Chlordiazepoxide and the determinants of negative contrast

Previous experiments have shown that the negative contrast effect in consummatory behavior that occurs when rats are shifted from 32% to 4% sucrose is alleviated by the tranquilizer chlordiazepoxide (CDP). However, in these experiments, CDP was effective on the second postshift day but not on the first postshift day. The three experiments described in this paper suggest that this differential effectiveness of CDP is not due to the difference in preshift-postshift retention intervals on Day 1 (24 h) and Day 2 (48 h), but is due instead to the necessity of some degree of experience (about 5 min) with the postshift solution. These results, combined with those of an earlier study which showed elevated corticosterone in shifted animals on the second postshift day but not on the first postshift day, suggest that negative contrast may be a dynamic process, involving sequential processes of detection, evaluation, and conflict over the postshift period. It was further suggested that CDP becomes effective in moderating contrast only when the conflict stage is reached.