Mateu L, Luzzati V, Borgo M, Vonasek E, Vargas R
Centro de Biofísica y Bioquímica IVIC, Caracas, Venezuela.
J Mol Biol. 1991 Jul 20;220(2):351-7. doi: 10.1016/0022-2836(91)90018-2.
An X-ray scattering study was performed on optic nerves dissected from rats aged from ten days to one year. The spectra were analysed using the procedure described in the previous papers of this series. Each experiment yields the values of a variety of parameters: the average D and the variance sigma D of the repeat distance, the average number mean value of N of motifs per crystallite, the fraction alpha loose of myelin that does not belong to the compact sheaths, the sets [idiff(h/D)] and [imotif(k/2D)] that suffice to define, respectively, the spurious scattering and the continuous intensity curve of the elementary membrane pair. A surprising result is that, in the native optic, as previously found in the swollen sciatic nerves, the stacking disorder affects the external space, whereas in native sciatic nerves the disorder affects the cytoplasmic space. An analysis of the evolution of the structure parameters as a function of the age of the animal and a comparison with the results previously obtained with rat sciatic nerves led to the following conclusions: the structure of the elementary membrane pair is constant throughout myelinogenesis; mean value of N is much smaller in optic than in sciatic nerves; mean value of N and the degree of myelination increase with age in the two types of nerve; D is smaller in optic than in sciatic nerves; in optic nerves, D decreases slightly with age, but in sciatic nerves it increases; sigma D is strongly age-dependent in optic nerves, but almost age-independent in sciatic nerves. In contrast to sciatic, the structure of optic nerve myelin was found to be almost insensitive to hypertonic solutions. Finally, a pair of electron density profiles was selected, quite similar to those selected previously in sciatic nerves, one corresponding to Caspar & Kirschner's the other to Worthington & McIntosh's proposals, neither of which can be ruled out according to the criteria used in this work.
对从10日龄至1岁大鼠身上解剖出的视神经进行了X射线散射研究。使用本系列前几篇论文中描述的程序对光谱进行了分析。每个实验都得出了各种参数的值：重复距离的平均D值和方差σD、每个微晶中基序的平均数量均值N、不属于紧密髓鞘的髓磷脂的松散部分α、分别足以定义基本膜对的杂散散射和连续强度曲线的集合[idiff(h/D)]和[imotif(k/2D)]。一个令人惊讶的结果是，在天然视神经中，正如之前在肿胀的坐骨神经中发现的那样，堆积紊乱影响外部空间，而在天然坐骨神经中，紊乱影响细胞质空间。对结构参数随动物年龄的变化进行分析，并与之前用大鼠坐骨神经获得的结果进行比较，得出了以下结论：基本膜对的结构在整个髓鞘形成过程中是恒定的；视神经中的N平均值比坐骨神经中的小得多；两种神经中N的平均值和髓鞘化程度均随年龄增加；视神经中的D比坐骨神经中的小；在视神经中，D随年龄略有下降，但在坐骨神经中则增加；σD在视神经中强烈依赖年龄，但在坐骨神经中几乎与年龄无关。与坐骨神经不同，发现视神经髓鞘的结构对高渗溶液几乎不敏感。最后，选择了一对电子密度分布图，与之前在坐骨神经中选择的非常相似，一个对应于卡斯帕和基尔施纳的提议，另一个对应于沃辛顿和麦金托什的提议，根据本研究中使用的标准，这两种提议都不能排除。
