Chloride Ionophore Research Articles

Intracerebroventricular 5,7-DHT alters the in vitro function of rat cortical GABA A/benzodiazepine chloride ionophore receptor complexes

We have earlier presented data indicating that the anxiolytic-like effect obtained in rats after depletion of brain 5-HT by means of PCPA or 5,7-DHT treatment is indirect and appears to involve the GABA A/benzodiazepine chloride ionophore receptor complex (GABA A/BDZ-RC), and that it is abolished by adrenalectomy. In the present series of experiments we have therefore investigated the 36Cl −-uptake in rat synaptoneurosomal preparations of central cortices from 5,7-DHT- and SHAM-lesioned animals. The GABA as well as the 3α,5α-tetrahydrodeoxycorticosterone (THDOC) induced picrotoxin-sensitive increase in 36Cl −-uptake was significantly lower than that observed in the SHAM-lesioned animals, indicating that the 5,7-DHT lesion has rendered the GABA A/BDZ-RC subsensitive to two of its tentative endogenous ligands. This effect of the 5,7-DHT lesion on the function on the GABA A/BDZ-RC was reversed by adrenalectomy, indicating that an intact adrenocortical function is required for the development of GABA A/BDZ-RC subsentivity in 5,7-DHT-lesioned rats. A tentative conclusion of these findings is that the 5,7-DHT lesion induces an increase in release of GABA and/or barbiturate-like steroids and that this increase is reversed by adrenalectomy. The findings from these in vitro studies parallel those from our previous behavioral experiments and provide further support for the notion that a decreased serotonergic influence in the central nervous system may, possibly via the adrenocortical system, enhance the function of the GABA A/BDZ-RC.

Flumazenil in the treatment of portal systemic encephalopathy —an overview

Hepatic encephalopathy is a complex neuropsychiatric syndrome associated with acute, subacute and chronic liver failure, involving increased neural inhibition by activation of the GABA/benzodiazepine inhibitory neurotransmitter system. Improvement by GABA and benzodiazepine receptor antagonists as well as by chloride ionophore blockers has been shown in animal experiments. Recent reports indicate that flumazenil may improve hepatic encephalopathy in man. To date 46 episodes of HE in 41 patients have been treated with flumazenil with a short term success rate of 72%. Most of the patients were screened for exogenous benzodiazepines and found negative. These interesting observations should now be investigated in a randomised double-blind controlled study in patients with HE to evaluate the efficiency of this therapy.

"In vivo" inhibition of GABAergic transmission increases 35S-TBPS binding in the rat brain.

Several lines of evidence have well established that the cage convulsant t-butylbicyclophosphorothionate (TBPS) inhibits the function of the central GABAergic transmission by binding to specific recognition sites present at the level of the chloride ionophore coupled to the GABAA/benzodiazepine receptor complex (Squires et al., 1983; Van Renterghem et al., 1987). This finding has given a rather unique tool to study biochemically the function of the GABA-dependent chloride channel. In fact, the specific binding of 35S-TBPS to the recognition sites associated to the GABAA receptor complex is modulated in an opposite manner by different compounds which specifically enhance (GABA agonists, benzodiazepines, imidazopyridines, anxiolytic and anticonvulsant ß-carbolines etc.) and inhibit (GABA antagonists, anxiogenic and convulsant ß-carbolines etc.) the function of the GABA-dependent chloride channel, respectively (Squires et al., 1983; Gee et al., 1986; Concas et al., 1988; Biggio et al., 1989; Serra et al., 1989; Sanna et al., 1990).KeywordsValproic AcidChloride ChannelKainic AcidGABAergic TransmissionGaba ContentThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Involvement of the GABA A/benzodiazepine chloride ionophore receptor complex in the 5,7-DHT induced anticonflict effect

