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 C57 BL /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 α ‐ MSH and β ‐endorphin ( β ‐ END ) levels. An in situ immunohistochemical examination was performed for melanocortin receptor 4 ( MC 4R) and POMC ‐derived α ‐ MSH . The expression of Pomc and MC 4R mRNA s was stimulated, whereas that of Ag RP was inhibited after exposure to UVB . It was accompanied by an increased number of both α ‐ MSH ‐ and MC 4R‐immunoreactive neurons in the ARC , and by increased levels of α ‐ MSH and β ‐ 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 α ‐ MSH and β ‐ 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.