moreover, pretreatment of mice with para-chlorophenylalanine (300 mg/kg/day × 3 days, i.p.) attenuated the effects of capsaicin and capsazepine, demonstrating a probable interplay between serotonin and TRPV1, at least in parts. Thus, our data indicate a possible role of TRPV1 in depressive-like symptoms. Copyright © 2012 Elsevier B.V. All rights reserved.

Heteroreceptor Complexes Formed by Dopamine D1, Histamine H3, and N-Methyl-D-Aspartate Glutamate Receptors as Targets to Prevent Neuronal Death in Alzheimer's Disease.

PubMed

Rodríguez-Ruiz, Mar; Moreno, Estefanía; Moreno-Delgado, David; Navarro, Gemma; Mallol, Josefa; Cortés, Antonio; Lluís, Carme; Canela, Enric I; Casadó, Vicent; McCormick, Peter J; Franco, Rafael

2017-08-01

Alzheimer's disease (AD) is a neurodegenerative disorder causing progressive memory loss and cognitive dysfunction. Anti-AD strategies targeting cell receptors consider them as isolated units. However, many cell surface receptors cooperate and physically contact each other forming complexes having different biochemical properties than individual receptors. We here report the discovery of dopamine D 1 , histamine H 3 , and N-methyl-D-aspartate (NMDA) glutamate receptor heteromers in heterologous systems and in rodent brain cortex. Heteromers were detected by co-immunoprecipitation and in situ proximity ligation assays (PLA) in the rat cortex where H 3 receptor agonists, via negative cross-talk, and H 3 receptor antagonists, via cross-antagonism, decreased D 1 receptor agonist signaling determined by ERK1/2 or Akt phosphorylation, and counteracted D 1 receptor-mediated excitotoxic cell death. Both D 1 and H 3 receptor antagonists also counteracted NMDA toxicity suggesting a complex interaction between NMDA receptors and D 1 -H 3 receptor heteromer function. Likely due to heteromerization, H 3 receptors act as allosteric regulator for D 1 and NMDA receptors. By bioluminescence resonance energy transfer (BRET), we demonstrated that D 1 or H 3 receptors form heteromers with NR1A/NR2B NMDA receptor subunits. D 1 -H 3 -NMDA receptor complexes were confirmed by BRET combined with fluorescence complementation. The endogenous expression of complexes in mouse cortex was determined by PLA and similar expression was observed in wild-type and APP/PS1 mice. Consistent with allosteric receptor-receptor interactions within the complex, H 3 receptor antagonists reduced NMDA or D 1 receptor-mediated excitotoxic cell death in cortical organotypic cultures. Moreover, H 3 receptor antagonists reverted the toxicity induced by ß 1-42 -amyloid peptide. Thus, histamine H 3 receptors in D 1 -H 3 -NMDA heteroreceptor complexes arise as promising targets to prevent neurodegeneration.

Pharmacological treatments of cerebellar ataxia.

PubMed

Ogawa, Masafumi

2004-01-01

The confirmed pharmacological treatment of cerebellar ataxia is still lacking. In a recent preliminary trial, we showed that D-cycloserine, a partial NMDA allosteric agonist, may relieve the symptoms. In this paper, major clinical trials to relieve ataxic symptoms are reviewed. Previous studies showed some efficacy of physostigmine in ataxic patients. However, physostigmine did not improve the ataxia in a recent double-blind crossover study. The replacement therapy of the deficient cholinergic system with choline or choline derivatives was tried in patients with Friedreich's ataxia and other ataxic patients, but the result was not definitive. A levorotatory form of hydroxytryptophan (a serotonin precursor), a serotoninergic 5-HT1A agonist, a serotoninergic 5-HT3 antagonist, and a serotonin reuptake inhibitor were also used for the therapy for ataxia. In a double-blind randomized study, buspirone, a 5-HT1A agonist was active in cerebellar ataxia, but the effect is partial and not major. The effects of the studies with the other serotoninergic drugs were not consistent. The effect of sulfamethoxazole-trimethoprim therapy in spinocerebellar ataxia type3/Machado-Joseph disease (MJD) was reported, although the therapy improved spasticity or rigidity, rather than ataxia. In contrast to previous studies, sulfamethoxazole-trimethoprim therapy in MJD had no effect in a 2001 double-blind crossover study. The thyrotropin-releasing hormone, D-cycloserine, and acetazolamide for SCA6 may have some efficacy. However, a well-designed double-blind crossover trial is needed to confirm the effect.

Rats selectively bred for low levels of play-induced 50 kHz vocalizations as a model for autism spectrum disorders: a role for NMDA receptors.

PubMed

Burgdorf, Jeffrey; Moskal, Joseph R; Brudzynski, Stefan M; Panksepp, Jaak

2013-08-15

Early childhood autism is characterized by deficits in social approach and play behaviors, socio-emotional relatedness, and communication/speech abnormalities, as well as repetitive behaviors. These core neuropsychological features of autism can be modeled in laboratory rats, and the results may be useful for drug discovery and therapeutic development. We review data that show that rats selectively bred for low rates of play-related pro-social ultrasonic vocalizations (USVs) can be used to model social deficit symptoms of autism. Low-line animals engage in less social contact time with conspecifics, show lower rates of play induced pro-social USVs, and show an increased proportion of non-frequency modulated (i.e. monotonous) ultrasonic vocalizations compared to non-selectively bred random-line animals. Gene expression patterns in the low-line animals show significant enrichment in autism-associated genes, and the NMDA receptor family was identified as a significant hub. Treatment of low-line animals with the NMDAR functional glycine site partial agonist, GLYX-13, rescued the deficits in play-induced pro-social 50-kHz USVs and reduced monotonous USVs. Since the NMDA receptor has been implicated in the genesis of autistic symptoms, it is possible that GLYX-13 may be of therapeutic value in the treatment of autism. Copyright © 2013 Elsevier B.V. All rights reserved.

Rats selectively bred for low levels of play-induced 50 kHz vocalizations as a model for Autism Spectrum Disorders: a role for NMDA receptors

PubMed Central

Burgdorf, Jeffrey; Moskal, Joseph R.; Brudzynski, Stefan M.; Panksepp, Jaak

2016-01-01

Early childhood autism is characterized by deficits in social approach and play behaviors, socio-emotional relatedness, and communication/speech abnormalities, as well as repetitive behaviors. These core neuropsychological features of autism can be modeled in laboratory rats, and the results may be useful for drug discovery and therapeutic development. We review data that show that rats selectively bred for low rates of play-related pro-social ultrasonic vocalizations (USVs) can be used to model social deficit symptoms of autism. Low-line animals engage in less social contact time with conspecifics, show lower rates of play induced pro-social USVs, and show an increased proportion of non-frequency modulated (i.e. monotonous) ultrasonic vocalizations compared to non-selectively bred random-line animals. Gene expression patterns in the low-line animals show significant enrichment in autism-associated genes, and the NMDA receptor family was identified as a significant hub. Treatment of low-line animals with the NMDAR functional glycine site partial agonist, GLYX-13, rescued the deficits in play-induced pro-social 50-kHz USVs and reduced monotonous USVs. Since the NMDA receptor has been implicated in the genesis of autistic symptoms, it is possible that GLYX-13 may be of therapeutic value in the treatment of autism. PMID:23623884

NMDA and D1 receptors are involved in one-trial tolerance to the anxiolytic-like effects of diazepam in the elevated plus maze test in rats.

PubMed

Zhou, Heng; Yu, Cheng-Long; Wang, Li-Ping; Yang, Yue-Xiong; Mao, Rong-Rong; Zhou, Qi-Xin; Xu, Lin

2015-08-01

The elevated plus maze (EPM) test is used to examine anxiety-like behaviors in rodents. One interesting phenomenon in the EPM test is one-trial tolerance (OTT), which refers to the reduction in the anxiolytic-like effects of benzodiazepines when rodents are re-exposed to the EPM. However, the underlying mechanism of OTT is still unclear. In this study, we reported that OTT occurred when re-exposure to the EPM (trial 2) only depended on the prior experience of the EPM (trial 1) rather than diazepam treatment. This process was memory-dependent, as it was prevented by the N-methyl-D-aspartate (NMDA) receptors antagonist MK-801 1.5h before trial 2. In addition, OTT was maintained for at least one week but was partially abolished after an interval of 28 days. Furthermore, the administration of the D1-like receptors agonist SKF38393 to the bilateral dorsal hippocampus largely prevented OTT, as demonstrated by the ability of the diazepam treatment to produce significant anxiolytic-like effects in trial 2 after a one-day interval. These findings suggest that OTT to the EPM test may occur via the activation of NMDA receptors and the inactivation of D1-like receptors in certain brain regions, including the hippocampus. Copyright © 2015 Elsevier Inc. All rights reserved.

Memantine block depends on agonist presentation at the NMDA receptor in substantia nigra pars compacta dopamine neurones

PubMed Central

Wild, A.R.; Akyol, E.; Brothwell, S.L.C.; Kimkool, P.; Skepper, J.N.; Gibb, A.J.; Jones, S.

2015-01-01

NMDA glutamate receptors (NMDARs) have critical functional roles in the nervous system but NMDAR over-activity can contribute to neuronal damage. The open channel NMDAR blocker, memantine is used to treat certain neurodegenerative diseases, including Parkinson’s disease (PD) and is well tolerated clinically. We have investigated memantine block of NMDARs in substantia nigra pars compacta (SNc) dopamine neurones, which show severe pathology in PD. Memantine (10 μM) caused robust inhibition of whole-cell (synaptic and extrasynaptic) NMDARs activated by NMDA at a high concentration or a long duration, low concentration. Less memantine block of NMDAR-EPSCs was seen in response to low frequency synaptic stimulation, while responses to high frequency synaptic stimulation were robustly inhibited by memantine; thus memantine inhibition of NMDAR-EPSCs showed frequency-dependence. By contrast, MK-801 (10 μM) inhibition of NMDAR-EPSCs was not significantly different at low versus high frequencies of synaptic stimulation. Using immunohistochemistry, confocal imaging and stereological analysis, NMDA was found to reduce the density of cells expressing tyrosine hydroxylase, a marker of viable dopamine neurones; memantine prevented the NMDA-evoked decrease. In conclusion, memantine blocked NMDAR populations in different subcellular locations in SNc dopamine neurones but the degree of block depended on the intensity of agonist presentation at the NMDAR. This profile may contribute to the beneficial effects of memantine in PD, as glutamatergic activity is reported to increase, and memantine could preferentially reduce over-activity while leaving some physiological signalling intact. PMID:23727219

Evaluation of the role of NMDA receptor function in antidepressant-like activity. A new study with citalopram and fluoxetine in the forced swim test in mice.

PubMed

Wolak, Małgorzata; Siwek, Agata; Szewczyk, Bernadeta; Poleszak, Ewa; Bystrowska, Beata; Moniczewski, Andrzej; Rutkowska, Anita; Młyniec, Katarzyna; Nowak, Gabriel

2015-06-01

The NMDA/glutamate receptors are involved in the mechanism of antidepressant activity. The present study was designed to investigate the effect of NMDA receptor ligands (agonists and antagonists of glutamate sites) on the antidepressant-like activity of selective serotonin reuptake inhibitors (SSRIs), citalopram and fluoxetine, in the forced swim test in mice. The antidepressant activity (reduction in immobility time) of citalopram but not of fluoxetine was antagonized by N-methyl-D-aspartate acid and enhanced by CGP37849 (antagonist of the NMDA receptor). The present literature data indicate that the antidepressant-like activity of conventional antidepressants is generally affected by the NMDA receptor, although by modulation from different sites of the complex. Thus, it supports the issue of the ability of NMDA receptor antagonists to enhance the antidepressant action in human depression. Copyright © 2014 Institute of Pharmacology, Polish Academy of Sciences. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.

Involvement of NMDA receptor in low-frequency magnetic field-induced anxiety in mice.

PubMed

Salunke, Balwant P; Umathe, Sudhir N; Chavan, Jagatpalsingh G

2014-12-01

It had been reported that exposure to extremely low-frequency magnetic field (ELFMF) induces anxiety in human and rodents. Anxiety mediates via the activation of N-methyl-d-aspartate (NMDA) receptor, whereas activation of γ-aminobutyric acid (GABA) receptor attenuates the same. Hence, the present study was carried out to understand the contribution of NMDA and/or GABA receptors modulation in ELFMF-induced anxiety for which Swiss albino mice were exposed to ELFMF (50 Hz, 10 G) by subjecting them to Helmholtz coils. The exposure was for 8 h/day for 7, 30, 60, 90 and 120 days. Anxiety level was assessed in elevated plus maze, open field test and social interaction test, on 7th, 30th, 60th, 90th and 120th exposure day, respectively. Moreover, the role of GABA and glutamate in ELFMF-induced anxiety was assessed by treating mice with muscimol [0.25 mg/kg intraperitoneally (i.p.)], bicuculline (1.0 mg/kg i.p.), NMDA (15 mg/kg i.p.) and MK-801 (0.03 mg/kg i.p.), as a GABAA and NMDA receptor agonist and antagonist, respectively. Glutamate receptor agonist exacerbated while inhibitor attenuated the ELFMF-induced anxiety. In addition, levels of GABA and glutamate were determined in regions of the brain viz, cortex, striatum, hippocampus and hypothalamus. Experiments demonstrated significant elevation of GABA and glutamate levels in the hippocampus and hypothalamus. However, GABA receptor modulators did not produce significant effect on ELFMF-induced anxiety and elevated levels of GABA at tested dose. Together, these findings suggest that ELFMF significantly induced anxiety behavior, and indicated the involvement of NMDA receptor in its effect.

Different MK-801 administration schedules induce mild to severe learning impairments in an operant conditioning task: role of buspirone and risperidone in ameliorating these cognitive deficits.

PubMed

Rapanelli, Maximiliano; Frick, Luciana Romina; Bernardez-Vidal, Micaela; Zanutto, Bonifacio Silvano

2013-11-15

Blockade of N-methyl-d-aspartate receptor (NMDA) by the noncompetitive NMDA receptor (NMDAR) antagonist MK-801 produces behavioral abnormalities and alterations in prefrontal cortex (PFC) functioning. Due to the critical role of the PFC in operant conditioning task learning, we evaluated the effects of acute, repeated postnatal injections of MK-801 (0.1mg/kg) on learning performance. We injected Long-Evans rats i.p. with MK-801 (0.1mg/kg) using three different administration schedules: injection 40 min before beginning the task (during) (n=12); injection twice daily for six consecutive days prior to beginning the experimental procedures (prior) (n=12); or twice daily subcutaneous injections from postnatal day 7 to 11 (postnatal) (n=12). Next, we orally administered risperidone (serotonin receptor 2A and dopamine receptor 2 antagonist, 1mg/kg) or buspirone (serotonin receptor 1A partial agonist, 10mg/kg) to animals treated with the MK-801 schedule described above. The postnatal and prior administration schedules produced severe learning deficits, whereas injection of MK-801 just before training sessions had only mild effects on acquisition of an operant conditioning. Risperidone was able to reverse the detrimental effect of MK-801 in the animals that were treated with MK-801 during and prior training sessions. In contrast, buspirone was only effective at mitigating the cognitive deficits induced by MK-801 when administered during the training procedures. The data demonstrates that NMDA antagonism disrupts basic mechanisms of learning in a simple PFC-mediated operant conditioning task, and that buspirone and risperidone failed to attenuate the learning deficits when NMDA neurotransmission was blocked in the early stages of the postnatal period. Copyright © 2013 Elsevier B.V. All rights reserved.

Effects of N-methyl-D-aspartate receptor ligands on sensitivity to reinforcer magnitude and delayed reinforcement in a delay-discounting procedure

PubMed Central

Yates, Justin R; Gunkel, Benjamin T; Rogers, Katherine K; Hughes, Mallory N; Prior, Nicholas A

2016-01-01

Rationale The N-methyl-D-aspartate (NMDA) receptor has been recently identified as an important mediator of impulsive choice, as assessed in delay discounting. Although discounting is independently influenced by sensitivity to reinforcer magnitude and delayed reinforcement, few studies have examined how NMDA receptor ligands differentially affect these parameters. Objectives The current study examined the effects of various NMDA receptor ligands on sensitivity to reinforcer magnitude and delayed reinforcement in a delay-discounting procedure. Methods Following behavioral training, rats received treatments of the following NMDA receptor ligands: the uncompetitive antagonists ketamine (0, 1.0, 5.0, or 10.0 mg/kg; i.p.), MK-801 (0, 0.003, 0.01, or 0.03 mg/kg; s.c.), and memantine (0, 2.5, 5.0, or 10.0 mg/kg; i.p.), the competitive antagonist CGS 19755 (0, 5.0, 10.0, or 20.0 mg/kg; s.c.), the non-competitive NR2B subunit-selective antagonist ifenprodil (0, 1.0, 3.0, or 10.0 mg/kg; i.p), and the partial agonist D-cycloserine (0, 3.25, 15.0, or 30.0 mg/kg; s.c.). Results When an exponential model was used to describe discounting, CGS 19755 (5.0 mg/kg) increased impulsive choice without altering sensitivity to reinforcer magnitude. Conversely, ketamine (10.0 mg/kg), memantine (5.0 mg/kg), and ifenprodil (10.0 mg/kg) decreased sensitivity to reinforcer magnitude without altering impulsive choice. MK-801 and D-cycloserine did not alter delay-discounting performance, although two-way ANOVA analyses indicated D-cycloserine (15.0 mg/kg) decreased impulsive choice. Conclusions The behavioral changes observed in delay discounting following administration of NMDA receptor antagonists do not always reflect an alteration in impulsive choice. These results emphasize the utility in employing quantitative methods to assess drug effects in delay discounting. PMID:27837332

Implication of NMDA type glutamate receptors in neural regeneration and neoformation of synapses after excitotoxic injury in the guinea pig cochlea.

PubMed

d'Aldin, C G; Ruel, J; Assié, R; Pujol, R; Puel, J L

1997-07-01

In the adult mammalian cochlea, the ability of nerve fibres to regenerate has been observed following disruption of the organ of Corti by various means, or transsection of the cochlear nerve in the internal auditory meatus. Based upon the implication of glutamate as a neurotransmitter at synapses between sensory hair cells and terminal dendrites of the auditory nerve in the mammalian cochlea, we have developed, in a previous study, an in vivo model of neural regeneration and formation of synapses after the destruction of the afferent nerve endings by local application of the glutamate agonist alpha-amino-3-hydroxy-5-methyl-isoxazol-propionic acid (AMPA). In situ hybridization experiments performed during the re-innervation process revealed an overexpression of mRNA coding for NR1 subunit of N-methyl-D-aspartate (NMDA) receptors in the spiral ganglion neurons, suggesting that these receptors are implicated in neural regenerative processes. The present study has been designed to study the functional implication of NMDA receptors in the regrowth and synaptic repair of auditory dendrites in the guinea pig cochlea, by blocking the NMDA receptors during the period of normal functional recovery. In a first set of experiments, we recorded compound action potential after acute perilymphatic perfusion of cumulative doses (0.03-10mM) of DL 2-amino-5-phosphonovalerate (D-AP5), a NMDA antagonist, to determine the efficiency of the drug. In a second set of experiments, the auditory dendrites were destroyed by local application of the glutamate agonist AMPA. The blockage of NMDA by the antagonist D-AP5 applied with an osmotic micropump delayed the functional recovery and the regrowth of auditory dendrites. The findings of our study support the hypothesis that, in addition to acting as a fast transmitter, glutamate has a neurotrophic role via the activation of NMDA receptors.

Schizophrenia, dissociative anaesthesia and near-death experience; three events meeting at the NMDA receptor.

PubMed

Bonta, Iván L

2004-01-01

The three events, viz. schizophrenia, dissociative anaesthesia and Near-Death Experience, despite their seemingly unrelated manifestation to each other, have nevertheless similar functional basis. All three events are linked to the glutamate sensitive N-methyl-D-aspartate (NMDA) receptor complex, which serves as their common functional denominator. Arguments and speculations are presented in favor of the view that, the three events might be considered as functional models of each other. Antagonism to the recognition NMDA-site of the receptor induces dissociative anaesthesia and precipitates Near-Death Experience. Agonist reinforcement at the modulatory glycine-site of the receptor counteracts negative symptoms of schizophrenia. Both types of challenges towards the receptor are compatible with a glutamate deficiency concept which underlies the meeting of the three events at the NMDA receptor.

Oxidative stress upregulates the NMDA receptor on cerebrovascular endothelium.

PubMed

Betzen, Christian; White, Robin; Zehendner, Christoph M; Pietrowski, Eweline; Bender, Bianca; Luhmann, Heiko J; Kuhlmann, Christoph R W

2009-10-15

N-methyl-d-aspartate receptor (NMDA-R)-mediated oxidative stress has been implicated in blood-brain barrier (BBB) disruption in a variety of neuropathological diseases. Although some interactions between both phenomena have been elucidated, possible influences of reactive oxygen species (ROS) on the NMDA-R itself have so far been neglected. The objective of this study was to examine how the cerebroendothelial NMDA-R is affected by exposure to oxidative stress and to assess possible influences on BBB integrity. RT-PCR confirmed several NMDA-R subunits (NR1, NR2B-D) expressed in the bEnd3 cell line (murine cerebrovascular endothelial cells). NR1 protein expression after exposure to ROS was observed via in-cell Western. The functionality of the expressed NMDA-R was determined by measuring DiBAC fluorescence in ROS-preexposed cells upon stimulation with the specific agonist NMDA. Finally, the effects on barrier integrity were evaluated using the ECIS system to detect changes in monolayer impedance upon NMDA-R stimulation after exposure to ROS. The expression of NR1 significantly (p<0.001) increased 72 h after 30 min exposure to superoxide (+33.8+/-7.5%), peroxynitrite (+84.9+/-10.7%), or hydrogen peroxide (+92.8+/-7.6%), resulting in increased cellular response to NMDA-R stimulation and diminished monolayer impedance. We conclude that oxidative stress upregulates NMDA-R on cerebrovascular endothelium and thus heightens susceptibility to glutamate-induced BBB disruption.

Characterization of N-methyl-D-aspartate-evoked taurine release in the developing and adult mouse hippocampus.

PubMed

Saransaari, P; Oja, S S

2003-01-01

Taurine is an inhibitory amino acid acting as an osmoregulator and neuroromodulator in the brain, with neuroprotective properties. The ionotropic glutamate receptor agonist N-methyl-D-aspartate (NMDA) greatly potentiates taurine release from brain preparations in both normal and ischemic conditions, the effect being particularly marked in the developing hippocampus. We now characterized the regulation of NMDA-stimulated taurine release from hippocampal slices from adult (3-month-old) and developing (7-day-old) mouse using a superfusion system. The NMDA-stimulated taurine release was receptor-mediated in both adult and developing mouse hippocampus. In adults, only NO-generating compounds, sodium nitroprusside, S-nitroso-N-acetylpenicillamine and hydroxylamine reduced the release, as did also NO synthase inhibitors, 7-nitroindazole and nitroarginine, indicating that the release is mediated by the NO/cGMP pathway. On the other hand, the regulation of the NMDA-evoked taurine release proved to be somewhat complex in the immature hippocampus. It was not affected by the NOergic compounds, but enhanced by the protein kinase C activator 4 beta-phorbol 12-myristate 13-acetate and adenosine receptor A(1) agonists, N(6)-cyclohexyladenosine and R(-)N(6)-(2-phenylisopropyl)adenosine in a receptor-mediated manner. The activation of both ionotropic 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors and metabotropic glutamate group I receptors also enhanced the evoked release. The NMDA-receptor-stimulated taurine release could be a part of the neuroprotective properties of taurine, being important particularly under cell-damaging conditions in the developing hippocampus and hence preventing excitotoxicity.

Control of cortical neuronal migration by glutamate and GABA

PubMed Central

Luhmann, Heiko J.; Fukuda, A.; Kilb, W.

2015-01-01

Neuronal migration in the cortex is controlled by the paracrine action of the classical neurotransmitters glutamate and GABA. Glutamate controls radial migration of pyramidal neurons by acting primarily on NMDA receptors and regulates tangential migration of inhibitory interneurons by activating non-NMDA and NMDA receptors. GABA, acting on ionotropic GABAA-rho and GABAA receptors, has a dichotomic action on radially migrating neurons by acting as a GO signal in lower layers and as a STOP signal in upper cortical plate (CP), respectively. Metabotropic GABAB receptors promote radial migration into the CP and tangential migration of interneurons. Besides GABA, the endogenous GABAergic agonist taurine is a relevant agonist controlling radial migration. To a smaller extent glycine receptor activation can also influence radial and tangential migration. Activation of glutamate and GABA receptors causes increases in intracellular Ca2+ transients, which promote neuronal migration by acting on the cytoskeleton. Pharmacological or genetic manipulation of glutamate or GABA receptors during early corticogenesis induce heterotopic cell clusters in upper layers and loss of cortical lamination, i.e., neuronal migration disorders which can be associated with neurological or neuropsychiatric diseases. The pivotal role of NMDA and ionotropic GABA receptors in cortical neuronal migration is of major clinical relevance, since a number of drugs acting on these receptors (e.g., anti-epileptics, anesthetics, alcohol) may disturb the normal migration pattern when present during early corticogenesis. PMID:25688185

Vinpocetine protects inner retinal neurons with functional NMDA glutamate receptors against retinal ischemia.

PubMed

Nivison-Smith, Lisa; Khoo, Pauline; Acosta, Monica L; Kalloniatis, Michael

2018-02-01

Retinal ischemia is involved in the pathogenesis of many major vision threatening diseases. Vinpocetine is a natural drug, which has a range of neuroprotective actions against retinal ischemia including modulating cation flow, improving metabolic activity and preventing apoptosis. The exact mechanism behind these actions remains unknown but may involve glutamate receptors, major components of the ischemic cascade. This study examined the effects of vinpocetine in association with specific ionotropic glutamate receptor agonists: N-methyl-D-aspartate (NMDA) and kainate. Vinpocetine's actions to improve cation channel permeability and cell marker immunoreactivity following ischemia appeared to be limited to NMDA activation with no changes observed following kainate stimulation. Vinpocetine's actions were lost in the presence of an NMDA receptor inhibitor further suggesting they may be secondary to NMDA receptor activation. NMDA receptor function was also necessary for vinpocetine's actions on glucose availability during ischemia but not lactate dehydrogenase (LDH) activity in the ischemic retina suggesting not all of vinpocetine's actions are linked to NMDA receptor function. These results may explain vinpocetine's effectiveness as a neuroprotective agent as the NMDA receptor is implicated in the pathogenesis of ischemia in a range of tissues of the central nervous system. Copyright © 2017 Elsevier Ltd. All rights reserved.

Prefrontal cortical network activity: Opposite effects of psychedelic hallucinogens and D1/D5 dopamine receptor activation

PubMed Central

Lambe, Evelyn K.; Aghajanian, George K.

2007-01-01

The fine-tuning of network activity provides a modulating influence on how information is processed and interpreted in the brain. Here, we use brain slices of rat prefrontal cortex to study how recurrent network activity is affected by neuromodulators known to alter normal cortical function. We previously determined that glutamate spillover and stimulation of extrasynaptic NMDA receptors are required to support hallucinogen-induced cortical network activity. Since microdialysis studies suggest that psychedelic hallucinogens and dopamine D1/D5 receptor agonists have opposite effects on extracellular glutamate in prefrontal cortex, we hypothesized that these two families of psychoactive drugs would have opposite effects on cortical network activity. We found that network activity can be enhanced by DOI (a psychedelic hallucinogen that is a partial agonist of serotonin 5-HT2A/2C receptors) and suppressed by the selective D1/D5 agonist SKF 38393. This suppression could be mimicked by direct activation of adenylyl cyclase with forskolin or by addition of a cAMP analog. These findings are consistent with previous work showing that activation of adenylyl cyclase can upregulate neuronal glutamate transporters, thereby decreasing synaptic spillover of glutamate. Consistent with this hypothesis, a low concentration of the glutamate transporter inhibitor TBOA restored electrically-evoked recurrent activity in the presence of a selective D1/D5 agonist, whereas recurrent activity in the presence of a low level of the GABAA antagonist bicuculline was not resistant to suppression by the D1/D5 agonist. The tempering of network UP states by D1/D5 receptor activation may have implications for the proposed use of D1/D5 agonists in the treatment of schizophrenia. PMID:17293055

Effects of chronic cocaine treatment during adolescence in Lewis and Fischer-344 rats: Novel location recognition impairment and changes in synaptic plasticity in adulthood.

PubMed

Fole, A; Martin, M; Morales, L; Del Olmo, N

2015-09-01

The use of Lewis (LEW) together with Fischer-344 (F344) rats has been proposed as an addiction model because of the addiction behavior differences of these two strains. We have previously suggested that these differences could be related to learning and memory processes and that they depend on the genetic background of these two strains of rats. Adolescence is a period of active synaptic remodeling, plasticity and particular vulnerability to the effects of environmental insults such as drugs of abuse. We have evaluated spatial memory using novel location recognition in LEW and F344 adult rats undergoing a chronic treatment with cocaine during adolescence or adulthood. In order to study whether synaptic plasticity mechanisms were involved in the possible changes in learning after chronic cocaine treatment, we carried out electrophysiological experiments in hippocampal slices from treated animals. Our results showed that, in LEW cocaine-treated rats, hippocampal memory was only significantly impaired when the drug was administered during adolescence whereas adult administration did not produce any detrimental effect in spatial memory measured in this protocol. Moreover, F344 rats showed clear difficulties carrying out the protocol even in standard conditions, confirming the spatial memory problems observed in previous reports and demonstrating the genetic differences in spatial learning and memory. Our experiments show that the effects in behavioral experiments are related to synaptic plasticity mechanisms. Long-term depression induced by the glutamate agonist NMDA (LTD-NMDA) is partially abolished in cocaine-treated animals in hippocampal slices from LEW rats. Hippocampal LTD-NMDA is partially inhibited in F344 animals regardless of whether saline or cocaine administration, suggesting the lack of plasticity of this strain that could be related to the inability of these animals to carry out the novel object location protocol. Copyright © 2015 Elsevier Inc. All rights reserved.

NMDA Receptors Are Not Required for Pattern Completion During Associative Memory Recall

PubMed Central

Gu, Yiran; Cui, Zhenzhong; Tsien, Joe Z.

2011-01-01

Pattern completion, the ability to retrieve complete memories initiated by subsets of external cues, has been a major focus of many computation models. A previously study reports that such pattern completion requires NMDA receptors in the hippocampus. However, such a claim was derived from a non-inducible gene knockout experiment in which the NMDA receptors were absent throughout all stages of memory processes as well as animal's adult life. This raises the critical question regarding whether the previously described results were truly resulting from the requirement of the NMDA receptors in retrieval. Here, we have examined the role of the NMDA receptors in pattern completion via inducible knockout of NMDA receptors limited to the memory retrieval stage. By using two independent mouse lines, we found that inducible knockout mice, lacking NMDA receptor in either forebrain or hippocampus CA1 region at the time of memory retrieval, exhibited normal recall of associative spatial reference memory regardless of whether retrievals took place under full-cue or partial-cue conditions. Moreover, systemic antagonism of NMDA receptor during retention tests also had no effect on full-cue or partial-cue recall of spatial water maze memories. Thus, both genetic and pharmacological experiments collectively demonstrate that pattern completion during spatial associative memory recall does not require the NMDA receptor in the hippocampus or forebrain. PMID:21559402

Functional characterization of α7 nicotinic acetylcholine and NMDA receptor signaling in SH-SY5Y neuroblastoma cells in an ERK phosphorylation assay.

PubMed

Elnagar, Mohamed R; Walls, Anne Byriel; Helal, Gouda K; Hamada, Farid M; Thomsen, Morten Skøtt; Jensen, Anders A

2018-05-05

In the present study, the functional properties of α7 nicotinic acetylcholine receptors (α7 nAChRs) and N-methyl-D-aspartate receptors (NMDARs) endogenously expressed in SH-SY5Y human neuroblastoma cells were characterized in an extracellular-signal regulated kinase (ERK) phosphorylation assay. Both choline and N-methyl-D-aspartate (NMDA) mediated robust concentration-dependent increases in ERK phosphorylation in the SH-SY5Y cells, exhibiting EC 50 values in good agreement with those reported for the agonists at recombinant α7 nAChRs and NMDARs, respectively. Importantly, the responses evoked by choline (10 mM) and by NMDA (50 μM) were significantly inhibited by the α7-selective antagonist α-bungarotoxin (100 nM) and by the NMDAR-selective antagonist MK-801 (50 μM), respectively. The increased ERK phosphorylation levels observed upon co-application of choline (1, 3, 10 mM) and NMDA (50 μM) compared to those produced by the two agonists on their own were fully reconcilable with additive effects and did not reveal substantial synergy between α7 nAChR and NMDAR signaling. Interestingly, however, the responses evoked by the "choline (10 mM) - NMDA (50 μM)" combination were almost completely inhibited by α-bungarotoxin (100 nM) as well as by MK-801 (50 μM), suggesting some sort of a link between α7 nAChR- and NMDAR-mediated ERK phosphorylation. Finally, oligomeric amyloid-β 1-42 peptide (1000 nM) mediated robust inhibition of the ERK phosphorylation induced by choline (10 mM), NMDA (50 μM) and the "choline (10 mM) - NMDA (50 μM)" combination. In conclusion, ERK phosphorylation measurements in SH-SY5Y cells provides a robust assay for studies of α7 nAChR- and NMDAR-mediating signaling and putative functional interactions between the receptors. Copyright © 2018 Elsevier B.V. All rights reserved.

NMDA receptor agonists reverse impaired psychomotor and cognitive functions associated with hippocampal Hbegf-deficiency in mice.

PubMed

Sasaki, Keita; Omotuyi, Olaposi Idowu; Ueda, Mutsumi; Shinohara, Kazuyuki; Ueda, Hiroshi

2015-12-04

Structural and functional changes of the hippocampus are correlated with psychiatric disorders and cognitive dysfunctions. Genetic deletion of heparin-binding epidermal growth factor-like growth factor (HB-EGF), which is predominantly expressed in cortex and hippocampus, also causes similar psychiatric and cognitive dysfunctions, accompanying down-regulated NMDA receptor signaling. However, little is known of such dysfunctions in hippocampus-specific Hbegf cKO mice. We successfully developed hippocampus-specific cKO mice by crossbreeding floxed Hbegf and Gng7-Cre knock-in mice, as Gng7 promoter-driven Cre is highly expressed in hippocampal neurons as well as striatal medium spiny neurons. In mice lacking hippocampus Hbegf gene, there was a decreased neurogenesis in the subgranular zone (SGZ) of the dentate gyrus as well as down-regulation of PSD-95/NMDA-receptor-NR1/NR2B subunits and related NMDA receptor signaling. Psychiatric, social-behavioral and cognitive abnormalities were also observed in hippocampal cKO mice. Interestingly, D-cycloserine and nefiracetam, positive allosteric modulators (PAMs) of NMDA receptor reversed the apparent reduction in NMDA receptor signaling and most behavioral abnormalities. Furthermore, decreased SGZ neurogenesis in hippocampal cKO mice was reversed by nefiracetam. The present study demonstrates that PAMs of NMDA receptor have pharmacotherapeutic potentials to reverse down-regulated NMDA receptor signaling, neuro-socio-cognitive abnormalities and decreased neurogenesis in hippocampal cKO mice.

NMDA Receptors as Potential Therapeutic Targets in Diabetic Nephropathy: Increased Renal NMDA Receptor Subunit Expression in Akita Mice and Reduced Nephropathy Following Sustained Treatment With Memantine or MK-801.

PubMed

Roshanravan, Hila; Kim, Eun Young; Dryer, Stuart E

2016-10-01

N-methyl-d-aspartate (NMDA) receptors are expressed throughout the kidney, and the abundance of these receptors and some of their endogenous agonists are increased in diabetes. Moreover, sustained activation of podocyte NMDA receptors induces Ca(2+) influx, oxidative stress, loss of slit diaphragm proteins, and apoptosis. We observed that NMDA receptor subunits and their transcripts are increased in podocytes and mesangial cells cultured in elevated glucose compared with controls. A similar increase in NMDA subunits, especially NR1, NR2A, and NR2C, was observed in glomeruli and tubules of Akita mice. Sustained continuous treatment with the strong NMDA receptor antagonist dizocilpine (MK-801) for 28 days starting at 8 weeks of age reduced 24-h albumin excretion and mesangial matrix expansion and improved glomerular ultrastructure in Akita mice. MK-801 did not alleviate reduced Akita mouse body weight and had no effect on kidney histology or ultrastructure in DBA/2J controls. The structurally dissimilar NMDA antagonist memantine also reduced diabetic nephropathy, although it was less effective than MK-801. Inhibition of NMDA receptors may represent a valid therapeutic approach to reduce renal complications of diabetes, and it is possible to develop well-tolerated agents with minimal central nervous system effects. Two such agents, memantine and dextromethorphan, are already in widespread clinical use. © 2016 by the American Diabetes Association.

Activation of N-methyl-d-aspartate receptors reduces heart rate variability and facilitates atrial fibrillation in rats.

PubMed

Shi, Shaobo; Liu, Tao; Wang, Dandan; Zhang, Yan; Liang, Jinjun; Yang, Bo; Hu, Dan

2017-07-01

The goal of this study was to assess the effects of N-methyl-d-aspartate (NMDA) receptors activation on heart rate variability (HRV) and susceptibility to atrial fibrillation (AF). Rats were randomized for treatment with saline, NMDA (agonist of NMDA receptors), or NMDA plus MK-801 (antagonist of NMDA receptors) for 2 weeks. Heart rate variability was evaluated by using implantable electrocardiogram telemeters. Atrial fibrillation susceptibility was assessed with programmed stimulation in isolated hearts. Compared with the controls, the NMDA-treated rats displayed a decrease in the standard deviation of normal RR intervals, the standard deviation of the average RR intervals, the mean of the 5-min standard deviations of RR intervals, the root mean square of successive differences, and high frequency (HF); and an increase in low frequency (LF) and LF/HF (all P< 0.01). Additionally, the NMDA-treated rats showed prolonged activation latency and reduced effective refractory period (all P< 0.01). Importantly, AF was induced in all NMDA-treated rats. While atrial fibrosis developed, connexin40 downgraded and metalloproteinase 9 upgraded in the NMDA-treated rats (all P< 0.01). Most of the above alterations were mitigated by co-administering with MK-801. These results indicate that NMDA receptors activation reduces HRV and enhances AF inducibility, with cardiac autonomic imbalance, atrial fibrosis, and degradation of gap junction protein identified as potential mechanistic contributors. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2016. For permissions please email: journals.permissions@oup.com.

Psychological effects of (S)-ketamine and N,N-dimethyltryptamine (DMT): a double-blind, cross-over study in healthy volunteers.

PubMed

Gouzoulis-Mayfrank, E; Heekeren, K; Neukirch, A; Stoll, M; Stock, C; Obradovic, M; Kovar, K-A

2005-11-01

Pharmacological challenges with hallucinogens are used as models for psychosis in experimental research. The state induced by glutamate antagonists such as phencyclidine (PCP) is often considered as a more appropriate model of psychosis than the state induced by serotonergic hallucinogens such as lysergic acid diethylamide (LSD), psilocybin and N,N-dimethyltryptamine (DMT). However, so far, the psychological profiles of the two types of hallucinogenic drugs have never been studied directly in an experimental within-subject design. Fifteen healthy volunteers were included in a double-blind, cross-over study with two doses of the serotonin 5-HT2A agonist DMT and the glutamate N-methyl-D-aspartate (NMDA) antagonist (S)-ketamine. Data are reported for nine subjects who completed both experimental days with both doses of the two drugs. The intensity of global psychological effects was similar for DMT and (S)-ketamine. However, phenomena resembling positive symptoms of schizophrenia, particularly positive formal thought disorder and inappropriate affect, were stronger after DMT. Phenomena resembling negative symptoms of schizophrenia, attention deficits, body perception disturbances and catatonia-like motor phenomena were stronger after (S)-ketamine. The present study suggests that the NMDA antagonist model of psychosis is not overall superior to the serotonin 5-HT2A agonist model. Rather, the two classes of drugs tend to model different aspects or types of schizophrenia. The NMDA antagonist state may be an appropriate model for psychoses with prominent negative and possibly also catatonic features, while the 5-HT2A agonist state may be a better model for psychoses of the paranoid type.

Simvastatin Prevents Dopaminergic Neurodegeneration in Experimental Parkinsonian Models: The Association with Anti-Inflammatory Responses

PubMed Central

Zhang, Limin; Wu, Aimin; Yang, Yu; Xiong, Zhaojun; Deng, Chao; Huang, Xu-Feng; Yenari, Midori A.; Yang, Yuan-Guo; Ying, Weihai; Wang, Qing

2011-01-01

Background In addition to their original applications to lowering cholesterol, statins display multiple neuroprotective effects. N-methyl-D-aspartate (NMDA) receptors interact closely with the dopaminergic system and are strongly implicated in therapeutic paradigms of Parkinson's disease (PD). This study aims to investigate how simvastatin impacts on experimental parkinsonian models via regulating NMDA receptors. Methodology/Principal Findings Regional changes in NMDA receptors in the rat brain and anxiolytic-like activity were examined after unilateral medial forebrain bundle lesion by 6-hydroxydopamine via a 3-week administration of simvastatin. NMDA receptor alterations in the post-mortem rat brain were detected by [3H]MK-801(Dizocilpine) binding autoradiography. 6-hydroxydopamine treated PC12 was applied to investigate the neuroprotection of simvastatin, the association with NMDA receptors, and the anti-inflammation. 6-hydroxydopamine induced anxiety and the downregulation of NMDA receptors in the hippocampus, CA1(Cornu Ammonis 1 Area), amygdala and caudate putamen was observed in 6-OHDA(6-hydroxydopamine) lesioned rats whereas simvastatin significantly ameliorated the anxiety-like activity and restored the expression of NMDA receptors in examined brain regions. Significant positive correlations were identified between anxiolytic-like activity and the restoration of expression of NMDA receptors in the hippocampus, amygdala and CA1 following simvastatin administration. Simvastatin exerted neuroprotection in 6-hydroxydopamine-lesioned rat brain and 6-hydroxydopamine treated PC12, partially by regulating NMDA receptors, MMP9 (matrix metalloproteinase-9), and TNF-a (tumour necrosis factor-alpha). Conclusions/Significance Our results provide strong evidence that NMDA receptor modulation after simvastatin treatment could partially explain its anxiolytic-like activity and anti-inflammatory mechanisms in experimental parkinsonian models. These findings contribute to a better understanding of the critical roles of simvastatin in treating PD via NMDA receptors. PMID:21731633

Simvastatin prevents dopaminergic neurodegeneration in experimental parkinsonian models: the association with anti-inflammatory responses.

PubMed

Yan, Junqiang; Xu, Yunqi; Zhu, Cansheng; Zhang, Limin; Wu, Aimin; Yang, Yu; Xiong, Zhaojun; Deng, Chao; Huang, Xu-Feng; Yenari, Midori A; Yang, Yuan-Guo; Ying, Weihai; Wang, Qing

2011-01-01

In addition to their original applications to lowering cholesterol, statins display multiple neuroprotective effects. N-methyl-D-aspartate (NMDA) receptors interact closely with the dopaminergic system and are strongly implicated in therapeutic paradigms of Parkinson's disease (PD). This study aims to investigate how simvastatin impacts on experimental parkinsonian models via regulating NMDA receptors. Regional changes in NMDA receptors in the rat brain and anxiolytic-like activity were examined after unilateral medial forebrain bundle lesion by 6-hydroxydopamine via a 3-week administration of simvastatin. NMDA receptor alterations in the post-mortem rat brain were detected by [³H]MK-801(Dizocilpine) binding autoradiography. 6-hydroxydopamine treated PC12 was applied to investigate the neuroprotection of simvastatin, the association with NMDA receptors, and the anti-inflammation. 6-hydroxydopamine induced anxiety and the downregulation of NMDA receptors in the hippocampus, CA1(Cornu Ammonis 1 Area), amygdala and caudate putamen was observed in 6-OHDA(6-hydroxydopamine) lesioned rats whereas simvastatin significantly ameliorated the anxiety-like activity and restored the expression of NMDA receptors in examined brain regions. Significant positive correlations were identified between anxiolytic-like activity and the restoration of expression of NMDA receptors in the hippocampus, amygdala and CA1 following simvastatin administration. Simvastatin exerted neuroprotection in 6-hydroxydopamine-lesioned rat brain and 6-hydroxydopamine treated PC12, partially by regulating NMDA receptors, MMP9 (matrix metalloproteinase-9), and TNF-a (tumour necrosis factor-alpha). Our results provide strong evidence that NMDA receptor modulation after simvastatin treatment could partially explain its anxiolytic-like activity and anti-inflammatory mechanisms in experimental parkinsonian models. These findings contribute to a better understanding of the critical roles of simvastatin in treating PD via NMDA receptors.

Glix 13, a new drug acting on glutamatergic pathways in children and animal models of autism spectrum disorders.

PubMed

Santini, Annamaria Chiara; Pierantoni, Giovanna Maria; Gerlini, Raffaele; Iorio, Rosamaria; Olabinjo, Yinka; Giovane, Alfonso; Di Domenico, Marina; Sogos, Carla

2014-01-01

Recently standardized diagnostic instruments have been developed in diagnostic and therapeutic procedures for Autism Spectrumv Disorders (ASD). According to the DSM-5 criteria, individuals with ASD must show symptoms from early childhood. These symptoms are communication deficits and restricted, repetitive patterns of behaviour. It was recently described by Bioinformatic analysis that 99 modified genes were associated with human autism. Gene expression patterns in the low-line animals show significant enrichment in autism-associated genes and the NMDA receptor gene family was identified among these. Using ultrasonic vocalizations, it was demonstrated that genetic variation has a direct impact on the expression of social interactions. It has been proposed that specific alleles interact with a social reward process in the adolescent mouse modifying their social interaction and their approach toward each other. In this review we report that the monoclonal antibody-derived tetrapeptide GLYX-13 was found to act as an N-methyl-D-aspartate receptor modulator and possesses the ability to readily cross the blood brain barrier. Treatment with the NMDAR glycine site partial agonist GLYX-13 rescued the deficit in the animal model. Thus, the NMDA receptor has been shown to play a functional role in autism, and GLYX-13 shows promise for the treatment of autism in autistic children.

The interplay of cannabinoid and NMDA glutamate receptor systems in humans: preliminary evidence of interactive effects of cannabidiol and ketamine in healthy human subjects.

PubMed

Hallak, Jaime E C; Dursun, Serdar M; Bosi, Daniel C; de Macedo, Ligia Ribeiro Horta; Machado-de-Sousa, João Paulo; Abrão, João; Crippa, José A S; McGuire, Phillip; Krystal, John H; Baker, Glen B; Zuardi, Antonio W

2011-01-15

Interactions between glutamatergic and endocannabinoid systems may contribute to schizophrenia, dissociative states, and other psychiatric conditions. Cannabidiol (CBD), a cannabinoid-1/2 (CB1/2) receptor weak partial agonist or antagonist, may play a role in the treatment of schizophrenia. This study tested the hypothesis that CBD would attenuate the behavioral effects of the NMDA receptor antagonist, ketamine, in healthy human subjects. Ten male healthy volunteers were evaluated twice in a randomized order. In both sessions they received ketamine (bolus of 0.26 mg/kg/1 min followed by IV infusion of 0.25mg/kg over 30 min) preceded by either CBD (600 mg) or placebo. Psychopathology was assessed using the Brief Psychiatric Rating Scale (BPRS) and the CADSS (Clinician Administered Dissociative States Scale) at regular intervals from 30 min before to 90 min after ketamine administration. CBD significantly augmented the activating effects of ketamine, as measured by the activation subscales of the BPRS. However, CBD also showed a non-significant trend to reduce ketamine-induced depersonalization, as measured by the CADSS. These data describe a complex pattern of psychopharmacologic interactions between CBD and ketamine at the doses of each agent studied in this experiment. Copyright © 2010 Elsevier B.V. All rights reserved.

Behavioural memory reconsolidation of food and fear memories

PubMed Central

Flavell, Charlotte R.; Barber, David J.; Lee, Jonathan L. C.

2012-01-01

The reactivation of a memory through retrieval can render it subject to disruption or modification through the process of memory reconsolidation. In both humans and rodents, briefly reactivating a fear memory results in effective erasure by subsequent extinction training. Here we show that a similar strategy is equally effective in the disruption of appetitive pavlovian cue–food memories. However, systemic administration of the NMDA receptor partial agonist D-cycloserine under the same behavioural conditions did not potentiate appetitive memory extinction, suggesting that reactivation does not enhance subsequent extinction learning. To confirm that reactivation followed by extinction reflects a behavioural analog of memory reconsolidation, we show that prevention of contextual fear memory reactivation by the LVGCC blocker nimodipine interferes with the amnestic outcome. Therefore, the reconsolidation process can be manipulated behaviourally to disrupt both aversive and appetitive memories. PMID:22009036

Co-agonists differentially tune GluN2B-NMDA receptor trafficking at hippocampal synapses

PubMed Central

Ferreira, Joana S; Papouin, Thomas; Ladépêche, Laurent; Yao, Andrea; Langlais, Valentin C; Bouchet, Delphine; Dulong, Jérôme; Mothet, Jean-Pierre; Sacchi, Silvia; Pollegioni, Loredano; Paoletti, Pierre; Oliet, Stéphane Henri Richard; Groc, Laurent

2017-01-01

The subunit composition of synaptic NMDA receptors (NMDAR), such as the relative content of GluN2A- and GluN2B-containing receptors, greatly influences the glutamate synaptic transmission. Receptor co-agonists, glycine and D-serine, have intriguingly emerged as potential regulators of the receptor trafficking in addition to their requirement for its activation. Using a combination of single-molecule imaging, biochemistry and electrophysiology, we show that glycine and D-serine relative availability at rat hippocampal glutamatergic synapses regulate the trafficking and synaptic content of NMDAR subtypes. Acute manipulations of co-agonist levels, both ex vivo and in vitro, unveil that D-serine alter the membrane dynamics and content of GluN2B-NMDAR, but not GluN2A-NMDAR, at synapses through a process requiring PDZ binding scaffold partners. In addition, using FRET-based FLIM approach, we demonstrate that D-serine rapidly induces a conformational change of the GluN1 subunit intracellular C-terminus domain. Together our data fuels the view that the extracellular microenvironment regulates synaptic NMDAR signaling. DOI: http://dx.doi.org/10.7554/eLife.25492.001 PMID:28598327

The NMDA antagonist ketamine and the 5-HT agonist psilocybin produce dissociable effects on structural encoding of emotional face expressions.

PubMed

Schmidt, André; Kometer, Michael; Bachmann, Rosilla; Seifritz, Erich; Vollenweider, Franz

2013-01-01

Both glutamate and serotonin (5-HT) play a key role in the pathophysiology of emotional biases. Recent studies indicate that the glutamate N-methyl-D-aspartate (NMDA) receptor antagonist ketamine and the 5-HT receptor agonist psilocybin are implicated in emotion processing. However, as yet, no study has systematically compared their contribution to emotional biases. This study used event-related potentials (ERPs) and signal detection theory to compare the effects of the NMDA (via S-ketamine) and 5-HT (via psilocybin) receptor system on non-conscious or conscious emotional face processing biases. S-ketamine or psilocybin was administrated to two groups of healthy subjects in a double-blind within-subject placebo-controlled design. We behaviorally assessed objective thresholds for non-conscious discrimination in all drug conditions. Electrophysiological responses to fearful, happy, and neutral faces were subsequently recorded with the face-specific P100 and N170 ERP. Both S-ketamine and psilocybin impaired the encoding of fearful faces as expressed by a reduced N170 over parieto-occipital brain regions. In contrast, while S-ketamine also impaired the encoding of happy facial expressions, psilocybin had no effect on the N170 in response to happy faces. This study demonstrates that the NMDA and 5-HT receptor systems differentially contribute to the structural encoding of emotional face expressions as expressed by the N170. These findings suggest that the assessment of early visual evoked responses might allow detecting pharmacologically induced changes in emotional processing biases and thus provides a framework to study the pathophysiology of dysfunctional emotional biases.

Central N-acetyl aspartylglutamate deficit: a possible pathogenesis of schizophrenia.

PubMed

Tsai, Shih-Jen

2005-09-01

The "glutamate hypothesis" of schizophrenia has emerged from the finding that phencyclidine (PCP) induces psychotic-like behaviors in rodents, possibly by blocking the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor, thereby causing increased glutamate release. N-acetyl aspartylglutamate (NAAG), an endogenous peptide abundant in mammalian nervous systems, is localized in certain brain cells, including cortical and hippocampal pyramidal neurons. NAAG is synthesized from N-acetylaspartate (NAA) and glutamate, and NAA availability may limit the rate of NAAG synthesis. Although NAAG is known to have some neurotransmitter-like functions, NAA does not. NAAG is a highly selective agonist of the type 3 metabotropic glutamate receptor (mGluR3, a presynaptic autoreceptor) and can inhibit glutamate release. In addition, at low levels, NAAG is an NMDA receptor antagonist, and blocking of NMDA receptors may increase glutamate release. Taken together, low central NAAG levels may antagonize the effect of glutamate at NMDA receptors and decrease its agonistic effect on presynaptic mGluR3; both activities could increase glutamate release, similar to the increase demonstrated in the PCP model of schizophrenia. In this report, it is suggested that the central NAAG deficit, possibly through decreased synthesis or increased degradation of NAAG, may play a role in the pathogenesis of schizophrenia. Evidence is presented and discussed from magnetic resonance, postmortem, animal model, schizophrenia treatment, and genetic studies. The central NAAG deficit model of schizophrenia could explain the disease process, from the perspectives of both neurodevelopment and neurodegeneration, and may point to potential treatments for schizophrenia.

Effects of NMDA and non-NMDA ionotropic glutamate receptors in the medial preoptic area on body temperature in awake rats.

PubMed

Sengupta, Trina; Jaryal, Ashok Kumar; Mallick, Hruda Nanda

2016-10-01

Glutamate when microinjected at the medial preoptic area (mPOA) influences brain temperature (T br ) and body temperature (T b ) in rats. Glutamate and its various receptors are present at the mPOA. The aim of this study was to identify the contribution of each of the ionotropic glutamatergic receptors at the mPOA on changes in T br and T b in freely moving rats. Adult male Wistar rats (n=40) were implanted with bilateral guide cannula with indwelling styli above the mPOA. A telemetric transmitter was implanted at the peritoneum to record T b and locomotor activity (LMA). A precalibrated thermocouple wire implanted near the hypothalamus was used to assess T br . Specific agonist for each ionotropic glutamate receptor was microinjected into the mPOA and its effects on temperature and LMA were measured in the rats. The rats were also microinjected with the respective ionotropic receptor antagonists, 15min prior to the microinjection of each agonist. Amongst amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), N-methyl-d-aspartate (NMDA) and kainic acid, AMPA increased T b and LMA when injected at the mPOA. Specific antagonists for AMPA receptors was able to attenuate this increase (p<0.005). Pharmacological blockade of NMDA was able to lower T br only. Microinjection of kainic acid and its antagonist had no effect on the variables. The finding of the study suggests that activation of the AMPA receptors at the mPOA, leads to the rise in body temperature. Copyright © 2016 Elsevier Ltd. All rights reserved.

Involvement of NMDA receptors in the antidepressant-like effect of tramadol in the mouse forced swimming test.

PubMed

Ostadhadi, Sattar; Norouzi-Javidan, Abbas; Chamanara, Mohsen; Akbarian, Reyhaneh; Imran-Khan, Muhammad; Ghasemi, Mehdi; Dehpour, Ahmad-Reza

2017-09-01

Tramadol is an analgesic agent that is mainly used to treat moderate to severe pain. There is evidence that tramadol may have antidepressant property. However, the mechanisms underlying the antidepressant effects of tramadol have not been elucidated yet. Considering that fact that N-methyl-d-aspartate (NMDA) receptor signaling may play an important role in the pathophysiology of depression, the aim of the present study was to investigate the role of NMDA receptor signaling in the possible antidepressant-like effects of tramadol in the mouse forced swimming test (mFST). We found that tramadol exerted antidepressant-like effects at high dose (40mg/kg, intraperitoneally [i.p.]) in the mFST. Co-administration of non-effective doses of NMDA receptor antagonists (ketamine [1mg/kg, i.p.], MK-801 [0.05mg/kg, i.p.], or magnesium sulfate [10mg/kg, i.p.]) with sub-effective dose of tramadol (20mg/kg, i.p.) exerted significant antidepressant-like effects in the mFST. The antidepressant-like effects of tramadol (40mg/kg) was also inhibited by pre-treatment with non-effective dose of the NMDA receptor agonist NMDA (75mg/kg, i.p.). Our data suggest a role for NMDA receptor signaling in the antidepressant-like effects of tramadol in the mFST. Copyright © 2017 Elsevier Inc. All rights reserved.

Spinal N-methyl-D-aspartate receptors and nociception-evoked release of primary afferent substance P.

PubMed

Nazarian, A; Gu, G; Gracias, N G; Wilkinson, K; Hua, X Y; Vasko, M R; Yaksh, T L

2008-03-03

Dorsal horn N-methyl-D-aspartate (NMDA) receptors contribute significantly to spinal nociceptive processing through an effect postsynaptic to non-primary glutamatergic axons, and perhaps presynaptic to the primary afferent terminals. The present study sought to examine the regulatory effects of NMDA receptors on primary afferent release of substance P (SP), as measured by neurokinin 1 receptor (NK1r) internalization in the spinal dorsal horn of rats. The effects of intrathecal NMDA alone or in combination with D-serine (a glycine site agonist) were initially examined on basal levels of NK1r internalization. NMDA alone or when co-administered with D-serine failed to induce NK1r internalization, whereas activation of spinal TRPV1 receptors by capsaicin resulted in a notable NK1r internalization. To determine whether NMDA receptor activation could potentiate NK1r internalization or pain behavior induced by a peripheral noxious stimulus, intrathecal NMDA was given prior to an intraplantar injection of formalin. NMDA did not alter the formalin-induced NK1r internalization nor did it enhance the formalin paw flinching behavior. To further characterize the effects of presynaptic NMDA receptors, the NMDA antagonists DL-2-amino-5-phosphonopentanoic acid (AP-5) and MK-801 were intrathecally administered to assess their regulatory effects on formalin-induced NK1r internalization and pain behavior. AP-5 had no effect on formalin-induced NK1r internalization, whereas MK-801 produced only a modest reduction. Both antagonists, however, reduced the formalin paw flinching behavior. In subsequent in vitro experiments, perfusion of NMDA in spinal cord slice preparations did not evoke basal release of SP or calcitonin gene-related peptide (CGRP). Likewise, perfusion of NMDA did not enhance capsaicin-evoked release of the two peptides. These results suggest that presynaptic NMDA receptors in the spinal cord play little if any role on the primary afferent release of SP.

Xylopia aethiopica fruit extract exhibits antidepressant-like effect via interaction with serotonergic neurotransmission in mice.

PubMed

Biney, Robert P; Benneh, Charles K; Ameyaw, Elvis O; Boakye-Gyasi, Eric; Woode, Eric

2016-05-26

Xylopia aethiopica has been used traditionally to treat some central nervous system disorders including epilepsy. Despite the central analgesic and sedative effects, there is little evidence for its traditional use for CNS disorders. This study thus assessed the antidepressant potential of Xylopia aethiopica ethanolic fruit extract (XAE). Antidepressant effect was assessed in the forced swim test (FST) and tail suspension test (TST) models in mice. The role of monoamines in the antidepressant effects of XAE was evaluated by selective depletion of serotonin and noradrenaline, whereas involvement of NMDA/nitric oxide was assessed with NMDA receptor co-modulators; d-serine and d-cycloserine and NOS inhibitor, l-NAME. Xylopia aethiopica (30, 100, 300mgkg(-1)) dose dependently reduced immobility in both FST and TST. The reduced immobility was reversed after 5-hydroxytryptamine (5-HT) depletion with tryptophan hydroxylase inhibitor-p-chlorophenylalanine (pCPA) and after monoamine depletion with vesicular monoamine transporter inhibitor-reserpine. The observed antidepressant effect was not affected by catecholamine depletion with the tyrosine hydroxylase inhibitor, α-methyl-p-tyrosine (AMPT). Similarly XAE did not potentiate the toxicity of a sub-lethal dose of noradrenaline. XAE had a synergistic effect with the glycineB receptor partial agonist, d-cycloserine and nitric oxide synthase inhibitor, l-NAME. However established antidepressant effects of XAE were abolished by NMDA and NOS activation with d-serine and l-arginine. This study shows that Xylopia aethiopica has antidepressant potential largely due to effects on 5-HT neurotransmission with possible glutamatergic effect through the glycineB co-binding site and nitric oxide synthase inhibition. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Differences in magnesium and calcium effects on N-methyl-D-aspartate- and quisqualate-induced decreases in extracellular sodium concentration in rat hippocampal slices.

PubMed

Köhr, G; Heinemann, U

1988-01-01

Decreases in extracellular sodium concentration [( Na+]o) and associated slow negative field potentials (fp's) were monitored with double barreled sodium sensitive/reference microelectrodes in area CA1 of rat hippocampal slices during iontophoretic application of the glutamate receptor agonists N-methyl-D-aspartate (NMDA) and quisqualate (quis). The effects of lowering [Ca2+]o on these signals were compared to those of lowering [Mg2+]o. Both NMDA- and quis-induced decreases in [Na+]o of up to 60 mM and in the fp's of up to 8 mV. Decreasing [Mg2+]o enhanced NMDA-induced signals, whereas quis-induced signals were unaffected. Lowering [Ca2+]o also enhanced NMDA signals, although somewhat less than lowering [Mg2+]o. This effect was still present, even when voltage dependent Na+ currents were blocked by 10(-7) tetrodotoxin. Interestingly, quis-induced signals could be enhanced in a low Ca2+ medium as well, but only when high quis concentrations were used. The results suggest that, during the sorts of large decreases of [Ca2+]o observed during seizure activity, activation of NMDA receptors is facilitated.

Evidence for the involvement of NMDA receptors in the antidepressant-like effect of nicotine in mouse forced swimming and tail suspension tests.

PubMed

Haj-Mirzaian, Arya; Kordjazy, Nastaran; Haj-Mirzaian, Arvin; Ostadhadi, Sattar; Ghasemi, Mehdi; Amiri, Shayan; Faizi, Mehrdad; Dehpour, AhmadReza

2015-10-01

The antidepressant action of acute nicotine administration in clinical and animal studies is well recognized. But the underlying mechanism for this effect has not been carefully discovered. We attempted to evaluate the possible role of N-Methyl-D-aspartate (NMDA) receptors in the antidepressant-like effect of nicotine. After the assessment of locomotor activity in the open-field test, forced swimming test (FST) and tail suspension test (TST) were used to evaluate the antidepressant-like effect of nicotine in mice. We performed intraperitoneal administration of nicotine at different doses and periods before the tests. To assess the possible involvement of NMDA receptors, non-effective doses of NMDA antagonists and an NMDA agonist were obtained and were administered simultaneously with the non-effective and effective doses of nicotine, respectively. Nicotine (0.2 mg/kg, 30 min before FST/TST) significantly reduced the immobility time of mice similar to fluoxetine (20 mg/kg). Nicotine did not affect the locomotor behavior of mice in open-field test. Co-administration of non-effective doses of NMDA receptor antagonists, ketamine (1 or 0.3 mg/kg), MK-801 (0.05 or 0.005 mg/kg), and magnesium sulfate (10 or 5 mg/kg) with nicotine (0.1 or 0.03 mg/kg) had remarkable synergistic antidepressant effect in both FST and TST. Also, non-effective NMDA (75 or 30 mg/kg) reversed the anti-immobility effect of nicotine (0.2 mg/kg) on mouse FST and TST. Our study has for the first time confirmed that the antidepressant-like effect of nicotine on mice is NMDA-mediated, and nicotine presumably exerts this effect by antagonizing the glutamatergic NMDA receptors.

Pharmacological enhancement of behavioral therapy: focus on posttraumatic stress disorder.

PubMed

Choi, Dennis C; Rothbaum, Barbara O; Gerardi, Maryrose; Ressler, Kerry J

2010-01-01

Improved efficacy in the treatment of posttraumatic stress disorder (PTSD) and other anxiety disorders is urgently needed. Traditional anxiety treatments of hypnosis and psychodynamic therapy may be of some help, but uncontrolled studies lead to inconclusive results on the efficacy of these treatment techniques. There is a larger literature supporting the efficacy of cognitive-behavioral procedures with PTSD, including prolonged exposure therapy, eye movement desensitization and reprocessing, and anxiety management techniques. The cutting-edge technology of virtual reality-based exposure therapy for PTSD is particularly exciting. To further build on effective psychosocial treatments, current pharmacological augmentation approaches to emotional learning are being combined with psychotherapy. In particular, D-cycloserine, a partial NMDA agonist, has shown to be effective in facilitating the exposure/extinction therapy to improve the efficacy of treating anxiety disorders, and may guide the way for new pharmacological enhancements of behavioral therapy.

Immunoneutralization of Agmatine Sensitizes Mice to μ-Opioid Receptor Tolerance

PubMed Central

Wade, Carrie L.; Eskridge, Lori L.; Nguyen, H. Oanh X.; Kitto, Kelley F.; Stone, Laura S.; Wilcox, George

2009-01-01

Systemically or centrally administered agmatine (decarboxylated arginine) prevents, moderates, or reverses opioid-induced tolerance and self-administration, inflammatory and neuropathic pain, and sequelae associated with ischemia and spinal cord injury in rodents. These behavioral models invoke the N-methyl-d-aspartate (NMDA) receptor/nitric-oxide synthase cascade. Agmatine (AG) antagonizes the NMDA receptor and inhibits nitric-oxide synthase in vitro and in vivo, which may explain its effect in models of neural plasticity. Agmatine has been detected biochemically and immunohistochemically in the central nervous system. Consequently, it is conceivable that agmatine operates in an anti-glutamatergic manner in vivo; the role of endogenous agmatine in the central nervous system remains minimally defined. The current study used an immunoneutralization strategy to evaluate the effect of sequestration of endogenous agmatine in acute opioid analgesic tolerance in mice. First, intrathecal pretreatment with an anti-AG IgG (but not normal IgG) reversed an established pharmacological effect of intrathecal agmatine: antagonism of NMDA-evoked behavior. This result justified the use of anti-AG IgG to sequester endogenous agmatine in vivo. Second, intrathecal pretreatment with the anti-AG IgG sensitized mice to induction of acute spinal tolerance of two μ-opioid receptor-selective agonists, [d-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin and endomorphin-2. A lower dose of either agonist that, under normal conditions, produces moderate or no tolerance was tolerance-inducing after intrathecal pretreatment of anti-AG IgG (but not normal IgG). The effect of the anti-AG IgG lasted for at least 24 h in both NMDA-evoked behavior and the acute opioid tolerance. These results suggest that endogenous spinal agmatine may moderate glutamate-dependent neuroplasticity. PMID:19684255

Immunoneutralization of agmatine sensitizes mice to micro-opioid receptor tolerance.

PubMed

Wade, Carrie L; Eskridge, Lori L; Nguyen, H Oanh X; Kitto, Kelley F; Stone, Laura S; Wilcox, George; Fairbanks, Carolyn A

2009-11-01

Systemically or centrally administered agmatine (decarboxylated arginine) prevents, moderates, or reverses opioid-induced tolerance and self-administration, inflammatory and neuropathic pain, and sequelae associated with ischemia and spinal cord injury in rodents. These behavioral models invoke the N-methyl-D-aspartate (NMDA) receptor/nitric-oxide synthase cascade. Agmatine (AG) antagonizes the NMDA receptor and inhibits nitric-oxide synthase in vitro and in vivo, which may explain its effect in models of neural plasticity. Agmatine has been detected biochemically and immunohistochemically in the central nervous system. Consequently, it is conceivable that agmatine operates in an anti-glutamatergic manner in vivo; the role of endogenous agmatine in the central nervous system remains minimally defined. The current study used an immunoneutralization strategy to evaluate the effect of sequestration of endogenous agmatine in acute opioid analgesic tolerance in mice. First, intrathecal pretreatment with an anti-AG IgG (but not normal IgG) reversed an established pharmacological effect of intrathecal agmatine: antagonism of NMDA-evoked behavior. This result justified the use of anti-AG IgG to sequester endogenous agmatine in vivo. Second, intrathecal pretreatment with the anti-AG IgG sensitized mice to induction of acute spinal tolerance of two micro-opioid receptor-selective agonists, [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin and endomorphin-2. A lower dose of either agonist that, under normal conditions, produces moderate or no tolerance was tolerance-inducing after intrathecal pretreatment of anti-AG IgG (but not normal IgG). The effect of the anti-AG IgG lasted for at least 24 h in both NMDA-evoked behavior and the acute opioid tolerance. These results suggest that endogenous spinal agmatine may moderate glutamate-dependent neuroplasticity.

Neurobiology of anxiety disorders and implications for treatment.

PubMed

Garakani, Amir; Mathew, Sanjay J; Charney, Dennis S

2006-11-01

The neurobiology of the anxiety disorders, which include panic disorder, post-traumatic stress disorder (PTSD), and specific phobias, among others, has been clarified by advances in the field of classical or Pavlovian conditioning, and in our understanding of basic mechanisms of memory and learning. Fear conditioning occurs when a neutral conditioned stimulus (such as a tone) is paired with an aversive, or unconditioned stimulus (such as a footshock), and then in the absence of the unconditioned stimulus, causes a conditioned fear response. Preclinical studies have shown that the amygdala plays a key role in fear circuitry, and that abnormalities in amygdala pathways can affect the acquisition and expression of fear conditioning. Drugs such as glutamate N-methyl-D-aspartate (NMDA) antagonists, and blockers of voltage-gated calcium channels, in the amygdala, may block these effects. There is also preliminary evidence for the use of centrally acting beta-adrenergic antagonists, like propranolol, to inhibit consolidation of traumatic memories in PTSD. Finally, fear extinction, which entails new learning of fear inhibition, is central to the mechanism of effective anti-anxiety treatments. Several pharmacological manipulations, such as D-cycloserine, a partial NMDA agonist, have been found to facilitate extinction. Combining these medication approaches with psychotherapies that promote extinction, such as cognitive behavioral therapy (CBT), may offer patients with anxiety disorders a rapid and robust treatment with good durability of effect.

Electrophysiological Perspectives on the Therapeutic Use of Nicotinic Acetylcholine Receptor Partial AgonistsS⃞

PubMed Central

Trocmé-Thibierge, Caryn; Guendisch, Daniela; Al Rubaiy, Shehd Abdullah Abbas; Bloom, Stephen A.

2011-01-01

Partial agonist therapies rely variously on two hypotheses: the partial agonists have their effects through chronic low-level receptor activation or the partial agonists work by decreasing the effects of endogenous or exogenous full agonists. The relative significance of these activities probably depends on whether acute or chronic effects are considered. We studied nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus laevis oocytes to test a model for the acute interactions between acetylcholine (ACh) and weak partial agonists. Data were best-fit to a basic competition model that included an additional factor for noncompetitive inhibition. Partial agonist effects were compared with the nAChR antagonist bupropion in prolonged bath application experiments that were designed to mimic prolonged drug exposure typical of therapeutic drug delivery. A primary effect of prolonged application of nicotine was to decrease the response of all nAChR subtypes to acute applications of ACh. In addition, nicotine, cytisine, and varenicline produced detectable steady-state activation of α4β2* [(α4)2(β2)3, (α4)3(β2)2, and (α4)2(β2)2α5)] receptor subtypes that was not seen with other test compounds. Partial agonists produced no detectable steady-state activation of α7 nAChR, but seemed to show small potentiation of ACh-evoked responses; however, “run-up” of α7 ACh responses was also sometimes observed under control conditions. Potential off-target effects of the partial agonists therefore included the modulation of α7 responses by α4β2 partial agonists and decreases in α4β2* responses by α7-selective agonists. These data indicate the dual effects expected for α4β2* partial agonists and provide models and insights for utility of partial agonists in therapeutic development. PMID:21285282

N-methyl-D-aspartate increases acetylcholine release from rat striatum and cortex: its effect is augmented by choline

NASA Technical Reports Server (NTRS)

Ulus, I. H.; Buyukuysal, R. L.; Wurtman, R. J.

1992-01-01

We examined the effects of N-methyl-D-aspartate (NMDA), a glutamate agonist, and of glutamate itself, on acetylcholine (ACh) release from superfused rat striatal slices. In a Mg(++)-free medium, NMDA (32-1000 microM) as well as glutamate (1 mM) increased basal ACh release by 35 to 100% (all indicated differences, P less than .05), without altering tissue ACh or choline contents. This augmentation was blocked by Mg++ (1.2 mM) or by MK-801 (10 microM). Electrical stimulation (15 Hz, 75 mA) increased ACh release 9-fold (from 400 to 3660 pmol/mg of protein): this was enhanced (to 4850 pmol/mg of protein) by NMDA (100 microM). ACh levels in stimulated slices fell by 50 or 65% depending on the absence or presence of NMDA. The addition of choline (40 microM) increased ACh release both basally (570 pmol/mg of protein) and with electrical stimulation (6900 pmol/mg of protein). In stimulated slices choline acted synergistically with NMDA, raising ACh release to 10,520 pmol/mg of protein. The presence of choline also blocked the fall in tissue ACh. No treatment affected tissue phospholipid or protein levels. NMDA (32-320 microM) also augmented basal ACh release from cortical but not hippocampal slices. Choline efflux from striatal and cortical (but not hippocampal) slices decreased by 34 to 50% in Mg(++)-free medium. These data indicate that NMDA-like drugs may be useful, particularly in combination with choline, to enhance striatal and cortical cholinergic activity. ACh release from rat hippocampus apparently is not affected by NMDA receptors.

Opiate and N-methyl-D-aspartate receptors in form-deprivation myopia.

PubMed

Fischer, A J; Seltner, R L; Stell, W K

1998-01-01

Pharmacological studies have implicated retinal opiate pathways in the visual regulation of ocular growth. However, the effects of opiate receptor subtype-specific compounds on form-deprivation myopia (FDM) are inconsistent (Seltner et al., 1997), and may be mediated by non-opiate receptors. The purpose of this study was to test whether opiate receptor-inactive (D-) enantiomers elicit the same FDM-suppressing effect as their opiate receptor-active (L-) counterparts. Since some opiates are thought to act at NMDA receptors, we also tested whether NMDA receptor agonists and antagonists influence ocular growth or FDM. We found that both L- and D- enantiomers of morphine-like compounds (dextrorphanol and levorphanol, and D- and L-naloxone) were equally effective in blocking FDM. The NMDA receptor antagonists dextromethorphan, MK801, and AP5 also suppressed FDM. A single toxic dose of NMDA, that destroys many subtypes of amacrine cells (including those that synthesize the opioid peptide enkephalin), induced myopia and ocular enlargement in ungoggled eyes, and eliminated the ability of form-deprivation to enhance ocular growth. The NR-1 subunit of the NMDA receptor was localized to a narrowly stratified, intense stratum at approximately 50% depth in the inner plexiform layer, diffusely throughout the proximal inner plexiform layer, and to many somata in the amacrine and ganglion cell layers. These observations suggest that most effects of opiate receptor ligands on FDM in the chick are mediated by non-opiate receptors, which are likely to include NMDA receptors. NMDA as an excitotoxin transiently enhances ocular growth, but thereafter disables retinal mechanisms that promote emmetropization and FDM. These observations are consistent with a prominent role for pathways utilizing NMDA receptors in FDM and ocular growth-control.

Identification of PPARgamma Partial Agonists of Natural Origin (I): Development of a Virtual Screening Procedure and In Vitro Validation

PubMed Central

Guasch, Laura; Sala, Esther; Castell-Auví, Anna; Cedó, Lidia; Liedl, Klaus R.; Wolber, Gerhard; Muehlbacher, Markus; Mulero, Miquel; Pinent, Montserrat; Ardévol, Anna; Valls, Cristina; Pujadas, Gerard; Garcia-Vallvé, Santiago

2012-01-01

Background Although there are successful examples of the discovery of new PPARγ agonists, it has recently been of great interest to identify new PPARγ partial agonists that do not present the adverse side effects caused by PPARγ full agonists. Consequently, the goal of this work was to design, apply and validate a virtual screening workflow to identify novel PPARγ partial agonists among natural products. Methodology/Principal Findings We have developed a virtual screening procedure based on structure-based pharmacophore construction, protein-ligand docking and electrostatic/shape similarity to discover novel scaffolds of PPARγ partial agonists. From an initial set of 89,165 natural products and natural product derivatives, 135 compounds were identified as potential PPARγ partial agonists with good ADME properties. Ten compounds that represent ten new chemical scaffolds for PPARγ partial agonists were selected for in vitro biological testing, but two of them were not assayed due to solubility problems. Five out of the remaining eight compounds were confirmed as PPARγ partial agonists: they bind to PPARγ, do not or only moderately stimulate the transactivation activity of PPARγ, do not induce adipogenesis of preadipocyte cells and stimulate the insulin-induced glucose uptake of adipocytes. Conclusions/Significance We have demonstrated that our virtual screening protocol was successful in identifying novel scaffolds for PPARγ partial agonists. PMID:23226391

Depression of NMDA receptor-mediated synaptic transmission by four α2 adrenoceptor agonists on the in vitro rat spinal cord preparation

PubMed Central

Faber, E S L; Chambers, J P; Evans, R H

1998-01-01

α2-Adrenoceptor agonists have a spinal site of analgesic action. In the current study the synaptic depressant actions of xylazine, detomidine, romifidine and dexmedetomidine have been compared on segmental reflexes containing NMDA receptor-mediated components in the neonatal rat hemisected spinal cord preparation in vitro.Reflexes were evoked in the ventral root following either supramaximal electrical stimulation of the corresponding ipsilateral lumbar dorsal root to evoke the high intensity excitatory postsynaptic potential (e.p.s.p.) involving all primary afferent fibres, or low intensity stimulation to evoke the solely A fibre-mediated low intensity e.p.s.p. The high intensity e.p.s.p. contains a greater NMDA receptor-mediated component.Xylazine, romifidine, detomidine and dexmedetomidine all depressed both the high intensity e.p.s.p. and the low intensity e.p.s.p. giving respective EC50 values of 0.91±0.2 μM (n=12), 23.4±3 nM (n=12), 37.7±7 nM (n=8) and 0.84±0.1 nM (n=4) for depression of the high intensity e.p.s.p. and 0.76±0.1 μM (n=12), 22.0±3 nM (n=12), 24.9±6 nM (n=4) and 2.7±0.6 nM (n=4) for depression of the low intensity e.p.s.p., respectively. Unlike the other three drugs, the two values for dexmedetomidine, showing a greater selectivity for the high intensity e.p.s.p., are significantly different.Each of these depressant actions was reversed by the selective α2-adrenoceptor antagonist atipamezole (1 μM).In contrast to previous reports of the actions of α2-adrenoceptor agonists on the in vitro spinal cord preparation, at concentrations ten fold higher than the above EC50 values xylazine, romifidine, detomidine and dexmedetomidine depressed the initial population spike of motoneurons (MSR). This depression was not reversed by atipamezole.Comparison of the rank order of the present EC50 values for depression of the high intensity e.p.s.p. with potency ratios from in vivo analgesic tests in previous studies show a close correlation between the present in vitro tests and analgesic potency. There is no correlation between the present data and previously obtained affinities of the agonists at non-adrenergic imidazoline binding sites.The current findings therefore suggest that xylazine, romifidine, detomidine and dexmedetomidine are exerting their central analgesic actions at the spinal level principally through α-2-adrenoceptors. All four agonists showed the same profile of selective depression of the NMDA receptor-mediated component of reflexes similar to that reported previously for clonidine. However dexmedetomidine, unlike the other ligands, selectively depressed the high intensity e.p.s.p. PMID:9647475

Evaluation of partial beta-adrenoceptor agonist activity.

PubMed

Lipworth, B J; Grove, A

1997-01-01

A partial beta-adrenoceptor (beta-AR) agonist will exhibit opposite agonist and antagonist activity depending on the prevailing degree of adrenergic tone or the presence of a beta-AR agonist with higher intrinsic activity. In vivo partial beta-AR agonist activity will be evident at rest with low endogenous adrenergic tone, as for example with chronotropicity (beta 1/beta 2), inotropicity (beta 1) or peripheral vasodilatation and finger tremor (beta 2). beta-AR blocking drugs which have partial agonist activity may exhibit a better therapeutic profile when used for hypertension because of maintained cardiac output without increased systemic vascular resistance, along with an improved lipid profile. In the presence of raised endogenous adrenergic tone such as exercise or an exogenous full agonist, beta-AR subtype antagonist activity will become evident in terms of effects on exercise induced heart rate (beta 1) and potassium (beta 2) responses. Reduction of exercise heart rate will occur to a lesser degree in the case of a beta-adrenoceptor blocker with partial beta 1-AR agonist activity compared with a beta-adrenoceptor blocker devoid of partial agonist activity. This may result in reduced therapeutic efficacy in the treatment of angina on effort when using beta-AR blocking drugs with partial beta 1-AR agonist activity. Effects on exercise hyperkalaemia are determined by the balance between beta 2-AR partial agonist activity and endogenous adrenergic activity. For predominantly beta 2-AR agonist such as salmeterol and salbutamol, potentiation of exercise hyperkalaemia occurs. For predominantly beta 2-AR antagonists such as carteolol, either potentiation or attenuation of exercise hyperkalaemia occurs at low and high doses respectively. beta 2-AR partial agonist activity may also be expressed as antagonism in the presence of an exogenous full agonist, as for example attenuation of fenoterol induced responses by salmeterol. Studies are required to investigate whether this phenomenon is relevant in the setting of acute severe asthma.

d-Cycloserine facilitates extinction learning and enhances extinction-related brain activation.

PubMed

Klass, Anne; Glaubitz, Benjamin; Tegenthoff, Martin; Lissek, Silke

2017-10-01

Extinction learning is modulated by N-methyl d-aspartate receptors (NMDAR) particularly in prefrontal and hippocampal brain regions. The use of of NMDA agonists in exposure therapy of anxiety disorders has been investigated in various patient groups. Behavioral results showed beneficial effects of pre-learning administration of the partial NMDAR agonist d-Cycloserine (DCS) on therapy success. However, the impact of DCS upon non-fear-related contextual extinction, and associated recruitment of extinction-relevant brain regions is as yet unknown. In the present fMRI study, healthy human participants performed a context-related associative learning and extinction task. A single dose of DCS, administered prior to extinction learning, enhanced extinction learning performance in an identical context, and increased activation in prefrontal, temporal as well as hippocampal/insular regions, compared to placebo controls. In contrast, DCS did not affect extinction learning in a novel context, nor the renewal effect, which describes the recovery of an extinguished response if the context of extinction differs from the context of recall. Our findings demonstrate a specific involvement of prefrontal and hippocampal NMDAR in the modification of established stimulus-outcome associations in identical contexts and thus their role in behavioral flexibility, underlining their potential for enhancing AAA extinction learning. Copyright © 2017. Published by Elsevier Inc.

The role of 5 HT6-receptor antagonists in Alzheimer's disease: an update.

PubMed

Khoury, Rita; Grysman, Noam; Gold, Jake; Patel, Kush; Grossberg, George T

2018-06-01

Despite recent advances in Alzheimer's disease (AD) research, no breakthrough treatments have been discovered. Cholinesterase inhibitors and the NMDA-receptor antagonist memantine are currently the two approved symptomatic treatments for AD. 5-HT6 receptor antagonism has recently emerged as a promising treatment strategy to improve cognition in AD, with a modest side-effect profile. Areas covered: 5-HT6 receptors, exclusively found in the central nervous system, modulate primarily GABA and glutamate levels, facilitating the secondary release of other neurotransmitters including dopamine, noradrenaline, and acetylcholine, all of which are compromised in AD. This review discusses findings of preclinical and phase I-III clinical trials conducted with three major 5-HT6 receptor antagonists: idalopirdine, intepirdine, and SUVN-502, in the field of AD. Expert opinion: Despite early positive findings, larger phase-III trials have failed to demonstrate any statistically significant impact on cognition for both idalopirdine and intepirdine, as adjunct to cholinesterase inhibitors. Paradoxically, 5-HT6 receptor agonists have also been shown to have cognitive enhancing properties. Thus, a better understanding of the mechanism of action of the 5-HT6 receptor and its ligands is warranted. Investigating 5-HT6 receptor partial or inverse agonists may be promising in future AD trials.

Premyelinated central axons express neurotoxic NMDA receptors: relevance to early developing white-matter injury

PubMed Central

Huria, Tahani; Beeraka, Narasimha Murthy; Al-Ghamdi, Badrah; Fern, Robert

2015-01-01

Ischemic-type injury to developing white matter is associated with the significant clinical condition cerebral palsy and with the cognitive deficits associated with premature birth. Premyelinated axons are the major cellular component of fetal white matter and loss of axon function underlies the disability, but the cellular mechanisms producing ischemic injury to premyelinated axons have not previously been described. Injury was found to require longer periods of modelled ischemia than at latter developmental points. Ischemia produced initial hyperexcitability in axons followed by loss of function after Na+ and Ca2+ influx. N-methyl-D-aspartate- (NMDA) type glutamate receptor (GluR) agonists potentiated axon injury while antagonists were protective. The NMDA GluR obligatory Nr1 subunit colocalized with markers of small premyelinated axons and expression was found at focal regions of axon injury. Ischemic injury of glial cells present in early developing white matter was NMDA GluR independent. Axons in human postconception week 18 to 23 white matter had a uniform prediameter expansion phenotype and postembedded immuno-gold labelling showed Nr1 subunit expression on the membrane of these axons, demonstrating a shared key neuropathologic feature with the rodent model. Premyelinated central axons therefore express high levels of functional NMDA GluRs that confer sensitivity to ischemic injury. PMID:25515212

An N-methyl-D-aspartate receptor-independent excitatory action of partial reduction of extracellular [Mg2+] in CA1-region of rat hippocampal slices.

PubMed

Hamon, B; Stanton, P K; Heinemann, U

1987-03-31

Partial reduction of [Mg2+]o from 2 to 1 mM markedly enhanced neuronal responses evoked by Schaffer collateral-commissural fiber stimulation in the CA1-region of rat hippocampal slices. The amplitude of extracellular population potentials recorded in the CA1-pyramidal cell layer and maximum dV/dt of extracellular population EPSP's recorded in the CA1-pyramidal apical dendritic layer were both increased. However, unlike findings from slices where Mg2+ was completely removed from the bathing medium, there was no spontaneous or evoked epileptiform activity, and the N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovalerate (2-APV) did not antagonize the enhancement of evoked responses. These results indicate that, in addition to the participation of NMDA receptors in the epileptiform activity observed when Mg2+ is completely removed from the bathing medium, there is also an NMDA receptor-independent excitatory action of partial reduction of [Mg2+]o in hippocampal slices.

Glycine triggers a non-ionotropic activity of GluN2A-containing NMDA receptors to confer neuroprotection.

PubMed

Hu, Rong; Chen, Juan; Lujan, Brendan; Lei, Ruixue; Zhang, Mi; Wang, Zefen; Liao, Mingxia; Li, Zhiqiang; Wan, Yu; Liu, Fang; Feng, Hua; Wan, Qi

2016-10-03

Ionotropic activation of NMDA receptors (NMDARs) requires agonist glutamate and co-agonist glycine. Here we show that glycine enhances the activation of cell survival-promoting kinase Akt in cultured cortical neurons in which both the channel activity of NMDARs and the glycine receptors are pre-inhibited. The effect of glycine is reduced by shRNA-mediated knockdown of GluN2A subunit-containing NMDARs (GluN2ARs), suggesting that a non-ionotropic activity of GluN2ARs mediates glycine-induced Akt activation. In support of this finding, glycine enhances Akt activation in HEK293 cells over-expressing GluN2ARs. The effect of glycine on Akt activation is sensitive to the antagonist of glycine-GluN1 binding site. As a functional consequence, glycine protects against excitotoxicity-induced neuronal death through the non-ionotropic activity of GluN2ARs and the neuroprotective effect is attenuated by Akt inhibition. Thus, this study reveals an unexpected role of glycine in eliciting a non-ionotropic activity of GluN2ARs to confer neuroprotection via Akt activation.

Glycine triggers a non-ionotropic activity of GluN2A-containing NMDA receptors to confer neuroprotection

PubMed Central

Hu, Rong; Chen, Juan; Lujan, Brendan; Lei, Ruixue; Zhang, Mi; Wang, Zefen; Liao, Mingxia; Li, Zhiqiang; Wan, Yu; Liu, Fang; Feng, Hua; Wan, Qi

2016-01-01

Ionotropic activation of NMDA receptors (NMDARs) requires agonist glutamate and co-agonist glycine. Here we show that glycine enhances the activation of cell survival-promoting kinase Akt in cultured cortical neurons in which both the channel activity of NMDARs and the glycine receptors are pre-inhibited. The effect of glycine is reduced by shRNA-mediated knockdown of GluN2A subunit-containing NMDARs (GluN2ARs), suggesting that a non-ionotropic activity of GluN2ARs mediates glycine-induced Akt activation. In support of this finding, glycine enhances Akt activation in HEK293 cells over-expressing GluN2ARs. The effect of glycine on Akt activation is sensitive to the antagonist of glycine-GluN1 binding site. As a functional consequence, glycine protects against excitotoxicity-induced neuronal death through the non-ionotropic activity of GluN2ARs and the neuroprotective effect is attenuated by Akt inhibition. Thus, this study reveals an unexpected role of glycine in eliciting a non-ionotropic activity of GluN2ARs to confer neuroprotection via Akt activation. PMID:27694970

Blockade of NMDA receptors prevents analgesic tolerance to repeated transcutaneous electrical nerve stimulation (TENS) in rats

PubMed Central

Hingne, Priyanka M.; Sluka, Kathleen A.

