Behavioral characterization of Co 134444 (3alpha-hydroxy-21-(1'-imidazolyl)-3beta-methoxymethyl-5alpha- pregnan-20-one), a novel sedative-hypnotic neuroactive steroid.

Rationale: Neuroactive steroids have been shown to exhibit a wide range of behavioral activities that are similar but not identical to those of benzodiazepines. These activities include anticonvulsant, anxiolytic and sedative-hypnotic effects.
Objective: The purpose of the present study was to characterize Co 134444 (3alpha-hydroxy-21-(1'-imidazolyl)-3 -methoxymethyl-5alpha-pregnan-20-one), a novel sedative-hypnotic neuroactive steroid, in a variety of behavioral procedures.
Methods: Anticonvulsant effects were determined by the ability to protect against pentylenetetrazol- and maximal electroshock-induced seizures in mice and rats. Anxiolytic-like effects were determined using a punished drinking procedure in rats. Ataxic effects were determined using a horizontal wire procedure in mice and a rotorod procedure in mice and rats. The discriminative stimulus effects were evaluated in rats trained to discriminate pregnanolone from vehicle.
Results: Co 134444 exhibited oral anticonvulsant activity against pentylenetetrazol and maximal electroshock with ED50s of 9.8 and 20.6 mg/kg, respectively, in mice and 23.6 and 25.3 mg/kg, respectively, in rats. Anxiolytic-like efficacy was observed at a dose as low as 3.0 mg/kg, PO, in rats. Ataxic effects were observed with rapid onset and short duration. TD50s were 17.4 and 21.2 mg/kg orally in mice in the horizontal wire and rotorod procedures, respectively, and 39.0 mg/kg in rats using the rotorod. Co 134444 completely substituted for pregnanolone as a discriminative stimulus with little effect on response rate.
Conclusions: Co 134444 exhibits a wide variety of behavioral effects; however, its rapid onset and short duration are consistent with its potential use as a sedative-hypnotic drug.