ReviewControl of GnRH secretion: One step back

The reproductive system is controlled by gonadotropin releasing hormone (GnRH) secretion from the brain, which is finely modulated by a number of factors including gonadal sex steroids. GnRH cells do not express estrogen receptor α, but feedback is transmitted by neurons that are at least 'one step back' from the GnRH cells. Modulation by season, stress and nutrition are effected by neuronal pathways that converge on the GnRH cells. Kisspeptin and gonadotropin inhibitory hormone (GnIH) neurons are regulators of GnRH secretion, the former being a major conduit for transmission of sex steroid feedback. GnIH cells project to GnRH cells and may play a role in the seasonal changes in reproductive activity in sheep. GnIH also modulates the action of GnRH at the level of the pituitary gonadotrope. This review focuses on the role that kisspeptin and GnIH neurons play, as modulators that are 'one step back' from GnRH neurons.

Research highlights► Kisspeptin cells express estrogen and progesterone receptors and relay feedback to GnRH cells. ► Kisspeptin cells also produce dynorphin and neurokinin B, which regulate GnRH cells. ► Gonadotropin inhibitory hormone (GnIH) negatively regulates GnRH cells. ► GnIH is a powerful negative regulator of pituitary gonadotropes. ► GnIH increases feeding; it may be a molecular switch for reproduction vs feeding.