Median Raphe Nucleus of adult rat: sexual dimorphism and effects of female gonadal steroid deprivation

During the last decades it is shown that the gonadal steroids affects the nervous system. Gonadal steroids easily cross the brain blood barrier and insert their effects on morphometric parameters of the certain areas of the mammalian brain despite their direct or indirect roles in sexual behavior, the effects that generally called sexual dimorphism (SD). Among the different brain neurotransmitter system, serotonergic system is of more inertest to study for SD due to its extensive projections and the role of its neurotransmitter, serotonin (5HT), in different physiological and pathological conditions including neuronal firing, human emotional control, and affective disorders. Although the fact that 5HT is affect by the sexual gonadal steroids, it is not known whether the nuclei related to this system also influenced by gonadal hormones. Median raphe nucleus (MRN) is the largest one among the other nuclei in human brain and involves in many important functional roles. There are not enough evidences regarding the SD in median raphe nucleus of mammalian brain and also the influence of gonadal steroids on its morphometric parameters. The present study was supposed to answer the mentioned doubtfully questions. Sixty adult male and female Sprague-Dawelly rats (200-230g) were used in this study. The animals randomly were divided to four groups including normal female group, normal male group, ovariectomized group (OVX) and sham surgery group. For SD the animals of normal male and female groups were compared and for the study of the effects of female gonadal steroids the normal female group compared with OVX group. The animals perfused and fixed transcardially, brain stem was removed, coronal sections were obtained and processed for light microscopic study. Nissl and Golgi staining used for study morphometric and neuronal morphologic parameters of MRN. Data analyzed and the results presented by means± SD. Based on our findings MRN showed sexual dimorphism and gonadal steroid deprivation via ovariectomy significantly influenced certain morphometric parameters of MRN. According to the results of this study, sexual dimorphism of MRN and the influence of female gonadal steroids on serotonergic nuclei should consider in normal and pathological conditions.