Presence of gonadotropin-releasing hormone immunoreactivity in dogfish and skate brains

Gonadotropin‐releasing hormone (GnRH) immunoreactivity was studied in two species of elasmobranchs, spiny dogfish (Squalus acanthias) and black skate (Bathyraja kincaidii). Immunoreactive material in brain sections was identified using the avidin‐biotin technique with the horseradish peroxidase reaction. Although there were a few GnRH immunoreactive cells, GnRH fibers were greatest in the telencephalon of both species and were associated primarily with the terminal nerve system. In the dogfish, many immunoreactive fibers extended towards the ventromedial surface of the caudal forebrain. This site may be the locus for neurosecretion. GnRH fibers were found in the preoptico‐hypophyseal tract of dogfish, but not in the media eminence or pituitary. Immunoreactive material was less abundant in other regions of the brain, although a diffuse fiber network throughout the brain including the brain stem was observed. © 1992 Wiley‐Liss, Inc.