Monosodium L-glutamate (MSG), as a neurotoxin, was administered subcutaneously at a dose of 4 mg/g body weight to rat pups on days 1 and 3 postnatally. The sexual receptivity expressed as lordosis quotient (LQ) in MSG-treated female rats (2.5 months old) was significantly lower than that of the normal female ones, and this poor sexual receptivity of MSG-treated females could be improved by pinealectomy at the age of six weeks. In order to investigate the relationship between the inhibitory role of the pineal gland and the extrahypothalamic inhibitory pathway, normal control and MSG-treated rats were ovariectomized and implanted subcutaneously with estradiol capsule (20% estradiol benzoate, in 2mm silastic tube) at the age of 2.5 months. Three days after implantation, sexual receptivity was observed. Then, the anterior roof deafferentation (ARD) was preformed one week later and the sexual receptivity in both groups was compared again. The results showed that there was no significant difference of the lordosis response between the MSG-treated and the control groups before ARD, and the level of restoration by ARD in LQ of MSG-treated rats was similar to that of the control group. It seems that the extrahypothalamic inhibitory pathway of sexual receptivity may not be influenced by neonatal MSG-treatment. Our previous results indicated that the behavioral sensitivity to estradiol was altered by ARD. However, in the present study, the lordosis responses of MSG-treated and pinealectomized female rats were not significantly different from that of the control group after ovariectomy and exogenous estradiol implantation. This means that the behavioral sensitivities to estradiol were not changed by MSG-treatment or pinealectomy.(ABSTRACT TRUNCATED AT 250 WORDS)