Dorsal and medial raphe nuclei participate differentially in reproductive functions of the male rat

Innervation of the hypothalamus and median eminence arise from the dorsal and medial raphe nuclei (DRN and MRN, respectively). The hypothalamus regulates the secretion of gonadotropins, which in turn regulate the reproductive function of males and females. However, it is not known the role of raphe nuclei in male reproductive function. Our goal was to investigate the role of the DRN and MRN in the regulation of the testicular function and secretion of gonadotropins in prepubertal rats. Dihydroxytryptamine (5,6-DHT) in ascorbic acid was used to chemically lesion the DRN or MRN. Rats were treated at 30 days-of-age and sacrificed at 45 or 65 days-of-age. Sham-treated controls were injected with ascorbic acid only. Negative controls were untreated rats. The damage induced by the 5,6-DHT was monitored in coronal serial sections of DRN and MRN; only the animals in which lesion of the DRN or MRN was detected were included in this study. As output parameters, we measured the concentrations of noradrenaline (NA), dopamine (DA) and serotonin (5-HT) in the anterior (AH) and medial (MH) hypothalamus by high performance liquid chromatography (HPLC); whereas, circulating concentrations of gonadotropins and sexual steroids were measured by radioimmunoassay. Seminiferous epithelium and sperm quality were also evaluated. Lesion of DRN or MRN does not induced changes in concentrations of LH, progesterone, and testosterone. Compared with the control group, the sham or lesion of the DRN or MRN did not modify noradrenaline or dopamine concentrations in the AH and MH at 45 or 65 days of age. Meanwhile, serotonin concentrations decreased significantly in lesioned rats. Lesion of DRN induced significantly lower concentrations of FSH regardless of age; similar lesion in the MRN had no impact on FSH levels. Sperm concentration and motility were significantly decreased in the same animals. The lesion of the MRN does not induced changes in the seminiferous epithelium or gonadotropin levels. Our results suggest that raphe nuclei regulate differentially the male reproductive functions. The DRN but not the MRN regulates the secretion of gonadotropins and testicular function.