Similar numbers of neurons are generated in the male and female rat preoptic area in utero.

The birth date of neurons comprising the sexually dimorphic nucleus of the rat preoptic area (SDN-POA) was determined by bromodeoxyuridine (BrdU) injections at a prescribed time during the embryonic period. Calbindin immunostaining was used as a marker to identity the SDN-POA. The animals were bred from dams injected with BrdU on days 14, 16 or 18 of pregnancy (fertilization defined as day 1). On day 15 after birth (PD), all offspring were euthanized and brain sections were prepared for histology. Neurogenesis in the SDN-POA began around embryonic day (ED) 14 and culminated on ED 18, whereas the preoptic neurons surrounding the SDN-POA generated earlier than did those of the SDN-POA. Although the SDN-POA was significantly larger in males than in females at PD15, the total numbers of neurons comprising the SDN-POA were not significantly different between sexes. Similar aggregates of somatostatin mRNA-positive cells in the central portion of the SDN-POA were observed in both sexes at PD8. On PD15, the aggregates became scattered in males, whereas the aggregates in females remained congested. These data suggest that sexual dimorphism in the SDN-POA results from male-specific postnatal radial spreading of cells rather than cell proliferation during embryonic neurogenesis.
(2010 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.)