Melanocortin MC4 receptor expression sites and local function

The melanocortin MC4 receptor plays an important role in energy metabolism, but also affects blood pressure, heart rate and erectile function. Localization of the receptors that fulfill these distinct roles is only partially known. Mapping of the melanocortin MC4 receptor has been stymied by the absence of a functional antibody. Several groups have examined mRNA expression of the melanocortin MC4 receptor in the rodent brain and transgenic approaches have also been utilized to visualize melanocortin MC4 receptor expression sites within the brain. Ligand expression and binding studies have provided additional information on the areas of the brain where this elusive receptor is functionally expressed. Finally, microinjection of melanocortin MC4 receptor ligands in specific nuclei has further served to elucidate the function of melanocortin MC4 receptors in these nuclei. These combined approaches have helped link the anatomy and function of this receptor, such as the role of paraventricular hypothalamic nucleus melanocortin MC4 receptor in the regulation of food intake. Intriguingly, however, numerous expression-sites have been identified that have not been linked to a specific receptor function such as those along the optic tract and olfactory tubercle. Further research is needed to clarify the function of the melanocortin MC4 receptor at these sites. (C) 2010 Elsevier B.V. All rights reserved.