2008-01-01

Repeated daily application transcutaneous electrical nerve stimulation (TENS) results in tolerance, at spinal opioid receptors, to the anti-hyperalgesia produced by TENS. Since N-Methyl-D-Aspartate (NMDA) receptor antagonists prevent analgesic tolerance to opioid agonists we hypothesized that blockade of NMDA receptors will prevent tolerance to TENS. In rats with knee joint inflammation, TENS was applied for 20 minute daily at high frequency (100 Hz), low frequency (4 Hz), or sham TENS. Rats were treated with the NMDA antagonist MK-801 (0.01 mg/kg-0.1 mg/kg) or vehicle daily before TENS. Paw withdrawal thresholds were tested before and after inflammation, and before and after TENS treatment for 4 days. On day 1 TENS reversed the decreased mechanical withdrawal threshold induced by joint inflammation. On day 4 TENS had no effect on the decreased withdrawal threshold in the group treated with vehicle demonstrating development of tolerance. However, in the group treated with 0.1 mg/kg MK-801, TENS significantly reversed the mechanical withdrawal thresholds on day 4 demonstrating that tolerance did not develop. Vehicle treated animals developed cross-tolerance at spinal opioid receptors. Treatment with MK-801 reversed this cross-tolerance at spinal opioid receptors. In summary, blockade of NMDA receptors prevents analgesic tolerance to daily TENS by preventing tolerance at spinal opioid receptors. Perspective Tolerance observed to the clinical treatment of TENS could be prevented by administration of pharmaceutical agents with NMDA receptors activity such as ketamine or dextromethorphan. PMID:18061543

D-cycloserine adjuvant therapy to molindone in the treatment of schizophrenia.

PubMed

Rosse, R B; Fay-McCarthy, M; Kendrick, K; Davis, R E; Deutsch, S I

1996-10-01

This preliminary investigation examined the therapeutic efficacy of two doses of oral D-cycloserine (5 and 15 mg p.o. b.i.d.) administered as an adjuvant to molindone (150 mg p.o. q.d.) in the treatment of schizophrenia. D-Cycloserine is an agonist at the N-methyl-D-aspartate (NMDA) subclass of glutamate receptor complex. An NMDA agonist intervention was studied because of the schizophreniform psychosis precipitated by phencyclidine (PCP), which is a noncompetitive antagonist at the NMDA glutamate receptor. The PCP model of schizophrenia is regarded as the most comprehensive pharmacological model of this disorder. In this preliminary, placebo-controlled, double-blind, parallel-group study, the measures of treatment efficacy were the Brief Psychiatric Rating Scale, Schedule for the Assessment of Negative Symptoms, and Clinical Global Impression Scale. The final scores for each item of the outcome measures employed were based on the consensus of at least two trained raters who were present during each rating interview. In the 13 subjects evaluated, although the D-cycloserine was well tolerated, neither dose seemed to possess adjuvant therapeutic efficacy. However, since another recent report of nine patients with schizophrenia treated for 2 weeks with a slightly higher dose of D-cycloserine (50 mg/day) described significant clinical and neuropsychological improvement, further study of the adjuvant potential of slightly higher doses of D-cycloserine seems warranted. Additionally, there might be a therapeutic window for D-cycloserine dosing, as daily doses of 250 mg have been associated with symptom worsening.

Taurine release from the developing and ageing hippocampus: stimulation by agonists of ionotropic glutamate receptors.

PubMed

Saransaari, P; Oja, S S

1997-12-30

The inhibitory amino acid taurine has been held to function as a modulator and osmoregulator in the brain, being of particular importance in the immature brain. The release of preloaded [3H]taurine was now studied in hippocampal slices from developing (7-day-old), adult (3-month-old) and ageing (6-24-month-old) mice focussing on the effects of agonists of ionotropic glutamate receptors. N-methyl-D-aspartate (NMDA), kainate and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) potentiated taurine release concentration-dependently at each age, more so in the immature than in the adult and ageing hippocampus. The effect of kainate was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in the developing and aged hippocampus and those of AMPA and NMDA by 6-nitro-7-sulphamoylbenzo[f]quinoxaline-2,3-dione (NBQX) and dizocilpine a(MK-801) at every age studied. This indicates the involvement of NMDA and AMPA receptors in taurine release throughout the life-span of mice, while the kainate-receptor-mediated release does not appear to function in adults. The increased hippocampal taurine release evoked by ionotropic glutamate receptors could act neuroprotectively, counteracting by several mechanisms the harmful effects of the simultaneous release of excitatory amino acids. The substantial release of taurine in the immature hippocampus might be particularly significant in view of the vulnerability of brain tissue to excitotoxicity at early age.

NMDA receptor mediates proliferation and CREB phosphorylation in postnatal Müller glia-derived retinal progenitors

PubMed Central

Ramírez, Mónica

2009-01-01

Purpose Postnatal retinal Müller glia are considered to be retinal progenitors as they retain the ability to dedifferentiate, proliferate, and differentiate to new retinal glia and neurons after injury. The proliferation and differentiation processes are coordinated by several extrinsic factors and neurotransmitters, including glutamate. Thus, the appropriate numbers and proportions of the different cell types are generated to form a functional retina during development and during injury repair. Here we analyze the changes in the proliferation of postnatal Müller glia-derived progenitors after activation of the N-methyl-D-aspartate (NMDA) glutamate receptors. Methods Müller glia-derived progenitor cell cultures were characterized by immunocytochemistry with antibodies against the NR1 subunit of the NMDA receptor and the progenitor cell marker nestin. The effect of glutamate receptor agonists and antagonists on cell proliferation was analyzed by BrdU incorporation or Ki67 immunostaining, cell counting, and by immunolabeling of phosphorylated cAMP response element binding protein (P-CREB) transcription factor. The effect of NMDA receptor activation was analyzed in vivo by P-CREB immunohistochemistry in retinal sections of Long-Evans NMDA injected rats. Results We show that NMDA receptor activation significantly increases the proliferation rate of Müller-glia derived progenitor cells and that this increase can be blocked by NMDA receptor antagonists. Furthermore, we show that CREB phosphorylation is induced in NMDA-treated Müller-glia derived progenitor cells in culture and that specific pharmacological inhibition of CREB phosphorylation results in a decreased number of proliferating cells. We confirmed the relevance of these observations by the analysis of retinal sections after NMDA injection in vivo where immunoreactivity to phosphorylated CREB is also increased after treatment. Conclusions In the present study we show that NMDA receptor activation induces postnatal Müller glia-derived retinal cell progenitor proliferation and transcription factor CREB phosphorylation both in culture and in vivo. The identification of the molecular determinants of mature retinal progenitors such as transcription factor CREB and NMDA receptor-induced players should facilitate the control of growth and manipulation of progenitor cell cultures and the possible identification of the molecular mechanisms involved in progenitor self-renewal. PMID:19365572

Glutamatergic neurotransmission modulation and the mechanisms of antipsychotic atypicality.

PubMed

Heresco-Levy, Uriel

2003-10-01

The neurotransmission mediated by the excitatory amino acids (EAA) glutamate (GLU) and aspartate is of interest to the pharmacotherapy of psychosis due to its role in neurodevelopment and neurotoxicity, its complex interactions with dopaminergic and other neurotransmitter systems and its pivotal importance in recent models of schizophrenia. Accumulating evidence indicates that modulation of glutamatergic neurotransmission may play an important role in the mechanisms of action of atypical antipsychotic drugs. The principles of the phencyclidine (PCP) model of schizophrenia suggest that conventional neuroleptics cannot counteract all aspects of schizophrenia symptomatology, while a more favorable outcome, including anti-negative and cognitive symptoms effects, would be expected with the use of treatment modalities targeting glutamatergic neurotransmission. Clozapine and other presently used atypical antipsychotics differ from conventional neuroleptics in the way they affect various aspects of glutamatergic receptors function. In this context, a specific hypothesis suggesting an agonistic role of clozapine at the N-methyl-D-aspartate (NMDA) subtype of GLU receptors has been postulated. Furthermore, the results of the first generation of clinical trials with glycine (GLY) site agonists of the NMDA receptor in schizophrenia suggest that this type of compounds (1) have efficacy and side effects profiles different than those of conventional neuroleptics and (2) differ in their synergic effects when used in addition to conventional neuroleptics versus clozapine and possibly additional atypical antipsychotics. These findings (1) bring further support to the hypothesis that glutamatergic effects may play an important role in the mechanism of action of atypical antipsychotics, (2) help explain the unique clinical profile of clozapine, and (3) suggest that GLY site agonists of the NMDA receptor may represent a new class of atypical antipsychotic medication. Future research in this area is bound to bring about a better understanding of the role of glutamatergic neurotransmission manipulation in the pharmacotherapy of psychosis and the development of novel pharmacological strategies targeting GLU brain systems.

Ligand-specific Deactivation Time Course of GluN1/GluN2D NMDA Receptors

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

K Vance; N Simorowski; S Traynelis

2011-12-31

N-methyl-D-aspartate (NMDA) receptors belong to the family of ionotropic glutamate receptors that mediate a majority of excitatory synaptic transmission. One unique property of GluN1/GluN2D NMDA receptors is an unusually prolonged deactivation time course following the removal of L-glutamate. Here we show, using x-ray crystallography and electrophysiology, that the deactivation time course of GluN1/GluN2D receptors is influenced by the conformational variability of the ligand-binding domain (LBD) as well as the structure of the activating ligand. L-glutamate and L-CCG-IV induce significantly slower deactivation time courses compared with other agonists. Crystal structures of the isolated GluN2D LBD in complex with various ligands revealmore » that the binding of L-glutamate induces a unique conformation at the backside of the ligand-binding site in proximity to the region at which the transmembrane domain would be located in the intact receptors. These data suggest that the activity of the GluN1/GluN2D NMDA receptor is controlled distinctively by the endogenous neurotransmitter L-glutamate.« less

[Neuroprotective effect of erigeron breviscapus (vant) hand-mazz on NMDA-induced retinal neuron injury in the rats].

PubMed

Shi, Jingming; Jiag, Youqin; Liu, Xuyang

2004-07-01

To investigate if Erigeron Breviscapus (vant) Hand-Mazz (EBHM) has a neuroprotective effect against NMDA-induced neuron death in retinal ganglion cell layer (RGCL). Sixty healthy SD rats were randomly divided into four groups. 6 animals were in normal control group (group A). The others were divided as group B (EBHM group), group C (normal saline+NMDA group), group D (EBHM+NMDA group). Each group has 18 rats. 10 nmol NMDA was chosen for intravitreal injection to cause partial damage of the neurons in RGCL in the right eyes of Groups C and D. Same volume PBS was intravitreal injected in the left eyes as self-control. Groups B and D were pre-treated intraperitoneally with 6% EBHM solution at a dose of 15 mg x 100 g(-1) x d(-1) seven days before and after NMDA treatment. Group C were administrated intraperitoneally with 0.9% normal saline at the same time of EBHM injection. Rats were sacrificed in 4, 7, 14 days after NMDA treatment. Flat preparation of whole retinas were stained with 0.5% cresyl violet and neuron counting in RGCL from both eyes. Each subgroup has 6 rats. There was no significant difference between the right eye and the left eye of neuron counting from RGCL in normal control group (group A) (P=0.200). There was no significant difference between normal control group and EBHM group either in the right eyes or in the left eye in 4 days, 7 days and 14 days respectively after intravitreal injection of 10 nmol NMDA in group C and group D. (P=0.636, P=0.193). Neuron counting from RGCL of group C and group D were significant decreased in the NMDA-treated eyes in 4 days, 7 days and 14 days after intravitreal injection (P < 0.001). There ws no significant difference between self-control eyes and normal control group (P > 0.05). Neuron counting was significantly higher in the EBHM+NMDA group than normal saline+NMDA group at 14 days after intraviteal injection (P=0.044). However,it is obvious that the difference was still significant between normal control group and EBHM+NMDA group (P < 0.05). EBHM has no effect on neuron counting of RGCL when administered alone in normal rats. It is suggested that EBHM has partial protective effect on NMDA-induced neuron loss in RGCL in the rat.

Evidence for involvement of nitric oxide and GABAB receptors in MK-801- stimulated release of glutamate in rat prefrontal cortex

PubMed Central

Roenker, Nicole L.; Gudelsky, Gary A.; Ahlbrand, Rebecca; Horn, Paul S.; Richtand, Neil M.

2012-01-01

Systemic administration of NMDA receptor antagonists elevates extracellular glutamate within prefrontal cortex. The cognitive and behavioral effects of NMDA receptor blockade have direct relevance to symptoms of schizophrenia, and recent studies demonstrate an important role for nitric oxide and GABAB receptors in mediating the effects of NMDA receptor blockade on these behaviors. We sought to extend those observations by directly measuring the effects of nitric oxide and GABAB receptor mechanisms on MK-801-induced glutamate release in the prefrontal cortex. Systemic MK-801 injection (0.3 mg/kg) to male Sprague-Dawley rats significantly increased extracellular glutamate levels in prefrontal cortex, as determined by microdialysis. This effect was blocked by pretreatment with the nitric oxide synthase inhibitor L-NAME (60 mg/kg). Reverse dialysis of the nitric oxide donor SNAP (0.5 – 5 mM) directly into prefrontal cortex mimicked the effect of systemic MK-801, dose-dependently elevating cortical extracellular glutamate. The effect of MK-801 was also blocked by systemic treatment with the GABAB receptor agonist baclofen (5 mg/kg). In combination, these data suggest increased nitric oxide formation is necessary for NMDA antagonist-induced elevations of extracellular glutamate in the prefrontal cortex. Additionally, the data suggest GABAB receptor activation can modulate the NMDA antagonist-induced increase in cortical glutamate release. PMID:22579658

A comparison of N-methyl-D-aspartate-evoked release of adenosine and ( sup 3 H)norepinephrine from rat cortical slices

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

Hoehn, K.; Craig, C.G.; White, T.D.

1990-10-01

Tetrodotoxin reduced N-methyl-D-aspartate (NMDA)-evoked release of adenosine by 35% but virtually abolished (3H)norepinephrine release. Although (3H)norepinephrine release from rat cortical slices evoked by 500 microM NMDA was abolished by 1.2 mM Mg++, which produces a voltage-sensitive, uncompetitive block of NMDA-channels, adenosine release was increased in the presence of Mg++. Partial depolarization with 12 mM K+ relieved the Mg++ block of 500 microM NMDA-evoked (3H)norepinephrine release but did not affect adenosine release, indicating that a Mg++ requirement for the adenosine release process per se cannot account for this discrepancy. NMDA was 33 times more potent in releasing adenosine than (3H)norepinephrine. Atmore » submaximal concentrations of NMDA (10 and 20 microM), adenosine release was augmented in Mg+(+)-free medium. Although a high concentration of the uncompetitive NMDA antagonist MK-801 ((+)-5-methyl-10,11,dihydro-5H-dibenzo(a,d)cyclohepten-5-10-imine maleate) (3 microM) blocked NMDA-evoked release of (3H)norepinephrine and adenosine, a lower concentration (300 nM) decreased NMDA-evoked (3H)norepinephrine release by 66% without affecting adenosine release. These findings suggest that maximal adenosine release occurs when relatively few NMDA receptors are activated, raising the possibility that spare receptors exist for NMDA-evoked adenosine release. Rather than acting as a protectant against excessive NMDA excitation, released adenosine might provide an inhibitory threshold which must be overcome for NMDA-mediated neurotransmission to proceed.« less

Effects of intra-accumbal administration of dopamine and ionotropic glutamate receptor drugs on delay discounting performance in rats.

PubMed

Yates, Justin R; Bardo, Michael T

2017-10-01

Nucleus accumbens core (NAcc) has been implicated in impulsive choice, as measured in delay discounting. The role of dopamine (DA) in impulsive choice has received considerable attention, whereas glutamate (Glu) has recently been shown to be an important mediator of discounting. However, research has not examined how DA or Glu receptors in NAcc mediate different aspects of delay discounting performance, that is, (a) sensitivity to reinforcer magnitude and (b) sensitivity to delayed reinforcement. Adult male Sprague-Dawley rats were first trained in a delay discounting task, in which the delay to a large magnitude food reinforcer increased across blocks of trials. Following behavioral training, rats received bilateral implantation of guide cannulas into NAcc. Half of the rats (n = 12) received infusions of the DA-selective ligands SKF 38393 (D1-like agonist: 0.03 or 0.1 μg), SCH 23390 (D1-like antagonist: 0.3 or 1.0 μg), quinpirole (D2-like agonist: 0.3 or 1.0 μg), and eticlopride (D2-like antagonist: 0.3 or 1.0 μg). The other half received infusions of the ionotropic Glu ligands MK-801 (NMDA uncompetitive antagonist: 0.3 or 1.0 μg), AP-5 (NMDA competitive antagonist: 0.3 or 1.0 μg), ifenprodil (noncompetitive antagonist at NR2B-containing NMDA receptors: 0.3 or 1.0 μg), and CNQX (AMPA competitive antagonist: 0.2 or 0.5 μg). Results showed that SCH 23390 (0.3 μg) decreased sensitivity to reinforcer magnitude without altering impulsive choice, whereas ifenprodil (1.0 μg) decreased sensitivity to delayed reinforcement (i.e., impulsive choice). The current results show that DA and NMDA receptors in NAcc mediate distinct aspects of discounting performance. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

On the ligand binding profile and desensitization of plant ionotropic glutamate receptor (iGluR)-like channels functioning in MAMP-triggered Ca²⁺ influx.

PubMed

Kwaaitaal, Mark; Maintz, Jens; Cavdar, Meltem; Panstruga, Ralph

2012-11-01

The generation of intracellular microbe-associated molecular pattern (MAMP)-triggered Ca²⁺ transients was recently demonstrated to involve ionotropic Glutamate Receptor (iGluR)-like channels in Arabidopsis and tobacco. Here we elaborate on our previous findings and refine our insights in the putative agonist binding profile and potential mode of desensitization of MAMP-activated plant iGluRs. Based on results from pharmacological inhibition and desensitization experiments, we propose that plant iGluR complexes responsible for the MAMP-triggered Ca²⁺ signature have a binding profile that combines the specificities of mammalian NMDA-and non-NMDA types of iGluRs, possibly reflecting the evolutionary history of plant and animal iGluRs. We further hypothesize that, analogous to the mammalian NMDA-NR1 receptor, desensitization of plant iGluR-like channels might involve binding of the ubiquitous Ca²⁺ sensor calmodulin to a cytoplasmic C-terminal domain.

The system N transporter SN2 doubles as a transmitter precursor furnisher and a potential regulator of NMDA receptors.

PubMed

Hamdani, El Hassan; Gudbrandsen, Marius; Bjørkmo, Mona; Chaudhry, Farrukh Abbas

2012-11-01

Activation of NMDA receptor requires two co-agonists, glutamate and glycine. Despite its intrinsic role in brain functions molecular mechanisms involved in glutamate replenishment and identification of the origin of glycine have eluded characterization. We have performed direct measurements of glycine flux by SN2 (Slc38a5; also known as SNAT5), executed extensive electrophysiological characterization as well as implemented ratiometric analyses to show that SN2 transport resembles SN1 in mechanism but differ in functional implications. We report that rat SN2 mediates electroneutral and bidirectional transport of glutamine and glycine at perisynaptic astroglial membranes. Sophisticated coupled and uncoupled movements of H(+) differentially associate with glutamine and glycine transport by SN2 and regulate pH(i) and the release mode of the transporter. Consequently, SN2 doubles as a transmitter precursor furnisher and a potential regulator of NMDA receptors. Copyright © 2012 Wiley Periodicals, Inc.

Mitochondrial dysfunction and lipid peroxidation in rat frontal cortex by chronic NMDA administration can be partially prevented by lithium treatment.

PubMed

Kim, Helena K; Isaacs-Trepanier, Cameron; Elmi, Nika; Rapoport, Stanley I; Andreazza, Ana C

2016-05-01

Chronic N-methyl-d-aspartate (NMDA) administration to rats may be a model to investigate excitotoxicity mediated by glutamatergic hyperactivity, and lithium has been reported to be neuroprotective. We hypothesized that glutamatergic hyperactivity in chronic NMDA injected rats would cause mitochondrial dysfunction and lipid peroxidation in the brain, and that chronic lithium treatment would ameliorate some of these NMDA-induced alterations. Rats treated with lithium for 6 weeks were injected i.p. 25 mg/kg NMDA on a daily basis for the last 21 days of lithium treatment. Brain was removed and frontal cortex was analyzed. Chronic NMDA decreased brain levels of mitochondrial complex I and III, and increased levels of the lipid oxidation products, 8-isoprostane and 4-hydroxynonenal, compared with non-NMDA injected rats. Lithium treatment prevented the NMDA-induced increments in 8-isoprostane and 4-hydroxynonenal. Our findings suggest that increased chronic activation of NMDA receptors can induce alterations in electron transport chain complexes I and III and in lipid peroxidation in brain. The NMDA-induced changes may contribute to glutamate-mediated excitotoxicity, which plays a role in brain diseases such as bipolar disorder. Lithium treatment prevented changes in 8-isoprostane and 4-hydroxynonenal, which may contribute to lithium's reported neuroprotective effect and efficacy in bipolar disorder. Copyright © 2016 Elsevier Ltd. All rights reserved.

Extinction of aversive memories associated with morphine withdrawal requires ERK-mediated epigenetic regulation of brain-derived neurotrophic factor transcription in the rat ventromedial prefrontal cortex.

PubMed

Wang, Wei-Sheng; Kang, Shuo; Liu, Wen-Tao; Li, Mu; Liu, Yao; Yu, Chuan; Chen, Jie; Chi, Zhi-Qiang; He, Ling; Liu, Jing-Gen

2012-10-03

Recent evidence suggests that histone deacetylase (HDAC) inhibitors facilitate extinction of rewarding memory of drug taking. However, little is known about the role of chromatin modification in the extinction of aversive memory of drug withdrawal. In this study, we used conditioned place aversion (CPA), a highly sensitive model for measuring aversive memory of drug withdrawal, to investigate the role of epigenetic regulation of brain-derived neurotrophic factor (BDNF) gene expression in extinction of aversive memory. We found that CPA extinction training induced an increase in recruiting cAMP response element-binding protein (CREB) to and acetylation of histone H3 at the promoters of BDNF exon I transcript and increased BDNF mRNA and protein expression in the ventromedial prefrontal cortex (vmPFC) of acute morphine-dependent rats and that such epigenetic regulation of BDNF gene transcription could be facilitated or diminished by intra-vmPFC infusion of HDAC inhibitor trichostatin A or extracellular signal-regulated kinase (ERK) inhibitor U0126 (1,4-diamino-2,3-dicyano-1,4-bis(methylthio)butadiene) before extinction training. Correspondingly, disruption of the epigenetic regulation of BDNF gene transcription with U0126 or suppression of BDNF signaling with Trk receptor antagonist K252a or BDNF scavenger tyrosine kinase receptor B (TrkB)-Fc blocked extinction of CPA behavior. We also found that extinction training-induced activation of ERK and CREB and extinction of CPA behavior could be potentiated or suppressed by intra-vmPFC infusion of d-cycloserine, a NMDA receptor partial agonist or aminophosphonopentanoic acid, a NMDA receptor antagonist. We conclude that extinction of aversive memory of morphine withdrawal requires epigenetic regulation of BDNF gene transcription in the vmPFC through activation of the ERK-CREB signaling pathway perhaps in a NMDA receptor-dependent manner.

D-cycloserine in Schizophrenia: New Strategies for Improving Clinical Outcomes by Enhancing Plasticity

PubMed Central

Goff, Donald C.

2017-01-01

Background Dysregulation of N-methyl D-aspartate (NMDA) receptor signaling is strongly implicated in schizophrenia. Based on the ketamine model of NMDA receptor hypoactivity, therapeutic approaches designed to maintain a sustained increase in agonist activity at the glycine site of the NMDA receptor have produced promising, although inconsistent, efficacy for negative symptoms. Methods A review of the published literature on D-cycloserine (DCS) pharmacology in animal models and in clinical studies was performed. Findings relevant to DCS effects on memory and plasticity and their potential clinical application to schizophrenia were summarized. Results Studies in animals and clinical trials in patients with anxiety disorders have demonstrated that single or intermittent dosing with DCS enhances memory consolidation. Preliminary trials in patients with schizophrenia suggest that intermittent dosing with DCS may produce persistent improvement of negative symptoms and enhance learning when combined with cognitive behavioral therapy for delusions or with cognitive remediation. The pharmacology of DCS is complex, since it acts as a “super agonist” at NMDA receptors containing GluN2C subunits and, under certain conditions, it may act as an antagonist at NMDA receptors containing GluN2B subunits. Conclusions There are preliminary findings that support a role for D-cycloserine in schizophrenia as a strategy to enhance neuroplasticity and memory. However, additional studies with DCS are needed to confirm these findings. In addition, clinical trials with positive and negative allosteric modulators with greater specificity for NMDA receptor subtypes are needed to identify the optimal strategy for enhancing neuroplasticity in schizophrenia. PMID:26915421

AVP and Glu systems interact to regulate levels of anxiety in BALB/cJ mice.

PubMed

An, Xiao-Lei; Tai, Fa-Dao

2014-07-01

Whilethe roles of glutamic acid (Glu), arginine vasopressin (AVP) and their respective receptors in anxiety have been thoroughly investigated, the effects of interactions among Glu, N-methyl-D-aspartic acid (NMDA) receptor, AVP and a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor on anxiety are still unclear. In the present study, the agonist and antagonist of the NMDA receptor and AMPA receptor, as well as the antagonist of AVP V1 receptor (V1aR) were introduced into BALB/cJ mice by intracerebroventricular microinjection, and the anxiety-like behaviors of the mice were evaluated by open field and elevated plus-maze tests. Compared with C57BL/6 mice, BALB/cJ mice displayed higher levels of anxiety-like behavior. Significant anxiolytic effects were found in the NMDA receptor antagonist (MK-801) and the AMPA receptor or V1aR antagonist (SSRI49415), as well as combinations of AVP/MK-801 and SSRI49415/DNQX. These results indicated that anxiety-like behaviors expressed in BALB/CJ mice may be due to a coordination disorder among glutamate, NMDA receptor, AMPA receptor, AVP and V1aR, resulting in the up-regulation of the NMDA receptor and V1aR and down-regulation of the AMPA receptor. However, because the AMPA receptor can execute its anxiolytic function by suppressing AVP and V1aR, we cannot exclude the possibility of the NMDA receptor being activated by AVP acting on V1aR.

Motor impairments, striatal degeneration, and altered dopamine-glutamate interplay in mice lacking PSD-95.

PubMed

Zhang, Jingping; Saur, Taixiang; Duke, Angela N; Grant, Seth G N; Platt, Donna M; Rowlett, James K; Isacson, Ole; Yao, Wei-Dong

2014-01-01

Excessive activation of the N-methyl-d-aspartate (NMDA) receptor and the neurotransmitter dopamine (DA) mediate neurotoxicity and neurodegeneration under many neurological conditions, including Huntington's disease (HD), an autosomal dominant neurodegenerative disease characterized by the preferential loss of medium spiny projection neurons (MSNs) in the striatum. PSD-95 is a major scaffolding protein in the postsynaptic density (PSD) of dendritic spines, where a classical role for PSD-95 is to stabilize glutamate receptors at sites of synaptic transmission. Our recent studies indicate that PSD-95 also interacts with the D1 DA receptor localized in spines and negatively regulates spine D1 signaling. Moreover, PSD-95 forms ternary protein complexes with D1 and NMDA receptors, and plays a role in limiting the reciprocal potentiation between both receptors from being escalated. These studies suggest a neuroprotective role for PSD-95. Here we show that mice lacking PSD-95, resulting from genetic deletion of the GK domain of PSD-95 (PSD-95-ΔGK mice), sporadically develop progressive neurological impairments characterized by hypolocomotion, limb clasping, and loss of DARPP-32-positive MSNs. Electrophysiological experiments indicated that NMDA receptors in mutant MSNs were overactive, suggested by larger, NMDA receptor-mediated miniature excitatory postsynaptic currents (EPSCs) and higher ratios of NMDA- to AMPA-mediated corticostriatal synaptic transmission. In addition, NMDA receptor currents in mutant cortical neurons were more sensitive to potentiation by the D1 receptor agonist SKF81297. Finally, repeated administration of the psychostimulant cocaine at a dose regimen not producing overt toxicity-related phenotypes in normal mice reliably converted asymptomatic mutant mice to clasping symptomatic mice. These results support the hypothesis that deletion of PSD-95 in mutant mice produces concomitant overactivation of both D1 and NMDA receptors that makes neurons more susceptible to NMDA excitotoxicity, causing neuronal damage and neurological impairments. Understanding PSD-95-dependent neuroprotective mechanisms may help elucidate processes underlying neurodegeneration in HD and other neurological disorders.

Recovery of NMDA receptor currents from MK-801 blockade is accelerated by Mg2+ and memantine under conditions of agonist exposure

PubMed Central

McKay, Sean; Bengtson, C. Peter; Bading, Hilmar; Wyllie, David J.A.; Hardingham, Giles E.

2013-01-01

MK-801 is a use-dependent NMDA receptor open channel blocker with a very slow off-rate. These properties can be exploited to ‘pre-block’ a population of NMDARs, such as synaptic ones, enabling the selective activation of a different population, such as extrasynaptic NMDARs. However, the usefulness of this approach is dependent on the stability of MK-801 blockade after washout. We have revisited this issue, and confirm that recovery of NMDAR currents from MK-801 blockade is enhanced by channel opening by NMDA, and find that it is further increased when Mg2+ is also present. In the presence of Mg2+, 50% recovery from MK-801 blockade is achieved after 10′ of 100 μM NMDA, or 30′ of 15 μM NMDA exposure. In Mg2+-free medium, NMDA-induced MK-801 dissociation was found to be much slower. Memantine, another PCP-site antagonist, could substitute for Mg2+ in accelerating the unblock of MK-801 in the presence of NMDA. This suggests a model whereby, upon dissociation from its binding site in the pore, MK-801 is able to re-bind in a process antagonized by Mg2+ or another PCP-site antagonist. Finally we show that even when all NMDARs are pre-blocked by MK-801, incubation of neurons with 100 μM NMDA in the presence of Mg2+ for 2.5 h triggers sufficient unblocking to kill >80% of neurons. We conclude that while synaptic MK-801 ‘pre-block’ protocols are useful for pharmacologically assessing synaptic vs. extrasynaptic contributions to NMDAR currents, or studying short-term effects, it is problematic to use this technique to attempt to study the effects of long-term selective extrasynaptic NMDAR activation. This article is part of the Special Issue entitled ‘Glutamate Receptor-Dependent Synaptic Plasticity’. PMID:23402996

Recovery of NMDA receptor currents from MK-801 blockade is accelerated by Mg2+ and memantine under conditions of agonist exposure.

PubMed

McKay, Sean; Bengtson, C Peter; Bading, Hilmar; Wyllie, David J A; Hardingham, Giles E

2013-11-01

MK-801 is a use-dependent NMDA receptor open channel blocker with a very slow off-rate. These properties can be exploited to 'pre-block' a population of NMDARs, such as synaptic ones, enabling the selective activation of a different population, such as extrasynaptic NMDARs. However, the usefulness of this approach is dependent on the stability of MK-801 blockade after washout. We have revisited this issue, and confirm that recovery of NMDAR currents from MK-801 blockade is enhanced by channel opening by NMDA, and find that it is further increased when Mg(2+) is also present. In the presence of Mg(2+), 50% recovery from MK-801 blockade is achieved after 10' of 100 μM NMDA, or 30' of 15 μM NMDA exposure. In Mg(2+)-free medium, NMDA-induced MK-801 dissociation was found to be much slower. Memantine, another PCP-site antagonist, could substitute for Mg(2+) in accelerating the unblock of MK-801 in the presence of NMDA. This suggests a model whereby, upon dissociation from its binding site in the pore, MK-801 is able to re-bind in a process antagonized by Mg(2+) or another PCP-site antagonist. Finally we show that even when all NMDARs are pre-blocked by MK-801, incubation of neurons with 100 μM NMDA in the presence of Mg(2+) for 2.5 h triggers sufficient unblocking to kill >80% of neurons. We conclude that while synaptic MK-801 'pre-block' protocols are useful for pharmacologically assessing synaptic vs. extrasynaptic contributions to NMDAR currents, or studying short-term effects, it is problematic to use this technique to attempt to study the effects of long-term selective extrasynaptic NMDAR activation. This article is part of the Special Issue entitled 'Glutamate Receptor-Dependent Synaptic Plasticity'. Copyright © 2013 Elsevier Ltd. All rights reserved.

Kynurenic acid analogues with improved affinity and selectivity for the glycine site on the N-methyl-D-aspartate receptor from rat brain.

PubMed

Foster, A C; Kemp, J A; Leeson, P D; Grimwood, S; Donald, A E; Marshall, G R; Priestley, T; Smith, J D; Carling, R W

1992-05-01

The glycine site on the N-methyl-D-aspartate (NMDA) subtype of receptors for the excitatory neurotransmitter glutamate is a potential target for the development of neuroprotective drugs. We report here two chemical series of glycine site antagonists derived from kynurenic acid (KYNA), with greatly improved potency and selectivity. Disubstitution with chlorine or bromine in the 5- and 7-positions of KYNA increased affinity for [3H]glycine binding sites in rat cortex/hippocampus P2 membranes, with a parallel increase of potency for antagonism of NMDA-evoked responses in the rat cortical wedge preparation. The optimal compound was 5-I,7-Cl-KYNA, with an IC50 for [3H]glycine binding of 29 nM and an apparent Kb in the cortical wedge preparation of 0.41 microM. Reduction of the right-hand ring of 5,7-diCl-KYNA reduced affinity by 10-fold, but this was restored by substitution in the 4-position with the trans-phenylamide and further improved in the trans-benzylamide. The optimal compound was the transphenylurea (L-689,560), with an IC50 of 7.4 nM and an apparent Kb of 0.13 microM. Both series of compounds displayed a high degree of selectivity for the glycine site, having IC50 values of greater than 10 microM versus radioligand binding to the glutamate recognition sites of NMDA, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), and kainate receptors and the strychnine-sensitive glycine receptor. Selectivity versus AMPA receptor-mediated responses was also apparent in the rat cortical wedge and in patch-clamp recordings of cortical neurons in culture. Experiments using [3H]dizocilpine (MK-801) binding indicated that 5,7-diBr-KYNA, 5,7-diCl-KYNA, 5-I,7-Cl-KYNA, and L-689,560 all behaved as full antagonists and were competitive with glycine. Patch-clamp recordings of cortical neurons in culture also indicated that NMDA-induced currents were antagonized by competition for the glycine site, and gave no evidence for partial agonist activity. pKi values for 5,7-diBr-KYNA and L-689,560 in these experiments were 7.2 and 7.98, respectively, similar to the affinities of these compounds in the glycine binding assay. The high affinity and selectivity of these new derivatives make them useful tools to investigate the function of the glycine site on the NMDA receptor.

Modulation of the storage of social recognition memory by neurotransmitter systems in the insular cortex.

PubMed

Cavalcante, Lorena E S; Zinn, Carolina G; Schmidt, Scheila D; Saenger, Bruna F; Ferreira, Flávia F; Furini, Cristiane R G; Myskiw, Jociane C; Izquierdo, Ivan

2017-09-15

The insular cortex (IC) receives projections from prefrontal, entorhinal and cingulate cortex, olfactory bulb and basal nuclei and has reciprocal connections with the amygdala and entorhinal cortex. These connections suggest a possible involvement in memory processes; this has been borne out by data on several behaviors. Social recognition memory (SRM) is essential to form social groups and to establish hierarchies and social and affective ties. Despite its importance, knowledge about the brain structures and the neurotransmitter mechanisms involved in its processing is still scarce. Here we study the participation of NMDA-glutamatergic, D1/D5-dopaminergic, H2-histaminergic, β-adrenergic and 5-HT 1A -serotoninergic receptors of the IC in the consolidation of SRM. Male Wistar rats received intra-IC infusions of substances acting on these receptors immediately after the sample phase of a social discrimination task and 24h later were exposed to a 5-min retention test. The intra-IC infusion of antagonists of D1/D5, β-adrenergic or 5-HT 1A receptors immediately after the sample phase impaired the consolidation of SRM. These effects were blocked by the concomitant intra-IC infusion of agonists of these receptors. Antagonists and agonists of NMDA and H2 receptors had no effect on SRM. The results suggest that the dopaminergic D1/D5, β-adrenergic and serotonergic 5-HT 1A receptors in the IC, but not glutamatergic NMDA and the histaminergic H2 receptors, participate in the consolidation of SRM in the IC. Copyright © 2017 Elsevier B.V. All rights reserved.

A novel principle for partial agonism of liver X receptor ligands. Competitive recruitment of activators and repressors.

PubMed

Albers, Michael; Blume, Beatrix; Schlueter, Thomas; Wright, Matthew B; Kober, Ingo; Kremoser, Claus; Deuschle, Ulrich; Koegl, Manfred

2006-02-24

Partial, selective activation of nuclear receptors is a central issue in molecular endocrinology but only partly understood. Using LXRs as an example, we show here that purely agonistic ligands can be clearly and quantitatively differentiated from partial agonists by the cofactor interactions they induce. Although a pure agonist induces a conformation that is incompatible with the binding of repressors, partial agonists such as GW3965 induce a state where the interaction not only with coactivators, but also corepressors is clearly enhanced over the unliganded state. The activities of the natural ligand 22(R)-hydroxycholesterol and of a novel quinazolinone ligand, LN6500 can be further differentiated from GW3965 and T0901317 by their weaker induction of coactivator binding. Using biochemical and cell-based assays, we show that the natural ligand of LXR is a comparably weak partial agonist. As predicted, we find that a change in the coactivator to corepressor ratio in the cell will affect NCoR recruiting compounds more dramatically than NCoR-dissociating compounds. Our data show how competitive binding of coactivators and corepressors can explain the tissue-specific behavior of partial agonists and open up new routes to a rational design of partial agonists for LXRs.

Partial agonists for α4β2 nicotinic receptors stimulate dopaminergic neuron firing with relatively enhanced maximal effects

PubMed Central

Chen, Ying; Broad, Lisa M; Phillips, Keith G; Zwart, Ruud

2012-01-01

BACKGROUND AND PURPOSE Partial agonists selective for α4β2 nicotinic ACh receptors have been developed for smoking cessation as they induce weak activation of native α4β2* receptors and inhibit effect of nicotine. However, it is unclear whether at brain functions there is an existence of receptor reserve that allows weak receptor activation to induce maximum physiological effects. We assessed the extent of α4β2 partial agonist-induced increase of firing rate in dopaminergic neurons and evaluated the influence of receptor reserve. EXPERIMENTAL APPROACH The relative maximal effects and potencies of six nicotinic agonists were assessed on recombinant human α4β2 and α7 receptors expressed in mammalian cell lines by measuring calcium influx. Agonist-induced increase of the spontaneous firing rate of dopaminergic neurons was recorded using microelectrodes in the ventral tegmental area of rat brain slices. KEY RESULTS All α4β2 partial and full agonists increased the firing rate concentration-dependently. Their sensitivity to subtype-selective antagonists showed predominant activation of native α4β2* receptors. However, partial agonists with relative maximal effects as low as 33% on α4β2 receptors maximally increased the firing rate and induced additional depolarization block of firing, demonstrating that partial activation of receptors caused the maximum increase in firing rate in the presence of a receptor reserve. CONCLUSIONS AND IMPLICATIONS Partial α4β2 agonists induced relatively enhanced effects on the firing rate of dopaminergic neurons, and the effect was mainly attributed to the existence of native α4β2* receptor reserve. The results have implications in the understanding of physiological effects and therapeutic efficacies of α4β2 partial agonists. PMID:21838750

5-HT2C Agonists Modulate Schizophrenia-Like Behaviors in Mice.

PubMed

Pogorelov, Vladimir M; Rodriguiz, Ramona M; Cheng, Jianjun; Huang, Mei; Schmerberg, Claire M; Meltzer, Herbert Y; Roth, Bryan L; Kozikowski, Alan P; Wetsel, William C

2017-10-01

All FDA-approved antipsychotic drugs (APDs) target primarily dopamine D 2 or serotonin (5-HT 2A ) receptors, or both; however, these medications are not universally effective, they may produce undesirable side effects, and provide only partial amelioration of negative and cognitive symptoms. The heterogeneity of pharmacological responses in schizophrenic patients suggests that additional drug targets may be effective in improving aspects of this syndrome. Recent evidence suggests that 5-HT 2C receptors may be a promising target for schizophrenia since their activation reduces mesolimbic nigrostriatal dopamine release (which conveys antipsychotic action), they are expressed almost exclusively in CNS, and have weight-loss-promoting capabilities. A difficulty in developing 5-HT 2C agonists is that most ligands also possess 5-HT 2B and/or 5-HT 2A activities. We have developed selective 5-HT 2C ligands and herein describe their preclinical effectiveness for treating schizophrenia-like behaviors. JJ-3-45, JJ-3-42, and JJ-5-34 reduced amphetamine-stimulated hyperlocomotion, restored amphetamine-disrupted prepulse inhibition, improved social behavior, and novel object recognition memory in NMDA receptor hypofunctioning NR1-knockdown mice, and were essentially devoid of catalepsy. However, they decreased motivation in a breakpoint assay and did not promote reversal learning in MK-801-treated mice. Somewhat similar effects were observed with lorcaserin, a 5-HT 2C agonist with potent 5-HT 2B and 5-HT 2A agonist activities, which is approved for treating obesity. Microdialysis studies revealed that both JJ-3-42 and lorcaserin reduced dopamine efflux in the infralimbic cortex, while only JJ-3-42 decreased it in striatum. Collectively, these results provide additional evidence that 5-HT 2C receptors are suitable drug targets with fewer side effects, greater therapeutic selectivity, and enhanced efficacy for treating schizophrenia and related disorders than current APDs.

Single-Molecule Patch-Clamp FRET Anisotropy Microscopy Studies of NMDA Receptor Ion Channel Activation and Deactivation under Agonist Ligand Binding in Living Cells.

PubMed

Sasmal, Dibyendu Kumar; Yadav, Rajeev; Lu, H Peter

2016-07-20

N-methyl-d-aspartate (NMDA) receptor ion channel is activated by the binding of two pairs of glycine and glutamate along with the application of action potential. Binding and unbinding of ligands changes its conformation that plays a critical role in the open-close activities of NMDA receptor. Conformation states and their dynamics due to ligand binding are extremely difficult to characterize either by conventional ensemble experiments or single-channel electrophysiology method. Here we report the development of a new correlated technical approach, single-molecule patch-clamp FRET anisotropy imaging and demonstrate by probing the dynamics of NMDA receptor ion channel and kinetics of glycine binding with its ligand binding domain. Experimentally determined kinetics of ligand binding with receptor is further verified by computational modeling. Single-channel patch-clamp and four-channel fluorescence measurement are recorded simultaneously to get correlation among electrical on and off states, optically determined conformational open and closed states by FRET, and binding-unbinding states of the glycine ligand by anisotropy measurement at the ligand binding domain of GluN1 subunit. This method has the ability to detect the intermediate states in addition to electrical on and off states. Based on our experimental results, we have proposed that NMDA receptor gating goes through at least one electrically intermediate off state, a desensitized state, when ligands remain bound at the ligand binding domain with the conformation similar to the fully open state.

NMDA receptor function and NMDA receptor-dependent phosphorylation of huntingtin is altered by the endocytic protein HIP1.

PubMed

Metzler, Martina; Gan, Lu; Wong, Tak Pan; Liu, Lidong; Helm, Jeffrey; Liu, Lili; Georgiou, John; Wang, Yushan; Bissada, Nagat; Cheng, Kevin; Roder, John C; Wang, Yu Tian; Hayden, Michael R

2007-02-28

Huntingtin-interacting protein 1 (HIP1) is an endocytic adaptor protein that plays a role in clathrin-mediated endocytosis and the ligand-induced internalization of AMPA receptors (AMPARs) (Metzler et al., 2003). In the present study, we investigated the role of HIP1 in NMDA receptor (NMDAR) function by analyzing NMDA-dependent transport and NMDA-induced excitotoxicity in neurons from HIP1-/- mice. HIP1 colocalizes with NMDARs in hippocampal and cortical neurons and affinity purifies with NMDARs by GST (glutathione S-transferase) pull down and coimmunoprecipitation. A profound decrease in NMDA-induced AMPAR internalization of 75% occurs in neurons from HIP1-/- mice compared with wild type, using a quantitative single-cell-based internalization assay. This defect in NMDA-dependent removal of surface AMPARs is in agreement with the observed defect in long-term depression induction in hippocampal brain slices of HIP1-/- mice and supports a role of HIP1 in AMPAR internalization in vivo. HIP1-/- neurons are partially protected from NMDA-induced excitotoxicity as assessed by LDH (lactate dehydrogenase) release, TUNEL (terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick end labeling) and caspase-3 activation assays, which points to a role of HIP1 in NMDA-induced cell death. Interestingly, phosphorylation of Akt and its substrate huntingtin (htt) decreases during NMDA-induced excitotoxicity by 48 and 31%, respectively. This decrease is significantly modulated by HIP1, resulting in 94 and 48% changes in P-Akt and P-htt levels in HIP1-/- neurons, respectively. In summary, we have shown that HIP1 influences important NMDAR functions and that both HIP1 and htt participate in NMDA-induced cell death. These findings may provide novel insights into the cellular mechanisms underlying enhanced NMDA-induced excitotoxicity in Huntington's disease.

Emerging drugs for neuropathic pain.

PubMed

Gilron, Ian; Dickenson, Anthony H

2014-09-01

Neuropathic pain is a costly and disabling condition, which affects up to 8% of the population. Available therapies often provide incomplete pain relief and treatment-related side effects are common. Preclinical neuropathic pain models have facilitated identification of several promising targets, which have progressed to human clinical phases of evaluation. A systematic database search yielded 25 new molecular entities with specified pharmacological mechanisms that have reached Phase II or III clinical trials. These include calcium channel antagonists, vanilloid receptor antagonists, potassium channel agonists, NMDA antagonists, novel opioid receptor agonists, histamine H3 receptor antagonists, a novel sodium channel antagonist, serotonin modulators, a novel acetylcholine receptor agonist, α-2b adrenoreceptor agonist, cannabinoid CB2 receptor agonist, nitric oxide synthase inhibitor, orexin receptor antagonist, angiotensin II 2 antagonist, imidazoline I2 receptor agonist, apoptosis inhibitor and fatty acid amide hydrolase inhibitor. Although the diversity of pharmacological mechanisms of interest emphasise the complexity of neuropathic pain transmission, the considerable number of agents under development reflect a continued enthusiasm in drug development for neuropathic pain. Ongoing enhancements in methodology of both preclinical and clinical research and closer translation in both directions are expected to more efficiently identify new agents, which will improve the management of neuropathic pain.

The N-methyl-D-aspartate-evoked cytoplasmic calcium increase in adult rat dorsal root ganglion neuronal somata was potentiated by substance P pretreatment in a protein kinase C-dependent manner.

PubMed

Castillo, C; Norcini, M; Baquero-Buitrago, J; Levacic, D; Medina, R; Montoya-Gacharna, J V; Blanck, T J J; Dubois, M; Recio-Pinto, E

2011-03-17

The involvement of substance P (SP) in neuronal sensitization through the activation of the neurokinin-1-receptor (NK1r) in postsynaptic dorsal horn neurons has been well established. In contrast, the role of SP and NK1r in primary sensory dorsal root ganglion (DRG) neurons, in particular in the soma, is not well understood. In this study, we evaluated whether SP modulated the NMDA-evoked transient increase in cytoplasmic Ca2+ ([Ca2+]cyt) in the soma of dissociated adult DRG neurons. Cultures were treated with nerve growth factor (NGF), prostaglandin E2 (PGE2) or both NGF+PGE2. Treatment with NGF+PGE2 increased the percentage of N-methyl-D-aspartate (NMDA) responsive neurons. There was no correlation between the percentage of NMDA responsive neurons and the level of expression of the NR1 and NR2B subunits of the NMDA receptor or of the NK1r. Pretreatment with SP did not alter the percentage of NMDA responsive neurons; while it potentiated the NMDA-evoked [Ca2+]cyt transient by increasing its magnitude and by prolonging the period during which small- and some medium-sized neurons remained NMDA responsive. The SP-mediated potentiation was blocked by the SP-antagonist ([D-Pro4, D-Trp7,9]-SP (4-11)) and by the protein kinase C (PKC) blocker bisindolylmaleimide I (BIM); and correlated with the phosphorylation of PKCε. The Nk1r agonist [Sar9, Met(O2)11]-SP (SarMet-SP) also potentiated the NMDA-evoked [Ca2+]cyt transient. Exposure to SP or SarMet-SP produced a rapid increase in the labeling of phosphorylated-PKCε. In none of the conditions we detected phosphorylation of the NR2B subunit at Ser-1303. Phosphorylation of the NR2B subunit at Tyr1472 was enhanced to a similar extent in cells exposed to NMDA, SP or NMDA+SP, and that enhancement was blocked by BIM. Our findings suggest that NGF and PGE2 may contribute to the injury-evoked sensitization of DRG neurons in part by enhancing their NMDA-evoked [Ca2+]cyt transient in all sized DRG neurons; and that SP may further contribute to the DRG sensitization by enhancing and prolonging the NMDA-evoked increase in [Ca2+]cyt in small- and medium-sized DRG neurons. Copyright © 2011 IBRO. Published by Elsevier Ltd. All rights reserved.

Quinolinic acid induces neuritogenesis in SH-SY5Y neuroblastoma cells independently of NMDA receptor activation.

PubMed

Hernandez-Martinez, Juan-Manuel; Forrest, Caroline M; Darlington, L Gail; Smith, Robert A; Stone, Trevor W

2017-03-01

Glutamate and nicotinamide adenine dinucleotide (NAD + ) have been implicated in neuronal development and several types of cancer. The kynurenine pathway of tryptophan metabolism includes quinolinic acid (QA) which is both a selective agonist at N-methyl-D-aspartate (NMDA) receptors and also a precursor for the formation of NAD + . The effect of QA on cell survival and differentiation has therefore been examined on SH-SY5Y human neuroblastoma cells. Retinoic acid (RA, 10 μm) induced differentiation of SH-SY5Y cells into a neuronal phenotype showing neurite growth. QA (50-150 nm) also caused a concentration-dependent increase in the neurite/soma ratio, indicating differentiation. Both RA and QA increased expression of the neuronal marker β3-tubulin in whole-cell homogenates and in the neuritic fraction assessed using a neurite outgrowth assay. Expression of the neuronal proliferation marker doublecortin revealed that, unlike RA, QA did not decrease the number of mitotic cells. QA-induced neuritogenesis coincided with an increase in the generation of reactive oxygen species. Neuritogenesis was prevented by diphenylene-iodonium (an inhibitor of NADPH oxidase) and superoxide dismutase, supporting the involvement of reactive oxygen species. NMDA itself did not promote neuritogenesis and the NMDA antagonist dizocilpine (MK-801) did not prevent quinolinate-induced neuritogenesis, indicating that the effects of QA were independent of NMDA receptors. Nicotinamide caused a significant increase in the neurite/soma ratio and the expression of β3-tubulin in the neuritic fraction. Taken together, these results suggest that QA induces neuritogenesis by promoting oxidizing conditions and affecting the availability of NAD + , independently of NMDA receptors. © 2016 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Periaqueductal gray glutamatergic, cannabinoid and vanilloid receptor interplay in defensive behavior and aversive memory formation.

PubMed

Back, Franklin P; Carobrez, Antonio P

2018-06-01

Stimulation of the midbrain periaqueductal gray matter (PAG) in humans elicits sensations of fear and impending terror, and mediates predator defensive responses in rodents. In rats, pharmacological stimulation of the dorsolateral portion of the PAG (dlPAG) with N-Methyl-d-Aspartate (NMDA) induces aversive conditioning that acts as an unconditioned stimulus (US). In the present work, we investigated the interplay between the vanilloid TRPV1 and cannabinoid CB1 receptors in the NMDA-dlPAG defensive response and in subsequent aversive learning. Rats were subjected to dlPAG NMDA infusion in an olfactory conditioned stimulus (CS) task allowing the evaluation of immediate and long-term defensive behavioral responses during CS presentation. The results indicated that an intermediate dose of NMDA (50 pmol) induced both immediate and long-term effects. A sub-effective dose of NMDA (25 pmol) was potentiated by the TRPV1 receptor agonist capsaicin (CAP, 1 nmol) and the CB1 receptor antagonist, AM251 (200 pmol). CAP (10 nmol) or the combination of CAP (1 nmol) and AM251 (200 pmol) induced long-term effects without increasing immediate defensive responses. The glutamate release inhibitor riluzole (2 or 4 nmol) and the AMPA/kainate receptor antagonist DNQX (2 or 4 nmol) potentiated the immediate effects but blocked the long-term effects. The results showed that immediate defensive responses rely on NMDA receptors, and aversive learning on the fine-tuning of TRPV1, CB1, metabotropic glutamate and AMPA receptors located in pre- and postsynaptic membranes. In conclusion, the activity of the dlPAG determines core affective aspects of aversive memory formation controlled by local TRPV1/CB1 balance. Copyright © 2018 Elsevier Ltd. All rights reserved.

Iron Mediates N-Methyl-d-aspartate Receptor-dependent Stimulation of Calcium-induced Pathways and Hippocampal Synaptic Plasticity*

PubMed Central

Muñoz, Pablo; Humeres, Alexis; Elgueta, Claudio; Kirkwood, Alfredo; Hidalgo, Cecilia; Núñez, Marco T.

2011-01-01

Iron deficiency hinders hippocampus-dependent learning processes and impairs cognitive performance, but current knowledge on the molecular mechanisms underlying the unique role of iron in neuronal function is sparse. Here, we investigated the participation of iron on calcium signal generation and ERK1/2 stimulation induced by the glutamate agonist N-methyl-d-aspartate (NMDA), and the effects of iron addition/chelation on hippocampal basal synaptic transmission and long-term potentiation (LTP). Addition of NMDA to primary hippocampal cultures elicited persistent calcium signals that required functional NMDA receptors and were independent of calcium influx through L-type calcium channels or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors; NMDA also promoted ERK1/2 phosphorylation and nuclear translocation. Iron chelation with desferrioxamine or inhibition of ryanodine receptor (RyR)-mediated calcium release with ryanodine-reduced calcium signal duration and prevented NMDA-induced ERK1/2 activation. Iron addition to hippocampal neurons readily increased the intracellular labile iron pool and stimulated reactive oxygen species production; the antioxidant N-acetylcysteine or the hydroxyl radical trapper MCI-186 prevented these responses. Iron addition to primary hippocampal cultures kept in calcium-free medium elicited calcium signals and stimulated ERK1/2 phosphorylation; RyR inhibition abolished these effects. Iron chelation decreased basal synaptic transmission in hippocampal slices, inhibited iron-induced synaptic stimulation, and impaired sustained LTP in hippocampal CA1 neurons induced by strong stimulation. In contrast, iron addition facilitated sustained LTP induction after suboptimal tetanic stimulation. Together, these results suggest that hippocampal neurons require iron to generate RyR-mediated calcium signals after NMDA receptor stimulation, which in turn promotes ERK1/2 activation, an essential step of sustained LTP. PMID:21296883

Involvement of N-methyl-d-aspartate receptors in the antidepressant-like effect of 5-hydroxytryptamine 3 antagonists in mouse forced swimming test and tail suspension test.

PubMed

Kordjazy, Nastaran; Haj-Mirzaian, Arya; Amiri, Shayan; Ostadhadi, Sattar; Amini-Khoei, Hossein; Dehpour, Ahmad Reza

2016-02-01

Recent evidence indicates that 5-hydroxytryptamine 3 (5-HT3) antagonists such as ondansetron and tropisetron exert positive behavioral effects in animal models of depression. Due to the ionotropic nature of 5-HT3 and N-methyl-d-aspartate (NMDA) receptors, plus their contribution to the pathophysiology of depression, we investigated the possible role of NMDA receptors in the antidepressant-like effect of 5-HT3 receptor antagonists in male mice. In order to evaluate the animals' behavior in response to different treatments, we performed open-field test (OFT), forced swimming test (FST), and tail-suspension test (TST), which are considered as valid tasks for measuring locomotor activity and depressive-like behaviors in mice. Our data revealed that intraperitoneal (i.p.) administration of tropisetron (5, 10, and 30mg/kg) and ondansetron (0.01, and 0.1μg/kg) significantly decreased the immobility time in FST and TST. Also, co-administration of subeffective doses of tropisetron (1mg/kg, i.p.) or ondansetron (0.001μg/kg, i.p.) with subeffective doses of NMDA receptor antagonists, ketamine (1mg/kg, i.p.), MK-801 (0.05mg/kg, i.p.) and magnesium sulfate (10mg/kg, i.p.) resulted in a reduced immobility time both in FST and TST. The subeffective dose of NMDA (NMDA receptor agonist, 75mg/kg, i.p.) abolished the effects of 5-HT3 antagonists in FST and TST, further supporting the presumed interaction between 5-HT3 and NMDA receptors. These treatments did not affect the locomotor behavior of animals in OFT. Finally, the results of our study suggest that the positive effects of 5-HT3 antagonists on the coping behavior of mice in FST and TST are at least partly mediated through NMDA receptors participation. Copyright © 2015 Elsevier Inc. All rights reserved.

Discussion of Bogerts' temporolimbic system theory of paranoid schizophrenia.

PubMed

Olney, J W; Farber, N B

1997-01-01

Olney and Farber present their work with N-methyl-D-aspartate (NMDA) antagonists, which are psychotogens, and propose that the structural changes described by Bogerts could be accounted for by a two-stage process. The first stage of the process would occur early in life and would culminate in the selective loss of NMDA-receptor bearing gamma-aminobutyric acid (GABA)ergic neurons and thus render the brain into a NMDA receptor hypofunctional (NRH) state. Such a loss would set the foundation for the second stage in which the neural circuits that have been altered by the loss of these GABAergic interneurons would become activated in late adolescence but would be dysfunctional. Dysfunction of this circuit would lead to the psychopathology of schizophrenia and potentially, if severe enough, to neuronal degeneration. Thus, the changes described by Bogerts could originate partially in early life and partially in adulthood. Based on their animal model, the authors suggest studies that should be carried out in humans.

Microinjection of l-glutamate into the nucleus ambiguus partially inhibits gastric motility through the NMDA receptor - nitric oxide pathway.

PubMed

Sun, Hong-Zhao; Zhao, Shu-Zhen; Ai, Hong-Bin

2014-06-01

We have previously reported that both l-glutamate (l-Glu) and nitric oxide (NO) modulate gastric motility in the nucleus ambiguus (NA). The aim of this study is to explore the potential correlation between the l-Glu and NO. A latex balloon connected to a pressure transducer was inserted into the pylorus through the fundus of anesthetized male Wistar rats to continuously record changes in gastric smooth muscle contractile curves. Pretreatment with the NO-synthase inhibitor N-nitro-l-arginine methylester (l-NAME) did not completely abolish the inhibitory effect of l-Glu on gastric motility, but intravenous injection of the ganglionic blocker hexamethonium bromide (Hb) did. By using a specific N-methyl-d-aspartic acid (NMDA) receptor antagonist, we blocked the inhibitory effect of the NO-donor sodium nitroprusside (SNP) on gastric motility. These results suggest that microinjections of l-Glu into the NA inhibits gastric motility by activating the cholinergic preganglionic neurons, partially through the NMDA receptor - NO pathway.

Autistic-like social behaviour in Shank2-mutant mice improved by restoring NMDA receptor function.

PubMed

Won, Hyejung; Lee, Hye-Ryeon; Gee, Heon Yung; Mah, Won; Kim, Jae-Ick; Lee, Jiseok; Ha, Seungmin; Chung, Changuk; Jung, Eun Suk; Cho, Yi Sul; Park, Sae-Geun; Lee, Jung-Soo; Lee, Kyungmin; Kim, Daesoo; Bae, Yong Chul; Kaang, Bong-Kiun; Lee, Min Goo; Kim, Eunjoon

2012-06-13

Autism spectrum disorder (ASD) is a group of conditions characterized by impaired social interaction and communication, and restricted and repetitive behaviours. ASD is a highly heritable disorder involving various genetic determinants. Shank2 (also known as ProSAP1) is a multi-domain scaffolding protein and signalling adaptor enriched at excitatory neuronal synapses, and mutations in the human SHANK2 gene have recently been associated with ASD and intellectual disability. Although ASD-associated genes are being increasingly identified and studied using various approaches, including mouse genetics, further efforts are required to delineate important causal mechanisms with the potential for therapeutic application. Here we show that Shank2-mutant (Shank2(-/-)) mice carrying a mutation identical to the ASD-associated microdeletion in the human SHANK2 gene exhibit ASD-like behaviours including reduced social interaction, reduced social communication by ultrasonic vocalizations, and repetitive jumping. These mice show a marked decrease in NMDA (N-methyl-D-aspartate) glutamate receptor (NMDAR) function. Direct stimulation of NMDARs with D-cycloserine, a partial agonist of NMDARs, normalizes NMDAR function and improves social interaction in Shank2(-/-) mice. Furthermore, treatment of Shank2(-/-) mice with a positive allosteric modulator of metabotropic glutamate receptor 5 (mGluR5), which enhances NMDAR function via mGluR5 activation, also normalizes NMDAR function and markedly enhances social interaction. These results suggest that reduced NMDAR function may contribute to the development of ASD-like phenotypes in Shank2(-/-) mice, and mGluR modulation of NMDARs offers a potential strategy to treat ASD.

Novel Functional Properties of Drosophila CNS Glutamate Receptors

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

Li, Yan; Dharkar, Poorva; Han, Tae-Hee

Phylogenetic analysis reveals AMPA, kainate, and NMDA receptor families in insect genomes, suggesting conserved functional properties corresponding to their vertebrate counterparts. However, heterologous expression of the Drosophila kainate receptor DKaiR1D and the AMPA receptor DGluR1A revealed novel ligand selectivity at odds with the classification used for vertebrate glutamate receptor ion channels (iGluRs). DKaiR1D forms a rapidly activating and desensitizing receptor that is inhibited by both NMDA and the NMDA receptor antagonist AP5; crystallization of the KaiR1D ligand-binding domain reveals that these ligands stabilize open cleft conformations, explaining their action as antagonists. Surprisingly, the AMPA receptor DGluR1A shows weak activation bymore » its namesake agonist AMPA and also by quisqualate. Crystallization of the DGluR1A ligand-binding domain reveals amino acid exchanges that interfere with binding of these ligands. The unexpected ligand-binding profiles of insect iGluRs allows classical tools to be used in novel approaches for the study of synaptic regulation.« less

P2X7, NMDA and BDNF receptors converge on GSK3 phosphorylation and cooperate to promote survival in cerebellar granule neurons.

PubMed

Ortega, Felipe; Pérez-Sen, Raquel; Morente, Verónica; Delicado, Esmerilda G; Miras-Portugal, Maria Teresa

2010-05-01

Glycogen synthase kinase-3 (GSK3) is a key player in the regulation of neuronal survival. Herein, we report evidence of an interaction between P2X7 receptors with NMDA and BDNF receptors at the level of GSK3 signalling and neuroprotection. The activation of these receptors in granule neurons led to a sustained pattern of GSK3 phosphorylation that was mainly PKC-dependent. BDNF was the most potent at inducing GSK3 phosphorylation, which was also dependent on PI3K. The P2X7 agonist, BzATP, exhibited additive effects with both NMDA and BDNF to rescue granule neurons from cell death induced by PI3K inhibition. This survival effect was mediated by the PKC-dependent GSK3 pathway. In addition, ERK1/2 proteins were also involved in BDNF protective effect. These results show the function of ATP in amplifying neuroprotective actions of glutamate and neurotrophins, and support the role of GSK3 as an important convergence point for these survival promoting factors in granule neurons.

Novel Functional Properties of Drosophila CNS Glutamate Receptors.

PubMed

Li, Yan; Dharkar, Poorva; Han, Tae-Hee; Serpe, Mihaela; Lee, Chi-Hon; Mayer, Mark L

2016-12-07

Phylogenetic analysis reveals AMPA, kainate, and NMDA receptor families in insect genomes, suggesting conserved functional properties corresponding to their vertebrate counterparts. However, heterologous expression of the Drosophila kainate receptor DKaiR1D and the AMPA receptor DGluR1A revealed novel ligand selectivity at odds with the classification used for vertebrate glutamate receptor ion channels (iGluRs). DKaiR1D forms a rapidly activating and desensitizing receptor that is inhibited by both NMDA and the NMDA receptor antagonist AP5; crystallization of the KaiR1D ligand-binding domain reveals that these ligands stabilize open cleft conformations, explaining their action as antagonists. Surprisingly, the AMPA receptor DGluR1A shows weak activation by its namesake agonist AMPA and also by quisqualate. Crystallization of the DGluR1A ligand-binding domain reveals amino acid exchanges that interfere with binding of these ligands. The unexpected ligand-binding profiles of insect iGluRs allows classical tools to be used in novel approaches for the study of synaptic regulation. VIDEO ABSTRACT. Published by Elsevier Inc.

Blonanserin ameliorates phencyclidine-induced visual-recognition memory deficits: the complex mechanism of blonanserin action involving D₃-5-HT₂A and D₁-NMDA receptors in the mPFC.

PubMed

Hida, Hirotake; Mouri, Akihiro; Mori, Kentaro; Matsumoto, Yurie; Seki, Takeshi; Taniguchi, Masayuki; Yamada, Kiyofumi; Iwamoto, Kunihiro; Ozaki, Norio; Nabeshima, Toshitaka; Noda, Yukihiro

2015-02-01

Blonanserin differs from currently used serotonin 5-HT₂A/dopamine-D₂ receptor antagonists in that it exhibits higher affinity for dopamine-D₂/₃ receptors than for serotonin 5-HT₂A receptors. We investigated the involvement of dopamine-D₃ receptors in the effects of blonanserin on cognitive impairment in an animal model of schizophrenia. We also sought to elucidate the molecular mechanism underlying this involvement. Blonanserin, as well as olanzapine, significantly ameliorated phencyclidine (PCP)-induced impairment of visual-recognition memory, as demonstrated by the novel-object recognition test (NORT) and increased extracellular dopamine levels in the medial prefrontal cortex (mPFC). With blonanserin, both of these effects were antagonized by DOI (a serotonin 5-HT₂A receptor agonist) and 7-OH-DPAT (a dopamine-D₃ receptor agonist), whereas the effects of olanzapine were antagonized by DOI but not by 7-OH-DPAT. The ameliorating effect was also antagonized by SCH23390 (a dopamine-D₁ receptor antagonist) and H-89 (a protein kinase A (PKA) inhibitor). Blonanserin significantly remediated the decrease in phosphorylation levels of PKA at Thr(197) and of NR1 (an essential subunit of N-methyl-D-aspartate (NMDA) receptors) at Ser(897) by PKA in the mPFC after a NORT training session in the PCP-administered mice. There were no differences in the levels of NR1 phosphorylated at Ser(896) by PKC in any group. These results suggest that the ameliorating effect of blonanserin on PCP-induced cognitive impairment is associated with indirect functional stimulation of the dopamine-D₁-PKA-NMDA receptor pathway following augmentation of dopaminergic neurotransmission due to inhibition of both dopamine-D₃ and serotonin 5-HT₂A receptors in the mPFC.

Rational design of orally-active, pyrrolidine-based progesterone receptor partial agonists

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

Thompson, Scott K.; Washburn, David G.; Frazee, James S.

2010-09-03

Using the X-ray crystal structure of an amide-based progesterone receptor (PR) partial agonist bound to the PR ligand binding domain, a novel PR partial agonist class containing a pyrrolidine ring was designed. Members of this class of N-alkylpyrrolidines demonstrate potent and highly selective partial agonism of the progesterone receptor, and one of these analogs was shown to be efficacious upon oral dosing in the OVX rat model of estrogen opposition.

Glycine Transporters and Their Inhibitors

NASA Astrophysics Data System (ADS)

Gilfillan, Robert; Kerr, Jennifer; Walker, Glenn; Wishart, Grant

Glycine plays a ubiquitous role in many biological processes. In the central nervous system it serves as an important neurotransmitter acting as an agonist at strychnine-sensitive glycine receptors and as an essential co-agonist with glutamate at the NMDA receptor complex. Control of glycine concentrations in the vicinity of these receptors is mediated by the specific glycine transporters, GlyT1 and GlyT2. Inhibition of these transporters has been postulated to be of potential benefit in several therapeutic indications including schizophrenia and pain. In this review we discuss our current knowledge of glycine transporters and focus on recent advances in the medicinal chemistry of GlyT1 and GlyT2 inhibitors.

SR2067 reveals a unique kinetic and structural signature for PPARγ partial agonism

DOE PAGES

van Marrewijk, Laura M.; Polyak, Steven W.; Hijnen, Marcel; ...

2015-11-18

Here, synthetic full agonists of PPARγ have been prescribed for the treatment of diabetes due to their ability to regulate glucose homeostasis and insulin sensitization. While the use of full agonists of PPARγ has been hampered due to severe side effects, partial agonists have shown promise due to their decreased incidence of such side effects in preclinical models. No kinetic information has been forthcoming in regard to the mechanism of full versus partial agonism of PPARγ to date. In this paper, we describe the discovery of a partial agonist, SR2067. A co-crystal structure obtained at 2.2 Å resolution demonstrates thatmore » interactions with the β-sheet are driven exclusively via hydrophobic interactions mediated through a naphthalene group, an observation that is unique from other partial agonists. Finally, surface plasmon resonance revealed that SR2067 binds to the receptor with higher affinity (K D = 513 nM) as compared to that of full agonist rosiglitazone, yet it has a much slower off rate compared to that of rosiglitazone.« less

PPARγ partial agonist GQ-16 strongly represses a subset of genes in 3T3-L1 adipocytes

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

Milton, Flora Aparecida; Genomic Medicine, Houston Methodist Research Institute, Houston, TX; Cvoro, Aleksandra

Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor gamma (PPARγ) agonists that improve insulin resistance but trigger side effects such as weight gain, edema, congestive heart failure and bone loss. GQ-16 is a PPARγ partial agonist that improves glucose tolerance and insulin sensitivity in mouse models of obesity and diabetes without inducing weight gain or edema. It is not clear whether GQ-16 acts as a partial agonist at all PPARγ target genes, or whether it displays gene-selective actions. To determine how GQ-16 influences PPARγ activity on a gene by gene basis, we compared effects of rosiglitazone (Rosi) and GQ-16 in mature 3T3-L1more » adipocytes using microarray and qRT-PCR. Rosi changed expression of 1156 genes in 3T3-L1, but GQ-16 only changed 89 genes. GQ-16 generally showed weak effects upon Rosi induced genes, consistent with partial agonist actions, but a subset of modestly Rosi induced and strongly repressed genes displayed disproportionately strong GQ-16 responses. PPARγ partial agonists MLR24 and SR1664 also exhibit disproportionately strong effects on transcriptional repression. We conclude that GQ-16 displays a continuum of weak partial agonist effects but efficiently represses some negatively regulated PPARγ responsive genes. Strong repressive effects could contribute to physiologic actions of GQ-16. - Highlights: • GQ-16 is an insulin sensitizing PPARγ ligand with reduced harmful side effects. • GQ-16 displays a continuum of weak partial agonist activities at PPARγ-induced genes. • GQ-16 exerts strong repressive effects at a subset of genes. • These inhibitor actions should be evaluated in models of adipose tissue inflammation.« less

A hypothalamic digoxin-mediated model for autism.

PubMed

Kurup, Ravi Kumar; Kurup, Parameswara Achutha

2003-11-01

The isoprenoid pathway and its metabolites--digoxin, dolichol, and ubiquinone--were assessed in autism. The isoprenoid pathway and digoxin status was also studied for comparison in individuals of differing hemispheric dominance to determine the role of cerebral dominance in the genesis of autism. There was an upregulation of the isoprenoid pathway as evidenced by elevated HMG CoA reductase activity in autism. Digoxin, an endogenous Na+-K+ ATPase inhibitor secreted by the hypothalamus, was found to be elevated and RBC membrane Na+-K+ ATPase activity was found to be reduced in autism. Membrane Na+-K+ ATPase inhibition can result in increased intracellular Ca2+ and reduced magnesium levels. Hypothalamic digoxin can modulate conscious and subliminal perception and its dysfunction may lead to autism. Digoxin can also preferentially upregulate tryptophan transport over tyrosine resulting in increased levels of depolarizing tryptophan catabolites--serotonin, quinolinic acid (NMDA agonist), strychnine (blocks glycinergic inhibitory transmission), and nicotine (promotes dopamine release) and decreased levels of hyperpolarizing tyrosine catabolites--dopamine, noradrenaline, and morphine--contributing to membrane Na+-K+ ATPase inhibition. Increased nicotine levels can produce increased dopaminergic transmission in the presence of low dopamine levels. NMDA excitotoxicity could result from hypomagnesemia induced by membrane Na+-K+ ATPase inhibition and quinolinic acid, an NMDA agonist acting on the NMDA receptor. Hypomagnesemia and increased dolichol level can affect glycoconjugate metabolism and membranogenesis leading on to disordered synaptic connectivity in the limbic allocortex and defective presentation of viral antigens and neuronal antigens contributing to autoimmunity and viral persistence important in the pathogenesis. Membrane Na+-K+ ATPase inhibition can produce immune activation, a component of autoimmunity. Mitochondrial dysfunction consequent to altered calcium/magnesium ratios and reduced ubiquinone levels can result in increased free radical generation and reduced free radical scavenging and defective apoptosis leading to abnormal synaptogenesis. Autism can thus be considered a syndrome of hypothalamic digoxin hypersecretion consequent to an upregulated isoprenoid pathway. The biochemical patterns including hyperdigoxinemia observed in autism correlated with those obtained in right hemispheric chemical dominance. Right hemispheric chemical dominance is a predisposing factor for autism.

Activation of Phosphoinositide Metabolism by Cholinergic Agents.

DTIC Science & Technology

1990-12-16

acid significantly inhibited NE-induced [3H]IP1 production in slices that had been prelabelled with [3H]inositol and baclofen , a specific GABAB...agonist, was as effective as GABA in enhancing the response to NE (Figure 15). Neither GABA nor baclofen significantly blocked the inhibitory effect of...quisqualate, but baclofen reduced the inhibitory effect of arachidonic acid. Effects of NMDA receptor antagonists on phosphoinositide hydrolysis MK-801 is

Medial prefrontal cortex TRPV1 and CB1 receptors modulate cardiac baroreflex activity by regulating the NMDA receptor/nitric oxide pathway.

PubMed

Lagatta, Davi C; Kuntze, Luciana B; Ferreira-Junior, Nilson C; Resstel, Leonardo B M

2018-05-29

The ventral medial prefrontal cortex (vMPFC) facilitates the cardiac baroreflex response through N-methyl-D-aspartate (NMDA) receptor activation and nitric oxide (NO) formation by neuronal NO synthase (nNOS) and soluble guanylate cyclase (sGC) triggering. Glutamatergic transmission is modulated by the cannabinoid receptor type 1 (CB 1 ) and transient receptor potential vanilloid type 1 (TRPV 1 ) receptors, which may inhibit or stimulate glutamate release in the brain, respectively. Interestingly, vMPFC CB 1 receptors decrease cardiac baroreflex responses, while TRPV 1 channels facilitate them. Therefore, the hypothesis of the present study is that the vMPFC NMDA/NO pathway is regulated by both CB 1 and TRPV 1 receptors in the modulation of cardiac baroreflex activity. In order to test this assumption, we used male Wistar rats that had stainless steel guide cannulae bilaterally implanted in the vMPFC. Subsequently, a catheter was inserted into the femoral artery, for cardiovascular recordings, and into the femoral vein for assessing baroreflex activation. The increase in tachycardic and bradycardic responses observed after the microinjection of a CB 1 receptors antagonist into the vMPFC was prevented by an NMDA antagonist as well as by the nNOS and sGC inhibition. NO extracellular scavenging also abolished these responses. These same pharmacological manipulations inhibited cardiac reflex enhancement induced by TRPV 1 agonist injection into the area. Based on these results, we conclude that vMPFC CB 1 and TRPV 1 receptors inhibit or facilitate the cardiac baroreflex activity by stimulating or blocking the NMDA activation and NO synthesis.

Metabotropic glutamate receptor 5 upregulates surface NMDA receptor expression in striatal neurons via CaMKII.

PubMed

Jin, Dao-Zhong; Xue, Bing; Mao, Li-Min; Wang, John Q

2015-10-22

Metabotropic and ionotropic glutamate receptors are closely clustered in postsynaptic membranes and are believed to interact actively with each other to control excitatory synaptic transmission. Metabotropic glutamate receptor 5 (mGluR5), for example, has been well documented to potentiate ionotropic NMDA receptor activity, although underlying mechanisms are poorly understood. In this study, we investigated the role of mGluR5 in regulating trafficking and subcellular distribution of NMDA receptors in adult rat striatal neurons. We found that the mGluR1/5 agonist DHPG concentration-dependently increased NMDA receptor GluN1 and GluN2B subunit expression in the surface membrane. Meanwhile, DHPG reduced GluN1 and GluN2B levels in the intracellular compartment. The effect of DHPG was blocked by an mGluR5 selective antagonist MTEP but not by an mGluR1 selective antagonist 3-MATIDA. Pretreatment with an inhibitor or a specific inhibitory peptide for synapse-enriched Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) also blocked the DHPG-stimulated redistribution of GluN1 and GluN2B. In addition, DHPG enhanced CaMKIIα activity and elevated GluN2B phosphorylation at a CaMKII-sensitive site (serine 1303). These results demonstrate that mGluR5 regulates trafficking of NMDA receptors in striatal neurons. Activation of mGluR5 appears to induce rapid trafficking of GluN1 and GluN2B to surface membranes through a signaling pathway involving CaMKII. Copyright © 2015 Elsevier B.V. All rights reserved.

(+)-Pentazocine Reduces NMDA-Induced Murine Retinal Ganglion Cell Death Through a σR1-Dependent Mechanism

PubMed Central

Zhao, Jing; Mysona, Barbara A.; Qureshi, Azam; Kim, Lily; Fields, Taylor; Gonsalvez, Graydon B.; Smith, Sylvia B.; Bollinger, Kathryn E.

2016-01-01

Purpose To evaluate, in vivo, the effects of the sigma-1 receptor (σR1) agonist, (+)-pentazocine, on N-methyl-D-aspartate (NMDA)-mediated retinal excitotoxicity. Methods Intravitreal NMDA injections were performed in C57BL/6J mice (wild type [WT]) and σR1−/− (σR1 knockout [KO]) mice. Fellow eyes were injected with phosphate-buffered saline (PBS). An experimental cohort of WT and σR1 KO mice was administered (+)-pentazocine by intraperitoneal injection, and untreated animals served as controls. Retinas derived from mice were flat-mounted and labeled for retinal ganglion cells (RGCs). The number of RGCs was compared between NMDA and PBS-injected eyes for all groups. Apoptosis was assessed using TUNEL assay. Levels of extracellular-signal–regulated kinases (ERK1/2) were analyzed by Western blot. Results N-methyl-D-aspartate induced a significant increase in TUNEL-positive nuclei and a dose-dependent loss of RGCs. Mice deficient in σR1 showed greater RGC loss (≈80%) than WT animals (≈50%). (+)-Pentazocine treatment promoted neuronal survival, and this effect was prevented by deletion of σR1. (+)-Pentazocine treatment resulted in enhanced activation of ERK at the 6-hour time point following NMDA injection. The (+)-pentazocine–induced ERK activation was diminished in σR1 KO mice. Conclusions Targeting σR1 activation prevented RGC death while enhancing activation of the mitogen-activated protein kinase (MAPK), ERK1/2. Sigma-1 receptor is a promising therapeutic target for retinal neurodegenerative diseases. PMID:26868747

Neuropeptide S attenuates neuropathological, neurochemical and behavioral changes induced by the NMDA receptor antagonist MK-801

PubMed Central

Okamura, Naoe; Reinscheid, Rainer K.; Ohgake, Shintaro; Iyo, Masaomi; Hashimoto, Kenji

2009-01-01

Neuropeptide S (NPS) and its cognate receptor were reported to mediate anxiolytic-like and arousal effects. NPS receptors are predominantly expressed in the brain, especially in limbic structures, including amygdala, olfactory nucleus, subiculum and retrosplenial cortex. In contrast, the NPS precursor is expressed in only a few brainstem nuclei where it is co-expressed with various excitatory transmitters, including glutamate. The current study investigates interactions of the NPS system with glutamatergic neurotransmission. It has been suggested that dysfunctions in glutamatergic neurotransmission via N-methyl-D-aspartate (NMDA) receptors might be involved in the pathophysiology of schizophrenia since NMDA receptor antagonists, such as MK-801, have been shown to induce psychotic-like behavior in humans and animal models. Also, MK-801 is known to produce histological changes such as cytoplasmic vacuoles in retrosplenial cortex neurons where NPS receptors are highly expressed. In this study we show that NPS is able to alleviate neuropathological, neurochemical and behavioral changes produced by NMDA receptor antagonists. NPS treatment attenuated MK-801-induced vacuolization in the rat retrosplenial cortex in a dose dependent manner that can be blocked by an NPS receptor-selective antagonist. NPS also suppressed MK-801-induced increases of extracellular acetylcholine levels in the retrosplenial cortex. In the prepulse inhibition (PPI) assay, animals pretreated with NPS recovered significantly from MK-801-induced disruption of PPI. Our study suggests that NPS may have protective effects against the neurotoxic and behavioral changes produced by NMDA receptor antagonists and that NPS receptor agonists may elicit antipsychotic effects. PMID:19576911

Activation of single heteromeric GABAA receptor ion channels by full and partial agonists

PubMed Central

Mortensen, Martin; Kristiansen, Uffe; Ebert, Bjarke; Frølund, Bente; Krogsgaard-Larsen, Povl; Smart, Trevor G

2004-01-01

The linkage between agonist binding and the activation of a GABAA receptor ion channel is yet to be resolved. This aspect was examined on human recombinant α1β2γ2S GABAA receptors expressed in human embryonic kidney cells using the following series of receptor agonists: GABA, isoguvacine, 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP), isonipecotic acid, piperidine-4-sulphonic acid (P4S), imidazole-4-acetic acid (IAA), 5-(4-piperidyl)-3-isothiazolol (thio-4-PIOL) and 5-(4-piperidyl)-3-isoxazolol (4-PIOL). Whole-cell concentration–response curves enabled the agonists to be categorized into four classes based upon their maximum responses. Single channel analyses revealed that the channel conductance of 25–27 pS was unaffected by the agonists. However, two open states were resolved from the open period distributions with mean open times reduced 5-fold by the weakest partial agonists. Using saturating agonist concentrations, estimates of the channel shutting rate, α, ranged from 200 to 600 s−1. The shut period distributions were described by three or four components and for the weakest partial agonists, the interburst shut periods increased whilst the mean burst durations and longest burst lengths were reduced relative to the full agonists. From the burst analyses, the opening rates for channel activation, β, and the total dissociation rates, k−1, for the agonists leaving the receptor were estimated. The agonist efficacies were larger for the full agonists (E ∼7−9) compared to the weak partial agonists (∼0.4–0.6). Overall, changes in agonist efficacy largely determined the different agonist profiles with contributions from the agonist affinities and the degree of receptor desensitization. From this we conclude that GABAA receptor activation does not occur in a switch-like manner since the agonist recognition sites are flexible, accommodating diverse agonist structures which differentially influence the opening and shutting rates of the ion channel. PMID:14990676

Mechanism of partial agonism in AMPA-type glutamate receptors

PubMed Central

Salazar, Hector; Eibl, Clarissa; Chebli, Miriam; Plested, Andrew

2017-01-01

Neurotransmitters trigger synaptic currents by activating ligand-gated ion channel receptors. Whereas most neurotransmitters are efficacious agonists, molecules that activate receptors more weakly—partial agonists—also exist. Whether these partial agonists have weak activity because they stabilize less active forms, sustain active states for a lesser fraction of the time or both, remains an open question. Here we describe the crystal structure of an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor (AMPAR) ligand binding domain (LBD) tetramer in complex with the partial agonist 5-fluorowillardiine (FW). We validate this structure, and others of different geometry, using engineered intersubunit bridges. We establish an inverse relation between the efficacy of an agonist and its promiscuity to drive the LBD layer into different conformations. These results suggest that partial agonists of the AMPAR are weak activators of the receptor because they stabilize multiple non-conducting conformations, indicating that agonism is a function of both the space and time domains. PMID:28211453

Active-State Model of a Dopamine D2 Receptor - Gαi Complex Stabilized by Aripiprazole-Type Partial Agonists

PubMed Central

Kling, Ralf C.; Tschammer, Nuska; Lanig, Harald; Clark, Timothy; Gmeiner, Peter

2014-01-01

Partial agonists exhibit a submaximal capacity to enhance the coupling of one receptor to an intracellular binding partner. Although a multitude of studies have reported different ligand-specific conformations for a given receptor, little is known about the mechanism by which different receptor conformations are connected to the capacity to activate the coupling to G-proteins. We have now performed molecular-dynamics simulations employing our recently described active-state homology model of the dopamine D2 receptor-Gαi protein-complex coupled to the partial agonists aripiprazole and FAUC350, in order to understand the structural determinants of partial agonism better. We have compared our findings with our model of the D2R-Gαi-complex in the presence of the full agonist dopamine. The two partial agonists are capable of inducing different conformations of important structural motifs, including the extracellular loop regions, the binding pocket and, in particular, intracellular G-protein-binding domains. As G-protein-coupling to certain intracellular epitopes of the receptor is considered the key step of allosterically triggered nucleotide-exchange, it is tempting to assume that impaired coupling between the receptor and the G-protein caused by distinct ligand-specific conformations is a major determinant of partial agonist efficacy. PMID:24932547

Trace and contextual fear conditioning require neural activity and NMDA receptor-dependent transmission in the medial prefrontal cortex

PubMed Central

Gilmartin, Marieke R.; Helmstetter, Fred J.

2010-01-01

The contribution of the medial prefrontal cortex (mPFC) to the formation of memory is a subject of considerable recent interest. Notably, the mechanisms supporting memory acquisition in this structure are poorly understood. The mPFC has been implicated in the acquisition of trace fear conditioning, a task that requires the association of a conditional stimulus (CS) and an aversive unconditional stimulus (UCS) across a temporal gap. In both rat and human subjects, frontal regions show increased activity during the trace interval separating the CS and UCS. We investigated the contribution of prefrontal neural activity in the rat to the acquisition of trace fear conditioning using microinfusions of the γ-aminobutyric acid type A (GABAA) receptor agonist muscimol. We also investigated the role of prefrontal N-methyl-d-aspartate (NMDA) receptor-mediated signaling in trace fear conditioning using the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid (APV). Temporary inactivation of prefrontal activity with muscimol or blockade of NMDA receptor-dependent transmission in mPFC impaired the acquisition of trace, but not delay, conditional fear responses. Simultaneously acquired contextual fear responses were also impaired in drug-treated rats exposed to trace or delay, but not unpaired, training protocols. Our results support the idea that synaptic plasticity within the mPFC is critical for the long-term storage of memory in trace fear conditioning. PMID:20504949

Central phencyclidine (PCP) receptor binding is glutamate dependent: evidence for a PCP/excitatory amino acid receptor (EAAR) complex

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

Loo, P.; Braunwalder, A.; Lehmann, J.

PCP and other dissociative anesthetica block the increase in neuronal firing rate evoked by the EAAR agonist, N-methyl-Daspartate. NMDA and other EAAs such as glutamate (glu) have not been previously shown to affect PCP ligand binding. In the present study, using once washed rat forebrain membranes, 10 ..mu..M-glu was found to increase the binding of (/sup 3/H)TCP, a PCP analog, to defined PCP recognition sites by 20%. Removal of glu and aspartate (asp) by extensive washing decreased TCP binding by 75-90%. In these membranes, 10 ..mu..M L-glu increased TCP binding 3-fold. This effect was stereospecific and evoked by other EAAsmore » with the order of activity, L-glu > D-asp > L- asp > NMDA > D-glu > quisqualate. Kainate, GABA, NE, DA, 5-HT, 2-chloroadenosine, oxotremorine and histamine had no effect on TCP binding at concentrations up to 100 ..mu..M. The effects of L-glu were attenuated by the NMDA-type receptor antagonist, 2-amino-7--phosphonoheptanoate (AP7; 10 ..mu..M-1 mM). These findings indicate that EAAS facilitate TCP binding, possibly through NMDA-type receptors. The observed interaction between the PCP receptor and EAARs may reflect the existence of a macromolecular receptor complex similar to that demonstrated for the benzodiazepines and GABA.« less

Pharmacological characterization of NMDA-like receptors in the single-celled organism Paramecium primaurelia.

