中文摘要：

目的进一步认识大鼠大脑海马内有髓神经纤维髓鞘的老年性改变。方法将16只雌性Long-Evans大鼠分为青年组（6月龄）5只、中老年组（18月龄）5只和老年组（27月龄）6只,运用新的体视学方法和透射电镜技术分别对大鼠大脑海马内有髓神经纤维直径,有髓神经纤维轴突直径,有髓神经纤维髓鞘内外周长和平均厚度进行定量研究。结果老年组有髓神经纤维平均直径较中老年组明显增加了10.8%（P〈0.05）,而与青年组比较则无显著性改变（P〉0.05）。老年组直径〈0.3μm的有髓神经纤维髓鞘厚度比中老年组减少了24.4%（P〈0.05）,老年组直径在0.4～0.5（不含0.5,以下类推）、0.5～0.6、0.7～0.8μm范围的有髓神经纤维髓鞘厚度较青年组均有明显增大（P〈0.05）。结论正常老年大脑海马结构内有髓神经纤维存在细小直径纤维脱髓鞘改变的同时,还存在中等直径的有髓神经纤维继续髓鞘化。

英文摘要：

Objective To further observe the age-related changes in myelin sheaths of myelinated fibers in rat hippocampus.Methods Sixteen Long-Evans rats were divided in young age group（6-month old,n =5）,middle age group（18-month old,n =5） and old age group（27-month old,n =6）.The mean diameter of myelinated fibers and axons,the inner and outer perimeter,and the mean thickness of myelin sheaths of myelinated fibers in rat hippocampus were measured with the new stereological methods and transmission electron microscope technique.Results The mean diameter of myelinated fibers in hippocampus was 10.8% higher in old age group than in middle age group（P 0.05） but no significant difference was found between young and old age groups（P 0.05）.The mean thickness of myelin sheaths of myelinated fibers with a diameter of less than 0.3 μm in hippocampus was 24.4% lower in old age group than in middle age group（P 0.05） and was significantly higher in old age group with a myelin sheath diameter of 0.4,0.5,and 0.7 μm than in young age group（P 0.05）.Conclusion Myelinated fibers with a small or a medium-sized diameter are demyelinated in hippocampus of normal old rats.