Cima C, Grant P
J Embryol Exp Morphol. 1982 Dec;72:251-67.
We studied the time of origin, development and location of glial elements in the developing optic nerve of Xenopus with light and electron microscopy. The first cells acting as a primitive glia are ependymal cells lying dorsal to the chiasmatic optic nerve (CON) at Nieuwkoop & Faber (1956) NF stage 39. Later (stage 47/48), immature astrocyte cell bodies migrate from the periphery of the middle optic nerve (MON) into the central fibre mass along cytoplasmic processes extending from the outer glia limitans. Shortly thereafter, oligodendrocyte cell bodies appear in the centre of the fibre mass and myelination begins, first in the middle of the MON, spreading from the centre distally towards the chiasm and proximally to the retina. In late tadpoles myelinated fibres appear first in the CON then in the retinal optic nerve (RON) increasing markedly in juveniles and adults. Segment-specific patterns of glia and myelination appear during optic nerve development. During metamorphic climax, the optic nerve shortens (Cullen & Webster, 1979), a process involving myelin and axon remodelling primarily in the MON. Neither the profound changes during metamorphosis, nor the processes of gliogenesis and myelination significantly alter the underlying chronotopic ordering in the tadpole nerve. In juvenile and adult optic nerves, however, as myelination and gliogenesis increase, and as more axons mature and grow in diameter, the dorsoventral chronotopic arrangement of axons becomes less apparent.
我们运用光学显微镜和电子显微镜研究了非洲爪蟾发育中的视神经中神经胶质成分的起源时间、发育过程及位置。最早充当原始神经胶质的细胞是位于交叉视神经（CON）背侧的室管膜细胞，处于Nieuwkoop和Faber（1956年）定义的NF 39期。之后（47/48期），未成熟的星形胶质细胞体沿着从外神经胶质界延伸出的细胞质突起，从中间视神经（MON）的周边迁移到中央纤维束。此后不久，少突胶质细胞体出现在纤维束中心，髓鞘形成开始，首先在MON中部，从中心向远端延伸至视交叉，向近端延伸至视网膜。在晚期蝌蚪中，有髓纤维首先出现在CON，然后出现在视网膜视神经（RON），在幼体和成体中显著增加。在视神经发育过程中出现了节段特异性的神经胶质和髓鞘形成模式。在变态高峰期，视神经缩短（Cullen和Webster，1979年），这一过程主要涉及MON中的髓鞘和轴突重塑。变态过程中的深刻变化以及神经胶质生成和髓鞘形成过程均未显著改变蝌蚪神经中潜在的时间顺序排列。然而，在幼体和成体视神经中，随着髓鞘形成和神经胶质生成增加，以及更多轴突成熟并增粗，轴突的背腹时间顺序排列变得不那么明显。
