Kisspeptin Cells in the Ovine Arcuate Nucleus Express Prolactin Receptor but not Melatonin Receptor

Abstract

Melatonin is secreted at night by the pineal gland and governs the reproductive system in seasonal breeders, such as sheep. The mechanism by which melatonin regulates reproduction is not known. The circannual rhythmicity of other factors, including prolactin, is also regulated by photoperiod via changes in melatonin secretion. In sheep, plasma prolactin levels are higher in the nonbreeding season than the breeding season. Kisspeptin, synthesised by neurones in the ovine arcuate nucleus (ARC) and preoptic area, is a key regulator of reproduction through stimulation of gonadotrophin-releasing hormone secretion and its expression in the ARC is reduced during the nonbreeding season. We hypothesi..