The effects of drugs interacting with the GABA A/benzodiazepine chloride ionophore receptor complex (GABA A/BDZ-RC) on the anticonflict and biochemical effects observed after intracerebroventricular (i.c.v.) administration of 5,7-dihydroxytryptamine (5,7-DHT; 450 μg -14 days) were investigated in the rat using a modified Vogel's drinking conflict test. The GABAergic antagonistic drugs bicuculline, picrotoxin and Ro 15-4513 all counteracted the 5,7-DHT induced anxiolytic-like action in doses that did not alter the behavior per se, whereas flumazenil was ineffective in this respect. Also i.c.v. administration of 5-HT antagonized the 5,7-DHT induced anticonflict effect. Furthermore, 5,7-DHT-lesioned animals appeared more sensitive to the anticonflict effects of diazepam than sham-lesioned controls. The 5,7-DHT treatment produced marked depletions of 5-HT in the limbic system (80–90%) and hippocampus (90–95%), and an inrease in the 5-HIAA/5-HT quotient in hippocampus. The effects on the levels of noradrenaline were comparatively small. The doses of bicuculline and picrotoxin antagonizing the 5,7-DHT induced anticonflict effect did not uniformly influence 5-HT levels or 5-HIAA/5-HT quotients. It is suggested that the anxiolytic-like effect observed in 5,7-DHT-lesioned rats in Vogel's drinking conflict test involves enhanced transmission at the GABA A/BDZ-RC.

Quenching of a proton gradient and concomitant increase of intragranular calcium in interstitial cells of Mytilus retractor muscle

The content of specific glio-interstitial granules in situ was studied in Mytilus retractor muscle using fluorescent probes and X-ray microanalysis. The granules readily take up the fluorescent monoamine dye acridine orange added to sea water (2.7×10-6 M) and appear red in fluorescence microscopy. The addition of ammonium chloride (10 mM) or various proton ionophores results in extinction of the granule fluorescence. In addition, a step-wise decrease in granule fluorescence is observed when the tissue is perfused with artificial sea water of decreasing pH. These granules thus appear to be acidic inside. The animals were maintained in artificial sea water containing 8.36 mM Ca2+ and 528.90 mM Na+, the ratio R=[Ca2+]0/[Na+]20 being thus equal to 3x10-5. Perfusions of the tissue with artificial sea water containing a higher calcium concentration (12.2 mM) and/or a higher [Ca2+]0/[Na+]20 ratio (R=4.5×10-5) result in a drastic reduction of the proton gradient, evidenced by a quenching of the acridine orange fluorescence. Under the same conditions, a significant increase of the total intragranular calcium concentration was demonstrated by quantitative X-ray micro-analysis of the tissue processed by quick freezing and freeze-substitution in the presence of oxalic acid. The fluorescence of the probe Fluo-3/AM, indicative of ionized calcium, is higher in the granules than in the surrounding cytoplasm; this suggests that calcium is accumulated in the granule against its concentration gradient. The acidic gradient of specific glio-interstitial cell granules could provide the energy needed for this calcium accumulation through a Ca2+/H+ exchange. These results are discussed with regard to the hypothesis that the glio-interstitial tissue can regulate pericellular calcium and/or hydrogen ion ioncentration in the vicinity of nerve and muscle cells.

γ-Aminobutyric acid antagonism produced by an organophosphate-containing combustion product

Results from [ 35S] t-butylbicyclophosphorothionate (TBPS) binding and γ-aminobutyric acid (GABA)-dependent 36Cl − uptake indicated that the pyrolysis product of liquid trimethylol propane (TMP) containing organic phosphates interacts with the GABA/benzodiazepine receptor chloride ionophore complex (GBRC) producing a receptor-mediated reduction in 36Cl − flux. The pyrolysate-ligand interaction was competitive and directly proportional to the trimethylol propane phosphate (TMPP) content of the combustion product. TBPS displacement demonstrated that TMPP had less affinity than did TBPS and picrotoxin, but greater affinity than GABA, racemic dimethylbutyl barbituric acid (DMBB), clonazepam, and phenobarbital for their respective recognition sites. Addition of exogenous GABA was a necessary condition for demonstrating clonazepam-induced ligand displacement, thus being indicative of an allosteric interaction. The same rank order held for altering GABA-dependent 36Cl − uptake with the caveat of inhibitors vs enhancers, and noting that pentobarbital was less potent than DMBB. Concentration-dependent ligand displacement by GBRC agonists and antagonists quantitatively correlated with alterations in GABA-dependent 36Cl − uptake. The median convulsant dose (CD50) of pyrolysate TMPP was higher than that of synthetic TMPP. The presence of combustion by-products altering the dispositional kinetics of the former is felt to be the reason for this difference. Under our experimental conditions, phenobarbital was the most effective antidote for pyrolysate (TMPP) toxicity. The inhalant convulsant, flurothyl, was found not to displace [ 35S]TBPS binding, not to affect GABA-dependent 36Cl − uptake, and not to respond to the anticonvulsants in a manner consistent with a strict GABA A receptor phenomenon.