PubMed

Ramoino, Paola; Candiani, Simona; Pittaluga, Anna Maria; Usai, Cesare; Gallus, Lorenzo; Ferrando, Sara; Milanese, Marco; Faimali, Marco; Bonanno, Giambattista

2014-02-01

Paramecium primaurelia is a unicellular eukaryote that moves in freshwater by ciliary beating and responds to environmental stimuli by altering motile behaviour. The movements of the cilia are controlled by the electrical changes of the cell membrane: when the intraciliary Ca(2+) concentration associated with plasma membrane depolarization increases, the ciliary beating reverses its direction, and consequently the swimming direction changes. The ciliary reversal duration is correlated with the amount of Ca(2+) influx. Here, we evaluated the effects due to the activation or blockade of N-methyl-d-aspartic acid (NMDA) receptors on swimming behaviour in Paramecium. Paramecia normally swim forward, drawing almost linear tracks. We observed that the simultaneous administration of NMDA and glycine induced a partial ciliary reversal (PaCR) leading to a continuous spiral-like swim. Furthermore, the duration of continuous ciliary reversal (CCR), triggered by high external KCl concentrations, was longer in NMDA+glycine-treated cells. NMDA action required the presence of Ca(2+), as the normal forward swimming was restored when the ion was omitted from the extracellular milieu. The PaCR and the enhancement of CCR duration significantly decreased when the antagonists of the glutamate site D-AP5 or CGS19755, the NMDA channel blocker MK-801 or the glycine site antagonist DCKA was added. The action of NMDA+glycine was also abolished by Zn(2+) or ifenprodil, the GluN2A and the GluN2B NMDA-containing subunit blockers, respectively. Searches of the Paramecium genome database currently available indicate that the NMDA-like receptor with ligand-binding characteristics of an NMDA receptor-like complex, purified from rat brain synaptic membranes and found in some metazoan genomes, is also present in Paramecium. These results provide evidence that functional NMDA receptors similar to those typical of mammalian neuronal cells are present in the single-celled organism Paramecium and thus suggest that the glutamatergic NMDA system is a phylogenetically old behaviour-controlling mechanism.

Exploring the binding energy profiles of full agonists, partial agonists, and antagonists of the α7 nicotinic acetylcholine receptor.

PubMed

Tabassum, Nargis; Ma, Qianyun; Wu, Guanzhao; Jiang, Tao; Yu, Rilei

2017-09-01

Nicotinic acetylcholine receptors (nAChRs) belong to the Cys-loop receptor family and are important drug targets for the treatment of neurological diseases. However, the precise determinants of the binding efficacies of ligands for these receptors are unclear. Therefore, in this study, the binding energy profiles of various ligands (full agonists, partial agonists, and antagonists) were quantified by docking those ligands with structural ensembles of the α7 nAChR exhibiting different degrees of C-loop closure. This approximate treatment of interactions suggested that full agonists, partial agonists, and antagonists of the α7 nAChR possess distinctive binding energy profiles. Results from docking revealed that ligand binding efficacy may be related to the capacity of the ligand to stabilize conformational states with a closed C loop.

Septal cholinergic neuromodulation tunes the astrocyte-dependent gating of hippocampal NMDA receptors to wakefulness

PubMed Central

Papouin, Thomas; Dunphy, Jaclyn; Tolman, Michaela; Dineley, Kelly T.; Haydon, Philip G.

2017-01-01

Summary The activation of the N-methyl D-aspartate receptor (NMDAR) is controlled by a glutamate-binding site and a distinct, independently regulated, co-agonist-binding site. In most brain regions, the NMDAR co-agonist is the astrocyte-derived gliotransmitter D-serine. We found that D-serine levels oscillate in mouse hippocampus as a function of wakefulness, in vitro and in vivo. This causes a full saturation of the NMDAR co-agonist site in the dark (active)-phase that dissipates to sub-saturating levels during the light (sleep)-phase, and influences learning performance throughout the day. We demonstrate that hippocampal astrocytes sense the wakefulness-dependent activity of septal cholinergic fibers through the α7-nicotinic acetylcholine receptor (α7nAChR), whose activation drives D-serine release. We conclude that astrocytes tune the gating of synaptic NMDARs to the vigilance state and demonstrate that this is directly relevant to schizophrenia, a disorder characterized by NMDAR and cholinergic hypofunctions. Indeed, bypassing cholinergic activity with a clinically-tested α7nAChR agonist successfully enhances NMDARs activation. PMID:28479102

Differential agonist and inverse agonist profile of antipsychotics at D2L receptors coupled to GIRK potassium channels.

PubMed

Heusler, Peter; Newman-Tancredi, Adrian; Castro-Fernandez, Annabelle; Cussac, Didier

2007-03-01

The D(2) dopaminergic receptor represents a major target of antipsychotic drugs. Using the coupling of the human D(2long) (hD(2L)) receptor to G protein-coupled inward rectifier potassium (GIRK) channels in Xenopus laevis oocytes, we examined the activity of antipsychotic agents of different classes - typical, atypical, and a "new generation" of compounds, exhibiting a preferential D(2) and 5-HT(1A) receptor profile. When the hD(2L) receptor was coexpressed with GIRK channels, a series of reference compounds exhibited full agonist (dopamine, and quinpirole), partial agonist (apomorphine, (-)3-PPP, and (+)-UH232) or inverse agonist (raclopride, and L741626) properties. Sarizotan exhibited only very weak partial agonist action. At higher levels of receptor cRNA injected per oocyte, both partial agonist activity and inverse agonist properties were generally more pronounced. The inverse agonist action of L741626 was reversed by interaction with sarizotan, thus confirming the constitutive activity of wild-type hD(2L) receptors in the oocyte expression system. When antipsychotic agents were tested for their actions at the hD(2L) receptor, typical (haloperidol) as well as atypical (nemonapride, ziprasidone, and clozapine) compounds acted as inverse agonists. In contrast, among D(2)/5-HT(1A) antipsychotics, only SLV313 and F15063 behaved as inverse agonists, whilst the other members of this group (bifeprunox, SSR181507 and the recently marketed antipsychotic, aripiprazole) exhibited partial agonist properties. Thus, the X. laevis oocyte expression system highlights markedly different activity of antipsychotics at the hD(2L) receptor. These differential properties may translate to distinct therapeutic potential of these compounds.

GPR40 partial agonists and AgoPAMs: Differentiating effects on glucose and hormonal secretions in the rodent

PubMed Central

Pachanski, Michele J.; Kirkland, Melissa E.; Kosinski, Daniel T.; Mane, Joel; Cheewatrakoolpong, Boonlert; Xue, Jiyan; Szeto, Daphne; Forrest, Gail; Miller, Corin; Bunzel, Michelle; Plummer, Christopher W.; Chobanian, Harry R.; Miller, Michael W.; Souza, Sarah; Thomas-Fowlkes, Brande S.; Ogawa, Aimie M.; Weinglass, Adam B.; Di Salvo, Jerry; Li, Xiaoyan; Feng, Yue; Tatosian, Daniel A.; Howard, Andrew D.; Colletti, Steven L.

2017-01-01

GPR40 agonists are effective antidiabetic agents believed to lower glucose through direct effects on the beta cell to increase glucose stimulated insulin secretion. However, not all GPR40 agonists are the same. Partial agonists lower glucose through direct effects on the pancreas, whereas GPR40 AgoPAMs may incorporate additional therapeutic effects through increases in insulinotrophic incretins secreted by the gut. Here we describe how GPR40 AgoPAMs stimulate both insulin and incretin secretion in vivo over time in diabetic GK rats. We also describe effects of AgoPAMs in vivo to lower glucose and body weight beyond what is seen with partial GPR40 agonists in both the acute and chronic setting. Further comparisons of the glucose lowering profile of AgoPAMs suggest these compounds may possess greater glucose control even in the presence of elevated glucagon secretion, an unexpected feature observed with both acute and chronic treatment with AgoPAMs. Together these studies highlight the complexity of GPR40 pharmacology and the potential additional benefits AgoPAMs may possess above partial agonists for the diabetic patient. PMID:29053717

Agonist Met antibodies define the signalling threshold required for a full mitogenic and invasive program of Kaposi's Sarcoma cells.

PubMed

Bardelli, Claudio; Sala, Marilena; Cavallazzi, Umberto; Prat, Maria

2005-09-09

We previously showed that the Kaposi Sarcoma line KS-IMM express a functional Met tyrosine kinase receptor, which, upon HGF stimulation, activates motogenic, proliferative, and invasive responses. In this study, we investigated the signalling pathways activated by HGF, as well as by Met monoclonal antibodies (Mabs), acting as full or partial agonists. The full agonist Mab mimics HGF in all biological and biochemical aspects. It elicits the whole spectrum of responses, while the partial agonist Mab induces only wound healing. These differences correlated with a more prolonged and sustained tyrosine phosphorylation of the receptor and MAPK evoked by HGF and by the full agonist Mab, relative to the partial agonist Mab. Since Gab1, JNK and PI 3-kinase are activated with same intensity and kinetics by HGF and by the two agonist antibodies, it is concluded that level and duration of MAPK activation by Met receptor are crucial for the induction of a full HGF-dependent mitogenic and invasive program in KS cells.

The lathyrus toxin, {beta}-N-oxalyl-L-{alpha},{beta}-diaminopropionic acid (ODAP), and homocysteic acid sensitize CA1 pyramidal neurons to cystine and L-2-amino-6-phosphonohexanoic acid

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

Chase, L.A.; Peterson, N.L.; Koerner, J.F.

2007-02-15

A brief exposure of hippocampal slices to L-quisqualic acid (QUIS) sensitizes CA1 pyramidal neurons 30- to 250-fold to depolarization by certain excitatory amino acids analogues, e.g., L-2-amino-6-phosphonohexanoic acid (L-AP6), and by the endogenous compound, L-cystine. This phenomenon has been termed QUIS sensitization. A mechanism similar to that previously described for QUIS neurotoxicity has been proposed to describe QUIS sensitization. Specifically, QUIS has been shown to be sequestered into GABAergic interneurons by the System x{sub c} {sup -} and subsequently released by heteroexchange with cystine or L-AP6, resulting in activation of non-NMDA receptors. We now report two additional neurotoxins, the Lathyrusmore » excitotoxin, {beta}-N-oxalyl-L-{alpha},{beta}-diaminopropionic acid (ODAP), and the endogenous compound, L-homocysteic acid (HCA), sensitize CA1 hippocampal neurons > 50-fold to L-AP6 and > 10-fold to cystine in a manner similar to QUIS. While the cystine- or L-AP6-mediated depolarization can be inhibited by the non-NMDA receptor antagonist CNQX in ODAP- or QUIS-sensitized slices, the NMDA antagonist D-AP5 inhibits depolarization by cystine or L-AP6 in HCA-sensitized slices. Thus, HCA is the first identified NMDA agonist that induces phosphonate or cystine sensitization. Like QUIS sensitization, the sensitization evoked by either ODAP or HCA can be reversed by a subsequent exposure to 2 mM {alpha}-aminoadipic acid. Finally, we have demonstrated that there is a correlation between the potency of inducers for triggering phosphonate or cystine sensitivity and their affinities for System x{sub c} {sup -} and either the non-NMDA or NMDA receptor. Thus, the results of this study support our previous model of QUIS sensitization and have important implications for the mechanisms of neurotoxicity, neurolathyrism and hyperhomocystinemia.« less

Harmaline competitively inhibits [3H]MK-801 binding to the NMDA receptor in rabbit brain.

PubMed

Du, W; Aloyo, V J; Harvey, J A

1997-10-03

Harmaline, a beta-carboline derivative, is known to produce tremor through a direct activation of cells in the inferior olive. However, the receptor(s) through which harmaline acts remains unknown. It was recently reported that the tremorogenic actions of harmaline could be blocked by the noncompetitive NMDA channel blocker, MK-801. This study examined whether the blockade of harmaline's action, in the rabbit, by MK-801 was due to a pharmacological antagonism at the MK-801 binding site. This was accomplished by measurement of [3H]MK-801 binding in membrane fractions derived from tissue containing the inferior olivary nucleus and from cerebral cortex. Harmaline completely displaced saturable [3H]MK-801 binding in both the inferior olive and cortex with apparent IC50 values of 60 and 170 microM, respectively. These IC50 values are consistent with the high doses of harmaline required to produce tremor, e.g., 10-30 mg/kg. Non-linear curve fitting analysis of [3H]MK-801 saturation experiments indicated that [3H]MK-801 bound to a single site and that harmaline's displacement of [3H]MK-801 binding to the NMDA receptor was competitive as indicated by a shift in Kd but not in Bmax. In addition, a Schild plot gave a slope that was not significantly different from 1 indicating that harmaline was producing a displacement of [3H]MK-801 from its binding site within the NMDA cation channel and not through an action at the glutamate or other allosteric sites on the NMDA receptor. These findings provide in vitro evidence that the competitive blockade of harmaline-induced tremor by MK-801 occurs within the calcium channel coupled to the NMDA receptor. Our hypothesis is that harmaline produces tremor by acting as an inverse agonist at the MK-801 binding site and thus opening the cation channel.

Antidepressant effect of pramipexole in mice forced swimming test: A cross talk between dopamine receptor and NMDA/nitric oxide/cGMP pathway.

PubMed

Ostadhadi, Sattar; Imran Khan, Muhammad; Norouzi-Javidan, Abbas; Dehpour, Ahmad-Reza

2016-07-01

Pramipexole is a dopamine D2 receptor agonist indicated for treating Parkinson disorder. This study was aimed to investigate the effect of pramipexole in forced swimming test (FST) in mice and the possible involvement of activation of D2 receptors and inhibition of N-methyl-d-aspartate (NMDA) receptors and nitric oxide-cyclic guanosine monophosphate (NO-cGMP) on this effect. Intraperitoneal administration of pramipexole (1-3mg/kg) reduced the immobility time in the FST similar to fluoxetine (20mg/kg, i.p.). This effect of pramipexole (1mg/kg, i.p.) was ceased when mice were pretreated with haloperidol (0.15mg/kg, i.p,) and sulpiride (5mg/kg, i.p) as D2 receptor antagonists, NMDA (75mg/kg,i.p.), l-arginine (750mg/kg, i.p., a substrate for nitric oxide synthase) or sildenafil (5mg/kg, i.p., a phosphodiesterase 5 inhibitor). The administration of MK-801 (0.05mg/kg, i.p., a NMDA receptor antagonist) l-NG-Nitro arginine methyl ester (l-NAME, 10mg/kg, i.p., a non-specific nitric oxide synthase (NOS) inhibitor), 7-nitroindazole (30mg/kg, i.p., a neuronal NOS inhibitor) and methylene blue (10mg/kg, i.p.), an inhibitor of both NOS and soluble guanylyl cyclase (sGC) in combination with the sub-effective dose of pramipexole (0.3mg/kg, i.p.) reduced the immobility. Altogether, our data suggest that the antidepressant-like effect of pramipexole is dependent on the activation of D2 receptor and inhibition of either NMDA receptors and/or NO-cGMP synthesis. These results contribute to the understanding of the mechanisms underlying the antidepressant-like effect of pramipexole and reinforce the role of D2 receptors, NMDA receptors and l-arginine-NO-GMP pathway in the antidepressant mechanism of this agent. Copyright © 2016. Published by Elsevier Masson SAS.

Cholinergic basal forebrain structures are not essential for mediation of the arousing action of glutamate.

PubMed

Lelkes, Zoltán; Abdurakhmanova, Shamsiiat; Porkka-Heiskanen, Tarja

2017-09-18

The cholinergic basal forebrain contributes to cortical activation and receives rich innervations from the ascending activating system. It is involved in the mediation of the arousing actions of noradrenaline and histamine. Glutamatergic stimulation in the basal forebrain results in cortical acetylcholine release and suppression of sleep. However, it is not known to what extent the cholinergic versus non-cholinergic basal forebrain projection neurones contribute to the arousing action of glutamate. To clarify this question, we administered N-methyl-D-aspartate (NMDA), a glutamate agonist, into the basal forebrain in intact rats and after destruction of the cholinergic cells in the basal forebrain with 192 immunoglobulin (Ig)G-saporin. In eight Han-Wistar rats with implanted electroencephalogram/electromyogram (EEG/EMG) electrodes and guide cannulas for microdialysis probes, 0.23 μg 192 IgG-saporin was administered into the basal forebrain, while the eight control animals received artificial cerebrospinal fluid. Two weeks later, a microdialysis probe targeted into the basal forebrain was perfused with cerebrospinal fluid on the baseline day and for 3 h with 0.3 mmNMDA on the subsequent day. Sleep-wake activity was recorded for 24 h on both days. NMDA exhibited a robust arousing effect in both the intact and the lesioned rats. Wakefulness was increased and both non-REM and REM sleep were decreased significantly during the 3-h NMDA perfusion. Destruction of the basal forebrain cholinergic neurones did not abolish the wake-enhancing action of NMDA. Thus, the cholinergic basal forebrain structures are not essential for the mediation of the arousing action of glutamate. © 2017 European Sleep Research Society.

Disruption of social approach by MK-801, amphetamine, and fluoxetine in adolescent C57BL/6J mice.

PubMed

Moy, Sheryl S; Nonneman, Randal J; Shafer, Geoffrey O; Nikolova, Viktoriya D; Riddick, Natallia V; Agster, Kara L; Baker, Lorinda K; Knapp, Darin J

2013-01-01

Autism is a severe neurodevelopmental disorder, diagnosed on the basis of core behavioral symptoms. Although the mechanistic basis for the disorder is not yet known, genetic analyses have suggested a role for abnormal excitatory/inhibitory signaling systems in brain, including dysregulation of glutamatergic neurotransmission. In mice, the constitutive knockdown of NMDA receptors leads to social deficits, repetitive behavior, and self-injurious responses that reflect aspects of the autism clinical profile. However, social phenotypes differ with age: mice with reduced NMDA-receptor function exhibit hypersociability in adolescence, but markedly deficient sociability in adulthood. The present studies determined whether acute disruption of NMDA neurotransmission leads to exaggerated social approach, similar to that observed with constitutive disruption, in adolescent C57BL/6J mice. The effects of MK-801, an NMDA receptor antagonist, were compared with amphetamine, a dopamine agonist, and fluoxetine, a selective serotonin reuptake inhibitor, on performance in a three-chamber choice task. Results showed that acute treatment with MK-801 led to social approach deficits at doses without effects on entry numbers. Amphetamine also decreased social preference, but increased number of entries at every dose. Fluoxetine (10 mg/kg) had selective effects on social novelty preference. Withdrawal from a chronic ethanol regimen decreased activity, but did not attenuate sociability. Low doses of MK-801 and amphetamine were also evaluated in a marble-burying assay for repetitive behavior. MK-801, at a dose that did not disrupt sociability or alter entries, led to a profound reduction in marble-burying. Overall, these findings demonstrate that moderate alteration of NMDA, dopamine, or serotonin function can attenuate social preference in wild type mice. Copyright © 2012 Elsevier Inc. All rights reserved.

Fyn kinase-mediated phosphorylation of NMDA receptor NR2B subunit at Tyr1472 is essential for maintenance of neuropathic pain.

PubMed

Abe, Tetsuya; Matsumura, Shinji; Katano, Tayo; Mabuchi, Tamaki; Takagi, Kunio; Xu, Li; Yamamoto, Akitsugu; Hattori, Kotaro; Yagi, Takeshi; Watanabe, Masahiko; Nakazawa, Takanobu; Yamamoto, Tadashi; Mishina, Masayoshi; Nakai, Yoshihide; Ito, Seiji

2005-09-01

Despite abundant evidence implicating the importance of N-methyl-D-aspartate (NMDA) receptors in the spinal cord for pain transmission, the signal transduction coupled to NMDA receptor activation is largely unknown for the neuropathic pain state that lasts over periods of weeks. To address this, we prepared mice with neuropathic pain by transection of spinal nerve L5. Wild-type, NR2A-deficient, and NR2D-deficient mice developed neuropathic pain; in addition, phosphorylation of NR2B subunits of NMDA receptors at Tyr1472 was observed in the superficial dorsal horn of the spinal cord 1 week after nerve injury. Neuropathic pain and NR2B phosphorylation at Tyr1472 were attenuated by the NR2B-selective antagonist CP-101,606 and disappeared in mice lacking Fyn kinase, a Src-family tyrosine kinase. Concomitant with the NR2B phosphorylation, an increase in neuronal nitric oxide synthase activity was visualized in the superficial dorsal horn of neuropathic pain mice by NADPH diaphorase histochemistry. Electron microscopy showed that the phosphorylated NR2B was localized at the postsynaptic density in the spinal cord of mice with neuropathic pain. Indomethacin, an inhibitor of prostaglandin (PG) synthesis, and PGE receptor subtype EP1-selective antagonist reduced the NR2B phosphorylation in these mice. Conversely, EP1-selective agonist stimulated Fyn kinase-dependent nitric oxide formation in the spinal cord. The present study demonstrates that Tyr1472 phosphorylation of NR2B subunits by Fyn kinase may have dual roles in the retention of NMDA receptors in the postsynaptic density and in activation of nitric oxide synthase, and suggests that PGE2 is involved in the maintenance of neuropathic pain via the EP1 subtype.

Toll-like receptor 4 enhancement of non-NMDA synaptic currents increases dentate excitability after brain injury.

PubMed

Li, Ying; Korgaonkar, Akshata A; Swietek, Bogumila; Wang, Jianfeng; Elgammal, Fatima S; Elkabes, Stella; Santhakumar, Vijayalakshmi

2015-02-01

Concussive brain injury results in neuronal degeneration, microglial activation and enhanced excitability in the hippocampal dentate gyrus, increasing the risk for epilepsy and memory dysfunction. Endogenous molecules released during injury can activate innate immune responses including toll-like receptor 4 (TLR4). Recent studies indicate that immune mediators can modulate neuronal excitability. Since non-specific agents that reduce TLR4 signaling can limit post-traumatic neuropathology, we examined whether TLR4 signaling contributes to early changes in dentate excitability after brain injury. Concussive brain injury caused a transient increase in hippocampal TLR4 expression within 4h, which peaked at 24h. Post-injury increase in TLR4 expression in the dentate gyrus was primarily neuronal and persisted for one week. Acute, in vitro treatment with TLR4 ligands caused bidirectional modulation of dentate excitability in control and brain-injured rats, with a reversal in the direction of modulation after brain injury. TLR4 antagonists decreased, and agonist increased, afferent-evoked dentate excitability one week after brain injury. NMDA receptor antagonist did not occlude the ability of LPS-RS, a TLR4 antagonist, to decrease post-traumatic dentate excitability. LPS-RS failed to modulate granule cell NMDA EPSCs but decreased perforant path-evoked non-NMDA EPSC peak amplitude and charge transfer in both granule cells and mossy cells. Our findings indicate an active role for TLR4 signaling in early post-traumatic dentate hyperexcitability. The novel TLR4 modulation of non-NMDA glutamatergic currents, identified herein, could represent a general mechanism by which immune activation influences neuronal excitability in neurological disorders that recruit sterile inflammatory responses. Copyright © 2014 Elsevier Inc. All rights reserved.

Control of βAR- and N-methyl-D-aspartate (NMDA) Receptor-Dependent cAMP Dynamics in Hippocampal Neurons

PubMed Central

Chay, Andrew; Zamparo, Ilaria; Koschinski, Andreas; Zaccolo, Manuela; Blackwell, Kim T.

2016-01-01

Norepinephrine, a neuromodulator that activates β-adrenergic receptors (βARs), facilitates learning and memory as well as the induction of synaptic plasticity in the hippocampus. Several forms of long-term potentiation (LTP) at the Schaffer collateral CA1 synapse require stimulation of both βARs and N-methyl-D-aspartate receptors (NMDARs). To understand the mechanisms mediating the interactions between βAR and NMDAR signaling pathways, we combined FRET imaging of cAMP in hippocampal neuron cultures with spatial mechanistic modeling of signaling pathways in the CA1 pyramidal neuron. Previous work implied that cAMP is synergistically produced in the presence of the βAR agonist isoproterenol and intracellular calcium. In contrast, we show that when application of isoproterenol precedes application of NMDA by several minutes, as is typical of βAR-facilitated LTP experiments, the average amplitude of the cAMP response to NMDA is attenuated compared with the response to NMDA alone. Models simulations suggest that, although the negative feedback loop formed by cAMP, cAMP-dependent protein kinase (PKA), and type 4 phosphodiesterase may be involved in attenuating the cAMP response to NMDA, it is insufficient to explain the range of experimental observations. Instead, attenuation of the cAMP response requires mechanisms upstream of adenylyl cyclase. Our model demonstrates that Gs-to-Gi switching due to PKA phosphorylation of βARs as well as Gi inhibition of type 1 adenylyl cyclase may underlie the experimental observations. This suggests that signaling by β-adrenergic receptors depends on temporal pattern of stimulation, and that switching may represent a novel mechanism for recruiting kinases involved in synaptic plasticity and memory. PMID:26901880

Disruption of social approach by MK-801, amphetamine, and fluoxetine in adolescent C57BL/6J mice

PubMed Central

Moy, Sheryl S.; Nonneman, Randal J.; Shafer, Geoffrey O.; Nikolova, Viktoriya D.; Riddick, Natallia V.; Agster, Kara L.; Baker, Lorinda K.; Knapp, Darin J.

2012-01-01

Autism is a severe neurodevelopmental disorder, diagnosed on the basis of core behavioral symptoms. Although the mechanistic basis for the disorder is not yet known, genetic analyses have suggested a role for abnormal excitatory/inhibitory signaling systems in brain, including dysregulation of glutamatergic neurotransmission. In mice, the constitutive knockdown of NMDA receptors leads to social deficits, repetitive behavior, and self-injurious responses that reflect aspects of the autism clinical profile. However, social phenotypes differ with age: mice with reduced NMDA-receptor function exhibit hypersociability in adolescence, but markedly deficient sociability in adulthood. The present studies determined whether acute disruption of NMDA neurotransmission leads to exaggerated social approach, similar to that observed with constitutive disruption, in adolescent C57BL/6J mice. The effects of MK-801, an NMDA receptor antagonist, were compared with amphetamine, a dopamine agonist, and fluoxetine, a selective serotonin reuptake inhibitor, on performance in a three-chamber choice task. Results showed that acute treatment with MK-801 led to social approach deficits at doses without effects on entry numbers. Amphetamine also decreased social preference, but increased number of entries at every dose. Fluoxetine (10 mg/kg) had selective effects on social novelty preference. Withdrawal from a chronic ethanol regimen decreased activity, but did not attenuate sociability. Low doses of MK-801 and amphetamine were also evaluated in a marble-burying assay for repetitive behavior. MK-801, at a dose that did not disrupt sociability or alter entries, led to a profound reduction in marble-burying. Overall, these findings demonstrate that moderate alteration of NMDA, dopamine, or serotonin function can attenuate social preference in wild type mice. PMID:22898204

GABAA overactivation potentiates the effects of NMDA blockade during the brain growth spurt in eliciting locomotor hyperactivity in juvenile mice.

PubMed

Oliveira-Pinto, Juliana; Paes-Branco, Danielle; Cristina-Rodrigues, Fabiana; Krahe, Thomas E; Manhães, Alex C; Abreu-Villaça, Yael; Filgueiras, Cláudio C

2015-01-01

Both NMDA receptor blockade and GABAA receptor overactivation during the brain growth spurt may contribute to the hyperactivity phenotype reminiscent of attention-deficit/hyperactivity disorder. Here, we evaluated the effects of exposure to MK801 (a NMDA antagonist) and/or to muscimol (a GABAA agonist) during the brain growth spurt on locomotor activity of juvenile Swiss mice. This study was carried out in two separate experiments. In the first experiment, pups received a single i.p. injection of either saline solution (SAL), MK801 (MK, 0.1, 0.3 or 0.5 mg/kg) or muscimol (MU, 0.02, 0.1 or 0.5 mg/kg) at the second postnatal day (PND2), and PNDs 4, 6 and 8. In the second experiment, we investigated the effects of a combined injection of MK (0.1 mg/kg) and MU (doses: 0.02, 0.1 or 0.5 mg/kg) following the same injection schedule of the first experiment. In both experiments, locomotor activity was assessed for 15 min at PND25. While MK promoted a dose-dependent increase in locomotor activity, exposure to MU failed to elicit significant effects. The combined exposure to the highest dose of MU and the lowest dose of MK induced marked hyperactivity. Moreover, the combination of the low dose of MK and the high dose of MU resulted in a reduced activity in the center of the open field, suggesting an increased anxiety-like behavior. These findings suggest that, during the brain growth spurt, the blockade of NMDA receptors induces juvenile locomotor hyperactivity whereas hyperactivation of GABAA receptors does not. However, GABAA overactivation during this period potentiates the effects of NMDA blockade in inducing locomotor hyperactivity. Copyright © 2015 Elsevier Inc. All rights reserved.

Effects of a glycine transporter-1 inhibitor and D-serine on MK-801-induced immobility in the forced swimming test in rats.

PubMed

Kawaura, Kazuaki; Koike, Hiroyuki; Kinoshita, Kohnosuke; Kambe, Daiji; Kaku, Ayaka; Karasawa, Jun-ichi; Chaki, Shigeyuki; Hikichi, Hirohiko

2015-02-01

Glutamatergic dysfunction, particularly the hypofunction of N-methyl-D-aspartate (NMDA) receptors, is involved in the pathophysiology of schizophrenia. The positive modulation of the glycine site on the NMDA receptor has been proposed as a novel therapeutic approach for schizophrenia. However, its efficacy against negative symptoms, which are poorly managed by current medications, has not been fully addressed. In the present study, the effects of the positive modulation of the glycine site on the NMDA receptor were investigated in an animal model of negative symptoms of schizophrenia. The subchronic administration of MK-801 increased immobility in the forced swimming test in rats without affecting spontaneous locomotor activity. The increased immobility induced by MK-801 was attenuated by the atypical antipsychotic clozapine but not by either the typical antipsychotic haloperidol or the antidepressant imipramine, indicating that the increased immobility induced by subchronic treatment with MK-801 in the forced swimming test may represent a negative symptom of schizophrenia. Likewise, positive modulation of the glycine sites on the NMDA receptor using an agonist for the glycine site, D-serine, and a glycine transporter-1 inhibitor, N-[(3R)-3-([1,1'-biphenyl]-4-yloxy)-3-(4-fluorophenyl)propyl]-N-methylglycine hydrochloride (NFPS), significantly reversed the increase in immobility in MK-801-treated rats without reducing the immobility time in vehicle-treated rats. The present results show that the stimulation of the NMDA receptor through the glycine site on the receptor either directly with D-serine or by blocking glycine transporter-1 attenuates the immobility elicited by the subchronic administration of MK-801 and may be potentially useful for the treatment of negative symptoms of schizophrenia. Copyright © 2014 Elsevier B.V. All rights reserved.

Rapamycin improves sociability in the BTBR T(+)Itpr3(tf)/J mouse model of autism spectrum disorders.

PubMed

Burket, Jessica A; Benson, Andrew D; Tang, Amy H; Deutsch, Stephen I

2014-01-01

Overactivation of the mammalian target of rapamycin (mTOR) has been implicated in the pathogenesis of syndromic forms of autism spectrum disorders (ASDs), such as tuberous sclerosis complex, neurofibromatosis 1, and fragile X syndrome. Administration of mTORC1 (mTOR complex 1) inhibitors (e.g. rapamycin) in syndromic mouse models of ASDs improved behavior, cognition, and neuropathology. However, since only a minority of ASDs are due to the effects of single genes (∼10%), there is a need to explore inhibition of mTOR activity in mouse models that may be more relevant to the majority of nonsyndromic presentations, such as the genetically inbred BTBR T(+)Itpr3(tf)/J (BTBR) mouse model of ASDs. BTBR mice have social impairment and exhibit increased stereotypic behavior. In prior work, d-cycloserine, a partial glycineB site agonist that targets the N-methyl-d-aspartate (NMDA) receptor, was shown to improve sociability in both Balb/c and BTBR mouse models of ASDs. Importantly, NMDA receptor activation regulates mTOR signaling activity. The current study investigated the ability of rapamycin (10mg/kg, i.p.×four days), an mTORC1 inhibitor, to improve sociability and stereotypic behavior in BTBR mice. Using a standard paradigm to assess mouse social behavior, rapamycin improved several measures of sociability in the BTBR mouse, suggesting that mTOR overactivation represents a therapeutic target that mediates or contributes to impaired sociability in the BTBR mouse model of ASDs. Interestingly, there was no effect of rapamycin on stereotypic behaviors in this mouse model. Copyright © 2013 Elsevier Inc. All rights reserved.

The Effect of Midazolam and Propranolol on Fear Memory Reconsolidation in Ethanol-Withdrawn Rats: Influence of D-Cycloserine

PubMed Central

Ortiz, Vanesa; Giachero, Marcelo; Espejo, Pablo Javier; Molina, Víctor Alejandro

2015-01-01

Background: Withdrawal from chronic ethanol facilitates the formation of contextual fear memory and delays the onset to extinction, with its retrieval promoting an increase in ethanol consumption. Consequently, manipulations aimed to reduce these aversive memories, may be beneficial in the treatment of alcohol discontinuation symptoms. Related to this, pharmacological memory reconsolidation blockade has received greater attention due to its therapeutic potential. Methods: Here, we examined the effect of post-reactivation amnestic treatments such as Midazolam (MDZ, 3 mg/kg i.p) and Propranolol (PROP, 5 mg/kg i.p) on contextual fear memory reconsolidation in ethanol- withdrawn (ETOH) rats. Next, we examined whether the activation of N-methyl-D-aspartate (NMDA) receptors induced by d-cycloserine (DCS, 5 mg/kg i.p., a NMDA partial agonist) before memory reactivation can facilitate the disruptive effect of PROP and MDZ on fear memory in ETOH rats. Results: We observed a resistance to the disruptive effect of both MDZ and PROP following memory reactivation. Although intra-basolateral amygdala (BLA; 1.25 ug/side) and systemic PROP administration attenuated fear memory in DCS pre-treated ETOH rats, DCS/MDZ treatment did not affect memory in these animals. Finally, a decrease of both total and surface protein expression of the α1 GABAA receptor (GABAA-R) subunit in BLA was found in the ETOH rats. Conclusions: Ethanol withdrawal facilitated the formation of fear memory resistant to labilization post-reactivation. DCS administration promoted the disruptive effect of PROP on memory reconsolidation in ETOH rats. The resistance to MDZ’s disruptive effect on fear memory reconsolidation may be, at least in part, associated with changes in the GABAA-R composition induced by chronic ethanol administration/withdrawal. PMID:25617327

Traxoprodil, a selective antagonist of the NR2B subunit of the NMDA receptor, potentiates the antidepressant-like effects of certain antidepressant drugs in the forced swim test in mice.

PubMed

Poleszak, Ewa; Stasiuk, Weronika; Szopa, Aleksandra; Wyska, Elżbieta; Serefko, Anna; Oniszczuk, Anna; Wośko, Sylwia; Świąder, Katarzyna; Wlaź, Piotr

2016-08-01

One of the newest substances, whose antidepressant activity was shown is traxoprodil, which is a selective antagonist of the NR2B subunit of the NMDA receptor. The main goal of the present study was to evaluate the effect of traxoprodil on animals' behavior using the forced swim test (FST), as well as the effect of traxoprodil (10 mg/kg) on the activity of antidepressants, such as imipramine (15 mg/kg), fluoxetine (5 mg/kg), escitalopram (2 mg/kg) and reboxetine (2.5 mg/kg). Serotonergic lesion and experiment using the selective agonists of serotonin receptors 5-HT1A and 5-HT2 was conducted to evaluate the role of the serotonergic system in the antidepressant action of traxoprodil. Brain concentrations of tested agents were determined using HPLC. The results showed that traxoprodil at a dose of 20 and 40 mg/kg exhibited antidepressant activity in the FST and it was not related to changes in animals' locomotor activity. Co-administration of traxoprodil with imipramine, fluoxetine or escitalopram, each in subtherapeutic doses, significantly affected the animals' behavior in the FST and, what is important, these changes were not due to the severity of locomotor activity. The observed effect of traxoprodil is only partially associated with serotonergic system and is independent of the effect on the 5-HT1A and 5-HT2 serotonin receptors. The results of an attempt to assess the nature of the interaction between traxoprodil and the tested drugs show that in the case of joint administration of traxoprodil and fluoxetine, imipramine or escitalopram, there were interactions in the pharmacokinetic phase.

Evaluation of the glycine transporter inhibitor Org 25935 as augmentation to cognitive-behavioral therapy for panic disorder: a multicenter, randomized, double-blind, placebo-controlled trial.

PubMed

Nations, Kari R; Smits, Jasper A J; Tolin, David F; Rothbaum, Barbara O; Hofmann, Stefan G; Tart, Candyce D; Lee, Allen; Schipper, Jacques; Sjogren, Magnus; Xue, Dixi; Szegedi, Armin; Otto, Michael W

2012-05-01

A growing body of evidence supports the efficacy of D-cycloserine (DCS), a partial agonist at the N-methyl-D-aspartate (NMDA) glutamate receptor, as augmentation to cognitive-behavioral therapy (CBT) in the treatment of anxiety disorders. Org 25935 is a glycine transporter 1 inhibitor that acts to increase synaptic glycine levels and enhance NMDA-mediated glutamatergic activity. The aim of this study was to examine the efficacy of a glutamatergic compound other than DCS in a CBT augmentation paradigm. This was a randomized, double-blind, placebo-controlled, parallel-group clinical trial for which participants were recruited from November 2008 through February 2010. Eligible adult patients diagnosed (DSM-IV) with panic disorder with or without agoraphobia (N = 40) were scheduled to receive 5 manualized CBT treatment sessions. Participants were randomly assigned to receive either a dose of Org 25935 (4 mg or 12 mg) or placebo 2 hours prior to the start of CBT sessions 3, 4, and 5. The primary endpoint was symptomatic change as measured by the Panic Disorder Severity Scale (PDSS) 1 week following the last CBT session. Although mean PDSS total scores decreased significantly from baseline to end of treatment in every group, no statistically significant benefit was observed for Org 25935 (4 or 12 mg) over placebo on the primary endpoint or on any secondary efficacy endpoint. Org 25935 showed no safety issues at either dose but was much better tolerated at the 4-mg dose level than at the 12-mg dose level. Org 25935 demonstrated no benefit over placebo in augmenting CBT for panic disorder. Study limitations and implications are discussed. clinicaltrials.gov Identifier: NCT00725725. © Copyright 2012 Physicians Postgraduate Press, Inc.

Effects of D-cycloserine on extinction of mesolimbic cue reactivity in alcoholism: a randomized placebo-controlled trial.

PubMed

Kiefer, Falk; Kirsch, Martina; Bach, Patrick; Hoffmann, Sabine; Reinhard, Iris; Jorde, Anne; von der Goltz, Christoph; Spanagel, Rainer; Mann, Karl; Loeber, Sabine; Vollstädt-Klein, Sabine

2015-07-01

Mesocorticolimbic reactivity to alcohol-associated cues has been shown to be associated with relapse to renewed drinking and to be decreased by cue-exposure-based extinction training (CET). Evidence from preclinical studies suggests that the extinction of conditioned alcohol-seeking behavior might be facilitated by drugs increasing N-methyl-D-aspartate (NMDA) receptor-associated memory consolidation. In this study, we assessed the efficacy of CET treatment supplemented with the partial NMDA-receptor agonist D-cycloserine (DCS) at reducing mesolimbic cue reactivity (CR), craving, and relapse risk in alcoholism. In a randomized, placebo-controlled, double-blind study, we recruited 76 recently detoxified abstinent alcohol-dependent patients. Thirty-two (16 DCS, 16 placebo) patients showed cue-induced ventral-striatal activation measured with functional magnetic resonance imaging (fMRI) prior to treatment and were thus included in the efficacy analyses. After inpatient detoxification, patients underwent nine sessions of CET spaced over 3 weeks, receiving either 50 mg DCS or placebo 1 h prior to each CET session. FMRI was conducted before treatment and 3 weeks after treatment onset. Following treatment with CET plus DCS, cue-induced brain activation in the ventral and dorsal striatum was decreased compared to treatment with CET plus placebo. Elevated posttreatment ventral striatal CR and increased craving (assessed using the Obsessive Compulsive Drinking Scale) were associated with increased relapse risk. DCS was shown to augment the effect of CET for alcohol-dependent subjects. The interaction between craving and ventral-striatal CR on treatment outcome suggests that CET might be especially effective in patients exhibiting both high craving and elevated CR.

Inhibition of DOR prevents remifentanil induced postoperative hyperalgesia through regulating the trafficking and function of spinal NMDA receptors in vivo and in vitro.

PubMed

Wang, Chunyan; Li, Yize; Wang, Haiyun; Xie, Keliang; Shu, Ruichen; Zhang, Linlin; Hu, Nan; Yu, Yonghao; Wang, Guolin

2015-01-01

Several studies have demonstrated that intraoperative remifentanil infusions have been associated with opioid-induced hyperalgesia (OIH). Activation of delta opioid receptor (DOR) and augmentation of N-methyl-d-aspartate (NMDA) receptor expression and function may play an important role in the development of OIH. The aim of this study was to investigate whether DOR inhibition could prevent remifentanil-induced hyperalgesia via regulating spinal NMDA receptor expression and function in vivo and in vitro. A rat model of remifentanil-induced postoperative hyperalgesia was performed with the DOR agonist deltorphin-deltorphin II or the DOR antagonist naltrindole injected intrathecally 10 min before remifentanil infusion. Mechanical and thermal hyperalgesia were measured at -24h, 2, 6, 24 and 48 h after remifentanil infusion. Western blot was applied to detect the membrane and total expression of DOR and NMDA receptor subunits (NR1, NR2A and NR2B) in spinal cord L4-L6 segments. In addition, whole-cell patch-clamp recording was used to investigate the effect of DOR inhibition on NMDA receptor-induced current in spinal cord slices in vitro. We found that membrane trafficking of DOR, NR1 and NR2B subunits in the spinal cord increased after remifentanil administration and surgery. The DOR antagonist naltrindole could attenuate mechanical and thermal hyperalgesia without affecting baseline nociceptive threshold, reduce membrane expression of DOR and decrease the membrane and total expressions of NR1 and NR2B subunits. Furthermore, the amplitude and the frequency of NMDA receptor-induced current were significantly increased by remifentanil incubation in neurons of the dorsal horn, which was reversed by the application of naltrindole. The above results indicate that inhibition of DOR could significantly inhibit remifentanil-induced hyperalgesia via modulating the total protein level, membrane trafficking and function of NMDA receptors in the dorsal horn of spinal cord, suggesting that naltrindole could be a potential anti-hyperalgesic agent for treating OIH. Copyright © 2014. Published by Elsevier Inc.

Hypothesis: is infantile autism a hypoglutamatergic disorder? Relevance of glutamate - serotonin interactions for pharmacotherapy.

PubMed

Carlsson, M L

1998-01-01

Based on 1) neuroanatomical and neuroimaging studies indicating aberrations in brain regions that are rich in glutamate neurons and 2) similarities between symptoms produced by N-methyl-D-aspartate (NMDA) antagonists in healthy subjects and those seen in autism, it is proposed in the present paper that infantile autism is a hypoglutamatergic disorder. Possible future pharmacological interventions in autism are discussed in the light of the intimate interplay between central glutamate and serotonin, notably the serotonin (5-HT) 2A receptor. The possible benefit of treatment with glutamate agonists [e.g. agents acting on the modulatory glycine site of the NMDA receptor, or so-called ampakines acting on the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor] is discussed, as well as the potential usefulness of a selective 5-HT2A receptor antagonist.

Synaptic Neurotransmitter-Gated Receptors

PubMed Central

Smart, Trevor G.; Paoletti, Pierre

2012-01-01

Since the discovery of the major excitatory and inhibitory neurotransmitters and their receptors in the brain, many have deliberated over their likely structures and how these may relate to function. This was initially satisfied by the determination of the first amino acid sequences of the Cys-loop receptors that recognized acetylcholine, serotonin, GABA, and glycine, followed later by similar determinations for the glutamate receptors, comprising non-NMDA and NMDA subtypes. The last decade has seen a rapid advance resulting in the first structures of Cys-loop receptors, related bacterial and molluscan homologs, and glutamate receptors, determined down to atomic resolution. This now provides a basis for determining not just the complete structures of these important receptor classes, but also for understanding how various domains and residues interact during agonist binding, receptor activation, and channel opening, including allosteric modulation. This article reviews our current understanding of these mechanisms for the Cys-loop and glutamate receptor families. PMID:22233560

An epigenetic intervention interacts with genetic strain differences to modulate the stress-induced reduction of flurazepam's antiseizure efficacy in the mouse.

PubMed

Deutsch, Stephen I; Mastropaolo, John; Burket, Jessica A; Rosse, Richard B

2009-06-01

Stress induces changes in the endogenous tone of both GABA and NMDA receptor-mediated neurotransmission in the intact mouse. Because changes are observed 24 h after stress, epigenetically-regulated alterations in gene expression may mediate these effects. In earlier work, sodium butyrate, a centrally-active histone deacetylase inhibitor that promotes gene expression, was shown to modulate the stress-induced reduction of the ability of MK-801 (dizocilpine), a noncompetitive NMDA receptor antagonist, to antagonize electrically-precipitated seizures. In the current study, we extended this work to look at sodium butyrate's modulatory effect on stress-induced changes in the antiseizure efficacy of flurazepam, a benzodiazepine receptor agonist, in two strains of mice. Epigenetic mechanisms, genetic strain differences and a standard stress interacted to alter flurazepam's antiseizure efficacy. These data support examination and development of epigenetic treatment strategies.

Effects of activation and blockade of NMDA receptors on the extinction of a conditioned passive avoidance response in mice with different levels of anxiety.

PubMed

Tomilenko, R A; Dubrovina, N I

2007-06-01

The effects of an agonist (D-cycloserine) and an antagonist (dizocilpine) of N-methyl-D-aspartate (NMDA) receptors on the learning and extinction of a conditioned passive avoidance response were studied in mice with low, intermediate, and high levels of anxiety. In intermediate-anxiety mice, D-cycloserine (30 mg/kg) had no effect on learning but accelerated extinction, while dizocilpine (0.15 mg/kg) degraded acquisition of the reflex but delayed extinction. In high-anxiety mice, with good learning and no extinction, D-cycloserine had no effect, while dizocilpine decreased learning and facilitated retention of performance of the memory trace at the ongoing level in conditions promoting extinction. In low-anxiety mice, D-cycloserine degraded learning and accelerated extinction, while dizocilpine completely blocked learning and the retention of the passive avoidance response.

The role of GABA-A and mitochondrial diazepam-binding inhibitor receptors on the effects of neurosteroids on food intake in mice.

PubMed

Reddy, D S; Kulkarni, S K

1998-06-01

The present studies were undertaken to investigate the neuroactive steroidal modulation of feeding behavior and possible involvement of gamma-aminobutyric acid type-A (GABA-A) and mitochondrial diazepam binding inhibitor (DBI) receptors (MDR) in food-deprived male mice. Allopregnanolone (0.5-2 mg/kg), a neurosteroid, progesterone (1-10 mg/kg), a neurosteroid precursor, and 4'-chlordiazepam (0.25-1 mg/kg), a specific high affinity MDR agonist, produced a dose-dependent hyperphagic effects. In contrast, neurosteroids pregnenolone sulfate (PS) (1-10 mg/kg) and dehydroepiandrosterone sulfate (DHEAS) (1-10 mg/kg) produced a hypophagic effect, in a dose-dependent manner. The allopregnanolone-, progesterone- and 4'-chlordiazepam-induced hyperphagic effect was blocked by picrotoxin (1 mg/kg), a GABA-A chloride channel antagonist, but not by flumazenil (2 mg/kg), a benzodiazepine (BZD) antagonist. The 4'-chlordiazepam-induced hyperphagic effect was prevented by pretreatment with PK11195 (2 mg/kg), a selective partial MDR antagonist. The hypophagic effect of DHEAS (10 mg/kg) was reversed by dizocilpine (10 microg/kg), an NMDA receptor antagonist, but resistant to muscimol (0.1 mg/kg), a selective GABA-A receptor agonist. In contrast, the PS (10 mg/kg)-induced hypophagic response was resistant to dizocilpine, but sensitive to muscimol (0.1 mg/kg). Both the sulfated neurosteroids PS and DHEAS also reversed the hyperphagic effect of allopregnanolone. In addition, the BZD agonist triazolam (0.05-0.25 mg/kg) also produced a flumazenil- and picrotoxin-sensitive hyperphagic effects, thereby suggesting the changes in feeding behavior by neurosteroids represent GABA-A receptor mediated hyperphagic action. Although the possible antistress or anxiolytic actions of neurosteroids may confound the hyperphagia, behavioral effects observed were specific to food because the mice were adopted to the test environment and diet, and of a possible variation between various neurosteroids in the extent to which antistress or anxiolytic effect produced at hyperphagic doses. The hyperphagic effects of progesterone and 4'-chlordiazepam resembled that of neurosteroid allopregnanolone. Therefore, the effect of progesterone may be imputed to its metabolism to allopregnanolone, while the 4'-chlordiazepam-induced hyperphagic response is related to its MDR-stimulated neurosteroidogenesis and subsequent modulation of GABA-A receptors. The hypophagic response following DHEAS may, at least partly, involve an NMDA receptor mechanism. However, PS-induced hypophagia may be mediated by GABA-A or other receptor systems. These data suggest a pivotal role for GABA-A and mitochondrial DBI receptors in the hyperphagic effects of neurosteroids and reinforces a role for endogenous neurosteroids in regulating feeding behavior. Future studies may lead to the development of neurosteroid-based anorectic/hyperphagic agents for therapeutic use.

Discovery of novel brain permeable and G protein-biased beta-1 adrenergic receptor partial agonists for the treatment of neurocognitive disorders

PubMed Central

Yi, Bitna; Jahangir, Alam; Evans, Andrew K.; Briggs, Denise; Ravina, Kristine; Ernest, Jacqueline; Farimani, Amir B.; Sun, Wenchao; Rajadas, Jayakumar; Green, Michael; Feinberg, Evan N.; Pande, Vijay S.

2017-01-01

The beta-1 adrenergic receptor (ADRB1) is a promising therapeutic target intrinsically involved in the cognitive deficits and pathological features associated with Alzheimer’s disease (AD). Evidence indicates that ADRB1 plays an important role in regulating neuroinflammatory processes, and activation of ADRB1 may produce neuroprotective effects in neuroinflammatory diseases. Novel small molecule modulators of ADRB1, engineered to be highly brain permeable and functionally selective for the G protein with partial agonistic activity, could have tremendous value both as pharmacological tools and potential lead molecules for further preclinical development. The present study describes our ongoing efforts toward the discovery of functionally selective partial agonists of ADRB1 that have potential therapeutic value for AD and neuroinflammatory disorders, which has led to the identification of the molecule STD-101-D1. As a functionally selective agonist of ADRB1, STD-101-D1 produces partial agonistic activity on G protein signaling with an EC50 value in the low nanomolar range, but engages very little beta-arrestin recruitment compared to the unbiased agonist isoproterenol. STD-101-D1 also inhibits the tumor necrosis factor α (TNFα) response induced by lipopolysaccharide (LPS) both in vitro and in vivo, and shows high brain penetration. Other than the therapeutic role, this newly identified, functionally selective, partial agonist of ADRB1 is an invaluable research tool to study mechanisms of G protein-coupled receptor signal transduction. PMID:28746336

Discovery of novel brain permeable and G protein-biased beta-1 adrenergic receptor partial agonists for the treatment of neurocognitive disorders.

PubMed

Yi, Bitna; Jahangir, Alam; Evans, Andrew K; Briggs, Denise; Ravina, Kristine; Ernest, Jacqueline; Farimani, Amir B; Sun, Wenchao; Rajadas, Jayakumar; Green, Michael; Feinberg, Evan N; Pande, Vijay S; Shamloo, Mehrdad

2017-01-01

The beta-1 adrenergic receptor (ADRB1) is a promising therapeutic target intrinsically involved in the cognitive deficits and pathological features associated with Alzheimer's disease (AD). Evidence indicates that ADRB1 plays an important role in regulating neuroinflammatory processes, and activation of ADRB1 may produce neuroprotective effects in neuroinflammatory diseases. Novel small molecule modulators of ADRB1, engineered to be highly brain permeable and functionally selective for the G protein with partial agonistic activity, could have tremendous value both as pharmacological tools and potential lead molecules for further preclinical development. The present study describes our ongoing efforts toward the discovery of functionally selective partial agonists of ADRB1 that have potential therapeutic value for AD and neuroinflammatory disorders, which has led to the identification of the molecule STD-101-D1. As a functionally selective agonist of ADRB1, STD-101-D1 produces partial agonistic activity on G protein signaling with an EC50 value in the low nanomolar range, but engages very little beta-arrestin recruitment compared to the unbiased agonist isoproterenol. STD-101-D1 also inhibits the tumor necrosis factor α (TNFα) response induced by lipopolysaccharide (LPS) both in vitro and in vivo, and shows high brain penetration. Other than the therapeutic role, this newly identified, functionally selective, partial agonist of ADRB1 is an invaluable research tool to study mechanisms of G protein-coupled receptor signal transduction.

NMDA receptor antagonists extend the sensitive period for imprinting.

PubMed

Parsons, C H; Rogers, L J

2000-03-01

Filial imprinting in the domestic chick occurs during a sensitive period of development. The exact timing of this period can vary according to the methods used to measure imprinting. Using our imprinting paradigm, we have shown that normal, dark-reared chicks lose the ability to imprint after the second day post-hatching. Further, we reported that chicks treated 10 h after hatching with a mixture of the noncompetitive NMDA receptor antagonist ketamine (55 mg/kg) and the alpha(2)-adrenergic receptor agonist xylazine (6 mg/kg) were able to imprint on day 8 after hatching, whereas controls treated with saline did not imprint. We now show that the effect of the ketamine-xylazine mixture can be mimicked by treating chicks with ketamine alone or with another noncompetitive NMDA receptor antagonist, MK-801 (5 mg/kg). Treating chicks with a single dose of ketamine (55 mg/kg) or with a single dose of xylazine (6 mg/kg) failed to produce the effect on the sensitive period. However, prolonging the action of ketamine by treating chicks with two doses of ketamine (at 10 and 12 h after hatching) did allow imprinting on day 8. In contrast, prolonging the action of xylazine had no effect on the sensitive period for imprinting. Chicks treated with MK-801 were also able to imprint on day 8. Thus, we have evidence that the NMDA receptor system is involved in the mechanisms that control the sensitive period for imprinting.

Functional expression of ionotropic glutamate receptors in the rabbit retinal ganglion cells.

PubMed

Chen, Yin-Peng; Chiao, Chuan-Chin

2012-01-03

It has been known that retinal ganglion cells (RGCs) with distinct morphologies have different physiological properties. It was hypothesized that different functions of RGCs may in part result from various expressions of N-methyl-d-aspartate (NMDA), α-amino-3-hydroxyl-5-methyl-isoxazole-4-propinoic acid (AMPA), and kainic acid (KA) receptors on their dendrites. In the present study, we aimed to characterize the functional expression of AMPA and NMDA receptors of morphologically identified RGCs in the wholemount rabbit retina. The agmatine (AGB) activation assay was used to reveal functional expression of ionotropic glutamate receptors after the RGCs were targeted by injecting Neurobiotin. To examine the excitability of these glutamate receptors in an agonist specific manner, the lower concentrations of AMPA (2 μM) and NMDA (100 μM) were chosen to examine G7 (ON-OFF direction selective ganglion cells) and G11 (alpha ganglion cells) types of RGCs. We found that less than 40% of G7 type RGCs had salient AGB activation when incubated with 2 μM AMPA or 100 μM NMDA. The G11 type RGCs also showed similar activation frequencies, except that all of the OFF subtype examined had no AGB permeation under the same AMPA concentration. These results suggest that RGCs with large somata (G7 and G11 types) may express various heterogeneous functional ionotropic glutamate receptors, thus in part rendering their functional diversity. Copyright © 2011 Elsevier B.V. All rights reserved.

Mixed Kappa/Mu Opioid Receptor Agonists: The 6β-Naltrexamines

PubMed Central

Cami-Kobeci, Gerta; Neal, Adrian P.; Bradbury, Faye A.; Purington, Lauren C.; Aceto, Mario D.; Harris, Louis S.; Lewis, John W.; Traynor, John R.; Husbands, Stephen M.

2011-01-01

Ligands from the naltrexamine series have consistently demonstrated agonist activity at kappa opioid receptors (KOR), with varying activity at the mu opioid receptor (MOR). Various 6β-cinnamoylamino derivatives were made with the aim of generating ligands with a KOR agonist/MOR partial agonist profile, as ligands with this activity may be of interest as treatment agents for cocaine abuse. The ligands all displayed the desired high affinity, non-selective binding in vitro and in the functional assays were high efficacy KOR agonists with some partial agonist activity at MOR. Two of the new ligands (12a, 12b) have been evaluated in vivo, with 12a acting as a KOR agonist, and therefore somewhat similar to the previously evaluated analogues 3–6, while 12b displayed predominant MOR agonist activity. PMID:19253970

Extrinsic factors regulate partial agonist efficacy of strychnine-sensitive glycine receptors

PubMed Central

Farroni, Jeffrey S; McCool, Brian A

2004-01-01

Background Strychnine-sensitive glycine receptors in many adult forebrain regions consist of alpha2 + beta heteromeric channels. This subunit composition is distinct from the alpha1 + beta channels found throughout the adult spinal cord. Unfortunately, the pharmacology of forebrain alpha2beta receptors are poorly defined compared to 'neonatal' alpha2 homomeric channels or 'spinal' alpha1beta heteromers. In addition, the pharmacologic properties of native alpha2beta glycine receptors have been generally distinct from receptors produced by heterologous expression. To identify subtype-specific pharmacologic tools for the forebrain alpha2beta receptors, it is important to identify a heterologous expression system that closely resembles these native glycine-gated chloride channels. Results While exploring pharmacological properties of alpha2beta glycine receptors compared to alpha2-homomers, we found that distinct heterologous expression systems appeared to differentially influence partial agonist pharmacology. The β-amino acid taurine possessed 30–50% efficacy for alpha2-containing receptor isoforms when expressed in HEK 293 cells. However, taurine efficacy was dramatically reduced in L-cell fibroblasts. Similar results were obtained for β-alanine. The efficacy of these partial agonists was also strongly reduced by the beta subunit. There were no significant differences in apparent strychnine affinity values calculated from concentration-response data between expression systems or subunit combinations. Nor did relative levels of expression correlate with partial agonist efficacy when compared within or between several different expression systems. Finally, disruption of the tubulin cytoskeleton reduced the efficacy of partial agonists in a subunit-dependent, but system-independent, fashion. Conclusions Our results suggest that different heterologous expression systems can dramatically influence the agonist pharmacology of strychnine-sensitive glycine receptors. In the systems examine here, these effects are independent of both absolute expression level and any system-related alterations in the agonist binding site. We conclude that complex interactions between receptor composition and extrinsic factors may play a significant role in determining strychnine-sensitive glycine receptor partial agonist pharmacology. PMID:15301692

Extrinsic factors regulate partial agonist efficacy of strychnine-sensitive glycine receptors.

PubMed

Farroni, Jeffrey S; McCool, Brian A

2004-08-09

Strychnine-sensitive glycine receptors in many adult forebrain regions consist of alpha2 + beta heteromeric channels. This subunit composition is distinct from the alpha1 + beta channels found throughout the adult spinal cord. Unfortunately, the pharmacology of forebrain alpha2beta receptors are poorly defined compared to 'neonatal' alpha2 homomeric channels or 'spinal' alpha1beta heteromers. In addition, the pharmacologic properties of native alpha2beta glycine receptors have been generally distinct from receptors produced by heterologous expression. To identify subtype-specific pharmacologic tools for the forebrain alpha2beta receptors, it is important to identify a heterologous expression system that closely resembles these native glycine-gated chloride channels. While exploring pharmacological properties of alpha2beta glycine receptors compared to alpha2-homomers, we found that distinct heterologous expression systems appeared to differentially influence partial agonist pharmacology. The beta-amino acid taurine possessed 30-50% efficacy for alpha2-containing receptor isoforms when expressed in HEK 293 cells. However, taurine efficacy was dramatically reduced in L-cell fibroblasts. Similar results were obtained for beta-alanine. The efficacy of these partial agonists was also strongly reduced by the beta subunit. There were no significant differences in apparent strychnine affinity values calculated from concentration-response data between expression systems or subunit combinations. Nor did relative levels of expression correlate with partial agonist efficacy when compared within or between several different expression systems. Finally, disruption of the tubulin cytoskeleton reduced the efficacy of partial agonists in a subunit-dependent, but system-independent, fashion. Our results suggest that different heterologous expression systems can dramatically influence the agonist pharmacology of strychnine-sensitive glycine receptors. In the systems examine here, these effects are independent of both absolute expression level and any system-related alterations in the agonist binding site. We conclude that complex interactions between receptor composition and extrinsic factors may play a significant role in determining strychnine-sensitive glycine receptor partial agonist pharmacology.

Blonanserin Ameliorates Phencyclidine-Induced Visual-Recognition Memory Deficits: the Complex Mechanism of Blonanserin Action Involving D3-5-HT2A and D1-NMDA Receptors in the mPFC

PubMed Central

Hida, Hirotake; Mouri, Akihiro; Mori, Kentaro; Matsumoto, Yurie; Seki, Takeshi; Taniguchi, Masayuki; Yamada, Kiyofumi; Iwamoto, Kunihiro; Ozaki, Norio; Nabeshima, Toshitaka; Noda, Yukihiro

2015-01-01

Blonanserin differs from currently used serotonin 5-HT2A/dopamine-D2 receptor antagonists in that it exhibits higher affinity for dopamine-D2/3 receptors than for serotonin 5-HT2A receptors. We investigated the involvement of dopamine-D3 receptors in the effects of blonanserin on cognitive impairment in an animal model of schizophrenia. We also sought to elucidate the molecular mechanism underlying this involvement. Blonanserin, as well as olanzapine, significantly ameliorated phencyclidine (PCP)-induced impairment of visual-recognition memory, as demonstrated by the novel-object recognition test (NORT) and increased extracellular dopamine levels in the medial prefrontal cortex (mPFC). With blonanserin, both of these effects were antagonized by DOI (a serotonin 5-HT2A receptor agonist) and 7-OH-DPAT (a dopamine-D3 receptor agonist), whereas the effects of olanzapine were antagonized by DOI but not by 7-OH-DPAT. The ameliorating effect was also antagonized by SCH23390 (a dopamine-D1 receptor antagonist) and H-89 (a protein kinase A (PKA) inhibitor). Blonanserin significantly remediated the decrease in phosphorylation levels of PKA at Thr197 and of NR1 (an essential subunit of N-methyl-D-aspartate (NMDA) receptors) at Ser897 by PKA in the mPFC after a NORT training session in the PCP-administered mice. There were no differences in the levels of NR1 phosphorylated at Ser896 by PKC in any group. These results suggest that the ameliorating effect of blonanserin on PCP-induced cognitive impairment is associated with indirect functional stimulation of the dopamine-D1-PKA-NMDA receptor pathway following augmentation of dopaminergic neurotransmission due to inhibition of both dopamine-D3 and serotonin 5-HT2A receptors in the mPFC. PMID:25120077

5-Fluorotryptamine is a partial agonist at 5-HT3 receptors, and reveals that size and electronegativity at the 5 position of tryptamine are critical for efficient receptor function.

PubMed

Bower, Kiowa S; Price, Kerry L; Sturdee, Laura E C; Dayrell, Mariza; Dougherty, Dennis A; Lummis, Sarah C R

2008-02-12

Antagonists, but not agonists, of the 5-HT3 receptor are useful therapeutic agents, and it is possible that partial agonists may also be potentially useful in the clinic. Here we show that 5-fluorotryptamine (5-FT) is a partial agonist at both 5-HT3A and 5-HT3AB receptors with an Rmax (Imax/Imax 5-HT) of 0.64 and 0.45 respectively. It is about 10 fold less potent than 5-HT: EC50=16 and 27 microM, and Ki for displacement of [3H]granisetron binding=0.8 and 1.8 microM for 5-HT3A and 5-HT3AB receptors respectively. We have also explored the potencies and efficacies of tryptamine and a range of 5-substituted tryptamine derivatives. At 5-HT3A receptors tryptamine is a weak (Rmax=0.15), low affinity (EC50=113 microM; Ki=4.8 microM) partial agonist, while 5-chlorotryptamine has a similar affinity to 5-FT (EC50=8.1 microM; Ki=2.7 microM) but is a very weak partial agonist (Rmax=0. 0037). These, and data from 5-methyltryptamine and 5-methoxytryptamine, reveal the importance of size and electronegativity at this location for efficient channel opening.

Fear extinction and BDNF: Translating animal models of PTSD to the clinic

PubMed Central

Andero, Raül; Ressler, Kerry J

2012-01-01

Brain-derived neurotrophic factor (BDNF) is the most studied neurotrophin involved in synaptic plasticity processes that are required for long-term learning and memory. Specifically, BDNF gene expression and activation of its high-affinity TrkB receptor are necessary in the amygdala, hippocampus and prefrontal cortex for the formation of emotional memories, including fear memories. Among the psychiatric disorders with altered fear processing there is Post-traumatic Stress Disorder (PTSD) which is characterized by an inability to extinguish fear memories. Since BDNF appears to enhance extinction of fear, targeting impaired extinction in anxiety disorders such as PTSD via BDNF signalling may be an important and novel way to enhance treatment efficacy. The aim of this review is to provide a translational point of view that stems from findings in the BDNF regulation of synaptic plasticity and fear extinction. In addition, there are different systems that seem to alter fear extinction through BDNF modulation like the endocannabionoid system and the hypothalamic-pituitary adrenal axis (HPA). Recent work also finds that the pituitary adenylate cyclase-activating polypeptide (PACAP) and PAC1 receptor, which are upstream of BDNF activation, may be implicated in PTSD. Especially interesting are data that exogenous fear extinction enhancers such as antidepressants, histone deacetylases inhibitors (HDACi) and D-cycloserine, a partial NMDA agonist, may act through or in concert with the BDNF-TrkB system. Finally, we review studies where recombinant BDNF and a putative TrkB agonist, 7,8-DHF, may enhance extinction of fear. These approaches may lead to novel agents that improve extinction in animal models and eventually humans. PMID:22530815

Immunocytochemical localization of the NMDA-R2A receptor subunit in the cat retina.

PubMed

Goebel, D J; Aurelia, J L; Tai, Q; Jojich, L; Poosch, M S

1998-10-19

Immunocytochemical studies were performed to determine the distribution and cellular localization of the NMDA-R2A receptor subunit (R2A) in the cat retina. R2A-immunoreactivity (R2A-IR) was noted in all layers of the retina, with specific localizations in the outer segments of red/green and blue cone photoreceptors, B-type horizontal cells, several types of amacrine cells, Müller cells and the majority of cells in the ganglion cell layer. In the inner nuclear layer, 48% of all cells residing in the amacrine cell layer were R2A-IR including a cell resembling the GABAergic A17 amacrine cell. Interestingly, the AII rod amacrine cell was devoid of R2A-IR. Although the localization of the R2A subunit was anticipated in ganglion cells, amacrines and Müller cells, the presence of this receptor subunit to the cells in the outer retina was not expected. Here, both the R2A and the R2B subunits were found to be present in the outer segments of cone photoreceptors and to the tips of rod outer segments. Although the function of these receptor subunits in rod and cone photoreceptors remains to be determined, the fact that both R2A and R2B receptor subunits are localized to cone outer segments suggests a possible alternative pathway for calcium entry into a region where this cation plays such a crucial role in the process of phototransduction. To further classify the cells that display NR2A-IR, we performed dual labeling experiments showing the relationship between R2A-labeled cells with GABA. Results showed that all GABAergic-amacrines and displaced amacrines express the R2A-subunit protein. In addition, approximately 11% of the NR2A-labeled amacrines, did not stain for GABA. These findings support pharmacological data showing that NMDA directly facilitates GABA release in retina and retinal cultures [I.L. Ferreira, C.B. Duarte, P.F. Santos, C.M. Carvalho, A.P. Carvalho, Release of [3H]GABA evoked by glutamate receptor agonist in cultured chick retinal cells: effect of Ca2+, Brain Res. 664 (1994) 252-256; G.D. Zeevalk, W.J. Nicklas, Action of the anti-ischemic agent ifenprodil on N-methyl-d-aspartate and kainate-mediated excitotoxicity, Brain Res. 522 (1990) 135-139; R. Huba, H.D. Hofmann, Transmitter-gated currents of GABAergic amacrine-like cells in chick retinal cultures, Vis. Neurosci. 6 (1991) 303-314; M. Yamashita, R. Huba, H.D. Hofmann, Early in vitro development of voltage- and transmitter-gated currents in GABAergic amacrine cells, Dev. Brain Res. 82 (1994) 95-102; R. Ientile, S. Pedale, V. Picciurro, V. Macaione, C. Fabiano, S. Macaione, Nitric oxide mediates NMDA-evoked [3H]GABA release from chick retina cells, FEBS Lett. 417 (1997) 345-348; R.C. Kubrusly, M.C. deMello, F.G. deMello, Aspartate as a selective NMDA agonist in cultured cells from the avian retina, Neurochem. Intl. 32 (1998) 47-52] or reduction of GABA in vivo [N.N. Osborn, A.J. Herrera, The effect of experimental ischaemia and excitatory amino acid agonist on the GABA and serotonin immunoreactivities in the rabbit retina, Neurosci. 59 (1994) 1071-1081]. Since the majority of GABAergic synapses in the inner retina are onto both rod and cone bipolar axon terminals [R.G. Pourcho, M.T. Owzcarzak, Distribution of GABA immunoreactivity in the cat retina: A light and electron-microscopic study, Vis. Neurosci. 2 (1989) 425-435], we hypothesize that the NMDA-receptor plays a crucial role in providing feedback inhibition onto rod and cone bipolar cells. Copyright 1998 Elsevier Science B.V.

Effects of the potential 5-HT7 receptor agonist AS 19 in an autoshaping learning task.

PubMed

Perez-García, Georgina S; Meneses, A

2005-08-30

This work aimed to evaluate further the role of 5-HT7 receptors during memory formation in an autoshaping Pavlovian/instrumental learning task. Post-training administration of the potential 5-HT7 receptor agonist AS 19 or antagonist SB-269970 enhanced memory formation or had no effect, respectively. The AS 19 facilitatory effect was reversed by SB-269970, but not by the selective 5-HT1A antagonist WAY100635. Amnesia induced by scopolamine (cholinergic antagonist) or dizocilpine (NMDA antagonist) was also reversed by AS 19. Certainly, reservations regarding the selectivity of AS 19 for 5-HT7 and other 5-HT receptors in vivo are noteworthy and, therefore, its validity for use in animal models as a pharmacological tool. Having mentioned that, it should be noticed that together these data are providing further support to the notion of the 5-HT7 receptors role in memory formation. Importantly, this 5-HT7 receptor agonist AS 19 appears to represent a step forward respect to the notion that potent and selective 5-HT7 receptor agonists can be useful in the treatment of dysfunctional memory in aged-related decline and Alzheimer's disease.

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

Lu, Jun; Byrne, Noel; Wang, John

Clinical studies indicate that partial agonists of the G-protein-coupled, free fatty acid receptor 1 GPR40 enhance glucose-dependent insulin secretion and represent a potential mechanism for the treatment of type 2 diabetes mellitus. Full allosteric agonists (AgoPAMs) of GPR40 bind to a site distinct from partial agonists and can provide additional efficacy. We report the 3.2-Å crystal structure of human GPR40 (hGPR40) in complex with both the partial agonist MK-8666 and an AgoPAM, which exposes a novel lipid-facing AgoPAM-binding pocket outside the transmembrane helical bundle. Comparison with an additional 2.2-Å structure of the hGPR40–MK-8666 binary complex reveals an induced-fit conformational couplingmore » between the partial agonist and AgoPAM binding sites, involving rearrangements of the transmembrane helices 4 and 5 (TM4 and TM5) and transition of the intracellular loop 2 (ICL2) into a short helix. These conformational changes likely prime GPR40 to a more active-like state and explain the binding cooperativity between these ligands.« less

D-amino acid oxidase is expressed in the ventral tegmental area and modulates cortical dopamine

PubMed Central

Betts, Jill F.; Schweimer, Judith V.; Burnham, Katherine E.; Burnet, Philip W. J.; Sharp, Trevor; Harrison, Paul J.

2014-01-01

D-amino acid oxidase (DAO, DAAO) degrades the NMDA receptor co-agonist D-serine, modulating D-serine levels and thence NMDA receptor function. DAO inhibitors are under development as a therapy for schizophrenia, a disorder involving both NMDA receptor and dopaminergic dysfunction. However, a direct role for DAO in dopamine regulation has not been demonstrated. Here, we address this question in two ways. First, using in situ hybridization and immunohistochemistry, we show that DAO mRNA and immunoreactivity are present in the ventral tegmental area (VTA) of the rat, in tyrosine hydroxylase (TH)-positive and -negative neurons, and in glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes. Second, we show that injection into the VTA of sodium benzoate, a DAO inhibitor, increases frontal cortex extracellular dopamine, as measured by in vivo microdialysis and high performance liquid chromatography. Combining sodium benzoate and D-serine did not enhance this effect, and injection of D-serine alone affected dopamine metabolites but not dopamine. These data show that DAO is expressed in the VTA, and suggest that it impacts on the mesocortical dopamine system. The mechanism by which the observed effects occur, and the implications of these findings for schizophrenia therapy, require further study. PMID:24822045

Antinociceptive actions of honokiol and magnolol on glutamatergic and inflammatory pain

PubMed Central

2009-01-01

The antinociceptive effects of honokiol and magnolol, two major bioactive constituents of the bark of Magnolia officinalis, were investigated on animal paw licking responses and thermal hyperalgesia induced by glutamate receptor agonists including glutamate, N-methyl-D-aspartate (NMDA), and metabotropic glutamate 5 receptor (mGluR5) activator (RS)-2-chloro-5-hydroxyphenylglycine (CHPG), as well as inflammatory mediators such as substance P and prostaglandin E2 (PGE2) in mice. The actions of honokiol and magnolol on glutamate-induced c-Fos expression in the spinal cord dorsal horn were also examined. Our data showed that honokiol and magnolol blocked glutamate-, substance P- and PGE2-induced inflammatory pain with similar potency and efficacy. Consistently, honokiol and magnolol significantly decreased glutamate-induced c-Fos protein expression in superficial (I-II) laminae of the L4-L5 lumbar dorsal horn. However, honokiol was more selective than magnolol for inhibition of NMDA-induced licking behavioral and thermal hyperalgesia. In contrast, magnolol was more potent to block CHPG-mediated thermal hyperalgesia. These results demonstrate that honokiol and magnolol effectively decreased the inflammatory pain. Furthermore, their different potency on inhibition of nociception provoked by NMDA receptor and mGluR5 activation should be considered. PMID:19832997

Albumin elicits calcium signals from astrocytes in brain slices from neonatal rat cortex

PubMed Central

Nadal, Angel; Sul, Jai-Yoon; Valdeolmillos, Miguel; McNaughton, Peter A

1998-01-01

Albumin causes calcium signals and mitosis in cultured astrocytes, but it has not been established whether astrocytes in intact brain also respond to albumin. The effect of albumin on intracellular calcium concentration ([Ca2+]i) in single cells was therefore studied in acutely isolated cortical brain slices from the neonatal rat.Physiological concentrations of albumin from plasma and from serum produced an increase in [Ca2+]i in a subpopulation of cortical cells. Trains of transient elevations in [Ca2+]i (Ca2+ spikes) were seen in 41 % of these cells.The cells responding to albumin are identified as astrocytes because the neurone-specific agonist NMDA caused much smaller and slower responses in these cells. On the other hand NMDA-responsive cells, which are probably neurones, exhibited only small and slow responses to albumin. The residual responses of astrocytes to NMDA and neurones to albumin are likely to be due to crosstalk with adjacent neurones and astrocytes, respectively.Methanol extraction of albumin removes a polar lipid and abolishes the ability of albumin to increase intracellular calcium.Astrocyte calcium signalling caused by albumin may have important physiological consequences when the blood-brain barrier breaks down and allows albumin to enter the CNS. PMID:9596793

Effect of partial agonist activity in beta blockers in severe angina pectoris: a double blind comparison of pindolol and atenolol.

PubMed Central

Quyyumi, A A; Wright, C; Mockus, L; Fox, K M

1984-01-01

The use of beta adrenoceptor blockade in the treatment of rest angina is controversial, and the effects on severe angina of partial agonist activity in beta blockers are unknown. Eight patients with effort angina and seven with effort and nocturnal angina and severe coronary artery disease were studied initially when they were not taking any antianginal drugs. Pindolol 5 mg thrice daily (with partial agonist activity) and atenolol 100 mg daily (without partial agonist activity) were given for five days each in a double blind randomised manner. Diaries of angina were kept and treadmill exercise testing and ambulatory ST monitoring performed during the last 48 hours of each period of treatment. Daytime and nocturnal resting heart rates and the frequency of angina were significantly reduced by atenolol compared with pindolol (p less than 0.01). The duration of exercise was significantly increased and the frequency, duration, and magnitude of daytime and nocturnal episodes of ST segment depression on ambulatory monitoring were reduced by atenolol. Reduction in resting heart rate is important in the treatment of both effort and nocturnal angina. Partial agonist activity in beta adrenoceptor antagonists may be deleterious in patients with severe angina pectoris. PMID:6148991

NMDA receptor activation regulates sociability by its effect on mTOR signaling activity.

PubMed

Burket, Jessica A; Benson, Andrew D; Tang, Amy H; Deutsch, Stephen I

2015-07-03

Tuberous Sclerosis Complex is one example of a syndromic form of autism spectrum disorder associated with disinhibited activity of mTORC1 in neurons (e.g., cerebellar Purkinje cells). mTORC1 is a complex protein possessing serine/threonine kinase activity and a key downstream molecule in a signaling cascade beginning at the cell surface with the transduction of neurotransmitters (e.g., glutamate and acetylcholine) and nerve growth factors (e.g., Brain-Derived Neurotrophic Factor). Interestingly, the severity of the intellectual disability in Tuberous Sclerosis Complex may relate more to this metabolic disturbance (i.e., overactivity of mTOR signaling) than the density of cortical tubers. Several recent reports showed that rapamycin, an inhibitor of mTORC1, improved sociability and other symptoms in mouse models of Tuberous Sclerosis Complex and autism spectrum disorder, consistent with mTORC1 overactivity playing an important pathogenic role. NMDA receptor activation may also dampen mTORC1 activity by at least two possible mechanisms: regulating intraneuronal accumulation of arginine and the phosphorylation status of a specific extracellular signal regulating kinase (i.e., ERK1/2), both of which are "drivers" of mTORC1 activity. Conceivably, the prosocial effects of targeting the NMDA receptor with agonists in mouse models of autism spectrum disorders result from their ability to dampen mTORC1 activity in neurons. Strategies for dampening mTORC1 overactivity by NMDA receptor activation may be preferred to its direct inhibition in chronic neurodevelopmental disorders, such as autism spectrum disorders. Copyright © 2015 Elsevier Inc. All rights reserved.

Ionotropic and metabotropic glutamate receptor mediation of glucocorticoid-induced apoptosis in hippocampal cells and the neuroprotective role of synaptic N-methyl-D-aspartate receptors.

PubMed

Lu, J; Goula, D; Sousa, N; Almeida, O F X

2003-01-01

Glutamate receptors have been proposed to mediate the apoptotic actions of glucocorticoids in hippocampal cells. To further analyze the role of glutamate receptors in this process, we pretreated primary hippocampal cells from neonatal (postnatal day 4) rats with antagonists of ionotropic glutamate receptor (iGluR) and metabotropic glutamate receptor (mGluR) antagonists before exposure to the specific glucocorticoid receptor agonist dexamethasone (DEX) at a dose of 1 microM. Dizocilpine (MK801; a general N-methyl-D-aspartic acid [NMDA] receptor antagonist, NMDAR antagonist) and ifenprodil (a specific ligand of the NMDAR 2B subunit, NR2B), were used to block iGluR; (RS)-alpha-ethyl-4-carboxyphenylglycine (E4CPG) and (RS)-alpha-cyclopropyl-4-phosphonophenyl-glycine (CPPG) were employed as I/II (E4CPG) and II/III (CPPG) mGluR antagonists. Blockade of iGluR resulted in a significant attenuation of DEX-induced cell death; the finding that ifenprodil exerted a similar potency to MK801 demonstrates the involvement of NR2B receptors in glucocorticoid-induced cell death. Apoptosis accounted for a significant amount of the cell loss observed, as detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling histochemistry for the in situ labeling of DNA breaks; apoptotic cells were distinguished from necrosis on the basis of morphological criteria, including chromatin condensation, membrane blebbing and presence of apoptotic bodies. Treatment with E4CPG and CPPG completely abolished the apoptotic response to DEX, thus showing the additional contribution of mGluR to the phenomenon. Further, dose-response studies with NMDA revealed that whereas high (10 microM) doses of NMDA themselves elicit cytotoxic responses, low (1-5 microM) concentrations of NMDA can effectively oppose DEX-induced cell death. Interestingly, the neuroprotective actions of low dose NMDA stimulation were abolished when either synaptic or extrasynaptic NMDA receptors were blocked with MK801 in combination with the GABA receptor antagonist bicuculline (synaptic) or ifenprodil (extrasynaptic). In summary, the present data show that both iGluR and mGluR mediate the neurotoxic effects of glucocorticoids on hippocampal cells and that pre-treatment with low doses of NMDA, by acting on synaptic and extrasynaptic receptors, render hippocampal cells less vulnerable to glucocorticoid insults.

Generalized concentration addition: a method for examining mixtures containing partial agonists.

PubMed

Howard, Gregory J; Webster, Thomas F

2009-08-07

Environmentally relevant toxic exposures often consist of simultaneous exposure to multiple agents. Methods to predict the expected outcome of such combinations are critical both to risk assessment and to an accurate judgment of whether combinations are synergistic or antagonistic. Concentration addition (CA) has commonly been used to assess the presence of synergy or antagonism in combinations of similarly acting chemicals, and to predict effects of combinations of such agents. CA has the advantage of clear graphical interpretation: Curves of constant joint effect (isoboles) must be negatively sloped straight lines if the mixture is concentration additive. However, CA cannot be directly used to assess combinations that include partial agonists, although such agents are of considerable interest. Here, we propose a natural extension of CA to a functional form that may be applied to mixtures including full agonists and partial agonists. This extended definition, for which we suggest the term "generalized concentration addition," encompasses linear isoboles with slopes of any sign. We apply this approach to the simple example of agents with dose-response relationships described by Hill functions with slope parameter n=1. The resulting isoboles are in all cases linear, with negative, zero and positive slopes. Using simple mechanistic models of ligand-receptor systems, we show that the same isobole pattern and joint effects are generated by modeled combinations of full and partial agonists. Special cases include combinations of two full agonists and a full agonist plus a competitive antagonist.

A role for N-methyl-D-aspartate receptors in norepinephrine-induced long-lasting potentiation in the dentate gyrus.

PubMed

Stanton, P K; Mody, I; Heinemann, U

1989-01-01

Mechanisms of action of norepinephrine (NE) on dentate gyrus granule cells were studied in rat hippocampal slices using extra- and intracellular recordings and measurements of stimulus and amino acid-induced changes in extracellular Ca2+ and K+ concentration. Bath application of NE (10-50 microM) induced long-lasting potentiation of perforant path evoked potentials, and markedly enhanced high-frequency stimulus-induced Ca2+ influx and K+ efflux, actions blocked by beta-receptor antagonists and mimicked by beta agonists. Enhanced Ca2+ influx was primarily postsynaptic, since presynaptic delta [Ca2+]o in the stratum moleculare synaptic field was not altered by NE. Interestingly, the potentiation of both ionic fluxes and evoked population potentials were antagonized by the N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovalerate (APV). Furthermore, NE selectively enhanced the delta [Ca2+]o delta [K+]o and extracellular slow negative field potentials elicited by iontophoretically applied NMDA, but not those induced by the excitatory amino acid quisqualate. These results suggest that granule cell influx of Ca2+ through NMDA ionophores is enhanced by NE via beta-receptor activation. In intracellular recordings, NE depolarized granule cells (4.8 +/- 1.1 mV), and increased input resistance (RN) by 34 +/- 6.5%. These actions were also blocked by either the beta-antagonist propranolol or specific beta 1-blocker metoprolol. Moreover, the depolarization and RN increase persisted for long periods (93 +/- 12 min) after NE washout. In contrast, while NE, in the presence of APV, still depolarized granule cells and increased RN, APV made these actions quickly reversible upon NE washout (16 +/- 9 min). This suggested that NE induction of long-term, but not short-term, plasticity in the dentate gyrus requires NMDA receptor activation. NE may be enhancing granule cell firing by some combination of blockade on the late Ca2+-activated K+ conductance and depolarization of granule cells, both actions that can bring granule cells into a voltage range where NMDA receptors are more easily activated. Furthermore, NE also elicited activity-independent long-lasting depolarization and RN increases, which required functional NMDA receptors to persist.

Activity-dependent ubiquitination of GluA1 mediates a distinct AMPA receptor endocytosis and sorting pathway.

PubMed

Schwarz, Lindsay A; Hall, Benjamin J; Patrick, Gentry N

2010-12-08

The accurate trafficking of AMPA receptors (AMPARs) to and from the synapse is a critical component of learning and memory in the brain, whereas dysfunction of AMPAR trafficking is hypothesized to be an underlying mechanism of Alzheimer's disease. Previous work has shown that ubiquitination of integral membrane proteins is a common posttranslational modification used to mediate endocytosis and endocytic sorting of surface proteins in eukaryotic cells. Here we report that mammalian AMPARs become ubiquitinated in response to their activation. Using a mutant of GluA1 that is unable to be ubiquitinated at lysines on its C-terminus, we demonstrate that ubiquitination is required for internalization of surface AMPARs and their trafficking to the lysosome in response to the AMPAR agonist AMPA but not for internalization of AMPARs in response to the NMDA receptor agonist NMDA. Through overexpression or RNA interference-mediated knockdown, we identify that a specific E3 ligase, Nedd4-1 (neural-precursor cell-expressed developmentally downregulated gene 4-1), is necessary for this process. Finally, we show that ubiquitination of GluA1 by Nedd4-1 becomes more prevalent as neurons mature. Together, these data show that ubiquitination of GluA1-containing AMPARs by Nedd4-1 mediates their endocytosis and trafficking to the lysosome. Furthermore, these results provide insight into how hippocampal neurons regulate AMPAR trafficking and degradation with high specificity in response to differing neuronal signaling cues and suggest that changes to this pathway may occur as neurons mature.

Activity-Dependent Ubiquitination of GluA1 Mediates a Distinct AMPAR Endocytosis and Sorting Pathway

PubMed Central

Schwarz, Lindsay A.; Hall, Benjamin J.; Patrick, Gentry N.

