Chapter 28 - Physiology of the Gonadotropin-Releasing Hormone Neuronal Network

Abstract

This chapter discusses the functioning of the gonadotropin-releasing hormone (GnRH) neuronal network under normal physiological conditions in reproductively mature adults. The GnRH neuronal network consists of GnRH neurons and associated assembly of brain cells responsible for controlling GnRH release into the pituitary portal circulation. The GnRH neuronal network integrates multiple internal homeostatic and external factors to achieve levels of fertility appropriate to the organism. The unique developmental origins of GnRH neurons and their subsequent migration into brain enable the GnRH cell bodies to reside as a scattered “continuum” along their migratory pathway within the mammalian forebrain. The GnRH cell bodies can be found to reside anywhere along an axis extending from the olfactory bulbs to the medial septal nuclei, diagonal band of Broca, and medial preoptic area through the mediobasal hypothalamus (MBH). This distribution is sometimes referred to as the “inverted Y” pattern, whereby the bottom of the “Y” is the rostral-most midline GnRH soma in the medial septum. Although this continuum appears to exist in all mammalian species, there are species differences in the locations along this pathway at which most GnRH neurons come to reside.