The rat corticosterone response: habituation and modification by chlordiazepoxide.

The rat plasma corticosterone response was measured in 3 novel situations that differed in the extent to which the rat's own behavior determined its sampling of novel stimuli. All 3 tests induced a significant rise in corticosterone concentrations and on repeated exposures the corticosterone significantly decreased. Acute administration of chlordiazepoxide (5 mg/kg) significantly reduced the corticosterone response to novelty and after 5 days of drug pretreatment chlordiazepoxide was even more effective at reducing the corticosterone response to novel situations. The corticosterone response to the stress of cold and restraint was reduced by an acute dose of 50 mg/kg chlordiazepoxide, and after 5 days of pretreatment by doses of 10 and 50 mg/kg. In all but one test tolerance developed to the corticosterone-blocking action of chlordiazepoxide after 10 days of drug treatment.