Figure 1.

Mechanism of appetite regulation by the hypothalamus and peripheral tissues. Leptin secreted by adipocytes travels through the circulation and acts on the hypothalamic arcuate nucleus, and gut peptides such as ghrelin and glucagon‐like peptide‐1 (GLP‐1) act on the hypothalamus through the vagus nerve. Black letters indicate appetite‐enhancing peptides and white letters indicate appetite‐suppressing peptides; the interactions of these peptides are mediated by the melanocortin 4 (MC4R), gamma amino butyric acid (GABA) and leptin receptors. The α‐melanocyte‐stimulating hormone produced by the pro‐opiomelanocortin (POMC) neuron is an MC4R agonist, and the agouti‐related regulatory peptide (AgRP) is an inverse agonist of MC4R, and these antagonistically regulate appetite. Suppression of POMC neurons by NPY/AgRP neurons through the GABA receptors is also important. Solid lines and dashed lines show the representative transmission of enhancing and suppressing actions, respectively, in the hypothalamus. CCK, cholecystokinin; CRH, corticotropin‐releasing hormone; MCH, melanin‐concentrating hormone; NPY, neuropeptide Y; PACAP, pituitary adenylate cyclase‐activating peptide; PYY, peptide YY; SF‐1, steroidogenic factor 1; TRH, thyrotropin‐releasing hormone.