Presence and biological activity of a GnRH‐like factor in the nervous system of Helisoma trivoluis

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Abstract
Gonadotropin‐releasing hormone (GnRH) constitutes a family of neuropeptides found throughout the vertebrates. Although a GnRH‐like peptide has also been isolated from yeast (α‐mating factor), the presence of GnRH has not been clearly demonstrated in inverterate phyla. In this study, we tested the hypothesis that GnRH‐like peptides are present and functional in the central nervous system (CNS) of the gastropod mollusc, Helisoma trivoluis. The presence of a GnRH‐like peptide was examined by three methods: (1) in immunofluorescence studies with four different 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 GnRH in stimulating gonadotropin release from dispersed goldfish pituitary cells in static culture.Two functional assays were carried out to examine the potential biological roles of GnRH‐like peptides in Helisoma. (1) Intracellular recordings of left‐parietal and visceral ganglion neurons revealed diverse electrophysiological responses to mGnRH. These effects were attenuated by a mGnRH antagonist. (2) Addition of mGnRH arrested neurite outgrowth in a subpopulation of dissociated embryonic Helisoma neurons in culture. Taken together, these results strongly suggest that a mGnRH‐like peptide is an important neuropeptide in Helisoma. A hypothesis is presented that GnRH‐like peptides may be ancient factors that are conserved both structurally and functionally in the evolution of animals.

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