Udin S B
Cell Mol Neurobiol. 1985 Jun;5(1-2):85-102. doi: 10.1007/BF00711087.
Many parts of the visual system contain topographic maps of the visual field. In such structures, the binocular portion of the visual field is generally represented by overlapping, matching projections relayed from the two eyes. One of the developmental factors which helps to bring the maps from the two eyes into register is visual input. The role of visual input is especially dramatic in the frog, Xenopus laevis. In tadpoles of this species, the eyes initially face laterally and have essentially no binocular overlap. At metamorphosis, the eyes begin to move rostrodorsally; eventually, their visual fields have a 170 degree region of binocular overlap. Despite this major change in binocular overlap, the maps from the ipsilateral and contralateral eyes to the optic tectum normally remain in register throughout development. This coordination of the two projections is disrupted by visual deprivation. In dark-reared Xenopus, the contralateral projection is nearly normal but the ipsilateral map is highly disorganized. The impact of visual input on the ipsilateral map also is shown by the effect of early rotation of one eye. Examination of the tectal lobe contralateral to the rotated eye reveals that both the contralateral and the ipsilateral maps to that tectum are rotated, even though the ipsilateral map originates from the normal eye. Thus, the ipsilateral map has changed orientation to remain in register with the contralateral map. Similarly, the two maps on the other tectal lobe are in register; in this case, both projections are normally oriented even though the ipsilateral map is from the rotated eye. The discovery that the ipsilateral eye's map reaches the tectum indirectly, via a relay in the nucleus isthmi, has made it possible to study the anatomical changes underlying visually dependent plasticity. Retrograde and anterograde tracing with horseradish peroxidase have shown that eye rotation causes isthmotectal axons to follow abnormal trajectories. An axon's route first goes toward the tectal site where it normally would arborize but then changes direction to reach a new tectal site. Such rearrangements bring the isthmotectal axons into proximity with retinotectal axons which have the same receptive fields. Anterograde horseradish peroxidase filling has also been used to study the trajectories and arborizations of developing isthmotectal axons. The results show that the axons enter the tectum before the onset of eye migration but do not begin to branch profusely until eye movement begins to create a zone of binocular space.(ABSTRACT TRUNCATED AT 400 WORDS)
视觉系统的许多部分都包含视野的地形图。在这样的结构中，视野的双眼部分通常由来自双眼的重叠、匹配投射来表示。有助于使来自双眼的地图对齐的发育因素之一是视觉输入。视觉输入的作用在非洲爪蟾（Xenopus laevis）中尤为显著。在该物种的蝌蚪中，眼睛最初朝侧面，基本上没有双眼重叠。在变态发育时，眼睛开始向前背侧移动；最终，它们的视野有一个170度的双眼重叠区域。尽管双眼重叠发生了这一重大变化，但从同侧眼和对侧眼到视顶盖的地图在整个发育过程中通常仍保持对齐。视觉剥夺会破坏这两个投射的协调。在黑暗饲养的非洲爪蟾中，对侧投射基本正常，但同侧地图高度紊乱。一只眼睛早期旋转的影响也表明了视觉输入对同侧地图的作用。对旋转眼对侧的顶盖叶进行检查发现，即使同侧地图来自正常眼睛，到该顶盖的对侧和同侧地图都会旋转。因此，同侧地图改变了方向以与对侧地图保持对齐。同样，另一个顶盖叶上的两个地图也对齐；在这种情况下，即使同侧地图来自旋转眼，两个投射通常也是正常定向的。同侧眼的地图通过峡核中的中继间接到达顶盖这一发现，使得研究视觉依赖性可塑性背后的解剖学变化成为可能。用辣根过氧化物酶进行逆行和顺行追踪表明，眼睛旋转会导致峡顶盖轴突沿着异常轨迹走行。轴突的路径首先朝向它通常会分支的顶盖部位，但随后会改变方向以到达一个新的顶盖部位。这种重新排列使峡顶盖轴突与具有相同感受野的视网膜顶盖轴突靠近。顺行辣根过氧化物酶填充也被用于研究发育中的峡顶盖轴突的轨迹和分支。结果表明，轴突在眼睛迁移开始之前就进入了顶盖，但直到眼睛运动开始形成双眼空间区域时才开始大量分支。（摘要截选至400字）
