Crooks J, Okada M, Hendrickson A E
Department of Biological Structure, University of Washington, Seattle 98195, USA.
J Comp Neurol. 1995 Sep 18;360(2):349-62. doi: 10.1002/cne.903600211.
Synaptogenesis has been tracked by using quantitative electron microscopic methods in the inner plexiform layer (IPL) of the developing Macaca monkey fovea from fetal day (Fd) 55 to Fd132. Vesicle-containing profiles were classified according to whether (1) they contained a ribbon indicating that they originated from a bipolar cell, or (2) the profile formed a junction. Group 2 was further subdivided by morphological characteristics into (2a) amacrine, (2b) bipolar, or (2c) unknown profiles. Ribbon-containing bipolar profiles are clearly identifiable at Fd55 when they occur at a density of 0.9/100 microns2. Bipolar synapses increase rapidly to 4.7/100 microns2 by Fd88, similar to their density at Fd132. Identifiable amacrine profiles forming a junction are rare at Fd55-68. By Fd88, amacrine synaptic density has jumped to 6.7/100 microns2 and continues to increase to 9.5/100 microns2 at Fd132. These quantitative data strongly suggest that, at the Macaca fovea, bipolar synaptogenesis both begins and ends before amacrine synaptogenesis. The large number of immature amacrine synaptic profiles and densities at Fd132 suggests that amacrine synapses continue to form after Fd132. This study confirms that cone-dominated monkey fovea has a different sequence of synaptogenesis than the rod-dominated peripheral retina (Nishimura and Rakic, [1985] J. Comp. Neurol 241:420-434). The data support the concept that synaptic developmental sequence is determined by the type of photoreceptor which dominates a particular retinal region or species. Bipolar ribbon synapses are observed in the outer half of the IPL at Fd55, are present in the inner IPL at Fd60, and then, with increasing age, are found throughout the IPL. This pattern strongly suggests that vertical OFF bipolar pathways form earlier than ON pathways in the IPL. In contrast, amacrine profiles are found throughout the IPL at the youngest ages, with an adult-like banding pattern present by Fd132.
通过定量电子显微镜方法，对发育中的猕猴中央凹内网状层（IPL）从胎儿期第55天（Fd55）到第132天（Fd132）的突触发生进行了追踪。含有囊泡的轮廓根据以下情况进行分类：（1）是否含有表明它们起源于双极细胞的带状结构，或（2）该轮廓是否形成连接。第2组根据形态特征进一步细分为（2a）无长突细胞、（2b）双极细胞或（2c）未知轮廓。当含带状双极轮廓以0.9/100平方微米的密度出现时，在Fd55时可清晰识别。到Fd88时，双极突触迅速增加到4.7/100平方微米，与Fd132时的密度相似。在Fd55 - 68时，形成连接的可识别无长突细胞轮廓很少见。到Fd88时，无长突细胞突触密度跃升至6.7/100平方微米，并在Fd132时继续增加到9.5/100平方微米。这些定量数据有力地表明，在猕猴中央凹，双极突触发生在无长突细胞突触发生之前开始并结束。在Fd132时大量未成熟的无长突细胞突触轮廓和密度表明，无长突细胞突触在Fd132之后继续形成。这项研究证实，以视锥细胞为主的猕猴中央凹具有与以视杆细胞为主的周边视网膜不同的突触发生顺序（西村和拉基克，[1985]《比较神经学杂志》241:420 - 434）。数据支持这样的概念，即突触发育顺序由主导特定视网膜区域或物种的光感受器类型决定。在Fd55时，在IPL的外半部分观察到双极带状突触，在Fd60时出现在IPL的内半部分，然后随着年龄增长，在整个IPL中都能发现。这种模式强烈表明，在IPL中垂直OFF双极通路比ON通路形成得更早。相比之下，在最年轻的时候，无长突细胞轮廓在整个IPL中都能发现，到Fd132时呈现出类似成年的带状模式。
