Glycine Antagonist Research Articles

Gasping is elicited by briefer hypoxia or ischemia following blockade of glycinergic transmission.

The 'switching model' for generation of respiratory rhythms holds that gasping represents the release of a rostral medullary pacemaker mechanism from the pontomedullary neuronal circuit that generates eupnea. In a perfused preparation of the decerebrate juvenile rat, exposure to ischemia or hypoxic-hypercapnia caused an alteration in integrated phrenic activity from the incrementing pattern of eupnea to the decrementing pattern of gasping. The time required to elicit gasping was not altered by multiple exposures to ischemia or hypoxic-hypercapnia. Furthermore, this time to gasping was not altered following addition to the perfusate of increasing concentrations of bicuculline or picrotoxin; both block GABA(A) receptors. Addition to the perfusate of strychnine, a glycine antagonist, significantly shortened the duration of ischemia or hypoxic-hypercapnia required to elicit gasping. These results support the concept that a loss of inhibitory glycinergic transmission is a critical factor in release of pacemaker mechanisms for gasping from the pontomedullary neuronal circuit for eupnea.

Vocalization Responses After Spinal Administration of Bicuculline or Strychnine in Rats

Objective. Spinal administration of compounds decreasing inhibition of spinal nociceptive pathways, such as antagonists of GABA or glycine receptors, leads to vocalization. This can be quantified semiautomatically and could be used as a research model. Materials and Methods. Vocalization after intrathecal administration of bicuculline and strychnine was measured in Sprague-Dawley rats. Results. Both bicuculline and strychnine produced short, dose-related vocalization responses that were not significantly different between models of peripheral inflammation and neuropathic pain and normal controls, except for reduced strychnine-induced vocalization during inflammation. The strychnine-induced vocalization responses were also reduced in freely moving rats and increased by light tactile stimulation. Conclusions. Bicuculline-induced vocalization seems to be related to facilitation of nociceptive transmission, and could have limited use as a model of nociception at the spinal level. However, peripheral inflammation or neuropathic pain did not affect it. Strychnine-induced vocalization responses seem to be related to non-noxious somatosensory input.

Long-lasting enhancement of corticostriatal neurotransmission by taurine.

Taurine occurs at high concentrations in the forebrain and its distribution varies with (patho)physiological conditions; however, its role in neural function is poorly understood. We have now characterized its effects on corticostriatal synaptic transmission. Bath application of taurine (10 mm) to slices obtained from mice and rats exerted a biphasic action on corticostriatal field potentials. The fast and reversible inhibition by taurine was accompanied by a depolarization and conductance increase in medium spiny neurons and was sensitive to gamma-aminobutyric acid (GABA)A and glycine receptor (GlyR) antagonists. A long-lasting enhancement (LLETAU) of field potentials was recorded after taurine withdrawal. The LLETAU was not prevented by N-methyl-d-aspartate (NMDA)- or by GABAA receptor-antagonists, but was sensitive to the GlyR-antagonist strychnine and blocked by the competitive taurine uptake inhibitor guanidinoethylsulphonate (GES, 1 mm). GES at 10 mm evoked an enhancement of field potentials similar to LLETAU. LLETAU depended on protein kinase C activation as it was blocked by chelerythrine, but was unaffected by trifluoperazine, and thus independent of calmodulin. LLETAU was significantly smaller in juvenile than in mature rodents. Activation of GlyRs and the specific taurine transporter by taurine evoke a long-lasting enhancement of corticostriatal transmission.

Why did NMDA receptor antagonists fail clinical trials for stroke and traumatic brain injury?

