Chan S O, Wong K F, Chung K Y, Yung W H
Department of Anatomy, Chinese University of Hong Kong, Shatin, N.T., Hong Kong, P.R. China.
Eur J Neurosci. 1998 Aug;10(8):2511-22. doi: 10.1046/j.1460-9568.1998.00257.x.
The growth of retinal axons was investigated in different regions of the optic chiasm in C57 pigmented mouse embryos aged embryonic day 13 (E13) to E15. Individual retinal axons and their growth cones were labelled anterogradely by DiI and imaged using a confocal imaging system. In aldehyde-fixed embryos, retinal growth cones display a simple form in the optic nerve and become more complex in morphology in the chiasm. The complex form is particularly prominent in those axons that turn to the ipsilateral tract in the premidline region of chiasm. Moreover, complex growth cones are also commonly found in axons in the postmidline chiasm, which are markedly different in morphology from those axons in the premidline region, suggesting that the postmidline chiasm contains a novel environment for the pathfinding of retinal axons. In another experiment, the dynamic growth of retinal axons is studied in a brain slice preparation of the living retinofugal pathway. Retinal axons show an intermittent growth across the premidline and postmidline chiasm. Extensive remodelling of growth cone form followed by a shift in growth direction is commonly seen during the pause periods, indicating that signals that guide axon growth across the chiasm are not restricted to the midline, but are laid down throughout the chiasm. Moreover, dramatic changes in axon trajectory are noted first at the premidline chiasm where the uncrossed axons segregate from the crossed axons, and second at the postmidline chiasm where specific sorting of retinal axons according to their position in the dorsal ventral retinal axis and their ages are known to take place. These results show that there are two distinct environments, separated by the midline in the chiasm, where axons show different responses to local guidance cues and develop the distinct fibre orders.
在胚胎第13天（E13）至E15的C57色素沉着小鼠胚胎中，研究了视交叉不同区域视网膜轴突的生长情况。通过DiI对单个视网膜轴突及其生长锥进行顺行标记，并使用共聚焦成像系统进行成像。在醛固定的胚胎中，视网膜生长锥在视神经中呈现简单形态，而在视交叉中形态变得更加复杂。这种复杂形态在视交叉中线前区域转向同侧束的轴突中尤为突出。此外，在视交叉中线后区域的轴突中也常见复杂的生长锥，其形态与中线前区域的轴突明显不同，这表明视交叉中线后区域为视网膜轴突的路径寻找提供了一个新的环境。在另一项实验中，在活体视网膜神经通路的脑片制备中研究了视网膜轴突的动态生长。视网膜轴突在穿过中线前和中线后的视交叉时表现出间歇性生长。在暂停期通常可以看到生长锥形态的广泛重塑，随后生长方向发生改变，这表明引导轴突穿过视交叉的信号并不局限于中线，而是分布在整个视交叉中。此外，轴突轨迹的显著变化首先出现在中线前视交叉处，未交叉的轴突与交叉的轴突分离，其次出现在中线后视交叉处，已知视网膜轴突会根据其在背腹视网膜轴上的位置和年龄进行特定的分选。这些结果表明，视交叉中被中线分隔的有两个不同的环境，轴突在其中对局部引导线索表现出不同的反应，并形成不同的纤维排列顺序。