Synthesis, metabolism, and pharmacological activity of 3.alpha.-hydroxy steroids which potentiate GABA-receptor-mediated chloride ion uptake in rat cerebral cortical synaptoneurosomes

Certain 3 alpha-hydroxy steroids have recently been shown to bind to the gamma-aminobutyric acid (GABA) receptor gated chloride ion channel with high affinity and to potentiate the inhibitory effects of GABA when measured both in vitro and in vivo. In the present study, a series of natural and synthetic 3 alpha-hydroxy steroids were tested for their ability to potentiate GABA-receptor-mediated chloride ion (Cl-) uptake into cerebral cortical synaptoneurosomes. The naturally occurring metabolites 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone) and 3 alpha,21-dihydroxy-5 alpha-pregnan-20-one (allotetrahydroDOC) were found to be the most active in augmenting GABAA-receptor-mediated Cl- uptake. Pharmacological activity was reduced in the corresponding isomers with the 5 beta-pregnane configuration and by some, but not all, modifications of the side chain. The ability of these steroids to potentiate muscimol-stimulated Cl- uptake is lost by acetylation at C3, introduction of unsaturation at C9(11), inversion to the 3 beta-hydroxy isomer, or inversion of configuration at C17. A facile procedure is reported for the synthesis of unlabeled and tritium-labeled allopregnanolone and allotetrahydroDOC. The 9 alpha,11 alpha,12 alpha-3H-labeled derivatives of allopregnanolone and allotetrahydroDOC were used to identify the distribution and metabolic products of these active steroids. Uptake of the more hydrophobic [3H]allopregnanolone into brain was significantly greater than that of [3H]allotetrahydroDOC. The principal 3H-labeled metabolites recovered from brain were the 3-ketone derivatives of allopregnanolone and allotetrahydroDOC, which are both inactive on GABA-receptor-mediated Cl- flux. Molecular modeling of the active steroids based on quantitative structure-activity relationships provides evidence to support the stereospecificity of the binding interactions and suggests that there may be more than one type of steroid binding site associated with the GABAA-receptor-mediated chloride ionophore.

Secondary generalization in non-kindled rats following acute administration of GABA-complex and adenosine antagonists

In order to test the GABA hypothesis of kindling, GABA-complex antagonists were administered in a dose-response paradigm to rats that had been implanted with indwelling forebrain electrodes, but not kindled. Focal seizures were then elicited from either the cortex or the amygdala to see whether kindling-like secondary generalization would occur. Norharmane, a benzodiazepine inverse agonist, failed to promote secondary generalization from either the cortex or the amygdala. Bicuculline, a GABA A receptor antagonist, and picrotoxin, a chloride ionophore antagonist, enhanced generalization from both sites and, in amygdala-implanted subjects, appeared to produce a significant acceleration of kindling as well. Aminophylline, an adenosine antagonist tested for purposes of comparison, also enhanced secondary generalization from both sites, and in amygdala-implanted subjects produced long electrographic discharges which sometimes developed into status epilepticus.

Differential immune responsiveness in mouse lines selectively bred for high and low sensitivity to ethanol

Natural killer cell activity was compared in the Long-Sleep and Short-Sleep mouse lines. These mice, initially selected for their sensitivities to a hypnotic dose of ethanol, are also differentially sensitive to other agents which act through the benzodiazepine/GABA receptor chloride ionophore complex. Natural killer cell activity was 40–59% lower in Short-Sleep when compared to Long-Sleep mice. Flow cytofluorometric analysis demonstrated that the number of Nk-1 + cells was also lower in the spleens of Short-Sleep than Long-Sleep mice. In addition, the incidence of 3-methylcholanthrene-induced tumors was significantly greater in Short-Sleep (85.7%) than in Long-Sleep (14.3%) mice. These results suggest that the Long-Sleep and Short-Sleep mouse lines may represent a unique model to assess the physiological role of the benzodiazepine/GABA receptor chloride ionophore complex in the neural modulation of immune function.

