The effect of single and prolonged ethanol administration on the sensitivity of central GABA-A and benzodiazepine receptors in vivo.

The response of GABA-modulin to various doses of diazepam and muscimol was used as an index of the sensitivity of central benzodiazepine and GABA-A receptors, respectively. Diazepam and muscimol induced a dose-dependent increase in cytosol GABA-modulin activity in rat nucleus accumbens, hippocampus and cerebellum. A single dose of ethanol (1 g/kg po) potentiated the action of diazepam and muscimol. Prolonged treatment with ethanol (5 g/kg/day for 21 days) did not affect the action of diazepam. In contrast, the effect of muscimol was greatly reduced. In the rats pretreated for 21 days with ethanol five times higher doses of muscimol than in control group were necessary to induce a statistically significant increase of GABA-modulin in the cytosol of the nucleus accumbens, hippocampus and cerebellum. Those results show that a single dose of ethanol enhances GABA-ergic transmission, whereas prolonged treatment with ethanol induces subsensitivity of GABA-A but not benzodiazepine receptors in the limbic system and in cerebellum.