The central melanocortin system is defined anatomically as a collection of central nervous system circuits which include: * Neurons that express hypothalamic neuropeptide Y and agouti gene-related protein or proopiomelanocortin and that originate in the arcuate nucleus. * Brainstem proopiomelanocortic neurons (POMC neurons) originating in the commissural nucleus of the solitary tract (cNTS). * Downstream targets of these proopiomelanocortic and agouti related protein neurons expressing the melanocortin-3 and melanocortin-4 receptors