Gonadotropin-inhibitory hormone in seasonally-breeding songbirds: neuroanatomy and functional biology

Abstract

The discovery of gonadotropin-inhibitory hormone (GnIH) in Japanese Quail Coturnix japonica has given us a new perspective on the neuroendocrine control of reproductive physiology and behavior. Using highly photoperiodic passerine songbirds as our model system, we have been able to investigate GnIH neuroanatomy and functional biology. The distribution of GnIH peptide is similar among the galliform and passerine species studied so far. We have identified GnIH cDNA and localized its transcript in Gambel's White-crowned Sparrow Zonotrichia leucophrys gambelii. There is a high degree of homology between the galliform and passerine GnIH cDNA sequences and peptides. Based on transcript localization, GnIH precursor polypeptide is only produced in the paraventricular nucleus, yet GnIH-immunoreactive fibers project to multiple brain areas, suggesting multiple physiological and behavioral functions. GnIH immunoreactive neurons appear to contact gonadotropin-releasing hormone (GnRH)-I and -II neurons, raising the possibility of direct regulation of GnRH by GnIH. In a photoperiod experiment, GnIH neurons increased in area during the termination of reproduction in Song Sparrows, Melospiza melodia, implying temporal photoperiodic regulation of this neuropeptide. Using peripheral administration of GnIH in vivo, we demonstrated rapid inhibition of LH release in laboratory and field experiments. Furthermore, we sought to determine the effects of central infusions of GnIH. Centrally-administered GnIH rapidly reduced circulating LH and significantly reduced the number of copulation solicitations performed in response to song playback, with no reduction of locomotor activity. Central infusion of rhodaminated GnIH elucidated putative GnIH binding sites in the median eminence close to GnRH-I fiber terminals, and in the midbrain on or close to GnRH-II neurons. These data demonstrate direct effects of GnIH upon reproductive physiology and behavior, possibly at multiple physiological levels and over different time-frames. Thus, the discovery of GnIH has unearthed a complex and interesting system for the regulation of avian reproductive biology.

The role of RFamide peptides in feeding

“…A prominent hypothalamic expression of LPXRFamide peptides has also been demonstrated in birds and other vertebrates. LPXRFamide neurons are localised to the PVN in the quail and sparrow (Tsutsui et al 2000, Bentley et al 2003, Osugi et al 2004, the suprachiasmatic nucleus in the frog (Chartrel et al 2002, Koda et al 2002, Sawada et al 2002a) and the nucleus posterior periventricularis in goldfish (Sawada et al 2002b). The conserved expression of LPXRFamide peptides in hypothalamic neurons (and especially in periventricular regions) suggests an important role of these peptides in neuroendocrine function.…”

Impact of growth trajectory on sexual maturation in layer chickens

“…In addition to its reproductive function, GnIH also possesses orexigenic effects that stimulate feed intake in chickens (Tachibana et al, 2005;Chowdhury et al, 2012). Increased levels of GnIH directly inhibit cGnRH-I (Bentley et al, 2003;Bentley et al, 2008) within the hypothalamus and reduce the release of gonadotropins (luteinizing hormone; LH and follicle-stimulating hormone; FSH; Tsutsui et al, 2000;Ciccone et al, 2004;Ikemoto and Park, 2005;Ubuka et al, 2006) by the anterior pituitary gland. Once released into the systemic circulation, LH and FSH initiate the maturation of small white follicles (SWFs), which gradually increase their production of estradiol (E 2 ; Williams and Sharp, 1978;Robinson and Etches, 1986).…”

Putting the brakes on reproduction: Implications for conservation, global climate change and biomedicine

“…Firstly, initial predictive cues such as the seasonal change in day length are very reliable environmental cues that trigger reproductive development, sustain mature capability through the breeding season and then terminate reproductive function usually through gonadal regression (Fig. 2, see Dawson et al, 2001;Bentley et al, 2007;Yoshimura, 2004;Silverin, 2002, 2009). Then there are local predictive cues (supplementary factors) that speed up or slow down effects of initial predictive cues so that mature capability and onset of breeding can be timed accurately.…”