Neurosteroids in alcohol and substance use

Allopregnanolone and related neurosteroids share effects with ethanol at several critical targets. Though data are equivocal in humans, acute administration of ethanol (and several other drugs of abuse) increases brain and plasma levels of allopregnanolone in animals. Evidence exists suggesting that this effect of ethanol is mediated via the peripheral or mitochondrial benzodiazepine receptor (PBR). PBR activation can stimulate neurosteroid synthesis and results in anxiolytic effects similar to ethanol, benzodiazepines, and neurosteroids. Further, finasteride, an inhibitor of neurosteroidogenesis, blunts some effects of ethanol in animals and humans. Thus, neurosteroids may modulate or mediate effects of ethanol, benzodiazepines, and barbiturates. Like ethanol and allopregnanolone, benzodiazepines and barbiturates are positive GABA-A receptor modulators. Accordingly, neurosteroids share discriminative stimulus properties with ethanol, benzodiazepines, and barbiturates. Allopregnanolone and related neurosteroids are self-administered by animals, similar to ethanol and other abused drugs. A role for neurosteroids in ethanol tolerance and withdrawal has also emerged, as rodents undergoing ethanol withdrawal are sensitized to neurosteroid effects and alcoholics in withdrawal display reduced allopregnanolone levels. While symmetrical cross tolerance develops between ethanol and benzodiazepines, asymmetrical cross tolerance develops between neurosteroids and benzodiazepines or ethanol, which could be exploited to help treat ethanol, benzodiazepine or barbiturate dependence and withdrawal.