Temporal dynamics of corticosterone elevation in successive negative contrast.

A negative contrast effect in consummatory behavior that occurred when rats were shifted from 32% to 4% sucrose was accompanied by elevations in corticosterone that were measurable at 10 and 20 min but not at 40 min after the second postshift day. No corticosterone elevations were found to accompany contrast at 10 or 15 min after the first postshift day in these experiments nor immediately after the first postshift day in an earlier experiment. The present study also found an anticipatory elevation in plasma corticosterone in shifted animals just before their placement in the apparatus on the second postshift day. These results are discussed in terms of a multistage hypothesis of successive negative contrast. The anticipatory elevation is discussed in terms of uncontrollability and unpredictability of aversive events.