Kisspeptin is essential in reproduction and acts by stimulating neurones expressing gonadotrophin-releasing hormone (GnRH). Recent studies suggest that kisspeptin has multiple roles in the modulation of neuronal circuits in systems outside the hypothalamic-pituitary-gonadal axis. Our recent research using in?situ hybridisation (ISH) clarified the histological distribution of Kiss1r (Gpr54)-expressing neurones in the rat brain that were presumed to be putative targets of kisspeptin. The arcuate nucleus (ARN) of the hypothalamus is one of the brain regions in which Kiss1r expression in non-GnRH neurones is prominent. However
the characteristics of Kiss1r-expressing neurones in the ARN remain unclear. The present study aimed to determine the neurochemical characteristics of Kiss1r-expressing neurones in the ARN using ISH and immunofluorescence. We revealed that the majority (approximately 63%) of Kiss1r-expressing neurones in the ARN were pro-opiomelanocortin (POMC) neurones
which have an anorexic effect in mammals. Additionally
a few Kiss1r-expressing neurones in the dorsal ARN are tuberoinfundibular dopamine (TIDA) neurones
which control milk production by inhibiting prolactin secretion from the anterior pituitary. TIDA neurones showed a relatively weak Kiss1r ISH signal compared to POMC neurones
as well as low co-expression of Kiss1r (approximately 15%). We also examined the expression of Kiss1r in neuropeptide Y and kisspeptin neurones
which are reported to arise from POMC-expressing progenitor cells during development. However
the vast majority of neuropeptide Y and kisspeptin neurones in the ARN did not express Kiss1r. These results suggest that kisspeptin may directly regulate energy homeostasis and milk production by modulating the activity of POMC and TIDA neurones
respectively. Our results provide an insight into the wide variety of roles that kisspeptin plays in homeostatic and neuroendocrine functions.
