The purpose of this study was to examine the effect of pinealectomy and the possible mechanism of the pineal gland on N-methyl-D-aspartate (NMDA)-associated receptivity in female rats. Monosodium L-glutamate (MSG) was used as a neurotoxin to induce hypogonadal status. Long-Evans rats were divided into four groups: (1) control (C), (2) pinealectomized (Px), (3) MSG-treated (MSG) and (4) pinealectomized MSG-treated (Px-MSG). Two injections of MSG were administered on the first and the third days postnatally with a dose of 4 mg/g body weight. Pinealectomy was performed at six weeks of age. In the first part of the experiment, all four groups of rats were ovariectomized at 3.5 months and implanted subcutaneously with a 2mm silastic capsule filled with 20% estradiol benzoate (EB). One week later, the sexual receptivity was estimated by lordosis quotient (LQ) before and ten minutes after 20 mg/kg B.W. NMDA administration. The result shows that NMDA caused a remarkable increase of LQ in control rats, but no significant effect on MSG-treated rats. There was no significant difference between control and Px rats before NMDA administration, but Px rats exhibited higher LQ than control rats after NMDA treatment. In the second part of the experiment, the effect of pinealectomy on releasability of LHRH neurons was examined indirectly by NMDA-evoked LH secretion. The dosage and sampling schedule were chosen by the dose-response and time course of LH response to NMDA, respectively. Serum samples were collected before and ten minutes after NMDA administration. Serum concentration of LH was measured by radioimmunoassay.(ABSTRACT TRUNCATED AT 250 WORDS)