Minireview: Kisspeptin neurons as central processors in the regulation of gonadotropin-releasing hormone secretion

The Kiss1 gene encodes a family of peptides called kisspeptins, which bind to the G protein-coupled receptor GPR54. Kisspeptin(s) and its receptor are expressed in the forebrain, and the discovery that mice and humans lacking a functional GPR54 fail to undergo puberty and exhibit hypogonadotropic hypogonadism implies that kisspeptin signaling plays an essential role in reproduction. Studies in several mammalian species have shown that kisspeptins stimulate the secretion of gonadotropins from the pituitary by stimulating the release of GnRH from the forebrain after the activation of GPR54, which is expressed by GnRH neurons. Kisspeptin is expressed abundantly in the arcuate nucleus (Arc) and the anteroventral periventricular nucleus (AVPV) of the forebrain. Both estradiol and testosterone regulate the expression of the Kiss1 gene in the Arc and AVPV; however, the response of the Kiss1 gene to these steroids is exactly opposite between these two nuclei. Estradiol and testosterone down-regulate Kiss1 mRNA in the Arc and up-regulate its expression in the AVPV. Thus, kisspeptin neurons in the Arc may participate in the negative feedback regulation of gonadotropin secretion, whereas kisspeptin neurons in the AVPV may contribute to generating the preovulatory gonadotropin surge in the female. Hypothalamic levels of Kiss1 and GPR54 mRNA increase dramatically at puberty, suggesting that kisspeptin signaling could mediate the neuroendocrine events that trigger the onset of puberty. Together, these observations demonstrate that kisspep-tinGPR54 signaling in the brain serves as an important conduit for controlling GnRH secretion in the developing and adult animal.