Discovery of gonadotropin-inhibitory hormone in a domesticated bird, its mode of action and functional significance
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Neuropeptide control of gonadotropin secretion at the level of the anterior pituitary gland is primarily through the stimulatory action of the hypothalamic decapeptide gonadotropin-releasing hormone (GnRH) in vertebrates. Until recently, no neuropeptide that directly inhibits gonadotropin secretion had been identified. In 2000, we discovered a novel hypothalamic dodecapeptide that directly inhibits gonadotropin release in quail and termed it gonadotropin-inhibitory hormone (GnIH). A gonadotropin inhibitory system is an intriguing concept and provides us with an unprecedented opportunity to study the regulation of avian reproduction from an entirely novel standpoint. To elucidate the mode of action of GnIH, we then identified a novel G protein-coupled receptor for GnIH in quail. The receptor possessed seven transmembrane domains and specifically bound to GnIH in a concentration-dependent manner. The GnIH receptor was found to be expressed in the pituitary and several brain regions including the hypothalamus. These results indicate that GnIH acts directly on the pituitary via GnIH receptor to inhibit gonadotropin release. GnIH may also act on the hypothalamus to inhibit GnRH release, because GnIH fibers were observed to contact GnRH cell bodies. To demonstrate the functional significance of GnIH and its potential role as a key neuropeptide involved in avian reproduction, we further investigated the action of GnIH on gonadal development and maintenance in quail. Chronic treatment with GnIH inhibited photoinduced testicular development and maintenance by decreasing gonadotropin synthesis and release. Melatonin is a key factor involved in GnIH neural function. Quail GnIH neurons were found to contain melatonin receptor and melatonin stimulated expression of GnIH mRNA and mature GnIH peptide in a dose-dependent manner. It is concluded that GnIH is capable of transducing photoperiodic information via changes in the melatonin signal and of influencing the reproductive axes of birds.
KeywordsGonadotropins Gonadotropin-inhibitory hormone (GnIH) Gonadotropin-releasing hormone (GnRH) Melatonin Hypothalamus Pituitary Reproduction
This work was supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Science, and Culture, Japan (15207007, 16086206 and 18107002) and NIH, USA (RO1 MH065974).
- Bentley GE, Ball GF (2000) Photoperiod-dependent and -independent regulation of melatonin receptors in the forebrain of songbirds. J Neuroendocrinol 12:745–752Google Scholar
- Bentley GE, Perfito N, Ukena K, Tsutsui K, Wingfield JC (2003) Gonadotropin-inhibitory peptide in song sparrows (Melospiza melodia) in different reproductive conditions, and in house sparrows (Passer domesticus) relative to chicken-gonadotropin-releasing hormone. J Neuroendocrinol 15:794–802PubMedCrossRefGoogle Scholar
- Ciccone NA, Dunn IC, Boswell T, Tsutsui K, Ubuka T, Ukena K, Sharp PJ (2004) Gonadotrophin inhibitory hormone depresses gonadotrophin α and follicle-stimulating hormone β subunit expression in the pituitary of the domestic chicken. J Neuroendocrinol 16:999–1006Google Scholar
- Miyamoto K, Hasegawa Y, Nomura M, Igarashi M, Kangawa K, Matsuo H (1984) Identification of the second gonadotrophin-releasing hormone in chicken hypothalamus: evidence that gonadotrophin secretion is probably controlled by two distinct gonadotropin-releasing hormones in avian species. Proc Natl Acad Sci USA 81:3874–3878PubMedCrossRefGoogle Scholar
- Osugi T, Ukena K, Bentley GE, O’Brien S, Moore IT, Wingfield JC, Tsutsui K (2004) Gonadotropin-inhibitory hormone in Gambel’s white-crowned sparrows: cDNA identification, transcript localization and functional effects in laboratory and field experiments. J Endocrinol 182:33–42PubMedCrossRefGoogle Scholar
- Sun Y-M, Dunn IC, Baines E, Talbot RT, Illing N, Millar RP, Sharp PJ (2001) Distribution and regulation by oestrogen of fully processed and variant transcripts of gonadotrophin releasing hormones I and gonadotrophin releasing hormone receptor mRNAs in the male chicken. J Neuroendocrinol 13:37–49PubMedCrossRefGoogle Scholar
- Tsutsui K, Bentley GE, Ciccone N (2005) Structure, action and functional significance of GnIH. In: Dawson A, Sharp PJ (eds) Functional avian endocrinology. Narosa, New Delhi, pp 73–82Google Scholar