PROJECT SUMMARY Excess weight and obesity affect over half of all Americans, putting them at risk of serious illness and representing a significant strain on the public health system. Methods for treating obesity are insufficient to supporting long-term weight loss in the broad population, highlighting the need for further basic research to inform treatment strategies. The mesolimbic dopamine system has generated significant interest as a target for the treatment of obesity due to its well-characterized role in reward learning and motivation. Importantly, neurons in this region show increased responses to food during hunger, suggesting that state-dependent changes in the brain heighten food salience and reward value. Understanding how physiological state boosts food-evoked dopamine signaling may inform new approaches to modulate food reward and thus assist efforts to consume fewer calories in order to lose weight. We recently demonstrated that hunger-sensitive Agouti-related protein (AgRP)-expressing neurons in the hypothalamus are sufficient to reproduce hunger’s effects on food-evoked dopamine release. This proposal will test the hypothesis that orexin 1 receptor (Ox1r)-expressing dopamine neurons in the ventral tegmental area (VTA) will respond to food specifically in hunger and during AgRP neuron activation. Aim 1 will use single-cell resolution two-photon calcium imaging in awake mice to (1) identify neurons in the VTA that are food-responsive during hunger and (2) determine whether AgRP neuron stimulation during satiety is sufficient to recapitulate the effects of hunger on individual VTA neurons. Aim 2 will use in situ hybridization to test the hypothesis that hunger enhances the sensitivity of Ox1r-expressing neurons to make them food-responsive. This hypothesis is built on the known role of VTA-projecting orexin neurons in regulating food reward and the fact that AgRP neurons project directly to the lateral hypothalamus where orexin neurons reside. Thus, we propose a novel circuit that links homeostatic and hedonic systems to regulate food intake. The training plan builds on my current training to learn two techniques – two-photon calcium imaging and fluorescent in situ hybridization – that will be critical as I continue in the field of behavioral neuroscience. The ability to identify how neural subpopulations in a heterogenous region contribute to behavior is highly relevant and requires techniques such as those proposed in these experiments. My sponsor, Dr. Nick Betley, is an expert in the neural circuitry underlying food intake and my co-sponsor, Dr. Ethan Goldberg, has extensive experience with two- photon microscopy in awake, behaving animals. My plan also includes training in writing and presentation skills to help prepare me for a career as an independent investigator. My success in graduate school to date shows that I am capable of completing the proposed project before beginning a postdoctoral fellowship during which I plan to c...