The neurons of the hypothalamus that synthesize melanin concentrating hormone (MCH) have been postulated to play a key role in the initiation of feeding and in energy homeostasis. MCH application in the brain increases feeding and weight gain, whereas loss of the MCH gene causes a decrease. Despite a large amount of fascinating data on the general actions of MCH, almost nothing is known about the cellular physiology of these cells. The primary focus of this proposal is to study the physiological characteristics, and the responses to neurotransmitters and neuropeptides postulated to play a role in energy homeostasis, and to examine the response of these neurons to metabolic signals. Whole cell patch clamp recording will be done in transgenic mouse hypothalamic slices containing MCH neurons identifiable by selective expression of GFP. First, we will study the passive and active membrane properties of the MCH cells to provide a foundation for subsequent work. Neuropeptide Y, an orexigenic peptide, has been suggested to increase feeding by activation of the MCH neurons. In contrast, we postulate that NPY exerts inhibitory actions on MCH neurons, consistent with previous electrophysiological data from other regions of the hypothalamus; parallel experiments will test the hypothesis that MCH cells are excited by melanocortin peptides such as alpha-MSH, postulated to inhibit food intake. The hypothesis that MCH neurons respond to metabolic signals relating to energy homeostasis will be tested, focusing on synaptic and cellular response to glucose, ghrelin, and leptin. To study mechanisms of release and modulation of presynaptic MCH axons, we will use an in vitro model where MCH axons terminate on the cell of origin; we will test the corroborating hypothesis that MCH cells synthesize and release the inhibitory transmitter GABA using dual ultrastructural immunocytochemistry and whole cell recording. The hypothesis that MCH inhibits the release of GABA, potentially leading to disinhibition, will be tested. Together, theses studies address questions relating to the cellular characteristics and responses of these unique hypothalamic neurons. Obesity has become a major health problem leading to increases in heart disease, strokes, mortality and other risks. Studies of the cellular physiology of MCH neurons should provide a better understanding of the role of this system in regulating energy homeostasis and obesity.
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