In order to evaluate the involvement of gonadotropin-releasing hormone (GnRH) in the effects of neuroexcitatory amino acids on luteinizing hormone (LH) secretion, N-methyl-D,L-aspartate (NMDA; 30 mg/kg s.c.) was administered to 50-day-old male rats. The in vitro release of GnRH from the hypothalamus showed a maximal increase (4.6-fold) in animals sacrificed 7.5 min after NMDA injection, while serum LH levels rose concomitantly. Incubation of rat hypothalami in vitro with kainate or NMDA concentrations > 0.1 mM resulted in a dose-related release of GnRH, NMDA being twofold more potent than kainate. Quisqualate (10 mM) did not affect the release of GnRH. On a molar basis, quinolinate (50 mM), a possible endogenous ligand for NMDA receptors, was the most effective in inducing GhRH secretion (34.9 ± 4.9 pg/7.5 min, mean increment ± SEM, n= 10). The effects of kainate and NMDA were mediated through different types of receptors, since GnRH response to kainate was unchanged in the absence of glycine or in the presence of increased concentrations of Mg²⁺ (2 mM) or Ca²⁺ (5.8 mM). In contrast, the GnRH response to NMDA was reduced by Ca²⁺ (5.8 mM) and abolished in the absence of glycine or in the presence of Mg²⁺ (2 mM). In addition, DL-amino-5-phosphonopentanoic acid (AP5), a competitive antagonist of NMDA receptors, prevented the NMDA-induced release of GnRH. The permissive effect of glycine on GnRH response to NMDA was 2.7-fold more important using glycine concentrations of 0.01 µM than when concentrations >100 µM were used. Intermittent incubation with NMDA in vitro (every other 7.5-min period) did not affect the amplitude of GnRH response, while continuous exposure to NMDA resulted in an initial and transient increase in GnRH release followed by a prolonged desensitization period. It is concluded that different neuroexcitatory amino acids acting through distinct receptor types may be involved in the hypothalamic control of LH release by regulating the secretion of GnRH.