The role of nongonadal restraint of gonadotropin secretion in the delay of the onset of puberty in the rhesus monkey (Macaca mulatta).

The neuroendocrine basis underlying timing of the onset of puberty in rhesus monkeys is examined in this review. The immediate stimulus responsible for the initiation of the pubertal process originates within the central nervous system and is relayed to the pituitary-gonadal axis by an intermittent pattern of gonadotropin releasing hormone (GnRH) secretion, which is viewed as being generated by a neural oscillator resident within the hypothalamus. While results of recent studies in male rhesus monkeys suggest that this hypothalamic oscillator is fully functional by the neonatal stage of ontogeny, sexual maturity in this species is not attained until after 3 to 4 yr of prepubertal development. This protracted delay in the onset of puberty cannot be accounted for by the "gonadostat" hypothesis, which states that increased sensitivity of the hypothalamic GnRH oscillator to gonadal steroid feedback is an essential feature of the prepubertal inhibition of gonadotropin secretion, because orchidectomy during neonatal development does not interrupt the prepubertal suppression of LH and FSH secretion. Instead, it is suggested that the prolonged phase of prepubertal development in higher primates is occasioned by nongonadal restraint of the hypothalamic GnRH oscillator which, in monkeys, appears to be brought into play during the second to third month of extrauterine life and sustained until approximately 3 yr of age. While the identity of the nongonadal inhibition responsible for the prepubertal quiescence of the neural oscillator governing pulsatile GnRH secretion remains to be determined, it does not appear to involve either the pineal or the adrenal.