Classical aversive conditioning of catecholamine and corticosterone responses.

Some earlier work, not rigorously controlled, suggested that conditional increases in sympathoadrenal stress hormones could occur. The purpose of this experiment was to test this idea further using an appropriately controlled design. To do this, we subjected rats living in a tether-type apparatus to differential fear conditioning. Chronic catheterization allowed us to sample blood before and after conditional stimulus probes without having to touch the rats. No evidence for conditional changes in norepinephrine and corticosterone was found. In contrast, differential conditioning of epinephrine responses was found. The conditional response, however, was not a simple one in that conditional increases in epinephrine following CS+ probes were not always seen. These data support the idea that learned changes in hormonal stress respondents can occur. But they leave open the question of why clear cut conditional changes in these visceral systems are so difficult to obtain.