Inhibitory Effect Of GABA Research Articles

Suppressive effect of GABA on insulin secretion from the pancreatic beta-cells in the rat

In order to investigate a possible role of GABA in the regulation of insulin secretion, we have studied the effect of GABA on insulin secretion from the isolated perfused rat pancreas in vitro and on the changes in the cytoplasmic Ca 2+ of Beta-cells from the isolated rat islets. When glucose is present, GABA caused a dose dependent inhibition of the first phase of arginine-induced insulin secretion during the range of 10–1000 μM, but GABA did not affect arginine-induced insulin secretion in the absence of glucose. GABA inhibited not only the first phase but also the second phase of glucose-induced insulin secretion. A GABA B-receptor agonist, baclofen, also inhibited both phases of insulin secretion induced by 16.7 mM glucose. Furthermore, GABA inhibited the rise in cytoplasmic Ca 2+ of Beta-cells in response to 16.7 mM glucose. These studies indicate that GABA decreases Beta cell secretory activity mainly in response to glucose. These inhibitory effects of GABA on insulin secretion may be mediated through GABA B-receptor and the inhibition of the rise in cytoplasmic Ca 2+.

The neurotransmitter of inhibitory synaptic inputs on inhibitory burst neurons (IBNs) controlling vestibular nystagmus in the cat.

In the pontine neural networks that govern vestibular nystagmus in the cat, inhibitory burst neurons (IBNs) are known to fire in bursts during the quick phase, and to suppress firing of the abducens motoneurons on the contralateral side. The present experiments were designed to identify the neurotransmitter controlling the burst firing pattern of IBNs. Inhibitory burst neuron activity was recorded extracellularly, and various chemicals were applied to the IBNs iontophoretically through multibarrel micropipettes. GABA and muscimol (a GABAA-receptor agonist) strongly suppressed IBN activity and eliminated the burst pattern. Bicuculline (a GABAA-receptor antagonist) increased the firing of IBNs and suppressed the inhibitory effect of GABA when applied simultaneously. Although baclofen (a GABAB-receptor agonist) had no inhibitory effect, it slightly shortened the duration of burst firing. Neither glycine nor serotonin, other inhibitory transmitter candidates, nor their respective antagonists, strychnine and methysergide, had any effect. Systemically administered picrotoxin prevented the GABA-induced suppression of IBNs. These results suggest that IBNs possess GABAA receptors and are controlled by higher GABA-liberating neurons and Cl- channels.

GABA, acting at both GABAA and GABAB receptors, inhibits the release of cholecystokinin-like material from the rat spinal cord in vitro

Superfusion of slices of the dorsal zone of the lumbar enlargement of the rat spinal cord with an artificial cerebrospinal fluid allowed the collection of cholecystokinin-like material (CCKLM) whose Ca2+-dependent release could be evoked by tissue depolarization with 30 mM K+. Studies on the possible influence of GABA and related agonists on this process showed that the amino acid, the GABAA agonist, muscimol, and the GABAB agonist, baclofen, inhibited the K+-evoked release of CCKLM from the rat spinal cord in a concentration-dependent manner. Maximal inhibition did not exceed −40% with either agonist. Furthermore, the effects of GABAA and GABAB receptor stimulation were not additive. Whereas the effects of muscimol (10 μM) and baclofen (1 μM) could be completely antagonized by bicuculline (1 μM) and phaclofen (10 μM), respectively, complete blockade of the inhibition by GABA (1 μM) could only be achieved in the presence of both antagonists. These data indicate that both GABAA and GABAB receptors are involved in the negative influence of GABA onto CCK-containing neurones within the dorsal horn of the rat spinal cord. Apparently, these receptors are not located on CCK-containing neurones themselves, since the inhibitory effect of GABA on the K+-evoked release of CCKLM could be completely prevented by tetrodotoxin (1 μM). As CCK acts centrally as an endogenous opioid antagonist, such a GABA-inhibitory control of spinal CCK-containing neurones might participate in the analgesic action of the amino acid via the intrathecal route.

