Neural control of ovulation.

Abstract

Pituitary gonadotrophin function is controlled to a great extent by the central nervous system and by the feedback action (positive and negative) of sex steroids. Neural structures involved in this mechanism may be divided into two levels. The first level is represented by the nervous structures releasing gonadotrophin-releasing hormone (GnRH) in a pulsatile manner into the portal circulation. The gene encoding the precursor protein for GnRH has been described recently. The precursor protein appears to be composed of 92 amino acids, in which the GnRH decapeptide is preceded by a signal peptide and followed by a peptide termed GAP for GnRH-associated peptide. The GnRH-synthesizing neurones and the nervous structures synchronizing the GnRH discharge (pulse generator) in the monkey, and probably also in the human, reside in the medial basal hypothalamus, which appears to have a highly integrated structure. The GnRH pulse generator is influenced by nervous structures outside the medial basal hypothalamus (second level of control) as well as by ovarian and other hormones. These influences probably impinge directly or indirectly on the hypothalamic oscillator. Concerning the chemical nature of the substances mediating the action, a large number of neurotransmitters and neuropeptides have been reported to influence GnRH secretion.