Evidences for the regulation of GnRH and GTH expression by GnIH in the goldfish, Carassius auratus

Gonadotrophin-inhibitory hormone (GnIH) plays an important role in regulating of reproduction in teleosts. To clarify the mode of action of GnIH on the synthesis of gonadotropin releasing hormone (GnRH) and gonadotrophin (GtH), three GnIHR cDNAs were cloned from the goldfish brain. In situ hybridization results showed that GnIHRs were localized to the hypothalamus and pituitary. In the hypothalamus, GnIHRs were found in the NPP, NPO and NLT, whereas sGnRH neurons were reported to be located, and potentially regulated by GnIH. In the pituitary, only two GnIHRs were observed and they were localized to the PI instead of the adenohypophysis where GtH-expressing cells are localized, suggesting indirect regulation of GtH by GnIH. In vivo, intraperitoneal (i.p.) injections of synthetic goldfish GnIH-II peptide and GnIH-III peptide significantly decreased sGnRH and FSH beta mRNA levels. Only GnIH-II decreased LH beta mRNA levels significantly. In vitro, both GnIH-II and GnIH-III showed no effect on GtH synthesis, but an inhibition of GnRH-stimulated LH beta and FSH beta synthesis was observed when GnIH-III was applied to primary pituitary cells in culture. Thus, GnIH could contribute to the regulation of gonadotropin in the brain and pituitary in teleosts. (C) 2012 Elsevier Ireland Ltd. All rights reserved.