Woodson W, Reiner A, Anderson K, Karten H J
Department of Neurosciences, University of California, San Diego, La Jolla 92093.
J Comp Neurol. 1991 Mar 15;305(3):470-88. doi: 10.1002/cne.903050310.
Retrograde transport of Phaseolus vulgaris leucoagglutinin (PHA-L), fluorogold, fast blue, rhodamine labelled microspheres, and horseradish peroxidase (HRP) was employed to study the distribution, laminar location within the optic tectum, and morphology of tectal cells projecting upon the isthmo-optic nucleus (ION) and the nucleus isthmi, pars parvocellularis (Ipc), in the pigeon and chick. Following injections into the ION, all retrograde markers labelled tecto-ION neurons and their dendrites in the ipsilateral tectum. The cells were located within a relatively narrow band at the border between layers 9 and 10 of the stratum griseum et fibrosum superficiale (SGFS). Retrogradely labelled neuronal somata were different in both dendritic branching and shape; however, tecto-ION neurons generally possessed non-spiny radially oriented and multi-branched dendrites. The apical processes extended into the retino-recipient layers (2-7) of the SGFS and basal dendrites extended into layers 12-14 of the SGFS. Positive neuronal somata were observed throughout the rostro-caudal extent of the optic tectum. The average distance between adjacent tecto-ION neurons varied from one region to another. Specifically, retrogradely labelled cells were more numerous in the caudal, lateral, and ventral tectum, and less numerous at rostro-dorsal levels. Approximately 12,000 tecto-ION neurons were labelled within the ipsilateral optic tectum following either PHA-L or fluorescent dye injections. While the regional distribution of tecto-Ipc neurons was not examined, the morphology indicated that the cells had a single radially oriented dendritic process. Therefore, the apical dendrites are more restricted than those of tecto-ION cells. Moreover, the dendrites were spiny and arborized within layers 3, 5, and 9 of the ipsilateral optic tectum. The axon of tecto-Ipc cells arise from the apical process as a shepherd's crook and descend into the deep layers of the optic tectum. These results indicate that 1) tecto-ION and tecto-Ipc neurons are possibly monosynaptically activated by retinal input, 2) tecto-ION neurons are heterogeneous in morphology, and 3) there is a differential distribution of the tecto-ION neurons throughout the rostro-caudal extent of the optic tectum, suggesting a greater representation of the caudo-ventral portion of the optic tectum within the ION. The discussion primarily concerns the organization of the retino-tecto-ION-retinal circuit in light of the distribution and morphology of tecto-ION neurons within the optic tectum.
采用菜豆白细胞凝集素（PHA-L）、荧光金、固蓝、罗丹明标记微球和辣根过氧化物酶（HRP）的逆行运输，研究家鸽和小鸡中投射到峡视核（ION）和峡核小细胞部（Ipc）的顶盖细胞在视顶盖中的分布、分层位置及形态。向ION注射后，所有逆行标记物均标记了同侧顶盖中投射到ION的神经元及其树突。这些细胞位于浅灰纤维层（SGFS）第9层和第10层之间相对较窄的带内。逆行标记的神经元胞体在树突分支和形状上存在差异；然而，投射到ION的顶盖神经元通常具有无棘的径向排列且多分支的树突。顶端突起延伸至SGFS的视网膜接受层（2 - 7层），基部树突延伸至SGFS的第12 - 14层。在视顶盖的整个前后范围内均观察到阳性神经元胞体。相邻的投射到ION的顶盖神经元之间的平均距离因区域而异。具体而言，逆行标记的细胞在顶盖的尾侧、外侧和腹侧较多，而在头背侧水平较少。注射PHA-L或荧光染料后，同侧视顶盖内约有12,000个投射到ION的顶盖神经元被标记。虽然未研究投射到Ipc的顶盖神经元的区域分布，但其形态表明这些细胞具有单个径向排列的树突过程。因此，其顶端树突比投射到ION的细胞的树突受限制更大。此外，树突有棘且在同侧视顶盖的第3、5和9层内分支。投射到Ipc的顶盖细胞的轴突从顶端突起处呈钩状发出并向下延伸至视顶盖的深层。这些结果表明：1）投射到ION和Ipc的顶盖神经元可能由视网膜输入单突触激活；2）投射到ION的顶盖神经元在形态上具有异质性；3）投射到ION的顶盖神经元在视顶盖的整个前后范围内分布不同，这表明视顶盖的尾腹侧部分在ION中具有更大的代表性。讨论主要围绕视顶盖中投射到ION的顶盖神经元的分布和形态，探讨视网膜-顶盖-ION-视网膜回路的组织。