Glutamate N-methyl-D-aspartate (NMDA) receptor antagonists (competitive receptor antagonists, ion channel blockers, and glycine antagonists)--such as selfotel, aptiganel, eliprodil, licostinel and gavestinel--failed to show efficacy in clinical trials of stroke or traumatic brain injury. This failure has been attributed to the deficient properties of the molecules that entered human trials and to inappropriate design of clinical studies. In this article we hypothesise that glutamate may be involved in the acute neurodestructive phase that occurs immediately after traumatic or ischaemic injury (excitotoxicity), but that, after this period, it assumes its normal physiological functions, which include promotion of neuronal survival. We propose that NMDA receptor antagonists failed stroke and traumatic brain injury trials in human beings because blockade of synaptic transmission mediated by NMDA receptors hinders neuronal survival.

A glycine receptor antagonist, strychnine, blocked NMDA receptor activation in the neonatal mouse neocortex.

The NMDA receptor (NMDAR) is a Ca (2+)-permeable cation channel that plays a critical role in neural network formation during brain development. Since it is blocked in a voltage-dependent manner by extracellular Mg(2+), in order for the NMDA to be activated, the membrane must be strongly depolarized. Immature neurons in the developing neocortex can be depolarized by ligand-gated Cl(-) channels, such as the glycine receptor (GlyR) or GABA(A) receptor (GABA(A) R). We here assess the contribution of GlyRs to Ca(2+) influx via NMDARs in neonatal mouse cortical neurons. The GlyR antagonist, strychnine, was more effective in suppressing postsynaptic Ca(2+) influx than the GABA(A) R antagonist, picrotoxin, suggesting greater potentiation of NMDARs by GlyRs than by GABA(A) Rs. The GlyR, known to be endogenously activated at this stage, may play a critical role in neocortical development.

Halothane suppression of spinal sensory neuronal responses to noxious peripheral stimuli is mediated, in part, by both GABA(A) and glycine receptor systems.

A major effect of general anesthesia is lack of response in the presence of a noxious stimulus. Anesthetic depression of spinal sensory neuronal responses to noxious stimuli is likely to contribute to that essential general anesthetic action. The authors tested the hypothesis that gamma-aminobutyric acid receptor type A (GABA(A)) and strychnine-sensitive glycine receptor systems mediate halothane depression of spinal sensory neuronal responses to noxious stimuli. Extracellular activity of single spinal dorsal horn wide dynamic range (WDR) neurons was recorded in decerebrate, spinal cord transected rats. Neuronal responses to noxious (thermal and mechanical) and nonnoxious stimuli were examined in the drug-free state. Subsequently, cumulative doses (0.1-2.0 mg/kg) of bicuculline (GABA(A) antagonist) or strychnine (glycine antagonist) were administered intravenously in the absence or presence of 1 minimum alveolar concentration (MAC) of halothane. Halothane, 1.1%, depressed the response of WDR neurons to both forms of noxious stimuli. Antagonists, by themselves, had no effect on noxiously evoked activity. However, bicuculline and strychnine (maximum cumulative dose, 2.0 mg/kg) partially but significantly reversed the halothane depression of noxiously evoked activity. Similar results were seen with most, but not all, forms of nonnoxiously evoked activity. In the absence of halothane, strychnine significantly increased neuronal responses to low threshold receptive field brushing. Halothane depression of spinal WDR neuronal responses to noxious and most nonnoxious stimuli is mediated, in part, by GABA(A) and strychnine-sensitive glycine systems. A spinal source of glycine tonically inhibits some forms of low threshold input to WDR neurons.

A novel N-methyl-D-aspartate receptor open channel blocker with in vivo neuroprotectant activity.

