ETHANOL ACTIONS AT THE GABA-BDZ-BARBITURATE RECEPTOR/CHLORIDE IONOPHORE

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Many pharmacological and physiological effects of ethanol have been postulated to be mediated via GABA-containing neuronal systems in the CNS. The GABA receptor exists as part of a complex containing receptors for benzodiazepines (BDZ), barbiturates and the chloride ion channel. To examine the effects of ethanol on this complex, we have studied the binding properties of 35-S-t-butylbicyclophosphorothionate (35-5-TBPS), a ligand which interacts with the regulatory site of the chloride ion channel, in membranes of cortex and cerebellum of C57B1 mice in the presence and absence of ethanol. In the presence of bromide ion in vitro, ethanol produced a dose-dependent inhibition of TBPS binding, but did not potentiate the inhibition of TBPS binding by GABA or pentobarbital. In the presence of chloride ion, ethanol was less potent at inhibiting TBPS binding. However, under these conditions, GABA and pentobarbital had biphasic effects on TBPS binding in cortex, and low concentrations of ethanol reduced the stimulatory effects of these compounds on TBPS binding. In order to correlate effects of ethanol on ligand binding in intact cells with a functional response (e.g. GABA-stimulated chloride flux), primary cultures of cerebellar granule cells have been developed. Behavioral studies of an imidobenzodiazepine, Ro15-4513, reported to antagonize the effects of ethanol on chloride transport and the intoxicating effect of ethanol in rats, have been performed. In mice, Ro15-4513 antagonized the ataxic effect of ethanol, apparently by interaction with a BZD receptor. However, Ro15-4513 did not antagonize the hypothermic effect of ethanol. The results indicate that Ro15-4513 is not a general antagonist of ethanol's actions, but that certain specific effects of ethanol may be mediated by an interaction with the GABA-BZD receptor-chloride channel complex.