Agents enhancing γ‐aminobutyric acid receptor‐coupled chloride ionophore function. Effects in a social interaction model of anxiety in the rat

AbstractA recently described social interaction (SI) model which is sensitive to single doses of benzodiazepines and novel non‐sedative anxiolytic agents has been used. Activities of drugs were compared in both an anxious (animals housed in pairs, tested with a novel partner) and a non‐anxious (animals housed in pairs, tested with the cage mate) condition. Diazepam displays a typical anxiolytic response, increasing SI in the anxious but not in the non‐anxious condition. This was associated with a decrease in aggression (AGG) and in locomotion (LOCO) at higher doses. Seven agents were tested which are thought to enhance central nervous system γ‐aminobutyric acid (GABA)‐mediated neurotransmission by increasing the activity of a receptor‐coupled chloride ionophore system as a major component of their action. Tracazolate, RL348, methaqualone, etomidate, LY81067, and pentobarbitone all significantly increased SI in the anxious but not the non‐anxious condition. In the anxious condition tracazolate and RL348 reduced AGG and all of these compounds except LY81067 reduced LOCO. Methaqualone and etomidate also reduced LOCO in the non‐anxious condition. In addition, an agent which reduces GABA function (picrotoxin) significantly reduced SI in already‐anxious animals, consistent with its known anxiogenic properties. Picrotoxin also reduced LOCO in both conditions. Phenobarbitone induced a non‐specific effect on SI (increased SI in both anxious and non‐anxious conditions), as well as reducing AGG in the anxious condition and LOCO in both conditions. These data suggest that agents enhancing GABA receptor‐coupled chloride ionophore function possess anxiolytic properties which may be attributed to this activity.

Antidepressant-anxiolytic interactions: Involvement of the benzodiazepine-GABA and serotonin systems

1. 1. Recent studies have demonstrated that antidepressant drugs are actually more effective than BZ's in the treatment of anxiety states. The role of two major neurochemical substrates that may be implicated in the anxiolytic activity of antidepressants, the benzodiazepine (BZ)-GABA receptor chloride ionophore complex and central serotonergic pathways, are focused on in this review. 2. 2. A wide range of antidepressants elicit a reduction in BZ receptors and display anxiolytic effects within a conflict paradigm. 3. 3. The anxiolytic activity of antidepressants, however, does not appear to be mediated via the BZ receptor, but possibly via another component of the complex such as the chloride channel-associated with the GABA A receptor. 4. 4. Additionally, as possible candidates for the mechanism of anxiolytic activity of these compounds, results of pharmacological, behavioral and clinical studies point to the importance of serotonin (5-HT) 1A receptors and 5-HT transporter sites as targets for the action of antidepressants, triazolobenzodiazepines and anxioselective piperazine derivatives.

Age‐Related Loss of t‐[35S]Butylbicyclophosphorothionate Binding to the γ‐Aminobutyric AcidA Receptor‐Coupled Chloride Ionophore in Rat Cerebral Cortex

Muscimol and t-butylbicyclophosphorothionate (TBPS) are known to label two distinct sites within the gamma-aminobutyric acidA (GABAA) receptor complex, i.e., the GABA recognition site and the chloride ionophore, respectively. Age-dependent changes in the specific binding of [3H]muscimol and [35S]TBPS were compared in membranes prepared from the cerebral cortex of rats, 2-800 days old. Perinatal (day 2) binding of muscimol and TBPS represented 8 and 20% of the respective values for adults (day 180). After the first week, muscimol binding increased more rapidly than TBPS binding. Levels near those of adults were reached at day 20 and remained practically unchanged in adulthood (day 180). In aged (780-day-old) rats, the binding of TBPS was significantly reduced, whereas muscimol binding did not change compared with adult values. This decrease of TBPS binding derived from a reduced density of binding sites, rather than from affinity changes. The allosteric responsiveness of TBPS binding to exogenous GABA was also reduced in aged animals. These findings indicate an age-related change in the molecular (structural) organization of the GABAA receptor-chloride ionophore complex in rat cerebral cortex.

Does the PCPA induced anticonflict effect involve activation of the GABAA/benzodiazepine chloride ionophore receptor complex?

The effects of the benzodiazepine (BDZ) receptor antagonist flumazenil (Ro 15-1788) and the GABAA receptor antagonist bicuculline on the anticonflict effect observed after depletion of brain serotonin (5-HT), were examined in a modified Vogel's punished drinking conflict model. Pretreatment with para-chlorophenylalanine (PCPA; 300 mg/kg/day for three days, last injection - 24 h) markedly decreased brain 5-HT levels and produced clearcut anticonflict effects. The anticonflict effect, but not the biochemical effect, of PCPA pretreatment was completely counteracted by both flumazenil (10 mg/kg, - 30 min) and bicuculline (2.0 mg/kg, - 10 min), in doses not altering the behavior per se. The findings suggest a behavioral interaction between 5-HT systems and the GABAA/BDZ chloride ionophore receptor complex, possibly involving a direct neuronal interaction, neuromodulation or hormonal alterations.

