Neurophysiology of puberty

Abstract

Puberty is the stage of development during which an individual first becomes capable of reproducing sexually and is characterized by maturation of the genital organs, the development of secondary sexual characteristics, and changes in mood and behavior. Although puberty is a phase of development, an introduction to the neurophysiology of the process is facilitated by a review of the essential features of the central neural control of the ovary and testis in the adult. In sexually mature individuals, the processes of ovulation, spermatogenesis, and sex steroid production are regulated by the pituitary gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH). The synthesis and secretion of the pituitary gonadotropins, in turn, are governed by the brain peptide gonadotropin-releasing hormone (GnRH), which is secreted by nerve terminals in the base of the forebrain into a specialized portal circulation subserving the pituitary gland. GnRH is not secreted continuously into the portal vasculature but instead is released as intermittent discharges with a frequency of approximately one pulse every 1 to 3 h. This pulsatile mode of GnRH release by the brain is absolutely essential for sustained gonadotropin secretion, and when GnRH stimulation of the pituitary is continuous, LH and FSH release is greatly reduced. As may be predicted from the foregoing considerations, if pulsatile secretion of GnRH by the brain of men and women is interrupted, as may be the case in highly trained ballerinas and female athletes or severely undernourished individuals, pituitary gonadotropin secretion is impaired and gonadal function arrested. Thus, the GnRH pulse-generating mechanism in the brain occupies a position of primacy in the control of reproduction in the adult. Moreover, the proximal trigger activating the pituitary gonadal axis at puberty is an increase in pulsatile GnRH release in association with a modest increase in the drive to express the gene encoding this neuropeptide. For the foregoing reasons, a consideration of the mechanisms underlying the pulsatile secretion of this brain hormone in the adult provides a point of departure for a discussion of the neurophysiology of puberty.