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Two types of exocytosis at retinal ribbon synapses and their functions in visual information processing

视网膜带突触的两种胞吐作用及其在视觉信息处理中的功能

基本信息

批准号：
18300132
负责人：
TACHIBANA Masao
金额：
$ 10.41万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18300132/
关键词：
Neuroscience Phvsiology Anatomy Brain Nerve Vision Retina Svnanse シグナル伝達伝達物質放出

项目摘要

Synaptic ribbons with a halo of synaptic vesicles are observed at the terminal of sensory neurons that release transmitter tonically. Thus, ribbons are assumed to be prerequisite to sustained exocytosis. Retinal bipolar cells have plenty of ribbons in their terminal and send outputs to ganglion and/or amacrine cells. In the present study, applying total internal reflection fluorescence microscopy to goldfish retinal Mb1 bipolar cell terminals under whole-cell voltage clamp, we visualized Ca^2+ entry sites, ribbons, and vesicle fusion events. We found that main Ca^2+ entry sites were located at ribbons, and that activation of the presynaptic L-type Ca^2+ current induced a transient high-rate vesicle fusion followed by a low-rate fusion inside the ribbon region and a delayed sustained fusion outside the ribbon region. Activation of protein kinase C (PKC) by phorbol ester specifically increased vesicle fusion events outside the ribbon region. Test for spatial randomness of vesicle fusion events revealed that vesicle fusion occurred not randomly but at "hot spots" in both regions. Electron microscopic examination of goldfish Mb1 bipolar cell terminals revealed that PKC activation selectively increased the number of docked vesicles at ribbon-free sites, which faced neuronal processes with the postsynaptic density (PSD). Reconstruction of the whole terminal of an Mb1 bipolar cell from serial ultra-thin sections showed that the number of ribbon-associated synapses with dyad processes was almost comparable to that of ribbon-free synapses with single processes. These results indicate that exocytosis may occur at both ribbon-associated and ribbon-free active zones. Dichotomy of transient and sustained photoresponses in retinal ganglion cells may be partly ascribed to two types of active zones in bipolar cell terminals.

在感觉神经元的末端观察到具有突触囊泡晕的突触带，其紧张性地释放递质。因此，带状物被认为是持续胞吐的先决条件。视网膜双极细胞的末端有大量的带状结构，并向神经节细胞和/或无长突细胞发送信号。在本研究中，应用全内反射荧光显微镜在全细胞电压钳下观察金鱼视网膜Mb 1双极细胞末梢，我们观察到Ca^2+进入位点、条带和囊泡融合事件。我们发现主要的Ca^2+进入位点位于带状区域，突触前L型Ca^2+电流的激活诱导了短暂的高速率囊泡融合，随后是带状区域内的低速率融合和带状区域外的延迟持续融合。蛋白激酶C（PKC）的激活佛波酯特异性地增加了带状区域外的囊泡融合事件。空间随机性测试的囊泡融合事件显示，囊泡融合发生不随机，但在“热点”在这两个地区。金鱼Mb 1双极细胞终末的电子显微镜检查显示，PKC激活选择性地增加了停靠在无带位点的囊泡的数量，这些囊泡面向具有突触后密度（PSD）的神经元过程。从连续超薄切片的Mb 1双极细胞的整个终端的重建表明，与二分体过程的带状相关突触的数量几乎可以与单突起的无带状突触相媲美。这些结果表明，胞吐作用可能发生在两个带相关和无带的活动区。视网膜神经节细胞的瞬时和持续光反应的二分法可能部分归因于双极细胞末端的两种类型的活动区。