Physiology, Gonadotropin Inhibitor

In 2000, an unidentified hypothalamic neuropeptide found in the quail bird was shown to inhibit gonadotropin hormone release, which researchers later termed gonadotropin-inhibitory hormone (GnIH). This was the first discovery of a hypothalamic neuropeptide inhibiting gonadotropin release in vertebrates. GnIH is a hormone considered to be one of the first avian RFamide peptides (a family of neuropeptides that contain a C-terminal Arg-The-NH2 motif and are members of the G-protein–coupled receptor superfamily) that inhibits both reproductive behaviors and pituitary gonadotrope (cells in the anterior pituitary that synthesize luteinizing hormone [LH] and follicular stimulating hormone [FSH]) function in birds and mammals. GnIH neurons are localized in the dorsomedial hypothalamus (DMH) and the paraventricular nucleus of the hypothalamus in mammals and birds, respectively. The GPR-147 receptor is a GnIH receptor expressed in both the gonadotropes and the gonadotropin-releasing hormone (GnRH) neurons. By binding to the GPR-147 receptor, GnIH exerts its inhibitory effects. It is important to note that much of the research done on GnIH and discussed within this paper has been done in the avian population and animals other than humans, equating to much room for expanding research. However, studies have shown that GnIH is highly conserved from the agnatha to humans, and the GnIH homologs RFRP-1 and RFRP-3 and the cognate receptor GPR147 that will be discussed have been discovered in the human hypothalamus.