Excitotoxicity has been implicated in the etiology of ischemic stroke, chronic neurodegenerative disorders, and very recently, in glioma growth. Thus, the development of novel neuroprotectant molecules that reduce excitotoxic brain damage is vigorously pursued. We have used an ionic current block-based cellular assay to screen a synthetic combinatorial library of trimers of N-alkylglycines on the N-methyl-D-aspartate (NMDA) receptor, a well known molecular target involved in excitotoxicity. We report the identification of a family of N-alkylglycines that selectively blocked the NMDA receptor. Notably, compound 3,3-diphenylpropyl-N-glycinamide (referred to as N20C) inhibited NMDA receptor channel activity with micromolar affinity, fast on-off blockade kinetics, and strong voltage dependence. Molecule N20C did not act as a competitive glutamate or glycine antagonist. In contrast, saturation of the blocker binding site with N20C prevented dizolcipine (MK-801) blockade of the NMDA receptor, implying that both drugs bind to the same receptor site. The N-alkylglycine efficiently prevented in vitro excitotoxic neurodegeneration of cerebellar and hippocampal neurons in culture. Attenuation of neuronal glutamate/NMDA-induced Ca(2+) overload and subsequent modulation of the glutamate-nitric oxide-cGMP pathway seems to underlie N20C neuroprotection. Noteworthy, this molecule exhibited significant in vivo neuroprotectant activity against an acute, severe, excitotoxic insult. Taken together, these findings indicate that N-alkylglycine N20C is a novel, low molecular weight, moderate-affinity NMDA receptor open channel blocker with in vitro and in vivo neuroprotective activity, which, in due turn, may become a tolerated drug for the treatment of neurodegenerative diseases and cancer.

State-Related Inhibition by GABA and Glycine of Transmission in Clarke's Column

During the state of active sleep (AS), Clarke9s column dorsal spinocerebellar tract (DSCT) neurons undergo a marked reduction in their spontaneous and excitatory amino acid (EAA)-evoked responses. The present study was performed to examine the magnitude, consistency of AS-specific suppression, and potential role of classical inhibitory amino acids GABA and glycine (GLY) in mediating this phenomenon. AS-specific suppression of DSCT neurons, expressed as the reduction in mean spontaneous firing rate during AS versus the preceding episode of wakefulness, was compared across three consecutive sleep cycles (SC), each consisting of wakefulness (W), AS, and awakening from AS (RW). Spontaneous spike rate did not differ during W or RW between SC1, SC2, and SC3. AS-specific suppression of spontaneous firing rate was found to be consistent and measured 40.3, 31.5, and 41.6% in SC1, SC2, and SC3, respectively, indicating that such inhibition is marked and stable for pharmacological analyses. Microiontophoretic experiments were performed in which the magnitude of AS-specific suppression of spontaneous spike activity was measured over three consecutive SCs: SC1-control (no drug), SC2-test (drug), and SC3-recovery (no drug). The magnitude of AS-specific suppression during SC2-test measured only 11.7 or 14.6% in the presence of GABA_A antagonist bicuculline (BIC) or GLY antagonist strychnine (STY), respectively. Coadministration of BIC and STY abolished AS-specific suppression. AS-specific suppression of EAA-evoked DSCT spike activity was also abolished in SC2-test after BIC or STY, respectively. We conclude that GABA and GLY mediate behavioral state-specific inhibition of ascending sensory transmission via Clarke9s column DSCT neurons.

Proconvulsant-induced seizures in α 4 nicotinic acetylcholine receptor subunit knockout mice

The genetic basis of a number of epilepsy syndromes has been identified but the precise mechanism whereby these mutations produce seizures is unknown. Three mutations of the α 4 subunit of the neuronal nicotinic acetylcholine receptor (nAChR) have been identified in autosomal dominant nocturnal frontal lobe epilepsy. In vitro studies of two mutations suggest an alteration of receptor function resulting in decreased ion channel current flow. We investigated the response of α 4 nAChR subunit knockout mice to the γ-aminobutyric acid (GABA) receptor antagonists; pentylenetetrazole (PTZ) and bicuculline (BIC), the glutamate receptor agonist kainic acid (KA), the glycine receptor antagonist strychnine and the K + channel blocker 4-aminopyridine (4-AP). Mutant (Mt) mice had a greater sensitivity to PTZ and BIC, with an increase in major motor seizures and seizure-related deaths. Furthermore, Mt mice were more sensitive to KA and strychnine, but the effects were much smaller compared to those seen with the GABA receptor antagonists. Paradoxically, Mt mice appeared to be relatively protected from 4-AP-induced major motor seizures and death. The results show that a functional deletion of the α 4 nAChR subunit in vivo is associated with a major increase in sensitivity to GABA receptor blockers.

