Strettoi E, Raviola E, Dacheux R F
Istituto di Neurofisiologia del C.N.R., Pisa, Italy.
J Comp Neurol. 1992 Nov 8;325(2):152-68. doi: 10.1002/cne.903250203.
The synaptic connections of the narrow-field, bistratified rod amacrine cell (AII) in the inner plexiform layer (IPL) of the rabbit retina were reconstructed from electron micrographs of continuous series of thin sections. The AII amacrine cell receives a large synaptic input from the axonal endings of rod bipolar cells in the most vitreal region of the IPL (sublamina b, S5) and a smaller input from axonal endings of cone bipolar cells in the scleral region of the IPL (sublamina a, S1-S2). Amacrine input, localized at multiple levels in the IPL, equals the total number of synapses received from bipolar cells. The axonal endings of cone bipolar cells represent the major target for the chemical output of the AII amacrine cell: these synapses are established by the lobular appendages in sublamina a (S1-S2). Ganglion cell dendrites represent only 4% of the output of the AII amacrine and most of them are also postsynaptic to the cone bipolars which receive AII input. The AII amacrine is not presynaptic to other amacrine cells. Finally, the AII amacrine makes gap junctions with the axonal arborizations of cone bipolars that stratify in sublamina b (S3-S4) as well as with other AII amacrine cells in S5. Therefore, in the rabbit retina 1) the rod pathway consists of five neurons arranged in series: rod-->rod bipolar-->AII amacrine-->cone bipolar-->ganglion cell; 2) it seems unlikely that a class of ganglion cells exists that is exclusively devoted to scotopic functions. In ventral, midperipheral retina, about nine rod bipolar cells converge onto a single AII amacrine, but one of them establishes a much higher proportion of synaptic contacts than the rest. Conversely, each rod bipolar cell diverges onto four AII amacrine cells, but one of them receives the largest fraction of synapses. Thus, within the pattern of convergence and divergence suggested by population studies, preferential synaptic pathways are established.
通过对兔视网膜内网状层（IPL）中窄场双分层视杆无长突细胞（AII）连续超薄切片系列的电子显微镜照片进行重构，研究了其突触连接。AII无长突细胞在IPL最玻璃体区域（b亚层，S5）接收来自视杆双极细胞轴突末梢的大量突触输入，并在IPL巩膜区域（a亚层，S1 - S2）接收来自视锥双极细胞轴突末梢的较小输入。无长突细胞输入位于IPL的多个层面，其数量与从双极细胞接收的突触总数相等。视锥双极细胞的轴突末梢是AII无长突细胞化学输出的主要靶点：这些突触由a亚层（S1 - S2）中的小叶附属物形成。神经节细胞树突仅占AII无长突细胞输出的4%，并且它们中的大多数也是接收AII输入的视锥双极细胞的突触后成分。AII无长突细胞对其他无长突细胞没有突触前作用。最后，AII无长突细胞与在b亚层（S3 - S4）分层的视锥双极细胞的轴突分支以及S5中的其他AII无长突细胞形成缝隙连接。因此，在兔视网膜中：1）视杆通路由五个串联排列的神经元组成：视杆→视杆双极细胞→AII无长突细胞→视锥双极细胞→神经节细胞；2）似乎不太可能存在一类专门负责暗视觉功能的神经节细胞。在腹侧中周视网膜，约九个视杆双极细胞汇聚到单个AII无长突细胞上，但其中一个建立的突触接触比例比其他细胞高得多。相反，每个视杆双极细胞发散到四个AII无长突细胞上，但其中一个接收的突触比例最大。因此，在群体研究提出的汇聚和发散模式内，建立了优先的突触通路。
