CHARACTERIZATION AND LOCALIZATION OF GONADOTROPIN-RELEASING-HORMONE IN THE BRAIN AND PITUITARY OF THE 3-SPINED STICKLEBACK, GASTEROSTEUS-ACULEATUS

Radioimmunoassay (RIA) studies on high-performance liquid chromatograp hy (HPLC) fractions of brain extracts of the three-spined stickleback, Gasterosteus aculeatus, provided evidence for at least two forms of g onadotropin-releasing hormone (GnRH). One form showed chromatographic and immunological properties similar to that of synthetic salmon GnRH (sGnRH). A second, unidentified form of GnRH eluted in the same positi on as chicken GnRH I (cGnRH-I); however, it did not cross-react in a c GnRH-I RIA. Furthermore, it cannot be excluded that chicken GnRH II (c GnRH-II) and maybe one other unidentified form are present in the stic kleback. The distribution of GnRH in the brain of breeding adult male sticklebacks was studied by use of immunohistochemistry. Two antisera against sGnRH and antisera against mGnRH and cGnRH-II were applied on cryosections and visualized using the peroxidase-antiperoxidase method . Staining patterns were similar after incubations with all four anti- sera. Immunoreactive fibers were found in most parts of the brain. Thr ee distinct groups of GnRH-immunoreactive perikarya were found in the nucleus olfactoretinalis, in the nucleus anterior periventricularis, a nd in the nucleus lateralis tuberis. Moreover, weakly stained cells oc curred in a periventricular position in the midbrain. The proximal par s distalis of the pituitary, housing the gonadotropic cells, was richl y innervated by GnRH-positive fibers. In the pars intermedia and in th e rostral pars distalis, immunoreactive fibers were absent.