Johnson R R, Burkhalter A
Department of Neurology, Washington University School of Medicine, St. Louis, MO 63110.
Exp Brain Res. 1992;89(1):20-30. doi: 10.1007/BF00228997.
To examine the organization of axon collaterals of neurons that selectively take up and transport excitatory amino acids, we have used retrograde tracing with D-[3H]Aspartate after injections into different layers of rat primary visual cortex. The results show cells in the lateral geniculate nucleus retrogradely labeled from the cortex. Additional topographically precise input to the thalamic recipient layer 4 originates from neurons in the visual cortex lying in layers 2/3, 5 and 6. These inputs are reciprocated by point-to-point projections from layer 4. Layer 2/3 cells project to layers 5 and 6 in columnar fashion. Putative excitatory input to layer 2/3 originates from a vertical column of cells in layer 5 and the middle of layer 6. In addition layer 2/3 receives input via horizontal collaterals of topographically distant upper layer neurons, from more widespread projections in lower layer 6, and from very widespread projections of cells at the layer 5/6 border. Cells in the depth of layer 5 also distribute collaterals within layers 5 and 6. Our findings provide anatomical evidence that the geniculo-cortical pathway in the mammalian visual system may use excitatory amino acid transmitters. In addition, the results support the notion that most long range connections that link distant points of the topographic map are excitatory.
为了研究选择性摄取和转运兴奋性氨基酸的神经元轴突侧支的组织情况，我们在将D-[3H]天冬氨酸注射到大鼠初级视觉皮层的不同层后，使用逆行追踪法进行了研究。结果显示，外侧膝状核中的细胞有从皮层逆行标记的情况。丘脑接受层4的额外地形精确输入源自位于第2/3、5和6层的视觉皮层中的神经元。这些输入通过来自第4层的点对点投射得到回应。第2/3层细胞以柱状方式投射到第5和6层。对第2/3层的假定兴奋性输入源自第5层和第6层中部的垂直细胞柱。此外，第2/3层通过地形上较远的上层神经元的水平侧支、第6层下部更广泛的投射以及第5/6层边界处细胞的非常广泛的投射接收输入。第5层深处的细胞也在第5和6层内分布侧支。我们的研究结果提供了解剖学证据，表明哺乳动物视觉系统中的膝状体-皮层通路可能使用兴奋性氨基酸递质。此外，结果支持这样一种观点，即连接地形图上远处点的大多数长距离连接是兴奋性的。
