Willshaw D J, Gaze R M
J Embryol Exp Morphol. 1986 Jun;94:121-37.
The establishment of retinotectal projections following transection of one optic nerve in developing Xenopus has been investigated. Between 3 weeks and 11 months after the operation, the nerve fibre tracer horseradish peroxidase (HRP) was applied to either the operated or the unoperated nerve, and the brains were prepared for examination as whole mounts. In most cases fibres from the operated nerve innervated both tecta, with the result that one tectum was doubly innervated and one tectum singly innervated. Two months after transection of the optic nerve in tadpole life, between stages 50 and 54, this nerve usually made a uniform projection on the contralateral tectum and a striped projection on the ipsilateral, doubly innervated, tectum. The projection made by the unoperated nerve on this tectum was a similar pattern of stripes, which ran generally rostrocaudally. Two months after transection of the optic nerve of newly metamorphosed animals, the projection formed by the operated nerve on the doubly innervated tectum was usually a pattern of spots or spots mixed together with stripes in no particular orientation superimposed on a roughly uniform background. In a small number of cases the projections made by the same nerve on the two tecta were approximately complementary; that is, the presence of label on one tectum corresponded with its absence on the other tectum. The results are examined in the context of the development of the retina and of the tectum. It is suggested that the consistently oriented stripes which result from nerve transection at a stage at which only a small proportion of the retinal fibres had reached the tectum are formed by the interaction of two equally matched sets of developing fibres, stripe orientation being determined by the mode of growth of the optic tectum. The formation of patterns of spots or spots mixed together with stripes following nerve transection after the end of the main phase of tectal histogenesis, and when 50% of the optic fibres had already reached the tectum, is attributed to an unequal competition between the two sets of fibres.
对发育中的非洲爪蟾一条视神经横断后视网膜 - 顶盖投射的建立进行了研究。在手术后3周和11个月之间，将神经纤维示踪剂辣根过氧化物酶（HRP）应用于手术侧或未手术侧神经，然后将脑制成整装标本进行检查。在大多数情况下，来自手术侧神经的纤维支配双侧顶盖，结果是一个顶盖接受双侧支配，另一个顶盖接受单侧支配。在蝌蚪期视神经横断后两个月，即在第50至54阶段之间，这条神经通常在对侧顶盖上形成均匀的投射，而在同侧接受双侧支配的顶盖上形成条纹状投射。未手术侧神经在这个顶盖上形成的投射是类似的条纹模式，通常沿前后方向排列。新变态动物视神经横断后两个月，手术侧神经在接受双侧支配的顶盖上形成的投射通常是斑点状模式，或者是斑点与条纹混合在一起，没有特定方向，叠加在大致均匀的背景上。在少数情况下，同一神经在两个顶盖上形成的投射大致互补；也就是说，一个顶盖上有标记，而另一个顶盖上没有标记。在视网膜和顶盖发育的背景下对结果进行了研究。有人提出，在只有一小部分视网膜纤维到达顶盖的阶段进行神经横断所产生的始终定向的条纹，是由两组发育程度相当的纤维相互作用形成的，条纹方向由视顶盖的生长方式决定。在顶盖组织发生的主要阶段结束后，当50%的视神经纤维已经到达顶盖时进行神经横断，形成斑点状或斑点与条纹混合的模式，这归因于两组纤维之间的不平等竞争。
