Ethanol potentiation of GABAergic transmission in cultured spinal cord neurons involves γ-aminobutyric acid(A)-gated chloride channels

The interaction of ethanol with γ-aminobutyric acid (GABA)-mediated ³⁶-Cl-influx and its modulation by various drugs was investigated in C57 mice spinal cord cultured neurons. Ethanol (5-100 mM) potentiated the effect of GABA on ³⁶Cl-influx; whereas at concentrations ≥50 mM ethanol activated Cl^- channels directly. The effect of ethanol was specific for GABA(A) receptor-gated Cl^- channels, as ethanol did not potentiate glycine-induced ³⁶Cl-influx in the same neurons. Both the enhancing and direct effects of ethanol on ³⁶Cl-influx were blocked by GABA antagonists like bicuculline, picrotoxinin and inverse agonists of the benzodiazepine site like the imidazodiazepine R015-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo [1,5α], [1,4]benzodiazepine-3-carboxylate) and N-methyl-β-carboline-3-carboxamide (FG-7142). Ethanol potentiating effect of GABA-induced ³⁶Cl-influx was also reversed by methyl-6,7-dimethyl-4-ethyl-β-carboline-3-carboxylate. The effects of the inverse agonists were blocked by the benzodiazepine receptor antagonist R015-1788. Both R015-4513 and FG-7142 reversed direct and GABA potentiating effects of ethanol effect at concentrations lower than those that exhibit inverse agonistic activity in the ³⁶Cl-influx assay in cultured neurons. These results suggest that ethanol facilitation of GABA(A)ergic transmission involves GABA receptor-gated Cl^- channels and that this interaction may be responsible for some of the pharmacological effects of ethanol.