中文摘要：

目的：研究正常年轻和中老年组雌雄性大鼠大脑白质及白质内有髓神经纤维之间的性别差异，并探讨大脑发育过程中性别差异随年龄增加的改变。方法：运用透射电子显微镜和体视学方法对6～8月龄的年轻Long—Evans大鼠及18月龄同种中老年大鼠大脑白质及其有髓神经纤维进行定量研究。结果：年轻组雄性大鼠大脑白质、有髓神经纤维及其髓鞘的总体积均显著大于雌性，而中老年组雌性大鼠大脑白质、有髓神经纤维体积密度、有髓神经纤维及其髓鞘的总体积均显著大于雄性。结论：年轻组及中老年组大鼠大脑白质、白质内有髓神经纤维及其髓鞘总体积均存在性别差异，随着年龄的增长，雄性大鼠大脑白质及白质内有髓神经纤维体积的减少较雌性更为明显。

英文摘要：

Objective： To investigate differences of the white matter and its myelinated fibers in the normal young and middleaged Long-Evans rats between female and male groups and to figure out the effects of aging on the sex differences in the white matter of Long-Evans rats. Methods： 10 young Long-Evans rats （5 female and 5 male; aged, 6-8 months） and 9 aged Long-Evans rats （5 female and 4 male; aged, 18 months） were used for quantitative analysis of the white matter and the myelinated fibers of it using transmission ：electron microscopic technique and stereological methods. Results： The white matter volume and the volume of the myelinated fibers and the myelin sheathes in the white matter of young male rats were significantly bigger than those of young female rats. However, the white matter volume, the volume density of the myelinated fibers in the white matter and the total volume of the myelinated fibers and myelin sheathes in the white matter of aged female rats were significantly bigger than those of middle-aged male rats. Conclusion： There was sexual dimorphism in the white matter volume and the volume of the myelinated fibers and the myelin sheathes in the white matter both in young and middle- aged Long-Evans rats. Age-related decrease in the white matter volume and the myelinated fiber volume in the white matter of male Long-Evans rats were more prominent than those of female Long-Evans rats.