Neuroendocrine changes characteristic of sexual maturation.

A general scheme of neuroendocrine factors influencing the onset of puberty is presented. Gonadotropin-releasing hormone (GnRH) is secreted in pulsatile fashion by the arcuate nucleus of the hypothalamus. Amplitude and probably frequency of the secretory pulses of GnRH increase at the time of puberty, stimulating the secretion of pituitary gonadotropins (LH and FSH). In turn, the gonadotropins induce the maturation of the ovarian follicles in the girls, spermatogenesis in the boys, and the secretion of estradiol or testosterone. The increase of the pulsatile secretion of GnRH is sufficient for explaining the onset of puberty. The response of the pituitary gonadotropins to GnRH would depend on the presence of sex steroids through the feedback mechanisms. The secretion of GnRH may be influenced by neurotransmitters. Norepinephrine, epinephrine and dopamine would stimulate GnRH secretion. Such effect, in fact, depends on the steroid milieu. Opposite effects can be observed in absence of estradiol. Serotonin has a negative effect on the GnRH secretion. Melatonin appears also to block GnRH secretion at the time of puberty. Finally, beta-endorphins decrease the frequency of GnRH secretion only in the presence of steroids. It is probable that stress and underweight act in blocking the pubertal development through the action of neurotransmitters, in particular catecholamines and beta-endorphins.