Regulation of the respiratory central pattern generator by chloride-dependent inhibition during development in the bullfrog (Rana catesbeiana).

Isolated brainstem preparations from larval (tadpole) and adult Rana catesbeiana were used to examine inhibitory mechanisms for developmental regulation of the respiratory central pattern generator (CPG). Preparations were superfused at 20-22 degrees C with Cl(-)-free artificial cerebrospinal fluid (aCSF) or with aCSF containing agonists/antagonists of gamma-aminobutyric acid (GABA) or glycine receptors. Respiratory motor output from the CPG, measured as neural activity from cranial nerve roots, was associated with fictive gill ventilation and lung ventilation in tadpoles and with fictive lung ventilation in adults. In tadpoles, fictive lung burst frequency was 0.8+/-0.2 min(-1) and did not change significantly with Cl(-)-free aCSF superfusion; however, lung burst amplitude increased by nearly 400 % (P<0.01). Fictive gill ventilation averaged 41.6+/-3.3 min(-1) and was reversibly abolished by Cl(-)-free aCSF. Superfusion with Cl(-)-free aCSF abolished lung bursts in two of seven adult preparations, and overall lung burst frequency decreased from 3.1+/-0.7 to 0.4+/-0.03 min(-1) (P<0.01), but burst amplitude was unchanged. Low concentrations of GABA (0.5 mmol l(-1)) produced a significant increase in lung burst frequency followed by almost complete inhibition at 5.0 mmol l(-1), accompanied by the abolition of gill ventilation at 2.5-5.0 mmol l(-1). By contrast, fictive lung ventilation in adults was inhibited in a dose-dependent manner by glycine and GABA, and inhibition occurred at approximately 10-fold lower concentrations compared with tadpoles. The glycine receptor antagonist strychnine (2.5-25.0 micromol l(-1)) and the GABA(A) receptor antagonist bicuculline (1-10 micromol l(-1)) inhibited fictive gill ventilation and increased fictive lung ventilation in tadpoles. However, bicuculline and strychnine inhibited fictive lung ventilation in adults. These results suggest that lung ventilation in the tadpole brainstem may be driven by a pacemaker-like mechanism since Cl(-)-free aCSF failed to abolish lung ventilation. Lung ventilation in adults and gill ventilation in tadpoles, however, appear to be dependent upon conventional Cl(-)-mediated synaptic inhibition. Thus, there may be a developmental change in the fundamental process driving lung ventilation in amphibians. We hypothesize that maturation of the bullfrog respiratory CPG reflects developmental changes in glycinergic and/or GABAergic synaptic inhibitory mechanisms.

ChemInform Abstract: Synthesis and Pharmacological Characterization of a Conformationally Restrained Series of Indole‐2‐carboxylates [cf. (VI)] as in vivo Potent Glycine Antagonists.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Neuroprotection Is Unlikely to Be Effective in Humans Using Current Trial Designs: An Opposing View

To summarize recent neuroprotective trials, there has been no useful balance of benefit over risk.1 It is premature to shoot the messenger without evidence either that the results have been misleading or that we have missed trends. Confirmatory trials and/or meta-analysis support the validity of the results, and similar designs have successfully revealed the risks and benefits of thrombolysis. Trial designs have been imperfect, but the message is accurate: the drugs or doses we tried were inadequate. We need safer and better drugs, we need to know when and how to use them, and we need to maximize the efficiency of our trials. All are possible with current designs.2 Originally, limited efficacy data from a single laboratory and an acceptable toxicity profile were sufficient to proceed to clinical development. Choice of dose range, the optimal duration of therapy, patient subgroup selection, and the likely extent of benefit were all reserved for testing in clinical trials. The misplaced optimism of such an approach is now recognized, however, and guidance on preclinical testing has been elaborated.3 Rigorous external scrutiny of preclinical data now occurs in the more informed companies,4 and clinical development is deferred pending resolution of any deficiencies. This is the first role of the (now mandatory) trial steering committee. The drug classes under investigation are evolving, and new approaches are still being discovered. Glutamate antagonists have been widely studied.1 While effective in small animal models, their short time window in the laboratory, failure to protect …

Neuroprotective potential of ionotropic glutamate receptor antagonists.