Inhibitory of gamma-aminobutyric acid on the contractility of isolated rat vas deferens

GABA is an inhibitory neurotransmitter in central nervous system and produce sedative, antianxiety and muscle reaxing effects via receptor or receptor. Recently it is known that GABA is widely distributed throughout peripheral organs and may playa physiological role in certain organ. The vas deferens is innervated by species-difference. These study, therefore, was performed to investigate the mode and the mechanism of action of GABA on the norepiniphrine-, ATP- and electric stimulation-induced contraction of vas deferens of rat. Sprague-Dawley rats were sacrificed by cervical dislocation. The smooth muscle strips were isolated from the prostastic portion and were mounted in the isolated muscle bath. PSS in the bath was aerated with 95/5%- at . Muscle tensions were measured by isometric tension transducer and were recorded by biological recording system. 1. GABA, muscimol, a agonist, and baclofen, a agonist inhibited the electric field stimulation(EFS, 0.2Hz, 1mSec, 80 V, monophasic square wave)-induced contraction with a rank order of potency of GABA greater than baclofen greater than muscimol. 2. The inhibitory effect of GABA was antagonized by delta aminovaleric acid(DAVA), a antagonist, but not by bicuculline, a mtagonist. 3. The inhibitory effect of baclofen was antagonized by DAVA, but the effect of muscimol was not antagonized by bicuculline. 4. Exogenous norepinephrine(NE) and ATP contracted muscle strip concentration dependently, but the effect of acetylcholine was negligible : and GABA did not affect the NE-and ATP-induced contractions. 5. GABA, baclofen and muscimol did not affect basal tone, and GABA did not affect the NE-and ATP-induced contractionsm 6. EFS-induced contraction was including 2 distinctable components. The first phasic component was inhibited by beta gamma-methylene ATP(mATP), a desensitizing agent of APT receptor and the second tonic component was reduced by pretreatment of reserpine(3 mg/Kg, IP). 7. GABA inhibited the EFS-induced contraction of reserpinized strips, but not the mATP-treated strips. These results suggest that in the prostatic portion of the rat vas deferens, adrenergic and purinergic neurotransmissions are exist, and GABA inhibits the release of ATP via presynaptic receptor on the excitatory neurons.

γ-Aminobutyric acid (GABA B) receptor-mediated inhibition of tyrosine hydroxylase activity in the striatum of rat

The effects of GABA and GABA agonists on calcium and depolarization-dependent stimulation of tyrosine hydroxylase activity in striatal slices were studied. γ-Aminobutyric acid and (−)baclofen inhibited, while muscimol and (+)baclofen did not affect, the stimulation of tyrosine hydroxylase. The inhibitory effect ofGABA and (−)baclofen was blocked by the GABA bB antagonist, phaclofen but not by the GABA A antagonist, picrotoxin. The data suggest that the activity of tyrosine hydroxylase on dopaminergic nigrostriatal terminals may be modulated by GABA via GABA B receptors.

Inhibitory effects of GABA on synaptic excitation in isolated rat hippocampal slices

In research on γ-aminobutyric acid (GABA) used at different concentrations on the amplitude of EPSP within populations (PEPSP), as recorded from dentrites in isolated hippocampal slices, GABA induced a dose-dependent reversible reduction in PEPSP amplitude with no noticeable signs of desensitization. Highest sensitivity to GABA was shown by PEPSP in hippocampal zone CA1 (threshold concentration: 3×10−5–2×10−4 M; (concentration at which the effect equal to 1/2 of maximum occurs) IC50: 5×10−4−1×10−3 M). The effects of GABA on PEPSP were not blocked by bicuculline, picrotoxin, or penicillin. Action of GABA on dendritic antidromic population spike (DAPS — postynaptic effects) were slightly diminished by these blockers. Baclofen inhibited PEPSP more powerfully than GABA (threshold concentration: 1×10−6 M: IC50: 3×10−6 M), although it only produced a minor reduction in DAPS amplitude even at high concentrations. It is concluded that the inhibitory effect of GABA on PEPSP in hippocampal zone CA1 may be put down mainly to its presynaptic action mediated by GABAB receptors on axonal terminals of Schaffer collaterals.

