Approximately two-thirds of adults in the United States are overweight or obese and therefore at increased risk for developing diabetes, coronary heart disease, stroke, some forms of cancer and other health serious problems. A better understanding of the physiological mechanisms that regulate energy balance is a key step towards developing therapeutic approaches to prevent and treat obesity. Proopiomelanocortin (POMC) neurons in the hypothalamic arcuate nucleus release multiple neuropeptides that are necessary for the maintenance of normal energy balance. POMC neurons also release classical neurotransmitters, however the role of synaptic transmitters in POMC neurons has not been well-studied. The goal of the proposed work is to test the overall hypothesis that subsets of POMC neurons release different classical neurotransmitters and that this heterogeneity among POMC neurons is important in the regulation of energy balance. The following specific hypotheses will be tested: 1) That subpopulations of POMC neurons can be defined by the presence and release of GABA or glutamate. Transgenic mice with co-labeled POMC, GABAergic and glutamatergic neurons will be used to examine the neurotransmitter phenotype of subsets of POMC neurons and the effects that obesity and leptin treatment have on the rapid transmitter phenotype of POMC neurons will be determined. 2) That there is differential regulation of subsets of POMC neurons. The presynaptic regulation and basal activity of subsets of POMC neurons will be studied using electrophysiological recordings and the effects that leptin and fasting have on these parameters in each subpopulation will be studied. 3) That GABAergic and glutamatergic POMC neurons project to distinct target sites. Retrograde labeling experiments will be performed in transgenic mice to identify where specific populations of POMC neurons project. The results of these studies will provide a clearer picture of how POMC neurons function in the CNS circuitry controlling energy balance. 7. PUBLIC HEALTH RELEVANCE: Obesity contributes to about 112,000 deaths per year and is the primary reason for over $75 billion in heath care expenditures in the United States. A better understanding of the physiological mechanisms that regulate energy balance is a key step towards developing therapeutic approaches to prevent and treat obesity. This study will determine how specific neurons in the brain that are critical for the maintenance of normal energy balance are regulated.