2010-01-01

The accurate trafficking of AMPA receptors (AMPARs) to and from the synapse is a critical component of learning and memory in the brain, while dysfunction of AMPAR trafficking is hypothesized to be an underlying mechanism of Alzheimer’s disease. Previous work has shown that ubiquitination of integral membrane proteins is a common post-translational modification used to mediate endocytosis and endocytic sorting of surface proteins in eukaryotic cells. Here we report that mammalian AMPARs become ubiquitinated in response to their activation. Using a mutant of GluA1 that is unable to be ubiquitinated at lysines on its carboxy-terminus, we demonstrate that ubiquitination is required for internalization of surface AMPARs and their trafficking to the lysosome in response to the AMPAR agonist AMPA, but not for internalization of AMPARs in response to the NMDA receptor (NMDAR) agonist NMDA. Through over-expression or RNAi-mediated knockdown, we identify that a specific E3 ligase, Nedd4-1, is necessary for this process. Finally, we show that ubiquitination of GluA1 by Nedd4-1 becomes more prevalent as neurons mature. Together, these data show that ubiquitination of GluA1-containing AMPARs by Nedd4-1 mediates their endocytosis and trafficking to the lysosome. Furthermore, these results provide insight into how hippocampal neurons regulate AMPAR trafficking and degradation with high specificity in response to differing neuronal signaling cues, and suggest that changes to this pathway may occur as neurons mature. PMID:21148011

Identification of Developmentally Regulated PCP-Responsive Non-Coding RNA, prt6, in the Rat Thalamus

PubMed Central

Umino, Asami; Nishikawa, Toru

2014-01-01

Schizophrenia and similar psychoses induced by NMDA-type glutamate receptor antagonists, such as phencyclidine (PCP) and ketamine, usually develop after adolescence. Moreover, adult-type behavioral disturbance following NMDA receptor antagonist application in rodents is observed after a critical period at around 3 postnatal weeks. These observations suggest that the schizophrenic symptoms caused by and psychotomimetic effects of NMDA antagonists require the maturation of certain brain neuron circuits and molecular networks, which differentially respond to NMDA receptor antagonists across adolescence and the critical period. From this viewpoint, we have identified a novel developmentally regulated phencyclidine-responsive transcript from the rat thalamus, designated as prt6, as a candidate molecule involved in the above schizophrenia-related systems using a DNA microarray technique. The transcript is a non-coding RNA that includes sequences of at least two microRNAs, miR132 and miR212, and is expressed strongly in the brain and testis, with trace or non-detectable levels in the spleen, heart, liver, kidney, lung and skeletal muscle, as revealed by Northern blot analysis. The systemic administration of PCP (7.5 mg/kg, subcutaneously (s.c.)) significantly elevated the expression of prt6 mRNA in the thalamus at postnatal days (PD) 32 and 50, but not at PD 8, 13, 20, or 24 as compared to saline-treated controls. At PD 50, another NMDA receptor antagonist, dizocilpine (0.5 mg/kg, s.c.), and a schizophrenomimetic dopamine agonist, methamphetamine (4.8 mg/kg, s.c.), mimicked a significant increase in the levels of thalamic prt6 mRNAs, while a D2 dopmamine receptor antagonist, haloperidol, partly inhibited the increasing influence of PCP on thalamic prt6 expression without its own effects. These data indicate that prt6 may be involved in the pathophysiology of the onset of drug-induced schizophrenia-like symptoms and schizophrenia through the possible dysregulation of target genes of the long non-coding RNA or microRNAs in the transcript. PMID:24886782

5-Fluorotryptamine is a partial agonist at 5-HT3 receptors, and reveals that size and electronegativity at the 5 position of tryptamine are critical for efficient receptor function

PubMed Central

Bower, Kiowa S.; Price, Kerry L.; Sturdee, Laura E.C.; Dayrell, Mariza; Dougherty, Dennis A.; Lummis, Sarah C.R.

2008-01-01

Antagonists, but not agonists, of the 5-HT3 receptor are useful therapeutic agents, and it is possible that partial agonists may also be potentially useful in the clinic. Here we show that 5-fluorotryptamine (5-FT) is a partial agonist at both 5-HT3A and 5-HT3AB receptors with an Rmax (Imax / Imax5-HT) of 0.64 and 0.45 respectively. It is about 10 fold less potent than 5-HT: EC50 = 16 and 27 μM, and Ki for displacement of [3H]granisetron binding = 0.8 and 1.8 μM for 5-HT3A and 5-HT3AB receptors respectively. We have also explored the potencies and efficacies of tryptamine and a range of 5-substituted tryptamine derivatives. At 5-HT3A receptors tryptamine is a weak (Rmax = 0.15), low affinity (EC50 = 113 μM; Ki = 4.8 μM) partial agonist, while 5-chlorotryptamine has a similar affinity to 5-FT (EC50 = 8.1 μM; Ki = 2.7 μM) but is a very weak partial agonist (Rmax = 0. 0037). These, and data from 5-methyltryptamine and 5-methoxytryptamine, reveal the importance of size and electronegativity at this location for efficient channel opening. PMID:18082160

Dynamic Changes in Cytosolic ATP Levels in Cultured Glutamatergic Neurons During NMDA-Induced Synaptic Activity Supported by Glucose or Lactate.

PubMed

Lange, Sofie C; Winkler, Ulrike; Andresen, Lars; Byhrø, Mathilde; Waagepetersen, Helle S; Hirrlinger, Johannes; Bak, Lasse K

2015-12-01

We have previously shown that synaptic transmission fails in cultured neurons in the presence of lactate as the sole substrate. Thus, to test the hypothesis that the failure of synaptic transmission is a consequence of insufficient energy supply, ATP levels were monitored employing the ATP biosensor Ateam1.03YEMK. While inducing synaptic activity by subjecting cultured neurons to two 30 s pulses of NMDA (30 µM) with a 4 min interval, changes in relative ATP levels were measured in the presence of lactate (1 mM), glucose (2.5 mM) or the combination of the two. ATP levels reversibly declined following NMDA-induced neurotransmission activity, as indicated by a reversible 10-20 % decrease in the response of the biosensor. The responses were absent when the NMDA receptor antagonist memantine was present. In the presence of lactate alone, the ATP response dropped significantly more than in the presence of glucose following the 2nd pulse of NMDA (approx. 10 vs. 20 %). Further, cytosolic Ca(2+) homeostasis during NMDA-induced synaptic transmission is partially inhibited by verapamil indicating that voltage-gated Ca(2+) channels are activated. Lastly, we showed that cytosolic Ca(2+) homeostasis is supported equally well by both glucose and lactate, and that a pulse of NMDA causes accumulation of Ca(2+) in the mitochondrial matrix. In summary, we have shown that ATP homeostasis during neurotransmission activity in cultured neurons is supported by both glucose and lactate. However, ATP homeostasis seems to be negatively affected by the presence of lactate alone, suggesting that glucose is needed to support neuronal energy metabolism during activation.

Na+,K+-ATPase functionally interacts with the plasma membrane Na+,Ca2+ exchanger to prevent Ca2+ overload and neuronal apoptosis in excitotoxic stress.

PubMed

Sibarov, Dmitry A; Bolshakov, Artemiy E; Abushik, Polina A; Krivoi, Igor I; Antonov, Sergei M

2012-12-01

Using a fluorescent viability assay, immunocytochemistry, patch-clamp recordings, and Ca(2+) imaging analysis, we report that ouabain, a specific ligand of the Na(+),K(+)-ATPase cardiac glycoside binding site, can prevent glutamate receptor agonist-induced apoptosis in cultured rat cortical neurons. In our model of excitotoxicity, a 240-min exposure to 30 μM N-methyl-d-aspartate (NMDA) or kainate caused apoptosis in ∼50% of neurons. These effects were accompanied by a significant decrease in the number of neurons that were immunopositive for the antiapoptotic peptide Bcl-2. Apoptotic injury was completely prevented when the agonists were applied together with 0.1 or 1 nM ouabain, resulting in a greater survival of neurons, and the percentage of neurons expressing Bcl-2 remained similar to those obtained without agonist treatments. In addition, subnanomolar concentrations of ouabain prevented the increase of spontaneous excitatory postsynaptic current's frequency and the intracellular Ca(2+) overload induced by excitotoxic insults. Loading neurons with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid or inhibition of the plasma membrane Na(+),Ca(2+)-exchanger by 2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate (KB-R7943) eliminated ouabain's effects on NMDA- or kainite-evoked enhancement of spontaneous synaptic activity. Our data suggest that during excitotoxic insults ouabain accelerates Ca(2+) extrusion from neurons via the Na(+),Ca(2+) exchanger. Because intracellular Ca(2+) accumulation caused by the activation of glutamate receptors and boosted synaptic activity represents a key factor in triggering neuronal apoptosis, up-regulation of Ca(2+) extrusion abolishes its development. These antiapoptotic effects are independent of Na(+),K(+)-ATPase ion transport function and are initiated by concentrations of ouabain that are within the range of an endogenous analog, suggesting a novel functional role for Na(+),K(+)-ATPase in neuroprotection.

Agonist-induced modulation of inverse agonist efficacy at the beta 2-adrenergic receptor.

PubMed

Chidiac, P; Nouet, S; Bouvier, M

1996-09-01

Sustained stimulation of several G protein-coupled receptors is known to lead to a reduction in the signaling efficacy. This phenomenon, named agonist-induced desensitization, has been best studied for the beta 2-adrenergic receptor (AR) and is characterized by a decreased efficacy of beta-adrenergic agonists to stimulate the adenylyl cyclase activity. Recently, several beta-adrenergic ligands were found to inhibit the spontaneous agonist-independent activity of the beta 2AR. These compounds, termed inverse agonists, have different inhibitory efficacies, ranging from almost neutral antagonists to full inverse agonists. The current study was undertaken to determine whether, as is the case for agonists, desensitization can affect the efficacies of inverse agonists. Agonist-promoted desensitization of the human beta 2AR expressed in Sf9 cells potentiated the inhibitory actions of the inverse agonists, with the extent of the potentiation being inversely proportional to their intrinsic activity. For example, desensitization increased the inhibitory action of the weak inverse agonist labetalol by 29%, whereas inhibition of the spontaneous activity by the strong inverse agonist timolol was not enhanced by the desensitizing stimuli. Interestingly, dichloroisoproterenol acted stochastically as either a weak partial agonist or a weak inverse agonist in control conditions but always behaved as an inverse agonist after desensitization. These data demonstrate that like for agonists, the efficacies of inverse agonists can be modulated by a desensitizing treatment. Also, the data show that the initial state of the receptor can determine whether a ligand behaves as a partial agonist or an inverse agonist.

Ligand-based receptor tyrosine kinase partial agonists: New paradigm for cancer drug discovery?

PubMed

Riese, David J

2011-02-01

INTRODUCTION: Receptor tyrosine kinases (RTKs) are validated targets for oncology drug discovery and several RTK antagonists have been approved for the treatment of human malignancies. Nonetheless, the discovery and development of RTK antagonists has lagged behind the discovery and development of agents that target G-protein coupled receptors. In part, this is because it has been difficult to discover analogs of naturally-occurring RTK agonists that function as antagonists. AREAS COVERED: Here we describe ligands of ErbB receptors that function as partial agonists for these receptors, thereby enabling these ligands to antagonize the activity of full agonists for these receptors. We provide insights into the mechanisms by which these ligands function as antagonists. We discuss how information concerning these mechanisms can be translated into screens for novel small molecule- and antibody-based antagonists of ErbB receptors and how such antagonists hold great potential as targeted cancer chemotherapeutics. EXPERT OPINION: While there have been a number of important key findings into this field, the identification of the structural basis of ligand functional specificity is still of the greatest importance. While it is true that, with some notable exceptions, peptide hormones and growth factors have not proven to be good platforms for oncology drug discovery; addressing the fundamental issues of antagonistic partial agonists for receptor tyrosine kinases has the potential to steer oncology drug discovery in new directions. Mechanism based approaches are now emerging to enable the discovery of RTK partial agonists that may antagonize both agonist-dependent and -independent RTK signaling and may hold tremendous promise as targeted cancer chemotherapeutics.

Activation and inhibition of adenylyl cyclase isoforms by forskolin analogs.

PubMed

Pinto, Cibele; Papa, Dan; Hübner, Melanie; Mou, Tung-Chung; Lushington, Gerald H; Seifert, Roland

2008-04-01

Adenylyl cyclase (AC) isoforms 1 to 9 are differentially expressed in tissues and constitute an interesting drug target. ACs 1 to 8 are activated by the diterpene, forskolin (FS). It is unfortunate that there is a paucity of AC isoform-selective activators. To develop such compounds, an understanding of the structure/activity relationships of diterpenes is necessary. Therefore, we examined the effects of FS and nine FS analogs on ACs 1, 2, and 5 expressed in Spodoptera frugiperda insect cells. Diterpenes showed the highest potencies at AC1 and the lowest potencies at AC2. We identified full agonists, partial agonists, antagonists, and inverse agonists, i.e., diterpenes that reduced basal AC activity. Each AC isoform exhibited a distinct pharmacological profile. AC2 showed the highest basal activity of all AC isoforms and highest sensitivity to inverse agonistic effects of 1-deoxy-forskolin, 7-deacetyl-1,9-dideoxy-forskolin, and, particularly, BODIPY-forskolin. In contrast, BODIPY-forskolin acted as partial agonist at the other ACs. 1-Deoxy-forskolin analogs were devoid of agonistic activity at ACs but antagonized the effects of FS in a mixed competitive/noncompetitive manner. At purified catalytic AC subunits, BODIPY-forskolin acted as weak partial agonist/strong partial antagonist. Molecular modeling revealed that the BODIPY group rotates promiscuously outside of the FS-binding site. Collectively, ACs are not uniformly activated and inhibited by FS and FS analogs, demonstrating the feasibility to design isoform-selective FS analogs. The two- and multiple-state models, originally developed to conceptualize ligand effects at G-protein-coupled receptors, can be applied to ACs to explain certain experimental data.

The potent free radical scavenger alpha-lipoic acid improves memory in aged mice: putative relationship to NMDA receptor deficits.

PubMed

Stoll, S; Hartmann, H; Cohen, S A; Müller, W E

1993-12-01

alpha-Lipoic acid (alpha-LA) improved longer-term memory of aged female NMRI mice in the habituation in the open field test at a dose of 100 mg/kg body weight for 15 days. In a separate experiment, no such effect could be found for young mice. alpha-LA alleviated age-related NMDA receptor deficits (Bmax) without changing muscarinic, benzodiazepine, and alpha 2-adrenergic receptor deficits in aged mice. The carbachol-stimulated accumulation of inositol monophosphates was not changed by the treatment with alpha-LA. These results give tentative support to the hypothesis that alpha-LA improves memory in aged mice, probably by a partial compensation of NMDA receptor deficits. Possible modes of action of alpha-LA based on its free radical scavenger properties are discussed in relation to the membrane hypothesis of aging.

Properties of glutamate-gated ion channels in horizontal cells of the perch retina.

PubMed

Schmidt, K F

1997-08-01

The effect of two different concentrations of L-glutamate and kainate on the gating kinetics of amino acid-sensitive non-NMDA channels were studied in cultured teleost retinal horizontal cells by single-channel recording and by noise analysis of whole-cell currents. When the glutamate agonist kainate was applied clearly parabolic mean-variance relations of whole-cell membrane currents (up to 3000 pA) indicated that this agonist was acting on one type of channels with a conductance of 5-10 pS. The cells were less sensitive when L-glutamate was used as the agonist and in most cases whole-cell currents amounted to less than 200 pA. The mean-variance relation of glutamate induced currents was complex, indicating that more than one type of channel opening could be involved. Power spectra of whole-cell currents were fitted with two Lorentzians with time constants of approx. 1 and 5-20 msec. Effects on amplitudes and time constants of agonist concentrations are demonstrated. Two categories of unitary events with mean open times of approx. 1 and 7 msec and conductances of approx. 7 and 12 pS, respectively, were obtained in single-channel recordings from cell-attached patches at different concentrations of glutamate in the pipette.

Citral: a monoterpene with prophylactic and therapeutic anti-nociceptive effects in experimental models of acute and chronic pain.

PubMed

Nishijima, Catarine M; Ganev, Ellen G; Mazzardo-Martins, Leidiane; Martins, Daniel F; Rocha, Lúcia R M; Santos, Adair R S; Hiruma-Lima, Clelia A

2014-08-05

Citral (3,7-dimethyl-2,6-octadienal) is an open-chain monoterpenoid present in the essential oils of several medicinal plants. The aim of this work was to evaluate the effects of orally administered citral in experimental models of acute and chronic nociception, inflammation, and gastric ulcers caused by non-steroidal anti-inflammatory drugs (NSAIDs). Oral treatment with citral significantly inhibited the neurogenic and inflammatory pain responses induced by intra-plantar injection of formalin. Citral also had prophylactic and therapeutic anti-nociceptive effects against mechanical hyperalgesia in plantar incision surgery, chronic regional pain syndrome, and partial ligation of sciatic nerve models, without producing any significant motor dysfunction. In addition, citral markedly attenuated the pain response induced by intra-plantar injection of glutamate and phorbol 12-myristate 13-acetate (PMA, a protein kinase C activator), as well as by intrathecal (i.t.) injection of ionotropic and metabotropic glutamate receptor agonists (N-methyl-D-aspartic acid [NMDA] and 1-amino-1,3-dicarboxycyclopentane [trans-ACPD], respectively), substance P, and cytokine tumour necrosis factor-α. However, citral potentiated behaviours indicative of pain caused by i.t., but not intra-plantar, injection of a transient receptor potential vanilloid receptor type 1 (TRPV1) agonist. Finally, the anti-nociceptive action of citral was found to involve significant activation of the 5-HT2A serotonin receptor. The effect of citral was accompanied by a gastro-protective effect against NSAID-induced ulcers. Together, these results show the potential of citral as a new drug for the treatment of pain. Copyright © 2014 Elsevier B.V. All rights reserved.

Primary afferent activity, putative excitatory transmitters and extracellular potassium levels in frog spinal cord.

PubMed Central

Davidoff, R A; Hackman, J C; Holohean, A M; Vega, J L; Zhang, D X

1988-01-01

1. Changes in extracellular K+ activity were measured with ion-selective microelectrodes in the grey matter of the isolated hemisected frog spinal cord. The magnitude of the elevation of [K+]o (delta[K+]o) produced by repetitive stimulation (25 Hz, 10 s) of afferent fibres in the sciatic nerve was monotonically related to the strength of the electrical stimuli applied to the sciatic nerve. Repetitive stimulation of the largest diameter A alpha and A beta fibres, which were found histologically to comprise only 11% of the afferent axons in the dorsal root, elevated [K+]o to approximately 60% of the maximum level seen when all afferent fibres were stimulated. 2. Addition of Mg2+ (20 mM) to Ringer solution devoid of Mg2+ reduced delta[K+]o by over 85% suggesting that about 15% of delta[K+]o results from action potentials in presynaptic primary afferents. When 20 mM-Mg2+ was added to spinal cords bathed in Ringer solution containing a physiological (i.e. 1.0 mM) concentration of Mg2+, delta[K+]o was reduced by ca. 65-75% indicating that in spinal cords bathed in medium containing 'physiological' concentrations of Mg2+ about 25-35% of the K+ is released from primary afferent fibres. 3. Application of excitatory amino acids and agonists increased [K+]o with the following potency pattern: quisqualate greater than kainate greater than NMDA (N-methyl-D-aspartate) greater than glutamate greater than aspartate. 4. D(-)-2-Amino-5-phosphonovalerate (APV), an NMDA antagonist, reduced [K+]o by only about 50%, but kynurenate, an NMDA and non-NMDA antagonist, reduced [K+]o by approximately 85%; i.e. the same levels observed when synaptic transmission was blocked with 20 mM-Mg2+. These findings support the idea that synaptic release of excitatory amino acids such as L-glutamate and/or L-aspartate and subsequent activation of specific receptors by these putative transmitters are necessary for the postsynaptic component of delta[K+]o. 5. Addition of tachykinins elevated [K+]o but the effect appeared to require the participation of excitatory amino acids because it was blocked by APV and by kynurenate. 6. The finding that tetrodotoxin substantially reduced the ability of excitatory amino acid agonists and tachykinins to elevate [K+]o suggests that discharges in interneurones as a result of excitatory amino acid receptor activation are responsible for the postsynaptic component of delta[K+]o. PMID:3261795

Primary afferent activity, putative excitatory transmitters and extracellular potassium levels in frog spinal cord.

PubMed

Davidoff, R A; Hackman, J C; Holohean, A M; Vega, J L; Zhang, D X

1988-03-01

1. Changes in extracellular K+ activity were measured with ion-selective microelectrodes in the grey matter of the isolated hemisected frog spinal cord. The magnitude of the elevation of [K+]o (delta[K+]o) produced by repetitive stimulation (25 Hz, 10 s) of afferent fibres in the sciatic nerve was monotonically related to the strength of the electrical stimuli applied to the sciatic nerve. Repetitive stimulation of the largest diameter A alpha and A beta fibres, which were found histologically to comprise only 11% of the afferent axons in the dorsal root, elevated [K+]o to approximately 60% of the maximum level seen when all afferent fibres were stimulated. 2. Addition of Mg2+ (20 mM) to Ringer solution devoid of Mg2+ reduced delta[K+]o by over 85% suggesting that about 15% of delta[K+]o results from action potentials in presynaptic primary afferents. When 20 mM-Mg2+ was added to spinal cords bathed in Ringer solution containing a physiological (i.e. 1.0 mM) concentration of Mg2+, delta[K+]o was reduced by ca. 65-75% indicating that in spinal cords bathed in medium containing 'physiological' concentrations of Mg2+ about 25-35% of the K+ is released from primary afferent fibres. 3. Application of excitatory amino acids and agonists increased [K+]o with the following potency pattern: quisqualate greater than kainate greater than NMDA (N-methyl-D-aspartate) greater than glutamate greater than aspartate. 4. D(-)-2-Amino-5-phosphonovalerate (APV), an NMDA antagonist, reduced [K+]o by only about 50%, but kynurenate, an NMDA and non-NMDA antagonist, reduced [K+]o by approximately 85%; i.e. the same levels observed when synaptic transmission was blocked with 20 mM-Mg2+. These findings support the idea that synaptic release of excitatory amino acids such as L-glutamate and/or L-aspartate and subsequent activation of specific receptors by these putative transmitters are necessary for the postsynaptic component of delta[K+]o. 5. Addition of tachykinins elevated [K+]o but the effect appeared to require the participation of excitatory amino acids because it was blocked by APV and by kynurenate. 6. The finding that tetrodotoxin substantially reduced the ability of excitatory amino acid agonists and tachykinins to elevate [K+]o suggests that discharges in interneurones as a result of excitatory amino acid receptor activation are responsible for the postsynaptic component of delta[K+]o.

D-Aspartate drinking solution alleviates pain and cognitive impairment in neuropathic mice.

PubMed

Palazzo, Enza; Luongo, Livio; Guida, Francesca; Marabese, Ida; Romano, Rosaria; Iannotta, Monica; Rossi, Francesca; D'Aniello, Antimo; Stella, Luigi; Marmo, Federica; Usiello, Alessandro; de Bartolomeis, Andrea; Maione, Sabatino; de Novellis, Vito

2016-07-01

D-Aspartate (D-Asp) is a free D-amino acid detected in multiple brain regions and putative precursor of endogenous N-methyl-D-aspartate (NMDA) acting as agonist at NMDA receptors. In this study, we investigated whether D-Asp (20 mM) in drinking solution for 1 month affects pain responses and pain-related emotional, and cognitive behaviour in a model of neuropathic pain induced by the spared nerve injury (SNI) of the sciatic nerve in mice. SNI mice developed mechanical allodynia and motor coordination impairment 30 days after SNI surgery. SNI mice showed cognitive impairment, anxiety and depression-like behaviour, reduced sociability in the three chamber sociability paradigm, increased expression of NR2B subunit of NMDA receptor and Homer 1a in the medial prefrontal cortex (mPFC). The expression of (post synaptic density) PSD-95 and Shank 1was instead unaffected in the mPFC of the SNI mice. Treatment with D-Asp drinking solution, started right after the SNI (day 0), alleviated mechanical allodynia, improved cognition and motor coordination and increased social interaction. D-Asp also restored the levels of extracellular D-Asp, Homer 1a and NR2B subunit of the NMDA receptor to physiological levels and reduced Shank1 and PSD-95 protein levels in the mPFC. Amitriptyline, a tricyclic antidepressant used also to alleviate neuropathic pain in humans, reverted mechanical allodynia and cognitive impairment, and unlike D-Asp, was effective in reducing depression and anxiety-like behaviour in the SNI mice and increased PSD protein level. Altogether these findings demonstrate that D-Asp improves sensorial, motor and cognitive-like symptoms related to chronic pain possibly through glutamate neurotransmission normalization in neuropathic mice.

Coping with dehydration: sympathetic activation and regulation of glutamatergic transmission in the hypothalamic PVN

PubMed Central

Bardgett, Megan E.; Chen, Qing-Hui; Guo, Qing; Calderon, Alfredo S.; Andrade, Mary Ann

2014-01-01

Autonomic and endocrine profiles of chronic hypertension and heart failure resemble those of acute dehydration. Importantly, all of these conditions are associated with exaggerated sympathetic nerve activity (SNA) driven by glutamatergic activation of the hypothalamic paraventricular nucleus (PVN). Here, studies sought to gain insight into mechanisms of disease by determining the role of PVN ionotropic glutamate receptors in supporting SNA and mean arterial pressure (MAP) during dehydration and by elucidating mechanisms regulating receptor activity. Blockade of PVN N-methyl-d-aspartate (NMDA) receptors reduced (P < 0.01) renal SNA and MAP in urethane-chloralose-anesthetized dehydrated (DH) (48 h water deprivation) rats, but had no effect in euhydrated (EH) controls. Blockade of PVN α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors had no effect in either group. NMDA in PVN caused dose-dependent increases of renal SNA and MAP in both groups, but the maximum agonist evoked response (Emax) of the renal SNA response was greater (P < 0.05) in DH rats. The latter was not explained by increased PVN expression of NMDA receptor NR1 subunit protein, increased PVN neuronal excitability, or decreased brain water content. Interestingly, PVN injection of the pan-specific excitatory amino acid transporter (EAAT) inhibitor dl-threo-β-benzyloxyaspartic acid produced smaller sympathoexcitatory and pressor responses in DH rats, which was associated with reduced glial expression of EAAT2 in PVN. Like chronic hypertension and heart failure, dehydration increases excitatory NMDA receptor tone in PVN. Reduced glial-mediated glutamate uptake was identified as a key contributing factor. Defective glutamate uptake in PVN could therefore be an important, but as yet unexplored, mechanism driving sympathetic hyperactivity in chronic cardiovascular diseases. PMID:24671240

The Prodrug 4-Chlorokynurenine Causes Ketamine-Like Antidepressant Effects, but Not Side Effects, by NMDA/GlycineB-Site Inhibition

PubMed Central

Zanos, Panos; Piantadosi, Sean C.; Wu, Hui-Qiu; Pribut, Heather J.; Dell, Matthew J.; Can, Adem; Snodgrass, H. Ralph; Zarate, Carlos A.; Schwarcz, Robert

2015-01-01

Currently approved antidepressant drug treatment typically takes several weeks to be effective. The noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist ketamine has shown efficacy as a rapid-acting treatment of depression, but its use is associated with significant side effects. We assessed effects following blockade of the glycineB co-agonist site of the NMDA receptor, located on the GluN1 subunit, by the selective full antagonist 7-chloro-kynurenic acid (7-Cl-KYNA), delivered by systemic administration of its brain-penetrant prodrug 4-chlorokynurenine (4-Cl-KYN) in mice. Following administration of 4-Cl-KYN, 7-Cl-KYNA was promptly recovered extracellularly in hippocampal microdialysate of freely moving animals. The behavioral responses of the animals were assessed using measures of ketamine-sensitive antidepressant efficacy (including the 24-hour forced swim test, learned helplessness test, and novelty-suppressed feeding test). In these tests, distinct from fluoxetine, and similar to ketamine, 4-Cl-KYN administration resulted in rapid, dose-dependent and persistent antidepressant-like effects following a single treatment. The antidepressant effects of 4-Cl-KYN were prevented by pretreatment with glycine or the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione (NBQX). 4-Cl-KYN administration was not associated with the rewarding and psychotomimetic effects of ketamine, and did not induce locomotor sensitization or stereotypic behaviors. Our results provide further support for antagonism of the glycineB site for the rapid treatment of treatment-resistant depression without the negative side effects seen with ketamine or other channel-blocking NMDA receptor antagonists. PMID:26265321

Using drug combinations to assess potential contributions of non-GABAA receptors in the discriminative stimulus effects of the neuroactive steroid pregnanolone in rats.

PubMed

Eppolito, Amy K; Kodeih, Hanna R; Gerak, Lisa R

2014-10-01

Neuroactive steroids are increasingly implicated in the development of depression and anxiety and have been suggested as possible treatments for these disorders. While neuroactive steroids, such as pregnanolone, act primarily at γ-aminobutyric acidA (GABAA) receptors, other mechanisms might contribute to their behavioral effects and could increase their clinical effectiveness, as compared with drugs acting exclusively at GABAA receptors (e.g., benzodiazepines). The current study examined the role of non-GABAA receptors, including N-methyl-d-aspartate (NMDA) and serotonin3 (5-HT3) receptors, in the discriminative stimulus effects of pregnanolone. Separate groups of rats discriminated either 3.2mg/kg pregnanolone from vehicle or 0.32mg/kg of the benzodiazepine midazolam from vehicle while responding under a fixed-ratio 10 schedule for food pellets. When administered alone in both groups, pregnanolone and midazolam produced ≥80% drug-lever responding, the NMDA receptor antagonists dizocilpine and phencyclidine produced ≥60 and ≥30% drug-lever responding, respectively, and the 5-HT3 receptor agonist 1-(m-chlorophenyl)-biguanide (CPBG) and morphine produced <20% drug-lever responding up to doses that markedly decreased response rates. When studied together, neither dizocilpine, phencyclidine, CPBG nor morphine significantly altered the midazolam dose-effect curve in either group. Given that CPBG is without effect, it is unlikely that 5-HT3 receptors contribute substantially to the discriminative stimulus effects of pregnanolone. Similarities across groups in effects of dizocilpine and phencyclidine suggest that NMDA receptors do not differentially contribute to the effects of pregnanolone. Thus, NMDA and 5-HT3 receptors are not involved in the discriminative stimulus effects of pregnanolone. Copyright © 2014 Elsevier Inc. All rights reserved.

The Prodrug 4-Chlorokynurenine Causes Ketamine-Like Antidepressant Effects, but Not Side Effects, by NMDA/GlycineB-Site Inhibition.

PubMed

Zanos, Panos; Piantadosi, Sean C; Wu, Hui-Qiu; Pribut, Heather J; Dell, Matthew J; Can, Adem; Snodgrass, H Ralph; Zarate, Carlos A; Schwarcz, Robert; Gould, Todd D

2015-10-01

Currently approved antidepressant drug treatment typically takes several weeks to be effective. The noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist ketamine has shown efficacy as a rapid-acting treatment of depression, but its use is associated with significant side effects. We assessed effects following blockade of the glycineB co-agonist site of the NMDA receptor, located on the GluN1 subunit, by the selective full antagonist 7-chloro-kynurenic acid (7-Cl-KYNA), delivered by systemic administration of its brain-penetrant prodrug 4-chlorokynurenine (4-Cl-KYN) in mice. Following administration of 4-Cl-KYN, 7-Cl-KYNA was promptly recovered extracellularly in hippocampal microdialysate of freely moving animals. The behavioral responses of the animals were assessed using measures of ketamine-sensitive antidepressant efficacy (including the 24-hour forced swim test, learned helplessness test, and novelty-suppressed feeding test). In these tests, distinct from fluoxetine, and similar to ketamine, 4-Cl-KYN administration resulted in rapid, dose-dependent and persistent antidepressant-like effects following a single treatment. The antidepressant effects of 4-Cl-KYN were prevented by pretreatment with glycine or the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione (NBQX). 4-Cl-KYN administration was not associated with the rewarding and psychotomimetic effects of ketamine, and did not induce locomotor sensitization or stereotypic behaviors. Our results provide further support for antagonism of the glycineB site for the rapid treatment of treatment-resistant depression without the negative side effects seen with ketamine or other channel-blocking NMDA receptor antagonists. Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.

Dorsal hippocampal NMDA receptors mediate the interactive effects of arachidonylcyclopropylamide and MDMA/ecstasy on memory retrieval in rats.

PubMed

Ghaderi, Marzieh; Rezayof, Ameneh; Vousooghi, Nasim; Zarrindast, Mohammad-Reza

2016-04-03

A combination of cannabis and ecstasy may change the cognitive functions more than either drug alone. The present study was designed to investigate the possible involvement of dorsal hippocampal NMDA receptors in the interactive effects of arachidonylcyclopropylamide (ACPA) and ecstasy/MDMA on memory retrieval. Adult male Wistar rats were cannulated into the CA1 regions of the dorsal hippocampus (intra-CA1) and memory retrieval was examined using the step-through type of passive avoidance task. Intra-CA1 microinjection of a selective CB1 receptor agonist, ACPA (0.5-4ng/rat) immediately before the testing phase (pre-test), but not after the training phase (post-training), impaired memory retrieval. In addition, pre-test intra-CA1 microinjection of MDMA (0.5-1μg/rat) dose-dependently decreased step-through latency, indicating an amnesic effect of the drug by itself. Interestingly, pre-test microinjection of a higher dose of MDMA into the CA1 regions significantly improved ACPA-induced memory impairment. Moreover, pre-test intra-CA1 microinjection of a selective NMDA receptor antagonist, D-AP5 (1 and 2μg/rat) inhibited the reversal effect of MDMA on the impairment of memory retrieval induced by ACPA. Pre-test intra-CA1 microinjection of the same doses of D-AP5 had no effect on memory retrieval alone. These findings suggest that ACPA or MDMA consumption can induce memory retrieval impairment, while their co-administration improves this amnesic effect through interacting with hippocampal glutamatergic-NMDA receptor mechanism. Thus, it seems that the tendency to abuse cannabis with ecstasy may be for avoiding cognitive dysfunction. Copyright © 2015. Published by Elsevier Inc.

Memantine alters striatal plasticity inducing a shift of synaptic responses toward long-term depression.

PubMed

Mancini, Maria; Ghiglieri, Veronica; Bagetta, Vincenza; Pendolino, Valentina; Vannelli, Anna; Cacace, Fabrizio; Mineo, Desireé; Calabresi, Paolo; Picconi, Barbara

2016-02-01

Memantine is an open channel blocker that antagonizes NMDA receptors reducing the inappropriate calcium (Ca(2+)) influx occurring in presence of moderately increased glutamate levels. At the same time, memantine has the ability to preserve the transient physiological activation of NMDA receptor, essential for learning and memory formation at synaptic level. In the present study we investigated the effects exerted by memantine on striatal synaptic plasticity in rat striatal spiny projection neurons (SPNs). In vitro application of memantine in striatal slices elicited a disruption of long-term potentiation (LTP) induction and maintenance, and revealed, in the majority of the recorded neurons, a long-term depression (LTD), whose amplitude was concentration-dependent (0.3-10 μM). Interestingly, preincubation with the dopamine (DA) D2 receptor antagonist sulpiride (10 μM) prevented memantine-induced LTD and restored LTP. Moreover, the DA D2 agonist quinpirole (10 μM), similarly to memantine, induced LTD in a subgroup of SPNs. In addition, memantine-induced LTD was also prevented by the CB1 endocannabinoid receptor antagonist AM 251 (1 μM). These results suggest that the actions exerted by memantine on striatal synaptic plasticity, and in particular the induction of LTD observed in SPNs, could be attributed to its ability to activate DA D2 receptors. By contrast, blockade of NMDA receptor is not involved in memantine-induced LTD since APV (30 μM) and MK801 (10 μM), two NMDA receptor antagonists, failed to induce this form of synaptic plasticity. Our data indicate that memantine could be used as treatment of neurological disorders in which DA D2 receptor represents a possible therapeutic target. Copyright © 2015 Elsevier Ltd. All rights reserved.

Isoflurane-Induced Caspase-3 Activation Is Dependent on Cytosolic Calcium and Can Be Attenuated by Memantine

PubMed Central

Zhang, Guohua; Dong, Yuanlin; Zhang, Bin; Ichinose, Fumito; Wu, Xu; Culley, Deborah J.; Crosby, Gregory

2008-01-01

Increasing evidence indicates that caspase activation and apoptosis are associated with a variety of neurodegenerative disorders, including Alzheimer's disease. We reported that anesthetic isoflurane can induce apoptosis, alter processing of the amyloid precursor protein (APP), and increase amyloid-β protein (Aβ) generation. However, the mechanism by which isoflurane induces apoptosis is primarily unknown. We therefore set out to assess effects of extracellular calcium concentration on isoflurane-induced caspase-3 activation in H4 human neuroglioma cells stably transfected to express human full-length APP (H4-APP cells). In addition, we tested effects of RNA interference (RNAi) silencing of IP3 receptor, NMDA receptor, and endoplasmic reticulum (ER) calcium pump, sacro-/ER calcium ATPase (SERCA1). Finally, we examined the effects of the NMDA receptor partial antagonist, memantine, in H4-APP cells and brain tissue of naive mice. EDTA (10 mm), BAPTA (10 μm), and RNAi silencing of IP3 receptor, NMDA receptor, or SERCA1 attenuated capase-3 activation. Memantine (4 μm) inhibited isoflurane-induced elevations in cytosolic calcium levels and attenuated isoflurane-induced caspase-3 activation, apoptosis, and cell viability. Memantine (20 mg/kg, i.p.) reduced isoflurane-induced caspase-3 activation in brain tissue of naive mice. These results suggest that disruption of calcium homeostasis underlies isoflurane-induced caspase activation and apoptosis. We also show for the first time that the NMDA receptor partial antagonist, memantine, can prevent isoflurane-induced caspase-3 activation and apoptosis in vivo and in vitro. These findings, indicating that isoflurane-induced caspase activation and apoptosis are dependent on cytosolic calcium levels, should facilitate the provision of safer anesthesia care, especially for Alzheimer's disease and elderly patients. PMID:18434534

An examination of the roles of glutamate and sex in latent inhibition: Relevance to the glutamate hypothesis of schizophrenia?

PubMed

Huang, Andrew Chih Wei; Bo-Han He, Alan; Chen, Chih-Chung

2017-10-01

The present study examined the effects of the glutamate receptor antagonist MK-801, the glutamate receptor agonist N-methyl-D-aspartate (NMDA), and sexual dimorphism on latent inhibition to elucidate the glutamate hypothesis of schizophrenia. During the pre-exposure phase, 56 male and 65 female Wistar rats were intracerebroventricularly administered normal saline, MK-801 or NMDA, in the left ventricle and then exposed to a passive avoidance box (or a different context) in three trials over 3 days. Then, all of the rats were placed in the light compartment of the passive avoidance box and were allowed to enter the dark compartment, where they each received a footshock (1mA, 2s) in five trials over 5 days. Injections of the glutamate drugs NMDA and MK-801 did not affect latent inhibition. Sexual dimorphism did not occur in latent inhibition. The present data on the male rats indicated that the glutamate system did not affect latent inhibition, indicating that the glutamate system was not like the dopamine system in terms of mediating the positive symptoms of schizophrenia. The glutamate system might be involved in the negative and cognitive symptoms of schizophrenia. The results may provide information for novel treatments of the negative and cognitive symptoms of schizophrenia. Copyright © 2017 Elsevier B.V. All rights reserved.

Modulation of NMDA and AMPA-Mediated Synaptic Transmission by CB1 Receptors in Frontal Cortical Pyramidal Cells

PubMed Central

Li, Qiang; Yan, Haidun; Wilson, Wilkie A.; Swartzwelder, H. Scott

2010-01-01

Although the endogenous cannabinoid system modulates a variety of physiological and pharmacological processes, the specific role of cannabinoid CB1 receptors in the modulation of glutamatergic neurotransmission and neural plasticity is not well understood. Using whole-cell patch clamp recording techniques, evoked or spontaneous excitatory postsynaptic currents (eEPSCs or sEPSCs) were recorded from visualized, layer II/III pyramidal cells in frontal cortical slices from rat brain. Bath application of the CB1 receptor agonist, WIN 55212-2 (WIN), reduced the amplitude of NMDA receptor-mediated EPSCs in a concentration-dependent manner. When co-applied with the specific CB1 antagonists, AM251 or AM281, WIN did not suppress NMDA receptor mediated EPSCs. WIN also reduced the amplitude of evoked AMPA receptor-mediated EPSCs, an effect that was also reversed by AM251. Both the frequency and amplitude of spontaneous AMPA receptor-mediated EPSCs were significantly reduced by WIN. In contrast, WIN reduced the frequency, but not the amplitude of miniature EPSCs, suggesting that the suppression of glutmatergic activity by CB1 receptors in the frontal neocortex is mediated by a pre-synaptic mechanism. Taken together, these data indicate a critical role for endocannabinoid signaling in the regulation of excitatory synaptic transmission in frontal neocortex, and suggest a possible neuronal mechanism whereby THC regulates cortical function. PMID:20420813

TAAR1 Modulates Cortical Glutamate NMDA Receptor Function

PubMed Central

Espinoza, Stefano; Lignani, Gabriele; Caffino, Lucia; Maggi, Silvia; Sukhanov, Ilya; Leo, Damiana; Mus, Liudmila; Emanuele, Marco; Ronzitti, Giuseppe; Harmeier, Anja; Medrihan, Lucian; Sotnikova, Tatyana D; Chieregatti, Evelina; Hoener, Marius C; Benfenati, Fabio; Tucci, Valter; Fumagalli, Fabio; Gainetdinov, Raul R

2015-01-01

Trace Amine-Associated Receptor 1 (TAAR1) is a G protein-coupled receptor expressed in the mammalian brain and known to influence subcortical monoaminergic transmission. Monoamines, such as dopamine, also play an important role within the prefrontal cortex (PFC) circuitry, which is critically involved in high-o5rder cognitive processes. TAAR1-selective ligands have shown potential antipsychotic, antidepressant, and pro-cognitive effects in experimental animal models; however, it remains unclear whether TAAR1 can affect PFC-related processes and functions. In this study, we document a distinct pattern of expression of TAAR1 in the PFC, as well as altered subunit composition and deficient functionality of the glutamate N-methyl-D-aspartate (NMDA) receptors in the pyramidal neurons of layer V of PFC in mice lacking TAAR1. The dysregulated cortical glutamate transmission in TAAR1-KO mice was associated with aberrant behaviors in several tests, indicating a perseverative and impulsive phenotype of mutants. Conversely, pharmacological activation of TAAR1 with selective agonists reduced premature impulsive responses observed in the fixed-interval conditioning schedule in normal mice. Our study indicates that TAAR1 plays an important role in the modulation of NMDA receptor-mediated glutamate transmission in the PFC and related functions. Furthermore, these data suggest that the development of TAAR1-based drugs could provide a novel therapeutic approach for the treatment of disorders related to aberrant cortical functions. PMID:25749299

Involvement of glutamatergic N-methyl-d-aspartate receptors in the expression of increased head-dipping behaviors in the hole-board tests of olfactory bulbectomized mice.

PubMed

Hirose, Noritaka; Saitoh, Akiyoshi; Kamei, Junzo

2016-10-01

Olfactory bulbectomized (OB) mice produce agitated anxiety-like behaviors in the hole-board test, which was expressed by an increase in head-dipping counts and a decrease in head-dipping latencies. However, the associated mechanisms remain unclear. In the present study, MK-801 (10, 100μg/kg), a selective N-methyl-d-aspartate (NMDA) receptor antagonist, significantly and dose-dependently suppressed the increased head-dipping behaviors in OB mice, without affecting sham mice. Similar results were obtained with another selective NMDA receptor antagonist D-AP5 treatment in OB mice. On the other hand, muscimol, a selective aminobutyric acid type A (GABAA) receptor agonist produced no effects on these hyperemotional behaviors in OB mice at a dose (100μg/kg) that produced anxiolytic-like effects in sham mice. Interestingly, glutamine contents and glutamine/glutamate ratios were significantly increased in the amygdala and frontal cortex of OB mice compared to sham mice. Based on these results, we concluded that the glutamatergic NMDA receptors are involved in the expression of increased head-dipping behaviors in the hole-board tests of OB mice. Accordingly, the changes in glutamatergic transmission in frontal cortex and amygdala may play important roles in the expression of these abnormal behaviors in OB mice. Copyright © 2016. Published by Elsevier B.V.

A FLEXIBLE APPROACH FOR EVALUATING FIXED RATIO MIXTURES OF FULL AND PARTIAL AGONISTS FOR MIXTURES OF MANY CHEMICALS.

EPA Science Inventory

Detecting interaction in chemical mixtures can be complicated by differences in the shapes of the dose-response curves of the individual components (e.g. mixtures of full and partial agonists with differing response maxima). We present an analysis scheme where flexible single che...

Identification of PPARgamma Partial Agonists of Natural Origin (II): In Silico Prediction in Natural Extracts with Known Antidiabetic Activity

PubMed Central

Guasch, Laura; Sala, Esther; Mulero, Miquel; Valls, Cristina; Salvadó, Maria Josepa; Pujadas, Gerard; Garcia-Vallvé, Santiago

2013-01-01

Background Natural extracts have played an important role in the prevention and treatment of diseases and are important sources for drug discovery. However, to be effectively used in these processes, natural extracts must be characterized through the identification of their active compounds and their modes of action. Methodology/Principal Findings From an initial set of 29,779 natural products that are annotated with their natural source and using a previously developed virtual screening procedure (carefully validated experimentally), we have predicted as potential peroxisome proliferators-activated receptor gamma (PPARγ) partial agonists 12 molecules from 11 extracts known to have antidiabetic activity. Six of these molecules are similar to molecules with described antidiabetic activity but whose mechanism of action is unknown. Therefore, it is plausible that these 12 molecules could be the bioactive molecules responsible, at least in part, for the antidiabetic activity of the extracts containing them. In addition, we have also identified as potential PPARγ partial agonists 10 molecules from 16 plants with undescribed antidiabetic activity but that are related (i.e., they are from the same genus) to plants with known antidiabetic properties. None of the 22 molecules that we predict as PPARγ partial agonists show chemical similarity with a group of 211 known PPARγ partial agonists obtained from the literature. Conclusions/Significance Our results provide a new hypothesis about the active molecules of natural extracts with antidiabetic properties and their mode of action. We also suggest plants with undescribed antidiabetic activity that may contain PPARγ partial agonists. These plants represent a new source of potential antidiabetic extracts. Consequently, our work opens the door to the discovery of new antidiabetic extracts and molecules that can be of use, for instance, in the design of new antidiabetic drugs or functional foods focused towards the prevention/treatment of type 2 Diabetes Mellitus. PMID:23405231

Clozapine Reverses Phencyclidine-Induced Desynchronization of Prefrontal Cortex through a 5-HT1A Receptor-Dependent Mechanism

PubMed Central

Kargieman, Lucila; Riga, Maurizio S; Artigas, Francesc; Celada, Pau

2012-01-01

The non-competitive NMDA receptor (NMDA-R) antagonist phencyclidine (PCP)—used as a pharmacological model of schizophrenia—disrupts prefrontal cortex (PFC) activity. PCP markedly increased the discharge rate of pyramidal neurons and reduced slow cortical oscillations (SCO; 0.15–4 Hz) in rat PFC. Both effects were reversed by classical (haloperidol) and atypical (clozapine) antipsychotic drugs. Here we extended these observations to mice brain and examined the potential involvement of 5-HT2A and 5-HT1A receptors (5-HT2AR and 5-HT1AR, respectively) in the reversal by clozapine of PCP actions. Clozapine shows high in vitro affinity for 5-HT2AR and behaves as partial agonist in vivo at 5-HT1AR. We used wild-type (WT) mice and 5-HT1AR and 5-HT2AR knockout mice of the same background (C57BL/6) (KO-1A and KO-2A, respectively). Local field potentials (LFPs) were recorded in the PFC of WT, KO-1A, and KO-2A mice. PCP (10 mg/kg, intraperitoneally) reduced SCO equally in WT, KO-2A, and KO-1A mice (58±4%, 42±7%, and 63±7% of pre-drug values, n=23, 13, 11, respectively; p<0.0003). Clozapine (0.5 mg/kg, intraperitoneally) significantly reversed PCP effect in WT and KO-2A mice, but not in KO-1A mice nor in WT mice pretreated with the selective 5-HT1AR antagonist WAY-100635.The PCP-induced disorganization of PFC activity does not appear to depend on serotonergic function. However, the lack of effect of clozapine in KO-1A mice and the prevention by WAY-100635 indicates that its therapeutic action involves 5-HT1AR activation without the need to block 5-HT2AR, as observed with clozapine-induced cortical dopamine release. PMID:22012474

An extension of hypotheses regarding rapid-acting, treatment-refractory, and conventional antidepressant activity of dextromethorphan and dextrorphan.

PubMed

Lauterbach, Edward C

2012-06-01

It was previously hypothesized that dextromethorphan (DM) and dextrorphan (DX) may possess antidepressant properties, including rapid and conventional onsets of action and utility in treatment-refractory depression, based on pharmacodynamic similarities to ketamine. These similarities included sigma-1 (σ(1)) agonist and NMDA antagonist properties, calcium channel blockade, muscarinic binding, serotonin transporter (5HTT) inhibition, and μ receptor potentiation. Here, six specific hypotheses are developed in light of additional mechanisms and evidence. Comparable potencies to ketamine for DM and DX are detailed for σ(1) (DX>DM>ketamine), NMDA PCP site (DX>ketamine>DM), and muscarinic (DX>ketamine>DM) receptors, 5HTT (DM>DX≫ketamine), and NMDA antagonist potentiation of μ receptor stimulation (DM>ketamine). Rapid acting antidepressant properties of DM include NMDA high-affinity site, NMDR-2A, and functional NMDR-2B receptor antagonism, σ(1) stimulation, putative mTOR activation (by σ(1) stimulation, μ potentiation, and 5HTT inhibition), putative AMPA receptor trafficking (by mTOR activation, PCP antagonism, σ(1) stimulation, μ potentiation, and 5HTT inhibition), and dendritogenesis, spinogenesis, synaptogenesis, and neuronal survival by NMDA antagonism and σ(1) and mTOR signaling. Those for dextrorphan include NMDA high-affinity site and NMDR-2A antagonism, σ(1) stimulation, putative mTOR activation (by σ(1) stimulation and ß adrenoreceptor stimulation), putative AMPA receptor trafficking (by mTOR activation, PCP antagonism, σ(1) stimulation, ß stimulation, and μ antagonism), and dendritogenesis, spinogenesis, synaptogenesis, and neuronal survival by NMDA antagonism and σ(1) and mTOR signaling. Conventional antidepressant properties for dextromethorphan and dextrorphan include 5HTT and norepinephrine transporter inhibition, σ(1) stimulation, NMDA and PCP antagonism, and possible serotonin 5HT1b/d receptor stimulation. Additional properties for dextromethorphan include possible presynaptic α(2) adrenoreceptor antagonism or postsynaptic α(2) stimulation and, for dextrorphan, ß stimulation and possible muscarinic and μ antagonism. Treatment-refractory depression properties include increased serotonin and norepinephrine availability, PCP, NMDR-2B, presynaptic alpha-2 antagonism, and the multiplicity of other antidepressant receptor mechanisms. Suggestions for clinical trials are provided for oral high-dose dextromethorphan and Nuedexta (dextromethorphan combined with quinidine to block metabolism to dextrorphan, thereby increasing dextromethorphan plasma concentrations). Suggestions include exclusionary criteria, oral dosing, observation periods, dose-response approaches, and safety and tolerability are considered. Although oral dextromethorphan may be somewhat more likely to show efficacy through complementary antidepressant mechanisms of dextrorphan, a clinical trial will be more logistically complex than one of Nuedexta due to high doses and plasma level variability. Clinical trials may increase our therapeutic armamentarium and our pharmacological understanding of treatment-refractory depression and antidepressant onset of action. Copyright © 2012 Elsevier Ltd. All rights reserved.

Relationship of resting brain hyperconnectivity and schizophrenia-like symptoms produced by the NMDA receptor antagonist ketamine in humans.

PubMed

Driesen, N R; McCarthy, G; Bhagwagar, Z; Bloch, M; Calhoun, V; D'Souza, D C; Gueorguieva, R; He, G; Ramachandran, R; Suckow, R F; Anticevic, A; Morgan, P T; Krystal, J H

2013-11-01

N-methyl-D-aspartate glutamate receptor (NMDA-R) antagonists produce schizophrenia-like positive and negative symptoms in healthy human subjects. Preclinical research suggests that NMDA-R antagonists interfere with the function of gamma-aminobutyric acid (GABA) neurons and alter the brain oscillations. These changes have been hypothesized to contribute to psychosis. In this investigation, we evaluated the hypothesis that the NMDA-R antagonist ketamine produces alterations in cortical functional connectivity during rest that are related to symptoms. We administered ketamine to a primary sample of 22 subjects and to an additional, partially overlapping, sample of 12 subjects. Symptoms before and after the experimental session were rated with the Positive and Negative Syndrome Scale (PANSS). In the primary sample, functional connectivity was measured via functional magnetic resonance imaging almost immediately after infusion began. In the additional sample, this assessment was repeated after 45 min of continuous ketamine infusion. Global, enhanced functional connectivity was observed at both timepoints, and this hyperconnectivity was related to symptoms in a region-specific manner. This study supports the hypothesis that pathological increases in resting brain functional connectivity contribute to the emergence of positive and negative symptoms associated with schizophrenia.

Relationship of Resting Brain Hyperconnectivity and Schizophrenia-like Symptoms Produced by the NMDA receptor Antagonist Ketamine in Humans

PubMed Central

Driesen, Naomi R.; McCarthy, Gregory; Bhagwagar, Zubin; Bloch, Michael; Calhoun, Vincent; D’Souza, Deepak C.; Gueorguieva, Ralitza; He, George; Ramachandran, Ramani; Suckow, Raymond F.; Anticevic, Alan; Morgan, Peter T.; Krystal, John H.

2012-01-01

N-methyl-D-aspartate glutamate receptor (NMDA-R) antagonists produce schizophrenia-like positive and negative symptoms in healthy human subjects. Preclinical research suggests that NMDA-R antagonists interfere with the function of gamma-aminobutyric acid (GABA) neurons and alter brain oscillations. These changes have been hypothesized to contribute to psychosis. In this investigation, we evaluated the hypothesis that the NMDA-R antagonist ketamine produces alterations in cortical functional connectivity during rest that are related to symptoms. We administered ketamine to a primary sample of twenty-two subjects and to an additional, partially overlapping, sample of twelve subjects. Symptoms before and after the experimental session were rated with the Positive and Negative Symptom Scale (PANSS). In the primary sample, functional connectivity was measured via functional magnetic resonance imaging almost immediately after infusion began. In the additional sample, this assessment was repeated after 45 minutes of continuous ketamine infusion. Global, enhanced functional connectivity was observed at both timepoints and this hyperconnectivity was related to symptoms in a region-specific manner. This study supports the hypothesis that pathological increases in resting brain functional connectivity contribute to the emergence of positive and negative symptoms associated with schizophrenia. PMID:23337947

Improving the developability profile of pyrrolidine progesterone receptor partial agonists

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

Kallander, Lara S.; Washburn, David G.; Hoang, Tram H.

2010-09-17

The previously reported pyrrolidine class of progesterone receptor partial agonists demonstrated excellent potency but suffered from serious liabilities including hERG blockade and high volume of distribution in the rat. The basic pyrrolidine amine was intentionally converted to a sulfonamide, carbamate, or amide to address these liabilities. The evaluation of the degree of partial agonism for these non-basic pyrrolidine derivatives and demonstration of their efficacy in an in vivo model of endometriosis is disclosed herein.

Modulation of taurine release by glutamate receptors and nitric oxide.

PubMed

Oja, S S; Saransaari, P

2000-11-01

Taurine is held to function as a modulator and osmoregulator in the central nervous system, being of particular importance in the immature brain. In view of the possible involvement of excitatory pathways in the regulation of taurine function in the brain, the interference of glutamate receptors with taurine release from different tissue preparations in vitro and from the brain in vivo is of special interest. The release of taurine from the brain is enhanced by glutamate receptor agonists. This enhancement is inhibited by the respective receptor antagonists both in vitro and in vivo. The ionotropic N-methyl-D-aspartate (NMDA) and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor agonists appear to be the most effective in enhancing taurine release, their effects being receptor-mediated. Kainate is less effective, particularly in adults. Of the glutamate receptors, the NMDA class seems to be the most susceptible to modulation by nitric oxide. Nitric oxide also modulates taurine release, enhancing the basal release in both immature and mature hippocampus, whereas the K(+)-stimulated release is generally inhibited. Metabotropic glutamate receptors also participate in the regulation of taurine release, group I metabotropic glutamate receptors potentiating the release in the developing hippocampus, while group III receptors may be involved in the adult. Under various cell-damaging conditions, including ischemia, hypoxia and hypoglycemia, taurine release is enhanced, together with an enhanced release of excitatory amino acids. The increase in extracellular taurine upon excessive stimulation of glutamate receptors and under cell-damaging conditions may serve as an important protective mechanism against excitotoxicity, being particularly effective in the immature brain.

Evaluation of 11C-Me-NB1 as a Potential PET Radioligand for Measuring GluN2B-Containing NMDA Receptors, Drug Occupancy, and Receptor Cross Talk.

PubMed

Krämer, Stefanie D; Betzel, Thomas; Mu, Linjing; Haider, Ahmed; Herde, Adrienne Müller; Boninsegni, Anna K; Keller, Claudia; Szermerski, Marina; Schibli, Roger; Wünsch, Bernhard; Ametamey, Simon M

2018-04-01

Clinical and preclinical research with modulators at the N -methyl-d-aspartate (NMDA) receptor GluN2B N-terminal domain (NTD) aims for the treatment of various neurologic diseases. The interpretation of the results is hampered by the lack of a suitable NMDA PET tracer for assessing the receptor occupancy of potential drugs. We have developed 11 C-Me-NB1 as a PET tracer for imaging GluN1/GluN2B-containing NMDA receptors and used it to investigate in rats the dose-dependent receptor occupancy of eliprodil, a GluN2B NTD modulator. Methods: 11 C-Me-NB1 was synthesized and characterized by in vitro displacement binding experiments with rat brain membranes, in vitro autoradiography, and blocking and displacement experiments by PET and PET kinetic modeling. Receptor occupancy by eliprodil was studied by PET with 11 C-Me-NB1. Results: 11 C-Me-NB1 was synthesized at 290 ± 90 GBq/μmol molar activity, 7.4 ± 1.9 GBq total activity at the end of synthesis ( n = 17), and more than 99% radiochemical purity. 11 C-Me-NB1 binding in rat brain was blocked in vitro and in vivo by the NTD modulators Ro-25-6981 and eliprodil. Half-maximal receptor occupancy by eliprodil occurred at 1.5 μg/kg. At 1 mg/kg of eliprodil, a dose with reported neuroprotective effects, more than 99.5% of binding sites were occupied. In vitro, 11 C-Me-NB1 binding was independent of the σ-1 receptor (Sigma1R), and the Sigma1R agonist (+)-pentazocine did not compete for high-affinity binding. In vivo, a 2.5 mg/kg dose of (+)-pentazocine abolished 11 C-Me-NB1-specific binding, indicating an indirect effect of Sigma1R on 11 C-Me-NB1 binding. Conclusion: 11 C-Me-NB1 is suitable for the in vivo imaging of NMDA GluN1/GluN2B receptors and the assessment of receptor occupancy by NTD modulators. GluN1/GluN2B NMDA receptors are fully occupied at neuroprotective doses of eliprodil. Furthermore, 11 C-Me-NB1 enables imaging of GluN1/GluN2B NMDA receptor cross talk. © 2018 by the Society of Nuclear Medicine and Molecular Imaging.

Pharmacological characterization of stress-induced hyperthermia in DBA/2 mice using metabotropic and ionotropic glutamate receptor ligands.

PubMed

Rorick-Kehn, Linda M; Hart, John C; McKinzie, David L

2005-12-01

Accumulating evidence suggests that drugs acting on the glutamatergic system may represent promising novel therapeutic targets for the treatment of anxiety disorders. The stress-induced hyperthermia paradigm has been used widely to model some of the physiological symptoms associated with anxiety disorders and has produced results that are predictive of clinical efficacy. We have modified this paradigm to measure the autonomic consequences of stress induced by the fear of predation in mice. To evaluate the efficacy of several classes of metabotropic and ionotropic glutamate receptor ligands, as well as known anxiolytics and psychotropic comparators, in attenuating predatory-stress-induced hyperthermia. Male DBA/2 mice were implanted with radiotelemetric transmitters in the peritoneal cavity to measure stress-related increases in core body temperature, following placement in a novel cage containing soiled rat shavings. Clinically active compounds such as chlordiazepoxide (5-10 mg/kg), alprazolam (0.3-3 mg/kg), and buspirone (10-30 mg/kg) exhibited an anxiolytic profile. Assessment of glutamatergic agents indicated that the mGlu1 receptor antagonist LY456236 (10-30 mg/kg), mGlu5 receptor antagonist MPEP (10-30 mg/kg), mGlu2/3 receptor agonist LY354740 (3-10 mg/kg), mGlu2 receptor potentiator LY566332 (30 and 100 mg/kg), mGlu8 receptor agonist (S)-3,4-dicarboxyphenylglycine (30-60 mg/kg), competitive NMDA receptor antagonist LY235959 (1 mg/kg), AMPA receptor antagonist GYKI-52466 (10-20 mg/kg), and glycine transporter-1 (GlyT-1) inhibitor ALX-5407 (3-10 mg/kg) dose-dependently attenuated stress-induced hyperthermia. The AMPA receptor potentiator LY451646, iGlu5 kainate receptor antagonist LY382884, glycine(B) receptor partial agonist D: -cycloserine, and GlyT-1 inhibitor ORG-24461 were ineffective in this model. Select metabotropic and ionotropic glutamate receptor ligands exhibited an anxiolytic profile, as measured by the attenuation of stress-induced hyperthermia, and may represent viable targets for the development of pharmacological treatments for anxiety-related disorders.

Direct Actions of Kisspeptins on GnRH Neurons Permit Attainment of Fertility but are Insufficient to Fully Preserve Gonadotropic Axis Activity

PubMed Central

León, Silvia; Barroso, Alexia; Vázquez, María J.; García-Galiano, David; Manfredi-Lozano, María; Ruiz-Pino, Francisco; Heras, Violeta; Romero-Ruiz, Antonio; Roa, Juan; Schutz, Günther; Kirilov, Milen; Gaytan, Francisco; Pinilla, Leonor; Tena-Sempere, Manuel

2016-01-01

Kisspeptins, ligands of the receptor, Gpr54, are potent stimulators of puberty and fertility. Yet, whether direct kisspeptin actions on GnRH neurons are sufficient for the whole repertoire of their reproductive effects remains debatable. To dissect out direct vs. indirect effects of kisspeptins on GnRH neurons in vivo, we report herein the detailed reproductive/gonadotropic characterization of a Gpr54 null mouse line with selective re-introduction of Gpr54 expression only in GnRH cells (Gpr54−/−Tg; rescued). Despite preserved fertility, adult rescued mice displayed abnormalities in gonadal microstructure, with signs of precocious ageing in females and elevated LH levels with normal-to-low testosterone secretion in males. Gpr54−/−Tg rescued mice showed also altered gonadotropin responses to negative feedback withdrawal, while luteinizing hormone responses to various gonadotropic regulators were variably affected, with partially blunted relative (but not absolute) responses to kisspeptin-10, NMDA and the agonist of tachykinin receptors, NK2R. Our data confirm that direct effects of kisspeptins on GnRH cells are sufficient to attain fertility. Yet, such direct actions appear to be insufficient to completely preserve proper functionality of gonadotropic axis, suggesting a role of kisspeptin signaling outside GnRH cells. PMID:26755241

d-Cycloserine combined with cue exposure therapy fails to attenuate subjective and physiological craving in cocaine dependence

PubMed Central

Santa Ana, Elizabeth J.; Prisciandaro, James J.; Saladin, Michael E.; McRae-Clark, Aimee L.; Shaftman, Stephanie R.; Nietert, Paul J.; Brady, Kathleen T.

2014-01-01

Background Based on preclinical studies showing that the partial N-methyl-d-aspartate (NMDA) agonist d-cycloserine (DCS) facilitates extinction of cocaine self-administration and cocaine-induced conditioned place preference, we evaluated whether 50 mg of DCS would reduce craving to cocaine cues when combined with cue exposure (CE) in cocaine dependent humans. Methods In this double-blind placebo-controlled pilot study, 47 cocaine dependent participants were randomized to DCS or placebo (PBO), plus CE. Participants received DCS or PBO 30 minutes prior to two CE sessions, conducted one day apart. Craving and heart rate was assessed prior to CE sessions, during CE trials, and after CE trials. These measures were assessed again at a 1-week follow-up (session 3) after the second CE session. Results DCS failed to significantly attenuate cocaine cue reactivity based on subjective craving and physiological reactivity (heart rate) compared to PBO. The CE protocol, consisting of repeated exposure to drug cues combined with skills training, resulted in extinction to cocaine cues as suggested by decreased craving within and between sessions in both treatment conditions. All participants exhibited elevated heart rate with repeated exposures, demonstrating a potentiation in heart rate between sessions. PMID:25808169

Differential pathway coupling efficiency of the activated insulin receptor drives signaling selectivity by XMetA, an allosteric partial agonist antibody

USDA-ARS?s Scientific Manuscript database

XMetA, an anti-insulin receptor (IR) monoclonal antibody, is an allosteric partial agonist of the IR. We have previously reported that XMetA activates the “metabolic-biased” Akt kinase signaling pathway while having little or no effect on the “mitogenic” MAPK signaling pathwayof ERK 1/2. To inves...

Differential pathway coupling efficiency of the activated insulin receptor drives signaling selectivity by xmeta, an allosteric partial agonist antibody

USDA-ARS?s Scientific Manuscript database

XMetA, an anti-insulin receptor (IR) monoclonal antibody, is an allosteric partial agonist of the IR. We have previously reported that XMetA activates the “metabolic-biased” Akt kinase signaling pathway while having little or no effect on the “mitogenic” MAPK signaling pathwayof ERK 1/2. To inves...

Partial agonist therapy in schizophrenia: relevance to diminished criminal responsibility.

PubMed

Gavaudan, Gilles; Magalon, David; Cohen, Julien; Lançon, Christophe; Léonetti, Georges; Pélissier-Alicot, Anne-Laure

2010-11-01

Pathological gambling (PG), classified in the DSM-IV among impulse control disorders, is defined as inappropriate, persistent gaming for money with serious personal, family, and social consequences. Offenses are frequently committed to obtain money for gambling. Pathological gambling, a planned and structured behavioral disorder, has often been described as a complication of dopamine agonist treatment in patients with Parkinson's disease. It has never been described in patients with schizophrenia receiving dopamine agonists. We present two patients with schizophrenia, previously treated with antipsychotic drugs without any suggestion of PG, who a short time after starting aripiprazole, a dopamine partial agonist, developed PG and criminal behavior, which totally resolved when aripiprazole was discontinued. Based on recent advances in research on PG and adverse drug reactions to dopamine agonists in Parkinson's disease, we postulate a link between aripiprazole and PG in both our patients with schizophrenia and raise the question of criminal responsibility. © 2010 American Academy of Forensic Sciences.

32nd National Medicinal Chemistry Symposium--medicinal chemistry developments for neurodegeneration, diabetes and cancer.

PubMed

Gater, Deborah

2010-08-01

The 32nd National Medicinal Chemistry Symposium, held in Minneapolis, MN, USA, included topics covering new developments in the field of medicinal chemistry. This conference report highlights selected presentations on NR2B subtype-selective NMDA receptor antagonists from Merck; selective neuronal nitric oxide synthase inhibitors from Northwestern University; novel GPR119 agonists, suchas GSK-1292263A (GlaxoSmithKline plc), PSN-821 ((OSI) Prosidion) and MBX-2982 (Metabolex Inc); a small-molecule Bcl inhibitor,navitoclax (Abbott Laboratories); and p53-targeting agents from sanofi-aventis and Ascenta Therapeutics Inc, including AT-219.

Gelidium amansii promotes dendritic spine morphology and synaptogenesis, and modulates NMDA receptor-mediated postsynaptic current.

PubMed

Hannan, Md Abdul; Mohibbullah, Md; Hong, Yong-Ki; Nam, Joo Hyun; Moon, Il Soo

2014-01-01

Neurotrophic factors are essential for the differentiation and maturation of developing neurons as well as providing survival support to the mature neurons. Moreover, therapeutically neurotrophic factors are promising to reconstruct partially damaged neuronal networks in neurodegenerative diseases. In the previous study, we reported that the ethanol extract of an edible marine alga, Gelidium amansii (GAE) had shown promising effects in the development and maturation of both axon and dendrites of hippocampal neurons. Here, we demonstrate that in primary culture of hippocampal neurons (1) GAE promotes a significant increase in the number of filopodia and dendritic spines; (2) promotes synaptogenesis; (3) enhances N-methyl-D-aspartic acid (NMDA) receptor recruitment; and (4) modulates NMDA-receptor-mediated postsynaptic current. Taken together these findings that GAE might be involved in both morphological and functional maturation of neurons suggest the possibility that GAE may constitute a promising candidate for novel compounds for the prevention and treatment of neurodegenerative diseases.

Peripheral NMDA Receptor/NO System Blockage Inhibits Itch Responses Induced by Chloroquine in Mice

PubMed Central

Haddadi, Nazgol-Sadat; Foroutan, Arash; Ostadhadi, Sattar; Azimi, Ehsan; Rahimi, Nastaran; Nateghpour, Mehdi; Lerner, Ethan A.; Dehpour, Ahmad Reza

2017-01-01

Intradermal administration of chloroquine (CQ) provokes scratching behavior in mice. Chloroquine-induced itch is histamine-independent and we have reported that the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway is involved in CQ-induced scratching behavior in mice. Previous studies have demonstrated that activation of N-methyl-d-aspartate receptors (NMDARs) induces NO production. Here we show that NMDAR antagonists significantly decrease CQ-induced scratching in mice while a non-effective dose of an NMDAR agonist potentiates the scratching behavior provoked by sub-effective doses of CQ. In contrast, combined pre-treatment with sub-effective doses of an NMDAR antagonist, MK-801, and the NO synthase inhibitor, L-N-nitro arginine methyl ester (L-NAME), decreases CQ-induced scratching behavior. While intradermal administration of CQ significantly increases the concentration of intradermal nitrite, the end product of NO metabolism, effective doses of intraperitoneal and intradermal MK-801 significantly decrease intradermal nitrite levels. Likewise, administration of an effective dose of L-NAME significantly decreases CQ-induced nitrite production. We conclude that the NMDA/NO pathway in the skin modulates CQ-induced scratching behavior. PMID:28119997

Nicotine Uses Neuron-Glia Communication to Enhance Hippocampal Synaptic Transmission and Long-term Memory

PubMed Central

López-Hidalgo, Mónica; Salgado-Puga, Karla; Alvarado-Martínez, Reynaldo; Medina, Andrea Cristina; Prado-Alcalá, Roberto A.; García-Colunga, Jesús

2012-01-01

Nicotine enhances synaptic transmission and facilitates long-term memory. Now it is known that bi-directional glia-neuron interactions play important roles in the physiology of the brain. However, the involvement of glial cells in the effects of nicotine has not been considered until now. In particular, the gliotransmitter D-serine, an endogenous co-agonist of NMDA receptors, enables different types of synaptic plasticity and memory in the hippocampus. Here, we report that hippocampal long-term synaptic plasticity induced by nicotine was annulled by an enzyme that degrades endogenous D-serine, or by an NMDA receptor antagonist that acts at the D-serine binding site. Accordingly, both effects of nicotine: the enhancement of synaptic transmission and facilitation of long-term memory were eliminated by impairing glial cells with fluoroacetate, and were restored with exogenous D-serine. Together, these results show that glial D-serine is essential for the long-term effects of nicotine on synaptic plasticity and memory, and they highlight the roles of glial cells as key participants in brain functions. PMID:23185511

A non-ionotropic activity of NMDA receptors contributes to glycine-induced neuroprotection in cerebral ischemia-reperfusion injury.

PubMed

Chen, Juan; Hu, Rong; Liao, Huabao; Zhang, Ya; Lei, Ruixue; Zhang, Zhifeng; Zhuang, Yang; Wan, Yu; Jin, Ping; Feng, Hua; Wan, Qi

2017-06-15

NMDA receptor (NMDAR) is known for its ionotropic function. But recent evidence suggests that NMDAR also has a non-ionotropic property. To determine the role of non-ionotropic activity of NMDARs in clinical relevant conditions, we tested the effect of glycine, a co-agonist of NMDARs, in rat middle cerebral artery occlusion (MCAO), an animal model of cerebral ischemia-reperfusion injury after the animals were injected with the NMDAR channel blocker MK-801 and the glycine receptor antagonist strychnine. We show that glycine reduces the infarct volume in the brain of ischemic stroke animals pre-injected with MK-801 and strychnine. The effect of glycine is sensitive to the antagonist of glycine-GluN1 binding site and blocked by Akt inhibition. In the neurobehavioral tests, glycine improves the functional recovery of stroke animals pre-injected with MK-801 and strychnine. This study suggests that glycine-induced neuroprotection is mediated in part by the non-ionotropic activity of NMDARs via Akt activation in cerebral ischemia-reperfusion injury.

Effect of cross-fostering on seizures in adult male offspring of methamphetamine-treated rat mothers.

PubMed

Slamberová, R; Hrubá, L; Bernásková, K; Matejovská, I; Rokyta, R

2010-10-01

Stimulant drugs are often associated with increased seizure susceptibility. Inhibitory gamma-aminobutyric acid (GABA) and excitatory N-methyl-D-aspartate (NMDA) systems play a role in the effect of stimulants in the genesis of epileptic seizures. Our previous studies showed that prenatal methamphetamine (MA) exposure induced long-term changes in seizure susceptibility. The aim of the present study was to investigate the effect of cross-fostering on the prenatal and postnatal MA-exposed rats, respectively, on their seizures in adulthood. Bicuculline (GABA(A) receptor antagonist), NMDA (NMDA receptor agonist) and flurothyl (a convulsant gas) were used to induce seizures in adult male offsprings. Female dams were injected with MA (5 mg/kg daily) or physiological saline (S) for approx. 9 week [about 3 week prior to impregnation, for the entire gestation period (22 days) and in preweaning period (21 days)]. Absolute controls (C) did not receive any injections. On postnatal day 1, pups were cross-fostered so that each mother received pups from all three treatments. Thus, nine groups (based on the prenatal and postnatal drug exposure) of adult male rats were tested in each seizure test: C/C; C/S; C/MA; S/C; S/S; S/MA; MA/C; MA/S; MA/MA. The present study demonstrates that the effect of prenatal and/or postnatal MA exposure is seizure model specific. In addition, our data show that there is an effect of cross-fostering on seizures; particularly, the effect of prenatal MA exposure shown in animals fostered by control mothers is no longer apparent in animals fostered postnatally by MA-treated mothers. Such effect of postnatal treatment is not manifested in prenatal controls. In summary, it seems that: (1) prenatal MA exposure alters seizure susceptibility more than postnatal MA exposure; (2) especially in seizures induced by chemicals that affect GABAergic system (bicuculline, flurothyl) notable effect of adoption (cross-fostering) is apparent; (3) in seizure models that are associated with NMDA system (NMDA, flurothyl), effect of prenatal stress seems to play a role. Copyright 2010 ISDN. Published by Elsevier Ltd. All rights reserved.

Metabotropic and ionotropic glutamate receptors mediate the modulation of acetylcholine release at the frog neuromuscular junction.

PubMed

Tsentsevitsky, Andrei; Nurullin, Leniz; Nikolsky, Evgeny; Malomouzh, Artem

2017-07-01

There is some evidence that glutamate (Glu) acts as a signaling molecule at vertebrate neuromuscular junctions where acetylcholine (ACh) serves as a neurotransmitter. In this study, performed on the cutaneous pectoris muscle of the frog Rana ridibunda, Glu receptor mechanisms that modulate ACh release processes were analyzed. Electrophysiological experiments showed that Glu reduces both spontaneous and evoked quantal secretion of ACh and synchronizes its release in response to electrical stimulation. Quisqualate, an agonist of ionotropic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptors and metabotropic Group I mGlu receptors, also exerted Glu-like inhibitory effects on the secretion of ACh but had no effect on the kinetics of quantal release. Quisqualate's inhibitory effect did not occur when a blocker of Group I mGlu receptors (LY 367385) or an inhibitor of phospholipase C (U73122) was present. An increase in the degree of synchrony of ACh quantal release, such as that produced by Glu, was obtained after application of N-methyl-D-aspartic acid (NMDA). The presence of Group I mGlu and NMDA receptors in the neuromuscular synapse was confirmed by immunocytochemistry. Thus, the data suggest that both metabotropic Group I mGlu receptors and ionotropic NMDA receptors are present at the neuromuscular synapse of amphibians, and that the activation of these receptors initiates different mechanisms for the regulation of ACh release from motor nerve terminals. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Differential effects of subtype-specific nicotinic acetylcholine receptor agonists on early and late hippocampal LTP.

PubMed

Kroker, Katja S; Rast, Georg; Rosenbrock, Holger

2011-12-05

Brain nicotinic acetylcholine receptors are involved in several neuropsychiatric disorders, e.g. Alzheimer's and Parkinson's diseases, Tourette's syndrome, schizophrenia, depression, autism, attention deficit hyperactivity disorder, and anxiety. Currently, approaches selectively targeting the activation of specific nicotinic acetylcholine receptors are in clinical development for treatment of memory impairment of Alzheimer's disease patients. These are α4β2 and α7 nicotinic acetylcholine receptor agonists which are believed to enhance cholinergic and glutamatergic neurotransmission, respectively. In order to gain a better insight into the mechanistic role of these two nicotinic acetylcholine receptors in learning and memory, we investigated the effects of the α4β2 nicotinic acetylcholine receptor agonist TC-1827 and the α7 nicotinic acetylcholine receptor partial agonist SSR180711 on hippocampal long-term potentiation (LTP), a widely accepted cellular experimental model of memory formation. Generally, LTP is distinguished in an early and a late form, the former being protein-synthesis independent and the latter being protein-synthesis dependent. TC-1827 was found to increase early LTP in a bell-shaped dose dependent manner, but did not affect late LTP. In contrast, the α7 nicotinic acetylcholine receptor partial agonist SSR180711 showed enhancing effects on both early and late LTP in a bell-shaped manner. Furthermore, SSR180711 not only increased early LTP, but also transformed it into late LTP, which was not observed with the α4β2 nicotinic acetylcholine receptor agonist. Therefore, based on these findings α7 nicotinic acetylcholine receptor (partial) agonists appear to exhibit stronger efficacy on memory improvement than α4β2 nicotinic acetylcholine receptor agonists. Copyright © 2011 Elsevier B.V. All rights reserved.

GPR40 partial agonist MK-2305 lower fasting glucose in the Goto Kakizaki rat via suppression of endogenous glucose production

PubMed Central

Kirkland, Melissa E.; Kosinski, Daniel T.; Mane, Joel; Bunzel, Michelle; Cao, Jin; Souza, Sarah; Thomas-Fowlkes, Brande; Di Salvo, Jerry; Weinglass, Adam B.; Li, Xiaoyan; Myers, Robert W.; Knagge, Kevin; Carrington, Paul E.; Hagmann, William K.

2017-01-01

GPR40 (FFA1) is a fatty acid receptor whose activation results in potent glucose lowering and insulinotropic effects in vivo. Several reports illustrate that GPR40 agonists exert glucose lowering in diabetic humans. To assess the mechanisms by which GPR40 partial agonists improve glucose homeostasis, we evaluated the effects of MK-2305, a potent and selective partial GPR40 agonist, in diabetic Goto Kakizaki rats. MK-2305 decreased fasting glucose after acute and chronic treatment. MK-2305-mediated changes in glucose were coupled with increases in plasma insulin during hyperglycemia and glucose challenges but not during fasting, when glucose was normalized. To determine the mechanism(s) mediating these changes in glucose metabolism, we measured the absolute contribution of precursors to glucose production in the presence or absence of MK-2305. MK-2305 treatment resulted in decreased endogenous glucose production (EGP) driven primarily through changes in gluconeogenesis from substrates entering at the TCA cycle. The decrease in EGP was not likely due to a direct effect on the liver, as isolated perfused liver studies showed no effect of MK-2305 ex vivo and GPR40 is not expressed in the liver. Taken together, our results suggest MK-2305 treatment increases glucose stimulated insulin secretion (GSIS), resulting in changes to hepatic substrate handling that improve glucose homeostasis in the diabetic state. Importantly, these data extend our understanding of the underlying mechanisms by which GPR40 partial agonists reduce hyperglycemia. PMID:28542610

Muscarinic and nicotinic acetylcholine receptor agonists: current scenario in Alzheimer's disease therapy.

PubMed

Verma, Stuti; Kumar, Ashwini; Tripathi, Timir; Kumar, Awanish

2018-04-16

Alzheimer's disease (AD) has become the primary cause of dementia. It shows a progressive cognitive dysfunction with degenerating neurons. Acetylcholine receptors (AChRs) propagate the cognitive ability and it consists of two primary members namely muscarinic (mAChRs) and nicotinic receptors (nAChRs). Where mAChRs is G-protein coupled receptor, (nAChRs) are ligand-gated ion channels. The conventional therapeutic regimen for AD consists of three acetylcholinestearse inhibitors while a single NMDA receptor antagonist. Researchers around the globe are developing new and modifying the existing AChRs agonists to develop lead candidates with lower risk to benefit ratio where benefits clearly outweigh the adverse events. We have searched PubMed, MEDLINE, Google scholar, Science Direct and, Web of Science with keywords "Muscarinic/Nicotinic acetylcholine receptor, agonists and, AD". The literature search included articles written in English. Scientific relevance for clinical studies, basic science studies is eligibility criteria for articles referred in this paper. M1 is the primary muscarinic subtype while α7 is the primary nAChR subtype that is responsible for cognition and memory and these two have been the major recent experimental targets for mAChR agonist strategy. The last cholinergic receptor agonist to enter phase 3 trial was EVP-6124 (Enceniclin) but was withdrawn due to severe gastrointestinal adverse effects. We aim to present an overview of the efforts and achievements in targeting Muscarinic and Nicotinic acetylcholine receptor in the current review for development of better AD therapeutics. © 2018 Royal Pharmaceutical Society.

Action of novel antipsychotics at human dopamine D3 receptors coupled to G protein and ERK1/2 activation.

PubMed

Bruins Slot, Liesbeth A; Palmier, Christiane; Tardif, Stéphanie; Cussac, Didier

2007-08-01

The effects of new generation antipsychotic drugs (APDs) targeting dopamine D(2) and serotonin 5-HT(1A) receptors were compared with typical and atypical APDs on phosphorylation of extracellular signal-regulated kinase 1/2 (ERK 1/2) and measures of G protein activation in CHO cell lines stably expressing the human dopamine D(3) receptor. The preferential dopamine D(3) agonists (+)-7-OH-DPAT and PD128907, like dopamine and quinelorane, efficaciously stimulated ERK 1/2 phosphorylation at dopamine D(3) receptors. In contrast, in [(35)S]GTPgammaS binding experiments, (+)-7-OH-DPAT exhibited partial agonist properties, while PD128907 and quinelorane maintained full agonist properties. The preferential dopamine D(3) ligand BP 897 and the antidyskinetic sarizotan partially activated ERK 1/2 phosphorylation while exerting no agonist activity on GTPgammaS binding, suggesting signal amplification at the MAP kinase level. Antipsychotics differed in their ability to inhibit both agonist-stimulated GTPgammaS binding and ERK 1/2 phosphorylation, but all typical and atypical compounds tested acted as dopamine D(3) receptor antagonists with the exception of n-desmethylclozapine, the active metabolite of clozapine, which partially activated dopamine D(3) receptor-mediated ERK 1/2 phosphorylation. Among the new generation dopamine D(2)/serotonin 5-HT(1A) antipsychotics, only F 15063 and SLV313 acted as pure dopamine D(3) receptor antagonists, bifeprunox was highly efficacious whereas SSR181507 and aripiprazole showed marked partial agonist properties for ERK 1/2 phosphorylation. In contrast, in the GTPgammaS binding study, aripiprazole was devoid of agonist properties and bifeprunox, and to an even lesser extent SSR181507, only weakly stimulated GTPgammaS binding. In summary, these findings underline the differences of dopamine D(3) properties of new generation antipsychotics which may need to be considered in understanding their diverse therapeutic actions.

Role of kappa-opioid receptors in the effects of salvinorin A and ketamine on attention in rats.

PubMed

Nemeth, Christina L; Paine, Tracie A; Rittiner, Joseph E; Béguin, Cécile; Carroll, F Ivy; Roth, Bryan L; Cohen, Bruce M; Carlezon, William A

2010-06-01

Disruptions in perception and cognition are characteristic of psychiatric conditions such as schizophrenia. Studies of pharmacological agents that alter perception and cognition in humans might provide a better understanding of the brain substrates of these complex processes. One way to study these states in rodents is with tests that require attention and visual perception for correct performance. We examined the effects of two drugs that cause disruptions in perception and cognition in humans-the kappa-opioid receptor (KOR) agonist salvinorin A (salvA; 0.125-4.0 mg/kg) and the non-competitive NMDA receptor antagonist ketamine (0.63-20 mg/kg)-on behavior in rats using the 5-choice serial reaction time task (5CSRTT), a food-motivated test that quantifies attention. We also compared the binding profiles of salvA and ketamine at KORs and NMDA receptors. SalvA and ketamine produced the same pattern of disruptive effects in the 5CSRTT, characterized by increases in signs often associated with reduced motivation (omission errors) and deficits in processing (elevated latencies to respond correctly). Sessions in which rats were fed before testing suggest that reduced motivation produces a subtly different pattern of behavior. Pretreatment with the KOR antagonist JDTic (10 mg/kg) blocked all salvA effects and some ketamine effects. Binding and function studies revealed that ketamine is a full agonist at KORs, although not as potent or selective as salvA. SalvA and ketamine have previously under-appreciated similarities in their behavioral effects and pharmacological profiles. By implication, KORs might be involved in some of the cognitive abnormalities observed in psychiatric disorders such as schizophrenia.

Oxytocin reversed MK-801-induced social interaction and aggression deficits in zebrafish.

PubMed

Zimmermann, Fernanda Francine; Gaspary, Karina Vidarte; Siebel, Anna Maria; Bonan, Carla Denise

2016-09-15

Changes in social behavior occur in several neuropsychiatric disorders such as schizophrenia and autism. The interaction between individuals is an essential aspect and an adaptive response of several species, among them the zebrafish. Oxytocin is a neuroendocrine hormone associated with social behavior. The aim of the present study was to investigate the effects of MK-801, a non-competitive antagonist of glutamate NMDA receptors, on social interaction and aggression in zebrafish. We also examined the modulation of those effects by oxytocin, the oxytocin receptor agonist carbetocin and the oxytocin receptor antagonist L-368,899. Our results showed that MK-801 induced a decrease in the time spent in the segment closest to the conspecific school and in the time spent in the segment nearest to the mirror image, suggesting an effect on social behavior. The treatment with oxytocin after the exposure to MK-801 was able to reestablish the time spent in the segment closest to the conspecific school, as well as the time spent in the segment nearest to the mirror image. In addition, in support of the role of the oxytocin pathway in modulating those responses, we showed that the oxytocin receptor agonist carbetocin reestablished the social and aggressive behavioral deficits induced by MK-801. However, the oxytocin receptor antagonist L-368,899 was not able to reverse the behavioral changes induced by MK-801. This study supports the critical role for NMDA receptors and the oxytocinergic system in the regulation of social behavior and aggression which may be relevant for the mechanisms associated to autism and schizophrenia. Copyright © 2016 Elsevier B.V. All rights reserved.

Neuropharmacology of light-induced locomotor activation.

PubMed

Amato, Davide; Pum, Martin E; Groos, Dominik; Lauber, Andrea C; Huston, Joseph P; Carey, Robert J; de Souza Silva, Maria A; Müller, Christian P

2015-08-01

Presentation of non-aversive light stimuli for several seconds was found to reliably induce locomotor activation and exploratory-like activity. Light-induced locomotor activity (LIA) can be considered a convenient simple model to study sensory-motor activation. LIA was previously shown to coincide with serotonergic and dopaminergic activation in specific cortical areas in freely moving and anesthetized animals. In the present study we explore the neuropharmacology of LIA using a receptor antagonist/agonist approach in rats. The non-selective 5-HT2-receptor antagonist ritanserin (1.5-6 mg/kg, i.p.) dose-dependently reduced LIA. Selective antagonism of either the 5-HT2A-receptor by MDL 11,939 (0.1-0.4 mg/kg, i.p.), or the 5-HT2C-receptor by SDZ SER 082 (0.125-0.5 mg/kg, i.p.), alone or in combination, had no significant influence on LIA. Also the selective 5-HT1A-receptor antagonist, WAY 100635 (0.4 mg/kg, i.p.) did not affect LIA. Neither did the preferential dopamine D2-receptor antagonist, haloperidol (0.025-0.1 mg/kg, i.p.) nor the D2/D3-receptor agonist, quinpirole (0.025-0.5 mg/kg, i.p.) affect the expression of LIA. However, blocking the glutamatergic NMDA-receptor with phencyclidine (PCP, 1.5-6 mg/kg, i.p.) dose-dependently reduced LIA. This effect was also observed with ketamine (10 mg/kg, i.p.). These findings suggest that serotonin and dopamine receptors abundantly expressed in the cortex do not mediate light-stimulus triggered locomotor activity. PCP and ketamine effects, however, suggest an important role of NMDA receptors in LIA. Copyright © 2015 Elsevier Ltd. All rights reserved.

