Metastin/kisspeptin and control of estrous cycle in rats

Estrous cyclicity is controlled by a cascade of neuroendocrine events, involving the activation of the hypothalamo-pituitary-gonadal axis. Two modes of gonadotropin-releasing hormone (GnRH) are well established to regulate the estrous cycle: one is a tonic or pulse mode of secretion which is responsible for the stimulation of follicular development and steroidogenesis; the other is a surge mode, which is solely responsible for the induction of luteinizing hormone (LH) surges, eventually leading to ovulation. Metastin/kisspeptin-GPR54 signaling has been suggested to control ovarian cyclicity through regulating the two modes of GnRH release. A population of metastin/kisspeptin neurons located in the anteroventral periventricular nucleus (AVPV) is considered to trigger GnRH surge and thus to mediate the estrogen positive feedback action on GnRH release. The other hypothalamic population of metastin/kisspeptin neurons is located in the arcuate nucleus (ARC) and could be involved in generating GnRH pulses and mediating negative feedback action of estrogen on GnRH release. GnRH neurons express mRNA for GPR54, a metastin/kisspeptin receptor, and have a close association with metastin/kisspeptin neurons at the cell body and terminal level, but the precise mechanism by which this peptide regulates the two modes of GnRH release needs to be determined. Metastin/kisspeptin, therefore, is a key hypothalamic neuropeptide, which is placed immediately upstream of GnRH neurons and relays the peripheral steroidal information to GnRH neurons to control estrous cyclicity.