Abstract
Sexual differentiation of the brain is regulated by the action of steroid hormones on target tissues during critical periods. These periods are associated with peaks of testosterone secretion in males to differentiate the brain sexually. We determined whether the proliferation of the neural stem cells (NSCs) during critical period contribute to the formation of the sexually dimorphic nucleus (AVPv, SDN-POA, BSTpr, SCN, VMH and MePD) or not. Neonatal rats were treated with 5-bromo-2'-deoxyuridine (BrdU; 100 mg/kg) 12 h, 24 h and 36 h after birth because testosterone secretion peaks occur 2 h after birth. Neonatal rat brains were removed on postnatal day 3 (P3) and were processed for Nissl staining or immunohistochemistry for BrdU. We found that the number of BrdU-labeled cells in the BSTpr and MePD was significantly higher in males than in females, which may lead to sexual differentiation of the brain during the development. These results suggest that the sex difference in proliferation activity of NSCs in BSTpr and MePD may result in the difference in the nuclear volume in the BSTpr and MePD in adulthood. [Jpn J Physiol 55 Suppl:S214 (2005)]
