EFFECTS OF CHRONIC STRESS ON FOOD ACQUISITION, PLASMA HORMONES, AND THE ESTROUS-CYCLE OF FEMALE RATS

Our laboratory has previously conducted a number of studies to determi ne the effects of chronic stress on the physiology and behavior of mal e rats. The present study was performed to extend these investigations to female rats. Female rats were chronically stressed using a behavio ral paradigm of around-the-clock signalled intermittent foot shock in which some rats can pull a chain to avoid/escape shock (stress) while another group of rats is yoked to the first group (yoked-stress) and d oes not have control over shock termination. Control rats were never s hocked but all groups lever pressed for food pellets on an FR1 schedul e (one pellet per lever press). Daily vaginal samples were obtained fo r several weeks prior to stress onset and throughout the chronic stres s period. After 14 days of stress, the experiment was terminated and m orning blood samples were collected for hormonal assays. Stress transi ently decreased lever pressing for food pellets and body weights, but both measures returned to prestress levels by day 14 of stress. Plasma adrenocorticotropic hormone (ACTH) concentrations were significantly elevated in the yoked-stress group compared to the other two groups, b ut there were no significant effects of 14 days of stress treatment on plasma corticosterone, prolactin, estradiol, or progesterone concentr ations. There were no significant differences in estrous cycle length among experimental groups.