The central action of the 5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) on cardiac inotropy and vascular resistance in the anaesthetized cat

PubMed Central

Ramage, Andrew G; de Burgh Daly, M

1998-01-01

Experiments were carried out to determine the effects of the application of the selective 5-HT2 receptor agonist DOI intravenously (in the presence of the peripherally acting 5-HT2 receptor antagonist, BW501C67, 1 mg kg−1, i.v.) or to the `glycine sensitive area' of the ventral surface (30 μg each side) on the left ventricular inotropic (left ventricular dP/dt max) and vascularly isolated hindlimb responses in anaesthetized cats. For the ventral surface experiments, NMDA (10 μg each side) was applied to act as a positive control. In all experiments heart rate and mean arterial blood pressure were held constant to exclude any secondary effects caused by changes in these variables.DOI (n=6) i.v or on the ventral surface had no effect on left ventricular dP/dt max but caused a significant increase in hindlimb perfusion pressure of 40±9 and 50±14 mmHg, respectively. Respiration was unaffected. NMDA (n=6), applied to the ventral surface, caused significant increases in both left ventricular dP/dt max and hindlimb perfusion pressure of 1950±349 mmHg s−1 and 69±17 mmHg respectively, with no associated change in left ventricular end-diastolic pressure. The amplitude of respiratory movements increased.It is concluded that activation of 5-HT2 receptors at the level of the rostral ventrolateral medulla (RVLM) excites sympathetic premotor neurons and/or their antecedents controlling hindlimb vascular resistance but not those controlling the inotropic effects on the left ventricle. PMID:9863644

Role of kappa-opioid receptors in the effects of salvinorin A and ketamine on attention in rats

PubMed Central

Nemeth, Christina L.; Paine, Tracie A.; Rittiner, Joseph E.; Béguin, Cécile; Carroll, F. Ivy; Roth, Bryan L.; Cohen, Bruce M.

2010-01-01

Background Disruptions in perception and cognition are characteristic of psychiatric conditions such as schizophrenia. Studies of pharmacological agents that alter perception and cognition in humans might provide a better understanding of the brain substrates of these complex processes. One way to study these states in rodents is with tests that require attention and visual perception for correct performance. Methods We examined the effects of two drugs that cause disruptions in perception and cognition in humans—the kappa-opioid receptor (KOR) agonist salvinorin A (salvA; 0.125–4.0 mg/kg) and the non-competitive NMDA receptor antagonist ketamine (0.63–20 mg/kg)—on behavior in rats using the 5-choice serial reaction time task (5CSRTT), a food-motivated test that quantifies attention. We also compared the binding profiles of salvA and ketamine at KORs and NMDA receptors. Results SalvA and ketamine produced the same pattern of disruptive effects in the 5CSRTT, characterized by increases in signs often associated with reduced motivation (omission errors) and deficits in processing (elevated latencies to respond correctly). Sessions in which rats were fed before testing suggest that reduced motivation produces a subtly different pattern of behavior. Pretreatment with the KOR antagonist JDTic (10 mg/kg) blocked all salvA effects and some ketamine effects. Binding and function studies revealed that ketamine is a full agonist at KORs, although not as potent or selective as salvA. Conclusions SalvA and ketamine have previously underappreciated similarities in their behavioral effects and pharmacological profiles. By implication, KORs might be involved in some of the cognitive abnormalities observed in psychiatric disorders such as schizophrenia. PMID:20358363

Leptin reverses corticosterone-induced inhibition of neural stem cell proliferation through activating the NR2B subunits of NMDA receptors

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

Shi, Wen-Zhu; Anesthesia and Operation Center, Chinese PLA General Hospital, Beijing 100853; Miao, Yu-Liang

Highlights: • Leptin promotes the proliferation of neural stem cells isolated from embryonic mouse hippocampus. • Leptin reverses corticosterone-induced inhibition of neural stem cell proliferation. • The effects of leptin are partially mediated by upregulating NR2B subunits. - Abstract: Corticosterone inhibits the proliferation of hippocampal neural stem cells (NSCs). The removal of corticosterone-induced inhibition of NSCs proliferation has been reported to contribute to neural regeneration. Leptin has been shown to regulate brain development, improve angiogenesis, and promote neural regeneration; however, its effects on corticosterone-induced inhibition of NSCs proliferation remain unclear. Here we reported that leptin significantly promoted the proliferation ofmore » hippocampal NSCs in a concentration-dependent pattern. Also, leptin efficiently reversed the inhibition of NSCs proliferation induced by corticosterone. Interestingly, pre-treatment with non-specific NMDA antagonist MK-801, specific NR2B antagonist Ro 25-6981, or small interfering RNA (siRNA) targeting NR2B, significantly blocked the effect of leptin on corticosterone-induced inhibition of NSCs proliferation. Furthermore, corticosterone significantly reduced the protein expression of NR2B, whereas pre-treatment with leptin greatly reversed the attenuation of NR2B expression caused by corticosterone in cultured hippocampal NSCs. Our findings demonstrate that leptin reverses the corticosterone-induced inhibition of NSCs proliferation. This process is, at least partially mediated by increased expression of NR2B subunits of NMDA receptors.« less

Improved resolution of single channel dwell times reveals mechanisms of binding, priming, and gating in muscle AChR

PubMed Central

Mukhtasimova, Nuriya; daCosta, Corrie J.B.

2016-01-01

The acetylcholine receptor (AChR) from vertebrate skeletal muscle initiates voluntary movement, and its kinetics of activation are crucial for maintaining the safety margin for neuromuscular transmission. Furthermore, the kinetic mechanism of the muscle AChR serves as an archetype for understanding activation mechanisms of related receptors from the Cys-loop superfamily. Here we record currents through single muscle AChR channels with improved temporal resolution approaching half an order of magnitude over our previous best. A range of concentrations of full and partial agonists are used to elicit currents from human wild-type and gain-of-function mutant AChRs. For each agonist–receptor combination, rate constants are estimated from maximum likelihood analysis using a kinetic scheme comprised of agonist binding, priming, and channel gating steps. The kinetic scheme and rate constants are tested by stochastic simulation, followed by incorporation of the experimental step response, sampling rate, background noise, and filter bandwidth. Analyses of the simulated data confirm all rate constants except those for channel gating, which are overestimated because of the established effect of noise on the briefest dwell times. Estimates of the gating rate constants were obtained through iterative simulation followed by kinetic fitting. The results reveal that the agonist association rate constants are independent of agonist occupancy but depend on receptor state, whereas those for agonist dissociation depend on occupancy but not on state. The priming rate and equilibrium constants increase with successive agonist occupancy, and for a full agonist, the forward rate constant increases more than the equilibrium constant; for a partial agonist, the forward rate and equilibrium constants increase equally. The gating rate and equilibrium constants also increase with successive agonist occupancy, but unlike priming, the equilibrium constants increase more than the forward rate constants. As observed for a full and a partial agonist, the gain-of-function mutation affects the relationship between rate and equilibrium constants for priming but not for channel gating. Thus, resolving brief single channel currents distinguishes priming from gating steps and reveals how the corresponding rate and equilibrium constants depend on agonist occupancy. PMID:27353445

Thermodynamics and Mechanism of the Interaction of Willardiine Partial Agonists with a Glutamate Receptor: Implications for Drug Development

PubMed Central

2015-01-01

Understanding the thermodynamics of binding of a lead compound to a receptor can provide valuable information for drug design. The binding of compounds, particularly partial agonists, to subtypes of the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor is, in some cases, driven by increases in entropy. Using a series of partial agonists based on the structure of the natural product, willardiine, we show that the charged state of the ligand determines the enthalpic contribution to binding. Willardiines have uracil rings with pKa values ranging from 5.5 to 10. The binding of the charged form is largely driven by enthalpy, while that of the uncharged form is largely driven by entropy. This is due at least in part to changes in the hydrogen bonding network within the binding site involving one water molecule. This work illustrates the importance of charge to the thermodynamics of binding of agonists and antagonists to AMPA receptors and provides clues for further drug discovery. PMID:24850223

[Dopamine agonists--clinical applications beyond Parkinson's disease].

PubMed

Kuran, Włodzimierz

2007-01-01

Contemporary experience and results of clinical trials concerning dopamine agonist application in the treatment of many different diseases (apart from Parkinson's disease) are presented in the paper. A basic clinical recommendation for agonists is restless legs syndrome. In this syndrome almost all agonists give a considerable subjective and objective improvement. Treatment of atypical parkinsonism (MSA, PSP, CBD) in the majority of patients is ineffective. The author also presents promising results of treatment with agonists in such diverse diseases as hyperkinetic syndromes, cocaine dependence, drug-resistant depression and erectile dysfunction (apomorphine). Dopamine partial agonists (e.g. aripiprazol) are recommended in the modern treatment of schizophrenia.

Identification of oligomer proanthocyanidins (F2) isolated from grape seeds as a formyl peptide receptor 1 partial agonist.

PubMed

Yang, Jingyu; Wang, Qing; Zhao, Ruijun; Sun, Baoshan; Wang, Lihui; Hou, Yue; Li, Xiaoqin; Wu, Chunfu

2013-04-01

Formyl peptide receptor 1 (FPR1) plays an important role in the rapid progression of glioblastoma and has been considered as a molecular target for the treatment. Previously, we have shown that oligomer proanthocyanidins (F2, degree of polymerization 2-15), isolated from grape seeds, inhibited FPR1-mediated chemotaxis of U-87 glioblastoma cells. In the present study, we investigated the capacity of F2 to interact with FPR1. The cross attenuation of chemotaxis revealed that F2 shared FPR1 with formyl-methionyl-leucyl-phenylalanine (fMLF), which is a prototype agonist of FPR1. F2 was chemotactic for U-87 cells, and the chemotactic response was abolished when FPR1 gene was silenced or FPR1 was competitively occupied. We further show that F2 specifically blocked the binding of fluorescent agonist to FPR1. Interestingly, F2 exhibited the characteristic of a partial agonist for FPR1, as shown by its capacity to activate FPR1-mediated PI3K-PKC-MAPK pathways. Meanwhile, F2 also attenuated fMLF-triggered MAPK activation, suggesting that F2 could antagonize the effect of an agonist. Furthermore, F2 abolished the invasion of U-87 cells induced by fMLF. Thus, we have identified F2 as a novel, partial agonist for FPR1, which may be useful for glioblastoma therapy. Copyright © 2013 Elsevier B.V. All rights reserved.

Allosteric nature of P2X receptor activation probed by photoaffinity labelling

PubMed Central

Bhargava, Y; Rettinger, J; Mourot, A

2012-01-01

BACKGROUND AND PURPOSE In P2X receptors, agonist binding at the interface between neighbouring subunits is efficiently transduced to ion channel gating. However, the relationship between binding and gating is difficult to study because agonists continuously bind and unbind. Here, we covalently incorporated agonists in the binding pocket of P2X receptors and examined how binding site occupancy affects the ability of the channel to gate. EXPERIMENTAL APPROACH We used a strategy for tethering agonists to their ATP-binding pocket, while simultaneously probing ion channel gating using electrophysiology. The agonist 2′,3′-O-(4-benzoylbenzoyl)-ATP (BzATP), a photoaffinity analogue of ATP, enabled us to trap rat homomeric P2X2 receptor and a P2X2/1 receptor chimera in different agonist-bound states. UV light was used to control the degree of covalent occupancy of the receptors. KEY RESULTS Irradiation of the P2X2/1 receptor chimera – BzATP complex resulted in a persistent current that lasted even after extensive washout, consistent with photochemical tethering of the agonist BzATP and trapping of the receptors in an open state. Partial labelling with BzATP primed subsequent agonist binding and modulated gating efficiency for both full and partial agonists. CONCLUSIONS AND IMPLICATIONS Our photolabelling strategy provides new molecular insights into the activation mechanism of the P2X receptor. We show here that priming with full agonist molecules leads to an increase in gating efficiency after subsequent agonist binding. PMID:22725669

Effects of AMPA receptor antagonist, NBQX, and extrasynaptic GABAA agonist, THIP, on social behavior of adolescent and adult rats.

PubMed

Dannenhoffer, Carol A; Varlinskaya, Elena I; Spear, Linda Patia

2018-05-22

Adolescence is characterized by high significance of social interactions, along with a propensity to exhibit social facilitating effects of ethanol while being less sensitive than adults to the inhibition of social behavior that emerges at higher doses of ethanol. Among the neural characteristics of adolescence are generally enhanced levels of glutamatergic (especially NMDA receptor) activity relative to adults, whereas the GABA system is still developmentally immature. Activation of NMDA receptors likely plays a role in modulation of social behavior in adolescent animals as well as in socially facilitating and suppressing effects of ethanol. For instance, adolescent and adult rats differ in their sensitivities to the effects of NMDA antagonists and ethanol on social behavior, with adolescents but not adults demonstrating social facilitation at lower doses of both drugs and adults being more sensitive to the socially suppressing effects evident at higher doses of each. The roles of AMPA and extrasynaptic GABA A receptors in modulation of social behavior during adolescence and in adulthood are still unknown. The present study was designed to assess whether pharmacological blockade of AMPA receptors and/or activation of extrasynaptic GABA A receptors results in age-dependent alterations of social behavior. Adolescent and adult male and female Sprague-Dawley rats were injected with an assigned dose of either a selective AMPA antagonist, NBQX (Experiment 1) or extrasynaptic GABA A agonist, THIP (Experiment 2) and placed into a modified social interaction chamber for a 30-min habituation period prior to a 10-min social interaction test with a novel age- and sex-matched partner. Behaviors such as social investigation, contact behavior and play behavior were scored from video recordings of the interaction tests. In Experiment 1, NBQX produced similar social inhibition at higher doses in both age groups. In Experiment 2, THIP induced inhibition in adolescents, but not adults. No social facilitation was evident following low doses of either drug. Therefore, AMPA and extrasynaptic GABA A receptors appear to play little role if any in modulation of peer-directed social behavior in adolescence and adulthood and not likely to contribute to previously observed age differences in the social effects of acute ethanol. Copyright © 2018 Elsevier Inc. All rights reserved.

Enhanced down regulation of cortical +-propranolol sensitive ( sup 3 H)-DHA binding sites by co-administration of DMI and 5-HT sub 1A partial agonist gepirone

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

Geissler, M.A.; Yocca, F.D.

1990-02-26

The putative interrelationship between the noradrenergic and serotonergic systems has been supported by numerous studies. Recently, Dudley et al. (1989) demonstrated significant down regulation of cortical {beta}-adrenergic receptors by co-administration of desipramine (DMI), a norepinephrine uptake inhibitor, and the full 5-HT{sub 1A} agonist 8-OH-DPAT. To this end, the effects of acute and chronic (4 and 14 day) administration of DMI, gepirone, a selective 5-HT{sub 1A} post-synaptic partial agonist, as well as a combination of the two, on cortical ({plus minus})-propranolol sensitive ({sup 3}H)-DHA binding sites were examined in rats. Down regulation was apparent after 4 and 14 day treatment withmore » DMI. However, this was not the case with gepirone. Of particular importance is the demonstration of a greater magnitude of down regulation with co-administration of a greater magnitude of down regulation with co-administration of DMI and gepirone. These results suggests that alteration in rat cortical ({plus minus})-propranolol sensitive ({sup 3}H)-DHA binding sites by noradrenergic uptake inhibitors can be further modulated by selective partial agonist activity at central 5-HT{sub 1A} postsynaptic receptors. Further data on the co-administration of DMI and BMY 7378 (7,9-dioxo-8-(2-(4-{und o}-methoxyphenylpiperazinyl)ethyl)-8-azaspiro(4,5)decane dihydrochloride), a weak partial agonist at postsynaptic 5-HT{sub 1A} receptors, are also presented.« less

Novel Podophyllotoxin Derivatives as Partial PPARγ Agonists and their Effects on Insulin Resistance and Type 2 Diabetes.

PubMed

Zhang, Xiangming; Liu, Huijuan; Sun, Bo; Sun, Yan; Zhong, Weilong; Liu, Yanrong; Chen, Shuang; Ling, Honglei; Zhou, Lei; Jing, Xiangyan; Qin, Yuan; Xiao, Ting; Sun, Tao; Zhou, Honggang; Yang, Cheng

2016-11-17

Peroxisome proliferator-activated receptor γ (PPARγ) is recognized as a key regulator of insulin resistance. In this study, we searched for novel PPARγ agonists in a library of structurally diverse organic compounds and determined that podophyllotoxin exhibits partial agonist activity toward PPARγ. Eight novel podophyllotoxin-like derivatives were synthesized and assayed for toxicity and functional activity toward PPARγ to reduce the possible systemic toxic effects of podophyllotoxin and to maintain partial agonist activity toward PPARγ. Cell-based transactivation assays showed that compounds (E)-3-(hydroxy(3,4,5-trimethoxyphenyl)methyl)-4-(4(trifluoromethyl)styryl)dihydrofuran-2(3H)-one (3a) and (E)-4-(3-acetylstyryl)-3-(hydroxyl (3,4,5-trimethoxyphenyl)methyl)dihydrofuran-2(3H)-one (3f) exhibited partial agonist activity. An experiment using human hepatocarcinoma cells (HepG2) that were induced to become an insulin-resistant model showed that compounds 3a and 3f improved insulin sensitivity and glucose consumption. In addition, compounds 3a and 3f significantly improved hyperglycemia and insulin resistance in high-fat diet-fed streptozotocin (HFD-STZ)-induced type 2 diabetic rats at a dose of 15 mg/kg/day administered orally for 45 days, without significant weight gain. Cell toxicity testing also showed that compounds 3a and 3f exhibited weaker toxicity than pioglitazone. These findings suggested that compounds 3a and 3f improved insulin resistance in vivo and in vitro and that the compounds exhibited potential for the treatment of type 2 diabetes mellitus.

Agonist and antagonist actions of antipsychotic agents at 5-HT1A receptors: a [35S]GTPgammaS binding study.

PubMed

Newman-Tancredi, A; Gavaudan, S; Conte, C; Chaput, C; Touzard, M; Verrièle, L; Audinot, V; Millan, M J

1998-08-21

Recombinant human (h) 5-HT1A receptor-mediated G-protein activation was characterised in membranes of transfected Chinese hamster ovary (CHO) cells by use of guanosine-5'-O-(3-[35S]thio)-triphosphate ([35S]GTPgammaS binding). The potency and efficacy of 21 5-HT receptor agonists and antagonists was determined. The agonists, 5-CT (carboxamidotryptamine) and flesinoxan displayed high affinity (subnanomolar Ki values) and high efficacy (Emax > 90%, relative to 5-HT = 100%). In contrast, ipsapirone, zalospirone and buspirone displayed partial agonist activity. EC50s for agonist stimulation of [35S]GTPgammaS binding correlated well with Ki values from competition binding (r = +0.99). Among the compounds tested for antagonist activity, methiothepin and (+)butaclamol exhibited 'inverse agonist' behaviour, inhibiting basal [35S]GTPgammaS binding. The actions of 17 antipsychotic agents were investigated. Clozapine and several putatively 'atypical' antipsychotic agents, including ziprasidone, quetiapine and tiospirone, exhibited partial agonist activity and marked affinity at h5-HT1A receptors, similar to their affinity at hD2 dopamine receptors. In contrast, risperidone and sertindole displayed low affinity at h5-HT1A receptors and behaved as 'neutral' antagonists, inhibiting 5-HT-stimulated [35S]GTPgammaS binding. Likewise the 'typical' neuroleptics, haloperidol, pimozide, raclopride and chlorpromazine exhibited relatively low affinity and 'neutral' antagonist activity at h5-HT1A receptors with Ki values which correlated with their respective Kb values. The present data show that (i) [35S]GTPgammaS binding is an effective method to evaluate the efficacy and potency of agonists and antagonists at recombinant human 5-HT1A receptors. (ii) Like clozapine, several putatively 'atypical' antipsychotic drugs display balanced serotonin h5-HT1A/dopamine hD2 receptor affinity and partial agonist activity at h5-HT1A receptors. (iii) Several 'typical' and some putatively 'atypical' antipsychotic agents displayed antagonist properties at h5-HT1A sites with generally much lower affinity than at hD2 dopamine receptors. It is suggested that agonist activity at 5-HT1A receptors may be of utility for certain antipsychotic agents.

Potentiation of low dose ketamine effects by naltrexone: potential implications for the pharmacotherapy of alcoholism.

PubMed

Krystal, John H; Madonick, Steven; Perry, Edward; Gueorguieva, Ralitza; Brush, Laura; Wray, Yola; Belger, Aysenil; D'Souza, Deepak Cyril

2006-08-01

The interplay of opiate and NMDA glutamate receptors may contribute to psychosis, cognitive function, alcoholism, and substance dependence. Ketamine and ethanol block the NMDA glutamate receptor. The purpose of this randomized double-blind, placebo-controlled human laboratory study was to evaluate whether the interactive effects of drugs acting at opiate and NMDA glutamate receptors might partially explain the efficacy of naltrexone for the treatment of alcoholism, that is, whether naltrexone 25 mg pretreatment would modulate ketamine effects in healthy human subjects. Two groups of healthy subjects were studied. An initial group (n=31) received a perception-altering subanesthetic dose of ketamine (bolus of 0.23 mg/kg over 1 min followed by a 60-min infusion of 0.58 mg/kg or saline bolus and infusion). A second group (n=24) completed the same testing procedures, but received a subperceptual ketamine dose (bolus 0.081 mg/kg over 10 min followed by an infusion of 0.4 mg/kg/h). Ketamine produced positive symptoms, negative symptoms, emotional discomfort, and cognitive effects as measured by the Positive and Negative Syndrome Scale (PANSS) in a dose-related fashion. The lower ketamine dose produced subjective effects similar to two standard ethanol drinks, whereas the higher ketamine dose produced effects similar to five standard drinks. Although naltrexone produced no significant behavioral effects, it significantly magnified the increase in the total PANSS score produced by the lower subperceptual dose of ketamine, but not the higher perception-altering dose of ketamine. These data suggest that the interplay of opiate receptor antagonism and NMDA receptor antagonism may be relevant to the protective effects of naltrexone on alcohol consumption via potentiation of dysphoric effects associated with the NMDA receptor antagonist effects of ethanol. However, these data suggest that at levels of NMDA receptor antagonism associated with heavy drinking, this protective effect of naltrexone on drinking is no longer present.

Olanzapine Reverses MK-801-Induced Cognitive Deficits and Region-Specific Alterations of NMDA Receptor Subunits

PubMed Central

Liu, Xiao; Li, Jitao; Guo, Chunmei; Wang, Hongli; Sun, Yaxin; Wang, Han; Su, Yun-Ai; Li, Keqing; Si, Tianmei

2018-01-01

Cognitive dysfunction constitutes an essential component in schizophrenia for its early presence in the pathophysiology of the disease and close relatedness to life quality of patients. To develop effective treatment of cognitive deficits, it is important to understand their neurobiological causes and to identify potential therapeutic targets. In this study, adopting repeated MK-801 treatment as an animal model of schizophrenia, we investigated whether antipsychotic drugs, olanzapine and haloperidol, can reverse MK-801-induced cognitive deficits and how the reversal processes recruited proteins involved in glutamate neurotransmission in rat medial prefrontal cortex (mPFC) and hippocampus. We found that low-dose chronic MK-801 treatment impaired object-in-context recognition memory and reversal learning in the Morris water maze, leaving reference memory relatively unaffected, and that these cognitive deficits can be partially reversed by olanzapine, not haloperidol, treatment. At the molecular level, chronic MK-801 treatment resulted in the reduction of multiple N-methyl-D-aspartate (NMDA) receptor subunits in rat mPFC and olanzapine, not haloperidol, treatment restored the levels of GluN1 and phosphorylated GluN2B in this region. Taken together, MK-801-induced cognitive deficits may be associated with region-specific changes in NMDA receptor subunits and the reversal of specific NMDA receptor subunits may underlie the cognition-enhancing effects of olanzapine. PMID:29375333

Factors Underlying Bursting Behavior in a Network of Cultured Hippocampal Neurons Exposed to Zero Magnesium

PubMed Central

Mangan, Patrick S.; Kapur, Jaideep

2010-01-01

Factors contributing to reduced magnesium-induced neuronal action potential bursting were investigated in primary hippocampal cell culture at high and low culture density. In nominally zero external magnesium medium, pyramidal neurons from high-density cultures produced recurrent spontaneous action potential bursts superimposed on prolonged depolarizations. These bursts were partially attenuated by the NMDA receptor antagonist D-APV. Pharmacological analysis of miniature excitatory postsynaptic currents (EPSCs) revealed 2 components: one sensitive to D-APV and another to the AMPA receptor antagonist DNQX. The components were kinetically distinct. Participation of NMDA receptors in reduced magnesium-induced synaptic events was supported by the localization of the NR1 subunit of the NMDA receptor with the presynaptic vesicular protein synaptophysin. Presynaptically, zero magnesium induced a significant increase in EPSC frequency likely attributable to increased neuronal hyperexcitability induced by reduced membrane surface charge screening. Mean quantal content was significantly increased in zero magnesium. Cells from low-density cultures did not exhibit action potential bursting in zero magnesium but did show increased EPSC frequency. Low-density neurons had less synaptophysin immunofluorescence and fewer active synapses as determined by FM1-43 analysis. These results demonstrate that multiple factors are involved in network bursting. Increased probability of transmitter release presynaptically, enhanced NMDA receptor-mediated excitability postsynaptically, and extent of neuronal interconnectivity contribute to initiation and maintenance of elevated network excitability. PMID:14534286

Asynchronous Movements Prior to Pore Opening in NMDA Receptors

PubMed Central

Kazi, Rashek; Gan, Quan; Talukder, Iehab; Markowitz, Michael; Salussolia, Catherine L.

2013-01-01

Glutamate-gated ion channels embedded within the neuronal membrane are the primary mediators of fast excitatory synaptic transmission in the CNS. The ion channel of these glutamate receptors contains a pore-lining transmembrane M3 helix surrounded by peripheral M1 and M4 helices. In the NMDA receptor subtype, opening of the ion channel pore, mediated by displacement of the M3 helices away from the central pore axis, occurs in a highly concerted fashion, but the associated temporal movements of the peripheral helices are unknown. To address the gating dynamics of the peripheral helices, we constrained the relative movements of the linkers that connect these helices to the ligand-binding domain using engineered cross-links, either within (intra-GluN1 or GluN2A) or between subunits. Constraining the peripheral linkers in any manner dramatically curtailed channel opening, highlighting the requirement for rearrangements of these peripheral structural elements for efficient gating to occur. However, the magnitude of this gating effect depended on the specific subunit being constrained, with the most dramatic effects occurring when the constraint was between subunits. Based on kinetic and thermodynamic analysis, our results suggest an asynchrony in the displacement of the peripheral linkers during the conformational and energetic changes leading to pore opening. Initially there are large-scale rearrangements occurring between the four subunits. Subsequently, rearrangements occur within individual subunits, mainly GluN2A, leading up to or in concert with pore opening. Thus, the conformational changes induced by agonist binding in NMDA receptors converge asynchronously to permit pore opening. PMID:23864691

[Studying specific effects of nootropic drugs on glutamate receptors in the rat brain].

PubMed

Firstova, Iu Iu; Vasil'eva, E V; Kovalev, G I

2011-01-01

The influence of nootropic drugs of different groups (piracetam, phenotropil, nooglutil, noopept, semax, meclofenoxate, pantocalcine, and dimebon) on the binding of the corresponding ligands to AMPA, NMDA, and mGlu receptors of rat brain has been studied by the method of radio-ligand binding in vitro. It is established that nooglutil exhibits pharmacologically significant competition with a selective agonist of AMPA receptors ([G-3H]Ro 48-8587) for the receptor binding sites (with IC50 = 6.4 +/- 0.2 microM), while the competition of noopept for these receptor binding sites was lower by an order of magnitude (IC50 = 80 +/- 5.6 microM). The heptapeptide drug semax was moderately competitive with [G-3H]LY 354740 for mGlu receptor sites (IC50 = 33 +/- 2.4 microM). Dimebon moderately influenced the specific binding of the ligand of NMDA receptor channel ([G-3H]MK-801) at IC50 = 59 +/- 3.6 microM. Nootropic drugs of the pyrrolidone group (piracetam, phenotropil) as well as meclofenoxate, pantocalcine (pantogam) in a broad rage of concentrations (10(-4)-10(-10) M) did not affect the binding of the corresponding ligands to glutamate receptors (IC50 100 pM). Thus, the direct neurochemical investigation was used for the first time to qualitatively characterize the specific binding sites for nooglutil and (to a lower extent) noopept on AMPA receptors, for semax on metabotropic glutamate receptors, and for dimebon on the channel region of NMDA receptors. The results are indicative of a selective action of some nootropes on the glutamate family.

Lack of the alanine-serine-cysteine transporter 1 causes tremors, seizures, and early postnatal death in mice.

PubMed

Xie, Xinmin; Dumas, Theodore; Tang, Lamont; Brennan, Thomas; Reeder, Thadd; Thomas, Winston; Klein, Robert D; Flores, Judith; O'Hara, Bruce F; Heller, H Craig; Franken, Paul

2005-08-09

The Na(+)-independent alanine-serine-cysteine transporter 1 (Asc-1) is exclusively expressed in neuronal structures throughout the central nervous system (CNS). Asc-1 transports small neutral amino acids with high affinity especially for D-serine and glycine (K(i): 8-12 microM), two endogenous glutamate co-agonists that activate N-methyl-D-aspartate (NMDA) receptors through interacting with the strychnine-insensitive glycine binding-site. By regulating D-serine (and possibly glycine) levels in the synaptic cleft, Asc-1 may play an important role in controlling neuronal excitability. We generated asc-1 gene knockout (asc-1(-/-)) mice to test this hypothesis. Behavioral phenotyping combined with electroencephalogram (EEG) recordings revealed that asc-1(-/-) mice developed tremors, ataxia, and seizures that resulted in early postnatal death. Both tremors and seizures were reduced by the NMDA receptor antagonist MK-801. Extracellular recordings from asc-1(-/-) brain slices indicated that the spontaneous seizure activity did not originate in the hippocampus, although, in this region, a relative increase in evoked synaptic responses was observed under nominal Mg(2+)-free conditions. Taken together with the known neurochemistry and neuronal distribution of the Asc-1 transporter, these results indicate that the mechanism underlying the behavioral hyperexcitability in mutant mice is likely due to overactivation of NMDA receptors, presumably resulting from elevated extracellular D-serine. Our study provides the first evidence to support the notion that Asc-1 transporter plays a critical role in regulating neuronal excitability, and indicate that the transporter is vital for normal CNS function and essential to postnatal survival of mice.

Sigma 1 receptor activation regulates brain-derived neurotrophic factor through NR2A-CaMKIV-TORC1 pathway to rescue the impairment of learning and memory induced by brain ischaemia/reperfusion.

PubMed

Xu, Qian; Ji, Xue-Fei; Chi, Tian-Yan; Liu, Peng; Jin, Ge; Gu, Shao-Li; Zou, Li-Bo

2015-05-01

Sigma-1 receptor (Sig-1R) agonists showed anti-amnesic properties in Alzheimer's disease models and anti-inflammatory properties in cerebrum ischaemia models. The agonist of Sig-1R was reported to up-regulate brain-derived neurotrophic factor (BDNF) levels in the hippocampus of mice. Here, we investigate whether the activation of Sig-1R attenuates the learning and memory impairment induced by ischaemia/reperfusion and how it affects the expression of BDNF. Bilateral common carotid artery occlusion (BCCAO) was induced for 20 min in C57BL/6 mice. Sig-1R agonist, PRE084, sigma 1/2 non-selective agonist, DTG, Sig-1R antagonist and BD1047 were injected once daily throughout the experiment. Behavioural tests were performed from day 8. On day 22 after BCCAO, mice were sacrificed for biochemical analysis. PRE084 and DTG ameliorated learning and memory impairments in the Y maze, novel object recognition, and water maze tasks and prevented the decline of synaptic proteins and BDNF expression in the hippocampus of BCCAO mice. Furthermore, PRE084 and DTG up-regulated the level of NMDA receptor 2A (NR2A), calcium/calmodulin-dependent protein kinase type IV (CaMKIV) and CREB-specific co-activator transducer of regulated CREB activity 1 (TORC1). Additionally, the effects of PRE084 and DTG were antagonised by the co-administration of BD1047. Sig-1R activation showed an attenuation in the ischaemia/reperfusion model and the activation of Sig-1R increased the expression of BDNF, possibly through the NR2A-CaMKIV-TORC1 pathway, and Sig-1R agonists might function as neuroprotectant agents in vascular dementia.

Anxiolytic effects of GLYX-13 in animal models of posttraumatic stress disorder-like behavior.

PubMed

Jin, Zeng-Liang; Liu, Jin-Xu; Liu, Xu; Zhang, Li-Ming; Ran, Yu-Hua; Zheng, Yuan-Yuan; Tang, Yu; Li, Yun-Feng; Xiong, Jie

2016-09-01

In the present study, we investigated the effectiveness of GLYX-13, an NMDA receptor glycine site functional partial agonist, to alleviate the enhanced anxiety and fear response in both a mouse and rat model of stress-induced behavioral changes that might be relevant to posttraumatic stress disorder (PTSD). Studies over the last decades have suggested that the hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis is one of the most consistent findings in stress-related disease. Herein, we used these animal models to further investigate the effect of GLYX-13 on the stress hormone levels and glucocorticoid receptor (GR) expression. We found that exposure to foot shock induced long-lasting behavioral deficiencies in mice, including freezing and anxiety-like behaviors, that were significantly ameliorated by the long-term administration of GLYX-13 (5 or 10 mg/kg). Our enzyme-linked immunosorbent assay results showed that long-term administration of GLYX-13 at behaviorally effective doses (5 or 10 mg/kg) significantly decreased the elevated serum levels of both corticosterone and its upstream stress hormone adrenocorticotropic hormone in rats subjected to the TDS procedure. These results suggest that GLYX-13 exerts a therapeutic effect on PTSD-like stress responding that is accompanied by (or associated with) modulation of the HPA axis, including inhibition of stress hormone levels and upregulation of hippocampal GR expression. © The Author(s) 2016.

Effects of D-cycloserine on the extinction of appetitive operant learning

PubMed Central

Vurbic, Drina; Gold, Benjamin; Bouton, Mark E.

2011-01-01

Four experiments with rat subjects examined whether D-cycloserine (DCS), a partial NMDA agonist, facilitates the extinction of operant lever-pressing reinforced by food. Previous research has demonstrated that DCS facilitates extinction learning with methods that involve Pavlovian extinction. In the current experiments, operant conditioning occurred in Context A, extinction in Context B, and then testing occurred in both the extinction and conditioning contexts. Experiments 1a and 1b tested the effects of three doses of DCS (5, 15, and 30 mg/kg) on the extinction of lever pressing trained as a free operant. Experiment 2 examined their effects when extinction of the free operant was conducted in the presence of non-response-contingent deliveries of the reinforcer (which theoretically reduced the role of generalization decrement in suppressing responding). Experiment 3 examined their effects on extinction of a discriminated operant, i.e., one that had been reinforced in the presence of a discriminative stimulus, but not in its absence. A strong ABA renewal effect was observed in all four experiments during testing. However, despite the use of DCS doses and a drug administration procedure that facilitates the extinction of Pavlovian learning, there was no evidence in any experiment that DCS facilitated operant extinction learning assessed in either the extinction or the conditioning context. DCS may primarily facilitate learning processes that underlie Pavlovian, rather than purely operant, extinction. PMID:21688894

Pharmacological interference with metabotropic glutamate receptor subtype 7 but not subtype 5 differentially affects within- and between-session extinction of Pavlovian conditioned fear.

PubMed

Toth, Iulia; Dietz, Monika; Peterlik, Daniel; Huber, Sabine E; Fendt, Markus; Neumann, Inga D; Flor, Peter J; Slattery, David A

2012-03-01

Fear extinction is defined as the attenuation of a conditioned-fear memory by re-exposing animals to the conditioned stimulus without the aversive stimulus. This process is known to be effectively enhanced via administration of D-cycloserine (DCS), a partial NMDA-receptor agonist. However, other glutamatergic mechanisms, such as interference with metabotropic glutamate receptor (mGluR) subtypes 5 and 7 in the extinction of aversive memories are insufficiently understood. Using the allosteric mGluR5 receptor antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP), the mGluR7 allosteric agonist N,N'-dibenzyhydryl-ethane-1,2-diamine dihydrochloride (AMN082), and DCS for comparison, we aimed to study how pharmacological blockade of mGluR5 and activation of mGluR7 influenced within- and between-session conditioned-fear extinction training and extinction retention in rats. We show that when injected before extinction training, mGluR7 activation with AMN082 enhanced freezing and thereby attenuated within-session fear extinction, whereas both DCS and the mGluR5 receptor antagonist MPEP had no effect on this process. However, these differential drug effects were not long lasting, as no difference in extinction retention were observed 24 h later. Therefore, we assessed whether the compounds affect 24 h consolidation of extinction training following incomplete extinction training (between-session extinction). Similar to DCS, AMN082- but not MPEP-treated rats showed facilitated extinction retention, as exhibited by decreased freezing. Finally, using fluoxetine, we provide evidence that the effect of AMN082 on between-session extinction retention is most likely not via increasing 5-HT transmission. These findings demonstrate that mGluR7 activation differentially modulates conditioned-fear extinction, in dependence on the protocol employed, and suggests drugs with AMN082-like mechanisms as potential add-on drugs following exposure-based psychotherapy for fear-related human disorders. Copyright © 2011 Elsevier Ltd. All rights reserved.

Glutamate may be an efferent transmitter that elicits inhibition in mouse taste buds.

PubMed

Huang, Yijen A; Grant, Jeff; Roper, Stephen

2012-01-01

Recent studies suggest that l-glutamate may be an efferent transmitter released from axons innervating taste buds. In this report, we determined the types of ionotropic synaptic glutamate receptors present on taste cells and that underlie this postulated efferent transmission. We also studied what effect glutamate exerts on taste bud function. We isolated mouse taste buds and taste cells, conducted functional imaging using Fura 2, and used cellular biosensors to monitor taste-evoked transmitter release. The findings show that a large fraction of Presynaptic (Type III) taste bud cells (∼50%) respond to 100 µM glutamate, NMDA, or kainic acid (KA) with an increase in intracellular Ca(2+). In contrast, Receptor (Type II) taste cells rarely (4%) responded to 100 µM glutamate. At this concentration and with these compounds, these agonists activate glutamatergic synaptic receptors, not glutamate taste (umami) receptors. Moreover, applying glutamate, NMDA, or KA caused taste buds to secrete 5-HT, a Presynaptic taste cell transmitter, but not ATP, a Receptor cell transmitter. Indeed, glutamate-evoked 5-HT release inhibited taste-evoked ATP secretion. The findings are consistent with a role for glutamate in taste buds as an inhibitory efferent transmitter that acts via ionotropic synaptic glutamate receptors.

Electrical stimulation or MK-801 in the inferior colliculus improve motor deficits in MPTP-treated mice.

PubMed

Melo-Thomas, L; Gil-Martínez, A L; Cuenca, L; Estrada, C; Gonzalez-Cuello, A; Schwarting, R K; Herrero, M T

2018-03-01

The inferior colliculus (IC) is an important midbrain relay station for the integration of descending and ascending auditory information. Additionally, the IC has been implicated in processing sensorimotor responses. Glutamatergic and GABAergic manipulations in the IC can improve motor deficits as demonstrated by the animal model of haloperidol-induced catalepsy. However, how the IC influences motor function remains unclear. We investigated the effects of either intracollicular deep brain stimulation (DBS) or microinjection of the glutamatergic antagonist MK-801 or the agonist NMDA in C57BL/6J mice chronically treated with saline or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). After DBS or microinjections, the mice were submitted to rotarod and open field tests, respectively. DBS in the IC was effective to increase the time spent on the rotarod in MPTP-treated mice. After unilateral microinjection of MK-801, but not NMDA, MPTP-treated mice increased the distance travelled in the open field (p < 0.05). In conclusion, intracollicular DBS or MK-801 microinjection can improve motor performance in parkinsonian mice suggesting the IC as a new and non-conventional therapeutic target in motor impairment. Copyright © 2018 Elsevier B.V. All rights reserved.

Guanosine-5'-monophosphate induces cell death in rat hippocampal slices via ionotropic glutamate receptors activation and glutamate uptake inhibition.

PubMed

Molz, Simone; Dal-Cim, Tharine; Tasca, Carla I

2009-12-01

Guanine derivatives modulate the glutamatergic system through displacement of binding of glutamate to its receptors acting as antagonist of glutamate receptors in moderate to high micromolar concentrations. Guanosine-5'-monophosphate (GMP) is shown to be neuroprotective against glutamate- or oxygen/glucose deprivation-induced neurotoxicity and also against NMDA-induced apoptosis in hippocampal slices. However, in this study we are showing that high extracellular GMP concentrations (5mM) reduced cell viability in hippocampal brain slices. The toxic effect of GMP was not blocked by dipyridamole, a nucleoside transport inhibitor, nor mimicked by guanosine, suggesting an extracellular mode of action to GMP which does not involve its hydrolysis to guanosine. GMP-dependent cell damage was not blocked by P1 purinergic receptor antagonists, neither altered by adenosine A(1) or A(2A) receptor agonists. The blockage of the ionotropic glutamate receptors AMPA or NMDA, but not KA or metabotropic glutamate receptors, reversed the toxicity induced by GMP. GMP (5mM) induced a decrease in glutamate uptake into hippocampal slices, which was reversed by dl-TBOA. Therefore, GMP-induced hippocampal cell damage involves activation of ionotropic glutamate receptors and inhibition of glutamate transporters activity.

NO-producing compounds transform neuron responses to glutamate.

PubMed

D'yakonova, T L

2000-01-01

We have previously shown that NO increases the excitatory effects of glutamate and blocks the desensitization of neurons to glutamate in the brain of the common snail. The aim of the present work was to identify the possible effect of NO on inhibitory responses to glutamate in the neurons of this mollusk. Electrophysiological investigations were performed on three identified neurons. The results showed that glutamate (0.05-0.1 mM) initially induced hyperpolarization and blocked the spike activity of these neurons. Simultaneous exposure to glutamate and the NO donor nitroprusside or preincubation with an NO donor had the effect that cells again responded to glutamate with depolarization and excitation. The transformed excitatory response lasted several minutes and could be reproduced even after 24 h of washing. The NO synthase blocker monomethylarginine blocked the excitatory response to glutamate. Another agonist of glutamate receptors, N-methyl-D-aspartate (NMDA, 0.1-1 mM), initially had excitatory effects on these neurons; this effect was significantly enhanced after transformation of the response to glutamate by NO donors. The results obtained here show that NO is involved in transforming the inhibitory responses to glutamate to excitatory responses, and that this effect may be mediated by NMDA-type receptors.

Toward molecular mechanism of xenon anesthesia: a link to studies of xenon complexes with small aromatic molecules.

PubMed

Andrijchenko, Natalya N; Ermilov, Alexander Yu; Khriachtchev, Leonid; Räsänen, Markku; Nemukhin, Alexander V

2015-03-19

The present study illustrates the steps toward understanding molecular mechanism of xenon anesthesia by focusing on a link to the structures and spectra of intermolecular complexes of xenon with small aromatic molecules. A primary cause of xenon anesthesia is attributed to inhibition of N-methyl-D-aspartate (NMDA) receptors by an unknown mechanism. Following the results of quantum mechanics/molecular mechanics (QM/MM) and molecular dynamics (MD) calculations we report plausible xenon action sites in the ligand binding domain of the NMDA receptor, which are due to interaction of xenon atoms with aromatic amino-acid residues. We rely in these calculations on computational protocols adjusted in combined experimental and theoretical studies of intermolecular complexes of xenon with phenol. Successful reproduction of vibrational shifts in molecular species upon complexation with xenon measured in low-temperature matrices allowed us to select a proper functional form in density functional theory (DFT) approach for use in QM subsystems, as well as to calibrate force field parameters for MD simulations. The results of molecular modeling show that xenon atoms can compete with agonists for a place in the corresponding protein cavity, thus indicating their active role in anesthetic action.

Effects of pyrazole partial agonists on HCA(2) -mediated flushing and VLDL-triglyceride levels in mice.

PubMed

Li, Zhaosha; Blad, Clara C; van der Sluis, Ronald J; de Vries, Henk; Van Berkel, Theo J C; Ijzerman, Adriaan P; Hoekstra, Menno

2012-10-01

Niacin can effectively treat dyslipidaemic disorders. However, its clinical use is limited due to the cutaneous flushing mediated by the nicotinic acid receptor HCA(2) . In the current study, we evaluated two partial agonists for HCA(2) , LUF6281 and LUF6283, with respect to their anti-dyslipidaemic potential and cutaneous flushing effect. In vitro potency and efficacy studies with niacin and the two HCA(2) partial agonists were performed using HEK293T cells stably expressing human HCA(2) . Normolipidaemic C57BL/6 mice received either niacin or the HCA(2) partial agonists (400 mg·kg(-1) ·day(-1) ) once a day for 4 weeks for evaluation of their effects in vivo. Radioligand competitive binding assay showed K(i) values for LUF6281 and LUF6283 of 3 and 0.55 µM. [(35) S]-GTPγS binding revealed the rank order of their potency as niacin > LUF6283 > LUF6281. All three compounds reduced plasma VLDL-triglyceride concentrations similarly, while LUF6281 and LUF6283, in contrast to niacin, did not also exhibit the unwanted flushing side effect in C57BL/6 mice. Niacin reduced the expression of lipolytic genes HSL and ATGL in adipose tissue by 50%, whereas LUF6281 and LUF6283 unexpectedly did not. In contrast, the decrease in VLDL-triglyceride concentration induced by LUF6281 and LUF6283 was associated with a parallel >40% reduced expression of APOB within the liver. The current study identifies LUF6281 and LUF6283, two HCA(2) partial agonists of the pyrazole class, as promising drug candidates to achieve the beneficial lipid lowering effect of niacin without producing the unwanted flushing side effect. © 2012 The Authors. British Journal of Pharmacology © 2012 The British Pharmacological Society.

A Metabotropic-Like Flux-Independent NMDA Receptor Regulates Ca2+ Exit from Endoplasmic Reticulum and Mitochondrial Membrane Potential in Cultured Astrocytes.

PubMed

Montes de Oca Balderas, Pavel; Aguilera, Penélope

2015-01-01

Astrocytes were long thought to be only structural cells in the CNS; however, their functional properties support their role in information processing and cognition. The ionotropic glutamate N-methyl D-aspartate (NMDA) receptor (NMDAR) is critical for CNS functions, but its expression and function in astrocytes is still a matter of research and debate. Here, we report immunofluorescence (IF) labeling in rat cultured cortical astrocytes (rCCA) of all NMDAR subunits, with phenotypes suggesting their intracellular transport, and their mRNA were detected by qRT-PCR. IF and Western Blot revealed GluN1 full-length synthesis, subunit critical for NMDAR assembly and transport, and its plasma membrane localization. Functionally, we found an iCa2+ rise after NMDA treatment in Fluo-4-AM labeled rCCA, an effect blocked by the NMDAR competitive inhibitors D(-)-2-amino-5-phosphonopentanoic acid (APV) and Kynurenic acid (KYNA) and dependent upon GluN1 expression as evidenced by siRNA knock down. Surprisingly, the iCa2+ rise was not blocked by MK-801, an NMDAR channel blocker, or by extracellular Ca2+ depletion, indicating flux-independent NMDAR function. In contrast, the IP3 receptor (IP3R) inhibitor XestosponginC did block this response, whereas a Ryanodine Receptor inhibitor did so only partially. Furthermore, tyrosine kinase inhibition with genistein enhanced the NMDA elicited iCa2+ rise to levels comparable to those reached by the gliotransmitter ATP, but with different population dynamics. Finally, NMDA depleted the rCCA mitochondrial membrane potential (mΔψ) measured with JC-1. Our results demonstrate that rCCA express NMDAR subunits which assemble into functional receptors that mediate a metabotropic-like, non-canonical, flux-independent iCa2+ increase.

Modulation of inhibitory activity markers by intermittent theta-burst stimulation in rat cortex is NMDA-receptor dependent.

PubMed

Labedi, Adnan; Benali, Alia; Mix, Annika; Neubacher, Ute; Funke, Klaus

2014-01-01

Intermittent theta-burst stimulation (iTBS) applied via transcranial magnetic stimulation has been shown to increase cortical excitability in humans. In the rat brain it strongly reduced the number of neurons expressing the 67-kD isoform of the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD67) and those expressing the calcium-binding proteins parvalbumin (PV) and calbindin (CB), specific markers of fast-spiking (FS) and non-FS inhibitory interneurons, respectively, an indication of modified cortical inhibition. Since iTBS effects in humans have been shown to be NMDA receptor sensitive, we wondered whether the iTBS-induced changes in the molecular phenotype of interneurons may be also sensitive to glutamatergic synaptic transmission mediated by NMDA receptors. In a sham-controlled fashion, five iTBS-blocks of 600 stimuli were applied to rats either lightly anesthetized by only urethane or by an additional low (subnarcotic) or high dose of the NMDA receptor antagonist ketamine before immunohistochemical analysis. iTBS reduced the number of neurons expressing GAD67, PV and CB. Except for CB, a low dose of ketamine partially prevented these effects while a higher dose almost completely abolished the iTBS effects. Our findings indicate that iTBS modulates the molecular, and likely also the electric, activity of cortical inhibitory interneurons and that the modulation of FS-type but less that of non-FS-type neurons is mediated by NMDA receptors. A combination of iTBS with pharmacological interventions affecting distinct receptor subtypes may thus offer options to enhance its selectivity in modulating the activity of distinct cell types and preventing others from being modulated. Copyright © 2014 Elsevier Inc. All rights reserved.

NMDA receptor antagonism disrupts the acquisition and retention of the Context Preexposure Facilitation Effect in adolescent rats

PubMed Central

Heroux, Nicholas A.; Robinson-Drummer, Patrese A.; Rosen, Jeffrey B.; Stanton, Mark E.

2016-01-01

The context preexposure facilitation effect (CPFE) is a contextual fear conditioning paradigm in which learning about the context, acquiring the context-shock association, and retrieving/expressing contextual fear are temporally dissociated. The current study investigated the involvement of NMDA receptors in contextual fear acquisition, retention, and expression across all phases of the CPFE in adolescent rats. In Experiment 1 systemic injections of 0.1 mg/kg MK-801, a non-competitive NMDA receptor antagonist, given before multiple context preexposure disrupted the acquisition of a context representation. In Experiment 2, pre-training MK-801 disrupted both immediate acquisition of contextual fear measured by postshock freezing, as well as retention test freezing 24 hours later. Experiment 3 showed that expression of contextual fear via a 24hr retention freezing test does not depend on NMDA receptors, indicating that MK-801 disrupts learning rather than performance of freezing behavior. In Experiment 4, consolidation of contextual information was partially disrupted by post-preexposure MK-801 whereas consolidation of contextual fear was not disrupted by post-training MK-801. Finally, Experiment 5 employed a dose-response design and found that a pre-training dose of 0.1 mg/kg MK-801 disrupted both postshock and retention test freezing while lower pre-training doses of MK-801 (0.025 or 0.05 mg/kg) only disrupted retention freezing. This is the first study to distinguish the role of NMDA receptors in acquisition (post-shock freezing), retention, expression, and consolidation of context vs. context-shock learning using the CPFE paradigm in adolescent rats. The findings provide a foundation for similar developmental studies examining these effects from early ontogeny through adulthood. PMID:26711910

Translocation of arrestin induced by human A(3) adenosine receptor ligands in an engineered cell line: comparison with G protein-dependent pathways.

PubMed

Gao, Zhan-Guo; Jacobson, Kenneth A

2008-04-01

Structurally diverse ligands were studied in A(3) adenosine receptor (AR)-mediated beta-arrestin translocation in engineered CHO cells. The agonist potency and efficacy were similar, although not identical, to their G protein signaling. However, differences have also been found. MRS542, MRS1760, and other adenosine derivatives, A(3)AR antagonists in cyclic AMP assays, were partial agonists in beta-arrestin translocation, indicating possible biased agonism. The xanthine 7-riboside DBXRM, a full agonist, was only partially efficacious in beta-arrestin translocation. DBXRM was shown to induce a lesser extent of desensitization compared with IB-MECA. In kinetic studies, MRS3558, a potent and selective A(3)AR agonist, induced beta-arrestin translocation significantly faster than IB-MECA and Cl-IB-MECA. Non-nucleoside antagonists showed similar inhibitory potencies as previously reported. PTX pretreatment completely abolished ERK1/2 activation, but not arrestin translocation. Thus, lead candidates for biased agonists at the A(3)AR have been identified with this arrestin-translocation assay, which promises to be an effective tool for ligand screening.

Glutamatergic dysfunction in catatonia? Successful treatment of three acute akinetic catatonic patients with the NMDA antagonist amantadine.

PubMed Central

Northoff, G; Eckert, J; Fritze, J

1997-01-01

Therapeutic efficiacy of the NMDA antagonist amantadine is reported in three acute neuroleptic free akinetic catatonic patients. Intravenous infusion of amantadine led to the resolution of catatonic symptoms and considerable reductions of scores in various motor scales (Simpson Angus scale for extrapyramidal side effects (SEPS), the abnormal involuntary movement scale (AIMS), Rogers catatonia and schizophrenia scales). The therapeutic effect of amantadine showed a characteristic temporal pattern with most pronounced effects four to six hours after administration and recurrence of catatonic symptoms by 24 hours later, at least partially. Such a temporal pattern of therapeutic efficacy and decreasing efficacy occurred in all three patients on all days. The results suggest the central importance of glutamatergic dysfunction in catatonic syndrome. PMID:9120462

Activity-dependent release of tissue plasminogen activator from the dendritic spines of hippocampal neurons revealed by live-cell imaging.

PubMed

Lochner, Janis E; Honigman, Leah S; Grant, Wilmon F; Gessford, Sarah K; Hansen, Alexis B; Silverman, Michael A; Scalettar, Bethe A

2006-05-01

Tissue plasminogen activator (tPA) has been implicated in a variety of important cellular functions, including learning-related synaptic plasticity and potentiating N-methyl-D-aspartate (NMDA) receptor-dependent signaling. These findings suggest that tPA may localize to, and undergo activity-dependent secretion from, synapses; however, conclusive data supporting these hypotheses have remained elusive. To elucidate these issues, we studied the distribution, dynamics, and depolarization-induced secretion of tPA in hippocampal neurons, using fluorescent chimeras of tPA. We found that tPA resides in dense-core granules (DCGs) that traffic to postsynaptic dendritic spines and that can remain in spines for extended periods. We also found that depolarization induced by high potassium levels elicits a slow, partial exocytotic release of tPA from DCGs in spines that is dependent on extracellular Ca(+2) concentrations. This slow, partial release demonstrates that exocytosis occurs via a mechanism, such as fuse-pinch-linger, that allows partial release and reuse of DCG cargo and suggests a mechanism that hippocampal neurons may rely upon to avoid depleting tPA at active synapses. Our results also demonstrate release of tPA at a site that facilitates interaction with NMDA-type glutamate receptors, and they provide direct confirmation of fundamental hypotheses about tPA localization and release that bear on its neuromodulatory functions, for example, in learning and memory.

Agonist-Directed Desensitization of the β2-Adrenergic Receptor

PubMed Central

Goral, Vasiliy; Jin, Yan; Sun, Haiyan; Ferrie, Ann M.; Wu, Qi; Fang, Ye

2011-01-01

The β2-adrenergic receptor (β2AR) agonists with reduced tachyphylaxis may offer new therapeutic agents with improved tolerance profile. However, receptor desensitization assays are often inferred at the single signaling molecule level, thus ligand-directed desensitization is poorly understood. Here we report a label-free biosensor whole cell assay with microfluidics to determine ligand-directed desensitization of the β2AR. Together with mechanistic deconvolution using small molecule inhibitors, the receptor desensitization and resensitization patterns under the short-term agonist exposure manifested the long-acting agonism of salmeterol, and differentiated the mechanisms of agonist-directed desensitization between a full agonist epinephrine and a partial agonist pindolol. This study reveals the cellular mechanisms of agonist-selective β2AR desensitization at the whole cell level. PMID:21541288

Medium Chain Fatty Acids Are Selective Peroxisome Proliferator Activated Receptor (PPAR) γ Activators and Pan-PPAR Partial Agonists

PubMed Central

Ayers, Steven D.; Lin, Jean Z.; Cvoro, Aleksandra; Silveira, Rodrigo L.; Martínez, Leandro; Souza, Paulo C. T.; Saidemberg, Daniel; Deng, Tuo; Amato, Angela Angelica; Togashi, Marie; Hsueh, Willa A.; Phillips, Kevin; Palma, Mário Sérgio; Neves, Francisco A. R.; Skaf, Munir S.; Webb, Paul; Polikarpov, Igor

2012-01-01

Thiazolidinediones (TZDs) act through peroxisome proliferator activated receptor (PPAR) γ to increase insulin sensitivity in type 2 diabetes (T2DM), but deleterious effects of these ligands mean that selective modulators with improved clinical profiles are needed. We obtained a crystal structure of PPARγ ligand binding domain (LBD) and found that the ligand binding pocket (LBP) is occupied by bacterial medium chain fatty acids (MCFAs). We verified that MCFAs (C8–C10) bind the PPARγ LBD in vitro and showed that they are low-potency partial agonists that display assay-specific actions relative to TZDs; they act as very weak partial agonists in transfections with PPARγ LBD, stronger partial agonists with full length PPARγ and exhibit full blockade of PPARγ phosphorylation by cyclin-dependent kinase 5 (cdk5), linked to reversal of adipose tissue insulin resistance. MCFAs that bind PPARγ also antagonize TZD-dependent adipogenesis in vitro. X-ray structure B-factor analysis and molecular dynamics (MD) simulations suggest that MCFAs weakly stabilize C-terminal activation helix (H) 12 relative to TZDs and this effect is highly dependent on chain length. By contrast, MCFAs preferentially stabilize the H2-H3/β-sheet region and the helix (H) 11-H12 loop relative to TZDs and we propose that MCFA assay-specific actions are linked to their unique binding mode and suggest that it may be possible to identify selective PPARγ modulators with useful clinical profiles among natural products. PMID:22649490

Medium chain fatty acids are selective peroxisome proliferator activated receptor (PPAR) γ activators and pan-PPAR partial agonists.

PubMed

Liberato, Marcelo Vizoná; Nascimento, Alessandro S; Ayers, Steven D; Lin, Jean Z; Cvoro, Aleksandra; Silveira, Rodrigo L; Martínez, Leandro; Souza, Paulo C T; Saidemberg, Daniel; Deng, Tuo; Amato, Angela Angelica; Togashi, Marie; Hsueh, Willa A; Phillips, Kevin; Palma, Mário Sérgio; Neves, Francisco A R; Skaf, Munir S; Webb, Paul; Polikarpov, Igor

2012-01-01

Thiazolidinediones (TZDs) act through peroxisome proliferator activated receptor (PPAR) γ to increase insulin sensitivity in type 2 diabetes (T2DM), but deleterious effects of these ligands mean that selective modulators with improved clinical profiles are needed. We obtained a crystal structure of PPARγ ligand binding domain (LBD) and found that the ligand binding pocket (LBP) is occupied by bacterial medium chain fatty acids (MCFAs). We verified that MCFAs (C8-C10) bind the PPARγ LBD in vitro and showed that they are low-potency partial agonists that display assay-specific actions relative to TZDs; they act as very weak partial agonists in transfections with PPARγ LBD, stronger partial agonists with full length PPARγ and exhibit full blockade of PPARγ phosphorylation by cyclin-dependent kinase 5 (cdk5), linked to reversal of adipose tissue insulin resistance. MCFAs that bind PPARγ also antagonize TZD-dependent adipogenesis in vitro. X-ray structure B-factor analysis and molecular dynamics (MD) simulations suggest that MCFAs weakly stabilize C-terminal activation helix (H) 12 relative to TZDs and this effect is highly dependent on chain length. By contrast, MCFAs preferentially stabilize the H2-H3/β-sheet region and the helix (H) 11-H12 loop relative to TZDs and we propose that MCFA assay-specific actions are linked to their unique binding mode and suggest that it may be possible to identify selective PPARγ modulators with useful clinical profiles among natural products.

Divergent functional effects of sazetidine-a and varenicline during nicotine withdrawal.

PubMed

Turner, Jill R; Wilkinson, Derek S; Poole, Rachel Lf; Gould, Thomas J; Carlson, Gregory C; Blendy, Julie A

2013-09-01

Smoking is the largest preventable cause of death in the United States. Furthermore, a recent study found that <10% of quit attempts resulted in continuous abstinence for 1 year. With the introduction of pharmacotherapies like Chantix (varenicline), a selective α4β2 nicotinic partial agonist, successful quit attempts have significantly increased. Therefore, novel subtype-specific nicotinic drugs, such as sazetidine-A, present a rich area for investigation of therapeutic potential in smoking cessation. The present studies examine the anxiety-related behavioral and functional effects of the nicotinic partial agonists varenicline and sazetidine-A during withdrawal from chronic nicotine in mice. Our studies indicate that ventral hippocampal-specific infusions of sazetidine-A, but not varenicline, are efficacious in reducing nicotine withdrawal-related anxiety-like phenotypes in the novelty-induced hypophagia (NIH) paradigm. To further investigate functional differences between these partial agonists, we utilized voltage-sensitive dye imaging (VSDi) in ventral hippocampal slices to determine the effects of sazetidine-A and varenicline in animals chronically treated with saline, nicotine, or undergoing 24 h withdrawal. These studies demonstrate a functional dissociation of varenicline and sazetidine-A on hippocampal network activity, which is directly related to previous drug exposure. Furthermore, the effects of the nicotinic partial agonists in VSDi assays are significantly correlated with their behavioral effects in the NIH test. These findings highlight the importance of drug history in understanding the mechanisms through which nicotinic compounds may be aiding smoking cessation in individuals experiencing withdrawal-associated anxiety.

Putative antipsychotics with pronounced agonism at serotonin 5-HT1A and partial agonist activity at dopamine D2 receptors disrupt basal PPI of the startle reflex in rats.

PubMed

Auclair, Agnès L; Galinier, Alexandra; Besnard, Joël; Newman-Tancredi, Adrian; Depoortère, Ronan

2007-07-01

Prepulse inhibition (PPI) of the startle reflex has been extensively studied because it is disrupted in several psychiatric diseases, most notably schizophrenia. In rats, and to a lesser extent, in humans, PPI can be diminished by dopamine (DA) D(2)/D(3) and serotonin 5-HT(1A) receptor agonists. A novel class of potential antipsychotics (SSR181507, bifeprunox, and SLV313) possess partial agonist/antagonist properties at D(2) receptors and various levels of 5-HT(1A) activation. It thus appeared warranted to assess, in Sprague-Dawley rats, the effects of these antipsychotics on basal PPI. SSR181507, sarizotan, and bifeprunox decreased PPI, with a near-complete abolition at 2.5-10 mg/kg; SLV313 had a significant effect at 0.16 mg/kg only. Co-treatment with the 5-HT(1A) receptor antagonist WAY100,635 (0.63 mg/kg) showed that the 5-HT(1A) agonist activity of SSR181507 was responsible for its effect. By contrast, antipsychotics with low affinity and/or efficacy at 5-HT(1A) receptors, such as aripiprazole (another DA D(2)/D(3) and 5-HT(1A) ligand), and established typical and atypical antipsychotics (haloperidol, clozapine, risperidone, olanzapine, quetiapine, and ziprasidone) had no effect on basal PPI (0.01-2.5 to 2.5-40 mg/kg). The present data demonstrate that some putative antipsychotics with pronounced 5-HT(1A) agonist activity, coupled with partial agonist activity at DA D(2) receptors, markedly diminish PPI of the startle reflex in rats. These data raise the issue of the influence of such compounds on sensorimotor gating in humans.

Comparison between basal and apical dendritic spines in estrogen-induced rapid spinogenesis of CA1 principal neurons in the adult hippocampus

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

Murakami, Gen; Mukai, Hideo; Hojo, Yasushi

2006-12-15

Modulation of hippocampal synaptic plasticity by estrogen has been attracting much attention. Here, we demonstrated the rapid effect of 17{beta}-estradiol on the density and morphology of spines in the stratum oriens (s.o., basal side) and in the stratum lacunosum-moleculare (s.l.m., apical side) by imaging Lucifer Yellow-injected CA1 neurons in adult male rat hippocampal slices, because spines in s.o. and s.l.m. have been poorly understood as compared with spines in the stratum radiatum. The application of 1 nM estradiol-induced a rapid increase in the density of spines of pyramidal neurons within 2 h. This increase by estradiol was blocked by Erkmore » MAP kinase inhibitor and estrogen receptor inhibitor in both regions. Effect of blockade by agonists of AMPA receptors and NMDA receptors was different between s.o. and s.l.m. In both regions, ER{alpha} agonist PPT induced the same enhancing effect of spinogenesis as that induced by estradiol.« less

NMDA-receptor dependent synaptic activation of TRPC channels in olfactory bulb granule cells

PubMed Central

Stroh, Olga; Freichel, Marc; Kretz, Oliver; Birnbaumer, Lutz; Hartmann, Jana; Egger, Veronica

2012-01-01

TRPC channels are widely expressed throughout the nervous system including the olfactory bulb where their function is largely unknown. Here we describe their contribution to central synaptic processing at the reciprocal mitral and tufted cell - granule cell microcircuit, the most abundant synapse of the mammalian olfactory bulb. Suprathreshold activation of the synapse causes sodium action potentials in mouse granule cells and a subsequent long-lasting depolarization (LLD) linked to a global dendritic postsynaptic calcium signal recorded with two-photon laser scanning microscopy. These signals are not observed after action potentials evoked by current injection in the same cells. The LLD persists in the presence of group I metabotropic glutamate receptor antagonists but is entirely absent from granule cells deficient for the NMDA receptor subunit NR1. Moreover, both depolarization and Ca2+ rise are sensitive to the blockade of NMDA receptors. The LLD and the accompanying Ca2+ rise are also absent in granule cells from mice deficient for both TRPC channel subtypes 1 and 4, whereas the deletion of either TRPC1 or TRPC4 results in only a partial reduction of the LLD. Recordings from mitral cells in the absence of both subunits reveal a reduction of asynchronous neurotransmitter release from the granule cells during recurrent inhibition. We conclude that TRPC1 and TRPC4 can be activated downstream of NMDA receptor activation and contribute to slow synaptic transmission in the olfactory bulb, including the calcium dynamics required for asynchronous release from the granule cell spine. PMID:22539836

Region-selective effects of neuroinflammation and antioxidant treatment on peripheral benzodiazepine receptors and NMDA receptors in the rat brain

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

Biegon, A.; Alvarado, M.; Budinger, T.F.

2001-12-10

Following induction of acute neuroinflammation by intracisternal injection of endotoxin (lipopolysaccharide) in rats, quantitative autoradiography was used to assess the regional level of microglial activation and glutamate (NMDA) receptor binding. The possible protective action of the antioxidant phenyl-tert-butyl nitrone in this model was tested by administering the drug in the drinking water for 6 days starting 24 hours after endotoxin injection. Animals were killed 7 days post-injection and consecutive cryostat brain sections labeled with [3H]PK11195 as a marker of activated microglia and [125I]iodoMK801 as a marker of the open-channel, activated state of NMDA receptors. Lipopolysaccharide increased [3H]PK11195 binding in themore » brain, with the largest increases (2-3 fold) in temporal and entorhinal cortex, hippocampus, and substantia innominata. A significant (>50 percent) decrease in [125I]iodoMK801 binding was found in the same brain regions. Phenyl-tert-butyl nitrone treatment resulted in a partial inhibition ({approx}25 percent decrease) of the lipopolysaccharide-induced increase in [3H]PK11195 binding but completely reversed the lipopolysaccharide-induced decrease in [125I]iodoMK80 binding in the entorhinal cortex, hippocampus, and substantia innominata. Loss of NMDA receptor function in cortical and hippocampal regions may contribute to the cognitive deficits observed in diseases with a neuroinflammatory component, such as meningitis or Alzheimer's disease.« less

The potency of different serotonergic agonists in counteracting opioid evoked cardiorespiratory disturbances

PubMed Central

Dutschmann, M.; Waki, H.; Manzke, T.; Simms, A. E.; Pickering, A. E.; Richter, D. W.; Paton, J. F. R.

2009-01-01

Serotonin receptor (5-HTR) agonists that target 5-HT4(a)R and 5-HT1AR can reverse μ-opioid receptor (μ-OR)-evoked respiratory depression. Here, we have tested whether such rescuing by serotonin agonists also applies to the cardiovascular system. In working heart–brainstem preparations in situ, we have recorded phrenic nerve activity, thoracic sympathetic chain activity (SCA), vascular resistance and heart rate (HR) and in conscious rats, diaphragmatic electromyogram, arterial blood pressure (BP) and HR via radio-telemetry. In addition, the distribution of 5-HT4(a)R and 5-HT1AR in ponto-medullary cardiorespiratory networks was identified using histochemistry. Systemic administration of the μ-OR agonist fentanyl in situ decreased HR, vascular resistance, SCA and phrenic nerve activity. Subsequent application of the 5-HT1AR agonist 8-OH-DPAT further enhanced bradycardia, but partially compensated the decrease in vascular resistance, sympathetic activity and restored breathing. By contrast, the 5-HT4(a)R agonist RS67333 further decreased vascular resistance, HR and sympathetic activity, but partially rescued breathing. In conscious rats, administration of remifentanyl caused severe respiratory depression, a decrease in mean BP accompanied by pronounced bradyarrhythmia. 8-OH-DPAT restored breathing and prevented the bradyarrhythmia; however, BP and HR remained below baseline. In contrast, RS67333 further suppressed cardiovascular functions in vivo and only partially recovered breathing in some cases. The better recovery of μ-OR cardiorespiratory disturbance by 5-HT1AR than 5-HT4(a)R is supported by the finding that 5-HT1AR was more densely expressed in key brainstem nuclei for cardiorespiratory control compared with 5-HT4(a)R. We conclude that during treatment of severe pain, 5-HT1AR agonists may provide a useful tool to counteract opioid-mediated cardiorespiratory disturbances. PMID:19651661

The partial dopamine D2 receptor agonist aripiprazole is associated with weight gain in adolescent anorexia nervosa.

PubMed

Frank, Guido K W; Shott, Megan E; Hagman, Jennifer O; Schiel, Marissa A; DeGuzman, Marisa C; Rossi, Brogan

2017-04-01

Finding medication to support treatment of anorexia nervosa has been difficult. Neuroscience-based approaches may help in this effort. Recent brain imaging studies in adults and adolescents with anorexia nervosa suggest that dopamine-related reward circuits are hypersensitive and could provide a treatment target. Here, we present a retrospective chart review of 106 adolescents with anorexia nervosa some of whom were treated with the dopamine D2 receptor partial agonist aripiprazole during treatment in a specialized eating disorder program. The results show that aripiprazole treatment was associated with greater increase in body mass index (BMI) during treatment. The use of dopamine receptor agonists may support treatment success in anorexia nervosa and should be further investigated. © 2017 Wiley Periodicals, Inc.

The effects of verapamil and its combinations with glutamate and glycine on cardiodynamics, coronary flow and oxidative stress in isolated rat heart.

PubMed

Stojic, Isidora; Srejovic, Ivan; Zivkovic, Vladimir; Jeremic, Nevena; Djuric, Marko; Stevanovic, Ana; Milanovic, Tamara; Djuric, Dragan; Jakovljevic, Vladimir

2017-02-01

The role of N-methyl-D-aspartate receptor (NMDA-R) in heart is still unclear. For these ionotropic glutamate receptors is characteristic the necessity of both co-agonists, glutamate and glycine, for their activation, which primarily allows influx of calcium. The aim of the present study was to examine the effects of verapamil, as a calcium channel blocker, alone and its combination with glycine and/or glutamate on cardiac function, coronary flow, and oxidative stress in isolated rat heart or to examine the effects of potential activation of NMDA-R in isolated rat heart. The hearts of male Wistar albino rats were excised and perfused according to Langendorff technique, and cardiodynamic parameters and coronary flow were determined during the administration of verapamil and its combinations with glutamate and/or glycine. The oxidative stress biomarkers, including thiobarbituric acid-reactive substances, nitrites, superoxide anion radical, and hydrogen peroxide, were each determined spectrophotometrically from coronary venous effluent. The greatest decline in parameters of cardiac contractility and systolic pressure was in the group that was treated with verapamil only, while minimal changes were observed in group treated with all three tested substances. Also, the largest changes in coronary flow were in the group treated only with verapamil, and at least in the group that received all three tested substances, as well as the largest increase in oxidative stress parameters. Based on the obtained results, it can be concluded that NMDA-R activation allows sufficient influx of calcium to increase myocardial contractility and systolic pressure, as well as short-term increase of oxidative stress.

Effects of VU0410120, a novel GlyT1 inhibitor, on measures of sociability, cognition and stereotypic behaviors in a mouse model of autism.

PubMed

Burket, Jessica A; Benson, Andrew D; Green, Torrian L; Rook, Jerri M; Lindsley, Craig W; Conn, P Jeffrey; Deutsch, Stephen I

2015-08-03

The NMDA receptor is a highly regulated glutamate-gated cationic channel receptor that has an important role in the regulation of sociability and cognition. The genetically-inbred Balb/c mouse has altered endogenous tone of NMDA receptor-mediated neurotransmission and is a model of impaired sociability, relevant to Autism Spectrum Disorders (ASDs). Because glycine is an obligatory co-agonist that works cooperatively with glutamate to promote opening of the ion channel, one prominent strategy to promote NMDA receptor-mediated neurotransmission involves inhibition of the glycine type 1 transporter (GlyT1). The current study evaluated the dose-dependent effects of VU0410120, a selective, high-affinity competitive GlyT1 inhibitor, on measures of sociability, cognition and stereotypic behaviors in Balb/c and Swiss Webster mice. The data show that doses of VU0410120 (i.e., 18 and 30mg/kg) that improve measures of sociability and spatial working memory in the Balb/c mouse strain elicit intense stereotypic behaviors in the Swiss Webster comparator strain (i.e., burrowing and jumping). Furthermore, the data suggest that selective GlyT1 inhibition improves sociability and spatial working memory at doses that do not worsen or elicit stereotypic behaviors in a social situation in the Balb/c strain. However, the elicitation of stereotypic behaviors in the Swiss Webster comparator strain at therapeutically relevant doses of VU0410120 suggest that genetic factors (i.e., mouse strain differences) influence sensitivity to GlyT1-elicited stereotypic behaviors, and emergence of intense stereotypic behaviors may be dose-limiting side effects of this interventional strategy. Copyright © 2015 Elsevier Inc. All rights reserved.

Communication between corneal epithelial cells and trigeminal neurons is facilitated by purinergic (P2) and glutamatergic receptors.

PubMed

Oswald, Duane J; Lee, Albert; Trinidad, Monique; Chi, Cheryl; Ren, Ruiyi; Rich, Celeste B; Trinkaus-Randall, Vickery

2012-01-01

Previously, we demonstrated that nucleotides released upon mechanical injury to corneal epithelium activate purinergic (P2) receptors resulting in mobilization of a Ca(2+) wave. However, the tissue is extensively innervated and communication between epithelium and neurons is critical and not well understood. Therefore, we developed a co-culture of primary trigeminal neurons and human corneal limbal epithelial cells. We demonstrated that trigeminal neurons expressed a repertoire of P2Yand P2X receptor transcripts and responded to P2 agonists in a concentration-dependent manner. Mechanical injuries to epithelia in the co-cultures elicited a Ca(2+) wave that mobilized to neurons and was attenuated by Apyrase, an ectonucleotidase. To elucidate the role of factors released from each cell type, epithelial and neuronal cells were cultured, injured, and the wound media from one cell type was collected and added to the other cell type. Epithelial wound media generated a rapid Ca(2+) mobilization in neuronal cells that was abrogated in the presence of Apyrase, while neuronal wound media elicited a complex response in epithelial cells. The rapid Ca(2+) mobilization was detected, which was abrogated with Apyrase, but it was followed by Ca(2+) waves that occurred in cell clusters. When neuronal wound media was preincubated with a cocktail of N-methyl-D-aspartate (NMDA) receptor inhibitors, the secondary response in epithelia was diminished. Glutamate was detected in the neuronal wound media and epithelial expression of NMDA receptor subunit transcripts was demonstrated. Our results indicate that corneal epithelia and neurons communicate via purinergic and NMDA receptors that mediate the wound response in a highly orchestrated manner.

Extrasynaptic targeting of NMDA receptors following D1 dopamine receptor activation and cocaine self-administration

PubMed Central

Ortinski, Pavel I.; Turner, Jill R.; Pierce, R. Christopher

2013-01-01

We previously showed that after repeated exposure to cocaine, D1-like dopamine receptor (D1DR) stimulation reverses plastic changes of AMPA receptor-mediated signaling in the nucleus accumbens shell. However, there is little information on the impact of cocaine self-administration on D1-NMDA receptor interactions in this brain region. Here, we assessed whether cocaine self-administration alters the effects of D1DR stimulation on synaptic and extrasynaptic NMDA receptors (NMDARs) using whole-cell patch-clamp recordings. In slices from cocaine-naïve rats, pre-treatment with a D1DR agonist decreased synaptic NMDAR receptor-mediated currents and increased the contribution of extrasynaptic NMDARs. In contrast, neither cocaine self-administration alone nor cocaine experience followed by D1DR stimulation had an effect on synaptic or extrasynaptic NMDAR signaling. Activation of extrasynaptic NMDARs relies on the availability of extracellular glutamate, which is regulated primarily by glutamate transporters. In cocaine-experienced animals, administration of a glutamate re-uptake blocker, DL-threo-β-benzyloxyaspartic acid (TBOA), revealed increased extrasynaptic NMDAR activity and stronger baseline activity of glutamate uptake transporters relative to cocaine-naïve rats. In cocaine-naïve rats, the D1DR-mediated increase in extrasynaptic NMDAR signaling was independent of the activity of glutamate re-uptake transporters. Taken together, these results indicate that cocaine experience blunts the influence of D1DRs on synaptic and extrasynaptic NMDAR signaling. Additionally, prior cocaine self-administration limits activation of the extrasynaptic NMDAR pool by increasing glutamate re-uptake. These findings outline a pattern of adaptive interactions between D1DRs and NMDARs in the nucleus accumbens shell and demonstrate up-regulation of extrasynaptic NMDAR signaling as a novel consequence of cocaine self-administration. PMID:23719812

The Role of Dopamine in Reinforcement: Changes in Reinforcement Sensitivity Induced by D[subscript 1]-Type, D[subscript 2]-Type, and Nonselective Dopamine Receptor Agonists

ERIC Educational Resources Information Center

Bratcher, Natalie A.; Farmer-Dougan, Valeri; Dougan, James D.; Heidenreich, Byron A.; Garris, Paul A.

2005-01-01

Dose-dependent changes in sensitivity to reinforcement were found when rats were treated with low, moderate, and high doses of the partial dopamine D[subscript 1]-type receptor agonist SKF38393 and with the nonselective dopamine agonist apomorphine, but did not change when rats were treated with similar doses of the selective dopamine D[subscript…

Structural basis of subunit selectivity for competitive NMDA receptor antagonists with preference for GluN2A over GluN2B subunits

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

Lind, Genevieve E.; Mou, Tung-Chung; Tamborini, Lucia

NMDA-type glutamate receptors are ligand-gated ion channels that contribute to excitatory neurotransmission in the central nervous system (CNS). Most NMDA receptors comprise two glycine-binding GluN1 and two glutamate-binding GluN2 subunits (GluN2A–D). We describe highly potent (S)-5-[(R)-2-amino-2-carboxyethyl]-4,5-dihydro-1H-pyrazole-3-carboxylic acid (ACEPC) competitive GluN2 antagonists, of which ST3 has a binding affinity of 52 nM at GluN1/2A and 782 nM at GluN1/2B receptors. This 15-fold preference of ST3 for GluN1/2A over GluN1/2B is improved compared with NVP-AAM077, a widely used GluN2A-selective antagonist, which we show has 11-fold preference for GluN1/2A over GluN1/2B. Crystal structures of the GluN1/2A agonist binding domain (ABD) heterodimer with boundmore » ACEPC antagonists reveal a binding mode in which the ligands occupy a cavity that extends toward the subunit interface between GluN1 and GluN2A ABDs. Mutational analyses show that the GluN2A preference of ST3 is primarily mediated by four nonconserved residues that are not directly contacting the ligand, but positioned within 12 Å of the glutamate binding site. Two of these residues influence the cavity occupied by ST3 in a manner that results in favorable binding to GluN2A, but occludes binding to GluN2B. Thus, we reveal opportunities for the design of subunit-selective competitive NMDA receptor antagonists by identifying a cavity for ligand binding in which variations exist between GluN2A and GluN2B subunits. This structural insight suggests that subunit selectivity of glutamate-site antagonists can be mediated by mechanisms in addition to direct contributions of contact residues to binding affinity.« less

Structural basis of subunit selectivity for competitive NMDA receptor antagonists with preference for GluN2A over GluN2B subunits

PubMed Central

Lind, Genevieve E.; Mou, Tung-Chung; Tamborini, Lucia; Pomper, Martin G.; De Micheli, Carlo; Conti, Paola; Pinto, Andrea

2017-01-01

NMDA-type glutamate receptors are ligand-gated ion channels that contribute to excitatory neurotransmission in the central nervous system (CNS). Most NMDA receptors comprise two glycine-binding GluN1 and two glutamate-binding GluN2 subunits (GluN2A–D). We describe highly potent (S)-5-[(R)-2-amino-2-carboxyethyl]-4,5-dihydro-1H-pyrazole-3-carboxylic acid (ACEPC) competitive GluN2 antagonists, of which ST3 has a binding affinity of 52 nM at GluN1/2A and 782 nM at GluN1/2B receptors. This 15-fold preference of ST3 for GluN1/2A over GluN1/2B is improved compared with NVP-AAM077, a widely used GluN2A-selective antagonist, which we show has 11-fold preference for GluN1/2A over GluN1/2B. Crystal structures of the GluN1/2A agonist binding domain (ABD) heterodimer with bound ACEPC antagonists reveal a binding mode in which the ligands occupy a cavity that extends toward the subunit interface between GluN1 and GluN2A ABDs. Mutational analyses show that the GluN2A preference of ST3 is primarily mediated by four nonconserved residues that are not directly contacting the ligand, but positioned within 12 Å of the glutamate binding site. Two of these residues influence the cavity occupied by ST3 in a manner that results in favorable binding to GluN2A, but occludes binding to GluN2B. Thus, we reveal opportunities for the design of subunit-selective competitive NMDA receptor antagonists by identifying a cavity for ligand binding in which variations exist between GluN2A and GluN2B subunits. This structural insight suggests that subunit selectivity of glutamate-site antagonists can be mediated by mechanisms in addition to direct contributions of contact residues to binding affinity. PMID:28760974

Spinal sigma-1 receptor activation increases the production of D-serine in astrocytes which contributes to the development of mechanical allodynia in a mouse model of neuropathic pain.

PubMed

Moon, Ji-Young; Choi, Sheu-Ran; Roh, Dae-Hyun; Yoon, Seo-Yeon; Kwon, Soon-Gu; Choi, Hoon-Seong; Kang, Suk-Yun; Han, Ho-Jae; Kim, Hyun-Woo; Beitz, Alvin J; Oh, Seog-Bae; Lee, Jang-Hern

2015-10-01

We have previously demonstrated that activation of the spinal sigma-1 receptor (Sig-1R) plays an important role in the development of mechanical allodynia (MA) via secondary activation of the N-methyl-d-aspartate (NMDA) receptor. Sig-1Rs have been shown to localize to astrocytes, and blockade of Sig-1Rs inhibits the pathologic activation of astrocytes in neuropathic mice. However, the mechanism by which Sig-1R activation in astrocytes modulates NMDA receptors in neurons is currently unknown. d-serine, synthesized from l-serine by serine racemase (Srr) in astrocytes, is an endogenous co-agonist for the NMDA receptor glycine site and can control NMDA receptor activity. Here, we investigated the role of d-serine in the development of MA induced by spinal Sig-1R activation in chronic constriction injury (CCI) mice. The production of d-serine and Srr expression were both significantly increased in the spinal cord dorsal horn post-CCI surgery. Srr and d-serine were only localized to astrocytes in the superficial dorsal horn, while d-serine was also localized to neurons in the deep dorsal horn. Moreover, we found that Srr exists in astrocytes that express Sig-1Rs. The CCI-induced increase in the levels of d-serine and Srr was attenuated by sustained intrathecal treatment with the Sig-1R antagonist, BD-1047 during the induction phase of neuropathic pain. In behavioral experiments, degradation of endogenous d-serine with DAAO, or selective blockade of Srr by LSOS, effectively reduced the development of MA, but not thermal hyperalgesia in CCI mice. Finally, BD-1047 administration inhibited the development of MA and this inhibition was reversed by intrathecal treatment with exogenous d-serine. These findings demonstrate for the first time that the activation of Sig-1Rs increases the expression of Srr and d-serine in astrocytes. The increased production of d-serine induced by CCI ultimately affects dorsal horn neurons that are involved in the development of MA in neuropathic mice. Copyright © 2015 Elsevier Ltd. All rights reserved.

In vitro pharmacology of aripiprazole, its metabolite and experimental dopamine partial agonists at human dopamine D2 and D3 receptors.

PubMed

Tadori, Yoshihiro; Forbes, Robert A; McQuade, Robert D; Kikuchi, Tetsuro

2011-10-15

Aripiprazole is the first dopamine D(2)/D(3) receptor partial agonist successfully developed and ultimately approved for treatment of a broad spectrum of psychiatric and neurological disorders. Aripiprazole's dopamine D(2) and serotonin 5-HT(1A) receptor partial agonist activities have been postulated to confer clinical efficacy without marked sedation, and a relatively favorable overall side-effect profile. Using aripiprazole's unique profile as a benchmark for new dopamine partial agonist development may facilitate discovery of new antipsychotics. We conducted an in vitro comparative analysis between aripiprazole, and its human metabolite OPC-14857 (7-(4-[4-(2,3-dichlorophenyl)-1-piperazinyl)butoxy)-2(1H)-quinolinone)); RGH-188 (trans-1-[4-[2-[4-(2,3-dichlorophenyl)piperazine-1-yl]ethyl]cyclohexyl]-3,3-dimethylurea), and its metabolite didesmethyl-RGH-188 (DDM-RGH-188); as well as bifeprunox, sarizotan, N-desmethylclozapine (NDMC; clozapine metabolite), and SDZ 208-912 (N-[(8α)-2-chloro-6-methylergolin-8-yl]-2,2-dimethylpropanamide). In vitro pharmacological assessment included inhibition of forskolin-stimulated cAMP accumulation and the reversal of dopamine-induced inhibition in clonal Chinese hamster ovary cell lines expressing D(2S), D(2L), D(3) Ser-9 and D(3) Gly-9 for human dopamine receptors. All test compounds behaved as dopamine D(2)/D(3) receptor partial agonists. Aripiprazole's intrinsic activity at dopamine D(2S) and D(2L) receptors was similar to that of OPC-14857 and RGH-188; lower than that of dopamine and bifeprunox; and higher than that of DDM-RGH-188, SDZ 208-912, sarizotan, and NDMC. Aripiprazole's intrinsic activity at dopamine D(3) Ser-9 and D(3) Gly-9 receptors was similar to that of OPC-14857 and sarizotan; lower than that of dopamine, bifeprunox, RGH-188 and DDM-RGH-188; and higher than that of SDZ 208-912 and NDMC. A consolidated assessment of these findings may help defining the most appropriate magnitude of intrinsic activity at dopamine D(2)/D(3) receptors for clinical efficacy and safety. Copyright © 2011 Elsevier B.V. All rights reserved.

The novel antidyskinetic drug sarizotan elicits different functional responses at human D2-like dopamine receptors.

PubMed

Kuzhikandathil, Eldo V; Bartoszyk, Gerd D

2006-09-01

Sarizotan (EMD 128130) is a chromane derivative that exhibits affinity at serotonin and dopamine receptors. Sarizotan effectively suppresses levodopa-induced dyskinesia in primate and rodent models of Parkinson's disease, and tardive dyskinesia in a rodent model. Results from clinical trials suggest that sarizotan significantly alleviates levodopa-induced dyskinesia. The functional effects of sarizotan on individual dopamine receptor subtypes are not known. Here we report the functional effects of sarizotan on human D2-like dopamine receptors (D2S, D2L, D3, D4.2 and D4.4) individually expressed in the AtT-20 neuroendocrine cell line. Using the coupling of D2-like dopamine receptors to G-protein coupled inward rectifier potassium channels we determined that sarizotan is a full agonist at D3 and D4.4 receptors (EC50=5.6 and 5.4 nM, respectively) but a partial agonist at D2S, D2L and D4.2 receptors (EC50=29, 23 and 4.5 nM, respectively). Consistent with its partial agonist property, sarizotan is an antagonist at D2S and D2L receptors (IC50=52 and 121 nM, respectively). Using the coupling of D2-like dopamine receptors to adenylyl cyclase we determined that sarizotan is a full agonist at D2L, D3, D4.2 and D4.4 receptors (EC50=0.51, 0.47, 0.48 and 0.23 nM, respectively) but a partial agonist at D2S receptors (EC50=0.6 nM).

New functional activity of aripiprazole revealed: robust antagonism of D2 dopamine receptor-stimulated Gβγ signaling

PubMed Central

Brust, Tarsis F.; Hayes, Michael P.; Roman, David L.; Watts, Val J.

