Orexin receptors are expressed in the adrenal medulla of the rat

Two recently discovered hypothalamic peptides, orexin-A and orexin-B, play a role as mediators in the central mechanisms that regulate feeding behavio r and sleep control. These peptides bind and activate two orexins receptors that belong to the G-protein coupled receptor superfamily. Morphological s tudies have detected mRNA expression of orexin receptors exclusively in the rat central nervous system. In this paper we demonstrate a strong level of expression of orexin receptor 1 and 2 in the adrenal medulla of the rat by RT-PCR and immunohistochemistry. The results of the present study provide the first evidence showing that the adrenal medulla expresses orexin recept ors, and thus appears to be a target tissue for orexins. This could open a new loop in which the central and autonomous nervous system may be involved in body weight homeostasis and sleep control.