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Glycine Receptors (glycine + receptor)

Distribution by Scientific Domains

Life Sciences	65%
Medical Sciences	34%

Selected Abstracts

Glycine Receptors Involved in Acamprosate's Modulation of Accumbal Dopamine Levels: An In Vivo Microdialysis Study

ALCOHOLISM, Issue 1 2010
PeiPei Chau
Background:, Glycine receptors (GlyRs) in the nucleus accumbens (nAc) and nicotinic acetylcholine receptors (nAChRs) in the ventral tegmental area (VTA) have been suggested to be involved in the positive reinforcing and dopamine elevating effects of ethanol. Recent studies have also shown that ethanol high-preferring rats substantially decrease their ethanol intake when treated with a glycine transporter 1 inhibitor (ORG 25935). Acamprosate, a drug used for relapse prevention in treatment of alcohol dependence, has also been demonstrated to elevate extracellular dopamine levels in the nAc. However, the underlying mechanism of action of acamprosate is not fully understood. Here we investigated whether acamprosate interferes with a neuronal circuitry that previously has been demonstrated to be involved in the dopamine elevating effects of ethanol and taurine. Methods:, In vivo microdialysis in freely moving rats was used to assess accumbal dopamine levels before and during local (nAc) or systemic administration of acamprosate. Results:, Perfusion of 0.5 mM acamprosate in the nAc significantly increased dopamine levels. Pretreatment either with 10 ,M strychnine in the nAc or 100 ,M mecamylamine in the VTA, completely antagonized the acamprosate-induced elevation of accumbal dopamine levels. Also, systemic acamprosate administration elevated accumbal dopamine output, an effect that was abolished by local (nAc) pretreatment with 10 ,M strychnine. Conclusions:, These results suggest that both systemic and local application of acamprosate elevate extracellular dopamine levels in the nAc by activating accumbal GlyRs, and, secondarily, tegmental nAChRs. [source]

Glycine Receptors in the Nucleus Accumbens Involved in the Ethanol Intake-Reducing Effect of Acamprosate

ALCOHOLISM, Issue 1 2010
PeiPei Chau
Background:, We have previously demonstrated that strychnine-sensitive glycine receptors (GlyRs) in the nucleus accumbens (nAc) and nicotinic acetylcholine receptors (nAChRs) in the ventral tegmental area are involved in mediating ethanol (EtOH)-induced elevation of dopamine in the rat mesolimbic dopamine system. This neuronal circuitry was also demonstrated to mediate dopamine elevation in the nAc after both taurine, an endogenous agonist of GlyRs, and acamprosate, a synthetic derivate of homotaurine. The aim of this study was to investigate whether the EtOH intake-reducing effect of acamprosate involves accumbal GlyRs. Methods:, For this purpose, we used a voluntary EtOH consumption model where EtOH medium- and high-preferring rats were implanted with guide cannulae in the nAc. The animals received daily injections of acamprosate or 0.9% NaCl before accessing a bottle of 6% EtOH and a bottle of water. After 2 days, a microinjection of strychnine or vehicle preceded the daily systemic injection and bottle-access period. Results:, Acamprosate, but not saline, decreased EtOH intake. Pretreatment with Ringer in the nAc did not influence EtOH intake in saline or acamprosate-treated animals. Pretreatment with strychnine had no effect on EtOH intake in saline-treated animals, whereas it completely reversed the EtOH intake-reducing effect of acamprosate. Conclusions:, Based on current and previous results, we suggest that acamprosate primarily interacts with accumbal GlyRs and secondarily with ventral tegmental nAChRs, in a similar manner to that previously observed with EtOH and taurine. The interaction between acamprosate and GlyRs does not only influence dopamine output in the nAc but also EtOH consumption, giving further support for our hypothesis that GlyRs are of importance in EtOH reinforcement. [source]

