Peptidergic mediation of the stress response: relationship between aversive and appetitive brain circuits

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The long-term objective of this research program is to better understand how the brain interprets various types of stressors or salient stimuli (including appetitive events) and coordinates internal bodily responses as well as behavioral outputs in response to these events. This is based on the observation that exposure to threatening (or aversive) stimuli or to appetitive (or rewarding) stimuli can activate some of the same neural circuits. In this project, we will explore the behavioral, neurochemical and neuroanatomical substrates underlying responses to 1) `classic stressors' including naturalistic psychogenic (psychological) stressors (exposure to a larger `bully' leading to social defeat), neurogenic stressors (physical restraint), which have psychological and physical attributes and pure physiological stressors (e.g. exposure to immune-type stressors) and 2) appetitive stimuli (sexual behavior, palatable snack). We have deliberately selected to study these types of naturalistic stressors, as they are ethologically sound and more likely to yield heuristically and practically useful information. Moreover, the selection of the appetitive stimuli was based on data showing comparable activation of the hypothalamic-pituitary adrenal axis to social defeat and restraint making these stressors of opposite valence well suited for comparative studies. The brain utilizes various chemical signals (neurotransmitters) to communicate not only with the rest of the body but also between different regions of the brain itself. One particular class of such transmitter molecules that seem important in responding to stress are small hormone-like molecules called peptides. We are able to monitor the release of various brain transmitters/peptides, in freely behaving animals - without them being 'aware' of this process. We will also monitor the release of various hormones and assess levels of motivation and emotional responses in these animals as stressor exposure is known to affect these behavioral processes. It is hoped that this work will shed new light on the stressor-specific neurochemical mechanisms that link perception of stress to its translation into the classical stress response. Moreover, we hope to uncover the links between stress and reward systems, which may have bearing on adaptive responses to stressors, and potentially uncover how stressful events come to influence motivational behavior and cognitive appraisal.**