A long-lasting decrease in the inhibitory effect of GABA on glutamate responses of hippocampal pyramidal neurons induced by kindling epileptogenesis

Experiments were carried out to test whether changes in the sensitivity of hippocampal pyramidal neurons to the neurotransmitters glutamate, GABA and noradrenaline may be associated with the establishment of an epileptogenic focus induced by kindling. The effects of iontophoretically applied neurotransmitters on the firing rate of single units were quantified in the rat hippocampal CA1 area in kindled and control animals. Kindling was induced by electrical tetanic stimulation of the Schaffer collateral/commissural fibers. Firing was evoked by local glutamate iontophoresis while simultaneous GABA or noradrenaline application suppressed this response. A significant reduction of the GABAergic inhibitory action on the firing rate in kindled animals studied around four or around 42 days after the last convulsion was found. In the same neurons, the suppressive effect of noradrenaline was not different from controls. The neurons of kindled animals, investigated around four days after the last seizure, had a reduced sensitivity for glutamate; more glutamate ejection current was needed to evoke firing or to evoke the maximum firing rate. In contrast, the responsiveness for glutamate was significantly increased long-term after the last convulsion. These findings demonstrate that hippocampal Schaffer collateral kindling is associated with a long-lasting reduced effectiveness of the GABA-mediated response on glutamate-evoked firing in CA1.

Prejunctional GABA-B inhibition of cholinergic, neurally-mediated airway contractions in guinea-pigs

GABA is a known inhibitory neurotransmitter in the CNS. Recent studies have also demonstrated the presence of GABA in peripheral tissue, including lung. To delineate a role for GABA in lung, the effect of GABA and selective GABA agonists and antagonists on neuronally-induced airway contractions in guinea pigs were studied. In vitro, tracheal contractions induced by electrical field stimulation (EFS) were inhibited by tetrodotoxin and atropine indicating that the contractions were mediated by neuronal release of acetylcholine. The contractions caused by EFS, but not those by exogenous acetylcholine, were inhibited by GABA (EC 50 = 4.5 μM) and the selective GABA-B agonist baclofen (EC 50 = 9 μM), but not by the GABA-A agonist, muscimol. The inhibitory effect of baclofen was not affected by the GABA-A antagonist, bicuculline, but was significantly reversed with the GABA-B antagonists, 3-aminopropylphosphonic acid (3-APPA) (pA 2 = 4.5) and 2-hydroxysaclofen (pA 2 = 4.1). In vivo, vagal nerve stimulation (5 V, 20 Hz, 0.5 ms, 5 s) in anesthetized, mechanically ventilated guinea-pigs caused cholinergic-dependent bronchospasms that were inhibited by intravenous GABA (3 and 10 mg/kg) and baclofen (1–10 mg/kg), but not by muscimol. The inhibitory effects of GABA and baclofen against vagal bronchospasm were blocked by 3-APPA (5 mg/kg, iv), but not by bicuculline. Responses to the GABA-B agonists were unaltered after the treatment of animals with phentolamine or propranolol to block α-adrenergic and β-adrenergic receptors, respectively. Bronchospasm due to intravenous methacholine was also unchanged by GABA and baclofen. These results demonstrate that GABA inhibits cholinergic bronchoconstriction in guinea-pigs and does so by a mechanism involving inhibitory prejunctional GABA-B receptors.

