The sensitivity of the rat corticosterone response to environmental manipulations and to chronic chlordiazepoxide treatment

Abstract

Rats that were exposed for 20 mins to an unfamiliar room had significant increases in plasma corticosterone concentrations, that were greater if the room was brightly lit than if it was dimly lit. Chlordiazepoxide (5 mg/kg for 5 days) significantly reduced the corticosterone response to a novel room, but was without effect on the levels in rats left undisturbed in the animal house. When pairs of rats were placed for 10 mins in an unfamiliar test box there was an increase in plasma corticosterone that was greater when the box was brightly lit; chlordiazepoxide (5 mg/kg for 5 days) significantly reduced these corticosterone responses. In rats repeatedly exposed to the same apparatus there was significant, but not complete, habituation of the corticosterone response in both singly tested rats and in those tested in pairs; manipulation of light levels no longer had a significant effect on the corticosterone levels; and chlordiazepoxide did not block the corticosterone response in these habituated rats.