Owen W G
Department of Biophysics and Medical Physics, University of California, Berkeley 94720.
J Comp Neurol. 1985 Oct 22;240(4):423-33. doi: 10.1002/cne.902400410.
Electron microscopic observation of the distal retina of the turtle, Chelydra serpentina, revealed that photoreceptors contact each other by means of a variety of junctions. The synaptic terminals of the primary and accessory members of a double cone invariably make punctate contact with each other distal to the basal surfaces. This type of contact was only rarely seen between the synaptic terminals of single photoreceptors. Photoreceptor telodendria which emanate from the basal surface of the synaptic terminal and ramify laterally for up to 40 microns in the outer plexiform layer give off branchlets which contact the terminals of both rods and cones. These contacts resemble superficial basal junctions and can be of the "wide-gap" or "narrow-gap" type. In cones the branchlets of the telodendria sometimes make a "distal junction" with one of the lateral elements of a synaptic dyad. Gap junctions were not found between the fins radiating from the myoids of adjacent receptors but were seen to occur en passant between photoreceptor telodendria in the outer plexiform layer. These junctions, though small, are probably of sufficient size to account for the rod-rod coupling observed physiologically in this retina. A prominent organelle resembling a synaptic lamella was occasionally seen in processes making contact with photoreceptors. These processes were identified as bipolar cell dendrites.
对蛇鳄龟（Chelydra serpentina）视网膜远端进行电子显微镜观察发现，光感受器通过多种连接方式相互接触。双锥体细胞的主细胞和辅助细胞的突触终末在基底面远端总是形成点状接触。这种接触类型在单个光感受器的突触终末之间很少见。从突触终末基底面发出并在外网状层横向分支达40微米的光感受器终末分支发出小分支，与视杆和视锥的终末相接触。这些接触类似于浅基连接，可为“宽间隙”或“窄间隙”类型。在视锥细胞中，终末分支有时与突触二联体的一个侧向成分形成“远端连接”。在相邻感受器肌样体发出的鳍状物之间未发现缝隙连接，但在外网状层的光感受器终末分支之间可见其呈过路形式出现。这些连接虽然小，但可能大小足以解释在此视网膜中生理上观察到的视杆 - 视杆耦合。在与光感受器接触的突起中偶尔可见一种类似突触板的突出细胞器。这些突起被鉴定为双极细胞树突。
