Potential functions of gonadotropin inhibitory hormone and dynorphin in broiler breeder reproduction
Stephens, Ashley Gera-Ann
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Broiler breeders given free access to feed can reach their ideal bodyweight for reproduction by 5 weeks of age, but functional sexual maturation of the brain does not occur until about 20 weeks of age. To match the ideal bodyweight for reproduction with brain-based sexual maturation, broiler breeders are severely feed restricted, and this optimizes their reproduction relative to that achieved if they are fed ad libitum. However, feed restriction management programs for broiler breeders result in fasting periods during which caloric insufficiency signals can negatively impact reproductive development and efficiency. The hormonal signal pathways activated by fasting are not well delineated in avian species. However, based on mammalian research and preliminary avian research, gonadotropin inhibitory hormone (GnIH), the gonadotropin inhibitory hormone receptor (GnIH-R), dynorphin, translated from the preprodynorphin (Pdyn) mRNA transcript, and dynorpin’s receptor, the kappa opioid receptor (KOR), may be key hormonal participants. Therefore, the mRNA expression of GnIH, GnIH-R, Pdyn, and KOR was investigated in the pituitary and follicular tissues of broiler breeder hens that had been fed daily or fasted for 72 hours. Expression of the transcripts of interest was also investigated in F1, F3, and small yellow follicle granulosa cells cultured with gonadotropins (LH and FSH) and steroid hormones (estrogen and testosterone). GnIH, GnIH-R, Pdyn, and KOR mRNA was detected in pituitary tissues, but only GnIH mRNA expression was significantly increased after 72 hours of fasting. GnIH mRNA was not detected in the follicular tissues of fed or fasted hens, but the mRNA transcripts for GnIH-R, Pdyn, and KOR were detected in fed and fasted follicular tissues. In freshly isolated granulosa cells from the F1 or F3 follicles, GnIH-R mRNA was not detected, but once the cells were cultured for 24 hours, expression of the mRNA for GnIH-R was induced, and LH and FSH do not prevent this induction. The results suggest that both the GnIH and dynorphin neuropeptide systems could play a role in follicular development both centrally and locally, and that increased production of pituitary GnIH during caloric insufficiency may be a key regulator in down regulating reproduction function during fasting.