Ultraviolet B stimulates proopiomelanocortin signalling in the arcuate nucleus of the hypothalamus in mice

We previously found that ultraviolet B (UVB) could stimulate the paraventricular nucleus (PVN) with activation the systemic hypothalamic-pituitary- adrenal (HPA) axis. To investigate whether UVB can also stimulate other hypothalamic nuclei, we tested its effect on the proopiomelanocortin (POMC) related signalling system in the arcuate nucleus (ARC) of female C57BL/6 and FVB albino mice. The shaved back skin of the mice was irradiated with either 100 or 400 mJ/cm(2) of UVB. After 1, 3, 6 and 12 h, blood and hypothalamus were collected and processed for gene and protein expression, and measurement of -MSH and -endorphin (-END) levels. An in situ immunohistochemical examination was performed for melanocortin receptor 4 (MC4R) and POMC-derived -MSH. The expression of Pomc and MC4R mRNAs was stimulated, whereas that of AgRP was inhibited after exposure to UVB. It was accompanied by an increased number of both -MSH- and MC4R-immunoreactive neurons in the ARC, and by increased levels of -MSH and -END (both found in the hypothalamus and plasma). This surprising discovery of UVB stimulating the POMC system in the ARC, accompanied by the increased plasma levels of -MSH and -END, paves the way for exciting areas of research on the communication between the skin and the brain, as well as is suggesting a new role for UVB in regulation of body metabolism.