PRESENCE AND BIOLOGICAL-ACTIVITY OF A GNRH-LIKE FACTOR IN THE NERVOUS-SYSTEM OF HELISOMA-TRIVOLVIS

Gonadotropin-releasing hormone (GnRH) constitutes a family of neuropep tides found throughout the vertebrates. Although a GnRH-like peptide h as also been isolated from yeast (a-mating factor), the presence of Gn RH has not been clearly demonstrated in invertebrate phyla. In this st udy, we tested the hypothesis that GnRH-like peptides are present and functional in the central nervous system (CNS) of the gastropod mollus c, Helisoma trivolvis. The presence of a GnRH-like peptide was examine d by three methods: (1) in immunofluorescence studies with four differ ent antibodies generated against several GnRH peptides, select neurons and putative neurosecretory cells were specifically and consistently labelled throughout the CNS; (2) reverse-phase high performance liquid chromatography (HPLC) and radioimmunoassay (RIA) analysis revealed a GnRH-like factor which co-migrates with mammalian (m)GnRH; and (3) in bioactivity experiments, extracts of Helisoma trivolvis CNS mimicked G nRH in stimulating gonadotropin release from dispersed goldfish pituit ary cells in static culture. Two functional assays were carried out to examine the potential biological roles of GnRH-like peptides in Helis oma. (1) Intracellular recordings of left-parietal and visceral gangli on neurons revealed diverse electrophysiological responses to mGnRH. T hese effects were attenuated by a mGnRH antagonist. (2) Addition of mG nRH arrested neurite outgrowth in a subpopulation of dissociated embry onic Helisoma neurons in culture. Taken together, these results strong ly suggest that a mGnRH-like peptide is an important neuropeptide in H elisoma. A hypothesis is presented that GnRH-like peptides may be anci ent factors that are conserved both structurally and functionally in t he evolution of animalS. (C) 1993 Wiley-Liss, Inc.