Horsburgh G M, Sefton A J
J Comp Neurol. 1986 Jan 22;243(4):547-60. doi: 10.1002/cne.902430409.
To establish the time course and major features of the development of the optic nerve and chiasm in the embryonic rat, the growth of axons from the retina to the brain has been studied by light and electron microscopy. On embryonic day 14 (E14), the first axons are generated by retinal ganglion cells. Fascicles of axons can be detected in the optic stalk at E14.5 and in the diencephalon by E15.0. In the vitreal retina and optic fissure, large extracellular spaces resemble the oriented channels previously described in the mouse. They form approximately 12 hours before the invasion of optic axons and contain hyaluronic acid. In the optic stalk and diencephalon of the rat, similar spaces are not present, but the timed autolysis of neuroepithelial cells could provide a pathway of minimal resistance for the earliest axons. Degenerating cells are prominent in the ventral stalk and rostral diencephalon prior to the arrival of the first optic axons that preferentially invade these regions. The role of pigment in the development of visual pathways is controversial. In one strain of rat, Manchester Hooded, the retinae are heavily pigmented, but little pigment is seen at any stage in the stalk; in albinos, pigment is absent from both retina and stalk. However, the distribution of axons within the developing optic stalk is very similar in both strains, suggesting that the reduction in size of the ipsilateral pathway observed in the albino rat compared with the Manchester Hooded is not due to a lack of pigment in the optic stalk early in development. Several factors previously reported to contribute to the development of retinotopic order in other species are also present in the rat. These include the sequence in which axons grow into the stalk, and fasciculation. Intermembranous contacts observed between growth cones and adjacent tissues suggest one mechanism by which fasciculation occurs. A small group of fascicles, which may represent the ipsilateral projection, diverges from the crossing fibers on E15.5, without evidence of being deflected by any glial or other structures.
为了确定胚胎期大鼠视神经和视交叉发育的时间进程及主要特征，通过光学显微镜和电子显微镜研究了从视网膜到脑的轴突生长情况。在胚胎第14天（E14），视网膜神经节细胞产生第一批轴突。在E14.5时可在视柄中检测到轴突束，到E15.0时在间脑中可检测到。在玻璃体视网膜和视裂中，大的细胞外间隙类似于先前在小鼠中描述的定向通道。它们在视神经轴突侵入前约12小时形成，且含有透明质酸。在大鼠的视柄和间脑中不存在类似的间隙，但神经上皮细胞的定时自溶可为最早的轴突提供阻力最小的通路。在第一批视神经轴突到达之前，退化细胞在腹侧视柄和间脑前部很突出，这些轴突优先侵入这些区域。色素在视觉通路发育中的作用存在争议。在一种大鼠品系——曼彻斯特头巾大鼠中，视网膜色素沉着严重，但在视柄的任何阶段都几乎看不到色素；在白化大鼠中，视网膜和视柄均无色素。然而，两种品系中发育中的视柄内轴突的分布非常相似，这表明与曼彻斯特头巾大鼠相比，白化大鼠中观察到的同侧通路尺寸减小并非由于发育早期视柄中缺乏色素。先前报道的有助于其他物种视网膜拓扑顺序发育的几个因素在大鼠中也存在。这些因素包括轴突长入视柄的顺序以及成束现象。生长锥与相邻组织之间观察到的膜间接触提示了成束发生的一种机制。一小群可能代表同侧投射的轴突束在E15.5时从交叉纤维分出，没有证据表明受到任何神经胶质或其他结构的偏转。
