Senoh K, Naito J
Department of Ophthalmology, School of Medicine, Iwate Medical University, Morioka, Japan.
Exp Brain Res. 1991;87(3):473-83. doi: 10.1007/BF00227073.
The fiber arrangement of the optic radiation was investigated in fourteen adult cats. The retinotopies of the lateral geniculate nucleus (LGN) were first identified electrophysiologically, and thereafter, wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was iontophoretically injected into defined positions of the LGN. These corresponded to the central (medial LGN), horizontal peripheral (lateral LGN), dorsal (rostral LGN), and ventral (caudal LGN) retina. Geniculocortical fibers from the each position of the LGN and corticogeniculate fibers projecting to these positions were always labeled reciprocally. Labeled terminals were found massively in layer IV with some extending to the lower part of layer III, but layers VI and I also contained substantial numbers. Although most of the labeled neurons were localized in layer VI, some neurons were labeled in layer V and transsynaptically in layer IV. Labeled fibers were superimposed in three-dimensionally reconstructed maps of the white matter for the easy understanding of the pathways connecting the LGN and the visual cortex. They were localized in certain zones in the white matter without wide dispersion; however, we did not obtain any findings which suggested clearly different populations of geniculocortical and corticogeniculate fibers. In agreement with previous studies, fibers from the rostral LGN and the caudal LGN projected to the striate cortex in a regular order, rostrocaudally, and fibers from the medial LGN and the lateral LGN projected to the striate cortex inversely (i.e. lateromedially). This inverse projection resulted because fibers from the lateral LGN traversed fibers from the medial LGN in a lateromedial direction; however, there was only partial crossing of these two pathways. The distribution of geniculocortical fibers together with corticogeniculate fibers formed topographic zones arrayed mediolaterally in the white matter. Thus, fibers of the medial LGN were positioned in the intermediate zone, and fibers of the rostral LGN and the lateral LGN were positioned in the rostral and caudal parts of the lateral zone, respectively. Fibers of the caudal LGN were found in the medial zone. This fiber arrangement displayed a rough centroperipheral retinotopy in that fibers representing the central area were placed between fibers representing the peripheral retina. Finally, this fiber arrangement was compared with that of the optic nerve and optic tract.
在14只成年猫中研究了视辐射的纤维排列。首先通过电生理学方法确定外侧膝状体核（LGN）的视网膜拓扑结构，然后将与辣根过氧化物酶结合的小麦胚芽凝集素（WGA-HRP）离子导入LGN的特定位置。这些位置对应于中央（内侧LGN）、水平周边（外侧LGN）、背侧（嘴侧LGN）和腹侧（尾侧LGN）视网膜。来自LGN每个位置的膝状皮质纤维和投射到这些位置的皮质膝状纤维总是相互标记。标记的终末大量出现在IV层，一些延伸到III层下部，但VI层和I层也含有大量标记。虽然大多数标记神经元位于VI层，但一些神经元在V层被标记，并且在IV层有跨突触标记。在白质的三维重建图中叠加标记纤维，以便于理解连接LGN和视觉皮层的通路。它们位于白质的特定区域，没有广泛分散；然而，我们没有获得任何表明膝状皮质纤维和皮质膝状纤维群体明显不同的发现。与先前的研究一致，来自嘴侧LGN和尾侧LGN的纤维按头尾顺序规则地投射到纹状皮质，来自内侧LGN和外侧LGN的纤维则反向投射（即从外侧向内侧）。这种反向投射是因为来自外侧LGN的纤维在外侧向内侧方向穿过来自内侧LGN的纤维；然而，这两条通路只有部分交叉。膝状皮质纤维与皮质膝状纤维的分布在白质中形成了从内侧到外侧排列的拓扑区域。因此，内侧LGN的纤维位于中间区域，嘴侧LGN和外侧LGN的纤维分别位于外侧区域的嘴侧和尾侧部分。尾侧LGN的纤维在内侧区域被发现。这种纤维排列显示出大致的中央到周边视网膜拓扑，即代表中央区域的纤维位于代表周边视网膜的纤维之间。最后，将这种纤维排列与视神经和视束的纤维排列进行了比较。
