5-HT1 and 5-HT2 receptor activation reduces N-methyl-D-aspartate (NMDA)-stimulated LH secretion in prepubertal male and female rats

Abstract

OBJECTIVE: Excitatory amino acids and serotonin are involved in the control of gonadotropin secretion. The actions of these neurotransmitters are interconnected and recently we have reported that 5-HT(1) and 5-HT(2) receptor agonists blunted (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-stimulated GH secretion in prepubertal rats. The present experiments were carried out to analyze the effects of activation of different 5-hydroxytryptamine (5-HT) receptor subtypes on gonadotropin secretion and their role in the N-methyl-d-aspartate (NMDA)-stimulated LH release. DESIGN AND METHODS: We analyzed the gonadotropin secretion after manipulation of serotoninergic and aminoacidergic systems and their interactions in 5-, 16- and 23-day-old male and female rats. To this end, serum LH and FSH concentrations were measured in rats treated with 5-hydroxytryptophan methyl ester (5-HTP) (a precursor of 5-HT synthesis) plus Fluoxetine (Fx, a blocker of 5-HT reuptake), d,l-p-chlorophenyl-alanine methyl ester (PCPA, a blocker of 5-HT synthesis), R-(+)-8-hydroxydipropylaminotetralin hydrobromide (8-OH-DPAT, an agonist of 5-HT(1A) receptors), (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) and alpha-methyl-5-hydroxytryptamine (alpha-Me-5-HT, agonists of 5-HT(2) receptors), and 1-Phenylbiguanide (1-PHE an agonist of 5-HT(3) receptors). In addition, the effects of 8-OH-DPAT and DOI on NMDA-stimulated LH secretion were analyzed. RESULTS: Neither the activation nor blockade of the serotoninergic system modified LH secretion. Basal gonadotropin secretion remained unchanged in 23-day-old male and female rats after activation of 5-HT(1A), 5-HT(2) and 5-HT(3) receptors. The stimulatory effect of NMDA on LH secretion was blocked in both sexes after activation of the serotoninergic system, through specific 5-HT(1) and 5-HT(2) receptor agonists. CONCLUSIONS: Activation of serotoninergic receptors decreased the stimulatory effect of NMDA on LH secretion in prepubertal male and female rats.