An updated model to describe the neuroendocrine control of reproduction in chickens

• Reproduction in chickens is under dual inhibitory/stimulatory control by GnIH/GnRH.
• Melatonin regulation of GnIH mediates photoperiodic and circadian reproduction.
• GnIH serves as a metabolic switch during the activation of reproduction in chickens.

Since its first identification in quail 15 years ago, gonadotropin inhibitory hormone (GnIH) has become a central regulator of reproduction in avian species. In this review, we have revisited our original model published in 2009 to incorporate recent experimental evidence suggesting that GnIH acts as a molecular switch during the integration of multiple external and internal cues that allow sexual maturation to proceed in chickens. Furthermore, we discuss the regulation of a dual inhibitory/stimulatory control of the hypothalamo-pituitary–gonadal axis involving the interaction between GnIH and gonadotropin releasing hormone (GnRH). Finally, beyond seasonality, we also propose that GnIH along with this dual control may be responsible for the circadian control of ovulation in chickens, allowing eggs to be laid in a synchronized manner.