Tolerance to suppressive effects of chlordiazepoxide on operant behavior: lack of cross tolerance to pentobarbital.

Pigeons responded under schedules in which either the 60th response (fixed-ratio schedule) or the first response after 3 minutes (fixed-interval schedule) resulted in food delivery. The effects of chlordiazepoxide HCl (1-30 mg/kg) and pentobarbital sodium (1-17 mg/kg) were determined before and during chronic daily exposure to either 10 or 17 mg/kg chlordiazepoxide--doses that markedly suppressed responding when given acutely. After about three weeks of daily injections of chlordiazepoxide, there was at least a three-fold shift to the right of the dose-effect curve for chlordiazepoxide, but not consistent change in the effects of pentobarbital.