High- and low-affinity GABA-receptors in cultured cerebellar granule cells regulate transmitter release by different mechanisms

Abstract The ability of high- and low-affinity GABA A -receptors, respectively to inhibit depolarization coupled transmitter release was studied in cultured glutamatergic cerebellar granule cells which, depending on the culture conditions, express either high-affinity GABA A -receptors alone or high-affinity receptors together with low-affinity receptors. In order to gain information about the coupling of these receptors to chloride channels the effect of picrotoxin and binding of [ 35 S]t-butylbicyclophosphorothionate, both of which interact specifically with such channels were studied. Moreover, the influence of Flunitrazepam on the GABA-mediated inhibition of transmitter release was investigated to see if the GABA-receptors are coupled to benzodiazepine binding sites. Under conditions where the granule cells express only high-affinity GABA A -receptors it was found that GABA was able to inhibit transmitter release elicited by mild depolarization induced either by 30 mM KCl or 25 μM glutamate. This effect of GABA could be enhanced by Flunitrazepam and blocked by picrotoxin. However, transmitter release from these neurones induced by a more pronounced depolarization (55 mM KCl) could not be inhibited by GABA. Under conditions where the neurons express both high- and low-affinity GABA A -receptors transmitter release elicited by 55 mM KCl could be inhibited by GABA but this inhibitory effect of GABA could not be blocked by picrotoxin, nor could it be enhanced by Flunitrazepam. These results strongly suggest that while the action of the high-affinity GABA A -receptors is coupled to chloride channels and benzodiazepine binding sites, the physiological action of the low-affinity GABA A -receptors is not. This lack of coupling between the low-affinity GABA A -receptors and chloride channels is further supported by the finding that the K D and B max values for [ 35 S]TBPS binding to the granule cells were independent of whether or not the cells expressed low-affinity GABA A -receptors. While the results clearly show that the inhibitory action of GABA mediated by low-affinity GABA A -receptors is not coupled to chloride channels, the exact mechanism of action of these receptors still remains to be elucidated.

Presynaptic effects of gamma-aminobutyric acid on norepinephrine release and uptake in rat pineal gland

The effect of tau-aminobutyric acid (GABA) on pineal norepinephrine (NE) release was examined in vitro in the rat pineal gland. Exposure of pineal explants previously loaded with 3H-NE to 1-100 microM GABA caused a dose-dependent decrease of 3H-NE release triggered by 60 mM K+, with a threshold GABA concentration of 1 microM and IC50 of about 10 microM. The inhibitory effect of GABA was mimicked by the type B GABA agonist baclofen, displaying a similar dose-response relationship as GABA. The type A GABA agonist muscimol increased depolarization-induced 3H-NE release, while the co-incubation with GABA and the type A receptor antagonist bicuculline augmented significantly GABA's depressive effect on 3H-NE release. Bicuculline alone brought about a significant decrease of 3H-NE release. Neither GABA, nor baclofen, muscimol or bicuculline, modified the spontaneous pineal 3H-NE efflux. Assessment of 3H-NE uptake at a low NE concentration (0.5 microM) indicated that GABA decreased it in a dose-dependent manner (IC50 = 100 microM) through an effect blocked by bicuculline and mimicked by muscimol but not by baclofen; at a 5 microM-3H-NE concentration a bicuculline-sensitive GABA augmentation of uptake was found. A kinetic analysis study of the pineal NE uptake process indicated that GABA augmented both Vmax and Km of transmitter uptake. These results indicate that GABA may be a significant regulatory signal for rat pineal sympathetic synapses.

Gamma‐Aminobutyric Acid Modulation of Corticotrophin‐Releasing Factor‐41 Secretion from the Rat Hypothalamus in vitro

