Guy J, Ellis E A, Hope G M, Emerson S
Department of Ophthalmology, University of Florida, College of Medicine, Gainesville 32610-0284.
Brain. 1991 Feb;114 ( Pt 1A):281-94.
The spectra of myelin sheath thickness and g ratio (axon diameter/fibre diameter) of guinea pig optic nerves for 8 animals with acute experimental allergic encephalomyelitis (EAE) were compared with those for 6 normal animals. The mean myelin sheath thickness of 0.12 microns for the animals with EAE was significantly lower than the value of 0.16 microns for the normal animals. Since fibre diameter comprises axon diameter plus the thickness of its surrounding myelin sheath, a reduction in mean fibre diameter from 1.52 microns in normals to 1.20 microns in EAE was expected, but it was surprising to find that a mean g ratio of 0.85 obtained for normal nerves was not substantially different from a value of 0.86 for demyelinated optic nerves. A decrease in the mean axon diameter of 1.24 microns for normal animals to 0.94 microns for those with EAE tended to offset the decrease in mean myelin sheath thickness and contributed to the relative stability of the g ratio with acute demyelination. Our results showing reduction in axonal calibre and myelin sheath thickness may offer an explanation for apparent discrepancies between electrophysiological delays in conduction characteristics of experimental and, if not the result of a maturational effect on myelination, human primary demyelinating disorders associated with the scant histopathological demyelination of initial attacks of EAE and the visually asymptomatic patients with multiple sclerosis.
将8只患有急性实验性过敏性脑脊髓炎（EAE）的豚鼠视神经的髓鞘厚度和g值（轴突直径/纤维直径）光谱与6只正常动物的进行了比较。患有EAE的动物的平均髓鞘厚度为0.12微米，显著低于正常动物的0.16微米。由于纤维直径包括轴突直径及其周围髓鞘的厚度，预计正常动物的平均纤维直径从1.52微米降至EAE动物的1.20微米，但令人惊讶的是，发现正常神经的平均g值为0.85与脱髓鞘视神经的0.86值没有实质性差异。正常动物的平均轴突直径从1.24微米降至患有EAE的动物的0.94微米，这往往抵消了平均髓鞘厚度的减少，并导致急性脱髓鞘时g值的相对稳定。我们的结果显示轴突口径和髓鞘厚度降低，这可能解释了实验性电生理传导特征延迟之间明显的差异，如果不是对髓鞘形成的成熟效应的结果，人类原发性脱髓鞘疾病与EAE初始发作时组织病理学脱髓鞘较少以及多发性硬化症的视觉无症状患者有关。
