Pharmacologic actions of subtype-selective and novel GABAergic ligands in rat lines with differential sensitivity to ethanol

Abstract

Alcohol-nontolerant (ANT) rats, produced by selective breeding for high sensitivity to motor-impairing effects of ethanol, have a point mutation in the cerebellar γ-aminobutyric acid type A (GABA A) receptor α6 subunit, which has been proposed to underlie enhanced sensitivity to benzodiazepine agonists as well. We compared ANT and alcohol-tolerant (AT) rats using behavioral and neurochemical methods to assess the significance of α6- and nonα6-containing GABA A receptor subtypes. Motor performance in a tilting plane test was largely unaffected by a type I benzodiazepine receptor-preferring agonist, zolpidem [1–10 mg/kg, intraperitoneally (IP)], partial benzodiazepine agonists bretazenil and ZG-63 (both at 40 mg/kg, IP), and a novel broad-spectrum anticonvulsant loreclezole (40 mg/kg, IP) in both ANT and AT rats. In contrast, diazepam (10 mg/kg, IP) impaired performance of the ANT but not AT animals. These data, supported by results from brain regional autoradiography of [ 3H]Ro15-4513 and membrane binding of [ 3H]ZG-63 and [ 35S]TBPS as influenced by these ligands, strongly suggest that only ligands with full agonist actions on mutant (ANT) but not wild-type (AT) α6-containing GABA A receptors are able to produce motor impairment in the ANT rats.