The overall goal of this proposal is to explore the processes underlying long-term habituation to repeated intermittent stress. Emotional stressors elicit a range of behavioral, autonomic, and endocrine responses that normally help organisms cope with challenging situations. However, prolonged or repeated exposure to stressful life events is frequently associated with several psychopathologies and physical disorders. Thus, habituation to stress is likely a vital mechanism allowing organisms to reduce the impact of repeatedly experienced stress situations. Unfortunately, the neural mechanisms specifically mediating normal stress habituation are unknown. Based on current evidence and preliminary studies, a model is proposed where the site of plasticity associated with habituation to stress is located at the interface between an auditory signaling pathway and a central effector region that controls many, if not all, responses normally associated with stress. Aim 1 provides an important evaluation of the hypothesis that several response systems, as measured with behavioral, autonomic, and endocrine responses, will vary in parallel during repeated intermittent loud noise exposures, suggesting that only a few or perhaps a unique brain region undergoes the plastic changes associated with habituation. These results will guide the performance of most following studies, and provide some spatial and temporal guidance as the number of brain regions underlying this form of plasticity. In Aim 2, functional manipulations of the auditory thalamus and auditory cortex will help determine the location, along the auditory system, where the auditory signal necessary and sufficient for habituation is derived from. Studies in Aim 3 are designed to ascertain the sympathetic premotor areas specifically controlling some of the measured autonomic responses, and help rule out the possibility that habituation to repeated loud noise is mediated by plasticity in these regions. Finally, the anatomical/functional studies of Aim 4 are designed to firmly establish the anatomical interface between activated auditory inputs and putative central integrative effector regions activated by loud noise. The hypothesis that functional inactivation of such central integrative effector region(s) will block habituation to repeated loud noise stress is also assessed.