[Hypothalamic neuropeptides and control of GnRH neurones. Neuroanatomical study in the ewe]

Reproduction in mammals is directly controlled by GnRH neurons. These neurons are regulated by many external and internal factors, among which sexual steroids, in particular oestradiol, play an important part. However the mechanisms through which these steroids regulate GnRH secretion are largely unappreciated, and the neurochemical identity of central neurons liable to transmit the steroidal information to GnRH neurons is not completely clarified. Many functional neuroanatomy studies have been carried out on the ovine model, which is particularly favorable to understand the neuroendocrine mechanisms controlling reproduction. These studies have brought about the identification of some of the potential actors in this regulation. The present review reports the major results concerning two recently discovered neuropeptides, galanin and kisspeptin, which appear to be major actors in integration of signals regulating reproduction, among which steroids. These results have revealed the major interaction sites between neurons expressing these neuropeptides and GnRH neurons.