Glycine Receptors Contribute to Hypnosis Induced by Ethanol

ALCOHOLISM, Issue 6 2009
Jiang H. Ye
Background:, Glycine is a major inhibitory neurotransmitter in the adult central nervous system (CNS), and its receptors (GlyRs) are well known for their effects in the spinal cord and the lower brainstem. Accumulating evidence indicates that GlyRs are more widely distributed in the CNS, including many supraspinal regions. Previous in vitro studies have demonstrated that ethanol potentiates the function of these brain GlyRs, yet the behavioral role of the brain GlyRs has not been well explored. Methods:, Experiments were conducted in rats. The loss of righting reflex (LORR) was used as a marker of the hypnotic state. We compared the LORR induced by systematic administration of ethanol and of ketamine in the absence and presence of the selective glycine receptor antagonist strychnine. Ketamine is a general anesthetic that does not affect GlyRs. Results:, Systemically administered (by intraperitoneal injection) ethanol and ketamine dose-dependently induced LORR in rats. Furthermore, systemically administered (by subcutaneous injection) strychnine dose-dependently reduced the percentage of rats exhibiting LORR induced by ethanol, increased the onset time, and decreased the duration of LORR. Strychnine had no effect, however, on the LORR induced by ketamine. Conclusions:, Given that hypnosis is caused by neuronal depression in upper brain areas, we therefore conclude that brain GlyRs contribute at least in part to the hypnosis induced by ethanol. [source]

Ethanol Potentiation of Glycine Receptors Expressed in Xenopus Oocytes Antagonized by Increased Atmospheric Pressure

ALCOHOLISM, Issue 5 2003
Daryl L. Davies
Background: Behavioral and biochemical studies indicate that exposure to 12 times normal atmospheric pressure (12 ATA) of helium-oxygen gas (heliox) is a direct, selective ethanol antagonist. The current study begins to test the hypothesis that ethanol acts by a common mechanism on ligand-gated ion channels by expanding previous hyperbaric investigations on ,-aminobutyric acid type A (GABAA) receptors (GABAARs) at the biochemical level to ,1glycine (GlyRs) expressed in Xenopus oocytes. Methods: Oocytes expressing wild-type ,1 homomeric GlyRs were voltage-clamped (,70 mV) and tested in the presence of glycine (EC2) ± ethanol (50,200 mM) under 1 ATA control and 3 to 12 ATA heliox conditions. Glycine concentration response curves, strychnine/glycine interactions, and zinc (Zn2+) modulation of GlyR function was also tested. Results: Pressure reversibly antagonized the action of ethanol. The degree of antagonism increased as pressure increased. Pressure did not significantly alter the effects of glycine, strychnine, or Zn2+, indicating that ethanol antagonism by pressure cannot be attributed to alterations by pressure of normal GlyR function. The antagonism did not reflect tolerance to ethanol, receptor desensitization, or receptor rundown. Conclusion: This is the first use of hyperbarics to investigate the mechanism of action of ethanol in recombinant receptors. The findings indicate that pressure directly and selectively antagonizes ethanol potentiation of ,1GlyR function in a reversible and concentration- and pressure-dependent manner. The sensitivity of ethanol potentiation of GlyR function to pressure antagonism indicates that ethanol acts by a common, pressure-antagonism,sensitive mechanism in GlyRs and GABAARs. The findings also support the hypothesis that ethanol potentiation of GlyR function plays a role in mediating the sedative-hypnotic effects of ethanol. [source]

Glycine Receptors Involved in Acamprosate's Modulation of Accumbal Dopamine Levels: An In Vivo Microdialysis Study

