Chronic ethanol treatment selectively increases the binding of inverse agonists for benzodiazepine binding sites in cultured spinal cord neurons.

The effect of chronic ethanol treatment, and its withdrawal on the binding of ligands to the benzodiazepine binding sites of gamma-aminobutyric acid (GABA) receptor complex, was investigated in C57BL/6J mice spinal cord cultured neurons. Chronic ethanol (50 mM) treatment increased the specific binding of inverse agonists of the benzodiazepine binding sites, without affecting the binding of agonist or antagonist to this site. Thus, chronic ethanol exposure of the neurons increased the binding of [3H] Ro 15-4513 [ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo [1,5-alpha][1,4]benzodiazepine-3-carboxylate] and methyl-1-beta carboline-3-carboxylate [( 3H]beta-CCM), but not the binding of [3H]flunitrazepam or [3H]Ro 15-1788 [ethyl-8-fluro-5-6-dihydro-5-methyl-6-OxO-4H-imidazo[1,5-alpha][1, 4] benzodiazepine-3-carboxylate]. This increase was due to an increase in the number of binding sites for Ro 15-4513 and beta-CCM, and not due to a change in receptor affinity. The increase was observed as early as after a 12-hr exposure of the neurons with ethanol, and remained elevated at 24-hr withdrawal, returning to control values at 48-hr withdrawal. These results further strengthen the notion that Ro 15-4513 and related inverse agonists binding site on the GABA-benzodiazepine receptor complex may be involved in ethanol-s behavioral, biochemical and pharmacological effects which are mediated via GABAA receptor system. The significance of the enhanced binding sites for Ro 15-4513 and beta-CCM in the actions of ethanol, tolerance and withdrawal is discussed.