Chun M H, Grünert U, Martin P R, Wässle H
Max-Planck-Institut für Hirnforschung, Frankfurt, Germany.
Vision Res. 1996 Nov;36(21):3383-95. doi: 10.1016/0042-6989(95)00334-7.
Parallel pathways for visual information processing start at the first synapse of the retina, at the cone pedicle. At least eight different types of bipolar cells receive direct synaptic input from an individual cone. The present study explores whether enough synaptic sites are available at the cone pedicle to supply all these bipolar cells. Monkey retinae were optimally fixed for electron microscopy. Serial horizontal sections were cut through the cone pedicle layer in a piece close to the fovea (eccentricity: 0.75 mm) and in a peripheral piece (eccentricity: 5-6 mm). The ribbon synapses (triads) at the cone pedicle base were analysed. The average number of synaptic ribbons per cone pedicle increased from 21.4 +/- 1.6 (n = 26) in central retina to 41.8 +/- 3 (n = 14) in peripheral retina. Five central and five peripheral pedicles were reconstructed and the invaginating bipolar cell dendrites forming the central elements of the triads were characterized. Close to the fovea an average of 18 invaginating bipolar cell dendrites was found, in peripheral retina the average was 90. Pedicles of foveal cones have one invaginating central process per ribbon, pedicles of peripheral cones have two. It is possible that midget bipolar cell dendrites occupy the majority of triads in the fovea, while in peripheral retina both midget and diffuse bipolar cell dendrites share the triads.
视觉信息处理的并行通路始于视网膜的第一个突触，即视锥细胞终足。至少有八种不同类型的双极细胞从单个视锥细胞接收直接的突触输入。本研究探讨在视锥细胞终足处是否有足够的突触位点来供应所有这些双极细胞。对猴视网膜进行最佳固定以用于电子显微镜观察。在靠近中央凹的一块区域（偏心度：0.75毫米）和一块周边区域（偏心度：5 - 6毫米），沿着视锥细胞终足层切取连续的水平切片。分析视锥细胞终足基部的带状突触（三联体）。每个视锥细胞终足的突触带平均数量从中央视网膜的21.4±1.6（n = 26）增加到周边视网膜的41.8±3（n = 14）。重建了五个中央和五个周边终足，并对形成三联体中央元件的内陷双极细胞树突进行了特征描述。在靠近中央凹处平均发现18个内陷双极细胞树突，在周边视网膜平均为90个。中央凹视锥细胞的终足每个突触带具有一个内陷的中央突起，周边视锥细胞的终足有两个。有可能侏儒双极细胞树突占据了中央凹处大多数的三联体，而在周边视网膜，侏儒双极细胞和弥散双极细胞的树突共同占据三联体。
