A selective imidazobenzodiazepine antagonist of ethanol in the rat

Ethanol, at pharmacologically relevant concentrations of 20 to 100 mM, stimulates γ-aminobutyric (GABA) receptor-mediated uptake of ³⁶Cl-labeled chlorine into isolated brain vesicles. One drug that acts at GABA-benzodiazepine receptors, the imidazobenzodiazepine Ro15-4513, has been found to be a potent antagonist of ethanol-stimulated ³⁶Cl ^- uptake into brain vesicles, but it fails to antagonize either pentobarbital- or muscimol-stimulated ³⁶Cl^- uptake. Pretreatment of rats with Ro15-4513 blocks the anticonflict activity of low doses of ethanol (but not pentobarbital) as well as the behavioral intoxication observed with higher doses of ethanol. The effects of Ro15-4513 in antagonizing ethanol-stimulated ³⁶Cl^- uptake and behavior are completely blocked by benzodiazepine receptor antagonists. However, other benzodiazepine receptor inverse agonists fail to antagonize the actions of ethanol in vitro or in vivo, suggesting a novel interaction of Ro15-4513 with the GABA receptor-coupled chloride ion channel complex. The identification of a selective benzodiazepine antagonist of ethanol-stimulated ³⁶Cl ^- uptake in vitro that blocks the anxiolytic and intoxicating actions of ethanol suggests that many of the neuropharmacologic actions of ethanol may be mediated via central GABA receptors.