Figure 3. Schematic diagram illustrating the central effects of hormones that control eating. Leptin and insulin are secreted in proportions to body fat mass and decrease appetite by inhibiting neurons that produce the NPY and AgRP, while stimulating melanocortin-producing neurons in the ARC region of the hypothalamus, near the third ventricle of the brain. NPY and AgRP stimulate eating, and melanocortins inhibit eating, via higher-order neurons. Activation of NPY/AgRP-expressing neurons inhibits melanocortin-producing neurons. The gastric hormone acyl-ghrelin stimulates appetite by activating the NPY/AgRP-expressing neurons. Gut hormones released from the GI tract in response to eating, including PYY, inhibit these neurons and thereby suppress appetite and decrease energy intake. Abbreviations: AgRP, agouti-related peptide; ARC, arcuate nucleus; CART, cocaine and amphetamine-regulated transcript; NPY, neuropeptide Y, PVN, paraventricular nucleus; PYY, peptide tyrosine-tyrosine 3-36; POMC, pro-opiomelanocortin: Lepr, Leptin receptor; GHSR, Ghrelin receptor, MC3R, Melanocortin 3 receptor, MC4R, Melanocortin 4 receptor, Y1r, NPY receptor; Y2r, NPY/PYY3-36 receptor.