From the therapeutic point of view, the real challenge is not only to improve the symptoms, but to interfere with the pathomechanism of the disease. That is why a considerable interest has recently been devoted to developing glutamate receptor antagonists (mainly of the NMDA type) for acute and chronic neurodegeneration. Developing such a treatment that slows down the progression of the disease is extremely time and cost consuming. At present there is consensus that competitive NMDA receptor antagonists will not find therapeutic applications, in contrast to agents acting at the glycine(B) site, or channel blockers. Recently, at least seven glycine(B) antagonists (e.g. ACEA 1021, GV-150526, GV-196771A, ZD-9379, MRZ 2/576) and over 10 NMDA channel blockers (e.g. Remacemide, ARL-15896AR, HU-211, ADCI, CNS-5161, Neramexane-MRZ 2/579) have been under development, most of them as neuroprotective agents for acute (stroke, trauma) or chronic insult (e.g. Huntington's or Alzheimer's disease). Several substances selective for NR2B NMDA receptor subtypes such as eliprodil, CP-101606 and Ro-25-6981 have been claimed to have a good neuroprotective profile. This presentation is an attempt to critically review preclinical and scarce clinical experience in the development of new NMDA receptor antagonists as neuroprotective agents according to the following scheme: rational, preclinical findings in animal models and finally clinical experience if available. The general impression is that NMDA receptor antagonists may find use in chronic type of neurodegeneration while AMPA antagonists seem to show better promise in acute insult.

NMDA and strychnine diversely modulate spinal dorsal horn noxious responsiveness in normal rats: potential significance to sensory disorders in neuropathic pain

Changes in neuronal excitability due to increase in excitatory transmitters and/or removal of local inhibition underlie central neuron sensitization and altered responsiveness related to painful sensory disorders. To distinguish the contribution of each of the two mechanisms, they have been mimicked separately in intact rats, by iontophoretically applying excitatory (NMDA) and disinhibitory (the glycine antagonist strychnine) substances during dorsal horn neuron recording. Wide dynamic range (WDR) neurons were extracellularly recorded at the L5-L6 lumbar level in anesthetized and paralyzed rats and an analysis was made, before and during the substance application, of the characteristics of the response to noxious stimuli applied to areas supplied by the ipsilateral sciatic nerve and the contralateral sciatic and saphenous nerves ("inappropriate" areas). The results show that the neuronal response properties were modified differently during the NMDA-induced hyperexcitability and strychnine-induced release of inhibition. Both manipulations brought about the unmasking of responses to previously ineffective, noxious stimuli applied to the contralateral sciatic and saphenous nerve areas, and the enhancement of the responses to noxious stimulation of the ipsilateral sciatic nerve area. However, it was only during the increased excitation induced by NMDA that the neurons exhibited hyperresponsiveness, with long-lasting afterdischarge, to noxious stimulation of the ipsi- and contralateral areas. Such response features resemble those described in sensitized neurons in neuropathic rats and associated with behavioral signs of hyperalgesia. This suggests, by inference, a crucial contribution of the NMDA-induced increased excitability to the expression of neuronal sensitization related to this painful sensory disorder.

Strychnine alters response properties of trigeminal nociceptive neurons in the rat.