Abstract There is increasing evidence for a centrally mediated inhibitory effect of the amino-acid neurotransmitter y-aminobutyric acid (GABA) on the hypothalamo-pituitary-adrenal axis. In the present study, the direct effect of GABA in modulating the release of the 41-residue corticotrophin-releasing factor (CRF-41), the major CRF identified so far, was investigated in acute hypothalamic explants by utilizing previously validated incubation and assay techniques. While GABA (10(-7)'to 10(-5) M) had no effect on basal CRF-41 release (P > 0.05), it significantly suppressed K (-) (28 mM)-stimulated release in a dose-dependent manner (P < 0.01). A similar inhibitory effect was observed with the GABA agonist muscimol (10(-7) to 10(-5) M). Noradrenaline (10(-6) M) -induced CRF-41 release was also significantly inhibited by GABA 10(-6) M. The inhibitory effect of GABA on K(+)-stimulated CRF-41 secretion was completely. reversed by the GABA antagonists bicuculline and picrotoxin (10(-6) to 10(-5) M) in a dose-dependent fashion. Both bicuculline and picrotoxin stimulated basal and K(+) (28 mM)-stimulated CRF-41 release, indicating the presence of tonic inhibition by endogenous GABA in the basal state. Finally, GABA 10(-5) M was able to significantly inhibit the stimulated release of CRF-41 from the isolated median eminence. In summary, the present data provide strong evidence that GABA-induced inhibition of the hypothalamo-pituitary-adrenal axis is mediated, at least in part, through an inhibitory action on CRF-41 secretion. It is likely that these GABA receptors are located directly on CRF-41 neurons, probably on nerve terminals in the median eminence.

The effect of ethanol on 35S-TBPS binding to mouse brain membranes in the presence of chloride.

The effect of in vitro and in vivo administration of ethanol on the binding of 35S-t-butyl-bicyclophosphorothionate (35S-TBPS) to cortical brain membranes of C57Bl mice was investigated using KCl (100 mM) containing assay media. The in vitro addition of ethanol produced a dose-dependent inhibition of basal 35S-TBPS binding. In the presence of chloride ions, GABA and pentobarbital had a biphasic action (stimulation followed by inhibition) on 35S-TBPS binding, whereas diazepam only stimulated the binding. Ethanol reduced the stimulatory effects of GABA and pentobarbital in a dose-dependent manner, but had no effect on the enhancement of 35S-TBPS binding produced by diazepam. 35S-TBPS binding to cortical brain membranes was inhibited by the putative Cl- channel blocking agent DIDS. This inhibitory action of DIDS was significantly, and dose-dependently reduced by ethanol (greater than or equal to 100 mM ethanol). Chronic ethanol ingestion in vivo, which produced tolerance to and physical dependence on ethanol in the animals, did not alter the stimulatory and inhibitory effects of GABA and pentobarbital on 35S-TBPS binding. The enhancement of 35S-TBPS binding produced by diazepam was slightly, but significantly, enhanced in brain membranes from animals which had undergone 24 hours of ethanol withdrawal. Chronic ethanol treatment did not change the potency of picrotoxin and of the peripheral BDZ-receptor ligand RO 5-4864 to competitively inhibit 35S-TBPS binding. Our results suggest that in vitro addition of ethanol alters the activity of the GABA/benzodiazepine (BDZ) receptor complex.(ABSTRACT TRUNCATED AT 250 WORDS)

On the role of GABA as an inhibitory neurotransmitter in inferior colliculus neurons: iontophoretic studies

Significant neurochemical, immunocytochemical, and ligand binding studies support a role for GABA as an inhibitory neurotransmitter in the inferior colliculus (IC). The present study attempted to satisfy some of the remaining criteria for establishing transmitter identity by utilizing iontophoretic application onto IC neurons of agents affecting the action of γ-aminobutyric acid (GABA). The agents examined include GABA, a GABA B agonist (baclofen), a GABA A antagonist (bicuculline), a GABA uptake inhibitor (nipecotic acid), and a benzodiazepine (flurazepam), thought to exert its actions on the GABA receptor complex. Application of GABA results in inhibition of the spontaneous firing and acoustically evoked responses of inferior colliculus neurons. The inhibitory effect of GABA is enhanced by the simultaneous application of nipecotic acid or flurazepam. These agents as well as baclofen produce firing reductions when applied alone in higher doses. The effect of GABA can be blocked by application of bicuculline, and acoustically evoked (binaural) inhibition can also be selectively blocked by low doses of this GABA A antagonist. These data along with previous studies utilizing different techniques fulfill many of the criteria for establishment of GABA as an important inhibitory transmitter in the inferior colliculus.

