Season- and age-related variation in neural cGnRH-I and cGnRH-II immunoreactivity in house sparrows (Passer domesticus).
Vertebrates exhibit several forms of gonadotropin-releasing hormone (GnRH). In birds, chicken GnRH-I (cGnRH-I) is the primary hypophysiotropic form that regulates the hypothalamo-pituitary-gonad (HPG) axis. In seasonally breeding songbirds, cGnRH-I immunoreactivity is primarily in the preoptic septo-infidibular regions and varies greatly between the breeding and non-breeding season. Chicken GnRH-II (cGnRH-II) is more widely distributed throughout the avian brain, but cGnRH-II immunoreactivity has been found in the median eminence of quail. Thus, cGnRH-II may function in addition to cGnRH-I in the regulation of the HPG axis. If so, we predicted that cGnRH-II immunoreactivity should exhibit seasonal and age related variation similar to that observed for cGnRH-I. In this study, we compared hypothalamic immunoreactivity of cGnRH-I and -II (ir-cGnRH-I and ir-cGnRH-II) between breeding and non-breeding adult and juvenile house sparrows (Passer domesticus). We used immunocytochemistry with highly specific antibodies developed for quail to examine brains of free-living house sparrows collected in the breeding and non-breeding season. Results showed a greater number of ir-cGnRH-I cell bodies and beaded fibres in breeding adult birds compared to non-breeding adult and juvenile birds. Moreover, there were significantly more ir-cGnRH-II fibres in the preoptic area of breeding adult birds compared to non-breeding adult and juvenile birds. These data suggest that cGnRH-II undergoes seasonal- and age-related changes similar to cGnRH-I and implicate a role in regulating reproduction.
Graduate Program in Neuroscience, University of Western Ontario, Canada.
Tyler J
TJ
Stevenson
Scott A
SA
Macdougall-Shackleton
D000375:Aging / Q000502:physiology*; D000818:Animals; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007032:Hypothalamus, Anterior / Q000378:metabolism*; D007120:Immunochemistry; D008297:Male; D008473:Median Eminence / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism*; D012098:Reproduction / Q000502:physiology*; D012621:Seasons; D046370:Sparrows
D007987:Gonadotropin-Releasing Hormone