Abstract
Pubertal onset is thought to be timed by an increase in pulsatile gonadotropin-releasing hormone (GnRH)/gonadotropin secretion in mammals. The underlying mechanism of pubertal onset in mammals is still an open question. Evidence accumulated in the last 15 years suggests that kisspeptin/neurokinin B/dynorphin A (KNDy) neurons in the hypothalamic arcuate nucleus play a key role in pubertal onset by triggering pulsatile GnRH/gonadotropin secretin in mammals. Specifically, KNDy neurons are now considered a part of GnRH pulse generator, in which neurokinin B facilitates and dynorphin A inhibits, the synchronized discharge of KNDy neurons in autocrine and/or paracrine manners. Kisspeptin serves as a potent secretagogue of GnRH secretion and thus its release is fundamental to pubertal increase in GnRH/gonadotropin secretion in mammals. Proposed mechanisms inhibiting Kiss1 (kisspeptin gene) expression during childhood to juvenile varies from species to species: we envisage that negative feedback action of estrogen plays a key role in the inhibition of Kiss1 expression in KNDy neurons in rodents and sheep, whereas estrogen-independent inhibition of kisspeptin secretion by γ-amino butyric acid or neuropeptide Y are suggested to be responsible for the pre-pubertal suppression of GnRH/gonadotropin secretion in primates. Taken together, the timing of pubertal onset is postulated to be controlled by upstream regulators for kisspeptin biosynthesis and secretion in mammals.
Highlights
The reproductive system is governed by the hypothalamo-pituitary-gonadal axis and has a unique functional quiescence during childhood in mammals
Increasing evidence suggests that hypothalamic kisspeptin [first named as metastin [25]] neurons play a key role in controlling pubertal onset via stimulation of gonadotropin-releasing hormone (GnRH)/gonadotropin secretion in mammals
Several lines of evidence suggest that the key players in this mechanism are arcuate nucleus (ARC) kisspeptin/neurokinin B/dynorphin A (KNDy) neurons, which serve as the GnRH pulse generator, regulate pulsatile GnRH/gonadotropin secretion and pubertal onset in mammals including rodents, ruminants, and primates
Summary
The reproductive system is governed by the hypothalamo-pituitary-gonadal axis and has a unique functional quiescence during childhood in mammals. Accumulating evidence suggests that pubertal onset is triggered by an increase in pulsatile secretion of GnRH/gonadotropins in several mammalian species [13,14,15,16]. Increasing evidence suggests that hypothalamic kisspeptin [first named as metastin [25]] neurons play a key role in controlling pubertal onset via stimulation of GnRH/gonadotropin secretion in mammals.
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