Neurobiological mechanisms of puberty in higher primates

Puberty in humans is comprised of two developmental processes; namely, gonadarche and adrenarche. Of the two, gonadarche is fundamentally the most important, and this review examines the neurobiological mechanisms that first prevent, and later trigger, progression into this critically important phase of human development when the ability to first reproduce is established. The review draws extensively upon results obtained by studies of the rhesus monkey (Macaca mulatta), a representative higher primate which, like man, exhibits a postnatal pattern in activity of the hypothalamic-pituitary-gonadal axis that is characterized by a prolonged period of relative quiescence from late infancy until the initiation of the pubertal process. The proximate cause of the prepubertal quiescence in this neuroendocrine axis is the arrest or restraint of the pulsatile mode of hypothalamic GnRH release by a neurobiological brake that holds in check release of this decapeptide, without seeming to down-regulate the transcriptional activity of the gene encoding GnRH (GnRH-I). Thus, if neurogenomes control the onset of gonadarche, they must reside upstream from that of the GnRH neuron. The genetic and physiological factors (with a particular emphasis on leptin) that time the application and duration of the prepubertal brake on GnRH release are also considered.