Glycinergic input of widefield, displaced amacrine cells of the mouse retina

THE JOURNAL OF PHYSIOLOGY, Issue 15 2009
Sriparna Majumdar
Glycine receptors (GlyRs) of displaced amacrine cells of the mouse retina were analysed using whole cell recordings and immunocytochemical staining with subunit-specific antibodies. During the recordings the cells were filled with a fluorescent tracer and 11 different morphological types could be identified. The studies were performed in wild-type mice and in mutant mice deficient in the GlyR,1 (Glra1spd-ot, ,oscillator' mouse), the GlyR,2 (Glra2,/,) and the GlyR,3 subunit (Glra3,/,). Based on their responses to the application of exogenous glycine in the retinas of wild-type and mutant mice, the cells were grouped into three major classes: group I cells (comprising the morphological types MA-S5, MA-S1, MA-S1/S5, A17, PA-S1, PA-S5 and WA-S1), group II cells (comprising the morphological types PA-S4, WA-S3 and WA-multi) and ON-starburst cells. For further analysis, spontaneous inhibitory postsynaptic currents (sIPSCs) were measured both in wild-type and mutant mouse retinas. Glycinergic sIPSCs and glycine induced currents of group I cells remained unaltered across wild-type and the three mutant mice (mean decay time constant of sIPSCs, ,,25 ms). Group II cells showed glycinergic sIPSCs and glycine induced currents in wild-type, Glra1spd-ot and Glra3,/, mice (,,25 ms); however, glycinergic currents were absent in group II cells of Glra2,/, mice. Glycine induced currents and sIPSCs recorded from ON-starburst amacrine cells did not differ significantly between wild-type and the mutant mouse retinas (,,50,70 ms). We propose that GlyRs of group II cells are dominated by the ,2 subunit; GlyRs of ON-starburst amacrine cells appear to be dominated by the ,4 subunit. [source]

Functional characterization of compound heterozygosity for GlyR,1 mutations in the startle disease hyperekplexia

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2002
Ruth Rea
Abstract The human disease hyperekplexia is characterized by excessive startle reactions to auditory and cutaneous stimuli. In its familial form, hyperekplexia has been associated with both dominant and recessive mutations of the GLRA1 gene encoding the glycine receptor ,1 subunit (GlyR,1), which mediates inhibitory transmission in the spinal cord and brainstem. Here we have examined the functional consequences of two amino acid substitutions found in a compound heterozygous family, R252H and R392H, to investigate the mechanisms determining this inheritance pattern. When expressed in Xenopus laevis oocytes, both mutations were non-functional. Neither mutant affected the electrophysiological properties of wild type GlyR,1 when co-expressed. We introduced a green fluorescent protein tag to mutant subunits and found that both mutant proteins were detectable. Evidence that subcellular localization differed from wild type was significant for one of the mutants. Thus, an effective loss of functional GlyR,1-mediated current underlies hyperekplexia in this family, whereas a partial loss is asymptomatic. [source]

Distribution of glycine receptor subunits on primate retinal ganglion cells: a quantitative analysis

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2000
Bin Lin
Abstract This study investigates the distribution of inhibitory neurotransmitter receptors on sensory neurons. Ganglion cells in the retina of a New World monkey, the common marmoset Callithrix jacchus, were injected with Lucifer yellow and Neurobiotin and subsequently processed with antibodies against one (,1), or against all subunits, of the glycine receptor, or against the anchoring protein gephyrin. Immunoreactive (IR) puncta representing glycine receptor or gephyrin clusters were found on the proximal and the distal dendrites of all ganglion cell types investigated. For both parasol and midget cells, the density of receptor clusters was greater on distal than proximal dendrites for all antibodies tested. In parasol cells the average density for the ,1 subunit of the glycine receptor was 0.087 IR puncta/µm of dendrite, and for all subunits it was 0.119 IR puncta/µm of dendrite. Thus, the majority of glycine receptors on parasol cells contain the ,1 subunit. For parasol cells, we estimated an average of 1.5 glycinergic synapses/100 µm2 dendritic membrane on proximal dendrites and about 9.4 glycinergic synapses/100 µm2 on distal dendrites. The segregation of receptors to the distal dendrites appears to be a common feature of inhibitory neurotransmitter input to parasol and midget cells, and might be associated with the receptive field surround mechanism. [source]

Gephyrin, a major postsynaptic protein of GABAergic synapses

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2000
Marco Sassoè-Pognetto
Abstract ,-aminobutyric acid type A (GABAA) receptors are located at the majority of inhibitory synapses in the mammalian brain. However, the mechanisms by which GABAA receptor subunits are targeted to, and clustered in, the postsynaptic membrane are poorly understood. Recent studies have demonstrated that gephyrin, a protein first identified as a component of the glycine receptor (GlyR) complex, is colocalized with several subtypes of GABAA receptors and is involved in the stabilization of postsynaptic GABAA receptor clusters. Thus, gephyrin functions as a clustering protein for major subtypes of inhibitory ion channel receptors. [source]

