Effect of lactation on the expression of gonadotropin-inhibitory hormone in dorsomedial and paraventricular nuclei of the rat hypothalamus

Introduction: Gonadotropin inhibitory hormone (GnIH) is believed to be an inhibitor of gonadotropin releasing hormone (GnRH) secretion. The role of GnIH in lactational inhibition of gonadotropin secretion is not well known therefore, the aim of the present study was to evaluate the effect of lactation on expression of GnIH in these nuclei of lactating and non-lactating rats. Methods: Ten postpartum rats of the Sprague-Dawley strain were randomly allotted into two groups. The number of pups was adjusted to five pups per suckling female, while the control non-lactating rats were separated from their pups immediately upon parturition. The lactating rats were allowed to suckle their pups for eight days. The number of GnIH neurons in the dorsomedial (DMH) and paraventricular (PVN) nuclei was estimated using an immunohistochemical method. Results: The number of GnIH neurons in DMH (P=0.005) and PVN (P=0.001) of lactating rats were significantly higher than those of the non-lactating rats. Moreover, fibers of GnIH neurons were observed in anteroventral periventricular nucleus (AVPV) in lactating rats. Conclusion: Lactation increased GnIH expression in DMH and PVN of the lactating rats, and thus may have a role in inhibiting GnRH and subsequently LH secretion during the lactation period.