Williams R W, Borodkin M, Rakic P
Section of Neuroanatomy, Yale University School of Medicine, New Haven, Connecticut 06510.
J Neurosci. 1991 Apr;11(4):1081-94. doi: 10.1523/JNEUROSCI.11-04-01081.1991.
The distribution of growth cones was studied in the optic nerve of monkeys during the first half of prenatal development using quantitative electron microscopic methods. Our aim was to test the hypothesis that ganglion cell growth cones extend predominantly along the surfaces of the nerve, just beneath the pia mater. A complete census of growth cones in cross sections of the nerve during the early phase of axon ingrowth, from embryonic day 39 (E39) to E41, demonstrates that growth cones are scattered within the majority of fascicles, even those located far from the surface of the nerve. By E45, growth cones are concentrated around the nasal, dorsal, and ventral edge of the optic nerve. They are less concentrated in the core and around the temporal edge. However, even as late as E49, virtually all fascicles in the nerve, whether deep or superficial, contain growth cones. Growth cones are dispersed within single fascicles and are often located far from glia. Thus, the newest fibers penetrate deep parts of the pathway and push through centers of densely packed bundles of older axons. This finding is consistent with the vagrant paths of growing axons reported in previous work on embryonic monkey optic nerve (Williams and Rakic, 1985). Our data challenge the hypotheses that growth cones extend selectively along the basal lamina, the pia mater, or glial end feet. Gradients found at later stages of development in the nerve are not due to a particular affinity of growth cones for non-neuronal substrata. The pattern we observed is much more likely to result from central-to-peripheral gradients in ganglion cell generation and possible associations between growth cones originating from the same regions of the retina.
利用定量电子显微镜方法，研究了产前发育前半期猴子视神经中生长锥的分布。我们的目的是检验这样一个假设，即神经节细胞生长锥主要沿着神经表面，在软脑膜下方延伸。在轴突长入的早期阶段，即从胚胎第39天（E39）到E41，对神经横切面中的生长锥进行了全面普查，结果表明，生长锥散布在大多数神经束内，即使是那些远离神经表面的神经束。到E45时，生长锥集中在视神经的鼻侧、背侧和腹侧边缘。它们在核心部位和颞侧边缘周围的集中程度较低。然而，甚至到E49时，神经中几乎所有的神经束，无论深浅，都含有生长锥。生长锥分散在单个神经束内，并且常常远离神经胶质细胞。因此，最新的纤维穿透通路的深部，穿过 older axons 的密集束中心。这一发现与先前关于胚胎猴子视神经的研究（Williams和Rakic，1985）中报道的生长轴突的无规律路径一致。我们的数据对生长锥沿着基膜、软脑膜或神经胶质终足选择性延伸的假设提出了挑战。在神经发育后期发现的梯度并非由于生长锥对非神经元基质的特殊亲和力。我们观察到的模式更有可能是由于神经节细胞生成过程中从中心到外周的梯度以及源自视网膜相同区域的生长锥之间可能的关联所致。
