Effects of ovarian steroids on the gonadotropin response to N-methyl-D-aspartate and on hypothalamic excitatory amino acid levels during sexual maturation in female rats.

In order to evaluate the involvement of estrogen-progesterone (EP) in the effects of N-methyl-D-aspartate (NMDA) receptor stimulation on gonadotropin secretion during sexual development in female rats, NMDA (30 mg/kg sc) was administered to 16- and 30-day-old female rats pretreated with EP. NMDA administration induced increases in plasma LH concentration that were 13.6-fold and 94.5-fold higher, respectively, than those found after NMDA alone. The increase of LH levels induced by NMDA was accompanied by a significant enhancement of the content of GnRH in the anterior and preoptic hypothalamic areas and in the medial basal hypothalamus (APOA/MBH). EP potentiated this increase of GnRH induced by NMDA. NMDA increased plasma FSH levels at 16 days of age, and this increase was inhibited by EP treatment. In 30-day-old rats EP induced FSH release in response to NMDA. This release was not observed in rats treated only with NMDA. In 16-day-old rats EP induced an increase in the concentrations of aspartate, glutamate, and glycine in the anterior and preoptic hypothalamic areas and in the medial basal hypothalamus, the excitatory amino acids involved in NMDA neurotransmission. This effect was not observed in rats of 30 days of age. In summary, the present results show that during sexual maturation ovarian steroids potentiated the LH-releasing response to NMDA probably by acting at the hypothalamic level; furthermore, during sexual maturation there are changes in the response to EP of the hypothalamic concentrations of excitatory amino acids. These findings could be related to the neuroendocrine mechanisms regulating the onset of puberty and the sexual cycle in female rats.