Melatonin--a modulator of the GnRH/LH axis in sheep.

The nocturnal secretion of pineal melatonin provides information to vertebrates on changes in day length under the circumstances in which they live. In sheep, which are seasonal breeders, the secretion of melatonin is also a signal to the neural structures controlling the secretion of gonadotropins from the pituitary gland to drive their activity in accordance with the season of the year. The sites and mechanisms of melatonin action on GnRH/LH secretion has been the subject of intensive studies in the last decade. This article briefly reviews the most important discoveries and methods used in this research, which has led to a better understanding of the role of melatonin in the modulation of hypothalamo-pituitary-gonadotropic axis activity in sheep. The identification of melatonin receptors within the central nervous system and in the pars tuberalis of the pituitary gland, as well as the use of specific techniques of micro-implantation and micro-infusion were crucial in this aspect.