THE FACILITATORY EFFECT OF N-METHYL-D-ASPARTATE ON SEXUAL RECEPTIVITY IN FEMALE RATS THROUGH GNRH RELEASE

The purpose of this study was to examine whether N-methyl-D-aspartate affects the sexual receptivity of female rats. Monosodium L-glutamate was used as a neurotoxin to induce hypogonadal status. Matured normal and monosodium L-glutamate-treated rats were ovariectomized and implanted subcutaneously with estradiol capsules. One week later, lordosis responsiveness was observed before and 10 min after N-methyl-D-aspartate (40 mg/kg of BW, ip) administration. The results showed that N-methyl-D-aspartate caused a remarkable increase of lordosis quotient in control rats but not in monosodium L-glutamate-treated rats. Moreover, the possible action site of N-methyl-D-aspartate in the enhancement of receptivity was evaluated by the post-castrational LH rise, pituitary LH release in response to GnRH, and N-methyl-D-aspartate-evoked GnRH releasability. The results revealed that: (a) serum levels of LH in monosodium L-glutamate-treated rats were lower (p < 0.01) than those of control rats after ovariectomy; (b) there was no significant difference of pituitary LH release responsiveness to GnRH test between two groups; and (c) N-methyl-D-aspartate-evoked LH release in monosodium L-glutamate-treated rats was similar to that in the control rats. In conclusion, N-methyl-D-aspartate may facilitate the sexual receptivity through stimulating GnRH release. The failure of N-methyl-D-aspartate in enhancing receptivity in monosodium L-glutamate-treated rats is probably due to the cellular damage by monosodium L-glutamate on specific areas responsible for lordosis.