Figure 3. Cartoon showing potential interactions of proopiomelanocortin neurons in appetite regulation. In the hypothalamus, nutrition and energy hemostasis is balanced by proopiomelanocortin and agouti-related peptide/neuropeptide Y through melanocortin receptors. This system is regulated by peripheral polypeptides such as leptin, ghrelin, insulin and peptide YY. In proopiomelanocortin deficiency, the appetite-stimulating effect of agouti-related peptide is not balanced by the appetite-suppressing effect of proopiomelanocortin. AgRP is co-expressed with neuropeptide Y. This peptide increases appetite and decreases energy use and metabolism. This system is mainly inhibited by leptin and stimulated by ghrelin NPY: neuropeptide Y, AgRP: agouti-related peptide, POMC: proopiomelanocortin, MSH: melanocyte-stimulating hormone, MC4R: melanocortin 4 receptors, PPY: peptide YY, GABA: gammα-amino butyric acid.