Mode of action and functional significance of avian gonadotropin-inhibitory hormone (GnIH): a review.
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). However, a hypothalamic neuropeptide acting at the level of the pituitary to negatively regulate gonadotropin secretion has, until recently, remained unknown in any vertebrate. In 2000, we discovered a novel hypothalamic neuropeptide inhibiting gonadotropin release at the level of the pituitary 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 further identified the receptor for GnIH and characterized its expression and binding activity in quail. The identified GnIH receptor possessed seven transmembrane domains and specifically bound to GnIH in a concentration-dependent manner. The expression of GnIH receptor was found in the pituitary and several brain regions including the hypothalamus. These results suggest 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. To understand the functional significance of GnIH in avian reproduction, we also investigated the mechanism that regulates GnIH expression. Interestingly, melatonin induced dose-dependently GnIH expression and melatonin receptor (Mel(1c)) was expressed in GnIH neurons. Thus melatonin appears to act directly on GnIH neurons via its receptor to induce GnIH expression. Based on these studies, GnIH is likely an important neuropeptide for the regulation of avian reproduction.
Tsutsui
Kazuyoshi
K
Laboratory of Brain Science, Faculty of Integrated Arts and Sciences, Hiroshima University, and Integrative Brain Science Center at Hiroshima University, Higashi-Hiroshima 739-8521, Japan.
Ubuka
Takayoshi
T
Yin
Hong
H
Osugi
Tomohiro
T
Ukena
Kazuyoshi
K
Bentley
George E
GE
Ciccone
Nick
N
Inoue
Kazuhiko
K
Chowdhury
Vishwajit S
VS
Sharp
Peter J
PJ
Wingfield
John C
JC
D000595:Amino Acid Sequence; D000818:Animals; D030161:Avian Proteins / Q000494:pharmacology* / Q000502:physiology; D001717:Birds / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D007028:Hypothalamic Hormones / Q000502:physiology; D008550:Melatonin / Q000502:physiology; D008969:Molecular Sequence Data; D012098:Reproduction / Q000502:physiology; D016415:Sequence Alignment
D030161:Avian Proteins; D007028:Hypothalamic Hormones; C413752:gonadotropin-inhibitory hormone, Coturnix japonica; D007987:Gonadotropin-Releasing Hormone; D008550:Melatonin