The purpose of this study was to examine the role of glycine in sensory processes in the spinal trigeminal nucleus oralis (Sp5O). We evaluated the effect of intravenous administration of strychnine, a glycine receptor antagonist, on the responses of Sp5O convergent neurons evoked by innocuous peripheral electrical and mechanical stimuli in halothane-anesthetized rats. Strychnine significantly increased the Abeta-fiber-evoked activities of Sp5O neurons to electrical stimulation in a dose-dependent (0.2-0.8 mg/kg) fashion. The response to air-jet stimulation was also significantly enhanced at the highest dose of strychnine. These findings indicate that glycinergic neurons participate in the control of the flow of information conveyed to Sp5O nociceptive neurons by myelinated low-threshold mechanoreceptive afferents. Thus, alteration of trigeminal glycinergic modulation may contribute to the dynamic mechanical allodynia that occurs in trigeminal neuropathies.

The Nonuniform Distribution of the GABAAReceptor α1 Subunit Influences Inhibitory Synaptic Transmission to Motoneurons within a Motor Nucleus

Using immunohistochemistry we studied the distribution of GABA(A) and glycine receptor alpha1 subunits in the rat hypoglossal nucleus during postnatal development. In the neonate [postnatal day (P) 1-3] and adult nucleus (P28-30), GABA(A) receptor alpha1 subunit labeling was relatively modest. However, in the juvenile nucleus (P9-13), labeling was strong in the ventrolateral region and moderate in the dorsal region. Glycine receptor alpha1 subunit labeling was strong and uniform in the juvenile and adult nucleus and absent in the neonate nucleus. GABA and glycine neurotransmitter labeling was uniform throughout the neonatal and juvenile nucleus. To study the functional consequences of this regional differential GABA(A) receptor alpha1 subunit distribution, we voltage clamped juvenile hypoglossal motoneurons (HMs) from the ventrolateral and dorsal regions and recorded spontaneous miniature IPSCs (mIPSCs). Pure GABAergic events had slower decay times than glycinergic events. Although pure GABAergic and glycinergic decay times did not differ depending on HM location, the decays of mixed mIPSCs from ventrolateral HMs, recorded without GABA(A) and glycine receptor antagonists, had significantly slower decays than mIPSCs from dorsal HMs. Focally applied GABA and glycine onto outside-out patches revealed that the GABAergic to glycinergic peak current amplitude ratio was larger for patches from ventrolateral HMs compared with dorsal HMs. Dual component mIPSCs, presumably caused by co-release of GABA and glycine, were recorded more frequently in the ventrolateral nucleus. These data suggest that the number of synapses using GABA(A) receptor-mediated transmission is greater on ventrolateral HMs than dorsal HMs, demonstrating a nonuniformity of synaptic function within a defined motor nucleus.

Properties and interconnections of trigeminal interneurons of the lateral pontine reticular formation in the rat.

Numerous evidence suggests that interneurons located in the lateral tegmentum at the level of the trigeminal motor nucleus contribute importantly to the circuitry involved in mastication. However, the question of whether these neurons participate actively to genesis of the rhythmic motor pattern or simply relay it to trigeminal motoneurons remains open. To answer this question, intracellular recordings were performed in an in vitro slice preparation comprising interneurons of the peritrigeminal area (PeriV) surrounding the trigeminal motor nucleus (NVmt) and the parvocellular reticular formation ventral and caudal to it (PCRt). Intracellular and extracellular injections of anterograde tracers were also used to examine the local connections established by these neurons. In 97% of recordings, electrical stimulation of adjacent areas evoked a postsynaptic potential (PSP). These PSPs were primarily excitatory, but inhibitory and biphasic responses were also induced. Most occurred at latencies longer than those required for monosynaptic transmission and were considered to involve oligosynaptic pathways. Both the anatomical and physiological findings show that all divisions of PeriV and PCRt are extensively interconnected. Most responses followed high-frequency stimulation (50 Hz) and showed little variability in latency indicating that the network reliably distributes inputs across all areas. In all neurons but one, excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs) were also elicited by stimulation of NVmt, suggesting the existence of excitatory and inhibitory interneurons within the motor nucleus. In a number of cases, these PSPs were reproduced by local injection of glutamate in lieu of the electrical stimulation. All EPSPs induced by stimulation of PeriV, PCRt, or NVmt were sensitive to ionotropic glutamate receptor antagonists 6-cyano-7-dinitroquinoxaline and D,L-2-amino-5-phosphonovaleric acid, while IPSPs were blocked by bicuculline and strychnine, antagonists of GABA(A) and glycine receptors. Examination of PeriV and PCRt intrinsic properties indicate that they form a fairly uniform network. Three types of neurons were identified on the basis of their firing adaptation properties. These types were not associated with particular regions. Only 5% of all neurons showed bursting behavior. Our results do not support the hypothesis that neurons of PeriV and PCRt participate actively to rhythm generation, but suggest instead that they are driven by rhythmical synaptic inputs. The organization of the network allows for rapid distribution of this rhythmic input across premotoneuron groups.

