Behavioral control, aversive stimulus frequency, and pituitary-adrenal response

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Six female Long-Evans rats were trained to leverpress under a free-operant shock postponement schedule, and each S was linked to a control that received shock whenever the S did to test the hypothesis that the pattern of corticosteroid response would be affected by both the frequency of shock received and the availability of behavioral control. The shock postponement interval (R-S) was varied (5, 10, 20, 40, or 80 sec) over blocks of sessions. Corticosteroid levels were taken prior to training and before and after selected sessions. Results show that frequency of shock had no major impact on physiological processes controlling the corticosteroid response; however, when Ss had the opportunity to control aversive events, a change in corticosteroid response was evident relative to controls. The rates of responding and of shock were inversely related to the R-S interval. Corticosteroid levels were unrelated to the R-S parameter. Corticosteroid levels of Ss were significantly higher than basal levels at the beginning of a session; by the end of a session, these levels were significantly reduced, although still above basal levels. These results were reversed for controls. (25 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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