title: Photo-induction of hypothalamic gonadotrophin releasing hormone-I mRNA in the domestic chicken: a role for oestrogen?
abstract: Photoinduced changes in GnRH neuronal function were investigated in prepubertal and in midpubertal cockerels and somatically mature hens. Photostimulation of short day mid-pubertal cockerels and somatically mature out-of-lay hens for 7 days significantly increased (P<0.05) total hypothalamic gonadotrophin releasing hormone-I (GnRH-I) mRNA. The increase in GnRH-I mRNA was associated with increased (P<0.05) plasma LH in the hens but not mid-pubertal cockerels. Photostimulation of short day prepubertal cockerels for 7 days also stimulated LH release (P<0.05) but in contrast did not increase total hypothalamic GnRH-I mRNA. Plasma LH and hypothalamic GnRH-I mRNA were depressed in (P<0.001) short day prepubertal cockerels chronically treated with oestradiol benzoate (0.5 mg/kg, on alternate days). However, photostimulation of oestrogenized prepubertal cockerels for 7 days stimulated LH release (P<0.001) and increased hypothalamic GnRH-I mRNA (P<0.001). It is concluded that photostimulatory inputs to GnRH neurones have the potential to increase GnRH-I mRNA transcription or stability and to increase GnRH-I release. The extent to which increased levels of GnRH-I mRNA or increased GnRH release from GnRH neurones are observed after photostimulation may depend on the interaction between the drive on GnRH-I neurone function, which increases at the onset of puberty, and the inhibitory action of oestrogen produced locally in the hypothalamus.
mesh_terms: D000818:Animals; D002645:Chickens; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004967:Estrogens / Q000502:physiology*; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics*; D007031:Hypothalamus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009929:Organ Size / Q000187:drug effects; D010775:Photic Stimulation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012741:Sexual Maturation / Q000187:drug effects; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects