IBN-9511349 and 9528213 Blanchard, D. C. and McEwen, Bruce Social stress is a common and enduring feature of life with important behavioral and physiological effects. A multidisciplinary research collaboration between the Laboratory of Behavioral Neurobiology at the University of Hawaii and the Laboratory of Neuroendocrinology at Rockefeller University is aimed at description and analysis of these effects. Previous work indicates that single, two-week stress periods can produce increased defensive behavior and decreased social and reproductive behavior; higher levels of stress hormones and impairment of mechanisms that normally limit stress hormone action; and widespread changes in brain neurochemical systems. Although these changes are beginning to provide insights into the dynamics of the physiological and behavioral response to chronic social stress, completed studies have measured only a single time point in the process. The proposed program will investigate the development of stress-related behavioral and physiological changes over time, and will determine the persistence of stress effects following single or multiple periods of chronic social stress. In addition, individual differences will be examined as determinants of responsivity to social stress. The proposed program will thus draw upon the different approaches and expertise of these two research groups to provide a uniquely comprehensive description and analysis of the effects of social stress in an ecologically appropriate situation.