Unilateral lesion of the suprachiasmatic nucleus impairs estradiol feedback, follicular development, estrous cycle and ovulation.

Abstract

Ovulation is timed by neural signals originating at the suprachiasmatic nucleus (SCN) that trigger ovulation when converge with high estradiol levels, which indicates the maturation of ovarian follicles. We have shown that the hypothalamic regulation of ovulation is asymmetrical and we hypothesized that the paired SCN could contribute to such symmetries. We unilaterally lesioned the SCN of rats at each stage of the estrous cycle and evaluated the acute effects on the progression of their estrous cycle, follicular development and ovulation. Lesions disrupted the estrous cycle when performed in estrus/metestrus but not in diestrus/proestrus. Abnormalities in follicular development were observed in the non-ovulating lesioned rats and this was independent of the side of the SCN destroyed and the stage of the cycle when surgery was performed. Groups of lesioned rats were then hormonally primed with GnRH or estradiol to assess the neuroendocrine pathway altered by the treatment. GnRH restored ovulation, suggesting that both SCN are needed for proper triggering of the preovulatory surge of GnRH and that unilateral lesion does not impair the sensitivity of the pituitary or the ovary to GnRH and gonadotropins, respectively. Estradiol was asymmetrically effective to restore ovulation in rats lesioned in estrous, partially effective on rats operated at diestrus and ineffective on metestrus. Our results indicate that the SCN regulates the activity of the hypothalamic-pituitary-ovarian axis not only by modulating the preovulatory surge of GnRH/gonadotropins, but also by promoting the hypothalamic integration of estrogenic signals from the ovaries in an asymmetric and stage-dependent fashion.