2014-01-01

The dopamine D2 receptor (DRD2) is a G protein-coupled receptor (GPCR) that is generally considered to be a primary target in the treatment of schizophrenia. First generation antipsychotic drugs (e.g. haloperidol) are antagonists of the DRD2, while second generation antipsychotic drugs (e.g. olanzapine) antagonize DRD2 and 5HT2A receptors. Notably, both these classes of drugs may cause side effects associated with D2 receptor antagonism (e.g. hyperprolactemia and extrapyramidal symptoms). The novel, “third generation” antipsychotic drug, aripiprazole is also used to treat schizophrenia, with the remarkable advantage that its tendency to cause extrapyramidal symptoms is minimal. Aripiprazole is considered a partial agonist of the DRD2, but it also has partial agonist/antagonist activity for other GPCRs. Further, aripiprazole has been reported to have a unique activity profile in functional assays with the DRD2. In the present study the molecular pharmacology of aripiprazole was further examined in HEK cell models stably expressing the DRD2 and specific isoforms of adenylyl cyclase to assess functional responses of Gα and Gβγ subunits. Additional studies examined the activity of aripiprazole in DRD2-mediated heterologous sensitization of adenylyl cyclase and cell-based dynamic mass redistribution (DMR). Aripiprazole displayed a unique functional profile for modulation of G proteins, being a partial agonist for Gαi/o and a robust antagonist for Gβγ signaling. Additionally, aripiprazole was a weak partial agonist for both heterologous sensitization and dynamic mass redistribution. PMID:25449598

Melanocortin tetrapeptide Ac-His-DPhe-Arg-Trp-NH2 modified at the para position of the benzyl side chain (DPhe): importance for mouse melanocortin-3 receptor agonist versus antagonist activity.

PubMed

Proneth, Bettina; Pogozheva, Irina D; Portillo, Federico P; Mosberg, Henry I; Haskell-Luevano, Carrie

2008-09-25

The melanocortin-3 and -4 receptors (MC3R, MC4R) have been implicated in energy homeostasis and obesity. Whereas the physiological role of the MC4R is extensively studied, little is known about the MC3R. One caveat is the limited availability of ligands that are selective for the MC3R. Previous studies identified Ac-His-DPhe(p-I)-Arg-Trp-NH 2, which possessed partial agonist/antagonist pharmacology at the mMC3R while retaining full nanomolar agonist pharmacology at the mMC4R. These data allowed for the hypothesis that the DPhe position in melanocortin tetrapeptides can be used to examine ligand side-chain determinants important for differentiation of mMC3R agonist versus antagonist activity. A series of 15 DPhe (7) modified Ac-His-DPhe (7)-Arg-Trp-NH 2 tetrapeptides has been synthesized and pharmacologically characterized. Most notable results include the identification of modifications that resulted in potent antagonists/partial agonists at the mMC3R and full, potent agonists at the mMC4R. These SAR studies provide experimental evidence that the molecular mechanism of antagonism at the mMC3R differentiates this subtype from the mMC4R.

Melanocortin Tetrapeptide Ac-His-DPhe-Arg-Trp-NH2 Modified at the Para Position of the Benzyl Side Chain (DPhe): Importance for Mouse Melanocortin-3 Receptor Agonist versus Antagonist Activity

PubMed Central

Proneth, Bettina; Pogozheva, Irina D.; Portillo, Federico P.; Mosberg, Henry I.; Haskell-Luevano, Carrie

2010-01-01

The melanocortin-3 and -4 receptors (MC3R, MC4R) have been implicated in energy homeostasis and obesity. Whereas the physiological role of the MC4R is extensively studied, little is known about the MC3R. One caveat is the limited availability of ligands that are selective for the MC3R. Previous studies identified Ac-His-DPhe(p-I)-Arg-Trp-NH2, which possessed partial agonist/antagonist pharmacology at the mMC3R while retaining full nanomolar agonist pharmacology at the mMC4R. These data allowed for the hypothesis that the DPhe position in melanocortin tetrapeptides can be used to examine ligand side-chain determinants important for differentiation of mMC3R agonist versus antagonist activity. A series of 15 DPhe7 modified Ac-His-DPhe7-Arg-Trp-NH2 tetrapeptides has been synthesized and pharmacologically characterized. Most notable results include the identification of modifications that resulted in potent antagonists/partial agonists at the mMC3R and full, potent agonists at the mMC4R. These SAR studies provide experimental evidence that the molecular mechanism of antagonism at the mMC3R differentiates this subtype from the mMC4R. PMID:18800761

GABAB-mediated rescue of altered excitatory-inhibitory balance, gamma synchrony and behavioral deficits following constitutive NMDAR-hypofunction.

PubMed

Gandal, M J; Sisti, J; Klook, K; Ortinski, P I; Leitman, V; Liang, Y; Thieu, T; Anderson, R; Pierce, R C; Jonak, G; Gur, R E; Carlson, G; Siegel, S J

2012-07-17

Reduced N-methyl-D-aspartate-receptor (NMDAR) signaling has been associated with schizophrenia, autism and intellectual disability. NMDAR-hypofunction is thought to contribute to social, cognitive and gamma (30-80 Hz) oscillatory abnormalities, phenotypes common to these disorders. However, circuit-level mechanisms underlying such deficits remain unclear. This study investigated the relationship between gamma synchrony, excitatory-inhibitory (E/I) signaling, and behavioral phenotypes in NMDA-NR1(neo-/-) mice, which have constitutively reduced expression of the obligate NR1 subunit to model disrupted developmental NMDAR function. Constitutive NMDAR-hypofunction caused a loss of E/I balance, with an increase in intrinsic pyramidal cell excitability and a selective disruption of parvalbumin-expressing interneurons. Disrupted E/I coupling was associated with deficits in auditory-evoked gamma signal-to-noise ratio (SNR). Gamma-band abnormalities predicted deficits in spatial working memory and social preference, linking cellular changes in E/I signaling to target behaviors. The GABA(B)-receptor agonist baclofen improved E/I balance, gamma-SNR and broadly reversed behavioral deficits. These data demonstrate a clinically relevant, highly translatable neural-activity-based biomarker for preclinical screening and therapeutic development across a broad range of disorders that share common endophenotypes and disrupted NMDA-receptor signaling.

Centralization of Noxious Stimulus-induced Analgesia (NSIA) is Related to Activity at Inhibitory Synapses in the Spinal Cord

PubMed Central

Tambeli, Claudia H.; Levine, Jon D.; Gear, Robert W.

2009-01-01

The duration of noxious stimulus-induced antinociception (NSIA) has been shown to outlast the pain stimulus that elicited it, however, the mechanism that determines the duration of analgesia is unknown. We evaluated the role of spinal excitatory and inhibitory receptors (NMDA, mGluR-5, mu-opioid, GABA-A, and GABA-B), previously implicated in NSIA initiation, in its maintenance. As in our previous studies, the supraspinal trigeminal jaw-opening reflex (JOR) in the rat was used for nociceptive testing because of its remoteness from the region of drug application, the lumbar spinal cord. NSIA was reversed by antagonists for two inhibitory receptors (GABA-B and mu-opioid) but not by antagonists for either of the two excitatory receptors (NMDA and mGluR-5), indicating that NSIA is maintained by ongoing activity at inhibitory synapses in the spinal cord. Furthermore, spinal administration of the GABA-B agonist baclofen mimicked NSIA in that it could be blocked by prior injection of the mu-opioid receptor antagonist H-D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP) in nucleus accumbens. CTAP also blocked baclofen antinociception when administered in the spinal cord. We conclude that analgesia induced by noxious stimulation is maintained by activity in spinal inhibitory receptors. PMID:19375225

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

Tiger, G.; Fowler, C.J.

The calcium and potassium ion dependency of the inositol phospholipid breakdown response to stimulatory agents has been investigated in rat cerebral cortical miniprisms. The calcium channel agonist BAY K-8644 potentiated the response to carbachol at 6 mM K{sup +} when Ca{sup 2+}-free, but not when 2.52 mM Ca{sup 2+} assay buffer was used. In Ca{sup 2+}-free buffer, verapamil inhibited the response to carbachol at both 6 and 18 mM K{sup +} but higher concentrations were needed when 2.52 mM Ca{sup 2+} was used. At these higher concentrations, however, verapamil inhibited the binding of 2 nM ({sup 3}H)pirenzepine to muscarinic recognitionmore » sites. N-Methyl-D-Aspartate (NMDA) significantly reduced the basal phosphoinositide breakdown rate at 18 mM K{sup +} at 1.3 mM Ca{sup 2+}, but was without effect on the basal rate at other K{sup +} and Ca{sup 2+} concentrations. In the presence of NMDA or quisqualate, the responses to carbachol were reduced, the degree of reduction showing a complex dependency upon the assay K{sup +} and Ca{sup 2+} concentrations used. These results indicate that the inositol phospholipid breakdown response to carbachol in cerebral cortical miniprisms can be modulated in a manner dependent upon the extracellular calcium and potassium concentrations used.« less

Bidirectional effects of inhibiting or activating NMDA receptors on extinction after cocaine self-administration in rats

PubMed Central

Hafenbreidel, Madalyn; Todd, Carolynn Rafa; Twining, Robert C.; Tuscher, Jennifer J.; Mueller, Devin

2014-01-01

Rationale Extinction of drug seeking is facilitated by NMDA receptor (NMDAr) agonists, but it remains unclear whether extinction is dependent on NMDAr activity. Objectives We investigated the necessity of NMDArs for extinction of cocaine seeking, and whether extinction altered NMDAr expression within extinction-related neuroanatomical loci. Methods Rats were trained to lever press for i.v. infusions of cocaine or sucrose reinforcement prior to extinction training or withdrawal. Results Administration of the NMDAr competitive antagonist CPP prior to four brief extinction sessions impaired subsequent extinction retention. In contrast, post-extinction administration of the NMDAr coagonist D-serine attenuated lever pressing across days as compared to saline administration, indicative of facilitated consolidation of extinction. Furthermore, expression of the NMDAr subunits, GluN2A and GluN2B, was not altered in the ventromedial prefrontal cortex. However, both GluN2A and GluN2B subunit expression in the nucleus accumbens was increased following cocaine self-administration, and this increased expression was relatively resistant to modulation by extinction. Conclusions Our findings demonstrate that extinction of cocaine seeking is bidirectionally mediated by NMDArs and suggest that selective modulation of NMDAr activity could facilitate extinction-based therapies for treatment of cocaine abuse. PMID:24847958

Discovery of SMP-304, a novel benzylpiperidine derivative with serotonin transporter inhibitory activity and 5-HT1A weak partial agonistic activity showing the antidepressant-like effect.

PubMed

Yoshinaga, Hidefumi; Masumoto, Shuji; Koyama, Koji; Kinomura, Naoya; Matsumoto, Yuji; Kato, Taro; Baba, Satoko; Matsumoto, Kenji; Horisawa, Tomoko; Oki, Hitomi; Yabuuchi, Kazuki; Kodo, Toru

2017-01-01

We report the discovery of a novel benzylpiperidine derivative with serotonin transporter (SERT) inhibitory activity and 5-HT 1A receptor weak partial agonistic activity showing the antidepressant-like effect. The 3-methoxyphenyl group and the phenethyl group of compound 1, which has weak SERT binding activity, but potent 5-HT 1A binding activity, were optimized, leading to compound 35 with potent and balanced dual SERT and 5-HT 1A binding activity, but also potent CYP2D6 inhibitory activity. Replacement of the methoxy group in the left part of compound 35 with a larger alkoxy group, such as ethoxy, isopropoxy or methoxy-ethoxy group ameliorated CYP2D6 inhibition, giving SMP-304 as a candidate. SMP-304 with serotonin uptake inhibitory activity and 5-HT 1A weak partial agonistic activity, which could work as a 5-HT 1A antagonist, displayed faster onset of antidepressant-like effect than a representative SSRI paroxetine in an animal model. Copyright © 2016 Elsevier Ltd. All rights reserved.

Opioid Dependence Treatment: Options In Pharmacotherapy

PubMed Central

Stotts, Angela L.; Dodrill, Carrie L.; Kosten, Thomas R.

2010-01-01

The development of effective treatments for opioid dependence is of great importance given the devastating consequences of the disease. Pharmacotherapies for opioid addiction include opioid agonists, partial agonists, opioid antagonists, and alpha-2-adrenergic agonists, which are targeted toward either detoxification or long-term agonist maintenance. Agonist maintenance therapy is currently the recommended treatment for opioid dependence due to its superior outcomes relative to detoxification. Detoxification protocols have limited long term efficacy and patient discomfort remains a significant therapy challenge. Buprenorphine’s effectiveness relative to methadone remains a controversy and may be most appropriate for patients in need of low doses of agonist treatment. Buprenorphine appears superior to alpha-2 agonists, however, and office-based treatment with buprenorphine in the US is gaining support. Studies of sustained-release formulations of naltrexone suggest improved effectiveness for retention and sustained abstinence, however, randomized clinical trials are needed. PMID:19538000

NMDA receptor modulation by dextromethorphan and acute stress selectively alters electroencephalographic indicators of partial report processing.

PubMed

Weckesser, Lisa J; Enge, Sören; Riedel, Philipp; Kirschbaum, Clemens; Miller, Robert

2017-10-01

Proceeding from a biophysical network model, the present study hypothesized that glutamatergic neurotransmission across the NMDA receptor (NMDAR) plays a key role in visual perception and its modulation by acute stress. To investigate these hypotheses, behavioral and electroencephalographic (EEG) indicators of partial report task processing were assessed in twenty-four healthy young men who randomly received a non-competitive NMDAR antagonist (0.8 mg/kg dextromethorphan, DXM) or a placebo, and concurrently accomplished a stress-induction (MAST) or control protocol in three consecutive sessions. Saliva samples served to quantify cortisol responses to the MAST, whereas a passive auditory oddball paradigm was implemented to verify the impact of DXM on the EEG-derived mismatch negativity component (MMN). DXM administration significantly increased MMN amplitudes but not salivary cortisol concentrations. By contrast, concurrent MAST exposure significantly reduced MMN latencies but also increased cortisol concentrations. With regard to EEG indicators, DXM administration reduced visually "evoked" (30Hz to 50Hz) and "induced" occipital gamma-band activity (70Hz to 100Hz), which was partly compensated by additional MAST exposure. However, neither the interventions nor EEG activity were significantly associated with behavioral partial report sensitivities. In summary, the present data suggest that glutamatergic neurotransmission across the NMDAR is only one among many determinants of intact visual perception. Accordingly, therapeutic doses of DXM and their inhibitory modulation by stress probably yield more pronounced electroencephalographic as compared with behavioural effects. Copyright © 2017 Elsevier B.V. and ECNP. All rights reserved.

DCS facilitation of fear extinction and exposure-based therapy may rely on lower-level, automatic mechanisms

PubMed Central

Grillon, Christian

2009-01-01

Exposure-based therapy (EBT), a leading technique in the treatment of a range of anxiety disorders, is facilitated by D-cycloserine (DCS), a partial N-methyl-D-aspartate (NMDA) receptor agonist. This review discusses the potential mechanisms involved in this facilitation, and its implications for developing theories of fear conditioning in humans. Basic research in rodents suggests that DCS acts by speeding up extinction. However, several lab-based investigations found that DCS had no effect on extinction in humans. This paper proposes that these observations can be accounted for by a dual-model theory of fear conditioning in humans that engages two complementary defensive systems: a reflexive lower-order system independent of conscious awareness and a higher-order cognitive system associated with conscious awareness of danger and expectation. DCS studies in animals appear to have explored lower-order conditioning mechanisms, whereas human studies have explored higher-order cognitive processes. These observations suggest that DCS may act preferentially on lower- rather than higher-order learning. This paper presents evidence suggesting that, in humans, DCS may similarly affect lower-order learning during EBT and, consequently, may be less effective during cognitive therapy (e.g., cognitive restructuring). Finally, it is recommended that extinction studies using DCS in humans be conducted using fear-relevant stimuli (e.g., snakes), short conditional stimulus-unconditioned stimulus (CS-US) intervals, and intense US in order to promote lower-order conditioning processes. PMID:19520359

Effects of D-cycloserine on the extinction of appetitive operant learning.

PubMed

Vurbic, Drina; Gold, Benjamin; Bouton, Mark E

2011-08-01

Four experiments with rat subjects examined whether D-cycloserine (DCS), a partial NMDA agonist, facilitates the extinction of operant lever-pressing reinforced by food. Previous research has demonstrated that DCS facilitates extinction learning with methods that involve Pavlovian extinction. In the current experiments, operant conditioning occurred in Context A, extinction in Context B, and then testing occurred in both the extinction and conditioning contexts. Experiments 1A and 1B tested the effects of three doses of DCS (5, 15, and 30 mg/kg) on the extinction of lever pressing trained as a free operant. Experiment 2 examined their effects when extinction of the free operant was conducted in the presence of nonresponse-contingent deliveries of the reinforcer (that theoretically reduced the role of generalization decrement in suppressing responding). Experiment 3 examined their effects on extinction of a discriminated operant, that is, one that had been reinforced in the presence of a discriminative stimulus, but not in its absence. A strong ABA renewal effect was observed in all four experiments during testing. However, despite the use of DCS doses and a drug administration procedure that facilitates the extinction of Pavlovian learning, there was no evidence in any experiment that DCS facilitated operant extinction learning assessed in either the extinction or the conditioning context. DCS may primarily facilitate learning processes that underlie Pavlovian, rather than purely operant, extinction. (PsycINFO Database Record (c) 2011 APA, all rights reserved).

Effects of D-cycloserine on extinction and reinstatement of morphine-induced conditioned place preference.

PubMed

Lu, Guan-Yi; Wu, Ning; Zhang, Zhao-Long; Ai, Jing; Li, Jin

2011-10-10

d-Cycloserine (DCS), a partial agonist at the strychnine-insensitive glycine recognition site on the N-methyl-d-aspartate (NMDA) receptor complex, has been shown to facilitate the extinction and prevent the relapse of cocaine-induced conditioned place preference (CPP) when administered before or after each extinction trail. However, some studies have suggested that DCS does not influence or even enhance relapse of seeking behavior on cocaine self-administration (SA) in rats or cocaine-dependent individuals undergoing clinical exposure treatment. Furthermore, there are no reports on the effects of DCS and the extinction of morphine-conditioned behaviors in mice. The present study investigated the effects of DCS on extinction by exposing mice to drug-paired cues and the subsequent reinstatement of morphine-primed CPP. Our results showed that DCS at doses of 7.5, 15, and 30mg/kg did not induce conditioned appetitive or aversive effects and DCS combined with morphine conditioning failed to affect the acquisition of morphine-induced CPP. Moreover, pretreatment with DCS (7.5, 15, and 30mg/kg, i.p.) prior to extinction training had no significant effects on the extinction and subsequent morphine-primed reinstatement of morphine-induced CPP. These results suggested that DCS may not be a powerful adjunct for cue exposure therapy of opioid addiction. In view of differing outcomes in both preclinical and clinical studies, the potential of DCS in exposure treatment of drug-seeking behaviors should be carefully evaluated. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

Administration of riluzole to the basolateral amygdala facilitates fear extinction in rats.

PubMed

Sugiyama, Azusa; Yamada, Misa; Saitoh, Akiyoshi; Oka, Jun-Ichiro; Yamada, Mitsuhiko

2018-01-15

A general understanding exists that inhibition of glutamatergic neurotransmission in the basolateral amygdala (BLA) impairs fear extinction in rodents. Surprisingly, we recently found that systemic administration of riluzole, which has been shown to inhibit the glutamatergic system, facilitates extinction learning in rats with a preconditioned contextual fear response. However, the mechanisms underlying this paradoxical effect of riluzole remain unclear. In this study, adult male Wistar rats were bilaterally cannulated in the BLA to examine the effects of intra-BLA administration of riluzole. We also compared the effects of riluzole with those of d-cycloserine, a partial agonist at the glycine-binding region of the N-methyl-d-aspartate (NMDA) receptor. In this study, intra-BLA administration of either riluzole or d-cycloserine facilitated extinction learning of contextual fear in conditioned rats. In addition, both riluzole and d-cycloserine enhanced the acquisition of recognition memory in the same model. However, intra-BLA injections of riluzole, but not d-cycloserine, had a potent anxiolytic-like effect when investigated using an elevated plus-maze test. Our findings suggest that riluzole-induced facilitation of extinction learning in rats with a preconditioned contextual fear reflects an indirect effect, resulting from the intra-BLA administration of the drug, and might not be directly related to inhibition of glutamatergic signaling. Further research is needed to clarify the mechanisms underlying the paradoxical effect of riluzole on fear extinction learning observed in this study. Copyright © 2017 Elsevier B.V. All rights reserved.

A molecular characterization of the agonist binding site of a nematode cys-loop GABA receptor

PubMed Central

Kaji, Mark D; Kwaka, Ariel; Callanan, Micah K; Nusrat, Humza; Desaulniers, Jean-Paul; Forrester, Sean G

2015-01-01

Background and Purpose Cys-loop GABA receptors represent important targets for human chemotherapeutics and insecticides and are potential targets for novel anthelmintics (nematicides). However, compared with insect and mammalian receptors, little is known regarding the pharmacological characteristics of nematode Cys-loop GABA receptors. Here we have investigated the agonist binding site of the Cys-loop GABA receptor UNC-49 (Hco-UNC-49) from the parasitic nematode Haemonchus contortus. Experimental Approach We used two-electrode voltage-clamp electrophysiology to measure channel activation by classical GABA receptor agonists on Hco-UNC-49 expressed in Xenopus laevis oocytes, along with site-directed mutagenesis and in silico homology modelling. Key Results The sulphonated molecules P4S and taurine had no effect on Hco-UNC-49. Other classical Cys-loop GABAA receptor agonists tested on the Hco-UNC-49B/C heteromeric channel had a rank order efficacy of GABA > trans-4-aminocrotonic acid > isoguvacine > imidazole-4-acetic acid (IMA) > (R)-(−)-4-amino-3-hydroxybutyric acid [R(−)-GABOB] > (S)-(+)-4-amino-3-hydroxybutyric acid [S(+)-GABOB] > guanidinoacetic acid > isonipecotic acid > 5-aminovaleric acid (DAVA) (partial agonist) > β-alanine (partial agonist). In silico ligand docking revealed some variation in binding between agonists. Mutagenesis of a key serine residue in binding loop C to threonine had minimal effects on GABA and IMA but significantly increased the maximal response to DAVA and decreased twofold the EC50 for R(−)- and S(+)-GABOB. Conclusions and Implications The pharmacological profile of Hco-UNC-49 differed from that of vertebrate Cys-loop GABA receptors and insect resistance to dieldrin receptors, suggesting differences in the agonist binding pocket. These findings could be exploited to develop new drugs that specifically target GABA receptors of parasitic nematodes. PMID:25850584

5-HT6 receptor agonists and antagonists enhance learning and memory in a conditioned emotion response paradigm by modulation of cholinergic and glutamatergic mechanisms

PubMed Central

Woods, S; Clarke, NN; Layfield, R; Fone, KCF

2012-01-01

BACKGROUND AND PURPOSE 5-HT6 receptors are abundant in the hippocampus, nucleus accumbens and striatum, supporting their role in learning and memory. Selective 5-HT6 receptor antagonists produce pro-cognitive effects in several learning and memory paradigms while 5-HT6 receptor agonists have been found to enhance and impair memory. EXPERIMENTAL APPROACH The conditioned emotion response (CER) paradigm was validated in rats. Then we examined the effect of the 5-HT6 receptor antagonist, EMD 386088 (10 mg·kg−1, i.p.), and agonists, E-6801 (2.5 mg·kg−1, i.p.) and EMD 386088 (5 mg·kg−1, i.p.) on CER-induced behaviour either alone or after induction of memory impairment by the muscarinic receptor antagonist, scopolamine (0.3 mg·kg−1, i.p) or the NMDA receptor antagonist, MK-801 (0.1 mg·kg−1, i.p). KEY RESULTS Pairing unavoidable foot shocks with a light and tone cue during CER training induced a robust freezing response, providing a quantitative index of contextual memory when the rat was returned to the shock chamber 24 h later. Pretreatment (−20 min pre-training) with scopolamine or MK-801 reduced contextual freezing 24 h after CER training, showing production of memory impairment. Immediate post-training administration of 5-HT6 receptor antagonist, SB-270146, and agonists, EMD 386088 and E-6801, had little effect on CER freezing when given alone, but all significantly reversed scopolamine- and MK-801-induced reduction in freezing. CONCLUSION AND IMPLICATIONS Both the 5-HT6 receptor agonists and antagonist reversed cholinergic- and glutamatergic-induced deficits in associative learning. These findings support the therapeutic potential of 5-HT6 receptor compounds in the treatment of cognitive dysfunction, such as seen in Alzheimer's disease and schizophrenia. PMID:22568655

Discovery of N-(4-aryl-5-aryloxy-thiazol-2-yl)-amides as potent RORγt inverse agonists.

PubMed

Wang, Yonghui; Yang, Ting; Liu, Qian; Ma, Yingli; Yang, Liuqing; Zhou, Ling; Xiang, Zhijun; Cheng, Ziqiang; Lu, Sijie; Orband-Miller, Lisa A; Zhang, Wei; Wu, Qianqian; Zhang, Kathleen; Li, Yi; Xiang, Jia-Ning; Elliott, John D; Leung, Stewart; Ren, Feng; Lin, Xichen

2015-09-01

A novel series of N-(4-aryl-5-aryloxy-thiazol-2-yl)-amides as RORγt inverse agonists was discovered. Binding mode analysis of a RORγt partial agonist (2c) revealed by co-crystal structure in RORγt LBD suggests that the inverse agonists do not directly interfere with the interaction between H12 and the RORγt LBD. Detailed SAR exploration led to identification of potent RORγt inverse agonists such as 3m with a pIC50 of 8.0. Selected compounds in the series showed reasonable activity in Th17 cell differentiation assay as well as low intrinsic clearance in mouse liver microsomes. Copyright © 2015 Elsevier Ltd. All rights reserved.

Structure-activity relationships of rosiglitazone for peroxisome proliferator-activated receptor gamma transrepression.

PubMed

Toyota, Yosuke; Nomura, Sayaka; Makishima, Makoto; Hashimoto, Yuichi; Ishikawa, Minoru

2017-06-15

Anti-inflammatory effects of peroxisome proliferator-activated receptor gamma (PPRAγ) ligands are thought to be largely due to PPARγ-mediated transrepression. Thus, transrepression-selective PPARγ ligands without agonistic activity or with only partial agonistic activity should exhibit anti-inflammatory properties with reduced side effects. Here, we investigated the structure-activity relationships (SARs) of PPARγ agonist rosiglitazone, focusing on transrepression activity. Alkenic analogs showed slightly more potent transrepression with reduced efficacy of transactivating agonistic activity. Removal of the alkyl group on the nitrogen atom improved selectivity for transrepression over transactivation. Among the synthesized compounds, 3l exhibited stronger transrepressional activity (IC 50 : 14μM) and weaker agonistic efficacy (11%) than rosiglitazone or pioglitazone. Copyright © 2017 Elsevier Ltd. All rights reserved.

Cholecystokinin type B receptor antagonist PD-136,450 is a partial secretory agonist in the stomach and a full agonist in the pancreas of the rat.

PubMed Central

Schmassmann, A; Garner, A; Flogerzi, B; Hasan, M Y; Sanner, M; Varga, L; Halter, F

1994-01-01

Gastrin (cholecystokinin type B (CCK-B)) receptor antagonists may help to elucidate the physiological role of gastrin, have therapeutic potential as acid antisecretory drugs, and may be of use as adjuvant therapy for gastrin sensitive tumours. In binding studies, the gastrin receptor antagonist PD-136,450 had at least 1000 fold greater affinity for gastrin (CCK-B) than CCK-A receptors. In this study the biological activity of PD-136,450 was evaluated in conscious and anaesthetised rats. PD-136,450 antagonised gastrin stimulated acid secretion after subcutaneous (IC50: 0.28 mumol/kg; conscious rats) and intravenous (IC50: 0.17 mumol/kg; anaesthetised rats) administration. In basal secreting fistula animals, the compound stimulated acid output to 30 (5)% of the maximal response to gastrin. Stimulant activity was not caused by gastrin release. As an agonist PD-136,450 was about 350 times less potent than gastrin-17 on a molar basis. In addition, PD-136,450 was a powerful agonist of pancreatic secretion in anaesthetised rats. The specific gastrin antagonist L-365,260 inhibited the (partial) agonist activity of PD-136,450 in the stomach and the specific CCK-A receptor antagonist L-364,718 inhibited the agonist activity of PD-136,450 in the pancreas. It is concluded that the agonist effect of PD-136,450 is mediated via interaction with the gastrin (CCK-B) receptor in the stomach and the CCK-A receptor in the pancreas. PMID:8307482

Selective enhancement of fentanyl-induced antinociception by the delta agonist SNC162 but not by ketamine in rhesus monkeys: Further evidence supportive of delta agonists as candidate adjuncts to mu opioid analgesics.

PubMed

Banks, Matthew L; Folk, John E; Rice, Kenner C; Negus, S Stevens

2010-12-01

Mu-opioid receptor agonists such as fentanyl are effective analgesics, but their clinical use is limited by untoward effects. Adjunct medications may improve the effectiveness and/or safety of opioid analgesics. This study compared interactions between fentanyl and either the noncompetitive N-methyl-D-aspartate (NMDA) glutamate receptor antagonist ketamine or the delta-opioid receptor agonist SNC162 [(+)-4-[(alphaR)-alpha-[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-phenyl)methyl]-N,N-diethylbenzamide] in two behavioral assays in rhesus monkeys. An assay of thermal nociception evaluated tail-withdrawal latencies from water heated to 50 and 54°C. An assay of schedule-controlled responding evaluated response rates maintained under a fixed-ratio 30 schedule of food presentation. Effects of each drug alone and of three mixtures of ketamine+fentanyl (22:1, 65:1, 195:1 ketamine/fentanyl) or SNC162+fentanyl (59:1, 176:1, 528:1 SNC162/fentanyl) were evaluated in each assay. All drugs and mixtures dose-dependently decreased rates of food-maintained responding, and drug proportions in the mixtures were based on relative potencies in this assay. Ketamine and SNC162 were inactive in the assay of thermal antinociception, but fentanyl and all mixtures produced dose-dependent antinociception. Drug interactions were evaluated using dose-addition and dose-ratio analysis. Dose-addition analysis revealed that interactions for all ketamine/fentanyl mixtures were additive in both assays. SNC162/fentanyl interactions were usually additive, but one mixture (176:1) produced synergistic antinociception at 50°C. Dose-ratio analysis indicated that ketamine failed to improve the relative potency of fentanyl to produce antinociception vs. rate suppression, whereas two SNC162/fentanyl mixtures (59:1 and 176:1) increased the relative potency of fentanyl to produce antinociception. These results suggest that delta agonists may produce more selective enhancement than ketamine of mu agonist-induced antinociception. Copyright © 2010 Elsevier Inc. All rights reserved.

CANNABINOID AND OPIOID MODULATION OF SOCIAL PLAY BEHAVIOR IN ADOLESCENT RATS: DIFFERENTIAL BEHAVIORAL MECHANISMS

PubMed Central

Trezza, Viviana; Vanderschuren, Louk J.M.J.

2008-01-01

We have recently shown that the pharmacological mechanisms through which cannabinoid and opioid drugs influence social play behavior in adolescent rats can be partially dissociated. Here, we characterize the effects of the direct cannabinoid agonist WIN55,212-2, the indirect cannabinoid agonist URB597 and the opioid agonist morphine on social play at the behavioral level. By treating either one or both partners of the test dyad, we show that these drugs differentially affect play solicitation and play responsiveness. By testing these drugs in animals which were either familiar or unfamiliar to the test cage, we show that environmental factors differentially modulate the effects of cannabinoid and opioid drugs on social play. These results support and extend our previous findings suggesting that, although cannabinoid and opioid systems interact in the modulation of social play behavior in adolescent rats, they do so through partially dissociable behavioral and pharmacological mechanisms. PMID:18434104

Function and structure in glycine receptors and some of their relatives.

PubMed

Colquhoun, David; Sivilotti, Lucia G

2004-06-01

In the field of ligand-gated ion channels, recent developments, both in the knowledge of structure and in the measurement of function at the single-channel level, have allowed a sensible start to be made on understanding the relationship between structure and function in these proteins. In this review, the cases of glycine, nicotinic ACh and glutamate receptors are compared and contrasted, and problems such as how binding of agonist causes the channel to open, and why partial agonists are partial, are considered. Some observations, both structural and functional, suggest that more attention needs to be paid to conformational changes that occur before the channel opens. Such changes might account for the interaction found between subunits of the glycine receptor while it is still shut and, perhaps, the agonist-dependent structural changes seen in AMPA receptors. They might also complicate our understanding of the binding-gating problem.

Graded activation and free energy landscapes of a muscarinic G-protein-coupled receptor.

PubMed

Miao, Yinglong; McCammon, J Andrew

2016-10-25

G-protein-coupled receptors (GPCRs) recognize ligands of widely different efficacies, from inverse to partial and full agonists, which transduce cellular signals at differentiated levels. However, the mechanism of such graded activation remains unclear. Using the Gaussian accelerated molecular dynamics (GaMD) method that enables both unconstrained enhanced sampling and free energy calculation, we have performed extensive GaMD simulations (∼19 μs in total) to investigate structural dynamics of the M 2 muscarinic GPCR that is bound by the full agonist iperoxo (IXO), the partial agonist arecoline (ARC), and the inverse agonist 3-quinuclidinyl-benzilate (QNB), in the presence or absence of the G-protein mimetic nanobody. In the receptor-nanobody complex, IXO binding leads to higher fluctuations in the protein-coupling interface than ARC, especially in the receptor transmembrane helix 5 (TM5), TM6, and TM7 intracellular domains that are essential elements for GPCR activation, but less flexibility in the receptor extracellular region due to stronger binding compared with ARC. Two different binding poses are revealed for ARC in the orthosteric pocket. Removal of the nanobody leads to GPCR deactivation that is characterized by inward movement of the TM6 intracellular end. Distinct low-energy intermediate conformational states are identified for the IXO- and ARC-bound M 2 receptor. Both dissociation and binding of an orthosteric ligand are observed in a single all-atom GPCR simulation in the case of partial agonist ARC binding to the M 2 receptor. This study demonstrates the applicability of GaMD for exploring free energy landscapes of large biomolecules and the simulations provide important insights into the GPCR functional mechanism.

Ear2 deletion causes early memory and learning deficits in APP/PS1 mice.

PubMed

Kummer, Markus P; Hammerschmidt, Thea; Martinez, Ana; Terwel, Dick; Eichele, Gregor; Witten, Anika; Figura, Stefanie; Stoll, Monika; Schwartz, Stephanie; Pape, Hans-Christian; Schultze, Joachim L; Weinshenker, David; Heneka, Michael T; Urban, Inga

2014-06-25

To assess the consequences of locus ceruleus (LC) degeneration and subsequent noradrenaline (NA) deficiency in early Alzheimer's disease (AD), mice overexpressing mutant amyloid precursor protein and presenilin-1 (APP/PS1) were crossed with Ear2(-/-) mice that have a severe loss of LC neurons projecting to the hippocampus and neocortex. Testing spatial memory and hippocampal long-term potentiation revealed an impairment in APP/PS1 Ear2(-/-) mice, whereas APP/PS1 or Ear2(-/-) mice showed only minor changes. These deficits were associated with distinct synaptic changes including reduced expression of the NMDA 2A subunit and increased levels of NMDA receptor 2B in APP/PS1 Ear2(-/-) mice. Acute pharmacological replacement of NA by L-threo-DOPS partially restored phosphorylation of β-CaMKII and spatial memory performance in APP/PS1 Ear2(-/-) mice. These changes were not accompanied by altered APP processing or amyloid β peptide (Aβ) deposition. Thus, early LC degeneration and subsequent NA reduction may contribute to cognitive deficits via CaMKII and NMDA receptor dysfunction independent of Aβ and suggests that NA supplementation could be beneficial in treating AD. Copyright © 2014 the authors 0270-6474/14/348845-10$15.00/0.

[NMDA-GluR Subunit Antibody-Positive Encephalitis: A Clinical Analysis of Five Cases].

PubMed

Kaneko, Chikako; Shakespear, Norshalena; Tuchiya, Mario; Kubo, Jin; Yamamoto, Teiji; Katayama, Soichi; Takahashi, Yukitoshi

2016-09-01

Five consecutive cases of anti-NMDA-receptor encephalitis that we encountered were marked by a rapidly fluctuating level of consciousness associated with psychotic and delirious mental states. Opisthotonus, catatonia, and rhythmic and non-rhythmic involuntary movements of the mouth and jaw were also characteristic features of these particular cases. Serious and potentially fatal problems included epilepsia partialis continua, partial and generalized seizures, and respiratory depression, resembling the symptoms of encephalitis lethargica. An epidemic of encephalitis lethargica, also known of Economo encephalitis, occurred around 1917. Magnetic resonance imaging revealed edema of the neocortex in two cases and electroencephalography showed polymorphic and monomorphic delta slowing in the acute stage, although electroencephalographic seizure activity were not apparent. Routine cerebrospinal fluid analyses revealed lymphocyte-dominant pleocytosis in three cases, but antibodies against the NMDA-GluR subunit, GluN2B N-terminal, were at a high level in the fluid. All patients recovered without apparent sequelae. Two patients found to have ovarian teratoma underwent surgery for tumor removal. Treatments included pulse intravenous methylprednisolone, high-dose immunoglobulin, and plasma exchange together with seizure control and respiratory support. However, rituximab and or cyclophosphamide pulse therapy should also be considered for intractable cases, as indicated by recent reports. (Received February 16, 2016; Accepted May 2, 2016; Published September 1, 2016).

Anti-epileptic activity of group II metabotropic glutamate receptor agonists (--)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268) and (--)-2-thia-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY389795).

PubMed

Moldrich, R X; Jeffrey, M; Talebi, A; Beart, P M; Chapman, A G; Meldrum, B S

2001-07-01

The selective group II metabotropic glutamate receptor (mGlu(2/3)) agonists (-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268) and (-)-2-thia-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY389795) have been evaluated as anti-epileptic drugs in dilute brown agouti (DBA/2) mice, lethargic (lh/lh) mice, genetically epilepsy-prone-9 (GEP) rats and amygdala-kindled rats. Sound-induced clonic seizures in DBA/2 mice were transiently inhibited by both agonists intracerebroventricularly (i.c.v.), LY379268 ED(50)=0.08 [0.02-0.33]nmol and LY389795 ED(50)=0.82 [0.27-3.24]nmol or intraperitoneally (i.p.), LY379268 ED(50)=2.9 [0.9-9.6]mg/kg and LY389795 ED(50)=3.4 [1.0-11.7]mg/kg. Both mGlu(2/3) agonists inhibited seizures induced by the group I mGlu receptor agonist (R,S)-3,5-dihydroxyphenylglycine (DHPG), where LY379268, i.c.v. ED(50)=0.3 [0.02-5.0]pmol and LY389795, i.c.v. ED(50)=0.03 [0.05-0.19]nmol. The spike and wave discharge (SWD) duration of absence seizures in lh/lh mice was significantly reduced by both agonists at 1 and 10nmol (i.c.v.) up to 90min following infusion. The electrically induced seizure score and afterdischarge duration of amygdala-kindled rats was partially inhibited by the agonists 30min after i.p. injection of 10mg/kg. The agonists did not inhibit sound-induced seizures in GEP rats (0.1-1mg/kg, 30min 1h, i.p.), but were proconvulsant following sound stimulus (> or =0.1mg/kg). These findings identify a potential role for mGlu(2/3) agonists in the amelioration of generalised and partial epileptic seizures.

Blonanserin reverses the phencyclidine (PCP)-induced impairment in novel object recognition (NOR) in rats: role of indirect 5-HT(1A) partial agonism.

PubMed

Horiguchi, M; Meltzer, H Y

2013-06-15

Blonanserin is an atypical antipsychotic drug (APD) which, compared to other atypical APDs, is a relatively selective serotonin (5-HT)2A and dopamine D2 antagonist. Comparing blonanserin with more broadly acting atypical APDs could be useful to test the contributions of actions at other monoamine receptors, e.g. 5-HT1A receptors, to the reversal of PCP-induced novel object recognition (NOR) deficit. In this study, we tested the effect of blonanserin alone, and in combination with 5-HT1A agents, on NOR deficit induced by subchronic treatment with the N-methyl-D-aspartate (NMDA) receptor antagonist, phencyclidine (PCP; 2 mg/kg), b.i.d., for 7 days. Blonanserin, 1mg/kg, but not 0.3mg/kg, improved the PCP-induced NOR deficit. However, at 1mg/kg, object exploration was diminished. Co-administration of sub-effective doses of blonanserin (0.3 mg/kg) and the 5-HT1A partial agonist, tandospirone (0.2 mg/kg), significantly reversed the NOR deficit without diminishing activity during the acquisition or retention periods. The combination of WAY100635 (0.6 mg/kg), a 5-HT1A antagonist, and blonanserin (1 mg/kg), also diminished object exploration which prevented assessment of the effect of this combination on NOR. WAY100635 (0.6 mg/kg) blocked the ameliorating effect of risperidone (0.1 mg/kg), another atypical APD with low affinity for 5-HT1A receptors, but did not impair exploration. These results suggest that blonansein and risperidone, atypical APDs which lack a direct action on 5-HT1A receptors require 5-HT1A receptor stimulation to reverse the subchronic PCP-induced NOR deficit and provide a support for clinical trial of blonanserin in combination with tandospirone to ameliorate cognitive impairment in schizophrenia and to have fewer side effects. Copyright © 2013 Elsevier B.V. All rights reserved.

Essential role of GluD1 in dendritic spine development and GluN2B to GluN2A NMDAR subunit switch in the cortex and hippocampus reveals ability of GluN2B inhibition in correcting hyperconnectivity.

PubMed

Gupta, Subhash C; Yadav, Roopali; Pavuluri, Ratnamala; Morley, Barbara J; Stairs, Dustin J; Dravid, Shashank M

2015-06-01

The glutamate delta-1 (GluD1) receptor is highly expressed in the forebrain. We have previously shown that loss of GluD1 leads to social and cognitive deficits in mice, however, its role in synaptic development and neurotransmission remains poorly understood. Here we report that GluD1 is enriched in the medial prefrontal cortex (mPFC) and GluD1 knockout mice exhibit a higher dendritic spine number, greater excitatory neurotransmission as well as higher number of synapses in mPFC. In addition abnormalities in the LIMK1-cofilin signaling, which regulates spine dynamics, and a lower ratio of GluN2A/GluN2B expression was observed in the mPFC in GluD1 knockout mice. Analysis of the GluD1 knockout CA1 hippocampus similarly indicated the presence of higher spine number and synapses and altered LIMK1-cofilin signaling. We found that systemic administration of an N-methyl-d-aspartate (NMDA) receptor partial agonist d-cycloserine (DCS) at a high-dose, but not at a low-dose, and a GluN2B-selective inhibitor Ro-25-6981 partially normalized the abnormalities in LIMK1-cofilin signaling and reduced excess spine number in mPFC and hippocampus. The molecular effects of high-dose DCS and GluN2B inhibitor correlated with their ability to reduce the higher stereotyped behavior and depression-like behavior in GluD1 knockout mice. Together these findings demonstrate a critical requirement for GluD1 in normal spine development in the cortex and hippocampus. Moreover, these results identify inhibition of GluN2B-containing receptors as a mechanism for reducing excess dendritic spines and stereotyped behavior which may have therapeutic value in certain neurodevelopmental disorders such as autism. Copyright © 2015 Elsevier Ltd. All rights reserved.

Proceedings of the International Conference on Cyclic Nucleotides, Calcium and Protein Phosphorylation (6th) Held in Bethesda, Maryland on September 2-7, 1986. Advances in Second Messenger and Phosphorprotein Research. Volume 21A. Abstracts Volume

DTIC Science & Technology

1988-11-16

oxoireamorine. Oxotremorine inhibited Ach release for a shorter duration. The ACh release-inhibition induced by 50 PH Aech-M was only acutely blocked...and the partial agonist oxotresorine in the presence of 59K of Lit. Carbacbol showed a 10-fold lover ECS0-value (3.7liM) and oxotremorine a 3-fold...however, only a decrease in the maximal response was seen. In both tissues, the maximal, response of the partial agonist oxotremorine was suppressed

Synthesis, Structure-Activity Relationships, and Preclinical Evaluation of Heteroaromatic Amides and 1,3,4-Oxadiazole Derivatives as 5-HT4 Receptor Partial Agonists.

PubMed

Nirogi, Ramakrishna; Mohammed, Abdul Rasheed; Shinde, Anil K; Gagginapally, Shankar Reddy; Kancharla, Durga Malleshwari; Middekadi, Vanaja Reddy; Bogaraju, Narsimha; Ravella, Srinivasa Rao; Singh, Pooja; Birangal, Sumit Raosaheb; Subramanian, Ramkumar; Palacharla, Raghava Choudary; Benade, Vijay; Muddana, Nageswararao; Jayarajan, Pradeep

2018-05-31

Alzheimer's disease (AD) is a neurodegenerative disorder that has a higher prevalence and incidence in people older than 60 years. The need for improved AD therapies is unmet as the current therapies are symptomatic with modest efficacy. Partial agonists of the 5-HT 4 receptor (5-HT 4 R) offer both symptomatic and disease-modifying treatments as they shift amyloid-precursor-protein (APP) processing from the amyloidogenic pathway to the nonamyloidogenic pathway by activating the α-secretase enzyme. In addition, they also offer symptomatic treatment by increasing levels of the neurotransmitter acetylcholine in the brain. Because of this fascinating dual mechanism of action, several chemical scaffolds having 5-HT 4 R pharmacophores were designed and evaluated. Most of the synthesized compounds showed potent in vitro affinities and in vivo efficacies. Upon analysis of focused structure-activity relationships, compound 4o was identified as a potent 5-HT 4 R partial agonist with favorable ADME properties and good in vivo efficacy. GR-125487, a selective 5-HT 4 R antagonist, attenuated the activity of compound 4o in the novel-object-recognition-test cognition model.

Methamphetamine-like discriminative stimulus effects of bupropion and its two hydroxy metabolites in male rhesus monkeys.

PubMed

Banks, Matthew L; Smith, Douglas A; Blough, Bruce E

2016-04-01

The dopamine transporter (DAT) inhibitor and nicotinic acetylcholine (nACh) receptor antagonist bupropion is being investigated as a candidate 'agonist' medication for methamphetamine addiction. In addition to its complex pharmacology, bupropion also has two distinct pharmacologically active metabolites. However, the mechanism by which bupropion produces methamphetamine-like 'agonist' effects remains unknown. The aim of the present study was to determine the role of DAT inhibition, nACh receptor antagonism, and the hydroxybupropion metabolites in the methamphetamine-like discriminative stimulus effects of bupropion in rhesus monkeys. In addition, varenicline, a partial agonist at the nACh receptor, and risperidone, a dopamine antagonist, were tested as controls. Monkeys (n=4) were trained to discriminate 0.18 mg/kg intramuscular methamphetamine from saline in a two-key food-reinforced discrimination procedure. The potency and time course of methamphetamine-like discriminative stimulus effects were determined for all compounds. Bupropion, methylphenidate, and 2S,3S-hydroxybupropion produced full, at least 90%, methamphetamine-like effects. 2R,3R-Hydroxybupropion, mecamylamine, and nicotine also produced full methamphetamine-like effects, but drug potency was more variable between monkeys. Varenicline produced partial methamphetamine-like effects, whereas risperidone did not. Overall, these results suggest DAT inhibition as the major mechanism of the methamphetamine-like 'agonist' effects of bupropion, although nACh receptor antagonism appeared, at least partially, to contribute. Furthermore, the contribution of the 2S,3S-hydroxybupropion metabolite could not be completely ruled out.

Somatostatin receptor subtypes SSTR2 and SSTR5 couple negatively to an L-type Ca2+ current in the pituitary cell line AtT-20.

PubMed

Tallent, M; Liapakis, G; O'Carroll, A M; Lolait, S J; Dichter, M; Reisine, T

1996-04-01

The somatostatin receptor subtypes SSTR2 and SSTR5 mediate distinct endocrine and exocrine functions of somatostatin and may also be involved in mediating the neuromodulatory actions of somatostatin in the brain. To investigate whether these receptors couple to voltage-sensitive Ca2+ channels, SSTR2 and SSTR5 selective agonists were tested for their effects on AtT-20 cells using whole cell patch clamp techniques. The SSTR2 selective agonist MK 678 inhibited Ca2+ currents in AtT-20 cells. The effects of MK 678 were reversible and blocked by pertussis toxin pretreatment, suggesting that SSTR2 couples to the L-type Ca2+ channels via G proteins. Other SSTR2-selective agonists, including BIM 23027 and NC8-12, were able to inhibit the Ca2+ currents in these cells. The SSTR5 selective agonist BIM 23052 also inhibited the Ca2+ currents in these cells and this effect was reversible and blocked by pertussis toxin treatment. The ability of SSTR5 to mediate inhibition of the Ca2+ current was greatly attenuated by pretreatment with the SSTR5-selective agonist BIM 23052, whereas SSTR2-mediated inhibition of the Ca2+ current was not altered by pretreatment with the SSTR2-selective agonist MK 678. Thus, the SSTR2 and SSTR5 couplings to the Ca2+ current are differentially regulated. The peptide L362,855, which we previously have shown to have high affinity for the cloned SSTR5, had minimal effects on Ca2+ currents in AtT-20 cells at concentrations up to 100 nM and did not alter the ability of MK 678 to inhibit Ca2+ currents. However, it completely antagonized the effects of the SSTR5-selective agonist BIM 23052 on the Ca2+ currents. L362,855 is an antagonist/partial agonist at SSTR5 since it can reduce Ca2+ currents in these cells at concentrations above 100 nM. L362,855 is also an antagonist/partial agonist at the cloned rat SSTR5 expressed in CHO cells since it is able to block the inhibition of cAMP accumulation induced by somatostatin at concentrations below 100 nM but at higher concentrations can inhibit cAMP formation itself. Structural analysis of L362,855 reveals that only a single hydroxyl group at residue seven in the peptide is needed to convert the compound from an antagonist/partial agonist to a full agonist at SSTR5. These studies reveal that two different somatostatin receptor subtypes, SSTR2 and SSTR5, can mediate the inhibition of an L-type Ca2+ channel in AtT-20 cells by somatostatin. The receptor subtype responses can be distinguished by selective agonists and antagonists and are regulated differently by agonist pretreatment. The inhibition of Ca2+ influx into endocrine cells and neurons may be a major cellular mechanism by which somatostatin modulates hormone and neurotransmitter release. Our results reveal that at least two receptor subtypes can mediate this cellular response.

Effects of D-cycloserine and aniracetam on spatial learning in rats with entorhinal cortex lesions.

PubMed

Zajaczkowski, W; Danysz, W

1997-01-01

A great body of behavioural and neurophysiological evidence suggests that excitatory amino acids are involved in mechanisms of learning and memory. Moreover, degeneration of glutamatergic pathways may underlie the cognitive deficits seen in various disorders such as Alzheimer's dementia. As direct stimulation of glutamatergic receptors with agonists may increase the risk of toxicity and accelerate neuropathological changes, a more valid approach seems to be positive modulation of glutamatergic receptors that may reverse the symptoms with a lower risk of excitotoxic effects. Such a possibility offered by partial agonists of the strychnine-insensitive glycine site of the NMDA receptor (Gly-B site) or positive modulators of AMPA receptors, such as aniracetam. In the present study, the effects of d-cycloserine and aniracetam were tested in two animal models of cognitive deficits (entorhinal cortex lesion-induced deficits evaluated in the radial maze and scopolamine-induced amnesia evaluated in passive avoidance test). D-cycloserine (6 mg/kg, for 10 days) had no effect on spatial working memory deficit induced by entorhinal cortex lesions. It did, however, reverse scopolamine-induced deficits in the passive avoidance test when given acutely at the same dose. In contrast, aniracetam (50 mg/kg, for 10 days) produced beneficial effects in the radial maze test in rats with entorhinal cortex lesions, but given at the same dose acutely did not influence scopolamine-induced amnesia. The positive effect of d-cycloserine against scopolamine-induced amnesia may be probably related to the cholinergic-glutamatergic interaction in the hippocampus. The negative data obtained with d-cycloserine in the model of entorhinal cortex lesions-induced cognitive deficits could be taken as a hint that it is probably not suitable for the symptomatological therapy of Alzheimer's disease. The mechanism of positive action of aniracetam cannot be explained on the basis of AMPA receptor modulation, as the dose used (50 mg/kg) is well below that required for the effect at AMPA receptors. Other actions such as peripheral effects or modulation of metabotropic receptors seem more likely.

Stereochemical requirements for central and peripheral muscarinic and antimuscarinic activity of some acetylenic compounds related to oxotremorine.

PubMed Central

Dahlbom, R.; Jenden, D. J.; Resul, B.; Ringdahl, B.

1982-01-01

1 The enantiomers of some analogues of the central muscarinic agent, oxotremorine, were prepared and investigated for tremorogenic and tremorolytic activity in intact mice and for muscarinic and antimuscarinic activity on the isolated ileum of the guinea-pig. 2 The R-isomers were more potent than the S-isomers both in vivo and in vitro regardless of whether the compounds are agonists, partial agonists or competitive antagonists. 3 It is suggested that in the oxotremorine series, agonists and antagonists interact with a common receptor site, in contrast to classical muscarinic antagonists which are believed to bind also to accessory receptor areas, located close to the agonist binding site. PMID:7093587

NMDA Receptor Signaling Is Important for Neural Tube Formation and for Preventing Antiepileptic Drug-Induced Neural Tube Defects.

PubMed

Sequerra, Eduardo B; Goyal, Raman; Castro, Patricio A; Levin, Jacqueline B; Borodinsky, Laura N

2018-05-16

Failure of neural tube closure leads to neural tube defects (NTDs), which can have serious neurological consequences or be lethal. Use of antiepileptic drugs (AEDs) during pregnancy increases the incidence of NTDs in offspring by unknown mechanisms. Here we show that during Xenopus laevis neural tube formation, neural plate cells exhibit spontaneous calcium dynamics that are partially mediated by glutamate signaling. We demonstrate that NMDA receptors are important for the formation of the neural tube and that the loss of their function induces an increase in neural plate cell proliferation and impairs neural cell migration, which result in NTDs. We present evidence that the AED valproic acid perturbs glutamate signaling, leading to NTDs that are rescued with varied efficacy by preventing DNA synthesis, activating NMDA receptors, or recruiting the NMDA receptor target ERK1/2. These findings may prompt mechanistic identification of AEDs that do not interfere with neural tube formation. SIGNIFICANCE STATEMENT Neural tube defects are one of the most common birth defects. Clinical investigations have determined that the use of antiepileptic drugs during pregnancy increases the incidence of these defects in the offspring by unknown mechanisms. This study discovers that glutamate signaling regulates neural plate cell proliferation and oriented migration and is necessary for neural tube formation. We demonstrate that the widely used antiepileptic drug valproic acid interferes with glutamate signaling and consequently induces neural tube defects, challenging the current hypotheses arguing that they are side effects of this antiepileptic drug that cause the increased incidence of these defects. Understanding the mechanisms of neurotransmitter signaling during neural tube formation may contribute to the identification and development of antiepileptic drugs that are safer during pregnancy. Copyright © 2018 the authors 0270-6474/18/384762-12$15.00/0.

THE REELIN RECEPTORS VLDLR AND ApoER2 REGULATE SENSORIMOTOR GATING IN MICE

PubMed Central

Barr, Alasdair M.; Fish, Kenneth N.; Markou, Athina

2007-01-01

Summary Postmortem brain loss of reelin is noted in schizophrenia patients. Accordingly, heterozygous reeler mutant mice have been proposed as a putative model of this disorder. Little is known, however, about the involvement of the two receptors for reelin, Very-Low-Density Lipoprotein Receptor (VLDLR) and Apolipoprotein E Receptor 2 (ApoER2), on pre-cognitive processes of relevance to deficits seen in schizophrenia. Thus, we evaluated sensorimotor gating in mutant mice heterozygous or homozygous for the two reelin receptors. Mutant mice lacking one of these reelin receptors were tested for prepulse inhibition (PPI) of the acoustic startle reflex prior to and following puberty, and on a crossmodal PPI task, involving the presentation of acoustic and tactile stimuli. Furthermore, because schizophrenia patients show increased sensitivity to N-methyl-D-aspartate (NMDA) receptor blockade, we assessed the sensitivity of these mice to the PPI-disruptive effects of the NMDA receptor antagonist phencyclidine. The results demonstrated that acoustic PPI did not differ between mutant and wildtype mice. However, VLDLR homozygous mice displayed significant deficits in crossmodal PPI, while ApoER2 heterozygous and homozygous mice displayed significantly increased crossmodal PPI. Both ApoER2 and VLDLR heterozygous and homozygous mice exhibited greater sensitivity to the PPI-disruptive effects of phencyclidine than wildtype mice. These results indicate that partial or complete loss of either one of the reelin receptors results in a complex pattern of alterations in PPI function that include alterations in crossmodal, but not acoustic, PPI and increased sensitivity to NMDA receptor blockade. Thus, reelin receptor function appears to be critically involved in crossmodal PPI and the modulation of the PPI response by NMDA receptors. These findings have relevance to a range of neuropsychiatric disorders that involve sensorimotor gating deficits, including schizophrenia.. PMID:17261317

Brain stem NO modulates ventilatory acclimatization to hypoxia in mice.

PubMed

El Hasnaoui-Saadani, R; Alayza, R Cardenas; Launay, T; Pichon, A; Quidu, P; Beaudry, M; Léon-Velarde, F; Richalet, J P; Duvallet, A; Favret, F

2007-11-01

The objective of our study was to assess the role of neuronal nitric oxide synthase (nNOS) in the ventilatory acclimatization to hypoxia. We measured the ventilation in acclimatized Bl6/CBA mice breathing 21% and 8% oxygen, used a nNOS inhibitor, and assessed the expression of N-methyl-d-aspartate (NMDA) glutamate receptor and nNOS (mRNA and protein). Two groups of Bl6/CBA mice (n = 60) were exposed during 2 wk either to hypoxia [barometric pressure (PB) = 420 mmHg] or normoxia (PB = 760 mmHg). At the end of exposure the medulla was removed to measure the concentration of nitric oxide (NO) metabolites, the expression of NMDA-NR1 receptor, and nNOS by real-time RT-PCR and Western blot. We also measured the ventilatory response [fraction of inspired O(2) (Fi(O(2))) = 0.21 and 0.08] before and after S-methyl-l-thiocitrulline treatment (SMTC, nNOS inhibitor, 10 mg/kg ip). Chronic hypoxia caused an increase in ventilation that was reduced after SMTC treatment mainly through a decrease in tidal volume (Vt) in normoxia and in acute hypoxia. However, the difference observed in the magnitude of acute hypoxic ventilatory response [minute ventilation (Ve) 8% - Ve 21%] in acclimatized mice was not different. Acclimatization to hypoxia induced a rise in NMDA receptor as well as in nNOS and NO production. In conclusion, our study provides evidence that activation of nNOS is involved in the ventilatory acclimatization to hypoxia in mice but not in the hypoxic ventilatory response (HVR) while the increased expression of NMDA receptor expression in the medulla of chronically hypoxic mice plays a role in acute HVR. These results are therefore consistent with central nervous system plasticity, partially involved in ventilatory acclimatization to hypoxia through nNOS.

Essential oils of culinary herbs and spices display agonist and antagonist activities at human aryl hydrocarbon receptor AhR.

PubMed

Bartoňková, Iveta; Dvořák, Zdeněk

2018-01-01

Essential oils (EOs) of culinary herbs and spices are used to flavor, color and preserve foods and drinks. Dietary intake of EOs is significant, deserving an attention of toxicologists. We examined the effects of 31 EOs of culinary herbs and spices on the transcriptional activity of human aryl hydrocarbon receptor (AhR), which is a pivotal xenobiotic sensor, having also multiple roles in human physiology. Tested EOs were sorted out into AhR-inactive ones (14 EOs) and AhR-active ones, including full agonists (cumin, jasmine, vanilla, bay leaf), partial agonists (cloves, dill, thyme, nutmeg, oregano) and antagonists (tarragon, caraway, turmeric, lovage, fennel, spearmint, star anise, anise). Major constituents (>10%) of AhR-active EOs were studied in more detail. We identified AhR partial agonists (carvacrol, ligustilide, eugenol, eugenyl acetate, thymol, ar-turmerone) and antagonists (trans-anethole, butylidine phtalide, R/S-carvones, p-cymene), which account for AhR-mediated activities of EOs of fennel, anise, star anise, caraway, spearmint, tarragon, cloves, dill, turmeric, lovage, thyme and oregano. We also show that AhR-mediated effects of some individual constituents of EOs differ from those manifested in mixtures. In conclusion, EOs of culinary herbs and spices are agonists and antagonists of human AhR, implying a potential for food-drug interactions and interference with endocrine pathways. Copyright © 2017 Elsevier Ltd. All rights reserved.

Context-Dependent Modulation of GABAAR-Mediated Tonic Currents.

PubMed

Patel, Bijal; Bright, Damian P; Mortensen, Martin; Frølund, Bente; Smart, Trevor G

2016-01-13

Tonic GABA currents mediated by high-affinity extrasynaptic GABAA receptors, are increasingly recognized as important regulators of cell and neuronal network excitability. Dysfunctional GABAA receptor signaling that results in modified tonic GABA currents is associated with a number of neurological disorders. Consequently, developing compounds to selectively modulate the activity of extrasynaptic GABAA receptors underlying tonic inhibition is likely to prove therapeutically useful. Here, we examine the GABAA receptor subtype selectivity of the weak partial agonist, 5-(4-piperidyl)isoxazol-3-ol (4-PIOL), as a potential mechanism for modulating extrasynaptic GABAA receptor-mediated tonic currents. By using recombinant GABAA receptors expressed in HEK293 cells, and native GABAA receptors of cerebellar granule cells, hippocampal neurons, and thalamic relay neurons, 4-PIOL evidently displayed differential agonist and antagonist-type profiles, depending on the extrasynaptic GABAA receptor isoforms targeted. For neurons, this resulted in differential modulation of GABA tonic currents, depending on the cell type studied, their respective GABAA receptor subunit compositions, and critically, on the ambient GABA levels. Unexpectedly, 4-PIOL revealed a significant population of relatively low-affinity γ2 subunit-containing GABAA receptors in the thalamus, which can contribute to tonic inhibition under specific conditions when GABA levels are raised. Together, these data indicate that partial agonists, such as 4-PIOL, may be useful for modulating GABAA receptor-mediated tonic currents, but the direction and extent of this modulation is strongly dependent on relative expression levels of different extrasynaptic GABAA receptor subtypes, and on the ambient GABA levels. A background level of inhibition (tonic) is important in the brain for controlling neuronal excitability. Increased levels of tonic inhibition are associated with some neurological disorders but there are no specific ligands capable of selectively reducing tonic inhibition. Here we explore the use of a GABA partial agonist as a selective chemical tool in three different brain regions. We discover that the activity of a partial agonist is heavily dependent upon the GABAA receptor subunit composition underpinning tonic inhibition, and on the ambient levels of GABA in the brain. Copyright © 2016 Patel et al.

Context-Dependent Modulation of GABAAR-Mediated Tonic Currents

PubMed Central

Patel, Bijal; Bright, Damian P.; Mortensen, Martin; Frølund, Bente

2016-01-01

Tonic GABA currents mediated by high-affinity extrasynaptic GABAA receptors, are increasingly recognized as important regulators of cell and neuronal network excitability. Dysfunctional GABAA receptor signaling that results in modified tonic GABA currents is associated with a number of neurological disorders. Consequently, developing compounds to selectively modulate the activity of extrasynaptic GABAA receptors underlying tonic inhibition is likely to prove therapeutically useful. Here, we examine the GABAA receptor subtype selectivity of the weak partial agonist, 5-(4-piperidyl)isoxazol-3-ol (4-PIOL), as a potential mechanism for modulating extrasynaptic GABAA receptor-mediated tonic currents. By using recombinant GABAA receptors expressed in HEK293 cells, and native GABAA receptors of cerebellar granule cells, hippocampal neurons, and thalamic relay neurons, 4-PIOL evidently displayed differential agonist and antagonist-type profiles, depending on the extrasynaptic GABAA receptor isoforms targeted. For neurons, this resulted in differential modulation of GABA tonic currents, depending on the cell type studied, their respective GABAA receptor subunit compositions, and critically, on the ambient GABA levels. Unexpectedly, 4-PIOL revealed a significant population of relatively low-affinity γ2 subunit-containing GABAA receptors in the thalamus, which can contribute to tonic inhibition under specific conditions when GABA levels are raised. Together, these data indicate that partial agonists, such as 4-PIOL, may be useful for modulating GABAA receptor-mediated tonic currents, but the direction and extent of this modulation is strongly dependent on relative expression levels of different extrasynaptic GABAA receptor subtypes, and on the ambient GABA levels. SIGNIFICANCE STATEMENT A background level of inhibition (tonic) is important in the brain for controlling neuronal excitability. Increased levels of tonic inhibition are associated with some neurological disorders but there are no specific ligands capable of selectively reducing tonic inhibition. Here we explore the use of a GABA partial agonist as a selective chemical tool in three different brain regions. We discover that the activity of a partial agonist is heavily dependent upon the GABAA receptor subunit composition underpinning tonic inhibition, and on the ambient levels of GABA in the brain. PMID:26758848

Differential effects of the new glucocorticoid receptor antagonist ORG 34517 and RU486 (mifepristone) on glucocorticoid receptor nuclear translocation in the AtT20 cell line.

PubMed

Peeters, B W M M; Ruigt, G S F; Craighead, M; Kitchener, P

2008-12-01

Glucocorticoid agonists bind to cytoplasmic glucocorticoid receptors (GRs) and subsequently translocate as an agonist-GR complex into the nucleus. In the nucleus the complex regulates the transcription of target genes. A number of GR antagonists (RU486, progesterone, RU40555) have also been shown to induce receptor translocation. These compounds should be regarded as partial agonists. For the nonselective progesterone receptor antagonists, RTI3021-012 and RTI3021-022, it was shown that GR antagonism is possible without the induction of GR translocation. In the present studies, the new GR antagonist, ORG 34517, was investigated for its potential to induce GR translocation and to antagonize corticosterone-induced GR translocation in the AtT20 (mouse pituitary) cell line. ORG 34517 was compared to RU486. In contrast to RU486, ORG 34517 (at doses up to 3 x 10(-7) M) did not induce GR translocation, but was able to block corticosterone (3 x 10(-8) M) induced GR translocation. ORG 34517 can be regarded as a true competitive GR antagonist without partial agonistic activities.

[Influence of activation and blockade of NMDA receptors on extinction of passive avoidance response in mice with different levels of anxiety].

PubMed

Tomilenko, R A; Dubrovina, N I

2006-03-01

Influence of agonist (D-cycloserine) and antagonist (dizocilpine) N-methyl-D-aspartate receptors on learning and extinction of passive avoidance response in medium-, high-, and low-anxious mice was studied. In medium-anxious mice, D-cycloserine (30 mg/kg) although not changing learning accelerated development of extinction, whereas dizocilpine (0.15 mg/kg), while impairing passive avoidance learning, detained the extinction. In high-anxious mice with good retrieval of memory trace and absence of extinction, D-cycloserine was ineffective, whereas dizocilpine reduced learning and promoted retention of memory trace retrieval at the generated level on extinction. In low-anxious mice, D-cycloserine impaired learning and accelerated extinction, whereas dizocilpine completely blocked learning and retention of passive avoidance response.

NMDA receptors in mouse anterior piriform cortex initialize early odor preference learning and L-type calcium channels engage for long-term memory.

PubMed

Mukherjee, Bandhan; Yuan, Qi

2016-10-14

The interactions of L-type calcium channels (LTCCs) and NMDA receptors (NMDARs) in memories are poorly understood. Here we investigated the specific roles of anterior piriform cortex (aPC) LTCCs and NMDARs in early odor preference memory in mice. Using calcium imaging in aPC slices, LTCC activation was shown to be dependent on NMDAR activation. Either D-APV (NMDAR antagonist) or nifedipine (LTCC antagonist) reduced somatic calcium transients in pyramidal cells evoked by lateral olfactory tract stimulation. However, nifedipine did not further reduce calcium in the presence of D-APV. In mice that underwent early odor preference training, blocking NMDARs in the aPC prevented short-term (3 hr) and long-term (24 hr) odor preference memory, and both memories were rescued when BayK-8644 (LTCC agonist) was co-infused. However, activating LTCCs in the absence of NMDARs resulted in loss of discrimination between the conditioned odor and a similar odor mixture at 3 hr. Elevated synaptic AMPAR expression at 3 hr was prevented by D-APV infusion but restored when LTCCs were directly activated, mirroring the behavioral outcomes. Blocking LTCCs prevented 24 hr memory and spared 3 hr memory. These results suggest that NMDARs mediate stimulus-specific encoding of odor memory while LTCCs mediate intracellular signaling leading to long-term memory.

Activation of 5-HT7 receptors reverses NMDA-R-dependent LTD by activating PKA in medial vestibular neurons.

PubMed

Li, Yan-Hai; Han, Lei; Wu, Kenneth Lap Kei; Chan, Ying-Shing

2017-09-01

The medial vestibular nucleus (MVN) is a major output station for neurons that project to the vestibulo-spinal pathway. MVN neurons show capacity for long-term depression (LTD) during the juvenile period. We investigated LTD of MVN neurons using whole-cell patch-clamp recordings. High frequency stimulation (HFS) robustly induced LTD in 90% of type B neurons in the MVN, while only 10% of type A neurons were responsive, indicating that type B neurons are the major contributors to LTD in the MVN. The neuromodulator serotonin (5-HT) is known to modulate LTD in neural circuits of the cerebral cortex and the hippocampus. We therefore aim to determine the action of 5-HT on the LTD of type B MVN neurons and elucidate the relevant 5-HT receptor subtypes responsible for its action. Using specific agonists and antagonists of 5-HT receptors, we found that selective activation of 5-HT 7 receptor in type B neurons in the MVN of juvenile (P13-16) rats completely abolished NMDA-receptor-mediated LTD in a protein kinase A (PKA)-dependent manner. Our finding that 5-HT restricts plasticity of type B MVN neurons via 5-HT 7 receptors offers a mechanism whereby vestibular tuning contributes to the maturation of the vestibulo-spinal circuit and highlights the role of 5-HT in postural control. Copyright © 2017 Elsevier Ltd. All rights reserved.

Differential profile of typical, atypical and third generation antipsychotics at human 5-HT7a receptors coupled to adenylyl cyclase: detection of agonist and inverse agonist properties.

PubMed

Rauly-Lestienne, Isabelle; Boutet-Robinet, Elisa; Ailhaud, Marie-Christine; Newman-Tancredi, Adrian; Cussac, Didier

2007-10-01

5-HT(7) receptors are present in thalamus and limbic structures, and a possible role of these receptors in the pathology of schizophrenia has been evoked. In this study, we examined binding affinity and agonist/antagonist/inverse agonist properties at these receptors of a large series of antipsychotics, i.e., typical, atypical, and third generation compounds preferentially targeting D(2) and 5-HT(1A) sites. Adenylyl cyclase (AC) activity was measured in HEK293 cells stably expressing the human (h) 5-HT(7a) receptor isoform. 5-HT and 5-CT increased cyclic adenosine monophosphate level by about 20-fold whereas (+)-8-OH-DPAT, the antidyskinetic agent sarizotan, and the novel antipsychotic compound bifeprunox exhibited partial agonist properties at h5-HT(7a) receptors stimulating AC. Other compounds antagonized 5-HT-induced AC activity with pK (B) values which correlated with their pK (i) as determined by competition binding vs [(3)H]5-CT. The selective 5-HT(7) receptor ligand, SB269970, was the most potent antagonist. For antipsychotic compounds, the following rank order of antagonism potency (pK (B)) was ziprasidone > tiospirone > SSR181507 > or = clozapine > or = olanzapine > SLV-314 > SLV-313 > or = aripiprazole > or = chlorpromazine > nemonapride > haloperidol. Interestingly, pretreatment of HEK293-h5-HT(7a) cells with forskolin enhanced basal AC activity and revealed inverse agonist properties for both typical and atypical antipsychotics as well as for aripiprazole. In contrast, other novel antipsychotics exhibited diverse 5-HT(7a) properties; SLV-313 and SLV-314 behaved as quasi-neutral antagonists, SSR181507 acted as an inverse agonist, and bifeprunox as a partial agonist, as mentioned above. In conclusion, the differential properties of third generation antipsychotics at 5-HT(7) receptors may influence their antipsychotic profile.

Mechanisms of perinatal cerebral injury in fetus and newborn.

PubMed

Delivoria-Papadopoulos, M; Mishra, O P

2000-01-01

Cerebral hypoxia in the fetus and newborn results in neonatal morbidity and mortality as well as long-term sequelae such as mental retardation, seizure disorders, and cerebral palsy. In the developing brain, determinants of susceptibility to hypoxia should include the lipid composition of the brain cell membrane, the rate of lipid peroxidation, the presence of antioxidant defenses, and the development and modulation of excitatory amino acid neurotransmitter receptors such as the N-methyl-D-aspartate (NMDA) receptor, the intracellular Ca2+, and the intranuclear Ca(2+)-dependent mechanisms. In addition to the developmental status of these cellular components, the response of these potential mechanisms to hypoxia determines the fate of the hypoxic brain cell in the developing brain. Using electron spin resonance spectroscopy of alpha-phenyl-N-tert-butyl-nitrone spin adducts, studies from our laboratory demonstrated that tissue hypoxia results in increased free radical generation in the cortex of fetal guinea pigs and newborn piglets. Pretreatment with MgSO4 significantly decreased the hypoxia-induced increase in free radical generation in the term fetal brain. We also showed that brain tissue hypoxia modifies the NMDA receptor ion-channel recognition and modulatory sites. Furthermore, a higher increase in NMDA receptor agonist-dependent Ca2+ in synaptosomes was demonstrated. The increase in intracellular Ca2+ may activate several enzymatic pathways such as phospholipase A2 and metabolism of archidonic acid by cyclooxygenase and lipoxygenase, conversion of xanthine dehydrogenase to xanthine oxidase by proteases, and activation of nitric oxide synthase. Using inhibitors of each of these enzymes such as cyclooxygenase (indomethacin), lipoxygenase (nordihydroguaiaretic acid), xanthine oxidase (allopurinol), and nitric oxide synthase (N-nitro-L-arginine), studies have shown that these enzyme reactions result in oxygen free radical generation, membrane peroxidation, and cell membrane dysfunction in the hypoxic brain. Specifically, generation of nitric oxide free radicals during hypoxia may lead to nitration and nitrosylation of specific membrane proteins and receptors, resulting in dysfunction of receptors and enzymes. We conclude that hypoxia-induced modification of the NMDA receptor leading to increased intracellular Ca2+ results in free radical generation and cell injury. We suggest that during hypoxia the increased intracellular Ca2+ may lead to increased intranuclear Ca2+ concentration and alter nuclear events including transcription of specific apoptotic genes and activation of endonucleases, resulting in programmed cell death.

[Effect of (+/-)-pindolol on the central 5-HT1A receptor by the use of in vivo microdialysis and hippocampal slice preparations].

PubMed

Tsuji, Keiichiro

2002-06-01

Although it is suggested that (+/-)-pindolol, a beta-adrenergic/5-HT1A receptor antagonist, may enhance the efficacy of selective serotonin reuptake inhibitors (SSRI), the results of double-blind studies are contradictory and recent animal studies suggest that (+/-)-pindolol may act as a partial agonist to the 5-HT1A receptor. In this study we have investigated the effect of (+/-)-pindolol on both pre- and postsynaptic 5-HT1A receptors using in vivo microdialysis and hippocampal slice preparations. (+/-)-pindolol and flesinoxan, a 5-HT1A receptor full agonist, significantly decreased the extracellular levels of 5-HT in the raphe and prefrontal cortex. The 5-HT and other 5-HT1A receptor agonists, flesinoxan and 8-hydroxy-2- (di-n-propylamino)tetralon (8-OH-DPAT), significantly decreased the population excitatory postsynaptic potential (EPSP) in the CA3-CA1 excitatory synapse in a dose-dependent manner. The effect of 5-HT and other 5-HT1A receptor agonists accompanied the increase in paired-pulse facilitation (ppf) induced by short-interval two stimuli and were reversed by the coadministration of the 5-HT1A receptor agonist, NAN-190, but not by (+/-)-pindolol. (+/-)-pindolol also suppressed the EPSP, but this effect was not reversed by NAN-190. These results suggest that (+/-)-pindolol acts as a partial agonist to the somatodendritic 5-HT1A receptor in the raphe, whereas it may have no action on the postsynaptic 5-HT1A receptor in the hippocampus.

Effects of the α subunit on imidacloprid sensitivity of recombinant nicotinic acetylcholine receptors

PubMed Central

Matsuda, K; Buckingham, S D; Freeman, J C; Squire, M D; Baylis, H A; Sattelle, D B

1998-01-01

Imidacloprid is a new insecticide with selective toxicity for insects over vertebrates. Recombinant (α4β2) chicken neuronal nicotinic acetylcholine receptors (AChRs) and a hybrid nicotinic AChR formed by co-expression of a Drosophila melanogaster neuronal α subunit (SAD) with the chicken β2 subunit were heterologously expressed in Xenopus oocytes by nuclear injection of cDNAs. The agonist actions of imidacloprid and other nicotinic AChR ligands ((+)-epibatidine, (−)-nicotine and acetylcholine) were compared on both recombinant nicotinic AChRs by use of two-electrode, voltage-clamp electrophysiology. Imidacloprid alone of the 4 agonists behaved as a partial agonist on the α4β2 receptor; (+)-epibatidine, (−)-nicotine and acetylcholine were all full, or near full, agonists. Imidacloprid was also a partial agonist of the hybrid Drosophila SAD chicken β2 receptor, as was (−)-nicotine, whereas (+)-epibatidine and acetylcholine were full agonists. The EC50 of imidacloprid was decreased by replacing the chicken α4 subunit with the Drosophila SAD α subunit. This α subunit substitution also resulted in an increase in the EC50 for (+)-epibatidine, (−)-nicotine and acetylcholine. Thus, the Drosophila (SAD) α subunit contributes to the greater apparent affinity of imidacloprid for recombinant insect/vertebrate nicotinic AChRs. Imidacloprid acted as a weak antagonist of ACh-mediated responses mediated by SADβ2 hybrid receptors and as a weak potentiator of ACh responses mediated by α4β2 receptors. This suggests that imidacloprid has complex effects upon these recombinant receptors, determined at least in part by the α subunit. PMID:9504393

Positive allosteric modulators as an approach to nicotinic acetylcholine receptor- targeted therapeutics: advantages and limitations

PubMed Central

Williams, Dustin K.; Wang, Jingyi; Papke, Roger L.

2011-01-01

Neuronal nicotinic acetylcholine receptors (nAChR), recognized targets for drug development in cognitive and neuro-degenerative disorders, are allosteric proteins with dynamic interconversions between multiple functional states. Activation of the nAChR ion channel is primarily controlled by the binding of ligands (agonists, partial agonists, competitive antagonists) at conventional agonist binding sites, but is also regulated in either negative or positive ways by the binding of ligands to other modulatory sites. In this review, we discuss models for the activation and desensitization of nAChR, and the discovery of multiple types of ligands that influence those processes in both heteromeric nAChR, such as the high affinity nicotine receptors of the brain, and homomeric α7-type receptors. In recent years, α7 nAChRs have been identified as a potential target for therapeutic indications leading to the development of α7-selective agonists and partial agonists. However, unique properties of α7 nAChR, including low probability of channel opening and rapid desensitization, may limit the therapeutic usefulness of ligands binding exclusively to conventional agonist binding sites. New enthusiasm for the therapeutic targeting of α7 has come from the identification of α7-selective positive allosteric modulators (PAMs) that work effectively on the intrinsic factors that limit α7 ion channel activation. While these new drugs appear promising for therapeutic development, we also consider potential caveats and possible limitations for their use, including PAM-insensitive forms of desensitization and cytotoxicity issues. PMID:21575610

Positive allosteric modulators as an approach to nicotinic acetylcholine receptor-targeted therapeutics: advantages and limitations.

PubMed

Williams, Dustin K; Wang, Jingyi; Papke, Roger L

2011-10-15

Neuronal nicotinic acetylcholine receptors (nAChR), recognized targets for drug development in cognitive and neuro-degenerative disorders, are allosteric proteins with dynamic interconversions between multiple functional states. Activation of the nAChR ion channel is primarily controlled by the binding of ligands (agonists, partial agonists, competitive antagonists) at conventional agonist binding sites, but is also regulated in either negative or positive ways by the binding of ligands to other modulatory sites. In this review, we discuss models for the activation and desensitization of nAChR, and the discovery of multiple types of ligands that influence those processes in both heteromeric nAChR, such as the high-affinity nicotine receptors of the brain, and homomeric α7-type receptors. In recent years, α7 nAChRs have been identified as a potential target for therapeutic indications leading to the development of α7-selective agonists and partial agonists. However, unique properties of α7 nAChR, including low probability of channel opening and rapid desensitization, may limit the therapeutic usefulness of ligands binding exclusively to conventional agonist binding sites. New enthusiasm for the therapeutic targeting of α7 has come from the identification of α7-selective positive allosteric modulators (PAMs) that work effectively on the intrinsic factors that limit α7 ion channel activation. While these new drugs appear promising for therapeutic development, we also consider potential caveats and possible limitations for their use, including PAM-insensitive forms of desensitization and cytotoxicity issues. Copyright © 2011 Elsevier Inc. All rights reserved.

Molecular determinants for the high constitutive activity of the human histamine H4 receptor: functional studies on orthologues and mutants

PubMed Central

Wifling, D; Löffel, K; Nordemann, U; Strasser, A; Bernhardt, G; Dove, S; Seifert, R; Buschauer, A

2015-01-01

Background and Purpose Some histamine H4 receptor ligands act as inverse agonists at the human H4 receptor (hH4R), a receptor with exceptionally high constitutive activity, but as neutral antagonists or partial agonists at the constitutively inactive mouse H4 receptor (mH4R) and rat H4 receptor (rH4R). To study molecular determinants of constitutive activity, H4 receptor reciprocal mutants were constructed: single mutants: hH4R-F169V, mH4R-V171F, hH4R-S179A, hH4R-S179M; double mutants: hH4R-F169V+S179A, hH4R-F169V+S179M and mH4R-V171F+M181S. Experimental Approach Site-directed mutagenesis with pVL1392 plasmids containing hH4 or mH4 receptors were performed. Wild-type or mutant receptors were co-expressed with Gαi2 and Gβ1γ2 in Sf9 cells. Membranes were studied in saturation and competition binding assays ([3H]-histamine), and in functional [35S]-GTPγS assays with inverse, partial and full agonists of the hH4 receptor. Key Results Constitutive activity decreased from the hH4 receptor via the hH4R-F169V mutant to the hH4R-F169V+S179A and hH4R-F169V+S179M double mutants. F169 alone or in concert with S179 plays a major role in stabilizing a ligand-free active state of the hH4 receptor. Partial inverse hH4 receptor agonists like JNJ7777120 behaved as neutral antagonists or partial agonists at species orthologues with lower or no constitutive activity. Some partial and full hH4 receptor agonists showed decreased maximal effects and potencies at hH4R-F169V and double mutants. However, the mutation of S179 in the hH4 receptor to M as in mH4 receptor or A as in rH4 receptor did not significantly reduce constitutive activity. Conclusions and Implications F169 and S179 are key amino acids for the high constitutive activity of hH4 receptors and may also be of relevance for other constitutively active GPCRs. Linked Articles This article is part of a themed issue on Histamine Pharmacology Update published in volume 170 issue 1. To view the other articles in this issue visit http://onlinelibrary.wiley.com/doi/10.1111/bph.2013.170.issue-1/issuetoc PMID:24903527

Altered hippocampal plasticity by prenatal kynurenine administration, kynurenine-3-monoxygenase (KMO) deletion or galantamine.

PubMed

Forrest, C M; McNair, K; Pisar, M; Khalil, O S; Darlington, L G; Stone, T W

2015-12-03

Glutamate receptors sensitive to N-methyl-D-aspartate (NMDA) are involved in embryonic brain development but their activity may be modulated by the kynurenine pathway of tryptophan metabolism which includes an agonist (quinolinic acid) and an antagonist (kynurenic acid) at these receptors. Our previous work has shown that prenatal inhibition of the pathway produces abnormalities of brain development. In the present study kynurenine and probenecid (both 100mg/kg, doses known to increase kynurenic acid levels in the brain) were administered to female Wistar rats on embryonic days E14, E16 and E18 of gestation and the litter was allowed to develop to post-natal day P60. Western blotting revealed no changes in hippocampal expression of several proteins previously found to be altered by inhibition of the kynurenine pathway including the NMDA receptor subunits GluN1, GluN2A and GluN2B, as well as doublecortin, Proliferating Cell Nuclear Antigen (PCNA), sonic hedgehog and unco-ordinated (unc)-5H1 and 5H3. Mice lacking the enzyme kynurenine-3-monoxygenase (KMO) also showed no changes in hippocampal expression of several of these proteins or the 70-kDa and 100-kDa variants of Disrupted in Schizophrenia-1 (DISC1). Electrical excitability of pyramidal neurons in the CA1 region of hippocampal slices was unchanged, as was paired-pulse facilitation and inhibition. Long-term potentiation was decreased in the kynurenine-treated rats and in the KMO(-/-) mice, but galantamine reversed this effect in the presence of nicotinic receptor antagonists, consistent with evidence that it can potentiate glutamate at NMDA receptors. It is concluded that interference with the kynurenine pathway in utero can have lasting effects on brain function of the offspring, implying that the kynurenine pathway is involved in the regulation of early brain development. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

Altered hippocampal plasticity by prenatal kynurenine administration, kynurenine-3-monoxygenase (KMO) deletion or galantamine

PubMed Central

Forrest, C.M.; McNair, K.; Pisar, M.; Khalil, O.S.; Darlington, L.G.; Stone, T.W.

2015-01-01

Glutamate receptors sensitive to N-methyl-d-aspartate (NMDA) are involved in embryonic brain development but their activity may be modulated by the kynurenine pathway of tryptophan metabolism which includes an agonist (quinolinic acid) and an antagonist (kynurenic acid) at these receptors. Our previous work has shown that prenatal inhibition of the pathway produces abnormalities of brain development. In the present study kynurenine and probenecid (both 100 mg/kg, doses known to increase kynurenic acid levels in the brain) were administered to female Wistar rats on embryonic days E14, E16 and E18 of gestation and the litter was allowed to develop to post-natal day P60. Western blotting revealed no changes in hippocampal expression of several proteins previously found to be altered by inhibition of the kynurenine pathway including the NMDA receptor subunits GluN1, GluN2A and GluN2B, as well as doublecortin, Proliferating Cell Nuclear Antigen (PCNA), sonic hedgehog and unco-ordinated (unc)-5H1 and 5H3. Mice lacking the enzyme kynurenine-3-monoxygenase (KMO) also showed no changes in hippocampal expression of several of these proteins or the 70-kDa and 100-kDa variants of Disrupted in Schizophrenia-1 (DISC1). Electrical excitability of pyramidal neurons in the CA1 region of hippocampal slices was unchanged, as was paired-pulse facilitation and inhibition. Long-term potentiation was decreased in the kynurenine-treated rats and in the KMO(−/−) mice, but galantamine reversed this effect in the presence of nicotinic receptor antagonists, consistent with evidence that it can potentiate glutamate at NMDA receptors. It is concluded that interference with the kynurenine pathway in utero can have lasting effects on brain function of the offspring, implying that the kynurenine pathway is involved in the regulation of early brain development. PMID:26365611

Characterization of Human Hippocampal Neural Stem/Progenitor Cells and Their Application to Physiologically Relevant Assays for Multiple Ionotropic Glutamate Receptors.

PubMed

Fukushima, Kazuyuki; Tabata, Yoshikuni; Imaizumi, Yoichi; Kohmura, Naohiro; Sugawara, Michiko; Sawada, Kohei; Yamazaki, Kazuto; Ito, Masashi

2014-09-01

The hippocampus is an important brain region that is involved in neurological disorders such as Alzheimer disease, schizophrenia, and epilepsy. Ionotropic glutamate receptors-namely,N-methyl-D-aspartate (NMDA) receptors (NMDARs), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors (AMPARs), and kainic acid (KA) receptors (KARs)-are well known to be involved in these diseases by mediating long-term potentiation, excitotoxicity, or both. To predict the therapeutic efficacy and neuronal toxicity of drug candidates acting on these receptors, physiologically relevant systems for assaying brain region-specific human neural cells are necessary. Here, we characterized the functional differentiation of human fetal hippocampus-derived neural stem/progenitor cells-namely, HIP-009 cells. Calcium rise assay demonstrated that, after a 4-week differentiation, the cells responded to NMDA (EC50= 7.5 ± 0.4 µM; n= 4), AMPA (EC50= 2.5 ± 0.1 µM; n= 3), or KA (EC50= 33.5 ± 1.1 µM; n= 3) in a concentration-dependent manner. An AMPA-evoked calcium rise was observed in the absence of the desensitization inhibitor cyclothiazide. In addition, the calcium rise induced by these agonists was inhibited by antagonists for each receptor-namely, MK-801 for NMDA stimulation (IC50= 0.6 ± 0.1 µM; n= 4) and NBQX for AMPA and KA stimulation (IC50= 0.7 ± 0.1 and 0.7 ± 0.03 µM, respectively; n= 3). The gene expression profile of differentiated HIP-009 cells was distinct from that of undifferentiated cells and closely resembled that of the human adult hippocampus. Our results show that HIP-009 cells are a unique tool for obtaining human hippocampal neural cells and are applicable to systems for assay of ionotropic glutamate receptors as a physiologically relevant in vitro model. © 2014 Society for Laboratory Automation and Screening.

