Interaction of some hormonal and neural pathways that regulate food intake and body fat mass. A decrease in fat cell mass is sensed in the arcuate nucleus (ARC) of the hypothalamus by a decrease in leptin and insulin concentrations, causing suppression of anorexigenic signals, such as α-MSH, and stimulation of orexigenic signals such as AGRP and NPY. Neurons from the arcuate nucleus project to the paraventricular nucleus (PVN) and lateral hypothalamic area (LHA) to decrease TRH and increase MCH synthesis. The decrease in α-MSH also decreases TRH biosynthesis and release. The gastrointestinal hormone, ghrelin, modulates these pathways through activation of NPY/AGRP neurons. The net balance of these signals results in an increase in food intake and a decrease in energy expenditure that ultimately aims to restore fat cell mass.