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 determine the effects of chronic stress on the physiology and behavior of male rats. The present study was performed to extend these investigations to female rats. Female rats were chronically stressed using a behavioral 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 does not have control over shock termination. Control rats were never shocked but all groups lever pressed for food pellets on an FR1 schedule (one pellet per lever press). Daily vaginal samples were obtained for several weeks prior to stress onset and throughout the chronic stress period. After 14 days of stress, the experiment was terminated and morning blood samples were collected for hormonal assays. Stress transiently 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, but there were no significant effects of 14 days of stress treatment on plasma corticosterone, prolactin, estradiol, or progesterone concentrations. There were no significant differences in estrous cycle length among experimental groups.