Gribnau A A, de Kort E J, Dederen P J, Nieuwenhuys R
Anat Embryol (Berl). 1986;175(1):101-10. doi: 10.1007/BF00315460.
An anterograde tracer study has been made of the developing corticospinal tract (CST) in the rat using wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Analysis of normal Rager stained material revealed that corticospinal axons reach upper cervical spinal cord levels at the day of birth (PO). Postnatal rats ranging in age from one (P1) to fourteen (P14) days received multiple WGA-HRP injections into the cortex of their left hemisphere and were allowed to survive for 24 h. The first labeled CST fibers caudally extend into the third thoracic spinal cord segment at P1; into the eighth thoracic segment at P3; into the first or second lumbar segment at P7 and into the second to third sacral segment at Pg. Thus the outgrowth of the leading 'pioneer' fibers of the CST is completed at P9 but later developing axons are continuously added even beyond P9. Quantitative analysis of the amount of label along the length of the outgrowing CST revealed a characteristic pattern of labeling varying with age. The most striking features of that pattern are: the formation of two standing peaks at the level of the cervical and lumbar enlargements respectively and the transient presence of a smaller running peak which moves caudally with the front of the outgrowing bundle. The standing peaks are ascribed to the branching of the axon terminals at both intumescences, whereas the running peak probably arises by the accumulation of tracer within the growth cones at the tips of the outgrowing CST axons. Factors such as the number of axons, the varying axon diameters, the branching collaterals, the presence of varicosities, the transport rate of the tracer, the uptake of the tracer at the injection site, which possibly may affect the amount of label present in both the entire bundle and in the individual axons are discussed. Current research is focused upon an analysis of the relation between the site of injection within the cortex and the pattern of labeling of the CST. A delay of two days was found between the arrival of the CST axons at a particular spinal cord level and their outgrowth into the adjacent spinal gray. However, combined HRP and electronmicroscopic experiments are necessary to determine the factors behind the maturation of the CST as well as the maturation of the spinal gray.
利用小麦胚芽凝集素结合辣根过氧化物酶（WGA-HRP）对大鼠发育中的皮质脊髓束（CST）进行了顺行示踪研究。对正常Rager染色材料的分析显示，皮质脊髓轴突在出生日（P0）到达颈上段脊髓水平。对出生后1天（P1）至14天（P14）的大鼠，将WGA-HRP多次注入其左半球皮质，并使其存活24小时。最早标记的CST纤维在P1时向尾侧延伸至第三胸段脊髓；在P3时延伸至第八胸段；在P7时延伸至第一或第二腰段；在P9时延伸至第二至第三骶段。因此，CST领先的“先驱”纤维的生长在P9时完成，但即使在P9之后，较晚发育的轴突也在不断增加。对生长中的CST长度上标记量的定量分析揭示了一种随年龄变化的特征性标记模式。该模式最显著的特征是：分别在颈膨大水平和腰膨大水平形成两个固定峰，以及一个较小的移动峰的短暂出现，该移动峰随着生长束的前端向尾侧移动。固定峰归因于两个膨大处轴突终末的分支，而移动峰可能是由于示踪剂在生长中的CST轴突末端生长锥内的积累所致。讨论了可能影响整个束和单个轴突中标记量的因素，如轴突数量、轴突直径变化、分支侧支、膨体的存在、示踪剂的运输速率、注射部位对示踪剂的摄取等。目前的研究集中在分析皮质内注射部位与CST标记模式之间的关系。发现CST轴突到达特定脊髓水平与它们向相邻脊髓灰质生长之间存在两天的延迟。然而，需要结合HRP和电子显微镜实验来确定CST成熟以及脊髓灰质成熟背后 的因素。
