Gonadotropin-releasing hormone neurons: their structure and function.

The gonadotropin-releasing hormone (GnRH) neurons are essential for reproduction. GnRH neurons must release GnRH in a pulsatile pattern for optimal secretion of LH and FSH. In some species, GnRH surges actively evoke the preovulatory LH surge, while in others, GnRH secretion may be permissive. The GnRH neurons have a unique anatomy. The neurons develop, not from the ventricular epithelium like other CNS neurons, but migrate from the olfactory epithelium during fetal life. This feature provides a basis for the clinical link between olfactory and reproductive function and helps explain the atypical distribution of cells and variations in GnRH cell location noted across species. The diffuse organization of GnRH neurons has made the task of understanding the control of GnRH neurons by other CNS neurons more difficult. Recent evidence has helped discriminate influences that are permissive for GnRH release from those that direct changes in GnRH release.