Characterization of a glycine receptor domain that controls the binding and gating mechanisms of the ,-amino acid agonist, taurine

JOURNAL OF NEUROCHEMISTRY, Issue 3 2001
Nian-Lin R. Han
The ,-amino acid, taurine, is a full agonist of the human glycine receptor ,1 subunit when recombinantly expressed in a mammalian (HEK293) cell line, but a partial agonist of the same receptor when expressed in Xenopus oocytes. Several residues in the Ala101,Thr112 domain have previously been identified as determinants of ,-amino acid binding and gating mechanisms in Xenopus oocyte-expressed receptors. The present study used the substituted cysteine accessibility method to investigate the role of this domain in controlling taurine-specific binding and gating mechanisms of glycine receptors recombinantly expressed in mammalian cells. Asn102 and Glu103 are identified as taurine and glycine binding sites, whereas Ala101 is eliminated as a possible binding site. The N102C mutation also abolished the antagonistic actions of taurine, indicating that this site does not discriminate between the putative agonist- and antagonist-bound conformations of ,-amino acids. The effects of mutations from Lys104,Thr112 indicate that the mechanism by which this domain controls ,-amino acid-specific binding and gating processes differs substantially depending on whether the receptor is expressed in mammalian cells or Xenopus oocytes. Thr112 is the only domain element in mammalian cell-expressed GlyRs which was demonstrated to discriminate between glycine and taurine. [source]

The Glycine Reuptake Inhibitor Org 25935 Interacts With Basal and Ethanol-Induced Dopamine Release in Rat Nucleus Accumbens

ALCOHOLISM, Issue 7 2009
Helga Höifödt Lidö
Background:, The mesolimbic dopamine (DA) projection from the ventral tegmental area to nucleus accumbens (nAc), a central part of the reward system, is activated by ethanol (EtOH) and other drugs of abuse. We have previously demonstrated that the glycine receptor in the nAc and its amino acid agonists may be implicated in the DA activation and reinforcing properties of EtOH. We have also reported that the glycine transporter 1 inhibitor, Org 25935, produces a robust and dose-dependent decrease in EtOH consumption in Wistar rats. The present study explores the interaction between EtOH and Org 25935 with respect to DA levels in the rat nAc. Methods:, The effects of Org 25935 (6 mg/kg, i.p.) and/or EtOH (2.5 g/kg, i.p.) on accumbal DA levels were examined by means of in vivo microdialysis (coupled to HPLC-ED) in freely moving male Wistar rats. The effect of Org 25935 on accumbal glycine output was also investigated. Results:, Systemic Org 25935 increased DA output in a subpopulation of rats (52% in Experiment 1 and 38% in Experiment 2). In Experiment 2, EtOH produced a significant increase in DA levels in vehicles (35%) and in Org 25935 nonresponders (19%), whereas EtOH did not further increase the DA level in rats responding to Org 25935 (2%). The same dose of Org 25935 increased glycine levels by 87% in nAc. Conclusions:, This study demonstrates that Org 25935, probably via increased glycine levels, (i) counteracts EtOH-induced increases of accumbal DA levels and (ii) increases basal DA levels in a subpopulation of rats. The results are in line with previous findings and it is suggested that the effects observed involve interference with accumbal GlyRs and are related to the alcohol consumption modulating effect of Org 25935. [source]

Identification of a de novo Lys304Gln mutation in the glycine receptor ,-1 subunit gene in a Korean infant with hyperekplexia

