Clock protein and hypothalamus-pituitary gonadal axis of female rodents

Abstract

The components of hypothalamus-pituitary-gonadal axis release their products in a circadian-temporal window; this is crucial for the reproductive success in either spontaneous or inducible ovulators. The preovulatory surge of luteinizing hormone (LH) is preceded by a hypersecretion of the gonadotrophin-releasing hormone (GnRH). In rodents, it is already known that the timed, preovulatory activation of GnRH-secreting neurons depends on a complex interacting neuroendocrine mechanism involving two cyclic signals: an ovarian estradiol rise in plasma levels during the follicular phase of the estrous cycle and a neural signal from the suprachiasmatic nuclei (SCN). Evidences supporting the hypothesis that the hypothalamic-pituitary axis function depends on the integrity of an autoregulatory loop of expression of clock proteins on each of its components are increasing. This review discusses these evidences