Williams R W, Rakic P
Proc Natl Acad Sci U S A. 1985 Jun;82(11):3906-10. doi: 10.1073/pnas.82.11.3906.
To determine whether individual optic fibers grow along constant sets of neighboring fibers, a group of 160 axons and 25 axonal growth cones were traced through a set of 500 serial electron micrographs of an optic nerve taken from a 39-day-old monkey embryo (Macaca mulatta). In single transverse sections, growth cones contact an average of 7.9 fibers, whereas axons contact 5.3 other fibers. The particular set of fibers in contact with one another changed rapidly, and, on average, growth cones and axons lost half of their original neighbors over a distance of only 8-10 micron. Between the first and last sections of the series, 92% of all initial contacts were lost. Individual axons moved freely between fiber fascicles, and the distance separating initial neighbors increased progressively. Most remarkably, the sets of fibers touched by the tips and the shanks of growth cones had no common neighbors in 17 out of 25 cases. These results demonstrate that, in primates, fibers in the optic nerve do not retain a particular set of immediate neighbors during their outgrowth.
为了确定单根视神经纤维是否沿着相邻纤维的固定组合生长，一组研究人员追踪了160根轴突和25个轴突生长锥，这些轴突和生长锥来自一只39天大的猕猴胚胎（Macaca mulatta）视神经的500张连续电子显微镜照片。在单个横切面上，生长锥平均接触7.9根纤维，而轴突接触5.3根其他纤维。相互接触的特定纤维组合变化迅速，平均而言，生长锥和轴突在仅8-10微米的距离内就失去了一半的原始邻居。在该系列的第一和最后切片之间，所有初始接触中有92%消失了。单个轴突在纤维束之间自由移动，初始邻居之间的距离逐渐增加。最值得注意的是，在25个案例中的17个案例中，生长锥尖端和柄部接触的纤维组没有共同的邻居。这些结果表明，在灵长类动物中，视神经纤维在生长过程中不会保留特定的一组直接邻居。
