Project Summary The development of therapeutic drugs to cure obesity has not been successful due to unwanted side effects and limited efficacy. Delineation of key brain neural pathways on body weight regulation is essential to fully understand the pathophysiology of obesity and to design an effective strategy against obesity. Given the rapid obesity epidemic coinciding with recent economic development and readily availability of high fat high caloric diet (HFD), it is well accepted that the increased HFD consumption contribute significantly to human obesity development. Compelling human studies also indicate a profound effect of stress on body weight regulation. However, little is known about the neural basis of stress and HFD induced obesity. The major brain neurons that respond to stressors are corticotropin releasing hormone (CRH) neurons, which are located in a few major brain sites including the paraventricular hypothalamus (PVH). PVH CRH neurons help maintain bodily homeostasis in response to stressors mainly through hormonal hypothalamus-pituitary axis (HPA) and direct projections to down-stream neurons known to be involved in behavioral adaptation. Our previous results demonstrate that clamping PVH CRH neuron activity at either high or low levels both leads to reduced neuron responsiveness and exacerbates high fat diet-induced obesity (DIO), which is associated with altered blood corticosteroid diurnal rhythms. Importantly, PVH CRH neuron responsiveness is dramatically reduced by HFD feeding, which is known to blunt HPA axis rhythmicity. In addition, body weight- reducing variable stress regimes in rodents augment PVH CRH responsiveness. Emerging studies also suggest that PVH CRH neuron responsiveness changes in response to reward and regulates choices on HFD intake. These observations lead to our central hypothesis that PVH CRH neuron responsiveness underlies HFD-induced obesity. Experiments in Aim 1 will determine the mechanism underlying reduced PVH CRH neuron responsiveness by HFD. Experiments in Aim 2 will identify the neurotransmitters that mediate the PVH CRH neuron effect in DIO with a focus on CRH and glutamate release. Experiments in Aim 3 will test whether PVH CRH neuron responsiveness mediates the known beneficial effects on metabolism induced by time- restricted feeding and circadian rhythm enhancing Nobiletin treatment. Results will fill in the knowledge gap in understanding the neural basis for integrating stress and HFD on obesity. Given the growing evidence on the impact of chronic stress in human obesity, this proposal aiming to identify PVH CRH neuron responsiveness as a fundamental mechanism for DIO is highly relevant to human obesity and significant for obesity treatment.