Little G J, Heath J W
Faculty of Medicine, University of Newcastle, New South Wales, Australia.
J Anat. 1994 Apr;184 ( Pt 2)(Pt 2):387-98.
In experimental studies addressing the regulation of myelin formation and maintenance by Schwann cells, the sympathetic nervous system of young adult rodents has served a key role as an essentially nonmyelinated yet modifiable control tissue. Nevertheless there is clear evidence of substantial myelination in the superior cervical ganglion (SCG) of normal mice and rats of more advanced age. Against this background, interpretation of experimental outcomes in particular sympathetic tissues will require detailed quantitative control data taking account of animal age. To provide a baseline for future investigations on myelin remodelling, an ultrastructural morphometric study of myelinated fibres in the SCG was undertaken in 4 strains (QS, Balb/C, C57 and CBA) of adult male mice aged 32-72 wk. Numbers of myelinated fibres in SCG cross-sections varied substantially between individual animals, and the mean numbers for QS (132), Balb/C (165) and CBA (254) were significantly higher than that for C57 (32). Both axonal and fibre diameter were distributed unimodally (means for the 4 strains ranged from 2.3-2.4 microns and 3.2-3.6 microns respectively). Myelin spiral length was distributed unimodally and skewed to the right (range of means = 227-357 microns) and was significantly greater in QS mice as compared with the other 3 strains. While the mean g ratio (axonal diameter/fibre diameter) was significantly lower in QS mice than in the other 3 strains, the range for mean g ratio was 0.64-0.73, indicating that myelination had proceeded appropriately even though late in onset in this tissue. The index of circularity was high in all strains, both for axons (range of means = 0.80-0.88) and fibres (range of means = 0.84-0.89). The small axonal and fibre diameter and unimodal distribution are consistent with the characteristics of autonomic myelinated fibres and it is probable that most are postganglionic sympathetic fibres arising within the SCG. In terms of providing a sufficient population of myelinated fibres for future experimental studies, the QS, Balb/C and CBA strains would be preferable to C57 mice.
在关于施万细胞对髓鞘形成和维持的调节的实验研究中，年轻成年啮齿动物的交感神经系统作为一种基本上无髓鞘但可调节的对照组织发挥了关键作用。然而，有明确证据表明，在年龄稍大的正常小鼠和大鼠的颈上神经节（SCG）中存在大量髓鞘形成。在此背景下，对特定交感组织的实验结果进行解释将需要考虑动物年龄的详细定量对照数据。为了为未来关于髓鞘重塑的研究提供基线，对32 - 72周龄的4种成年雄性小鼠品系（QS、Balb/C、C57和CBA）的SCG中有髓纤维进行了超微结构形态计量学研究。SCG横切面中有髓纤维的数量在个体动物之间差异很大，QS（132）、Balb/C（165）和CBA（254）的平均数量显著高于C57（32）。轴突直径和纤维直径均呈单峰分布（4种品系的平均值范围分别为2.3 - 2.4微米和3.2 - 3.6微米）。髓鞘螺旋长度呈单峰分布且向右偏斜（平均值范围 = 227 - 357微米），与其他3种品系相比，QS小鼠的髓鞘螺旋长度显著更长。虽然QS小鼠的平均g比值（轴突直径/纤维直径）显著低于其他3种品系，但平均g比值范围为0.64 - 0.73，这表明尽管该组织中髓鞘形成开始较晚，但髓鞘形成过程是正常的。所有品系的轴突（平均值范围 = 0.80 - 0.88）和纤维（平均值范围 = 0.84 - 0.89）的圆度指数都很高。轴突和纤维直径小以及单峰分布与自主神经有髓纤维的特征一致，很可能大多数是起源于SCG内的节后交感纤维。就为未来实验研究提供足够数量的有髓纤维而言，QS、Balb/C和CBA品系比C57小鼠更可取。