Effects of Amperozide in Two Animal Models of Anxiety

The novel psychotropic agent amperozide (amp) was investigated in two different rat anxiety models, Vogel's conflict test (VT) and Montgomery's conflict test (MT). In the VT, amp in lower doses (0.2-0.6 mg/kg subcutaneously) increased the number of shocks accepted, as compared to controls. Pretreatment with the specific benzodiazepine receptor antagonist Ro 15-1788 (10.0 mg/kg orally) or the GABA-A receptor antagonist bicuculline (2.0 mg/kg intraperitoneally) antagonized the anticonflict effect of amp (0.4 mg/kg subcutaneously). At the highest dose tried (2.0 mg/kg subcutaneously) amp instead decreased the number of shocks accepted. Both 0.4 mg/kg and 2.0 mg/kg of amp raised the shock threshold, as compared to controls. The latter dose also decreased the motivation to drink. Pretreatment with Ro 15-1788 (10.0 mg/kg orally) did not significantly change the shock threshold or the drinking motivation, as compared to the group receiving amp alone. In the MT, amp (0.05-0.1 mg/kg subcutaneously) increased the percentage time spent in the open arms, while no changes were seen in the number of entries made into these arms. After higher doses (0.4-0.8 mg/kg subcutaneously) no differences, as compared to controls, were observed. Amp (1 nM-10microM) exhibited no affinity for 3H-flunitrazepam binding sites in mouse forebrain membranes in vitro. Taken together, the present data suggest that amp in low doses produces anticonflict (anxiolytic-like) effects. These effects appear to be mediated through an indirect (via 5-HT and/or DA systems?) activation of the GABA/benzodiazepine chloride ionophore receptor complex.

Distribution and Pharmacological Properties of the GABAA/ Benzodiazepine/Chloride Ionophore Receptor Complex in the Brain of the Fish Anguilla anguilla

In the present study, we characterized the distribution and the pharmacological properties of the different components of the GABAA receptor complex in the brain of the eel (Anguilla anguilla). Benzodiazepine recognition sites labeled "in vitro" with [3H]flunitrazepam ([3H]FNT) were present in highest concentration in the optic lobe and in lowest concentration in the medulla oblongata and spinal cord. A similar distribution was observed in the density of gamma-[3H]aminobutyric acid ([3H]GABA) binding sites. GABA increased the binding of [3H]FNT in a concentration-dependent manner, with a maximal enhancement of 45% above the control value, and, vice versa, diazepam stimulated the binding of [3H]GABA to eel brain membrane preparations. The density of benzodiazepine and GABA recognition sites and their reciprocal regulation were similar to those observed in the rat brain. In contrast, the binding of the specific ligand for the Cl- ionophore, t-[35S]butylbicyclophosphorothionate ([35S]TBPS), to eel brain membranes was lower than that found in the rat brain. In addition, [35S]TBPS binding in eel brain was less sensitive to the inhibitory effects of GABA and muscimol and much more sensitive to the stimulatory effect of bicuculline, when compared with [35S]TBPS binding in the rat brain. Moreover, the uptake of 36Cl- into eel brain membrane vesicles was only marginally stimulated by concentrations of GABA or muscimol that significantly enhanced the 36Cl- uptake into rat brain membrane vesicles. Finally, intravenous administration of the beta-carboline inverse agonist 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylic acid methyl ester (20 mg/kg) and of the chloride channel blocker pentylenetetrazole (80 mg/kg) produced convulsions in eels that were antagonized by diazepam at doses five to 20 times higher than those required to produce similar effects in rats. The results may indicate a different functional activity of the GABA-coupled chloride ionophore in the fish brain as compared with the mammalian brain.

Complex interactions between pregnenolone sulfate and the t-butylbicyclophosphorothionate-labeled chloride ionophore in rat brain

Detailed studies of the interactions between the ‘neuroactive’ steroid, pregnenolone sulfate (PS), and the γ-aminobutyric acid (GABA)/benzodiazepine receptor-linked chloride ionophore (GBRC) labeled by [ 35S] t-butylbicyclophosphorothionate ([ 35S]TBPS) in the rat brain reveal a site of action allosteric to the TBPS-labeled site as demonstrated by the ability of PS to accelerate TBPS-initiated dissociation of [ 35S]TBPS. In contrast to previous findings, PS modulates [ 35S]TBPS binding in a GABA ‘agonist’-like fashion with micromolar potencies. The role of PS in the regulation of neuronal excitability through the GBRC is questioned, based upon the observation that brain concentrations of PS are 2–3 orders of magnitude less than that necessary for the modulation of chloride conductance in vitro.

