Project Summary The development of therapeutic drugs to cure obesity has not been successful due to unwanted side effects and limited efficacy. My long-term research goal is to delineate neural pathways responsible for body weight homeostasis, and provide a framework for effective and specific therapeutics against obesity. Research in the last decades has identified arcuate neurons in the hypothalamus expressing agouti-related protein (AgRP) as a key node in feeding. Recently, we and others demonstrate that chronic activation of AgRP neurons or adult deletion of leptin receptors in these neurons leads to massive obesity on chow diet that is comparable to leptin deficiency. AgRP neurons are known to release GABA, NPY and AgRP and send independent and parallel projections to several key brain sites. Importantly, the expression of leptin receptor has been suggested to be more prominent in those AgRP neurons that project to extra-hypothalamic areas. However, how the neurotransmitters and the individual AgRP neuron projections mediate the obesity produced by chronic activation of AgRP neurons are unknown. Additionally, how the individual AgRP neuron projections mediates leptin action on obesity is also unknown To address these knowledge gaps, we aim to examine the role of AgRP individual neurotransmitters (Aim 1), projection-specific subpopulations of AgRP neurons (Aim 2) and their LepR expression (Aim 3) in mediating the obesity development produced by chronic AgRP neuron activation. Advanced viral tracing and intersectional mouse genetics will be used to achieve projection-specific manipulations in AgRP neurons to achieve robust investigation. This proposal is based on our previously established massive obese mouse models with chronic AgRP neuron activation or LepR deletion in AgRP neurons, and utilizes a combination of inducible deletion and tracing to ex-amine the relative importance of individual transmitters and projections in obesity development. The results will fill the gap in the underlying neurocircuit mechanism for AgRP neurons on obesity development and will set up stages to identify key downstream mediators and neurons mediating leptin and AgRP neurons in obesity development, representing a significant step in understanding brain mechanisms in body weight regulation.