MOVEMENT DISORDERS, Issue 4 2008
Hoon-Chul Kang MD
Abstract Startle disease or hyperekplexia (STHE; MIM 149400) is a rare disorder that is characterized by marked muscular hypertonia in infancy and an exaggerated startle response to unexpected acoustic or tactile stimuli. Mutations in the gene encoding the ,-1 subunit of the inhibitory glycine receptor (GLRA1) were reported as causes of STHE. Recently, we encountered a Korean male infant with generalized stiffness that was observed from the first 3 days of life. The abnormal startle response was evident from the fourth week of life, and he showed marked improvement in the startle response and muscle hypertonia after being administered phenobarbital and clonazepam. Direct sequencing analysis of the infant and his parents revealed a de novo variation (c.910A>C) in the GLRA1 gene, resulting in a novel Lys304Gln missense mutation. © 2007 Movement Disorder Society [source]

Genetic variation of the human glycine receptor subunit genes GLRA3 and GLRB and susceptibility to idiopathic generalized epilepsies

AMERICAN JOURNAL OF MEDICAL GENETICS, Issue 6 2001
Diana Sobetzko
Abstract Alterations of glycine receptor ,1 and , subunit genes have been associated with hypertonic motor disorders in both mice and humans. Mutations in genes encoding other ligand- and voltage-gated ion channels have been identified in rare monogenic forms of idiopathic generalized epilepsies (IGE). We tested the hypothesis that allelic variants of the glycine receptor subunit genes, GLRA3 and GLRB, both localized on chromosome 4q, confer susceptibility to common subtypes of IGE. Mutation screening was carried out in index patients of 14 IGE families. No pathogenic mutation was found, but two intronic polymorphisms were detected in the GLRB gene, and four intronic, three exonic, and one 3,-UTR polymorphisms were identified for the GLRA3 gene. Subsequent screening for exonic and 3,-UTR polymorphisms in GLRA3 showed no statistical difference between a group of sporadic IGE patients (n,=,104) and a control group (n,=,141). The genotype frequencies for exonic and 3,-UTR polymorphisms in GLRA3 showed no statistically significant difference between IGE patients (n,=,104) and an ethnically matched control group (n,=,141). Thus, no association between IGE and alterations in GLRA3 or GLRB genes could be detected, indicating that both genes do not play a major causative role in the epileptogenesis of common IGE subtypes. Still, these novel single nucleotide polymorphisms may be useful markers for candidate gene analyses of other disorders. © 2001 Wiley-Liss, Inc. [source]

Developmental shift in bidirectional functions of taurine-sensitive chloride channels during cortical circuit formation in postnatal mouse brain

DEVELOPMENTAL NEUROBIOLOGY, Issue 2 2004
Mika Yoshida
Abstract Taurine (2-aminoethanesulfonic acid) is the most abundant free amino acid in the developing mammalian cerebral cortex, however, few studies have reported its neurobiological functions during development. In this study, by means of whole-cell patch-clamp recordings, we examined the effects of taurine on chloride channel receptors in neocortical neurons from early to late postnatal stages, which cover a critical period in cortical circuit formation. We show here that taurine activates chloride channels in cortical neurons throughout the postnatal stages examined (from postnatal day 2 to day 36). The physiological effects of taurine changed from excitatory to inhibitory due to variations in the intracellular Cl, concentration during development. An antagonist blocking analysis also demonstrated a developmental shift in the receptor target of taurine, from glycine receptors to GABAA receptors. Taken together, these results may reflect genetically programmed, bidirectional functions of taurine. At the early developmental stage, taurine acting on glycine receptors would serve to promote cortical circuit formation. As cortical circuit has to be regulated in the later stages, taurine would serve as a safeguard against hyperexcitable circuit. © 2004 Wiley Periodicals, Inc. J Neurobiol 60: 166,175, 2004 [source]

