The opioid system and excitatory amino acids in the onset of puberty in female rats.

The control of sexual maturation by the hypothalamus is incompletely understood. The activation and/or removal of inhibition of gonadotropin-releasing hormone (GnRH) secretion at puberty involves several neurotransmitters. Excitatory amino acids (EAA), such as L-glutamic acid (L-GLU), may increase gonadotropin secretion acting on N-methyl-D-aspartate (NMDA) and non-NMDA receptors. Endogenous opiates peptides (EOP) play an inhibitory role on gonadotropin secretion, and the opiate antagonist naloxone (NAL) increases serum LH levels. We tested the effect of drugs acting on the opiate and EAA systems. We treated prepubertal rats with intraperitoneal injections of NAL, NMDA antagonist dextromethorphan (DMT) and non-NMDA antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX), alone and in combinations among them. The onset of puberty was assessed by the vaginal opening (VO). Female Wistar rats (25 days old), weaned at 21 days of age, were randomly assigned to one of seven groups (15 rats each). The groups were treated with 1) DMT (18 mg/kg b.w.), 2) DNQX (17 micrograms/kg), 3) NAL (0.5 mg/kg), 4) NAL plus DMT, 5) NAL plus DNQX, 6) DMT plus DNQX and 7) control vehicle: distilled water). The age at VO among groups was significant by survival time analysis (x2 = 15.18, p = 0.018). Analysis of covariance controlling for weight and length at 21 days showed that the groups treated with NAL alone (p = 0.003) or combined with DMT (p = 0.012) and DNQX (p = 0.005) had earlier age at VO. NMDA and non-NMDA antagonist used alone or combined were not different from the control group.(ABSTRACT TRUNCATED AT 250 WORDS)