Chronic stress depresses exploratory activity and behavioral performance in the forced swimming test without altering ACTH response to a novel acute stressor.

The present study investigated the effects of chronic stress on some behavioral and endocrine variables in adult male rats. The variables were always measured the day that followed the stress session to chronically stressed rats. Two stress models were used: chronic shock (CS), and a combination of various stressors randomly chosen each day (CV). Chronic but not acute exposure to the stressors resulted in decreased exploratory activity in the holeboard. Likewise, only chronic exposure to shock or variable stressors resulted in increased immobility in the Porsolt's test. Taken together these results suggest that changes in exploratory and forced swimming activities might be affected by chronic stress. In contrast, neither CS nor CV rats showed altered basal or stress-induced levels of ACTH which suggests that the activity of the axis was unchanged. Although the present data indicate that chronic stress caused behavioral abnormalities closely related to that expected to take place in some type of depressive disorders, endocrine data are not in good agreement with those occurring in depression.