Partial GABA agonist activity of SR 95531 on the binding of [ 35S]TBPS, [ 3H]DMCM and [ 3H]lormetazepam to rat brain membranes

A recently developed series of pyridazinyl-GABA derivatives has been classified as GABA antagonists in electrophysiological, behavioural and biochemical experiments. These substances seemed superior to the classical GABA antagonist bicuculline because of their water-solubility, high potency and apparent selectivity for GABA A receptors. In the present study the most potent representative of this class, SR 95531 almost completely reversed the stimulatory or inhibitory effect of GABA on [ 3H]Iormetazepam and [ 35S]TBPS binding, respectively. To a lesser extent, it antagonized the inhibition of [ 3H]DMCM binding by GABA. However, the interaction of SR 95531 with the GABA receptor seems to be of a complex nature since the compound enhanced the binding of [ 3H]lormetazepam by 28% at 37° in the presence of 200 mM Cl −. Bicuculline inhibited [ 3H]lormetazepam binding under these conditions, presumably by antagonizing the effect of residual endogenous GABA. Similar to GABA and THIP, SR 95531 potently inhibited the binding of [ 3H]DMCM and [ 35S]TBPS, suggesting SR 95531 to be a partial agonist at the GABA Areceptor.

Neurotransmitter effects on inhibitory burst neurons in the cat.

The present experiment was designed to determine which neurotransmitter influences the burst pattern in the firing of the inhibitory burst neurons (IBN) during vestibular nystagmus. Cats were anesthetized with ether and mounted in a stereotaxic apparatus on a turntable, implanted stimulation electrodes, removed occipital bone and aspirated the vermal part of cerebellum. After the operation ether was discontinued. The recordings took place with the cats in an alert condition created by upper cervical cord transsection, artificial respiration and local anesthesia by infiltrating 0.5% lidocaine into the semilunar ganglions every two hours. We also employed iontophoretic application of the various drugs: GABA, muscimol, glycine, serotonin (5-HT) and bicuculline through seven-barrelled glass micropipettes. GABA or muscimol did not influence nystagmus rhythm, but both chemicals caused strong suppression of burst activities in IBN. Since this inhibitory effect of GABA was suppressed by the simultaneous application of bicuculline, IBNs appear to be controlled by GABAA receptor. Glycine and 5-HT did not change the firing pattern of IBN. Application of bicuculline itself caused an increase of tonic discharges of IBN. These findings suggest that IBN receive inhibitory impulses from the higher GABAergic neurons.

A GABA-mediated inhibition of neurones in the nucleus tractus solitarius of the cat that respond to electrical stimulation of the carotid sinus nerve

Extracellular recordings were made from 39 single neurones in the nucleus tractus solitarius which were activated following electrical stimulation of the carotid sinus nerve in chloralose anaesthetised cats. Iontophoretic application of GABA abolished or markedly reduced the evoked activity of all neurones. The inhibitory effect of GABA could be antagonised by the simultaneous iontophoretic application of bicuculline. The iontophoretic application of bicuculline alone resulted in a significant increase in the evoked activity of eleven out of seventeen neurones. These results support the notion that a GABAergic inhibitory system, with the potential to modulate sinus nerve reflexes, acts within the nucleus tractus solitarius.

Independent gabaergic and cholinergic modulation of apomorphine-induced stereotyped rearing in the rat

The injection of GABA into the caudate nucleus inhibited the stereotyped rearing induced by apomorphine in a dose-related manner. Muscimol, a potent GABAergic agonist shared this effect. The inhibitory effect of GABA was easily counteracted by bicuculline but not by pretreatment with atropine. Injection of carbachol into the caudate nucleus inhibited the stereotyped rearing induced by systemically-applied apomorphine in a dose-related manner. This inhibitory effect was easily abolished by atropine but not bicuculline. Thus, the stereotyped rearing induced by apomorphine, an effect due to an increased excitatory state of the dopaminergic system in the caudate nucleus, could be modified (inhibited) by augmentation of either the GABAergic or of the cholinergic state excitation. The two modulatory systems did not appear to be interlinked; most probably, they influence the dopaminergic effect independently of one another.

