Axon kinematics change during growth and development
Axon kinematics change during growth and development
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DOI：
10.1115/1.2746372
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发表时间：
2007-08-01
影响因子：
1.7
通讯作者：
Shreiber, David I.
中科院分区：
文献类型：
--
作者：
Hao, Hailing;Shreiber, David I.
研究了发育中的鸡胚脊髓在快速生长和髓鞘形成时期轴突对机械拉伸的微运动学响应。在受精后（E12、E14、E16和E18）胚胎发育的不同天数分离脊髓，分别拉伸0%、5%、10%、15%和20%。在此期间，脊髓长度增长约55%，白质束明显有髓鞘形成。脊髓拉伸后用多聚甲醛固定，切片，用非组织化学染色检测神经丝蛋白，并用荧光显微镜成像。未拉伸脊髓的轴突表现为不同程度的波动或扭曲，并随着拉伸而呈现伸直。通过跟踪数百个随机选择的轴突，量化每个脊髓的扭曲程度（节段路径长度与其端到端长度之比）。弹性分布随拉伸的变化表明，轴突从低拉伸水平下的非仿射、不耦合行为转变为高拉伸水平下的仿射、耦合行为，这与之前关于成人轴突行为的报道一致。豚鼠视神经（Bain, Shreiber and Meaney， J. Biomech）。Eng。， 125(6)，第798-804页)。先前由Bain等人提出的数学模型被用于量化运动行为的转变。结果表明，轴突在每个阶段都表现出明显的纯非仿射行为，但这一比例从E12的64%下降到E18的30%。随着发育，轴突的减少与长度和髓鞘形成的增加负相关，但轴突运动学的变化不能用脊髓物理生长过程中施加的拉伸来解释。组织水平和轴突水平变形之间的关系随着发育而变化，这可能对生长和创伤期间经历的生理力的反应具有重要意义。
The microkinematic response of axons to mechanical stretch was examined in the developing chick embryo spinal cord during a period of rapid growth and myelination. Spinal cords were isolated at different days of embryonic (E) development post-fertilization (E12, E14, E16, and E18) and stretched 0%, 5%, 10%, 15%, and 20%, respectively. During this period, the spinal cord grew similar to 55% in length, and white matter tracts were myelinated significantly. The spinal cords were fixed with paraformaldehyde at the stretched length, sectioned, stained inununohistochemically for neurofilament proteins, and imaged with epifluorescence microscopy. Axons in unstretched spinal cords were undulated, or tortuous, to varying degrees, and appeared to straighten with stretch. The degree of tortuosity (ratio of the segment's pathlength to its end-to-end length) was quantified in each spinal cord by tracing several hundred randomly selected axons. The change in tormosity distributions with stretch indicated that axons switched from non-affine, uncoupled behavior at low stretch levels to affine, coupled behavior at high stretch levels, which was consistent with previous reports of axon behavior in the adult. guinea pig optic nerve (Bain, Shreiber and Meaney, J. Biomech. Eng., 125(6), pp. 798-804). A mathematical model previously proposed by Bain et al. was applied to quantify the transition in kinematic behavior. The results indicated that significant percentages of axons demonstrated purely non-affine behavior at each stage, but that this percentage decreased from 64% at E12 to 30% at E18. The decrease correlated negatively to increases in both length and myelination with development, but the change in axon kinematics could not be explained by stretch applied during physical growth of the spinal cord. The relationship between tissue-level and axonal-level deformation changes with development, which can have important implications in the response to physiological forces experienced during growth and trauma.