Molecular neurobiology: Implications for insecticide action and resistance

Recent advances in molecular neurobiology have provided an unprecedented insight into the structure and function of the three principal target sites for neurotoxic insecticides: acetylcholinesterase, the 4-aminobutyric acid (GABA) receptor–chloride ionophore complex, and the voltage-sensitive sodium channel. This paper reviews some of these advances and their current or potential application to problems in insecticide resistance. It particularly emphasizes studies of the molecular biology of voltage-dependent sodium channels in the context of resistance to DDT and pyrethroids resulting from reduced neuronal sensitivity.

Antagonism of ethanol effects by Ro 15‐4513: An electrophysiological analysis

Ethanol (ETH) and general anesthetics have been reported to facilitate the chloride channel opening, possibly, or at least partly, through an interaction with the GABA-benzodiazepine (BZ) receptor-gated chloride ionophore "supramolecular complex". Recently Ro 15-4513, a novel BZ ligand, has been indicated as a potent and selective antagonist of various ETH-induced behavioral and biochemical effects. However, since its precise characterization is still a matter of debate, we have tested and compared the effect of Ro 15-4513, as well as its antagonism against ETH, in two objective electrophysiological parameters, i.e., the electroencephalograph (EEG) pattern in freely moving rats and single unit activity of reticulata neurons. Ro 15-4513 produced an EEG state of alertness and antagonized the behavioral impairment and the EEG deterioration by ETH. However, while its protective action was consistent against moderate doses (2 g/kg) of ETH, it was much less evident versus higher doses (4 and 8 g/kg). On reticulata cells, Ro 15-4513 potently stimulated their spontaneous firing and reversed the depression by both ETH and Na-pentobarbital. Moreover, the beta-carboline DMCM also had similar effects. The "pure" BZ antagonist Ro 15-1788 was completely inefective against ETH, yet fully cancelled the reversing actions of Ro 15-4513 and DMCM upon ETH or Na-pentobarbital effects. It is concluded that Ro 15-4513 behaves as a BZ inverse agonist, so that its opposition to ETH and Na-pentobarbital is probably the result of its "negative" coupling with the BZ recognition site that triggers the closing of chloride channels. It suggests that BZ inverse agonists might constitute, in the near future, a new class of analeptic drugs.

35S]TBPS binding to purified benzodiazepine-GABA-ionophore receptor complex: the effect of GABA on the modulation exerted by benzodiazepine site ligands

Benzodiazepine GABA-ionophore receptor complex ligands showed persistent modulation of the chloride ionophore, labeled by [(35)S]TBPS, even after receptor complex extensive purification. GABA caused inhibition of [(35)S]TBPS binding, while benzodiazepine agonists increased and benzodiazepine inverse agonists decreased the specific [(35)S]TBPS binding to the purified receptor. When GABA binding sites were occupied by the neurotransmitter benzodiazepine receptor agonists and antagonists reversed their effects clonazepam in fact inhibited and ?-carboline ethyl ester increased [(35)S]TBPS binding in the presence of GABA. The antagonist flumazenil showed no effect both in the presence or absence of GABA.

Asymmetrical activation of GABA-gated chloride channels in cerebral cortex

A pronounced left/right asymmetry of GABA-gated chloride channels was observed in rat cerebral cortex. This asymmetry was manifest as a higher apparent affinity and density of binding sites for the “cage” convulsant [ 35S]t-butylbicyclophosphorothionate (TBPS) in the right compared to left cortex. Asymmetries in [ 35S]TBPS binding were not observed in other brain areas, and were restricted to the occipital and entorhinal/pyriform areas of cerebral cortex. Evaluation of other components of the benzodiazepine/GABA receptor chloride ionophore complex in cerebral cortex suggests that this asymmetry is not present in either benzodiazepine receptors or that population of GABA receptors linked to benzodiazepine receptors. Brief restraint-stress significantly increased both the apparent affinity and number of [ 35S]TBPS binding sites in cortex, but the left/right asymmetry was no longer apparent. These findings indicate a time-dependent, asymmetric response of cortical GABA-gated chloride channels to stress rather than an anatomical hemispheric difference, and suggest that GABA-gated chloride channels may be involved in a differential processing of stressful stimuli by the cerebral hemispheres.