Okada M, Erickson A, Hendrickson A
Department of Ophthalmology, University of Washington, Seattle 98195.
J Comp Neurol. 1994 Jan 22;339(4):535-58. doi: 10.1002/cne.903390406.
The development of synapses has been followed in Macaca monkey fetal and infant retina using immunocytochemical labeling for the transmembrane synaptic vesicle glycoprotein, SV2. Electron microscopy (EM) was used to verify the presence of morphological synapses at selected ages. EM immunocytochemical labeling in adult retina showed that all synaptic types contained SV2 in inner (IPL) and outer (OPL) plexiform layers. In fetal retina, SV2 expression and the appearance of morphological synapses were closely related in time, demonstrating that SV2 is a reliable marker for synaptogenesis. SV2 expression appears along a foveal to peripheral gradient. Both SV2 and synapses appear in the foveal IPL at Fd50-55, and reach the retinal edge by Fd90-103. Cone ribbon synapses and SV2 labeling are not present in the foveal OPL until Fd60. Photoreceptors in the far periphery contain SV2 by Fd119-125. This pattern demonstrates an "inner to outer" direction of synaptogenesis. Cones show SV2 labeling before rods at the same retinal eccentricity. In the cone-dominated fovea, SV2 labeling and bipolar cell ribbon-containing terminals are present at Fd55 when amacrine cell conventional terminals are very scarce, indicating that bipolar synapses precede amacrine synapses in monkey foveal IPL. SV2 labeling and bipolar terminals appear first in the outer IPL which contains "OFF" ganglion and bipolar processes in the adult, suggesting that "OFF" midget bipolar cells may form the first synapses. Both SV2 immunocytochemical labeling and EM morphology find that monkey retina follows a generalized inner before outer, and cone before rod synaptic developmental pattern, similar to that in other mammals. The cone-dominated fovea initiates synaptogenesis, and shows a different synaptic sequence from rod-dominated peripheral retina.
利用跨膜突触小泡糖蛋白SV2的免疫细胞化学标记，对猕猴胎儿和婴儿视网膜中突触的发育进行了追踪研究。运用电子显微镜（EM）来证实特定年龄阶段形态学突触的存在。对成年视网膜进行的EM免疫细胞化学标记显示，所有突触类型在内部（内网层，IPL）和外部（外网层，OPL）神经纤维层中均含有SV2。在胎儿视网膜中，SV2表达与形态学突触的出现时间密切相关，表明SV2是突触发生的可靠标志物。SV2表达呈现出从中央凹到周边的梯度变化。SV2和突触在胎龄50 - 55天时出现在中央凹内网层，并在胎龄90 - 103天时到达视网膜边缘。直到胎龄60天时，中央凹外网层才出现视锥细胞带状突触和SV2标记。到胎龄119 - 125天时，最周边的光感受器含有SV2。这种模式显示出突触发生的“从内到外”方向。在相同的视网膜离心度下，视锥细胞比视杆细胞更早出现SV2标记。在以视锥细胞为主的中央凹，当无长突细胞的传统终末非常稀少时，胎龄55天时就出现了SV2标记和含有双极细胞带状终末，这表明在猕猴中央凹内网层中双极突触先于无长突细胞突触形成。SV2标记和双极终末首先出现在成年时包含“OFF”神经节细胞和双极细胞突起的外部内网层，这表明“OFF”侏儒双极细胞可能形成最早的突触。SV2免疫细胞化学标记和EM形态学研究均发现，猕猴视网膜遵循一种普遍的从内到外、视锥细胞突触先于视杆细胞突触的发育模式，这与其他哺乳动物相似。以视锥细胞为主的中央凹启动突触发生，并呈现出与以视杆细胞为主的周边视网膜不同的突触形成顺序。