Long-range oscillatory Ca2+ waves in rat spinal dorsal horn

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2005
Ruth Ruscheweyh
Abstract Synchronous activity of large populations of neurons shapes neuronal networks during development. However, re-emergence of such activity at later stages of development could severely disrupt the orderly processing of sensory information, e.g. in the spinal dorsal horn. We used Ca2+ imaging in spinal cord slices of neonatal and young rats to assess under which conditions synchronous activity occurs in dorsal horn. No spontaneous synchronous Ca2+ transients were detected. However, increasing neuronal excitability by application of 4-aminopyridine after pretreatment of the slice with blockers of (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate, ,-aminobutyric acid (GABA)A and glycine receptors evoked repetitive Ca2+ waves in dorsal horn. These waves spread mediolaterally with a speed of 1.0 ± 0.1 mm/s and affected virtually every dorsal horn neuron. The Ca2+ waves were associated with large depolarizing shifts of the membrane potential of participating neurons and were most likely synaptically mediated because they were abolished by blockade of action potentials or N -methyl- d -aspartate (NMDA) receptors. They were most pronounced in the superficial dorsal horn and absent from the ventral horn. A significant proportion of the Ca2+ waves spread to the contralateral dorsal horn. This seemed to be enabled by disinhibition as primary afferent-induced dorsal horn excitation crossed the midline only when GABAA and glycine receptors were blocked. Interestingly, the Ca2+ waves occurred under conditions where AMPA/kainate receptors were blocked. Thus, superficial dorsal horn NMDA receptors are able to sustain synchronous neuronal excitation in the absence of functional AMPA/kainate receptors. [source]

GABA and glycine are protective to mature but toxic to immature rat cortical neurons under hypoxia

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2005
Peng Zhao
Abstract Although recent studies suggest that ,-aminobutyric acid (GABA) and glycine may be ,inhibitory' to mature neurons, but ,excitatory' to immature neurons under normoxia, it is unknown whether inhibitory neurotransmitters are differentially involved in neuronal response to hypoxia in immature and mature neurons. In the present study, we exposed rat cortical neurons to hypoxia (1% O2) and examined the effects of three major inhibitory neurotransmitters (GABA, glycine and taurine) on the hypoxic neurons at different neuronal ages [days in vitro (DIV)4,20]. Our data showed that the cortical neurons expressed both GABAA and glycine receptors with differential developmental profiles. GABA (10,2000 µm) was neuroprotective to hypoxic neurons of DIV20, but enhanced hypoxic injury in neurons of <,DIV20. Glycine at low concentrations (10,100 µm) exhibited a similar pattern to GABA. However, higher concentrations of glycine (1000,2000 µm) for long-term exposure (48,72 h) displayed neuroprotection at all ages (DIV4,20). Taurine (10,2000 µm), unlike GABA and glycine, displayed protection only in DIV4 neurons, and was slightly toxic to neurons >,DIV4. In comparison with delta-opioid receptor (DOR)-induced protection in DIV20 neurons exposed to 72 h of hypoxia, glycine-induced protection was weaker than that of DOR but stronger than that of GABA and taurine. These data suggest that the effects of the inhibitory neurotransmitters on hypoxic cortical neurons are age-dependent, with GABA and glycine being neurotoxic to immature neurons and neuroprotective to mature neurons. [source]

Modulation of glycine responses by dihydropyridines and verapamil in rat spinal neurons

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2001
Dominique Chesnoy-Marchais
Abstract Although glycine receptors (GlyRs) are responsible for the main spinal inhibitory responses in adult vertebrates, in the embryo they have been reported to mediate depolarizing responses, which can sometimes activate dihydropyridine-sensitive l -type calcium channels. However, these channels are not the only targets of dihydropyridines (DHPs), and we questioned whether GlyRs might be directly modulated by DHPs. By whole-cell recording of cultured spinal neurons, we investigated modulation of glycine responses by the calcium channel antagonists, nifedipine, nitrendipine, nicardipine and (R)-Bay K 8644, and by the calcium channel, agonist (S)-Bay K 8644. At concentrations between 1 and 10 µm, all these DHPs could block glycine responses, even in the absence of extracellular Ca2+. The block was stronger at higher glycine concentrations, and increased with time during each glycine application. Nicardipine blocked GABAA responses from the same neurons in a similar manner. In addition to their blocking effects, nitrendipine and nicardipine potentiated the peak responses to low glycine concentrations. Both effects of extracellular nitrendipine on glycine responses persisted when the drug was present in the intracellular solution. Thus, these modulations are related neither to calcium channel modulation nor to possible intracellular effects of DHPs. Another type of calcium antagonist, verapamil (10,50 µm), also blocked glycine responses. Our results suggest that some of the effects of calcium antagonists, including the neuroprotective and anticonvulsant effects of DHPs, might result partly from their interactions with ligand-gated chloride channels. [source]