The NH2-terminus of substance P modulates NMDA-induced activity in the mouse spinal cord.

PubMed

Hornfeldt, C S; Sun, X; Larson, A A

1994-05-01

Excitatory amino acids (EAAs) and substance P are believed to transmit nociceptive information in the spinal cord. As substance P NH2-terminal fragments can modulate non-NMDA EAA-mediated activity, we examined the effects of substance P fragments to ascertain whether the COOH- or NH2-terminus of substance P modulates the actions of NMDA in the spinal cord. NMDA activity was measured by the intensity of behaviors produced by NMDA (0.2 nmol) administered intrathecally in the mouse. The NMDA response was attenuated after pretreatment with either substance P (22.5 pmol, 30 min) or the NH2-terminal fragment of substance P, SP-(1-7). Pretreatment with the COOH-terminal fragment SP-(5-11) (22.5 pmol, 30 min), a neurokinin ligand, had no effect on NMDA-induced behaviors, suggesting that the inhibitory effect of substance P is caused by the NH2-terminus. Pretreatment with D-Pro2,D-Phe7 substance P-(1-7), a SP-(1-7) antagonist, potentiated NMDA activity, suggesting a tonic inhibitory effect of the substance P NH2-terminus. Desensitization to NMDA typically develops when NMDA is injected at 2 min intervals. While pretreatment with SP-(1-7) inhibited NMDA, coadministration of SP-(1-7) (22.5 pmol), with the first of four injections of NMDA, first inhibited but then potentiated responses to each challenge with NMDA. Coadministration of the same dose of SP-(1-7) with the fourth injection of NMDA immediately potentiated the response to NMDA.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological properties of excitatory amino acid induced changes in extracellular calcium concentration in rat hippocampal slices.

PubMed

Arens, J; Stabel, J; Heinemann, U

1992-01-01

We have studied extracellular ionic changes induced by iontophoretic application of excitatory amino acids in rat hippocampal slices. In contrast to kinetics of changes in [Ca2+]o, kinetics of changes in [K+]o, [Na+]o, [Cl-]o as well as in extracellular space size were comparable for different glutamate receptor agonists. Thus, alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA), quisqualate (quis), and kainate caused reductions in [Ca2+]o followed by an increase of [Ca2+]o above baseline, whereas glutamate, aspartate, N-methyl-D-aspartate (NMDA), and DL-homocysteic acid caused only reductions in [Ca2+]o. After blocking the NMDA receptors with ketamine and 2-amino-5- phosphonovaleric acid (2-APV), glutamate-induced decreases in [Ca2+]o were followed by an overshoot. Reduction of the transmembrane Na+ gradient by lowering [Na+]o, blocking of the Na(+)-K+ ATPase by lowering [K+]o, and application of ouabain blocked the overshoots after quis application, whereas vanadate, a blocker of the Ca(2+)-Mg2+ ATPase, had no effects. Lithium enhanced the reductions in [Ca2+]o and blocked the overshoots. Amiloride also reduced the overshoots. All organic Ca2+ entry blockers diminished reductions of [Ca2+]o but increased the overshoots. Inorganic Ca2+ antagonists had variable effects. Ni2+ had similar effects as the organic Ca2+ entry blockers while Cd2+ reduced both the [Ca2+]o decreases as well as the subsequent overshoots. Co2+ had initially a similar action as Ni2+. With prolonged application, [Ca2+]o decreases became augmented and, during wash, overshoots could no longer be elicited. We suggest that the overshoots in [Ca2+]o are due to a combined effect of extracellular space shrinkage and activation of the Na+/Ca2+ exchangers. This would imply that NMDA receptor activation blocks extrusion of Ca2+ from the cells. We tested the hypothesis that quis-induced intracellular Ca2+ release and extrusion of Ca2+ from the cells contributed to the overshoots. Dantrolene was without effect on the quis-induced signals, while ryanodine reduced the overshoots. Caffeine on the other hand diminished the [Ca2+]o decreases with no effects on the overshoots. To test for possible second messenger routes by which NMDA receptor activation might slow Ca2+ extrusion from cells, we investigated the effects of arachidonic acid and N-monomethyl-D- arginine on the quis-induced signals. While these agents reduced decreases in [Ca2+]o, they had no clear effects on the overshoots. Thus a possible route by which NMDA receptor activation may affect Ca2+ extrusion from cells has still to be elucidated.

Buprenorphine: revisiting the efficacy of transdermal delivery system.

PubMed

Kitzmiller, Joseph P; Barnett, Christopher J; Steiner, Nathan S; Stoicea, Nicoleta; Kamar, Nawal; Luzum, Jasmine A; Mikulik, Eduard; Bergese, Sergio D

2015-01-01

Buprenorphine is a lipid-soluble pharmaceutic used in the management of chronic pain. It is a partial agonist at μ-opioid receptors, an antagonist at κ-opioid receptors, an agonist at δ-opioid receptors and a partial agonist at ORL-1 (nociceptin) receptors. An extensive literature search, including Google Scholar and Pubmed database, was conducted. Terms including and associated to 'efficacy of transdermal buprenorphine' were utilized to procure contemporary research articles in order to evaluate and compare the transdermal buprenorphine patch to commonly used traditional pain management medications. Transdermal buprenorphine has demonstrated better efficacy than conventional pain management pharmacotherapies. Side effects were similar to those associated with other opioids and included headache, dizziness, somnolence, constipation, dry mouth, nausea, vomiting, pruritus and erythema. Similar to transdermal delivery systems used with other medication, transdermal buprenorphine was associated with application-site pruritus and application-site reactions. Transdermal buprenorphine has significant potential for managing chronic pain. In addition to increased convenience and efficacy, advantages of transdermal buprenorphine include decreased tolerance and decreased withdrawal.

D-cycloserine combined with cue exposure therapy fails to attenuate subjective and physiological craving in cocaine dependence.

PubMed

Santa Ana, Elizabeth J; Prisciandaro, James J; Saladin, Michael E; McRae-Clark, Aimee L; Shaftman, Stephanie R; Nietert, Paul J; Brady, Kathleen T

2015-04-01

Based on preclinical studies showing that the partial N-methyl-D-aspartate (NMDA) agonist D-cycloserine (DCS) facilitates extinction of cocaine self-administration and cocaine-induced conditioned place preference, we evaluated whether 50 mg of DCS would reduce craving to cocaine cues when combined with cue exposure (CE) in cocaine dependent humans. In this double-blind placebo-controlled pilot study, 47 cocaine dependent participants were randomized to DCS or placebo (PBO), plus CE. Participants received DCS or PBO 30 minutes prior to two CE sessions, conducted one day apart. Craving and heart rate was assessed prior to CE sessions, during CE trials, and after CE trials. These measures were assessed again at a 1-week follow-up (session 3) after the second CE session. DCS failed to significantly attenuate cocaine cue reactivity based on subjective craving and physiological reactivity (heart rate) compared to PBO. The CE protocol, consisting of repeated exposure to drug cues combined with skills training, resulted in extinction to cocaine cues as suggested by decreased craving within and between sessions in both treatment conditions. All participants exhibited elevated heart rate with repeated exposures, demonstrating a potentiation in heart rate between sessions. 50 mg of DCS may not be effective for extinguishing reactivity to drug cues for individuals with cocaine dependence. Future studies examining the effect of DCS on facilitating extinction to drug cues should examine variations in cue exposure length, number of CE presentations, and timing of DCS dose administration prior to cue exposures, which may differentially impact drug cue reactivity. © American Academy of Addiction Psychiatry.

Intra-hippocampal D-cycloserine rescues decreased social memory, spatial learning reversal, and synaptophysin levels in aged rats.

PubMed

Portero-Tresserra, Marta; Martí-Nicolovius, Margarita; Tarrés-Gatius, Mireia; Candalija, Ana; Guillazo-Blanch, Gemma; Vale-Martínez, Anna

2018-05-01

Aging is characterized by a decrease in N-methyl-D-aspartate receptors (NMDARs) in the hippocampus, which might be one of the factors involved in the age-dependent cognitive decline. D-Cycloserine (DCS), a partial agonist of the NMDAR glycine recognition site, could improve memory deficits associated to neurodegenerative disorders and cognitive deficits observed in normal aging. The aim of the present study was to explore whether DCS would reverse age-dependent memory deficits and decreases in NMDA receptor subunits (GluN1, GluN2A, and GluN2B) and the presynaptic protein synaptophysin in Wistar rats. We investigated the effects of pre-training infusions of DCS (10 μg/hemisphere) in the ventral hippocampus on two hippocampal-dependent learning tasks, the social transmission of food preference (STFP), and the Morris water maze (MWM). The results revealed that infusions of DCS administered before the acquisition sessions rescued deficits in the STFP retention and MWM reversal learning in old rats. DCS also significantly increased the hippocampal levels of synaptophysin in old rats, which correlated with STFP and MWM performance in all tests. Moreover, although the levels of the GluN1 subunit correlated with the MWM acquisition and reversal, DCS did not enhance the expression of such synaptic protein. The present behavioral results support the role of DCS as a cognitive enhancer and suggest that enhancing the function of NMDARs and synaptic plasticity in the hippocampus may be related to improvement in social memory and spatial learning reversal in aged animals.

Characterization of ionotropic glutamate receptors in human lymphocytes

PubMed Central

Lombardi, Grazia; Dianzani, Chiara; Miglio, Gianluca; Canonico, Pier Luigi; Fantozzi, Roberto

2001-01-01

The effect of L-glutamate (Glu) on human lymphocyte function was studied by measuring anti-CD3 monoclonal antibody (mAb) or phytohaemagglutinin (PHA)-induced intracellular Ca2+ ([Ca2+]i) rise (Fura-2 method), and cell proliferation (MTT assay). Glu (0.001 – 100 μM) did not modify basal lymphocyte [Ca2+]i, but significantly potentiated the effects of anti-CD3 mAb or PHA. Maximal [Ca2+]i rises over resting cells were: 165±8 and 247±10 nM at 3.0×10−2 mg ml−1 anti-CD3 mAb; 201±4 and 266±9 nM at 5.0×10−2 mg ml−1 PHA, in the absence or presence of 1 μM Glu, respectively. The Glu effect showed a bell-shape concentration-dependent relationship, with a maximum (+90±3% for anti-CD3 mAb and +57±2% for PHA over Glu-untreated cells) at 1 μM. Non-NMDA receptor agonists (1 μM) showed a greater efficacy (+76±2% for (S)-AMPA; +78±4% for KA), if compared to NMDA (+46±2%), or Glu itself. Ionotropic Glu receptor antagonists completely inhibited the effects of the corresponding specific receptor agonists (1 μM). The IC50 values calculated were: 0.9 μM for D-AP5; 0.6 μM for (+)-MK801; 0.3 μM for NBQX. Both NBQX and KYNA were able to abolish Glu effect. The IC50s calculated were: 3.4 μM for NBQX; 0.4 μM for KYNA. Glu (0.1 – 1 mM) did not change the resting cell proliferation, whereas Glu (1 mM) significant inhibited (−27±4%) PHA (1.0×10−2 mg ml−1)-induced lymphocyte proliferation at 72 h. In conclusion, human lymphocytes express ionotropic Glu receptors functionally operating as modulators of cell activation. PMID:11454668

Interplay between non-NMDA and NMDA receptor activation during oscillatory wave propagation: Analyses of caffeine-induced oscillations in the visual cortex of rats.

PubMed

Yoshimura, Hiroshi; Sugai, Tokio; Kato, Nobuo; Tominaga, Takashi; Tominaga, Yoko; Hasegawa, Takahiro; Yao, Chenjuan; Akamatsu, Tetsuya

2016-07-01

Generation and propagation of oscillatory activities in cortical networks are important features of the brain. However, many issues related to oscillatory phenomena are unclear. We previously reported neocortical oscillation following caffeine treatment of rat brain slices. Input to the primary visual cortex (Oc1) generates N-methyl-d-aspartate (NMDA) receptor-dependent oscillations, and we proposed that the oscillatory signals originate in the secondary visual cortex (Oc2). Because non-NMDA and NMDA receptors cooperate in synaptic transmission, non-NMDA receptors may also play an important role in oscillatory activities. Here we investigated how non-NMDA receptor activities contribute to NMDA receptor-dependent oscillations by using optical recording methods. After induction of stable oscillations with caffeine application, blockade of NMDA receptors abolished the late stable oscillatory phase, but elicited 'hidden' non-NMDA receptor-dependent oscillation during the early depolarizing phase. An interesting finding is that the origin of the non-NMDA receptor-dependent oscillation moved from the Oc1, during the early phase, toward the origin of the NMDA receptor-dependent oscillation that is fixed in the Oc2. In addition, the frequency of the non-NMDA receptor-dependent oscillation was higher than that of the NMDA receptor-dependent oscillation. Thus, in one course of spatiotemporal oscillatory activities, the relative balance in receptor activities between non-NMDA and NMDA receptors gradually changes, and this may be due to the different kinetics of the two receptor types. These results suggest that interplay between the two receptor types in the areas of Oc1 and Oc2 may play an important role in oscillatory signal communication. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effect of thiopental sodium on N-methyl-D-aspartate-gated currents.

PubMed

Liu, Hongliang; Dai, Tijun; Yao, Shanglong

2006-05-01

N-methyl-D-aspartate (NMDA) receptors in the prefrontal cortex (PFC) are closely related with the excitability of pyramidal neurons and PFC function. As the effect of thiopental sodium on the central nervous system may partly result from the inhibition of PFC NMDA receptors, we investigated the effect of thiopental sodium with different concentrations on NMDA-gated currents in acutely dissociated rat PFC pyramidal neurons. We sought to determine whether thiopental sodium inhibits NMDA receptor function. Three to four week old male Sprague-Dawley rats were sacrificed and the PFC was dissected. Pyramidal neurons from the PFC were prepared and standard whole-cell patch clamp recordings were performed. Escalating concentrations from 3-1000 microM NMDA were applied 100 microm from the pyramidal cells, and the concentration in the effect compartment related to 50% effect (EC50) of NMDA was determined for the ensuing experiments. One hundred microM NMDA alone (control) or NMDA with different concentrations (10-1000 microM) of thiopental sodium were applied. After the inhibitory concentration, in 50% of NMDA effect (IC50) of thiopental sodium was established this IC50 and NMDA 3-1000 microM were applied 100 microm from the pyramidal cells. The EC50 value of NMDA under the effect of IC50 thiopental sodium was determined. N-methyl-D-aspartate induced inward currents in a concentration-dependent manner, which were completely antagonized by 50 microM AP5. The maximal amplitude of NMDA-induced current was 1.15 +/- 0.27 nA. The EC50 of NMDA was 53.6 +/- 12.4 microM. The NMDA (100 microM)-gated current was inhibited by thiopental sodium in a concentration-dependent manner, and the IC50 of thiopental sodium was 33.6 +/- 6.1 microM. Under the effect of 33.6 microM thiopental sodium, the maximal amplitude of NMDA-induced current was 0.87 +/- 0.17 nA. The concentration-response curve of NMDA was shifted rightwards. The EC50 of NMDA was 128 +/- 15 microM, which was greater than that of NMDA without thiopental sodium (P < 0.01). Thiopental sodium decreases NMDA-gated currents in acutely dissociated rat prefrontal cortical pyramidal neurons in a concentration-dependent manner.

Activation of Cyclic AMP Synthesis by Full and Partial Beta-Adrenergic Receptor Agonists in Chicken Skeletal Muscle Cells

NASA Technical Reports Server (NTRS)

Young, R. B.; Bridge, K. Y.

2003-01-01

Several beta-adrenergic receptor (bAR) agonists are known to cause hypertrophy of skeletal muscle tissue. Accordingly, five bAR agonists encompassing a range in activity from strong to weak were evaluated for their ability to stimulate CAMP accumulation in embryonic chicken skeletal muscle cells in culture. Two strong agonists (epinephrine and isoproterenol), one moderate agonist (albuterol), and two weak agonists known to cause hypertrophy in animals (clenbuterol and cimaterol) were studied. Dose response curves were determined over six orders of magnitude in concentration for each agonist, and values were determined for their maximum stimulation of CAMP synthesis rate (Bmax) and the agonist concentration at which 50% stimulation of CAMP synthesis (EC50) occurred. Bmax values decreased in the following order: isoproterenol, epinephrine, albuterol, cimaterol, clenbuterol. Cimaterol and clenbuterol at their Bmax concentrations were approximately 15-fold weaker than isoproterenol in stimulating the rate of CAMP synthesis. When cimaterol and clenbuterol were added to culture media at concentrations known to cause significant muscle hypertrophy in animals, there was no detectable effect on stimulation of CAMP synthesis. Finally, these same levels of cimaterol and clenbuterol did not antagonize the stimulation of CAMP by either epinephrine or isoproterenol.

Effects of kappa opioid agonists alone and in combination with cocaine on heart rate and blood pressure in conscious squirrel monkeys.

PubMed

Schindler, Charles W; Graczyk, Zofi; Gilman, Joanne P; Negus, S Stevens; Bergman, Jack; Mello, Nancy K; Goldberg, Steven R

2007-12-08

As kappa agonists have been proposed as treatments for cocaine abuse, the cardiovascular effects of the kappa opioid receptor agonists ethylketocyclazocine (EKC) and enadoline were investigated in conscious squirrel monkeys. Both EKC and enadoline increased heart rate with little effect on blood pressure. This effect appeared to be specific for kappa receptors as the mu opioid agonist morphine did not mimic the effects of the kappa agonists. The opioid antagonist naltrexone, at a dose of 1.0 mg/kg, blocked the effect of EKC. An action at both central and peripheral receptors may be responsible for the heart rate increase following kappa agonist treatment. The ganglionic blocker chlorisondamine partially antagonized the effect of EKC on heart rate, suggesting central involvement, while the peripherally-acting agonist ICI 204,448 ((+/-)-1-[2,3- (Dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride) also increased heart rate, supporting a peripheral site of action. When given in combination with cocaine, EKC produced effects that were sub-additive, suggesting that the kappa agonists may be used safely as cocaine abuse treatments.

Glutaric Acid-Mediated Apoptosis in Primary Striatal Neurons

PubMed Central

Tian, Fengyan; Fu, Xi; Gao, Jinzhi; Ying, Yanqin; Hou, Ling; Liang, Yan; Ning, Qin; Luo, Xiaoping

2014-01-01

Glutaric acid (GA) has been implicated in the mechanism of neurodegeneration in glutaric aciduria type I. In the present study, the potential cytotoxic effects of GA (0.1~50 mM for 24~96 h) were examined in cultured primary rat striatal neurons. Results showed increase in the number of cells labeled by annexin-V or with apoptotic features shown by Hoechst/PI staining and transmission electron microscopy (TEM) and upregulation of the expression of mRNA as well as the active protein fragments caspase 3, suggesting involvement of the caspase 3-dependent apoptotic pathway in GA-induced striatal neuronal death. This effect was in part suppressed by the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 but not the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) antagonist 6-cyano-7-nitroquinoxalone-2,3-dione (CNQX). Thus, GA may trigger neuronal damage partially through apoptotic pathway and via activation of NMDA receptors in cultured primary striatal neurons. PMID:24900967

Update on the mechanism of action of antiepileptic drugs.

PubMed

Meldrum, B S

1996-01-01

Novel antiepileptic drugs (AEDs) are thought to act on voltage-sensitive ion channels, on inhibitory neurotransmission or on excitatory neurotransmission. Two successful examples of rational AED design that potentiate GABA-mediated inhibition are vigabatrin (VGB) by irreversible inhibition of GABA-transaminase, and tiagabine (TGB) by blocking GABA uptake. Lamotrigine (LTG) prolongs inactivation of voltage-dependent sodium channels. The anticonvulsant action of remacemide (RCM) is probably largely due to blockade of NMDA receptors and prolonged inactivation of sodium channels induced by its desglycinated metabolite. Felbamate (FBM) apparently blocks NMDA receptors, potentiates GABA-mediated responses, blocks L-type calcium channels, and possibly also prolongs sodium channel inactivation. Similarly, topiramate (TPM) has multiple probable sites of action, including sodium channels, GABA receptors, and glutamate (AMPA) receptors. Gabapentin (GBP) apparently has a completely novel type of action, probably involving potentiation of GABA-mediated inhibition and possibly also inactivation of sodium channels. The therapeutic advantages of the novel AEDs are as yet only partially explained by our present understanding of their mechanisms of action.

Partial agonist clonidine mediates alpha(2)-AR subtypes specific regulation of cAMP accumulation in adenylyl cyclase II transfected DDT1-MF2 cells.

PubMed

Limon-Boulez, I; Bouet-Alard, R; Gettys, T W; Lanier, S M; Maltier, J P; Legrand, C

2001-02-01

alpha2-Adrenergic receptor (alpha(2)-AR) activation in the pregnant rat myometrium at midterm potentiates beta(2)-AR stimulation of adenylyl cyclase (AC) via Gbetagamma regulation of the type II isoform of adenylyl cyclase. However, at term, alpha(2)-AR activation inhibits beta(2)-AR stimulation of AC. This phenomenon is associated with changes in alpha(2)-AR subtype expression (midterm alpha(2A/D)-AR > alpha(2B)-AR; term alpha(2B) >or =alpha(2A/D)-AR), without any change in ACII mRNA, suggesting that alpha(2A/D)- and alpha(2B)-AR differentially regulate beta(2)-cAMP production. To address this issue, we have stably expressed the same density of alpha(2A/D)- or alpha(2B)-AR with AC II in DDT1-MF2 cells. Clonidine (partial agonist) increased beta(2)-AR-stimulated cAMP production in alpha(2A/D)-AR-ACII transfectants but inhibited it in alpha(2B)-AR-ACII transfectants. In contrast, epinephrine (full agonist) enhanced beta(2)-stimulated ACII in both alpha(2A)- and alpha(2B)-ACII clonal cell lines. 4-Azidoanilido-[alpha-(32)P]GTP-labeling of activated G proteins indicated that, in alpha(2B)-AR transfectants, clonidine activated only Gi(2), whereas epinephrine, the full agonist, effectively coupled to Gi(2) and Gi(3). Thus, partial and full agonists selectively activate G proteins that lead to drug specific effects on effectors. Moreover, these data indicate that Gi(3) activation is required for potentiation of beta(2)-AR stimulation of AC by alpha(2A/D) and alpha(2B)-AR in DDT1-MF2 cells. This may reflect an issue of the amount of Gbetagamma released upon receptor activation and/or betagamma composition of Gi(3) versus Gi(2).

Activation of α4β2*/α6β2* nicotinic receptors alleviates anxiety during nicotine withdrawal without upregulating nicotinic receptors.

PubMed

Yohn, Nicole L; Turner, Jill R; Blendy, Julie A

2014-05-01

Although nicotine mediates its effects through several nicotinic acetylcholine receptor (nAChR) subtypes, it remains to be determined which nAChR subtypes directly mediate heightened anxiety during withdrawal. Relative success in abstinence has been found with the nAChR partial agonist varenicline (Chantix; Pfizer, Groton, CT); however, treatment with this drug fails to alleviate anxiety in individuals during nicotine withdrawal. Therefore, it is hypothesized that success can be found by the repurposing of other nAChR partial agonists for cessation therapies that target anxiety. It is noteworthy that the selective partial agonists for α4β2, ABT-089 [2-methyl-3-[2(S)-pyrrolidinylmethoxy]pyridine], and α7, ABT-107 [5-(6-[(3R)-1-azabicyclo[2.2.2]oct-3-yloxy] pyridazin-3-yl)-1H-indole] (AbbVie, North Chicago, IL), have not been evaluated as possible therapeutics for nicotine cessation. Therefore, we examined the effect of ABT-089 and ABT-107 on anxiety during withdrawal from nicotine in the novelty-induced hypophagia (NIH) paradigm. We found that short-term administration of ABT-089 and ABT-107 alleviate anxiety-like behavior during withdrawal from nicotine while long-term administration of ABT-089 but not ABT-107 reduces anxiety-like behavior during withdrawal. After behavioral testing, brains were harvested and β2-containing nAChRs were measured using [(3)H]epibaditine. ABT-089 and ABT-107 do not upregulate nAChRs, which is in contrast to the upregulation of nAChRs observed after nicotine. Furthermore, ABT-089 is anxiogenic in nicotine naive animals, suggesting that the effects on anxiety are specifically related to the nicotine-dependent state. Together, these studies identify additional nAChR partial agonists that may aid in the rational development of smoking cessation aids.

In vitro binding and receptor-mediated activity of terlipressin at vasopressin receptors V1 and V2

PubMed Central

Jamil, Khurram; Pappas, Stephen Chris; Devarakonda, Krishna R

2018-01-01

Terlipressin, a synthetic, systemic vasoconstrictor with selective activity at vasopressin-1 (V1) receptors, is a pro-drug for the endogenous/natural porcine hormone [Lys8]-vasopressin (LVP). We investigated binding and receptor-mediated cellular activities of terlipressin, LVP, and endogenous human hormone [Arg8]-vasopressin (AVP) at V1 and vasopressin-2 (V2) receptors. Cell membrane homogenates of Chinese hamster ovary cells expressing human V1 and V2 receptors were used in competitive binding assays to measure receptor-binding activity. These cells were used in functional assays to measure receptor-mediated cellular activity of terlipressin, LVP, and AVP. Binding was measured by [3H]AVP counts, and the activity was measured by fluorometric detection of intracellular calcium mobilization (V1) and cyclic adenosine monophosphate (V2). Binding potency at V1 and V2 was AVP>LVP>>terlipressin. LVP and terlipressin had approximately sixfold higher affinity for V1 than for V2. Cellular activity potency was also AVP>LVP>>terlipressin. Terlipressin was a partial agonist at V1 and a full agonist at V2; LVP was a full agonist at both V1 and V2. The in vivo response to terlipressin is likely due to the partial V1 agonist activity of terlipressin and full V1 agonist activity of its metabolite, LVP. These results provide supportive evidence for previous findings and further establish terlipressin pharmacology for vasopressin receptors. PMID:29302194

In vitro binding and receptor-mediated activity of terlipressin at vasopressin receptors V1 and V2.

PubMed

Jamil, Khurram; Pappas, Stephen Chris; Devarakonda, Krishna R

2018-01-01

Terlipressin, a synthetic, systemic vasoconstrictor with selective activity at vasopressin-1 (V 1 ) receptors, is a pro-drug for the endogenous/natural porcine hormone [Lys 8 ]-vasopressin (LVP). We investigated binding and receptor-mediated cellular activities of terlipressin, LVP, and endogenous human hormone [Arg 8 ]-vasopressin (AVP) at V 1 and vasopressin-2 (V 2 ) receptors. Cell membrane homogenates of Chinese hamster ovary cells expressing human V 1 and V 2 receptors were used in competitive binding assays to measure receptor-binding activity. These cells were used in functional assays to measure receptor-mediated cellular activity of terlipressin, LVP, and AVP. Binding was measured by [ 3 H]AVP counts, and the activity was measured by fluorometric detection of intracellular calcium mobilization (V 1 ) and cyclic adenosine monophosphate (V 2 ). Binding potency at V 1 and V 2 was AVP>LVP>terlipressin. LVP and terlipressin had approximately sixfold higher affinity for V 1 than for V 2 . Cellular activity potency was also AVP>LVP>terlipressin. Terlipressin was a partial agonist at V 1 and a full agonist at V 2 ; LVP was a full agonist at both V 1 and V 2 . The in vivo response to terlipressin is likely due to the partial V 1 agonist activity of terlipressin and full V 1 agonist activity of its metabolite, LVP. These results provide supportive evidence for previous findings and further establish terlipressin pharmacology for vasopressin receptors.

Electrophysiological evidence showing muscarinic agonist-antagonist activities of N-desmethylclozapine using hippocampal excitatory and inhibitory neurons.

PubMed

Sugawara, Yuto; Kikuchi, Yui; Yoneda, Mitsugu; Ohno-Shosaku, Takako

2016-07-01

The atypical antipsychotic clozapine is widely used for treatment-resistant schizophrenic patients. Clozapine and its major active metabolite, N-desmethylclozapine (NDMC), have complex pharmacological properties, and interact with various neurotransmitter receptors. There are several biochemical studies reporting that NDMC exhibits a partial agonist profile at the human recombinant M1 muscarinic receptors. However, direct electrophysiological evidence showing the ability of NDMC to activate native M1 receptors in intact neurons is poor. Using rat hippocampal neurons, we previously demonstrated that activation of muscarinic receptors by a muscarinic agonist, oxotremorine M (oxo-M), induces a decrease in outward K(+)current at -40mV. In the present study, using this muscarinic current response we assessed agonist and antagonist activities of clozapine and NDMC at native muscarinic receptors in intact hippocampal excitatory and inhibitory neurons. Suppression of the oxo-M-induced current response by the M1 antagonist pirenzepine was evident only in excitatory neurons, while the M3 antagonist darifenacin was effective in both types of neurons. Muscarinic agonist activity of NDMC was higher than that of clozapine, higher in excitatory neurons than in inhibitory neurons, sensitive to pirenzepine, and partially masked when co-applied with clozapine. Muscarinic antagonist activity of clozapine as well as NDMC was not different between excitatory and inhibitory neurons, but clozapine was more effective than NDMC. These results demonstrate that NDMC has the ability to activate native M1 receptors expressed in hippocampal excitatory neurons, but its agonist activity might be limited in clozapine-treated patients because of the presence of excessive clozapine with muscarinic antagonist activity. Copyright © 2016 Elsevier B.V. All rights reserved.

Modeling the effect of glutamate diffusion and uptake on NMDA and non-NMDA receptor saturation.

PubMed Central

Holmes, W R

1995-01-01

One- and two-dimensional models of glutamate diffusion, uptake, and binding in the synaptic cleft were developed to determine if the release of single vesicles of glutamate would saturate NMDA and non-NMDA receptors. Ranges of parameter values were used in the simulations to determine the conditions when saturation could occur. Single vesicles of glutamate did not saturate NMDA receptors unless diffusion was very slow and the number of glutamate molecules in a vesicle was large. However, the release of eight vesicles at 400 Hz caused NMDA receptor saturation for all parameter values tested. Glutamate uptake was found to reduce NMDA receptor saturation, but the effect was smaller than that of changes in the diffusion coefficient or in the number of glutamate molecules in a vesicle. Non-NMDA receptors were not saturated unless diffusion was very slow and the number of glutamate molecules in a vesicle was large. The release of eight vesicles at 400 Hz caused significant non-NMDA receptor desensitization. The results suggest that NMDA and non-NMDA receptors are not saturated by single vesicles of glutamate under usual conditions, and that tetanic input, of the type typically used to induce long-term potentiation, will increase calcium influx by increasing receptor binding as well as by reducing voltage-dependent block of NMDA receptors. Images FIGURE 1 PMID:8580317

Effects of tobacco smoke constituents, anabasine and anatabine, on memory and attention in female rats.

PubMed

Levin, Edward D; Hao, Ian; Burke, Dennis A; Cauley, Marty; Hall, Brandon J; Rezvani, Amir H

2014-10-01

Nicotine has been well characterized to improve memory and attention. Nicotine is the primary, but not only neuroactive compound in tobacco. Other tobacco constituents such as anabasine and anatabine also have agonist actions on nicotinic receptors. The current study investigated the effects of anabasine and anatabine on memory and attention. Adult female Sprague-Dawley rats were trained on a win-shift spatial working and reference memory task in the 16-arm radial maze or a visual signal detection operant task to test attention. Acute dose-effect functions of anabasine and anatabine over two orders of magnitude were evaluated for both tasks. In the radial-arm maze memory test, anabasine but not anatabine significantly reduced the memory impairment caused by the NMDA antagonist dizocilpine (MK-801). In the signal detection attentional task, anatabine but not anabasine significantly attenuated the attentional impairment caused by dizocilpine. These studies show that non-nicotine nicotinic agonists in tobacco, similar to nicotine, can significantly improve memory and attentional function. Both anabasine and anatabine produced cognitive improvement, but their effectiveness differed with regard to memory and attention. Follow-up studies with anabasine and anatabine are called for to determine their efficacy as therapeutics for memory and attentional dysfunction. © The Author(s) 2014.

The novel antiepileptic drug imepitoin compares favourably to other GABA-mimetic drugs in a seizure threshold model in mice and dogs.

PubMed

Löscher, Wolfgang; Hoffmann, Katrin; Twele, Friederike; Potschka, Heidrun; Töllner, Kathrin

2013-11-01

Recently, the imidazolinone derivative imepitoin has been approved for treatment of canine epilepsy. Imepitoin acts as a low-affinity partial agonist at the benzodiazepine (BZD) site of the GABAA receptor and is the first compound with such mechanism that has been developed as an antiepileptic drug (AED). This mechanism offers several advantages compared to full agonists, including less severe adverse effects and a lack of tolerance and dependence liability, which has been demonstrated in rodents, dogs, and nonhuman primates. In clinical trials in epileptic dogs, imepitoin was shown to be an effective and safe AED. Recently, seizures in dogs have been proposed as a translational platform for human therapeutic trials on new epilepsy treatments. In the present study, we compared the anticonvulsant efficacy of imepitoin, phenobarbital and the high-affinity partial BZD agonist abecarnil in the timed i.v. pentylenetetrazole (PTZ) seizure threshold test in dogs and, for comparison, in mice. Furthermore, adverse effects of treatments were compared in both species. All drugs dose-dependently increased the PTZ threshold in both species, but anticonvulsant efficacy was higher in dogs than mice. At the doses selected for this study, imepitoin was slightly less potent than phenobarbital in increasing seizure threshold, but markedly more tolerable in both species. Effective doses of imepitoin in the PTZ seizure model were in the same range as those suppressing spontaneous recurrent seizures in epileptic dogs. The study demonstrates that low-affinity partial agonists at the benzodiazepine site of the GABAA receptor, such as imepitoin, offer advantages as a new category of AEDs. Copyright © 2013 Elsevier Ltd. All rights reserved.

NMDA receptor modulators: an updated patent review (2013-2014).

PubMed

Strong, Katie L; Jing, Yao; Prosser, Anthony R; Traynelis, Stephen F; Liotta, Dennis C

2014-12-01

The NMDA receptor mediates a slow component of excitatory synaptic transmission, and NMDA receptor dysfunction has been implicated in numerous neurological disorders. Thus, interest in developing modulators that are capable of regulating the channel continues to be strong. Recent research has led to the discovery of a number of compounds that hold therapeutic and clinical value. Deeper insight into the NMDA intersubunit interactions and structural motifs gleaned from the recently solved crystal structures of the NMDA receptor should facilitate a deeper understanding of how these compounds modulate the receptor. This article discusses the known pharmacology of NMDA receptors. A discussion of the patent literature since 2012 is also included, with an emphasis on those that claimed new chemical entities as regulators of the NMDA receptor. The number of patents involving novel NMDA receptor modulators suggests a renewed interest in the NMDA receptor as a therapeutic target. Subunit-selective modulators continue to show promise, and the development of new subunit-selective NMDA receptor modulators appears poised for continued growth. Although a modest number of channel blocker patents were published, successful clinical outcomes involving ketamine have led to a resurgent interest in low-affinity channel blockers as therapeutics.

A segmental chronic pain syndrome in rats associated with intrathecal infusion of NMDA: evidence for selective action in the dorsal horn.

PubMed

Zochodne, D W; Murray, M; Nag, S; Riopelle, R J

1994-02-01

We explored the effects of chronic lumbar intrathecal NMDA infusion (mini-osmotic pumps) in Sprague-Dawley rats on motor and sensory axon integrity. Several different infusion protocols, each given over a 4 week period were examined: 0.15 M NMDA in phosphate buffered saline; phosphate buffered saline without NMDA; and 0.20 M magnesium sulfate plus 0.15 M NMDA; 0.35 M NMDA. In two additional protocols, 0.15 M NMDA or phosphate buffered saline were infused for a total of 8 weeks. Within 1-2 weeks of the onset of NMDA, but not phosphate buffered saline infusions, the rats exhibited irritability, circling, biting and excessive grooming resulting in loss of hair, and skin ulcerations from autotomy localized to lumbar and sacral innervated dermatomes. Co-infusion of NMDA with magnesium sulfate almost completely prevented these findings. The behavioural changes were not associated with abnormalities of sensory or motor conduction. Intrathecal infusion of NMDA induces a chronic "central" experimental pain disorder in rats, localized to the cord segment with the greatest exposure to the infusion, without involvement of peripheral sensory axons and sparing the axonal integrity of anterior horn cells.

Prenatal inhibition of the kynurenine pathway leads to structural changes in the hippocampus of adult rat offspring

PubMed Central

Khalil, Omari S; Pisar, Mazura; Forrest, Caroline M; Vincenten, Maria C J; Darlington, L Gail; Stone, Trevor W

2014-01-01

Glutamate receptors for N-methyl-d-aspartate (NMDA) are involved in early brain development. The kynurenine pathway of tryptophan metabolism includes the NMDA receptor agonist quinolinic acid and the antagonist kynurenic acid. We now report that prenatal inhibition of the pathway in rats with 3,4-dimethoxy-N-[4-(3-nitrophenyl)thiazol-2-yl]benzenesulphonamide (Ro61-8048) produces marked changes in hippocampal neuron morphology, spine density and the immunocytochemical localisation of developmental proteins in the offspring at postnatal day 60. Golgi–Cox silver staining revealed decreased overall numbers and lengths of CA1 basal dendrites and secondary basal dendrites, together with fewer basal dendritic spines and less overall dendritic complexity in the basal arbour. Fewer dendrites and less complexity were also noted in the dentate gyrus granule cells. More neurons containing the nuclear marker NeuN and the developmental protein sonic hedgehog were detected in the CA1 region and dentate gyrus. Staining for doublecortin revealed fewer newly generated granule cells bearing extended dendritic processes. The number of neuron terminals staining for vesicular glutamate transporter (VGLUT)-1 and VGLUT-2 was increased by Ro61-8048, with no change in expression of vesicular GABA transporter or its co-localisation with vesicle-associated membrane protein-1. These data support the view that constitutive kynurenine metabolism normally plays a role in early embryonic brain development, and that interfering with it has profound consequences for neuronal structure and morphology, lasting into adulthood. PMID:24646396

Pharmacology of dextromethorphan: Relevance to dextromethorphan/quinidine (Nuedexta®) clinical use.

PubMed

Taylor, Charles P; Traynelis, Stephen F; Siffert, Joao; Pope, Laura E; Matsumoto, Rae R

2016-08-01

Dextromethorphan (DM) has been used for more than 50years as an over-the-counter antitussive. Studies have revealed a complex pharmacology of DM with mechanisms beyond blockade of N-methyl-d-aspartate (NMDA) receptors and inhibition of glutamate excitotoxicity, likely contributing to its pharmacological activity and clinical potential. DM is rapidly metabolized to dextrorphan, which has hampered the exploration of DM therapy separate from its metabolites. Coadministration of DM with a low dose of quinidine inhibits DM metabolism, yields greater bioavailability and enables more specific testing of the therapeutic properties of DM apart from its metabolites. The development of the drug combination DM hydrobromide and quinidine sulfate (DM/Q), with subsequent approval by the US Food and Drug Administration for pseudobulbar affect, led to renewed interest in understanding DM pharmacology. This review summarizes the interactions of DM with brain receptors and transporters and also considers its metabolic and pharmacokinetic properties. To assess the potential clinical relevance of these interactions, we provide an analysis comparing DM activity from in vitro functional assays with the estimated free drug DM concentrations in the brain following oral DM/Q administration. The findings suggest that DM/Q likely inhibits serotonin and norepinephrine reuptake and also blocks NMDA receptors with rapid kinetics. Use of DM/Q may also antagonize nicotinic acetylcholine receptors, particularly those composed of α3β4 subunits, and cause agonist activity at sigma-1 receptors. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

NGP1-01, a multi-targeted polycyclic cage amine, attenuates brain endothelial cell death in iron overload conditions.

PubMed

Lockman, J A; Geldenhuys, W J; Jones-Higgins, M R; Patrick, J D; Allen, D D; Van der Schyf, C J

2012-12-13

Development and progression of neurodegenerative disorders have, amongst other potential causes, been attributed to a disruption of iron regulatory mechanisms and iron accumulation. Excess extracellular iron may enter cells via nontraditional routes such as voltage-gated calcium channels and N-methyl-d-aspartate (NMDA) receptors leading to intracellular oxidative damage and ultimately mitochondrial failure. Nimodipine, an L-type calcium channel blocker has been shown to reduce iron-induced toxicity in neuronal and brain endothelial cells. Our current study investigates NGP1-01, a multimodal drug acting as an antagonist at both the NMDA receptor and the L-type calcium channel. Our previous studies support NGP1-01 as a promising neuroprotective agent in diseases involving calcium-related excitotoxicity. We demonstrate here that NGP1-01 (1 and 10μM) pretreatment abrogates the effects of iron overload in brain endothelial cells protecting cellular viability. Both concentrations of NGP1-01 were found to attenuate iron-induced reduction in cellular viability to a similar extent, and were statistically significant. To further verify the mechanism, the L-type calcium channel agonist FPL 64176 was administered to promote iron uptake. Addition of NGP1-01 dose-dependently reduced FPL 64176 stimulated uptake of iron. These data support further evaluation of NGP1-01 as a neuroprotective agent, not only in diseases associated with excitotoxicity, but also in those of iron overload. Copyright © 2012 Elsevier B.V. All rights reserved.

The influence of ionotropic and metabotropic glutamate receptor ligands on anxiety-like effect of amphetamine withdrawal in rats.

PubMed

Koltunowska, D; Gibula-Bruzda, E; Kotlinska, J H

2013-08-01

Chronic amphetamine use results in anxiety-like states after drug cessation. The aim of the study was to determine a role of ionotropic and metabotropic glutamate receptor ligands in amphetamine-evoked withdrawal anxiety in the elevated plus-maze test in rats. In our study memantine (8 and 12 mg/kg), a noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist did not reduce amphetamine withdrawal anxiety. Acamprosate (NMDA and metabotropic glutamate 5 receptor (mGluR5) antagonist) at the dose 200 and 400mg/kg showed anxiolytic-like effect, thus increasing the percent of time spent in open arms and a number of open arm entries. mGluR5 selective antagonist, MTEP (3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine hydrochloride) and mGluR2/3 agonist, LY354740 (1S,2S,5R,6S)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylic acid), caused effects similar to acamprosate at doses 1.25-5mg/kg and 2.5-5mg/kg, respectively. None of the glutamate ligands influenced locomotor activity of rats when given to the saline-treated group. Taking into account the positive correlation between amphetamine withdrawal-induced anxiety and relapse to amphetamine taking, our results suggest that modulation of mGluRs may prevent relapse to amphetamine and might pose a new direction in amphetamine abuse therapy. Copyright © 2013 Elsevier Inc. All rights reserved.

Cholinergic agonists increase intracellular calcium concentration in guinea pig vestibular hair cells.

PubMed

Han, W; Zhang, S; Han, D; Jiang, S; Yang, W

2001-07-01

To better understand the cholinergic receptors in vestibular hair cells (VHC) and their subtypes, and to investigate the effects of cholinergic agonists on intracellular calcium concentration ([Ca2+]i) in guinea pig VHCs. VHCs were isolated from guinea pig crista ampullaris by enzymatic and mechanical methods. The effect of cholinergic agonists on [Ca2+]i was examined using laser scanning confocal microscopy and the Ca2+ sensitive dye Fluo-3. The results showed that the addition of acetylcholine (ACh) and carbachol (CCh), muscamic and nicotinic agonists, induced [Ca2+]i increases in all the VHCs, whereas acetylcholine bromide (ACh-Br), a nicotinic agonist, induced the [Ca2+]i increase in only a small percentage of VHCs. The ACh or CCh-induced Ca2+ response could be partially suppressed by atropine. In the presence of 0.1 mmol/L atropine, the amplitudes of ACh or CCh-induced [Ca2+]i responses became significantly smaller than those in atropine free medium (P < 0.01). The results suggest the existence of cholinergic receptors in guinea pig VHCs. It is the muscamic agonists rather than nicontic receptors that dominate [Ca2+]i variation. Atropine can suppress muscamic agonist-induced Ca2+ responses.

Tumor necrosis factor regulates NMDA receptor-mediated airway smooth muscle contractile function and airway responsiveness.

PubMed

Anaparti, Vidyanand; Pascoe, Christopher D; Jha, Aruni; Mahood, Thomas H; Ilarraza, Ramses; Unruh, Helmut; Moqbel, Redwan; Halayko, Andrew J

2016-08-01

We have shown that N-methyl-d-aspartate receptors (NMDA-Rs) are receptor-operated calcium entry channels in human airway smooth muscle (HASM) during contraction. Tumor necrosis factor (TNF) augments smooth muscle contractility by influencing pathways that regulate intracellular calcium flux and can alter NMDA-R expression and activity in cortical neurons and glial cells. We hypothesized that NMDA-R-mediated Ca(2+) and contractile responses of ASM can be altered by inflammatory mediators, including TNF. In cultured HASM cells, we assessed TNF (10 ng/ml, 48 h) effect on NMDA-R subunit abundance by quantitative PCR, confocal imaging, and immunoblotting. We observed dose- and time-dependent changes in NMDA-R composition: increased obligatory NR1 subunit expression and altered regulatory NR2 and inhibitory NR3 subunits. Measuring intracellular Ca(2+) flux in Fura-2-loaded HASM cultures, we observed that TNF exposure enhanced cytosolic Ca(2+) mobilization and changed the temporal pattern of Ca(2+) flux in individual myocytes induced by NMDA, an NMDA-R selective analog of glutamate. We measured airway responses to NMDA in murine thin-cut lung slices (TCLS) from allergen-naive animals and observed significant airway contraction. However, NMDA acted as a bronchodilator in TCLS from house dust mice-challenged mice and in allergen-naive TCLS subjected to TNF exposure. All contractile or bronchodilator responses were blocked by a selective NMDA-R antagonist, (2R)-amino-5-phosphonopentanoate, and bronchodilator responses were prevented by N(G)-nitro-l-arginine methyl ester (nitric oxide synthase inhibitor) or indomethacin (cyclooxygenase inhibitor). Collectively, we show that TNF augments NMDA-R-mediated Ca(2+) mobilization in HASM cells, whereas in multicellular TCLSs allergic inflammation and TNF exposure leads to NMDA-R-mediated bronchodilation. These findings reveal the unique contribution of ionotrophic NMDA-R to airway hyperreactivity. Copyright © 2016 the American Physiological Society.

Activation of Cyclic AMP Synthesis by Full and Partial Beta-Adrenergic Receptor Agonists in Chicken Skeletal Muscle Cells

NASA Technical Reports Server (NTRS)

Young, R. B.; Bridge, K. Y.; Cureri, Peter A. (Technical Monitor)

2002-01-01

Several beta-adrenergic receptor (bAR) agonists are known to cause hypertrophy of skeletal muscle tissue. Accordingly, five bAR agonists encompassing a range in activity from strong to weak were evaluated for their ability to stimulate cAMP accumulation in embryonic chicken skeletal muscle cells in culture. Two strong agonists (epinephrine and isoproterenol), one moderate agonist (albuterol), and two weak agonists known to cause hypertrophy in animals (clenbuterol and cimaterol) were studied. Dose response curves were determined over six orders of magnitude in concentration for each agonist, and values were determined for their maximum stimulation of cAMP synthesis rate (Bmax) and the agonist concentration at which 50% stimulation of cAMP synthesis (EC50) occurred. Bmax values decreased in the following order: isoproterenol, epinephrine, albuterol, cimaterol, clenbuterol. Cimaterol and clenbuterol at their Bmax concentrations were approximately 15-fold weaker than isoproterenol in stimulating the rate of cAMP synthesis. When cimaterol and clenbuterol were added to culture media at concentrations known to cause significant muscle hypertrophy in animals, there was no detectable effect on stimulation of cAMP synthesis. Finally, these same levels of cimaterol and clenbuterol did not antagonize the stimulation of cAMP by either epinephrine or isoproterenol.

NMDA inhibits oxotremorine-induced acid secretion via the NO-dependent cyclic GMP system in rat stomach.

PubMed

Tsai, L H; Lee, Y J

2001-12-31

The mechanism of N-methyl-D-aspartate (NMDA) inhibits oxotremorine-induced acid secretion was examined in rat stomach, in relation to the cyclic GMP system. NMDA (10(-7) M) did not affect the spontaneous acid secretion from the everted preparations of isolated rat stomach, but inhibited the acid secretion stimulated by oxotremorine, and this effect of NMDA was antagonized by 2-amino-5-phosphonovaleric acid (AP-5), (+/-)3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) or N(G)-nitro-L-arginine (L-NNA). NMDA also elevated the cyclic GMP content of mucosal slices from rat stomach, and this effect of NMDA was antagonized by L-NNA. These results indicate that NMDA receptors are present in the rat stomach and regulate the gastric acid secretion. The mechanism underlying the effect of NMDA inhibits oxotremorine-induced acid secretion may be mediated by the NO-dependent cyclic GMP system.

Assessments of cellular melatonin receptor signaling pathways: β-arrestin recruitment, receptor internalization, and impedance variations.

PubMed

Dupré, Clémence; Bruno, Olivier; Bonnaud, Anne; Giganti, Adeline; Nosjean, Olivier; Legros, Céline; Boutin, Jean A

2018-01-05

Melatonin receptors belong to the family of G-protein coupled receptors. Agonist-induced receptor activation is terminated with the recruitment of β-arrestin, which leads to receptor internalization. Furthermore, agonist binding induces a shift in cellular shape that translates into a change in the electric impedance of the cell. In the present study, we employed engineered cells to study these internalization-related processes in the context of the two melatonin receptors, MT 1 and MT 2 . To assess these three receptor internalization-related functions and validate the results, we employed four classical ligands of melatonin receptors: the natural agonist melatonin; the super-agonist 2-iodo-melatonin and the two antagonists luzindole and 4-phenyl-2-propionamidotetralin. The assessments confirmed the nature of the agonistic ligands but showed that 4-phenyl-2-propionamidotetralin, a described antagonist, is a biased partial agonist at MT 2 with poorer affinity for MT 1 . The methods are now available to be applied to any receptor system for which multiple signaling pathways must be evaluated for new molecules. Copyright © 2017 Elsevier B.V. All rights reserved.

Evolution of the Bifunctional Lead μ Agonist / δ Antagonist Containing the Dmt-Tic Opioid Pharmacophore.

PubMed

Balboni, Gianfranco; Salvadori, Severo; Trapella, Claudio; Knapp, Brian I; Bidlack, Jean M; Lazarus, Lawrence H; Peng, Xuemei; Neumeyer, John L

2010-02-17

Based on a renewed importance recently attributed to bi- or multifunctional opioids, we report the synthesis and pharmacological evaluation of some analogues derived from our lead μ agonist / δ antagonist, H-Dmt-Tic-Gly-NH-Bzl. Our previous studies focused on the importance of the C-teminal benzyl function in the induction of such bifunctional activity. The introduction of some substituents in the para position of the phenyl ring (-Cl, -CH(3), partially -NO(2), inactive -NH(2)) was found to give a more potent μ agonist / antagonist effect associated with a relatively unmodified δ antagonist activity (pA(2) = 8.28-9.02). Increasing the steric hindrance of the benzyl group (using diphenylmethyl and tetrahydroisoquinoline functionalities) substantially maintained the μ agonist and δ antagonist activities of the lead compound. Finally and quite unexpectedly D-Tic2, considered as a wrong opioid message now; inserted into the reference compound in lieu of L-Tic, provided a μ agonist / δ agonist better than our reference ligand (H-Dmt-Tic-Gly-NH-Ph) and was endowed with the same pharmacological profile.

Medical management of levodopa-associated motor complications in patients with Parkinson's disease.

PubMed

Jankovic, Joseph; Stacy, Mark

2007-01-01

Parkinson's disease is a neurodegenerative disorder that affects approximately 1% of people over the age of 60 years. Levodopa is standard, and often initial, therapy for patients with this condition; however, with continued treatment and as the disease progresses, up to 80% of patients experience 'wearing-off' symptoms, dyskinesias and other motor complications. These levodopa-associated problems may become disabling and profoundly affect quality of life. Medications commonly used to manage these symptoms include monoamine oxidase type B (MAO-B) inhibitors, catechol-O-methyltransferase (COMT) inhibitors, the NMDA receptor antagonist amantadine and dopamine receptor agonists. Agents that block MAO-B, such as rasagiline and selegiline, are used as both initial and adjunctive therapy in patients with Parkinson's disease. These medications increase concentrations of dopamine in the brain by blocking its reuptake from the synaptic cleft, a mechanism that can slow motor decline, increase 'on' time and improve symptoms of Parkinson's disease. Adverse events with these agents can include confusion, hallucination and orthostatic hypotension. MAO-B inhibition may elicit drug-drug interactions if administered with TCAs, SSRIs or SNRIs. Conventional oral selegiline is associated with potentially harmful plasma concentrations of three major amphetamine metabolites, although metabolite concentrations are significantly lower with a new orally disintegrating tablet (ODT) selegiline formulation. Selegiline ODT is also absorbed more efficiently and shows less pharmacokinetic variability than conventional oral selegiline.COMT mediates peripheral catabolism of levodopa. Therefore, agents that block COMT, such as tolcapone and entacapone, increase the elimination half-life of levodopa. Given adjunctively with levodopa, COMT inhibitors can decrease 'off' time and increase 'on' time, as well as lower the daily levodopa dose. Although more potent than entacapone, tolcapone requires monitoring for hepatotoxicity. Amantadine is a noncompetitive NMDA receptor antagonist shown to lower dyskinesia scores and improve motor complications in patients with Parkinson's disease when given adjunctively with levodopa. Dopamine agonists, also used as initial and adjunctive therapy in Parkinson's disease, improve motor response and decrease 'off' time purportedly through direct stimulation of dopamine receptors. Current dopamine agonists include bromocriptine, pergolide, cabergoline, lisuride, apomorphine, pramipexole, ropinirole and rotigotine. Although effective, this class of medications can be associated with cardiovascular and psychiatric adverse effects that can limit their utility. All medications used to manage levodopa-associated motor complications in patients with Parkinson's disease have had differing degrees of success. Although head-to-head comparisons of drugs within classes are rare, some differences have emerged related to effects on motor fluctuations, dyskinesias and on/off times, as well as to adverse effects. When choosing a drug to treat levodopa-induced complications, it is important to consider the risks and benefits of the different classes and of the specific agents within each class, given the different efficacy and safety profiles of each.

A critical role of spinal Shank2 proteins in NMDA-induced pain hypersensitivity

PubMed Central

Yoon, Seo-Yeon; Kwon, Soon-Gu; Kim, Yong Ho; Yeo, Ji-Hee; Ko, Hyoung-Gon; Roh, Dae-Hyun; Kaang, Bong-Kiun; Beitz, Alvin J; Lee, Jang-Hern

2017-01-01

Background Self-injurious behaviors (SIBs) are devastating traits in autism spectrum disorder (ASD). Although deficits in pain sensation might be one of the contributing factors underlying the development of SIBs, the mechanisms have yet to be addressed. Recently, the Shank2 synaptic protein has been considered to be a key component in ASD, and mutations of SHANK2 gene induce the dysfunction of N-methyl-D-aspartate (NMDA) receptors, suggesting a link between Shank2 and NMDA receptors in ASD. Given that spinal NMDA receptors play a pivotal role in pain hypersensitivity, we investigated the possible role of Shank2 in nociceptive hypersensitivity by examining changes in spontaneous pain following intrathecal NMDA injection in Shank2−/− (Shank2 knock-out, KO) mice. Results Intrathecal NMDA injection evoked spontaneous nociceptive behaviors. These NMDA-induced nociceptive responses were significantly reduced in Shank2 KO mice. We also observed a significant decrease of NMDA currents in the spinal dorsal horn of Shank2 KO mice. Subsequently, we examined whether mitogen-activated protein kinase or AKT signaling is involved in this reduced pain behavior in Shank2 KO mice because the NMDA receptor is closely related to these signaling molecules. Western blotting and immunohistochemistry revealed that spinally administered NMDA increased the expression of a phosphorylated form of extracellular signal-regulated kinase (p-ERK) which was significantly reduced in Shank2 KO mice. However, p38, JNK, or AKT were not changed by NMDA administration. The ERK inhibitor, PD98059, decreased NMDA-induced spontaneous pain behaviors in a dose-dependent manner in wild-type mice. Moreover, it was found that the NMDA-induced increase in p-ERK was primarily colocalized with Shank2 proteins in the spinal cord dorsal horn. Conclusion Shank2 protein is involved in spinal NMDA receptor-mediated pain, and mutations of Shank2 may suppress NMDA-ERK signaling in spinal pain transmission. This study provides new clues into the mechanisms underlying pain deficits associated with SIB and deserves further study in patients with ASD. PMID:28326932

A critical role of spinal Shank2 proteins in NMDA-induced pain hypersensitivity.

PubMed

Yoon, Seo-Yeon; Kwon, Soon-Gu; Kim, Yong Ho; Yeo, Ji-Hee; Ko, Hyoung-Gon; Roh, Dae-Hyun; Kaang, Bong-Kiun; Beitz, Alvin J; Lee, Jang-Hern; Oh, Seog Bae

2017-01-01

Background Self-injurious behaviors (SIBs) are devastating traits in autism spectrum disorder (ASD). Although deficits in pain sensation might be one of the contributing factors underlying the development of SIBs, the mechanisms have yet to be addressed. Recently, the Shank2 synaptic protein has been considered to be a key component in ASD, and mutations of SHANK2 gene induce the dysfunction of N-methyl-D-aspartate (NMDA) receptors, suggesting a link between Shank2 and NMDA receptors in ASD. Given that spinal NMDA receptors play a pivotal role in pain hypersensitivity, we investigated the possible role of Shank2 in nociceptive hypersensitivity by examining changes in spontaneous pain following intrathecal NMDA injection in S hank2-/- ( Shank2 knock-out, KO) mice. Results Intrathecal NMDA injection evoked spontaneous nociceptive behaviors. These NMDA-induced nociceptive responses were significantly reduced in Shank2 KO mice. We also observed a significant decrease of NMDA currents in the spinal dorsal horn of Shank2 KO mice. Subsequently, we examined whether mitogen-activated protein kinase or AKT signaling is involved in this reduced pain behavior in Shank2 KO mice because the NMDA receptor is closely related to these signaling molecules. Western blotting and immunohistochemistry revealed that spinally administered NMDA increased the expression of a phosphorylated form of extracellular signal-regulated kinase (p-ERK) which was significantly reduced in Shank2 KO mice. However, p38, JNK, or AKT were not changed by NMDA administration. The ERK inhibitor, PD98059, decreased NMDA-induced spontaneous pain behaviors in a dose-dependent manner in wild-type mice. Moreover, it was found that the NMDA-induced increase in p-ERK was primarily colocalized with Shank2 proteins in the spinal cord dorsal horn. Conclusion Shank2 protein is involved in spinal NMDA receptor-mediated pain, and mutations of Shank2 may suppress NMDA-ERK signaling in spinal pain transmission. This study provides new clues into the mechanisms underlying pain deficits associated with SIB and deserves further study in patients with ASD.

Short-term sleep deprivation impairs spatial working memory and modulates expression levels of ionotropic glutamate receptor subunits in hippocampus.

PubMed

Xie, Meilan; Yan, Jie; He, Chao; Yang, Li; Tan, Gang; Li, Chao; Hu, Zhian; Wang, Jiali

2015-06-01

Hippocampus-dependent learning memory is sensitive to sleep deprivation (SD). Although the ionotropic glutamate receptors play a vital role in synaptic plasticity and learning and memory, however, whether the expression of these receptor subunits is modulated by sleep loss remains unclear. In the present study, western blotting was performed by probing with specific antibodies against the ionotropic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits GluA1, GluA2, GluA3, and against the N-methyl-d-aspartate (NMDA) glutamate receptor subunits GluN1, GluN2A, GluN2B. In hippocampus, down regulation of surface GluA1 and GluN2A surface expression were observed in both SD groups. However, surface expression level of GluA2, GluA3, GluN1 and GluN2B was significantly up-regulated in 8h-SD rats when compared to the 4h-SD rats. In parallel with the complex changes in AMPA and NMDA receptor subunit expressions, we found the 8h-SD impaired rat spatial working memory in 30-s-delay T-maze task, whereas no impairment of spatial learning was observed in 4h-SD rats. These results indicate that sleep loss alters the relative expression levels of the AMPA and NMDA receptors, thus affects the synaptic strength and capacity for plasticity and partially contributes to spatial memory impairment. Copyright © 2015. Published by Elsevier B.V.

6'-Guanidinonaltrindole (6'-GNTI) is a G protein-biased κ-opioid receptor agonist that inhibits arrestin recruitment.

PubMed

Rives, Marie-Laure; Rossillo, Mary; Liu-Chen, Lee-Yuan; Javitch, Jonathan A

2012-08-03

κ-Opioid receptor (KOR) agonists do not activate the reward pathway stimulated by morphine-like μ-opioid receptor (MOR) agonists and thus have been considered to be promising nonaddictive analgesics. However, KOR agonists produce other adverse effects, including dysphoria, diuresis, and constipation. The therapeutic promise of KOR agonists has nonetheless recently been revived by studies showing that their dysphoric effects require arrestin recruitment, whereas their analgesic effects do not. Moreover, KOR agonist-induced antinociceptive tolerance observed in vivo has also been proposed to be correlated to the ability to induce arrestin-dependent phosphorylation, desensitization, and internalization of the receptor. The discovery of functionally selective drugs that are therapeutically effective without the adverse effects triggered by the arrestin pathway is thus an important goal. We have identified such an extreme G protein-biased KOR compound, 6'-guanidinonaltrindole (6'-GNTI), a potent partial agonist at the KOR receptor for the G protein activation pathway that does not recruit arrestin. Indeed, 6'-GNTI functions as an antagonist to block the arrestin recruitment and KOR internalization induced by other nonbiased agonists. As an extremely G protein-biased KOR agonist, 6'-GNTI represents a promising lead compound in the search for nonaddictive opioid analgesic as its signaling profile suggests that it will be without the dysphoria and other adverse effects promoted by arrestin recruitment and its downstream signaling.

2-(2-Bromophenyl)-formononetin and 2-heptyl-formononetin are PPARγ partial agonists and reduce lipid accumulation in 3T3-L1 adipocytes.

PubMed

Andersen, Charlotte; Kotowska, Dorota; Tortzen, Christian G; Kristiansen, Karsten; Nielsen, John; Petersen, Rasmus Koefoed

2014-11-01

Isoflavones are bioactive compounds that have been shown to decrease lipid accumulation in vitro. However, the knowledge of the isoflavone formononetin is limited. The aim of the study was to assess the effects of formononetin and its two synthetic analogues, 2-(2-bromophenyl)-formononetin and 2-heptyl-formononetin, on lipid accumulation in 3T3-L1 adipocytes and investigate possible mechanisms. Formononetin and the two analogues were added day 0-8 or day 8-10 of the differentiation period, and lipid accumulation, glycerol release and gene expression were measured. Additionally, competitive peroxisome proliferator-activated receptor (PPAR)-γ binding assay, PPARγ transactivation assay and Western blot for phosphorylated AMP-activated protein kinase (AMPK) were performed. Chronic treatment (day 0-8) with formononetin increased lipid accumulation, whereas the two analogues decreased lipid accumulation partly due to decreased differentiation. The two analogues, but not formononetin, also decreased lipid content in mature adipocytes. 2-Heptyl-formononetin increased glycerol release and lipolytic gene expression and decreased lipogenic gene expression. Formononetin did not bind to or activate PPARγ whereas both analogues bound to the receptor and behaved as PPARγ partial agonists in the transactivation assay. Neither of the compounds affected phosphorylation of AMPK. In conclusion, the analogues of formononetin decreased lipid accumulation possibly in part by acting as PPARγ partial agonists. Copyright © 2014 Elsevier Ltd. All rights reserved.

Structure-activity relationship of cyclic peptide penta-c[Asp-His(6)-DPhe(7)-Arg(8)-Trp(9)-Lys]-NH(2) at the human melanocortin-1 and -4 receptors: His(6) substitution.

PubMed

Cheung, Adrian Wai-Hing; Danho, Waleed; Swistok, Joseph; Qi, Lida; Kurylko, Grazyna; Rowan, Karen; Yeon, Mitch; Franco, Lucia; Chu, Xin-Jie; Chen, Li; Yagaloff, Keith

2003-04-07

A series of MT-II related cyclic peptides, based on potent but non-selective hMC4R agonist (Penta-c[Asp-His(6)-DPhe(7)-Arg(8)-Trp(9)-Lys]-NH(2)) was prepared in which His(6) residue was systematically substituted. Two of the most interesting peptides identified in this study are Penta-c[Asp-5-ClAtc-DPhe-Arg-Trp-Lys]-NH(2) and Penta-c[Asp-5-ClAtc-DPhe-Cit-Trp-Lys]-NH(2) which are potent hMC4R agonists and are either inactive or weak partial agonists (not tested for their antagonist activities) in hMC1R, hMC3R and hMC5R agonist assays.

Dopamine D3 and D2 Receptor Mechanisms in the Abuse-Related Behavioral Effects of Cocaine: Studies with Preferential Antagonists in Squirrel Monkeys

PubMed Central

Grundt, Peter; Cao, Jianjing; Platt, Donna M.; Newman, Amy Hauck; Spealman, Roger D.

2010-01-01

Dopamine (DA) D3 and D2 receptor mechanisms are implicated in cocaine's abuse-related behavioral effects, but the relative contribution of the two receptor subtypes is only partially characterized. This study investigated the role of D3 and D2 subtype mechanisms by determining the degree to which the D3-preferring antagonist PG01037 [N-{4-[4-(2,3-dichlorophenyl)-piperazin- 1-yl]-trans-but-2-enyl}-4-pyridine-2-yl-benzamide HCl] and the D2-preferring antagonist L-741626 [3-[4-(4-chlorophenyl)-4- hydroxypiperidin-1-yl]methyl-1H-indole] attenuated several behavioral effects of cocaine in squirrel monkeys. Quantitative observational studies established doses of each antagonist that did not produce untoward effects, which were used in subsequent comparisons. In addition, the ability of the D3-preferring agonist PD128907 [(R-(+)-trans-3,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4,3-b]-1,4-oxazin-9-ol)] and the D2-preferring agonist sumanirole [(R)-5,6-dihydro-5-(methylamino)-4H- imidazo[4,5,1-ij]quinolin-2(1H)-one(Z)-2-butenedioate] to reproduce cocaine's discriminative stimulus (DS) and priming effects were compared. In monkeys trained to discriminate cocaine from vehicle, both DA antagonists attenuated and both DA agonists partially reproduced cocaine's DS effects. PG01037 also selectively attenuated the cocaine-like DS effects of PD128907, whereas L-741626 attenuated the cocaine-like DS effects of both agonists. In self-administration studies, L-741626 nonselectively reduced cocaine- and food-maintained responding, whereas PG01037 was ineffective against either reinforcer. In studies involving reinstatement of extinguished cocaine seeking, both antagonists attenuated cocaine-induced reinstatement of responding, and both agonists induced at least partial reinstatement of cocaine seeking. L-741626 also attenuated sumanirole-induced, but not PD128907-induced, reinstatement of responding, whereas PG01037 was ineffective against either DA agonist. The results are consistent with a role for D3 and D2 receptor mechanisms in cocaine's DS effects and cocaine-induced reinstatement of drug seeking, but provide no evidence for a major role of D3 receptors in the direct reinforcing effects of cocaine. PMID:20494958

Mechanism of agonism and antagonism of the Pseudomonas aeruginosa quorum sensing regulator QscR with non-native ligands.

PubMed

Wysoczynski-Horita, Christina L; Boursier, Michelle E; Hill, Ryan; Hansen, Kirk; Blackwell, Helen E; Churchill, Mair E A

2018-05-01

Pseudomonas aeruginosa is an opportunistic pathogen that uses the process of quorum sensing (QS) to coordinate the expression of many virulence genes. During quorum sensing, N-acyl-homoserine lactone (AHL) signaling molecules regulate the activity of three LuxR-type transcription factors, LasR, RhlR and QscR. To better understand P. aeruginosa QS signal reception, we examined the mechanism underlying the response of QscR to synthetic agonists and antagonists using biophysical and structural approaches. The structure of QscR bound to a synthetic agonist reveals a novel mode of ligand binding supporting a general mechanism for agonist activity. In turn, antagonists of QscR with partial agonist activity were found to destabilize and greatly impair QscR dimerization and DNA binding. These results highlight the diversity of LuxR-type receptor responses to small molecule agonists and antagonists and demonstrate the potential for chemical strategies for the selective targeting of individual QS systems. © 2018 John Wiley & Sons Ltd.

Mixed nicotinic-muscarinic properties of the alpha9 nicotinic cholinergic receptor.

PubMed

Verbitsky, M; Rothlin, C V; Katz, E; Elgoyhen, A B

2000-10-01

The rat alpha9 nicotinic acetylcholine receptor (nAChR) was expressed in Xenopus laevis oocytes and tested for its sensitivity to a wide variety of cholinergic compounds. Acetylcholine (ACh), carbachol, choline and methylcarbachol elicited agonist-evoked currents, giving maximal or near maximal responses. Both the nicotinic agonist suberyldicholine as well as the muscarinic agonists McN-A-343 and methylfurtrethonium behaved as weak partial agonists of the receptor. Most classical cholinergic compounds tested, being either nicotinic (nicotine, epibatidine, cytisine, methyllycaconitine, mecamylamine, dihydro-beta-erythroidine), or muscarinic (muscarine, atropine, gallamine, pilocarpine, bethanechol) agonists and antagonists, blocked the recombinant alpha9 receptor. Block by nicotine, epibatidine, cytisine, methyllycaconitine and atropine was overcome at high ACh concentrations, suggesting a competitive type of block. The present results indicate that alpha9 displays mixed nicotinic-muscarinic features that resemble the ones described for the cholinergic receptor of cochlear outer hair cells (OHCs). We suggest that alpha9 contains the structural determinants responsible for the pharmacological properties of the native receptor.

Aging and cholinergic responses in bovine trachealis muscle.

PubMed Central

Wills, M.; Douglas, J. S.

1988-01-01

1. The relative potencies of muscarinic agonists on bovine tracheal smooth muscle were unchanged as a consequence of aging and were carbachol greater than oxotremorine greater than muscarine greater than pilocarpine greater than McNeil A-343. 2. During aging, the potencies of carbachol, oxotremorine, McNeil A-343 and pilocarpine, but not muscarine, were reduced. 3. Maximal induced tensions to all the agents studied were reduced as a consequence of age. 4. Irreversible antagonism with benzilylcholine mustard showed that agonist efficacy was significantly reduced during aging. 5. Estimated receptor occupancy at the EC50 was significantly greater in tracheal tissues from the mature versus immature cows for every agonist studied. 6. The dissociation constants for full agonists (carbachol, oxotremorine and methacholine) were decreased with maturation while the converse was observed with partial agonists (McNeil A-343, pilocarpine). 7. We conclude that there are significant changes in the properties and coupling of muscarinic receptors during aging. These changes may contribute to the reduced airway reactivity seen in vivo. PMID:3390660

Receptor specificity and trigemino-vascular inhibitory actions of a novel 5-HT1B/1D receptor partial agonist, 311C90 (zolmitriptan).

PubMed

Martin, G R; Robertson, A D; MacLennan, S J; Prentice, D J; Barrett, V J; Buckingham, J; Honey, A C; Giles, H; Moncada, S

1997-05-01

1. 311C90 (zolmitriptan zomig: (S)-4[[3-[2-(dimethylamino)ethyl]-1H-indol-5-yl]methyl]-2-oxazolidinone) is a novel 5-HT1B/1D receptor agonist with proven efficacy in the acute treatment of migraine. Here, we describe the receptor specificity of the drug and its actions on trigeminal-evoked plasma protein extravasation into the dura mater of the anaesthetized guinea-pig. 2. At the "5-HT1B-like' receptor mediating vascular contraction (rabbit saphenous vein), the compound was a potent (p[A50] = 6.79 +/- 0.06) partial agonist achieving 77 +/- 4% of the maximum effect to 5-hydroxytryptamine (5-HT). In the same experiments, sumatriptan (p[A50] = 6.48 +/- 0.04) was half as potent as 311C90 and produced 97 +/- 2% of the 5-HT maximum effect. Studies in which receptor inactivation methods were used to estimate the affinity (pKA) and efficacy relative to 5-HT (tau rel) for each agonist confirmed that 311C90 exhibits higher affinity than sumatriptan (pKA = 6.63 +/- 0.04 and 6.16 +/- 0.03, respectively) and that both drugs are partial agonists relative to 5-HT (tau rel = 0.61 +/- 0.03 and 0.63 +/- 0.10, respectively, compared to 5-HT = 1.0). 3. Consistent with its effects in rabbit saphenous vein, 311C90 also produced concentration-dependent contractions of primate basilar artery and human epicardial coronary artery rings. In basilar artery, agonist potency (p[A50] = 6.92 +/- 0.07) was similar to that demonstrated in rabbit saphenous vein, again being 2-3 fold higher than for sumatriptan (p[A50] = 6.46 +/- 0.03). Both agonists produced about 50% of the maximum response obtained with 5-HT in the same preparations. In rings of human coronary artery, the absolute potency of 311C90 and sumatriptan was higher than in primate basilar artery (p[A50] = 7.3 +/- 0.1 and 6.7 +/- 0.1, respectively), but maximum effects relative to 5-HT were lower (37 +/- 8% and 35 +/- 7%, respectively). In both types of vessel, the inability of 5-HT1B/1D agonists to achieve the same maximum as the endogenous agonist 5-HT is explained by the additional presence of 5-HT2A receptors. 4. 311C90 displayed high affinity at human recombinant 5-HT1D (formerly 5-HT1D alpha) and 5-HT1B (formerly 5-HT1D beta) receptors in transfected CHO-K1 cell membranes (pIC50 values = 9.16 +/- 0.12 and 8.32 +/- 0.09, respectively). In intact cells, the drug produced concentration-dependent inhibition of forskolin-stimulated adenylyl cyclase (p[A50] = 9.9 and 9.5, respectively) achieving the same maximum effect as 5-HT. Excepting human recombinant 5-HT1A and 5-ht1F receptors at which the drug behaved as an agonist with modest affinity (pIC50 = 6.45 +/- 0.11 and 7.22 +/- 0.12, respectively), 311C90 exhibited low, or no detectable affinity (pKi or pKB < or = 5.5) at numerous other monoamine receptors, including other 5-HT receptor subtypes. 5. When administered to anaesthetized guinea-pigs ten minutes before unilateral electrical stimulation of the trigeminal ganglion (1.2 mA, 5 Hz, 5 ms, 5 min), 311C90 (3-30 micrograms kg-1, i.v.) caused a dose-dependent inhibition of [125I]-albumin extravasation within the ipsilateral dura mater. At the same doses, the drug also produced dose-dependent falls in cranial vascular conductance (32.3 +/- 7.5% at 30 micrograms kg-1), as measured in the ear by laser doppler flowmetry. 6. These results show that 311C90, a novel member of the 5-HT1B/1D agonist drug class, exhibits a high degree of pharmacological specificity. Its potent partial agonist action at "5-HT1B-like' receptors in intracranial arteries, coupled with potent agonism at 5-HT1D and 5-HT1B receptors and an ability to inhibit neurogenic plasma protein extravasation in the dura, are consistent with its utility as an effective acute treatment for migraine.

Scale-Up Synthesis and Identification of GLYX-13, a NMDAR Glycine-Site Partial Agonist for the Treatment of Major Depressive Disorder.

PubMed

Li, Wenchao; Liu, Jingjian; Fan, Minghua; Li, Zhongtang; Chen, Yin; Zhang, Guisen; Huang, Zhuo; Zhang, Liangren

2018-04-24

GLYX-13, a NMDAR glycine-site partial agonist, was discovered as a promising antidepressant with rapidly acting effects but no ketamine-like side effects. However, the reported synthetic process route had deficiencies of low yield and the use of unfriendly reagents. Here, we report a scaled-up synthesis of GLYX-13 with an overall yield of 30% on the hectogram scale with a column chromatography-free strategy, where the coupling and deprotection reaction conditions were systematically optimized. Meanwhile, the absolute configuration of precursor compound of GLYX-13 was identified by X-ray single crystal diffraction. Finally, the activity of GLYX-13 was verified in the cortical neurons of mice through whole-cell voltage-clamp technique.

Cholesterol modulates open probability and desensitization of NMDA receptors

PubMed Central

Korinek, Miloslav; Vyklicky, Vojtech; Borovska, Jirina; Lichnerova, Katarina; Kaniakova, Martina; Krausova, Barbora; Krusek, Jan; Balik, Ales; Smejkalova, Tereza; Horak, Martin; Vyklicky, Ladislav

2015-01-01

NMDA receptors (NMDARs) are glutamate-gated ion channels that mediate excitatory neurotransmission in the CNS. Although these receptors are in direct contact with plasma membrane, lipid–NMDAR interactions are little understood. In the present study, we aimed at characterizing the effect of cholesterol on the ionotropic glutamate receptors. Whole-cell current responses induced by fast application of NMDA in cultured rat cerebellar granule cells (CGCs) were almost abolished (reduced to 3%) and the relative degree of receptor desensitization was increased (by seven-fold) after acute cholesterol depletion by methyl-β-cyclodextrin. Both of these effects were fully reversible by cholesterol repletion. By contrast, the responses mediated by AMPA/kainate receptors were not affected by cholesterol depletion. Similar results were obtained in CGCs after chronic inhibition of cholesterol biosynthesis by simvastatin and acute enzymatic cholesterol degradation to 4-cholesten-3-one by cholesterol oxidase. Fluorescence anisotropy measurements showed that membrane fluidity increased after methyl-β-cyclodextrin pretreatment. However, no change in fluidity was observed after cholesterol enzymatic degradation, suggesting that the effect of cholesterol on NMDARs is not mediated by changes in membrane fluidity. Our data show that diminution of NMDAR responses by cholesterol depletion is the result of a reduction of the open probability, whereas the increase in receptor desensitization is the result of an increase in the rate constant of entry into the desensitized state. Surface NMDAR population, agonist affinity, single-channel conductance and open time were not altered in cholesterol-depleted CGCs. The results of our experiments show that cholesterol is a strong endogenous modulator of NMDARs. Key points NMDA receptors (NMDARs) are tetrameric cation channels permeable to calcium; they mediate excitatory synaptic transmission in the CNS and their excessive activation can lead to neurodegeneration. Although these receptors are in direct contact with plasma membrane, lipid–NMDAR interactions are little understood. Using cultured rat cerebellar granule cells, we show that acute and chronic pretreatments resulting in cell cholesterol depletion profoundly diminish NMDAR responses and increase NMDAR desensitization, and also that cholesterol enrichment potentiates NMDAR responses; however, cholesterol manipulation has no effect on the amplitude of AMPA/kainate receptor responses. Diminution of NMDAR responses by cholesterol depletion is the result of a reduction of the ion channel open probability, whereas the increase in receptor desensitization is the result of an increase in the rate constant of entry into the desensitized state. These results demonstrate the physiological role of membrane lipids in the modulation of NMDAR activity. PMID:25651798

Translation of Novel Serotonin 5-HT7 Agonist Drug Candidates in Rodent Models of Fragile X Syndrome

DTIC Science & Technology

2016-09-01

President of DELSIA (Delivering Science Innovation for Autism ) and Vice President, Innovative Technologies at Autism Speaks, Daniel Smith, who...in autism and Fragile X syndrome. Notably, there are no 9  pharmacotherapies approved for core symptoms of autism or Fragile X syndrome, thus, our...HT1A partial agonist for autism . 6th Cisbio HTRF symposium (Brewster, MA), September 14-17, 2015. Acknowledged DOD funding. Teaching Lectures. 10

Labeled ALPHA4BETA2 ligands and methods therefor

DOEpatents

Mukherjee, Jogeshwar; Pichika, Ramaiah; Potkin, Steven; Leslie, Frances; Chattopadhyay, Sankha

2013-02-19

Contemplated compositions and methods are employed to bind in vitro and in vivo to an .alpha.4.beta.2 nicotinic acetylcholine receptor in a highly selective manner. Where such compounds are labeled, compositions and methods employing such compounds can be used for PET and SPECT analysis. Alternatively, and/or additionally contemplated compounds can be used as antagonists, partial agonists or agonists in the treatment of diseases or conditions associated with .alpha.4.beta..beta.2 dysfunction.

Voltage-dependent calcium channel involvement in NMDA-induced activation of NOS.

PubMed

Alagarsamy, S; Johnson, K M

1995-11-13

We have previously shown that N-methyl-D-aspartate (NMDA) increases nitric oxide synthase (NOS) activity in rat frontal cortex; however, the actual mechanism of this activation has not been addressed. Tetrodotoxin (TTX; 0.05 microM) inhibited NMDA-activated NOS, suggesting that TTX-sensitive Na+ channels are interposed between the NMDA receptors and the NOS cellular compartment. The NMDA response was also blocked by voltage-dependent Ca2+ channel (VDCC) blockers including Cd2+, Co2+, funnel web spider toxin (FTX) and omega-Aga IVa, but not by nifedipine or omega-conotoxin. These data suggest that Ca2+ flux through P- and/or Q-type VDCC subsequent to NMDA-induced depolarization may be at least as important for NOS activation as Ca2+ entry through the NMDA receptor.

Effects of chronic sazetidine-A, a selective α4β2 neuronal nicotinic acetylcholine receptors desensitizing agent on pharmacologically-induced impaired attention in rats.

PubMed

Rezvani, Amir H; Cauley, Marty; Xiao, Yingxian; Kellar, Kenneth J; Levin, Edward D

2013-03-01

Nicotine and nicotinic agonists have been shown to improve attentional function. Nicotinic receptors are easily desensitized, and all nicotinic agonists are also desensitizing agents. Although both receptor activation and desensitization are components of the mechanism that mediates the overall effects of nicotinic agonists, it is not clear how each of the two opposed actions contributes to attentional improvements. Sazetidine-A has high binding affinity at α4β2 nicotinic receptors and causes a relatively brief activation followed by a long-lasting desensitization of the receptors. Acute administration of sazetidine-A has been shown to significantly improve attention by reversing impairments caused by the muscarinic cholinergic antagonist scopolamine and the NMDA glutamate antagonist dizocilpine. In the current study, we tested the effects of chronic subcutaneous infusion of sazetidine-A (0, 2, or 6 mg/kg/day) on attention in Sprague-Dawley rats. Furthermore, we investigated the effects of chronic sazetidine-A treatment on attentional impairment induced by an acute administration of 0.02 mg/kg scopolamine. During the first week period, the 6-mg/kg/day sazetidine-A dose significantly reversed the attentional impairment induced by scopolamine. During weeks 3 and 4, the scopolamine-induced impairment was no longer seen, but sazetidine-A (6 mg/kg/day) significantly improved attentional performance on its own. Chronic sazetidine-A also reduced response latency and response omissions. This study demonstrated that similar to its acute effects, chronic infusions of sazetidine-A improve attentional performance. The results indicate that the desensitization of α4β2 nicotinic receptors with some activation of these receptors may play an important role in improving effects of sazetidine-A on attention.

Neurophysiological mechanisms of cortical plasticity impairments in schizophrenia and modulation by the NMDA receptor agonist D-serine

PubMed Central

Kantrowitz, Joshua T.; Epstein, Michael L.; Beggel, Odeta; Rohrig, Stephanie; Lehrfeld, Jonathan M.; Revheim, Nadine; Lehrfeld, Nayla P.; Reep, Jacob; Parker, Emily; Silipo, Gail; Ahissar, Merav; Javitt, Daniel C.

2016-01-01

Schizophrenia is associated with deficits in cortical plasticity that affect sensory brain regions and lead to impaired cognitive performance. Here we examined underlying neural mechanisms of auditory plasticity deficits using combined behavioural and neurophysiological assessment, along with neuropharmacological manipulation targeted at the N-methyl-D-aspartate type glutamate receptor (NMDAR). Cortical plasticity was assessed in a cohort of 40 schizophrenia/schizoaffective patients relative to 42 healthy control subjects using a fixed reference tone auditory plasticity task. In a second cohort (n = 21 schizophrenia/schizoaffective patients, n = 13 healthy controls), event-related potential and event-related time–frequency measures of auditory dysfunction were assessed during administration of the NMDAR agonist d-serine. Mismatch negativity was used as a functional read-out of auditory-level function. Clinical trials registration numbers were NCT01474395/NCT02156908. Schizophrenia/schizoaffective patients showed significantly reduced auditory plasticity versus healthy controls (P = 0.001) that correlated with measures of cognitive, occupational and social dysfunction. In event-related potential/time-frequency analyses, patients showed highly significant reductions in sensory N1 that reflected underlying impairments in θ responses (P < 0.001), along with reduced θ and β-power modulation during retention and motor-preparation intervals. Repeated administration of d-serine led to intercorrelated improvements in (i) auditory plasticity (P < 0.001); (ii) θ-frequency response (P < 0.05); and (iii) mismatch negativity generation to trained versus untrained tones (P = 0.02). Schizophrenia/schizoaffective patients show highly significant deficits in auditory plasticity that contribute to cognitive, occupational and social dysfunction. d-serine studies suggest first that NMDAR dysfunction may contribute to underlying cortical plasticity deficits and, second, that repeated NMDAR agonist administration may enhance cortical plasticity in schizophrenia. PMID:27913408

Icilin-evoked behavioral stimulation is attenuated by alpha2-adrenoceptor activation

PubMed Central

Kim, Jae; Cowan, Alan; Lisek, Renata; Raymondi, Natalie; Rosenthal, Aaron; Hirsch, Daniel D.; Rawls, Scott M.

2011-01-01

Icilin is a transient receptor potential cation channel subfamily M (TRPM8) agonist that produces behavioral activation in rats and mice. Its hallmark overt pharmacological effect is wet-dog shakes (WDS) in rats. The vigorous shaking associated with icilin is dependent on NMDA receptor activation and nitric oxide production, but little else is known about the biological systems that modulate the behavioral phenomenon. The present study investigated the hypothesis that alpha2-adrenoceptor activation inhibits icilin-induced WDS. Rats injected with icilin (0.5, 1, 2.5, 5 mg/kg, i.p.) displayed dose-related WDS that were inhibited by pretreatment with a fixed dose of clonidine (0.15 mg/kg, s.c.). Shaking behavior caused by a fixed dose (2.5 mg/kg) of icilin was also inhibited in a dose-related manner by clonidine pretreatment (0.03–0.15 mg/kg, s.c.) and reduced by clonidine posttreatment (0.15 mg/kg, s.c.). Pretreatment with a peripherally restricted alpha2-adrenoceptor agonist, ST91 (0.075, 0.15 mg/kg), also decreased the incidence of shaking elicited by 2.5 mg/kg of icilin. Pretreatment with yohimbine (2 mg/kg, i.p.) enhanced the shaking induced by a low dose of icilin (0.5 mg/kg). The imidazoline site agonists, agmatine (150 mg/kg, i.p.) and 2-BFI (7 mg/kg, i.p.), did not affect icilin-evoked shaking. These results suggest that alpha2-adrenoceptor activation inhibits shaking induced by icilin and that increases in peripheral, as well as central, alpha2-adrenoceptor signaling oppose the behavioral stimulant effect of icilin. PMID:21315691

CORM-A1 prevents blood-brain barrier dysfunction caused by ionotropic glutamate receptor-mediated endothelial oxidative stress and apoptosis.

PubMed

Basuroy, Shyamali; Leffler, Charles W; Parfenova, Helena

2013-06-01

In cerebral microvascular endothelial cells (CMVEC) of newborn pigs, glutamate at excitotoxic concentrations (mM) causes apoptosis mediated by reactive oxygen species (ROS). Carbon monoxide (CO) produced by CMVEC or delivered by a CO-releasing molecule, CORM-A1, has antioxidant properties. We tested the hypothesis that CORM-A1 prevents cerebrovascular endothelial barrier dysfunction caused by glutamate excitotoxicity. First, we identified the glutamate receptors (GluRs) and enzymatic sources of ROS involved in the mechanism of endothelial apoptosis. In glutamate-exposed CMVEC, ROS formation and apoptosis were blocked by rotenone, 2-thenoyltrifluoroacetone (TTFA), and antimycin, indicating that mitochondrial complexes I, II, and III are the major sources of oxidative stress. Agonists of ionotropic GluRs (iGluRs) N-methyl-D-aspartate (NMDA), cis-ACPD, AMPA, and kainate increased ROS production and apoptosis, whereas iGluR antagonists exhibited antiapoptotic properties, suggesting that iGluRs mediate glutamate-induced endothelial apoptosis. The functional consequences of endothelial injury were tested in the model of blood-brain barrier (BBB) composed of CMVEC monolayer on semipermeable membranes. Glutamate and iGluR agonists reduced transendothelial electrical resistance and increased endothelial paracellular permeability to 3-kDa dextran. CORM-A1 exhibited potent antioxidant and antiapoptotic properties in CMVEC and completely prevented BBB dysfunction caused by glutamate and iGluR agonists. Overall, the endothelial component of the BBB is a cellular target for excitotoxic glutamate that, via a mechanism involving a iGluR-mediated activation of mitochondrial ROS production and apoptosis, leads to BBB opening that may be prevented by the antioxidant and antiapoptotic actions of CORMs. Antioxidant CORMs therapy may help preserve BBB functional integrity in neonatal cerebrovascular disease.