Presence of neurons with GABA-like immunoreactivity in the superior cervical ganglion of the rat

Using antibodies raised against γ-aminobutyric acid (GABA)-glutaraldehyde complexes, we have found neurons with GABA-like immunoreactivity in the superior cervical ganglion of adult rats. The processes of these neurons formed pericellular networks around the principal ganglion cells. Electron microscopy revealed that the immunoreactive dendrites were innervated by non-reactive axon terminals which formed asymmetrical synapses and probably originated from the preganglionic nerve. Axons with GABA-like immunoreactivity, especially axonal varicosities filled with synaptic vesicles, were found in direct apposition to principal ganglion cells. The GABA-positive axons and axon varicosities persisted in experimentally decentralized (deafferented) ganglia, suggesting that the perikarya of the immunoreactive neurons were intrinsic to the superior cervical ganglion. Taken together with data on inhibitory effects of GABA in sympathetic ganglia, these findings suggest that the superior cervical ganglion of rats contains a subpopulation of inhibitory interneurons which is GABAergic. This would indicate that GABAergic neurons do not only occur in the central but also in the peripheral nervous system.

Effect of ethanol on the binding of 35STbutylbicyclophosphorothionate to mouse brain membranes

The effect of in vitro addition of ethanol (0.02–1.0 M) on the binding of 35STBPS was examined in brain membranes from cerebellum and cortex of naive or chronically ethanol-treated C57B1 mice. In brain membranes of untreated animals, increasing concentrations of ethanol produced a dose-related inhibition of 35STBPS binding in the brain areas investigated. Additional studies showed that this effect of ethanol was due to a decreased affinity of 35STBPS for its binding sites. Chronic treatment of the animals with ethanol, which produced tolerance to and dependence on ethanol, did not alter ethanol's ability to inhibit the binding of 35STBPS. In naive animals, the in vitro addition of GABA or pentobarbital produced a pronounced inhibition of 35STBPS, both drugs being more potent in the cerebellum than in the cortex. Picrotoxin also produced a dose-dependent inhibition at 35STBPS, but was equally potent in the brain areas investigated. The inhibition by GABA or pentobarbital was not influenced by in vitro addition of a physiologically relevant concentration of ethanol (100 mM), whereas ethanol produced a significant increase in the IC 50 values for picrotoxin both in the cortex and in the cerebellum. Furthermore, the inhibitory effects of GABA or pentobarbital on 35STBPS binding remained unchanged in animals chronically treated with ethanol for 7 days. Our data indicate that ethanol may affect the GABA receptor system through a rather specific interaction with the 35STBPS recognition site, but that this action of ethanol is not altered by the development of tolerance to and dependence on ethanol.

Type A and B gaba receptors mediate inhibition of acetylcholine release from cholinergic nerve terminals in the superior cervical ganglion of rat

The effects of ?-amino-n-butyric acid (GABA), (+)bicuculline, isoguvacine and 3-(4-chlorophenyl)-4-aminobutyrate [(+/-)baclofen] on the K-induced release of [(3)H]acetylcholine (ACh) were studied in the superior cervical ganglia of the rat in vitro. GABA and isoguvacine inhibited [(3)H]ACh release and these inhibitions were reversible by (+)bicuculline. Furthermore, the release of [(3)H]ACh was also inhibited by (+/-)baclofen. In receptor-binding studies, binding of [(3)H]GABA to membrane preparations from the superior cervical ganglia was inhibited by both (+/-)baclofen and (+)bicuculline. It is concluded that the inhibitory effect of GABA on the release of ACh can be mediated by GABA(A)(bicuculline-sensitive) and by GABA(B) (baclofen-activated) receptors. Our findings are compatible with the existence of a non-synaptic GABAergic inhibitory system involving GABA(A) and GABA(B) receptors on cholinergic nerve terminals in the superior cervical ganglion of rat.