Positive allosteric modulators of the GABAA receptor: differential interaction of benzodiazepines and neuroactive steroids with ethanol

Abstract

Endogenous pregnane steroids, such as allopregnanolone (3α-hydroxy-5α-pregnan-20-one; 3α, 5α-P) and pregnanolone (3α-hydroxy-5β-pregnan-20-one; 3α,5β-P), allosterically modulate GABA_A receptor function and exhibit behavioral effects similar to benzodiazepines, though acting at a distinct recognition site. Inasmuch as some positive allosteric modulators of GABA_A receptor function exhibit profound interactions with ethanol, the effects of 3α,5α-P and 3α,5β-P were compared to those of two benzodiazepines, triazolam and diazepam, on the motor function of mice and rats when administered either alone or in combination with ethanol. All four test compounds exhibited dose-related impairment of motor function in the horizontal wire task in mice and the rotorod task in rats. Ethanol caused a marked enhancement of triazolam- and diazepam-induced motor impairment. In contrast, ethanol enhanced to a lesser extent the motor impairment induced by both neurosteroids in mice and not at all in rats. All four compounds increased ethanol-induced behavioral sleep time in mice, although the benzodiazepines did so at a much smaller fraction of their ataxic doses as compared to the neurosteroids. As one of the undesired side-effects of therapeutic use of benzodiazepines is their interaction with ethanol, development of neuroactive steroids as drugs may offer therapeutic advantages.