Does anesthetic additivity imply a similar molecular mechanism of anesthetic action at N-methyl-D-aspartate receptors?

PubMed

Brosnan, Robert J; Pham, Trung L

2011-03-01

Isoflurane and carbon dioxide (CO(2)) negatively modulate N-methyl-d-aspartate (NMDA) receptors, but via different mechanisms. Isoflurane is a competitive antagonist at the NMDA receptor glycine binding site, whereas CO(2) inhibits NMDA receptor current through extracellular acidification. Isoflurane and CO(2) exhibit additive minimum alveolar concentration effects in rats, but we hypothesized that they would not additively inhibit NMDA receptor currents in vitro because they act at different molecular sites. NMDA receptors were expressed in frog oocytes and studied using 2-electrode voltage clamp techniques. A glycine concentration response for NMDA was measured in the presence and absence of CO(2). Concentration-response curves for isoflurane, H(+), CO(2), and ketamine as a function of NMDA inhibition were measured, and a Hill equation was used to calculate the EC(50) for each compound. Binary drug combinations containing ½ EC(50) were additive if NMDA current inhibition was not statistically different from 50%. The ½ EC(50) binary drug combinations decreased the percentage baseline NMDA receptor current as follows (mean ± SD, n = 5 to 6 oocytes each): CO(2)+ H(+) (51% ± 5%), CO(2 )+ isoflurane (54% ± 5%), H(+) + isoflurane (51% ± 3%), CO(2)+ ketamine (67% ± 8%), and H(+) + ketamine (64% ± 2%). In contrast to our hypothesis, NMDA receptor inhibition by CO(2) and isoflurane is additive. Possibly, CO(2) acidification modulates a pH-sensitive loop on the NMDA receptor that in turn alters glycine binding affinity on the GluN1 subunit. However, ketamine plus either CO(2) or H(+) synergistically inhibits NMDA receptor currents. Drugs acting via different mechanisms can thus exhibit additive or synergistic receptor effects. Additivity may not robustly indicate commonality between molecular anesthetic mechanisms.

NMDA receptor blockade in the prelimbic cortex activates the mesolimbic system and dopamine-dependent opiate reward signaling.

PubMed

Tan, Huibing; Rosen, Laura G; Ng, Garye A; Rushlow, Walter J; Laviolette, Steven R

2014-12-01

N-Methyl-D-aspartate (NMDA) receptors in the medial prefrontal cortex (mPFC) are involved in opiate reward processing and modulate sub-cortical dopamine (DA) activity. NMDA receptor blockade in the prelimbic (PLC) division of the mPFC strongly potentiates the rewarding behavioural properties of normally sub-reward threshold doses of opiates. However, the possible functional interactions between cortical NMDA and sub-cortical DAergic motivational neural pathways underlying these effects are not understood. This study examines how NMDA receptor modulation in the PLC influences opiate reward processing via interactions with sub-cortical DAergic transmission. We further examined whether direct intra-PLC NMDA receptor modulation may activate DA-dependent opiate reward signaling via interactions with the ventral tegmental area (VTA). Using an unbiased place conditioning procedure (CPP) in rats, we performed bilateral intra-PLC microinfusions of the competitive NMDA receptor antagonist, (2R)-amino-5-phosphonovaleric acid (AP-5), prior to behavioural morphine place conditioning and challenged the rewarding effects of morphine with DA receptor blockade. We next examined the effects of intra-PLC NMDA receptor blockade on the spontaneous activity patterns of presumptive VTA DA or GABAergic neurons, using single-unit, extracellular in vivo neuronal recordings. We show that intra-PLC NMDA receptor blockade strongly activates sub-cortical DA neurons within the VTA while inhibiting presumptive non-DA GABAergic neurons. Behaviourally, NMDA receptor blockade activates a DA-dependent opiate reward system, as pharmacological blockade of DA transmission blocked morphine reward only in the presence of intra-PLC NMDA receptor antagonism. These findings demonstrate a cortical NMDA-mediated mechanism controlling mesolimbic DAergic modulation of opiate reward processing.

Rapid surface accumulation of NMDA receptors increases glutamatergic excitation during status epilepticus.

PubMed

Naylor, David E; Liu, Hantao; Niquet, Jerome; Wasterlain, Claude G

2013-06-01

After 1h of lithium-pilocarpine status epilepticus (SE), immunocytochemical labeling of NMDA receptor NR1 subunits reveals relocation of subunits from the interior to the cell surface of dentate gyrus granule cells and CA3 pyramidal cells. Simultaneously, an increase in NMDA-miniature excitatory postsynaptic currents (mEPSC) as well as an increase in NMDA receptor-mediated tonic currents is observed in hippocampal slices after SE. Mean-variance analysis of NMDA-mEPSCs estimates that the number of functional postsynaptic NMDA receptors per synapse increases 38% during SE, and antagonism by ifenprodil suggests that an increase in the surface representation of NR2B-containing NMDA receptors is responsible for the augmentation of both the phasic and tonic excitatory currents with SE. These results provide a potential mechanism for an enhancement of glutamatergic excitation that maintains SE and may contribute to excitotoxic injury during SE. Therapies that directly antagonize NMDA receptors may be a useful therapeutic strategy during refractory SE. Copyright © 2013 Elsevier Inc. All rights reserved.

Rapid surface accumulation of NMDA receptors increases glutamatergic excitation during status epilepticus

PubMed Central

Naylor, David E.; Liu, Hantao; Niquet, Jerome; Wasterlain, Claude G.

2017-01-01

After 1 h of lithium-pilocarpine status epilepticus (SE), immunocytochemical labeling of NMDA receptor NR1 subunits reveals relocation of subunits from the interior to the cell surface of dentate gyrus granule cells and CA3 pyramidal cells. Simultaneously, an increase in NMDA-miniature excitatory postsynaptic currents (mEPSC) as well as an increase in NMDA receptor-mediated tonic currents is observed in hippocampal slices after SE. Mean-variance analysis of NMDA-mEPSCs estimates that the number of functional postsynaptic NMDA receptors per synapse increases 38% during SE, and antagonism by ifenprodil suggests that an increase in the surface representation of NR2B-containing NMDA receptors is responsible for the augmentation of both the phasic and tonic excitatory currents with SE. These results provide a potential mechanism for an enhancement of glutamatergic excitation that maintains SE and may contribute to excitotoxic injury during SE. Therapies that directly antagonize NMDA receptors may be a useful therapeutic strategy during refractory SE. PMID:23313318

NMDA receptor gating of information flow through the striatum in vivo.

PubMed

Pomata, Pablo E; Belluscio, Mariano A; Riquelme, Luis A; Murer, M Gustavo

2008-12-10

A role of NMDA receptors in corticostriatal synaptic plasticity is widely acknowledged. However, the conditions that allow NMDA receptor activation in the striatum in vivo remain obscure. Here we show that NMDA receptors contribute to sustain the membrane potential of striatal medium spiny projection neurons close to threshold during spontaneous UP states in vivo. Moreover, we found that the blockade of striatal NMDA receptors reduces markedly the spontaneous firing of ensembles of medium spiny neurons during slow waves in urethane-anesthetized rats. We speculate that recurrent activation of NMDA receptors during UP states allows off-line information flow through the striatum and system level consolidation during habit formation.

Study of the n-methyl-d-aspartate antagonistic properties of anticholinergic drugs

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

McDonough, J.H.; Shih, T.M.

1995-12-31

A study of the N-methyl-D-aspartate antagonistic properties of anticholinergic drugs. PHARMACOL BIOCHEM BEHAV. 51(2/3) 249-253, 1995. Drugs that act at the N-methyl-D-aspartate (NMDA) receptor complex have the ability to terminate nerve agent-induced seizures and modulate the neuropathologic consequences of agent exposure. Drugs with mixed anticholinergic and anti-NMDA properties potentially provide an ideal class of compounds for development as anticonvulsant treatments for nerve agent casualties. The present experiment evaluated the potential NMDA antagonist activity of 11 anticholinergic drugs by determining whether pretreatment with the compound was capable of protecting mice from the lethal effects of NMDA. The following anticholinergic drugs antagonizedmore » NMDA lethality and are ranked according to their potency: mecamylamine > procyclidine = benactyzine > biperiden > tribexyphenidyl. The anticholinergics atropine, aprophen, azaprophen, benztropine, 3-quinudidinyl benzilate (QNB), and scopolamine failed to show NMDA antagonist properties. In addition, and unexpectedly, diazepam, ethanol, and pentobarbital were also shown to be capable of antagonizing NMDA lethality over a certain range of doses. The advantages and limitations of using antagonism of NMDA lethality in mice as a bioassay for determining the NMDA antagonist properties of drugs are also discussed.« less

EVALUATING THE NMDA-GLUTAMATE RECEPTOR AS A SITE OF ACTION FOR TOLUENE, IN VIVO

EPA Science Inventory

In vitro, toluene disrupts the function of NMDA-glutamate receptors, indicating that effects on NMDA receptor function may contribute to toluene neurotoxicity. NMDA-glutamate receptors are widely present in the visual system and contribute to pattern-elicited visual evoked potent...

The CRF₁ receptor antagonist SSR125543 prevents stress-induced long-lasting sleep disturbances in a mouse model of PTSD: comparison with paroxetine and d-cycloserine.

PubMed

Philbert, Julie; Beeské, Sandra; Belzung, Catherine; Griebel, Guy

2015-02-15

The selective CRF₁ (corticotropin releasing factor type 1) receptor antagonist SSR125543 has been previously shown to attenuate the long-term behavioral and electrophysiological effects produced by traumatic stress exposure in mice. Sleep disturbances are one of the most commonly reported symptoms by people with post-traumatic stress disorder (PTSD). The present study aims at investigating whether SSR125543 (10 mg/kg/day/i.p. for 2 weeks) is able to attenuate sleep/wakefulness impairment induced by traumatic stress exposure in a model of PTSD in mice using electroencephalographic (EEG) analysis. Effects of SSR125543 were compared to those of the 5-HT reuptake inhibitor, paroxetine (10 mg/kg/day/i.p.), and the partial N-methyl-d-aspartate (NMDA) receptor agonist, d-cycloserine (10 mg/kg/day/i.p.), two compounds which have demonstrated clinical efficacy against PTSD. Baseline EEG recording was performed in the home cage for 6h prior to the application of two electric foot-shocks of 1.5 mA. Drugs were administered from day 1 post-stress to the day preceding the second EEG recording session, performed 14 days later. Results showed that at day 14 post-stress, shocked mice displayed sleep fragmentation as shown by an increase in the occurrence of both non-rapid eye movement (NREM) sleep and wakefulness bouts. The duration of wakefulness, NREM and REM sleep were not significantly affected. The stress-induced effects were prevented by repeated administration of SSR125543, paroxetine and D-cycloserine. These findings confirm further that the CRF₁ receptor antagonist SSR125543 is able to attenuate the deleterious effects of traumatic stress exposure. Copyright © 2014 Elsevier B.V. All rights reserved.

Combining D-cycloserine with appetitive extinction learning modulates amygdala activity during recall.

PubMed

Ebrahimi, Claudia; Koch, Stefan P; Friedel, Eva; Crespo, Ilsoray; Fydrich, Thomas; Ströhle, Andreas; Heinz, Andreas; Schlagenhauf, Florian

2017-07-01

Appetitive Pavlovian conditioning plays a crucial role in the pathogenesis of drug addiction and conditioned reward cues can trigger craving and relapse even after long phases of abstinence. Promising preclinical work showed that the NMDA-receptor partial agonist D-cycloserine (DCS) facilitates Pavlovian extinction learning of fear and drug cues. Furthermore, DCS-augmented exposure therapy seems to be beneficial in various anxiety disorders, while the supposed working mechanism of DCS during human appetitive or aversive extinction learning is still not confirmed. To test the hypothesis that DCS administration before extinction training improves extinction learning, healthy adults (n=32) underwent conditioning, extinction, and extinction recall on three successive days in a randomized, double-blind, placebo-controlled fMRI design. Monetary wins and losses served as unconditioned stimuli during conditioning to probe appetitive and aversive learning. An oral dose of 50mg of DCS or placebo was administered 1h before extinction training and DCS effects during extinction recall were evaluated on a behavioral and neuronal level. We found attenuated amygdala activation in the DCS compared to the placebo group during recall of the extinguished appetitive cue, along with evidence for enhanced functional amygdala-vmPFC coupling in the DCS group. While the absence of additional physiological measures of conditioned responses during recall in this study prevent the evaluation of a behavioral DCS effect, our neuronal findings are in accordance with recent theories linking successful extinction recall in humans to modulatory top-down influences from the vmPFC that inhibit amygdala activation. Our results should encourage further translational studies concerning the usefulness of DCS to target maladaptive Pavlovian reward associations. Copyright © 2017 Elsevier Inc. All rights reserved.

Stress-induced resistance to the fear memory labilization/reconsolidation process. Involvement of the basolateral amygdala complex.

PubMed

Espejo, Pablo Javier; Ortiz, Vanesa; Martijena, Irene Delia; Molina, Victor Alejandro

2016-10-01

Consolidated memories can enter into a labile state after reactivation followed by a restabilization process defined as reconsolidation. This process can be interfered with Midazolam (MDZ), a positive allosteric modulator of the GABA-A receptor. The present study has evaluated the influence of prior stress on MDZ's interfering effect. We also assessed the influence of both systemic and intra-basolateral amygdala (BLA) infusion of d-cycloserine (DCS), a partial agonist of the NMDA receptors, on the MDZ effect in previously stressed rats. Furthermore, we analyzed the effect of stress on the expression of Zif-268 and the GluN2B sites, two molecular markers of the labilization/reconsolidation process, following reactivation. The results revealed that prior stress resulted into a memory trace that was insensitive to the MDZ impairing effect. Both systemic and intra-BLA DCS administration previous to reactivation restored MDZ's disruptive effect on memory reconsolidation in stressed animals. Further, reactivation enhanced Zif-268 expression in the BLA in control unstressed rats, whereas no elevation was observed in stressed animals. In agreement with the behavioral findings, DCS restored the increased level of Zif-268 expression in the BLA in stressed animals. Moreover, memory reactivation in unstressed animals elevated GluN2B expression in the BLA, thus suggesting that this effect is involved in memory destabilization, whereas stressed animals did not reveal any changes. These findings are consistent with resistance to the MDZ effect in these rats, indicating that stress exposure prevents the onset of destabilization following reactivation. In summary, prior stress limited both the occurrence of the reactivation-induced destabilization and restabilization. Copyright © 2016 Elsevier Ltd. All rights reserved.

Combining d-cycloserine with motor training does not result in improved general motor learning in neurologically intact people or in people with stroke

PubMed Central

Cherry, Kendra M.; Lenze, Eric J.

2014-01-01

Neurological rehabilitation involving motor training has resulted in clinically meaningful improvements in function but is unable to eliminate many of the impairments associated with neurological injury. Thus there is a growing need for interventions that facilitate motor learning during rehabilitation therapy, to optimize recovery. d-Cycloserine (DCS), a partial N-methyl-d-aspartate (NMDA) receptor agonist that enhances neurotransmission throughout the central nervous system (Ressler KJ, Rothbaum BO, Tannenbaum L, Anderson P, Graap K, Zimand E, Hodges L, Davis M. Arch Gen Psychiatry 61: 1136–1144, 2004), has been shown to facilitate declarative and emotional learning. We therefore tested whether combining DCS with motor training facilitates motor learning after stroke in a series of two experiments. Forty-one healthy adults participated in experiment I, and twenty adults with stroke participated in experiment II of this two-session, double-blind study. Session one consisted of baseline assessment, subject randomization, and oral administration of DCS or placebo (250 mg). Subjects then participated in training on a balancing task, a simulated feeding task, and a cognitive task. Subjects returned 1–3 days later for posttest assessment. We found that all subjects had improved performance from pretest to posttest on the balancing task, the simulated feeding task, and the cognitive task. Subjects who were given DCS before motor training, however, did not show enhanced learning on the balancing task, the simulated feeding task, or the associative recognition task compared with subjects given placebo. Moreover, training on the balancing task did not generalize to a similar, untrained balance task. Our findings suggest that DCS does not enhance motor learning or motor skill generalization in neurologically intact adults or in adults with stroke. PMID:24671538

Activation of GPR30 attenuates chronic pain-related anxiety in ovariectomized mice.

PubMed

Liu, Shui-bing; Tian, Zhen; Guo, Yan-yan; Zhang, Nan; Feng, Bin; Zhao, Ming-gao

2015-03-01

Estrogen regulates neuroendocrine and inflammatory processes that play critical roles in neuroinflammation, anxiety, and chronic pain. Patients suffering from chronic pain often complain of anxiety. However, limited information is available regarding the neural circuitry of chronic pain-related anxiety and the related function of estrogen. Hindpaw injection of complete Freund's adjuvant (CFA) and chronic constriction injury (CCI) of the sciatic nerve induced notable pain sensitization and anxiety-like behavior in ovariectomized (OVX) mice. We found that the level of G-protein-coupled receptor 30 (GPR30), a membrane estrogen receptor, was significantly increased in the basolateral amygdala (BLA) of ovariectomized (OVX) mice suffering from chronic inflammatory and neuropathic pain. Subcutaneous injection or BLA local infusion of the GPR30 agonist G1 significantly reduced anxiety-like behavior in CFA-injected and CCI-OVX mice; however, this treatment did not alter the nociceptive threshold. GPR30 knock down by shRNA in the BLA of OVX mice inhibited the anxiolytic effects of GPR30 activation. G1 administration reversed the upregulation of GluR1 subunit in AMPA and NR2A-containing NMDA receptors and the downregulation of GABAA receptors in the BLA of CFA-injected and CCI-OVX mice. Electrophysiological recording revealed that GPR30 activation could prevent imbalance between excitatory and inhibitory transmissions in the BLA synapses of CFA-injected OVX mice. In conclusion, GPR30 activation induced anxiolytic effects but did not affect the nociceptive threshold of mice under chronic pain. The anxiolytic effects of GPR30 were partially due to maintaining the balance between excitatory and inhibitory transmissions in the BLA. Copyright © 2015 Elsevier Ltd. All rights reserved.

Successful pharmacotherapy for the treatment of severe feeding aversion with mechanistic insights from cross-species neuronal remodeling

PubMed Central

Sharp, W G; Allen, A G; Stubbs, K H; Criado, K K; Sanders, R; McCracken, C E; Parsons, R G; Scahill, L; Gourley, S L

2017-01-01

Pediatric feeding disorders affect up to 5% of children, causing severe food intake problems that can result in serious medical and developmental outcomes. Behavioral intervention (BI) is effective in extinguishing feeding aversions, and also expert-dependent, time/labor-intensive and not well understood at a neurobiological level. Here we first conducted a double-blind, placebo-controlled trial comparing BI with BI plus d-cycloserine (DCS). DCS is a partial N-methyl-d-aspartate (NMDA) receptor agonist shown to augment extinction therapies in multiple anxiety disorders. We examined whether DCS enhanced extinction of feeding aversion in 15 children with avoidant/restrictive food intake disorder (ages 20–58 months). After five treatment days, BI improved feeding by 37%. By contrast, BI+DCS improved feeding by 76%. To gain insight into possible mechanisms of successful intervention, we next tested the neurobiological consequences of DCS in a murine model of feeding aversion and avoidance. In mice with conditioned food aversion, DCS enhanced avoidance extinction across a broad dose range. Confocal fluorescence microscopy and three-dimensional neuronal reconstruction indicated that DCS enlarged dendritic spine heads—the primary sites of excitatory plasticity in the brain—within the orbitofrontal prefrontal cortex, a sensory-cognition integration hub. DCS also increased phosphorylation of the plasticity-associated extracellular signal-regulated kinase 1/2. In summary, DCS successfully augments the extinction of food aversion in children and mice, an effect that may involve plasticity in the orbitofrontal cortex. These results warrant a larger-scale efficacy study of DCS for the treatment of pediatric feeding disorders and further investigations of neural mechanisms. PMID:28632204

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

Lima,Santiago; Kumar,Sunil; Gawandi,Vijay

Homo sapiens kynureninase is a pyridoxal-5'-phosphate dependent enzyme that catalyzes the hydrolytic cleavage of 3-hydroxykynurenine to yield 3-hydroxyanthranilate and L-alanine as part of the tryptophan catabolic pathway leading to the de novo biosynthesis of NAD{sup +}. This pathway results in quinolinate, an excitotoxin that is an NMDA receptor agonist. High levels of quinolinate have been correlated with the etiology of neurodegenerative disorders such as AIDS-related dementia and Alzheimer's disease. We have synthesized a novel kynureninase inhibitor, 3-hydroxyhippurate, cocrystallized it with human kynureninase, and solved the atomic structure. On the basis of an analysis of the complex, we designed a seriesmore » of His-102, Ser-332, and Asn-333 mutants. The H102W/N333T and H102W/S332G/N333T mutants showed complete reversal of substrate specificity between 3-hydroxykynurenine and L-kynurenine, thus defining the primary residues contributing to substrate specificity in kynureninases.« less

The sigma-1 receptor modulates NMDA receptor synaptic transmission and plasticity via SK channels in rat hippocampus

PubMed Central

Martina, Marzia; Turcotte, Marie-Eve B; Halman, Samantha; Bergeron, Richard

2007-01-01

The sigma receptor (σR), once considered a subtype of the opioid receptor, is now described as a distinct pharmacological entity. Modulation of N-methyl-d-aspartate receptor (NMDAR) functions by σR-1 ligands is well documented; however, its mechanism is not fully understood. Using patch-clamp whole-cell recordings in CA1 pyramidal cells of rat hippocampus and (+)pentazocine, a high-affinity σR-1 agonist, we found that σR-1 activation potentiates NMDAR responses and long-term potentiation (LTP) by preventing a small conductance Ca2+-activated K+ current (SK channels), known to shunt NMDAR responses, to open. Therefore, the block of SK channels and the resulting increased Ca2+ influx through the NMDAR enhances NMDAR responses and LTP. These results emphasize the importance of the σR-1 as postsynaptic regulator of synaptic transmission. PMID:17068104

The sigma-1 receptor modulates NMDA receptor synaptic transmission and plasticity via SK channels in rat hippocampus.

PubMed

Martina, Marzia; Turcotte, Marie-Eve B; Halman, Samantha; Bergeron, Richard

2007-01-01

The sigma receptor (sigmaR), once considered a subtype of the opioid receptor, is now described as a distinct pharmacological entity. Modulation of N-methyl-D-aspartate receptor (NMDAR) functions by sigmaR-1 ligands is well documented; however, its mechanism is not fully understood. Using patch-clamp whole-cell recordings in CA1 pyramidal cells of rat hippocampus and (+)pentazocine, a high-affinity sigmaR-1 agonist, we found that sigmaR-1 activation potentiates NMDAR responses and long-term potentiation (LTP) by preventing a small conductance Ca2+-activated K+ current (SK channels), known to shunt NMDAR responses, to open. Therefore, the block of SK channels and the resulting increased Ca2+ influx through the NMDAR enhances NMDAR responses and LTP. These results emphasize the importance of the sigmaR-1 as postsynaptic regulator of synaptic transmission.

NMDA Receptor Autoantibodies in Autoimmune Encephalitis Cause a Subunit-Specific Nanoscale Redistribution of NMDA Receptors.

PubMed

Ladépêche, Laurent; Planagumà, Jesús; Thakur, Shreyasi; Suárez, Irina; Hara, Makoto; Borbely, Joseph Steven; Sandoval, Angel; Laparra-Cuervo, Lara; Dalmau, Josep; Lakadamyali, Melike

2018-06-26

Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is a severe neuropsychiatric disorder mediated by autoantibodies against the GluN1 subunit of the NMDAR. Patients' antibodies cause cross-linking and internalization of NMDAR, but the synaptic events leading to depletion of NMDAR are poorly understood. Using super-resolution microscopy, we studied the effects of the autoantibodies on the nanoscale distribution of NMDAR in cultured neurons. Our findings show that, under control conditions, NMDARs form nanosized objects and patients' antibodies increase the clustering of synaptic and extrasynaptic receptors inside the nano-objects. This clustering is subunit specific and predominantly affects GluN2B-NMDARs. Following internalization, the remaining surface NMDARs return to control clustering levels but are preferentially retained at the synapse. Monte Carlo simulations using a model in which antibodies induce NMDAR cross-linking and disruption of interactions with other proteins recapitulated these results. Finally, activation of EphB2 receptor partially antagonized the antibody-mediated disorganization of the nanoscale surface distribution of NMDARs. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

Antagonism of methoxyflurane-induced anesthesia in rats by benzodiazepine inverse agonists.

PubMed

Miller, D W; Yourick, D L; Tessel, R E

1989-11-28

Injection of the partial benzodiazepine inverse agonist Ro15-4513 (1-32 mg/kg i.p.) or nonconvulsant i.v. doses of the full benzodiazepine inverse agonist beta-CCE immediately following cessation of exposure of rats to an anesthetic concentration of methoxyflurane significantly antagonized the duration of methoxyflurane anesthesia as measured by recovery of the righting reflex and/or pain sensitivity. This antagonism was inhibited by the benzodiazepine antagonist Ro15-1788 at doses which alone did not alter the duration of methoxyflurane anesthesia. In addition, high-dose Ro15-4513 pretreatment (32 mg/kg) antagonized the induction and duration of methoxyflurane anesthesia but was unable to prevent methoxyflurane anesthesia or affect the induction or duration of anesthesia induced by the dissociative anesthetic ketamine (100 mg/kg). These findings indicate that methoxyflurane anesthesia can be selectively antagonized by the inverse agonistic action of Ro15-4513 and beta-CCE.

Oxyntomodulin differentially affects glucagon-like peptide-1 receptor beta-arrestin recruitment and signaling through Galpha(s).

PubMed

Jorgensen, Rasmus; Kubale, Valentina; Vrecl, Milka; Schwartz, Thue W; Elling, Christian E

2007-07-01

The glucagon-like peptide (GLP)-1 receptor is a promising target for the treatment of type 2 diabetes and obesity, and there is great interest in characterizing the pharmacology of the GLP-1 receptor and its ligands. In the present report, we have applied bioluminescence resonance energy transfer assays to measure agonist-induced recruitment of betaarrestins and G-protein-coupled receptor kinase (GRK) 2 to the GLP-1 receptor in addition to traditional measurements of second messenger generation. The peptide hormone oxyntomodulin is described in the literature as a full agonist on the glucagon and GLP-1 receptors. Surprisingly, despite being full agonists in GLP-1 receptor-mediated cAMP accumulation, oxyntomodulin and glucagon were observed to be partial agonists in recruiting betaarrestins and GRK2 to the GLP-1 receptor. We suggest that oxyntomodulin and glucagon are biased ligands on the GLP-1 receptor.

5-Amino-6-chloro-N-[(1-isobutylpiperidin-4-yl)methyl]-2-methylimidazo[1,2-alpha]pyridine-8-carboxamide (CJ-033,466), a novel and selective 5-hydroxytryptamine4 receptor partial agonist: pharmacological profile in vitro and gastroprokinetic effect in conscious dogs.

PubMed

Mikami, Tadayoshi; Ochi, Yasuo; Suzuki, Keiko; Saito, Toshiyuki; Sugie, Yutaka; Sakakibara, Minoru

2008-04-01

5-Hydroxytryptamine (5-HT) receptors and dopamine(2) (D(2)) receptor modulate gastrointestinal motility. Gastroprokinetic agents that act on several 5-HT receptor subtypes and/or D(2) receptors are used clinically. Although the 5-HT(4) receptor is known to mediate the gastroprokinetic effects of these agents, the absence of highly selective 5-HT(4) receptor agonists has made it difficult to confirm the physiological consequences of selective 5-HT(4) receptor stimulation. In this study, we report the in vitro pharmacological profiles and the in vivo gastroprokinetic effects of 5-amino-6-chloro-N-[(1-isobutylpiperidin-4-yl)methyl]-2-methylimidazo[1,2-alpha]pyridine-8-carboxamide (CJ-033,466), a novel, potent, and selective 5-HT(4) partial agonist. Compared with preceding 5-HT(4) agonists such as cisapride, mosapride, and tegaserod, CJ-033,466 had a superior in vitro profile, with nanomolar agonistic activities for the 5-HT(4) receptor and 1000-fold greater selectivity for the 5-HT(4) receptor over other 5-HT and D(2) receptors. In vivo studies in conscious dogs showed that CJ-033,466 dose-dependently stimulated gastric antral motility in both the fasted and postprandial states at the same dose range and that it was 30 times more potent than cisapride. Furthermore, CJ-033,466 accelerated the gastric emptying rate in a gastroparesis dog model at the minimally effective dose established in the gastric motility study. In conclusion, CJ-033,466 is a potent and highly selective 5-HT(4) agonist that stimulates physiologically coordinated gastric motility, and it has no activity on other 5-HT receptor subtypes and D(2) receptors. Therefore, CJ-033,466 could be used to treat gastroparesis, providing better gastroprokinetics and reduced side effects mediated by the other receptors.

Coadministration of VDR and RXR agonists synergistically alleviates atherosclerosis through inhibition of oxidative stress: An in vivo and in vitro study.

PubMed

Lin, L M; Peng, F; Liu, Y P; Chai, D J; Ning, R B; Xu, C S; Lin, J X

2016-08-01

Diabetes contributes to atherosclerosis partially through induction of oxidative stress. Both vitamin D receptor (VDR) and retinoid X receptor (RXR) agonists exhibit anti-atherogenic effects. We explored the effects of combination treatment with VDR and RXR agonists (represented by calcitriol and bexarotene, respectively) on atherosclerosis progression and the mechanisms involved, using a diabetes model of mice. The animals were intragastrically fed calcitriol (200 ng/kg, twice-a-week), bexarotene (10 mg/kg, once-daily) either alone or in combination for 12 weeks. VDR and RXR agonists delayed atherosclerosis progression independent of serum lipid and glucose levels, and significantly reduced the protein expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit gp91phox and nuclear factor-kappa B (NF-κB) subunit p65, as well as plasma biomarkers of oxidative stress and inflammation. Combination therapy alleviated atherosclerosis and inhibited indexes of oxidative stress and inflammation to a greater extent than either monotherapy. In the in vitro study, naturally occurring VDR ligand 1α,25-dihydroxyvitamin D3 (1,25[OH]2D3) and RXR ligand 9-cis retinoic acid (9-cis-RA), both significantly inhibited high-glucose-induced endothelial cell apoptosis. Co-administration of VDR and RXR ligands produced synergistic protection against endothelial apoptosis by antagonizing the protein kinase C /NADPH oxidase/reactive oxygen species pathway. The inhibitory effects of 9-cis-RA on oxidative stress was attenuated when VDR was downregulated by VDR siRNA; however, downregulation of RXR by RXR siRNA imposed no influence on the effects of 1,25(OH)2D3. Combination treatment with VDR and RXR agonists synergistically alleviated diabetic atherosclerosis through inhibition of oxidative stress, and the preventive effects of RXR agonist may partially depend on VDR activation. Copyright © 2016. Published by Elsevier Ireland Ltd.

Acute Ethanol Exposure Prevents PMA-mediated Augmentation of N-methyl-d-aspartate Receptor Function in Primary Cultured Cerebellar Granule Cells

PubMed Central

Reneau, Jason; Reyland, Mary E.; Popp, R. Lisa

2011-01-01

Many intracellular proteins and signaling cascades contribute to the ethanol sensitivity of native N-methyl-d-aspartate receptors (NMDARs). One putative protein is the serine / threonine kinase, Protein kinase C (PKC). The purpose of this study was to assess if PKC modulates the ethanol sensitivity of native NMDARs expressed in primary cultured cerebellar granule cells (CGCs). With the whole-cell patch-clamp technique, we assessed if ethanol inhibition of NMDA-induced currents (INMDA) (100 μM NMDA plus 10 μM glycine) were altered in CGCs in which the novel and classical PKC isoforms were activated by phorbol-12-myristate-13-acetate (PMA). Percent inhibition by 10, 50 or 100 mM ethanol of NMDA-induced steady-state (ISS) or peak current amplitudes (IPk) of NMDARs expressed in CGCs in which PKC was activated by a 12.5 min, 100 nM PMA exposure at 37° C did not differ from currents obtained from receptors contained in control cells. However, PMA-mediated augmentation of IPk in the absence of ethanol was abolished after brief applications of 10 or 1 mM ethanol co-applied with agonists, and this suppression of enhanced receptor function was observed for up to eight minutes post-ethanol exposure. Because we had previously shown that PMA-mediated augmentation of INMDA of NMDARs expressed in these cells is by activation of PKCα, we assessed the effect of ethanol (1, 10, 50 and 100 mM) on PKCα activity. Ethanol decreased PKCα activity by 18% for 1 mM ethanol and activity decreased with increasing ethanol concentrations with a 50% inhibition observed with 100 mM ethanol. The data suggest that ethanol disruption of PMA-mediated augmentation of INMDA may be due to a decrease in PKCα activity by ethanol. However, given the incomplete blockade of PKCα activity and the low concentration of ethanol at which this phenomenon is observed, other ethanol-sensitive signaling cascades must also be involved. PMID:21624785

Glutamatergic modulation of separation distress: profound emotional effects of excitatory amino acids in chicks.

PubMed

Normansell, Larry; Panksepp, Jaak

2011-10-01

Pre-clinical models of brain affective circuits provide relevant evidence for understanding the brain systems that figure heavily in psychiatric disorders. Social isolation and the resulting separation distress contribute to the onset of depression. In this work, the effects of excitatory amino acids (EAA) on isolation-induced distress vocalization (DV) were assessed in young domestic chicks. Both glutamate and quisqualate (QA) produced dose-dependent reductions in DVs, while N-methyl-d-aspartate (NMDA) and kainate (KA) increased DVs. Such a differential pattern of responsiveness may indicate the presence of reciprocal or interacting EAA systems in the brain control of separation distress. Administration of either the NMDA receptor antagonist 2-amino-5-phosphonovalerate (APV) or the broad-spectrum antagonist gamma-d-glutamylglycine (DGG) greatly reduced DVs, as did the antagonist 2-amino-4-phosphonobutyrate (APB). APV did not attenuate the increase in vocalizations seen after NMDA or KA administration. DGG, however, was able to block the increase in calling produced by either of these agonists, suggesting a KA receptor mechanism. KA treatment inhibited the ability of other chicks, or auditory and somatosensory information, to suppress DVs. KA-treated animals exhibited a hyperemotional behavior pattern during which a variety of motivated behaviors were disrupted including reactions to novel objects, approaching the flock, and foraging. They could not sustain a coherent flock-like social cohesion, but exhibited strong fixed-action patterns of flight interspersed with hiding and crouching behaviors. The evident behavioral changes suggest that glutamatergic synapses directly influence sensory, motor and emotional processes in the brain and may be especially important in the integration of environmental stimuli with emotional central state processes of animals. Considering that unresolved social loss and grief have been deemed to be among the main precipitating causes of depression, and glutamate plays a large role in the production of negative effect related to separation distress, these results are consistent with the emerging work targeting glutamate blockade as a way to produce rapid anti-depressant effects. Copyright © 2011 Elsevier Ltd. All rights reserved.

Involvement of CRF but not NPY in the anxiety regulation via NMDA receptors.

PubMed

Wierońska, Joanna M; Szewczyk, Bernadeta; Pałucha, Agnieszka; Brański, Piotr; Smiałowska, Maria

2003-01-01

The study attempts to evaluate whether neuropeptide Y (NPY) and corticotropin-releasing factor (CRF) are involved in anxiogenic and anxiolytic reactions induced by NMDA receptor ligands. The animals were given MK-801 (1 mg/kg, ip), a non-competitive NMDA-receptor antagonist, which acts as anxiolytic agent, or NMDA (15 mg/kg, ip), which has an anxiogenic effect. The anxiogenic or anxiolytic actions of these compounds were evaluated in the plus-maze test. The animals, which were given MK-801, were administered BIBO 3304 (130 ng/0.5 microl/site) intraamygdalarly and the animals which were given NMDA were administered alpha-helical CRF (500 ng/0.5 microl/site). BIBO 3304 did not attenuate MK-801-induced anxiolysis and alpha-helical CRF abolished NMDA-induced anxiogenesis. Our results show that anxiogenic effect of NMDA is mediated via CRF1 receptors and anxiolytic action of MK-801 is not dependent on Y1 receptors.

Some cannabinoid receptor ligands and their distomers are direct-acting openers of SUR1 KATP channels

PubMed Central

Zhou, Qing; Shyng, Show-Ling; Heal, David J.; Cheetham, Sharon C.; Dickinson, Keith; Gregory, Peter; Firnges, Michael; Nordheim, Ulrich; Goshorn, Stephanie; Reiche, Dania; Turski, Lechoslaw; Antel, Jochen

2012-01-01

Here, we examined the chronic effects of two cannabinoid receptor-1 (CB1) inverse agonists, rimonabant and ibipinabant, in hyperinsulinemic Zucker rats to determine their chronic effects on insulinemia. Rimonabant and ibipinabant (10 mg·kg−1·day−1) elicited body weight-independent improvements in insulinemia and glycemia during 10 wk of chronic treatment. To elucidate the mechanism of insulin lowering, acute in vivo and in vitro studies were then performed. Surprisingly, chronic treatment was not required for insulin lowering. In acute in vivo and in vitro studies, the CB1 inverse agonists exhibited acute K channel opener (KCO; e.g., diazoxide and NN414)-like effects on glucose tolerance and glucose-stimulated insulin secretion (GSIS) with approximately fivefold better potency than diazoxide. Followup studies implied that these effects were inconsistent with a CB1-mediated mechanism. Thus effects of several CB1 agonists, inverse agonists, and distomers during GTTs or GSIS studies using perifused rat islets were unpredictable from their known CB1 activities. In vivo rimonabant and ibipinabant caused glucose intolerance in CB1 but not SUR1-KO mice. Electrophysiological studies indicated that, compared with diazoxide, 3 μM rimonabant and ibipinabant are partial agonists for K channel opening. Partial agonism was consistent with data from radioligand binding assays designed to detect SUR1 KATP KCOs where rimonabant and ibipinabant allosterically regulated 3H-glibenclamide-specific binding in the presence of MgATP, as did diazoxide and NN414. Our findings indicate that some CB1 ligands may directly bind and allosterically regulate Kir6.2/SUR1 KATP channels like other KCOs. This mechanism appears to be compatible with and may contribute to their acute and chronic effects on GSIS and insulinemia. PMID:22167524

Interactions of ligands with active and inactive conformations of the dopamine D2 receptor.

PubMed

Malmberg, A; Mohell, N; Backlund Höök, B; Johansson, A M; Hacksell, U; Nordvall, G

1998-04-10

The affinities of 19 pharmacologically diverse dopamine D2 receptor ligands were determined for the active and inactive conformations of cloned human dopamine D2 receptors expressed in Ltk cells. The agonist [3H]quinpirole was used to selectively label the guanine nucleotide-binding protein-coupled, active receptor conformation. The antagonist [3H]raclopride, in the presence of the non-hydrolysable GTP-analogue Gpp(NH)p and sodium ions and in the absence of magnesium ions, was used to label the free inactive receptor conformation. The intrinsic activities of the ligands were determined in a forskolin-stimulated cyclic AMP assay using the same cells. An excellent correlation was shown between the affinity ratios (KR/KRG) of the ligands for the two receptor conformations and their intrinsic activity (r=0.96). The ligands included eight structurally related and enantiopure 2-aminotetralin derivatives; the enantiomers of 5-hydroxy-2-(dipropylamino)tetralin, 5-methoxy-2-(dipropylamino)tetralin, 5-fluoro-2-(dipropylamino)tetralin and 2-(dipropylamino)tetralin. The (S)-enantiomers behaved as full agonists in the cyclic AMP assay and displayed a large KR/KRG ratio. The (R)-enantiomers were classified as partial agonists and had lower ratios. The structure-affinity relationships of these compounds at the active and the inactive receptor conformations were analysed separately, and used in conjunction with a homology based receptor model of the dopamine D2 receptor. This led to proposed binding modes for agonists, antagonists and partial agonists in the 2-aminotetralin series. The concepts used in this study should be of value in the design of ligands with predetermined affinity and intrinsic activity.

The G‐protein biased partial κ opioid receptor agonist 6′‐GNTI blocks hippocampal paroxysmal discharges without inducing aversion

PubMed Central

Zangrandi, Luca; Burtscher, Johannes; MacKay, James P; Colmers, William F

2016-01-01

Background and Purpose With a prevalence of 1–2%, epilepsies belong to the most frequent neurological diseases worldwide. Although antiepileptic drugs are available since several decades, the incidence of patients that are refractory to medication is still over 30%. Antiepileptic effects of κ opioid receptor (κ receptor) agonists have been proposed since the 1980s. However, their clinical use was hampered by dysphoric side effects. Recently, G‐protein biased κ receptor agonists were developed, suggesting reduced aversive effects. Experimental Approach We investigated the effects of the κ receptor agonist U‐50488H and the G‐protein biased partial κ receptor agonist 6′‐GNTI in models of acute seizures and drug‐resistant temporal lobe epilepsy and in the conditioned place avoidance (CPA) test. Moreover, we performed slice electrophysiology to understand the functional mechanisms of 6′‐GNTI. Key Results As previously shown for U‐50488H, 6′‐GNTI markedly increased the threshold for pentylenetetrazole‐induced seizures. All treated mice displayed reduced paroxysmal activity in response to U‐50488H (20 mg·kg−1) or 6′‐GNTI (10–30 nmoles) treatment in the mouse model of intra‐hippocampal injection of kainic acid. Single cell recordings on hippocampal pyramidal cells revealed enhanced inhibitory signalling as potential mechanisms causing the reduction of paroxysmal activity. Effects of 6′‐GNTI were blocked in both seizure models by the κ receptor antagonist 5′‐GNTI. Moreover, 6′‐GNTI did not induce CPA, a measure of aversive effects, while U‐50488H did. Conclusions and Implications Our data provide the proof of principle that anticonvulsant/antiseizure and aversive effects of κ receptor activation can be pharmacologically separated in vivo. PMID:26928671

Transcriptional Modulation of the Immune Response by Peroxisome Proliferator-Activated Receptor-α Agonists in Autoimmune Disease1

PubMed Central

Gocke, Anne R.; Hussain, Rehana Z.; Yang, Yuhong; Peng, Haiyan; Weiner, Jeffrey; Ben, Li-Hong; Drew, Paul D.; Stuve, Olaf; Lovett-Racke, Amy E.; Racke, Michael K.

2010-01-01

Peroxisome proliferator-activated receptor-α (PPARα) agonists have been shown to have a therapeutic benefit in experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis (MS). In this study, we investigated the mechanism by which the PPARα agonist gemfibrozil induces immune deviation and protects mice from EAE. We demonstrated that treatment with gemfibrozil increases expression of the Th2 transcription factor GATA-3 and decreases expression of the Th1 transcription factor T-bet in vitro and directly ex vivo. These changes correlated with an increase in nuclear PPARα expression. Moreover, the protective effects of PPARα agonists in EAE were shown to be partially dependent on IL-4 and to occur in a receptor-dependent manner. PPARα was demonstrated, for the first time, to regulate the IL-4 and IL-5 genes and to bind the IL-4 promoter in the presence of steroid receptor coactivator-1, indicating that PPARα can directly transactivate the IL-4 gene. Finally, therapeutic administration of PPARα agonists ameliorated clinically established EAE, suggesting that PPARα agonists may provide a treatment option for immune-mediated inflammatory diseases. PMID:19299749

N-Methyl-d-aspartate Modulation of Nucleus Accumbens Dopamine Release by Metabotropic Glutamate Receptors: Fast Cyclic Voltammetry Studies in Rat Brain Slices in Vitro.

PubMed

Yavas, Ersin; Young, Andrew M J

2017-02-15

The N-methyl-d-aspartate (NMDA) receptor antagonist, phencyclidine, induces behavioral changes in rodents mimicking symptoms of schizophrenia, possibly mediated through dysregulation of glutamatergic control of mesolimbic dopamine release. We tested the hypothesis that NMDA receptor activation modulates accumbens dopamine release, and that phencyclidine pretreatment altered this modulation. NMDA caused a receptor-specific, dose-dependent decrease in electrically stimulated dopamine release in nucleus accumbens brain slices. This decrease was unaffected by picrotoxin, making it unlikely to be mediated through GABAergic neurones, but was decreased by the metabotropic glutamate receptor antagonist, (RS)-α-methyl-4-sulfonophenylglycine, indicating that NMDA activates mechanisms controlled by these receptors to decrease stimulated dopamine release. The effect of NMDA was unchanged by in vivo pretreatment with phencyclidine (twice daily for 5 days), with a washout period of at least 7 days before experimentation, which supports the hypothesis that there is no enduring direct effect of PCP at NMDA receptors after this pretreatment procedure. We propose that NMDA depression of accumbal dopamine release is mediated by metabotropic glutamate receptors located pre- or perisynaptically, and suggest that NMDA evoked increased extrasynaptic spillover of glutamate is sufficient to activate these receptors that, in turn, inhibit dopamine release. Furthermore, we suggest that enduring functional changes brought about by subchronic phencyclidine pretreatment, modeling deficits in schizophrenia, are downstream effects consequent on chronic blockade of NMDA receptors, rather than direct effects on NMDA receptors themselves.

Ethanol (EtOH) inhibition of NMDA-activated ion current is not voltage-dependent and EtOH does not interact with other binding sites on the NMDA receptor/ionophore complex

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

Lovinger, D.M.; White, G.; Weight, F.F.

1990-02-26

Recent studies indicate that intoxicating concentrations of EtOH inhibit neuronal responses to activation of NMDA-type glutamate receptors. The authors have observed that the potency of different alcohols for inhibiting NMDA-activated ion current in hippocampal neurons increases as a function of increasing hydrophobicity, suggesting that EtOH acts at a hydrophobic site. To further characterize the mechanisms of this effect, the authors examined the voltage-dependence of the EtOH inhibition of NMDA-activated ion current as well as potential interactions of EtOH with other effectors of the NMDA receptor/ionophore complex. The amount of inhibition of peak NMDA-activated current by 50 mM EtOH did notmore » differ over a range of membrane potentials from {minus}60 to +60 mV, and EtOH did not alter the reversal potential of NMDA-activated current. The percent inhibition observed in the presence of 10-100 mM EtOH did not differ with NMDA concentrations from 10-100 {mu}M. The percent inhibition by 50 mM EtOH (30-48%) did not differ in the absence or presence of the channel blockers Mg{sup 2+} (50-500 {mu}M), Zn{sup 2+} (5 and 20 {mu}M) or ketamine (2 and 10 {mu}M), or with increasing concentrations of the NMDA receptor cofactor glycine (0.01-1 {mu}M). These data indicate that: (i) EtOH does not change the ion selectivity of the ionophore, and (ii) EtOH does not appear to interact with previously described binding sites on the NMDA receptor/ionophore complex.« less

Estrogen induces rapid decrease in dendritic thorns of CA3 pyramidal neurons in adult male rat hippocampus

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

Tsurugizawa, Tomokazu; Core Research for Evolutional Science and Technology Project of Japan Science and Technology Agency, Graduate School of Arts and Sciences, University of Tokyo at Komaba, 3-8-1 Meguro, Tokyo 153; Mukai, Hideo

2005-12-02

Modulation of hippocampal synaptic plasticity by estrogen has been attracting much attention. Thorns of thorny excrescences of CA3 hippocampal neurons are post-synaptic regions whose presynaptic partners are mossy fiber terminals. Here we demonstrated the rapid effect of estradiol on the density of thorns of thorny excrescences, by imaging Lucifer Yellow-injected CA3 neurons in adult male rat hippocampal slices. The application of 1 nM estradiol induced rapid decrease in the density of thorns on pyramidal neurons within 2 h. The estradiol-mediated decrease in the density of thorns was blocked by CNQX (AMPA receptor antagonist) and PD98059 (MAP kinase inhibitor), but notmore » by MK-801 (NMDA receptor antagonist). ER{alpha} agonist PPT induced the same suppressive effect as that induced by estradiol on the density of thorns, but ER{beta} agonist DPN did not affect the density of thorns. Note that a 1 nM estradiol treatment did not affect the density of spines in the stratum radiatum and stratum oriens. A search for synaptic ER{alpha} was performed using purified RC-19 antibody. The localization of ER{alpha} (67 kDa) in the CA3 mossy fiber terminals and thorns was demonstrated using immunogold electron microscopy. These results imply that estradiol drives the signaling pathway including ER{alpha} and MAP kinase.« less

Angiotensin II attenuates NMDA receptor-mediated neuronal cell death and prevents the associated reduction in Bcl-2 expression.

PubMed

Schelman, William R; Andres, Robert; Ferguson, Paul; Orr, Brent; Kang, Evan; Weyhenmeyer, James A

2004-09-10

While angiotensin II (Ang II) plays a major role in the regulation of blood pressure, fluid homeostasis and neuroendocrine function, recent studies have also implicated the peptide hormone in cell growth, differentiation and apoptosis. In support of this, we have previously demonstrated that Ang II attenuates N-methyl-D-aspartate (NMDA) receptor signaling [Molec. Brain Res. 48 (1997) 197]. To further examine the modulatory role of Ang II on NMDA receptor function, we investigated the effect of angiotensin receptor (AT) activation on NMDA-mediated cell death and the accompanying decrease in Bcl-2 expression. The viability of differentiated N1E-115 and NG108-15 neuronal cell lines was reduced following exposure to NMDA in a dose-dependent manner. MTT analysis (mitochondrial integrity) revealed a decrease in cell survival of 49.4+/-12.3% in NG108 cells and 79.9+/-6.8% in N1E cells following treatment with 10 mM NMDA for 20 h. Cytotoxicity in N1E cells was inhibited by the noncompetitive NMDA receptor antagonist, MK-801. Further, NMDA receptor-mediated cell death in NG108 cells was attenuated by treatment with Ang II. The Ang II effect was inhibited by both AT1 and AT2 receptor antagonists, losartan and PD123319, respectively, suggesting that both receptor subtypes may play a role in the survival effect of Ang II. Since it has been shown that activation of NMDA receptors alters the expression of Bcl-2 family proteins, Western blot analysis was performed in N1E cells to determine whether Ang II alters the NMDA-induced changes in Bcl-2 expression. A concentration-dependent decrease of intracellular Bcl-2 protein levels was observed following treatment with NMDA, and this reduction was inhibited by MK801. Addition of Ang II suppressed the NMDA receptor-mediated reduction in Bcl-2. The Ang II effect on NMDA-mediated changes in Bcl-2 levels was blocked by PD123319, but was not significantly changed by losartan, suggesting AT2 receptor specificity. Taken together, these results suggest that Ang II attenuates NMDA receptor-mediated neurotoxicity and that this effect may be due, in part, to an alteration in Bcl-2 expression.

New PPARγ partial agonist improves obesity-induced metabolic alterations and atherosclerosis in LDLr(-/-) mice.

PubMed

Silva, Jacqueline C; César, Fernanda A; de Oliveira, Edson M; Turato, Walter M; Tripodi, Gustavo L; Castilho, Gabriela; Machado-Lima, Adriana; de Las Heras, Beatriz; Boscá, Lisardo; Rabello, Marcelo M; Hernandes, Marcelo Z; Pitta, Marina G R; Pitta, Ivan R; Passarelli, Marisa; Rudnicki, Martina; Abdalla, Dulcineia S P

2016-02-01

Peroxisome proliferator-activated receptor gamma (PPARγ) regulates multiple pathways involved in the pathogenesis of obesity and atherosclerosis. Here, we evaluated the therapeutic potential of GQ-177, a new thiazolidinedione, on diet-induced obesity and atherosclerosis. The intermolecular interaction between PPARγ and GQ-177 was examined by virtual docking and PPAR activation was determined by reporter gene assay identifying GQ-177 as a partial and selective PPARγ agonist. For the evaluation of biological activity of GQ-177, low-density lipoprotein receptor-deficient (LDLr(-/-)) C57/BL6 mice were fed either a high fat diabetogenic diet (diet-induced obesity), or a high fat atherogenic diet, and treated with vehicle, GQ-177 (20mg/kg/day), pioglitazone (20mg/kg/day, diet-induced obesity model) or rosiglitazone (15mg/kg/day, atherosclerosis model) for 28 days. In diet-induced obesity mice, GQ-177 improved insulin sensitivity and lipid profile, increased plasma adiponectin and GLUT4 mRNA in adipose tissue, without affecting body weight, food consumption, fat accumulation and bone density. Moreover, GQ-177 enhanced hepatic mRNA levels of proteins involved in lipid metabolism. In the atherosclerosis mice, GQ-177 inhibited atherosclerotic lesion progression, increased plasma HDL and mRNA levels of PPARγ and ATP-binding cassette A1 in atherosclerotic lesions. GQ-177 acts as a partial PPARγ agonist that improves obesity-associated insulin resistance and dyslipidemia with atheroprotective effects in LDLr(-/-) mice. Copyright © 2015 Elsevier Ltd. All rights reserved.

The imidazobenzodiazepine Ro 15-4513 antagonizes methoxyflurane anesthesia.

PubMed

Moody, E J; Skolnick, P

1988-01-01

Parenteral administration of the imidazobenzodiazepine Ro 15-4513 (a high affinity ligand of the benzodiazepine receptor with partial inverse agonist qualities) produced a dose dependent reduction in sleep time of mice exposed to the inhalation anesthetic, methoxyflurane. The reductions in methoxyflurane sleep time ranged from approximately 20% at 4 mg/kg to approximately 38% at 32 mg/kg of Ro 15-4513. Co-administration of the benzodiazepine receptor antagonist Ro 15-1788 (16 mg/kg) or the inverse agonists DMCM (5-20 mg/kg) and FG 7142 (22.5 mg/kg) blocks this effect which suggests that the reductions in methoxyflurane sleep time produced by Ro 15-4513 are mediated via occupation of benzodiazepine receptors. Moreover, neither DMCM (5-20 mg/kg) nor FG 7142 (22.5 mg/kg) reduced methoxyflurane sleep time which suggests this effect of Ro 15-4513 cannot be attributed solely to its partial inverse agonist properties. These observations support recent findings that inhalation anesthetics may produce their depressant effects via perturbation of the benzodiazepine/GABA receptor chloride channel complex, and suggest that Ro 15-4513 may serve as a prototype of agents capable of antagonizing the depressant effects of inhalation anesthetics such as methoxyflurane.

Addiction-like synaptic impairments in diet-induced obesity

PubMed Central

Spencer, Sade; Garcia-Keller, Constanza; Spanswick, David C; Lawrence, Andrew John; Simonds, Stephanie Elise; Schwartz, Danielle Joy; Jordan, Kelsey Ann; Jhou, Thomas Clayton; Kalivas, Peter William

2016-01-01

Background There is increasing evidence that the pathological overeating underlying some forms of obesity is compulsive in nature, and therefore contains elements of an addictive disorder. However, direct physiological evidence linking obesity to synaptic plasticity akin to that occurring in addiction is lacking. We sought to establish whether the propensity to diet-induced obesity (DIO) is associated with addictive-like behavior, as well as synaptic impairments in the nucleus accumbens core (NAcore) considered hallmarks of addiction. Methods Sprague-Dawley rats were allowed free access to a palatable diet for 8 weeks then separated by weight gain into DIO prone (OP) and resistant (OR) subgroups. Access to palatable food was then restricted to daily operant self-administration sessions using fixed (FR1, 3 and 5) and progressive ratio (PR) schedules. Subsequently, NAcore brain slices were prepared and we tested for changes in the ratio between AMPA and NMDA currents (AMPA/NMDA) and the ability to exhibit long-term depression (LTD). Results We found that propensity to develop DIO is linked to deficits in the ability to induce LTD in the NAcore, as well as increased potentiation at these synapses as measured by AMPA/NMDA currents. Consistent with these impairments, we observed addictive-like behavior in OP rats, including i) heightened motivation for palatable food (ii) excessive intake and (iii) increased food-seeking when food was unavailable. Conclusions Our results show overlap between the propensity for DIO and the synaptic changes associated with facets of addictive behavior, supporting partial coincident neurological underpinnings for compulsive overeating and drug addiction. PMID:26826876

Compromised NMDA/Glutamate Receptor Expression in Dopaminergic Neurons Impairs Instrumental Learning, But Not Pavlovian Goal Tracking or Sign Tracking

PubMed

James, Alex S; Pennington, Zachary T; Tran, Phu; Jentsch, James David

2015-01-01

Two theories regarding the role for dopamine neurons in learning include the concepts that their activity serves as a (1) mechanism that confers incentive salience onto rewards and associated cues and/or (2) contingency teaching signal reflecting reward prediction error. While both theories are provocative, the causal role for dopamine cell activity in either mechanism remains controversial. In this study mice that either fully or partially lacked NMDARs in dopamine neurons exclusively, as well as appropriate controls, were evaluated for reward-related learning; this experimental design allowed for a test of the premise that NMDA/glutamate receptor (NMDAR)-mediated mechanisms in dopamine neurons, including NMDA-dependent regulation of phasic discharge activity of these cells, modulate either the instrumental learning processes or the likelihood of pavlovian cues to become highly motivating incentive stimuli that directly attract behavior. Loss of NMDARs in dopamine neurons did not significantly affect baseline dopamine utilization in the striatum, novelty evoked locomotor behavior, or consumption of a freely available, palatable food solution. On the other hand, animals lacking NMDARs in dopamine cells exhibited a selective reduction in reinforced lever responses that emerged over the course of instrumental learning. Loss of receptor expression did not, however, influence the likelihood of an animal acquiring a pavlovian conditional response associated with attribution of incentive salience to reward-paired cues (sign tracking). These data support the view that reductions in NMDAR signaling in dopamine neurons affect instrumental reward-related learning but do not lend support to hypotheses that suggest that the behavioral significance of this signaling includes incentive salience attribution.

A Novel Method for Analyzing Extremely Biased Agonism at G Protein–Coupled Receptors

PubMed Central

Zhou, Lei; Ehlert, Frederick J.; Bohn, Laura M.

2015-01-01

Seven transmembrane receptors were originally named and characterized based on their ability to couple to heterotrimeric G proteins. The assortment of coupling partners for G protein–coupled receptors has subsequently expanded to include other effectors (most notably the βarrestins). This diversity of partners available to the receptor has prompted the pursuit of ligands that selectively activate only a subset of the available partners. A biased or functionally selective ligand may be able to distinguish between different active states of the receptor, and this would result in the preferential activation of one signaling cascade more than another. Although application of the “standard” operational model for analyzing ligand bias is useful and suitable in most cases, there are limitations that arise when the biased agonist fails to induce a significant response in one of the assays being compared. In this article, we describe a quantitative method for measuring ligand bias that is particularly useful for such cases of extreme bias. Using simulations and experimental evidence from several κ opioid receptor agonists, we illustrate a “competitive” model for quantitating the degree and direction of bias. By comparing the results obtained from the competitive model with the standard model, we demonstrate that the competitive model expands the potential for evaluating the bias of very partial agonists. We conclude the competitive model provides a useful mechanism for analyzing the bias of partial agonists that exhibit extreme bias. PMID:25680753

Functional Comparison of Neuronal Cells Differentiated from Human Induced Pluripotent Stem Cell-Derived Neural Stem Cells under Different Oxygen and Medium Conditions.

PubMed

Yamazaki, Kazuto; Fukushima, Kazuyuki; Sugawara, Michiko; Tabata, Yoshikuni; Imaizumi, Yoichi; Ishihara, Yasuharu; Ito, Masashi; Tsukahara, Kappei; Kohyama, Jun; Okano, Hideyuki

2016-12-01

Because neurons are difficult to obtain from humans, generating functional neurons from human induced pluripotent stem cells (hiPSCs) is important for establishing physiological or disease-relevant screening systems for drug discovery. To examine the culture conditions leading to efficient differentiation of functional neural cells, we investigated the effects of oxygen stress (2% or 20% O 2 ) and differentiation medium (DMEM/F12:Neurobasal-based [DN] or commercial [PhoenixSongs Biologicals; PS]) on the expression of genes related to neural differentiation, glutamate receptor function, and the formation of networks of neurons differentiated from hiPSCs (201B7) via long-term self-renewing neuroepithelial-like stem (lt-NES) cells. Expression of genes related to neural differentiation occurred more quickly in PS and/or 2% O 2 than in DN and/or 20% O 2 , resulting in high responsiveness of neural cells to glutamate, N-methyl-d-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), and ( S)-3,5-dihydroxyphenylglycine (an agonist for mGluR 1/5 ), as revealed by calcium imaging assays. NMDA receptors, AMPA receptors, mGluR 1 , and mGluR 5 were functionally validated by using the specific antagonists MK-801, NBQX, JNJ16259685, and 2-methyl-6-(phenylethynyl)-pyridine, respectively. Multielectrode array analysis showed that spontaneous firing occurred earlier in cells cultured in 2% O 2 than in 20% O 2 . Optimization of O 2 tension and culture medium for neural differentiation of hiPSCs can efficiently generate physiologically relevant cells for screening systems.

Dopamine D2/D3 but not dopamine D1 receptors are involved in the rapid antidepressant-like effects of ketamine in the forced swim test.

PubMed

Li, Yan; Zhu, Zhuo R; Ou, Bao C; Wang, Ya Q; Tan, Zhou B; Deng, Chang M; Gao, Yi Y; Tang, Ming; So, Ji H; Mu, Yang L; Zhang, Lan Q

2015-02-15

Major depressive disorder is one of the most prevalent and life-threatening forms of mental illnesses. The traditional antidepressants often take several weeks, even months, to obtain clinical effects. However, recent clinical studies have shown that ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, exerts rapid antidepressant effects within 2h and are long-lasting. The aim of the present study was to investigate whether dopaminergic system was involved in the rapid antidepressant effects of ketamine. The acute administration of ketamine (20 mg/kg) significantly reduced the immobility time in the forced swim test. MK-801 (0.1 mg/kg), the more selective NMDA antagonist, also exerted rapid antidepressant-like effects. In contrast, fluoxetine (10 mg/kg) did not significantly reduced the immobility time in the forced swim test after 30 min administration. Notably, pretreatment with haloperidol (0.15 mg/kg, a nonselective dopamine D2/D3 antagonist), but not SCH23390 (0.04 and 0.1 mg/kg, a selective dopamine D1 receptor antagonist), significantly prevented the effects of ketamine or MK-801. Moreover, the administration of sub-effective dose of ketamine (10 mg/kg) in combination with pramipexole (0.3 mg/kg, a dopamine D2/D3 receptor agonist) exerted antidepressant-like effects compared with each drug alone. In conclusion, our results indicated that the dopamine D2/D3 receptors, but not D1 receptors, are involved in the rapid antidepressant-like effects of ketamine. Copyright © 2014 Elsevier B.V. All rights reserved.

Recent advances in the treatment of amyotrophic lateral sclerosis. Emphasis on kynurenine pathway inhibitors.

PubMed

Chen, Yiquan; Meininger, Vincent; Guillemin, Gilles J

2009-03-01

Amyotrophic lateral sclerosis (ALS) is an adult onset, progressive and fatal motor neuron degenerative disease [1]. The aetiology of ALS is currently unknown, though strongly suggested to be multifactorial. Recently, the kynurenine pathway (KP) has emerged as a potential contributing factor [2]. The KP is a major route for the metabolism of tryptophan, generating neuroactive intermediates in the process. These catabolites include the excitotoxic N-methyl-D-aspartate (NMDA) receptor agonist, quinolinic acid (QUIN) [3] and the neuroprotective NMDA receptor antagonist, kynurenic acid (KYNA) [4,5]. These catabolites appear to play a key role in the communication between the nervous and immune systems, and also in modulating cell proliferation and tissue function [6]. As the cause of ALS is still unknown, there is presently no efficient treatment for it. Currently, Riluzole is the drug of choice but its effect is relatively modest [7]. Targeting the KP, hence, could offer a new therapeutic option to improve ALS treatment [8]. Several drugs that block the KP are already under investigation by our laboratory and others, some of which are in or about to enter clinical trials for other diseases. For example, the KP inhibitors, Teriflunomide (Sanofi-Aventis) and Laquinimod (Teva Neuroscience). Recently, a KP inhibitor has also reached the Japan market as an immunomodulative drug [9]: Tranilast/Rizaben (Angiogen Ltd.) is an anthranilic acid derivative [8]. Finally, the 8-hydroxyquinolinine metal attenuating compounds, Clioquinol and PBT2, interestingly have close structural similarity with KYNA and QUIN. Such drugs would open a new and important therapeutic door for ALS.

Prenatal inhibition of the kynurenine pathway leads to structural changes in the hippocampus of adult rat offspring.

PubMed

Khalil, Omari S; Pisar, Mazura; Forrest, Caroline M; Vincenten, Maria C J; Darlington, L Gail; Stone, Trevor W

2014-05-01

Glutamate receptors for N-methyl-d-aspartate (NMDA) are involved in early brain development. The kynurenine pathway of tryptophan metabolism includes the NMDA receptor agonist quinolinic acid and the antagonist kynurenic acid. We now report that prenatal inhibition of the pathway in rats with 3,4-dimethoxy-N-[4-(3-nitrophenyl)thiazol-2-yl]benzenesulphonamide (Ro61-8048) produces marked changes in hippocampal neuron morphology, spine density and the immunocytochemical localisation of developmental proteins in the offspring at postnatal day 60. Golgi-Cox silver staining revealed decreased overall numbers and lengths of CA1 basal dendrites and secondary basal dendrites, together with fewer basal dendritic spines and less overall dendritic complexity in the basal arbour. Fewer dendrites and less complexity were also noted in the dentate gyrus granule cells. More neurons containing the nuclear marker NeuN and the developmental protein sonic hedgehog were detected in the CA1 region and dentate gyrus. Staining for doublecortin revealed fewer newly generated granule cells bearing extended dendritic processes. The number of neuron terminals staining for vesicular glutamate transporter (VGLUT)-1 and VGLUT-2 was increased by Ro61-8048, with no change in expression of vesicular GABA transporter or its co-localisation with vesicle-associated membrane protein-1. These data support the view that constitutive kynurenine metabolism normally plays a role in early embryonic brain development, and that interfering with it has profound consequences for neuronal structure and morphology, lasting into adulthood. © 2014 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Metabotropic glutamate receptor 5 responses dictate differentiation of neural progenitors to NMDA-responsive cells in fragile X syndrome.

PubMed

Achuta, Venkat Swaroop; Grym, Heli; Putkonen, Noora; Louhivuori, Verna; Kärkkäinen, Virve; Koistinaho, Jari; Roybon, Laurent; Castrén, Maija L

2017-04-01

Disrupted metabotropic glutamate receptor 5 (mGluR5) signaling is implicated in many neuropsychiatric disorders, including autism spectrum disorder, found in fragile X syndrome (FXS). Here we report that intracellular calcium responses to the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG) are augmented, and calcium-dependent mGluR5-mediated mechanisms alter the differentiation of neural progenitors in neurospheres derived from human induced pluripotent FXS stem cells and the brains of mouse model of FXS. Treatment with the mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) prevents an abnormal clustering of DHPG-responsive cells that are responsive to activation of ionotropic receptors in mouse FXS neurospheres. MPEP also corrects morphological defects of differentiated cells and enhanced migration of neuron-like cells in mouse FXS neurospheres. Unlike in mouse neurospheres, MPEP increases the differentiation of DHPG-responsive radial glial cells as well as the subpopulation of cells responsive to both DHPG and activation of ionotropic receptors in human neurospheres. However, MPEP normalizes the FXS-specific increase in the differentiation of cells responsive only to N-methyl-d-aspartate (NMDA) present in human neurospheres. Exposure to MPEP prevents the accumulation of intermediate basal progenitors in embryonic FXS mouse brain suggesting that rescue effects of GluR5 antagonist are progenitor type-dependent and species-specific differences of basal progenitors may modify effects of MPEP on the cortical development. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 419-437, 2017. © 2016 Wiley Periodicals, Inc.

Agmatine protects against cell damage induced by NMDA and glutamate in cultured hippocampal neurons

PubMed Central

Wang, Wei-Ping; Iyo, Abiye H.; Miguel-Hidalgo, Javier; Regunathan, Soundar; Zhu, Meng-Yang

2010-01-01

Agmatine is a polyamine and has been considered as a novel neurotransmitter or neuromodulator in the central nervous system. In the present study, the neuroprotective effect of agmatine against cell damage caused by N-methyl-d-aspartate (NMDA) and glutamate was investigated in cultured rat hippocampal neurons. Lactate dehydrogenase (LDH) activity assay, β-tubulin III immunocytochemical staining and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end-labeling (TUNEL) assay were conducted to detect cell damage. Exposure of 12-day neuronal cultures of rat hippocampus to NMDA or glutamate for 1 h caused a concentration-dependent neurotoxicity, as indicated by the significant increase in released LDH activities. Addition of 100 µM agmatine into media ablated the neurotoxicity induced by NMDA or glutamate, an effect also produced by the specific NMDA receptor antagonist dizocilpine hydrogen maleate (MK801). Arcaine, an analog of agmatine with similar structure as agmatine, fully prevented the NMDA- or glutamate-induced neuronal damage. Spermine and putrescine, the endogenous polyamine and metabolic products of agmatine without the guanidine moiety of agmatine, failed to show this effect, indicating a structural relevance for this neuroprotection. Immunocytochemical staining and TUNEL assay confirmed the findings in the LDH measurement. That is, agmatine and MK801 markedly attenuated NMDA-induced neuronal death and significantly reduced TUNEL-positive cell numbers induced by exposure of cultured hippocampal neurons to NMDA. Taken together, these results demonstrate that agmatine can protect cultured hippocampal neurons from NMDA- or glutamate-induced excitotoxicity, through a possible blockade of the NMDA receptor channels or a potential anti-apoptotic property. PMID:16546145

Role of AMPA and NMDA receptors and back-propagating action potentials in spike timing-dependent plasticity.

PubMed

Fuenzalida, Marco; Fernández de Sevilla, David; Couve, Alejandro; Buño, Washington

2010-01-01

The cellular mechanisms that mediate spike timing-dependent plasticity (STDP) are largely unknown. We studied in vitro in CA1 pyramidal neurons the contribution of AMPA and N-methyl-d-aspartate (NMDA) components of Schaffer collateral (SC) excitatory postsynaptic potentials (EPSPs; EPSP(AMPA) and EPSP(NMDA)) and of the back-propagating action potential (BAP) to the long-term potentiation (LTP) induced by a STDP protocol that consisted in pairing an EPSP and a BAP. Transient blockade of EPSP(AMPA) with 7-nitro-2,3-dioxo-1,4-dihydroquinoxaline-6-carbonitrile (CNQX) during the STDP protocol prevented LTP. Contrastingly LTP was induced under transient inhibition of EPSP(AMPA) by combining SC stimulation, an imposed EPSP(AMPA)-like depolarization, and BAP or by coupling the EPSP(NMDA) evoked under sustained depolarization (approximately -40 mV) and BAP. In Mg(2+)-free solution EPSP(NMDA) and BAP also produced LTP. Suppression of EPSP(NMDA) or BAP always prevented LTP. Thus activation of NMDA receptors and BAPs are needed but not sufficient because AMPA receptor activation is also obligatory for STDP. However, a transient depolarization of another origin that unblocks NMDA receptors and a BAP may also trigger LTP.

Comparison of the Pharmacological Effects of a Novel Selective Androgen Receptor Modulator, the 5α-Reductase Inhibitor Finasteride, and the Antiandrogen Hydroxyflutamide in Intact Rats: New Approach for Benign Prostate Hyperplasia

PubMed Central

Gao, Wenqing; Kearbey, Jeffrey D.; Nair, Vipin A.; Chung, Kiwon; Parlow, A. F.; Miller, Duane D.; Dalton, James T.

2007-01-01

Tissue-selective androgen receptor modulators (SARMs) demonstrate tissue selectivity in both castrated and intact male rats, behaving as partial agonists in androgenic tissues (i.e. prostate and seminal vesicle), but full agonists in anabolic tissues (i.e. levator ani muscle). The partial agonist activity of SARMs (compounds S-1 and S-4) in the prostate of intact rats suggested that SARM could be used for androgen suppression in the treatment of benign prostate hyperplasia (BPH). This study was designed to explore the mechanisms of action of SARM and to characterize the tissue selectivity of S-1 in intact male rats compared with that of hydroxyflutamide (antiandrogen) and finasteride (5α-reductase inhibitor), two major drugs used for androgen suppression treatment of BPH. In intact male rats, S-1 (5, 10, and 25 mg/kg) selectively decreased the prostate weight with similar efficacy to finasteride (5 mg/kg), without affecting the levator ani muscle or increasing the plasma levels of testosterone, LH, and FSH. Hydroxyflutamide (0.5, 1, 5, 10, and 25 mg/kg), however, decreased both the prostate and levator ani muscle weights without any selectivity and increased plasma hormone levels in a dose-dependent manner. Furthermore, S-1 and S-4 showed very weak inhibitory effects toward transiently expressed type I and II human 5α-reductase (Ki, >20 µM) during in vitro assays. Therefore, although S-1 and finasteride showed very similar suppressive effects in the prostate of intact male rats, they decreased prostate size via different mechanisms of action. S-1 simply worked as androgen receptor partial agonist, whereas finasteride inhibited prostatic 5α-reductase. These studies indicate that SARMs may demonstrate clinical utility as single agent or combination therapy for BPH. PMID:15308613

Analysis of the V2 Vasopressin Receptor (V2R) Mutations Causing Partial Nephrogenic Diabetes Insipidus Highlights a Sustainable Signaling by a Non-peptide V2R Agonist.

PubMed

Makita, Noriko; Sato, Tomohiko; Yajima-Shoji, Yuki; Sato, Junichiro; Manaka, Katsunori; Eda-Hashimoto, Makiko; Ootaki, Masanori; Matsumoto, Naoki; Nangaku, Masaomi; Iiri, Taroh

2016-10-21

Disease-causing mutations in G protein-coupled receptor (GPCR) genes, including the V2 vasopressin receptor (V2R) gene, often cause misfolded receptors, leading to a defect in plasma membrane trafficking. A novel V2R mutation, T273M, identified in a boy with partial nephrogenic diabetes insipidus (NDI), shows intracellular localization and partial defects similar to the two mutants we described previously (10). Although non-peptide V2R antagonists have been shown to rescue the membrane localization of V2R mutants, their level of functional rescue is weak. Interestingly, it has been reported that a non-peptide agonist, OPC51803, activates misfolded V2R mutants intracellularly without degradation, thus potentially serving as a therapeutic agent against NDI (14). In our current experiments, however, a peptide antagonist blocked arginine vasopressin (AVP)- or OPC51803-stimulated cAMP accumulation both in COS-7 and MDCK cells, suggesting that OPC51803 mainly stimulates cell surface V2R mutants. In addition, our analyses revealed that OPC51803 works not only as a non-peptide agonist that causes activation/β-arrestin-dependent desensitization of V2R mutants expressed at the plasma membrane but also as a pharmacochaperone that promotes the endoplasmic reticulum-retained mutant maturation and trafficking to the plasma membrane. The ratio of the pharmacochaperone effect to the desensitization effect likely correlates negatively with the residual function of the tested mutants, suggesting that OPC5 has a more favorable effect on the V2R mutants with a less residual function. We speculated that the canceling of the desensitization effect of OPC51803 by the pharmacochaperone effect after long-term treatment may produce sustainable signaling, and thus pharmacochaperone agonists such as OPC51803 may serve as promising therapeutics for NDI caused by misfolded V2R mutants. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Analysis of the V2 Vasopressin Receptor (V2R) Mutations Causing Partial Nephrogenic Diabetes Insipidus Highlights a Sustainable Signaling by a Non-peptide V2R Agonist*

PubMed Central

Makita, Noriko; Sato, Tomohiko; Yajima-Shoji, Yuki; Sato, Junichiro; Manaka, Katsunori; Eda-Hashimoto, Makiko; Ootaki, Masanori; Matsumoto, Naoki; Nangaku, Masaomi; Iiri, Taroh

2016-01-01

Disease-causing mutations in G protein-coupled receptor (GPCR) genes, including the V2 vasopressin receptor (V2R) gene, often cause misfolded receptors, leading to a defect in plasma membrane trafficking. A novel V2R mutation, T273M, identified in a boy with partial nephrogenic diabetes insipidus (NDI), shows intracellular localization and partial defects similar to the two mutants we described previously (10). Although non-peptide V2R antagonists have been shown to rescue the membrane localization of V2R mutants, their level of functional rescue is weak. Interestingly, it has been reported that a non-peptide agonist, OPC51803, activates misfolded V2R mutants intracellularly without degradation, thus potentially serving as a therapeutic agent against NDI (14). In our current experiments, however, a peptide antagonist blocked arginine vasopressin (AVP)- or OPC51803-stimulated cAMP accumulation both in COS-7 and MDCK cells, suggesting that OPC51803 mainly stimulates cell surface V2R mutants. In addition, our analyses revealed that OPC51803 works not only as a non-peptide agonist that causes activation/β-arrestin-dependent desensitization of V2R mutants expressed at the plasma membrane but also as a pharmacochaperone that promotes the endoplasmic reticulum-retained mutant maturation and trafficking to the plasma membrane. The ratio of the pharmacochaperone effect to the desensitization effect likely correlates negatively with the residual function of the tested mutants, suggesting that OPC5 has a more favorable effect on the V2R mutants with a less residual function. We speculated that the canceling of the desensitization effect of OPC51803 by the pharmacochaperone effect after long-term treatment may produce sustainable signaling, and thus pharmacochaperone agonists such as OPC51803 may serve as promising therapeutics for NDI caused by misfolded V2R mutants. PMID:27601473

Functional Characterization of 5-HT1B Receptor Drugs in Nonhuman Primates Using Simultaneous PET-MR.

PubMed

Hansen, Hanne D; Mandeville, Joseph B; Sander, Christin Y; Hooker, Jacob M; Catana, Ciprian; Rosen, Bruce R; Knudsen, Gitte M

2017-11-01

In the present study, we used a simultaneous PET-MR experimental design to investigate the effects of functionally different compounds (agonist, partial agonist, and antagonist) on 5-HT 1B receptor (5-HT 1B R) occupancy and the associated hemodynamic responses. In anesthetized male nonhuman primates ( n = 3), we used positron emission tomography (PET) imaging with the radioligand [ 11 C]AZ10419369 administered as a bolus followed by constant infusion to measure changes in 5-HT 1B R occupancy. Simultaneously, we measured changes in cerebral blood volume (CBV) as a proxy of drug effects on neuronal activity. The 5-HT 1B R partial agonist AZ10419369 elicited a dose-dependent biphasic hemodynamic response that was related to the 5-HT 1B R occupancy. The magnitude of the response was spatially overlapping with high cerebral 5-HT 1B R densities. High doses of AZ10419369 exerted an extracranial tissue vasoconstriction that was comparable to the less blood-brain barrier-permeable 5-HT 1B R agonist sumatriptan. By contrast, injection of the antagonist GR127935 did not elicit significant hemodynamic responses, even at a 5-HT 1B R cerebral occupancy similar to the one obtained with a high dose of AZ10419369. Given the knowledge we have of the 5-HT 1B R and its function and distribution in the brain, the hemodynamic response informs us about the functionality of the given drug: changes in CBV are only produced when the receptor is stimulated by the partial agonist AZ10419369 and not by the antagonist GR127935, consistent with low basal occupancy by endogenous serotonin. SIGNIFICANCE STATEMENT We here show that combined simultaneous positron emission tomography and magnetic resonance imaging uniquely enables the assessment of CNS active compounds. We conducted a series of pharmacological interventions to interrogate 5-HT 1B receptor binding and function and determined blood-brain barrier passage of drugs and demonstrate target involvement. Importantly, we show how the spatial and temporal effects on brain hemodynamics provide information about pharmacologically driven downstream CNS drug effects; the brain hemodynamic response shows characteristic dose-related effects that differ depending on agonistic or antagonistic drug characteristics and on local 5-HT 1B receptor density. The technique lends itself to a comprehensive in vivo investigation and understanding of drugs' effects in the brain. Copyright © 2017 the authors 0270-6474/17/3710671-08$15.00/0.

The NMDA receptor/ion channel complex: a drug target for modulating synaptic plasticity and excitotoxicity.

PubMed

Albensi, Benedict C

2007-01-01

A recent search on PubMed for the phrase NMDA receptor results in 2,190 hits on this topic for review articles and 20,100 hits for experimental papers. This is a direct reflection of the intensiveness, significance, and complexity associated with the research on this key receptor protein over the last several decades. In this review, we briefly describe the NMDA receptor structure, discuss the role of NMDA receptors in modulating synaptic plasticity and excitotoxicity, explore age-dependent changes in NMDA receptor functioning, and survey interesting NMDA receptor blockers. Given the huge existing literature on the subject, an exhaustive review has not been endeavored. Instead, an attempt was made to point out those studies that have been instrumental in the field or that are of special interest.

Role of Phosphatidylinositol-3 Kinase Pathway in NMDA Preconditioning: Different Mechanisms for Seizures and Hippocampal Neuronal Degeneration Induced by Quinolinic Acid.

PubMed

Constantino, Leandra C; Binder, Luisa B; Vandresen-Filho, Samuel; Viola, Giordano G; Ludka, Fabiana K; Lopes, Mark W; Leal, Rodrigo B; Tasca, Carla I

2018-04-20

N-methyl D-aspartate (NMDA) preconditioning is evoked by the administration of a subtoxic dose of NMDA and is protective against neuronal excitotoxicity. This effect may involve a diversity of targets and cell signaling cascades associated to neuroprotection. Phosphatidylinositol-3 kinase/protein kinase B (PI3K/Akt) and mitogen-activated protein kinases (MAPKs) such as extracellular regulated protein kinase 1/2 (ERK1/2) and p38 MAPK pathways play a major role in neuroprotective mechanisms. However, their involvement in NMDA preconditioning was not yet fully investigated. The present study aimed to evaluate the effect of NMDA preconditioning on PI3K/Akt, ERK1/2, and p38 MAPK pathways in the hippocampus of mice and characterize the involvement of PI3K on NMDA preconditioning-evoked prevention of seizures and hippocampal cell damage induced by quinolinic acid (QA). Thus, mice received wortmannin (a PI3K inhibitor) and 15 min later a subconvulsant dose of NMDA (preconditioning) or saline. After 24 h of this treatment, an intracerebroventricular QA infusion was administered. Phosphorylation levels and total content of Akt, glycogen synthase protein kinase-3β (GSK-3β), ERK1/2, and p38 MAPK were not altered after 24 h of NMDA preconditioning with or without wortmmanin pretreatment. Moreover, after QA administration, behavioral seizures, hippocampal neuronal degeneration, and Akt activation were evaluated. Inhibition of PI3K pathway was effective in abolishing the protective effect of NMDA preconditioning against QA-induced seizures, but did not modify neuronal protection promoted by preconditioning as evaluated by Fluoro-Jade B staining. The study confirms that PI3K participates in the mechanism of protection induced by NMDA preconditioning against QA-induced seizures. Conversely, NMDA preconditioning-evoked protection against neuronal degeneration is not altered by PI3K signaling pathway inhibition. These results point to differential mechanisms regarding protection against a behavioral and cellular manifestation of neural damage.

Suppression of Neurotoxic Lesion-Induced Seizure Activity: Evidence for a Permanent Role for the Hippocampus in Contextual Memory

PubMed Central

Sparks, Fraser T.; Lehmann, Hugo; Hernandez, Khadaryna; Sutherland, Robert J.

2011-01-01

Damage to the hippocampus (HPC) using the excitotoxin N-methyl-D-aspartate (NMDA) can cause retrograde amnesia for contextual fear memory. This amnesia is typically attributed to loss of cells in the HPC. However, NMDA is also known to cause intense neuronal discharge (seizure activity) during the hours that follow its injection. These seizures may have detrimental effects on retrieval of memories. Here we evaluate the possibility that retrograde amnesia is due to NMDA-induced seizure activity or cell damage per se. To assess the effects of NMDA induced activity on contextual memory, we developed a lesion technique that utilizes the neurotoxic effects of NMDA while at the same time suppressing possible associated seizure activity. NMDA and tetrodotoxin (TTX), a sodium channel blocker, are simultaneously infused into the rat HPC, resulting in extensive bilateral damage to the HPC. TTX, co-infused with NMDA, suppresses propagation of seizure activity. Rats received pairings of a novel context with foot shock, after which they received NMDA-induced, TTX+NMDA-induced, or no damage to the HPC at a recent (24 hours) or remote (5 weeks) time point. After recovery, the rats were placed into the shock context and freezing was scored as an index of fear memory. Rats with an intact HPC exhibited robust memory for the aversive context at both time points, whereas rats that received NMDA or NMDA+TTX lesions showed a significant reduction in learned fear of equal magnitude at both the recent and remote time points. Therefore, it is unlikely that observed retrograde amnesia in contextual fear conditioning are due to disruption of non-HPC networks by propagated seizure activity. Moreover, the memory deficit observed at both time points offers additional evidence supporting the proposition that the HPC has a continuing role in maintaining contextual memories. PMID:22110648

Temporal and regional alterations in NMDA receptor expression in Mecp2-null mice

PubMed Central

Blue, Mary E.; Kaufmann, Walter E.; Bressler, Joseph; Eyring, Charlotte; O’Driscoll, Cliona; Naidu, SakkuBai; Johnston, Michael V.

2014-01-01

Our previous postmortem study of girls with Rett Syndrome (RTT), a development disorder caused by MECP2 mutations, found increases in the density of NMDA receptors in the prefrontal cortex of 2–8 year-old girls, while girls older than 10 years had reductions in NMDA receptors compared to age matched controls (Blue et al., 1999b). Using [3H]-CGP to label NMDA type glutamate receptors in 2 and 7 week old wildtype (WT), Mecp2-null and Mecp2-heterozygous (HET) mice (Bird model), we found that frontal areas of the brain also exhibited a bimodal pattern in NMDA expression, with increased densities of NMDA receptors in Mecp2-null mice at 2 weeks of age, but decreased densities at 7 weeks of age. Visual cortex showed a similar pattern, while other cortical regions only exhibited changes in NMDA receptor densities at 2 weeks (retrosplenial granular) or 7 weeks (somatosensory). In thalamus of null mice, NMDA receptors were increased at 2 and 7 weeks. No significant differences in density were found between HET and WT mice at both ages. Western blots for NMDAR1 expression in frontal brain showed higher levels of expression in Mecp2-null mice at two weeks of age, but not at 1 or 7 weeks of age. Our mouse data support the notion that deficient MeCP2 function is the primary cause of the NMDA receptor changes we observed in RTT. Furthermore, the findings of regional and temporal differences in NMDA expression illustrate the importance of age and brain region in evaluating different genotypes of mice. PMID:21901842

BDNF released during neuropathic pain potentiates NMDA receptors in primary afferent terminals

PubMed Central

Chen, Wenling; Walwyn, Wendy; Ennes, Helena S.; Kim, Hyeyoung; McRoberts, James A.; Marvizón, Juan Carlos G.

2014-01-01

NMDA receptors in primary afferent terminals can contribute to hyperalgesia by increasing neurotransmitter release. In rats and mice, we found that the ability of intrathecal NMDA to induce neurokinin 1 receptor (NK1R) internalization (a measure of substance P release) required a previous injection of BDNF. Selective knock-down of NMDA receptors in primary afferents decreased NMDA-induced NK1R internalization, confirming the presynaptic location of these receptors. The effect of BDNF was mediated by tropomyosin-related kinase B (trkB) receptors and not p75 neurotrophin receptors (p75NTR), because it was not produced by proBDNF and was inhibited by the trkB antagonist ANA-12 but not by the p75NTR inhibitor TAT-Pep5. These effects are probably mediated through the truncated form of the trkB receptor as there is little expression of full-length trkB in dorsal root ganglion (DRG) neurons. Src family kinase inhibitors blocked the effect of BDNF, suggesting that trkB receptors promote the activation of these NMDA receptors by Src family kinase phosphorylation. Western blots of cultured DRG neurons revealed that BDNF increased Tyr1472 phosphorylation of the NR2B subunit of the NMDA receptor, known to have a potentiating effect. Patch-clamp recordings showed that BDNF, but not proBDNF, increased NMDA receptor currents in cultured DRG neurons. NMDA-induced NK1R internalization was also enabled in a neuropathic pain model or by activating dorsal horn microglia with lipopolysaccharide. These effects were decreased by a BDNF scavenger, a trkB receptor antagonist and an Src family kinase inhibitor, indicating that BDNF released by microglia potentiates NMDA receptors in primary afferents during neuropathic pain. PMID:24611998