title: Ovarian steroid withdrawal results in GABAAreceptor upregulation in the photoperiodic neuroendocrine pathways of the turkey hen.
abstract: The mechanism(s) underlying photorefractoriness in temperate zone seasonally breeding birds remains undetermined. Our recent findings reveal a link between the upregulation of GABAAreceptors (GABAARs) in the premammillary nucleus (PMM) and the state of photorefractoriness. Gonadal steroid levels fluctuate during the breeding season; increasing after gonadal recrudescence and declining sharply once gonadal regression begins. Here, we examined the effect of gonadal steroid withdrawal on the expression of GABAARs in the turkey PMM. Exogenous ovarian steroids were administered and then withdrawn from turkey hens to mimic the decline of ovarian steroids levels at the end of a breeding season. The upregulation of GABAAR α3, α4, δ, π, and γ2-subunits was observed in the PMM of the steroid withdrawal group when compared to the non-steroid treatment group. The level of tyrosine hydroxylase, photopigment melanopsin, and circadian clock genes in the PMM of the steroid withdrawal group resembled the levels observed in the natural photorefractory hens and were significantly lower than those of the short-day light stimulated group. A reduction in gonadotropin-releasing hormone-I mRNA expressed within the nucleus commissurae pallii was also observed in hens undergoing steroid withdrawal. These results suggest that the natural decline in circulating ovarian steroid levels may modulate the GABAergic system in the PMM through the upregulation of GABAAreceptors. This, in turn, could diminish the reproductive neuroendocrine responses to light and favor a condition resembling the state of photorefractoriness.
authors.affiliation: Department of Animal Science, University of Minnesota, Saint Paul, MN 55108, USA.
authors.forename: Voravasa
authors.initials: V
authors.lastname: Chaiworakul
authors.affiliation: Department of Animal Science, University of Minnesota, Saint Paul, MN 55108, USA.
authors.forename: Sunantha
authors.initials: S
authors.lastname: Kosonsiriluk
authors.affiliation: Department of Animal Science, University of Minnesota, Saint Paul, MN 55108, USA.
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Mauro
authors.affiliation: Department of Animal Science, University of Minnesota, Saint Paul, MN 55108, USA. Electronic address: elhal001@umn.edu.
authors.forename: Mohamed E
authors.initials: ME
authors.lastname: El Halawani
mesh_terms: D000818:Animals; D005260:Female; D009490:Neurosecretory Systems / Q000378:metabolism*; D010053:Ovary / Q000378:metabolism*; D017440:Photoperiod; D011963:Receptors, GABA-A / Q000235:genetics*; D013256:Steroids / Q000737:chemistry*; D014422:Turkeys; D015854:Up-Regulation
chemical_list: D011963:Receptors, GABA-A; D013256:Steroids
keywords: GABA(A) receptor; Gamma-aminobutyric acid; Ovarian steroid withdrawal; Photorefractoriness; Premammillary nucleus; Seasonally breeding birds