Distribution of glycine receptor subunits on primate retinal ganglion cells: a quantitative analysis

Ethanol Enhances Taurine-Activated Glycine Receptor Function

ALCOHOLISM, Issue 9 2010
Brian T. Welsh
Background:, Emerging evidence suggests that taurine acts as a partial agonist on glycine receptors (GlyR) in vitro and in vivo. Ethanol acts as an allosteric modulator on the GlyR producing a leftward shift of the glycine concentration,response curve, with no enhancing effects observed at saturating glycine concentrations. However, to date, no electrophysiological studies have been performed on ethanol modulation of taurine-activated GlyR. Methods:, Wild-type ,1 GlyR, or those bearing a serine-267 to isoleucine replacement (S267I), were homomerically expressed in Xenopus oocytes and voltage clamped at ,70 mV. Ethanol was co-applied with varying concentrations of glycine or taurine and the enhancing effects of ethanol compared. Results:, Ethanol potentiated glycine- and taurine-activated GlyR responses in a concentration-dependent manner. It shifted taurine and glycine concentration,response curves to the left, having no effects at saturating agonist concentrations. Chelation of zinc by tricine decreased ethanol enhancement of taurine-gated GlyR function. The S267I mutation prevented ethanol enhancement of taurine-mediated responses as previously also reported for glycine. Conclusion:, Ethanol modulates taurine activation of GlyR function by a mechanism similar to that of the full agonist glycine. The lack of effect of ethanol at saturating taurine concentrations provides mechanistic information on alcohol actions at the GlyR. [source]

Glycine Receptors in the Nucleus Accumbens Involved in the Ethanol Intake-Reducing Effect of Acamprosate

Caffeine inhibition of ionotropic glycine receptors

THE JOURNAL OF PHYSIOLOGY, Issue 16 2009
Lei Duan
We found that caffeine is a structural analogue of strychnine and a competitive antagonist at ionotropic glycine receptors (GlyRs). Docking simulations indicate that caffeine and strychnine may bind to similar sites at the GlyR. The R131A GlyR mutation, which reduces strychnine antagonism without suppressing activation by glycine, also reduces caffeine antagonism. GlyR subtypes have differing caffeine sensitivity. Tested against the EC50 of each GlyR subtype, the order of caffeine potency (IC50) is: ,2, (248 ± 32 ,m) ,,3, (255 ± 16 ,m) > ,4, (517 ± 50 ,m) > ,1,(837 ± 132 ,m). However, because the ,3, GlyR is more than 3-fold less sensitive to glycine than any of the other GlyR subtypes, this receptor is most effectively blocked by caffeine. The glycine dose,response curves and the effects of caffeine indicate that amphibian retinal ganglion cells do not express a plethora of GlyR subtypes and are dominated by the ,1, GlyR. Comparing the effects of caffeine on glycinergic spontaneous and evoked IPSCs indicates that evoked release elevates the glycine concentration at some synapses whereas summation elicits evoked IPSCs at other synapses. Caffeine serves to identify the pharmacophore of strychnine and produces near-complete inhibition of glycine receptors at concentrations commonly employed to stimulate ryanodine receptors. [source]

Properties of glycine receptors underlying synaptic currents in presynaptic axon terminals of rod bipolar cells in the rat retina