Ethanol Inhibition ofN-Methyl-d-aspartate Receptors Is Reduced by Site-directed Mutagenesis of a Transmembrane Domain Phenylalanine Residue

N-Methyl-D-aspartate (NMDA) receptors (NRs) are ionotropic receptors activated by glutamate and the co-agonist glycine. Ethanol inhibits NMDA receptor function, although its site of action is undefined. We hypothesized that ethanol acts at specific amino acids contained within the transmembrane (TM) domains of the receptor. In this study, NR1 and NR2A subunits were altered by mutagenesis and tested for sensitivity to ethanol. Three NR1 mutants (W636A, F817A, and L819A) and one NR2A mutant (F637A) failed to generate functional receptors. Pre-TM1 (I546A, L551A, F554A, and F558A), TM1 (W563A), and TM2 (W611A) NR1 mutations did not affect ethanol sensitivity of heteromeric receptors. In contrast, altering a TM3 phenylalanine to alanine (F639A) reduced the ethanol inhibition of NMDA receptors expressed in oocytes and human embryonic kidney 293 cells. Mutation of the nearby methionine (M641) to alanine did not affect ethanol sensitivity, whereas changing Phe(639) to tryptophan slightly enhanced ethanol inhibition. NR1(F639A) did not alter the agonist potency of glutamate but did produce a leftward shift in the glycine concentration response for receptors containing NR2A and NR2B subunits. NR1(F639A) also reduced the potency of the competitive glycine antagonist 5,7-dichlorokynurenic acid and increased the efficacy of the glycine partial agonist 3-amino-1-hydroxy-2-pyrrolidinone ((+)-HA-966). These results suggest that ethanol may interact with amino acids contained in the TM3 domain of NMDA subunits that are involved in transducing agonist binding to channel opening.

BN52021, a platelet activating factor antagonist, is a selective blocker of glycine-gated chloride channel

We have found that the platelet activating factor antagonist (BN52021) is an effective blocker of the glycine (Gly) receptor-mediated responses in the hippocampal pyramidal neurons of rat. Using the whole-cell voltage clamp and concentration clamp recording techniques, we investigated the mechanism underlying the inhibitory action of this terpenoid on the glycine-induced chloride current. BN52021 selectively and reversibly inhibits glycine current in a non-competitive and voltage-dependent fashion. The antagonistic effect of this substance is more pronounced at positive membrane potentials. At holding potential −70 mV and in the presence of 200 μM glycine IC 50 value for the blocking action of BN52021 was 270±10 nM. Repetitive applications of BN52021 reveal the use-dependence of its blocking action. When co-applied with strychnine (STR), a competitive glycine receptor antagonist, BN52021 does not alter the IC 50 value for strychnine. The inhibitory effect of BN52021 on gamma-aminobutyric acid (GABA) current is at least 25 times less potent than the effect on glycine current. This substance fails to affect AMPA and NMDA responses. It may be concluded that BN52021 inhibits glycine-gated Cl − channels by interacting with the pore region and does not compete for the strychnine-binding centre.

Glycine Antagonist in Neuroprotection for Patients With Acute Stroke. GAIN Americas: A Randomized Controlled Trial.

Glycine Antagonist in Neuroprotection for Patients With Acute Stroke. GAIN Americas: A Randomized Controlled Trial.