Differential distribution of orexin-A-like and orexin receptor 1 (OX1R)-like immunoreactivities in the Xenopus pituitary.

Immunohistochemical techniques were employed to investigate orexin-A-like and orexin receptor 1 (OX1R)-like immunoreactivities in the Xenopus pituitary gland. Orexin-A-immunoreactive cells were mainly scattered in the posterior half of the pars distalis. They corresponded to thyroid-stimulating hormone (TSH)-containing cells and so far have not corresponded to other types of pituitary adenocytes. On the other hand, OX1R-immunoreactive cells were mainly distributed in the anterior half of the pars distalis and corresponded to prolactin (PRL)-containing cells; however, we found that OX1R-immunoreactive cells did not correspond to other types of adenocytes in the Xenopus pituitary. These results suggest that an orexin-A-like substance secretes with and/or without TSH from TSH-containing cells and that the peptide modulates the functions of PRL-containing cells via OX1R in a paracrine fashion.