THE JOURNAL OF PHYSIOLOGY, Issue 15 2009
Svein Harald Mørkve
The excitability of presynaptic terminals can be controlled by synaptic input that directly targets the terminals. Retinal rod bipolar axon terminals receive presynaptic input from different types of amacrine cells, some of which are glycinergic. Here, we have performed patch-clamp recordings from rod bipolar axon terminals in rat retinal slices. We used whole-cell recordings to study glycinergic inhibitory postsynaptic currents (IPSCs) under conditions of adequate local voltage clamp and outside-out patch recordings to study biophysical and pharmacological properties of the glycine receptors with ultrafast application. Glycinergic IPSCs, recorded in both intact cells and isolated terminals, were strychnine sensitive and displayed fast kinetics with a double-exponential decay. Ultrafast application of brief (,1 ms) pulses of glycine (3 mm) to patches evoked responses with fast, double-exponential deactivation kinetics, no evidence of desensitization in double-pulse experiments, relatively low apparent affinity (EC50,100 ,m), and high maximum open probability (,0.9). Longer pulses evoked slow, double-exponential desensitization and double-pulse experiments indicated slow, double-exponential recovery from desensitization. Non-stationary noise analysis of IPSCs and patch responses yielded single-channel conductances of ,41 pS and ,64 pS, respectively. Directly observed single-channel gating occurred at ,40,50 pS and ,80,90 pS in both types of responses, suggesting a mixture of heteromeric and homomeric receptors. Synaptic release of glycine leads to transient receptor activation, with about eight receptors available to bind transmitter after release of a single vesicle. With a low intracellular chloride concentration, this leads to either hyperpolarizing or shunting inhibition that will counteract passive and regenerative depolarization and depolarization-evoked transmitter release. [source]

Spontaneous IPSCs and glycine receptors with slow kinetics in wide-field amacrine cells in the mature rat retina

THE JOURNAL OF PHYSIOLOGY, Issue 1 2007
Margaret Lin Veruki
The functional properties of glycine receptors were analysed in different types of wide-field amacrine cells, narrowly stratifying cells considered to play a role in larger-scale integration across the retina. The patch-clamp technique was used to record spontaneous IPSCs (spIPSCs) and glycine-evoked patch responses from mature rat retinal slices (4,7 weeks postnatal). Glycinergic spIPSCs were blocked reversibly by strychnine (300 nm). Compared to previously described spIPSCs in AII amacrine cells, the spIPSCs in wide-field amacrine cells displayed a very slow decay time course (,fast, 15 ms; ,slow, 57 ms). The kinetic properties of spIPSCs in whole-cell recordings were paralleled by even slower deactivation kinetics of responses evoked by brief pulses of glycine (3 mm) to outside-out patches from wide-field amacrine cells (,fast, 45 ms; ,slow, 350 ms). Non-stationary noise analysis of patch responses and spIPSCs yielded similar average single-channel conductances (,31 and ,34 pS, respectively). Similar, as well as both lower- and higher-conductance levels could be identified from directly observed single-channel gating during the decay phase of spIPSCs and patch responses. These results suggest that the slow glycinergic spIPSCs in wide-field amacrine cells involve ,2, heteromeric receptors. Taken together with previous work, the kinetic properties of glycine receptors in different types of amacrine cells display a considerable range that is probably a direct consequence of differential expression of receptor subunits. Unique kinetic properties are likely to differentially shape the glycinergic input to different types of amacrine cells and thereby contribute to distinct integrative properties among these cells. [source]

Stoichiometry of a pore mutation that abolishes picrotoxin-mediated antagonism of the GABAA receptor

THE JOURNAL OF PHYSIOLOGY, Issue 2 2006
Anna Sedelnikova
Picrotoxin, a potent antagonist of the inhibitory central nervous system GABAA and glycine receptors, is believed to interact with residues that line the central ion pore. These pore-lining residues are in the second transmembrane domain (TM2) of each of the five constituent subunits. One of these amino acids, a threonine at the 6, location, when mutated to phenylalanine, abolishes picrotoxin sensitivity. It has been suggested that this threonine, via hydrogen bonding, directly interacts with the picrotoxin molecule. We previously demonstrated that this mutation, in the ,, , or , subunit, can impart picrotoxin resistance to the GABA receptor. Since the functional pentameric GABA receptor contains two , subunits, two , subunits and one , subunit, it is not clear how many , and , subunits must carry this mutation to impart the resistant phenotype. In this study, by coexpression of mutant , or , subunits with their wild-type counterparts in various defined ratios, we demonstrate that any single subunit carrying the 6, mutation imparts picrotoxin resistance. Implications of this finding in terms of the mechanism of antagonism are considered. [source]