Sex-specific hypnotic effects of the neuroactive steroid (3b,5b,17b)-3-hydroxyandrostane-17-carbonitrile are mediated by peripheral metabolism into an active hypnotic steroid

Background: The novel synthetic neuroactive steroid (313,513,1713)-3-hydroxyandrostane-17-carbonitrile (313-OH) blocks T -type calcium channels but does not directly modulate neuronal g-aminobutyric acid type A (GABAA) currents like other anaesthetic neurosteroids. As 313-OH has sex-specific hypnotic effects in adult rats, we studied the mechanism contributing to sex differences in its effects.Methods: We used a combination of behavioural loss of righting reflex, neuroendocrine, pharmacokinetic, in vitro patch -clamp electrophysiology, and in vivo electrophysiological approaches in wild-type mice and in genetic knockouts of the CaV3.1 T-type calcium channel isoform to study the mechanisms by which 313-OH and its metabolite produces sex -specific hypnotic effects.Results: Adult male mice were less sensitive to the hypnotic effects of 313-OH compared with female mice, and these differences appeared during development. Adult males had higher 313-OH brain concentrations despite being less sen-sitive to its hypnotic effects. Females metabolised 313-OH into the active GABAA receptor positive allosteric modulator (3a,513,1713)-3-hydroxyandrostane-17-carbonitrile (3a-OH) to a greater extent than males. The 3a-OH metabolite has T -channel blocking properties with sex-specific hypnotic and pharmacokinetic effects. Sex-dependent suppression of the cortical electroencephalogram is more pronounced with 3a-OH compared with 313-OH.Conclusions: The sex-specific differences in the hypnotic effect of 313-OH in mice are attributable to differences in its peripheral metabolism into the more potent hypnotic metabolite 3a-OH.