Berthold C H, Carlstedt T
J Comp Neurol. 1982 Aug 10;209(3):225-32. doi: 10.1002/cne.902090302.
Samples of S1 dorsal root nerve fibers from cats of different pre- and postnatal ages were examined electron microscopically with regard to axon caliber and number of myelin lamellae. Each root was examined at four different cross-sectional levels. Two levels were situation close to the spinal cord entrance on each side of the peripheral (PNS) and central nervous system (CNS) border. The third and fourth levels were located more distally. The first compact myelin lamella was observed in the CNS part of the root in a 47-day-old fetus. In the 53-day-old fetus the degree of myelination was the same in the CNS as distal in the PNS part of the root. Surprisingly, all axons appeared unmyelinated close to the PNS-CNS border and remained so for a further 10-day period. After this time lag, this part of the root became myelinated and showed a rapid increase in myelin sheath thickness. Calculations of axonal growth, mesaxonal length, and myelin volume indicated a maturation process that progressed discontinuously. Myelination did not proceed in a strict somatofugal direction, but was a regionally differentiated process. The maximal myelin production, expressed as the increase in myelin volume per Schwann cell, was found during the second to fourth postnatal months, i.e., very late in development.
对不同产前和产后年龄猫的S1背根神经纤维样本进行了电子显微镜检查，观察轴突直径和髓鞘板层数。每个神经根在四个不同的横截面上进行检查。两个层面位于外周神经系统（PNS）和中枢神经系统（CNS）边界两侧靠近脊髓入口处。第三和第四层面位于更远处。在47日龄胎儿的神经根中枢神经系统部分观察到了第一个紧密髓鞘板。在53日龄胎儿中，中枢神经系统的髓鞘化程度与神经根PNS部分远端相同。令人惊讶的是，所有轴突在靠近PNS-CNS边界处似乎无髓鞘，并在接下来的10天内一直保持这种状态。在此时间滞后之后，该部分神经根开始髓鞘化，髓鞘厚度迅速增加。轴突生长、轴系膜长度和髓鞘体积的计算表明，成熟过程是不连续进行的。髓鞘形成并非严格地沿躯体离心方向进行，而是一个区域分化过程。以每个施万细胞髓鞘体积增加表示的最大髓鞘生成量在出生后第二至第四个月出现，即在发育后期。
