青年猫和老年猫视神经超微结构观察比较

目的探讨青年猫和老年猫视神经年龄相关的形态学变化及可能造成的生理影响。方法取4只青年猫(2-3岁,2-2.5kg)和4只老年猫(10-13岁,2.5-3.5kg)颅内相对应部分视神经,制作横向半薄切片和超薄切片,半薄切片用甲苯胺蓝硼砂溶液染色,光镜观察、测量视神经的直径(不含外层神经膜);超薄切片标本用醋酸和柠檬酸铅染色,电镜观察、计数视神经纤维密度、测量视神经纤维外径D(含髓鞘)和内径d(不含髓鞘),按一定分级范围算出各种直径的纤维及各种d/D比值的纤维所占百分比,分别画出直方图,对实验结果进行统计学分析并绘制纤维直径谱。结果与青年猫相比,老年猫视神经直径显著增大(P0.05);纤维数量显著下降(P0.05)。纤维直径谱分析结果显示,青、老年猫纤维直径分布范围相似,但老年猫纤维的峰直径及纤维平均直径比青年猫的显著减小(P0.05),老年猫视神经纤维的d/D比值亦明显降低。另外,老年猫视神经中部分轴突肿胀,髓鞘疏松、结构紊乱,板层脱离、空泡化,有的轴索髓鞘溶解。结论在衰老过程中,老年猫视神经纤维丢失,纤维直径减小,d/D比值下降,以及纤维髓鞘的松散解体,这些变化均可能导致视神经纤维对视觉信息的传导速度减慢,是老年个体视觉分析速度下降的重要原因。

COMPARISON OF ULTRASTRUCTURAL CHANGES IN OPTIC NERVE OF YOUNG AND OLD CATS

Objective To investigave age-related changes of optic nerves in old and young adult cats, and to explore the probable impact of these changes on physiological functions.Methods The optic nerves of the same intracranial segment in 4 young adult （1-3 years） and 4 old cats （10-13 years） were processed to make semithin and ultrathin transverse slides. Under microscopy, the diameter of optic nerve（not including the outer nerve membrane） was measured in toludine blue stained semithin slides. Under electron microscopy, the density and diameter （including sheath, D） of nerve fibers as well as the axon diameter （not including sheath, d） were statistically measured in uranium acetate and lead citrate stained ultrathin slides. All results were subjected to statistical analysis. The diameter spectrum of optic nerve fibers （D） and their ratio of d/D were quantitatively compared between young adult and old cats. Results Compared with young adults, the old cats showed a significant decrease both in the diameter（P0.05） and the density（P0.05）of optic nerve fibers. The range of the diameter spectrum was similar in both age groups. but the old animals showed a smaller peak diameter, average diameter and d/D ratio than young cohorts did （P0.05）.In addition, axons of some nerve fibers in old cats swelled, accompanied with loosened sheath, structural disorder, lamella vacuolization and even sheath collapse.Conclusion The nerve fibers exhibit a significant loss during senescence. A significant decrease in average diameter and d/D of nerve fibers might greatly slow down visual information conduction, which might be an important cause of visual processing deceleration in aged individuals.