Reproduction is controlled by the brain through the hormone gonadotropin releasing hormone (GnRH). Leptin from fat acts on the brain to 'inform' GnRH cells of metabolic state; low levels signal lack of energy stores and suppress reproduction. Leptin treatment of lean individuals restores reproductive function, but the mechanism is not clear. Our data implicate the melanocortins as a means of transmitting information on metabolic state to GnRH cells and the project investigates this pathway.