Coexpression of MT1 and RORα1 melatonin receptors in the Syrian hamster Harderian gland

Melatonin acts through several specific receptors, including membrane receptors (MT1 and MT2) and members of the RZR/ROR nuclear receptors family, which have been identified in a large variety of mammalian and nonmammalian cells types. Both membrane and nuclear melatonin receptors have been partially characterized in Harderian gland of the Syrian hamster. Nevertheless, the identities of these receptors were unknown until this study, where the coexistence of MT1 and ROR alpha(1) in this gland was determined by nested RT-PCR followed by amplicon sequencing and Western-blot. Furthermore, the cellular localization of both receptors was determined by immunohistochemistry. Thus, MT1 receptor was localized exclusively at the basal side of the cell acini, supporting the hypothesis that this receptor is activated by the pineal-synthesized melatonin. On the contrary, although a ROR alpha(1)-immunoreactivity was observed in nuclei of epithelial cells of both sexes, an extranuclear specific staining, which was more frequently among those cells of males, was also seen. The implication of this possible nuclear exclusion of ROR alpha(1) on the role of this indoleamine against oxidative stress is discussed.