A study on the spatio-temporal mechanisms of the vertebrate outer retina.

在脊椎动物视网膜中，由光感受器、水平细胞和双极细胞之间的突触连接组成的外丛状层在颜色和空间信息处理中起着重要作用。为了阐明视网膜功能的潜在机制，我们利用多输入技术、细胞内钙的光学成像和外视网膜的定量模型进行了以下研究。为了表征视网膜水平细胞的感受野特性，在彩色显示器上显示由241个密集排列的六边形元素组成的刺激，记录了L型和R/ g型水平细胞在细胞内的反应。每个刺激元素按照二值m序列在黑色和彩色（R、G、B和白色）之间独立变化。一阶核与L型和R/ g型水平细胞的传统感受野性质很好地对应。结果表明，多输入技术能够以高时空分辨率表征视网膜水平细胞的二维感受野特性。这种新方法可能成为分析视网膜信息处理的一种强有力的电生理学工具。神经元细胞内钙系统对突触传递和离子电流特性起着重要的控制作用。为了阐明钙的作用机制，我们利用钙成像系统分析了光感受器中细胞内钙的时空特性。研究发现，光感受器细胞内钙离子浓度存在时空梯度，这是细胞膜离子通道和细胞内钙调节系统定位的结果。基于这些研究，我们建立了外视网膜的定量模型，这对于更好地理解外丛状层是必不可少的。提出了光感受器、水平细胞和双极细胞的离子电流模型。这些模型提供了对离子电流的功能作用的详细理解，离子电流在视网膜外细胞中产生电反应。我们还讨论了如何利用基于离子电流的单细胞模型构建网络模型来研究视网膜外网状层的功能。少

In the vertebrate retina, the outer plexiform layr which consists of synaptic connections among photoreceptors, horizontal cells and bipolar cells, plays a fundamental role in color- and spatil-information processings. In order to elucidate the underlying mechanisms of the retinal functions, we have made the following studies by using a multi-input technique, an optical imaging of the intracellular calcium and a quantitative model of the outer retina.In order to characterize the receptive field properties of retinal horizontal cells, intracellular responses were recorded from L- and R/G-type horizontal cells with the stimulus consisted of a densely packed array of 241 hexagonal elements displayd on a color monitor. Each stimulus element was changed independently between black and colored (R,G,B and white) according to a binary m-sequence. The first order kernels are well corresponded to the traditional receptive field properties of L- and R/G-type horizontal cells. The results suggest … More that the multi-input technique enable to characterize the two-dimensional receptive field properties of retinal horizontal cells with high spatio-temporal resolution. This new method could be a powerful elctrophysiological tool for analyzing the retinal information processings.The intracellular calcium system in neurons plays an important role to control the synaptic transmission and ionic current characteristics. In order to clarify the calcium mechanisms, we analyzed the spatio-temporal properties of the intracellular calcium in the photoreceptor by using a calcium imaging system. It was found that there is a spatio-temporal gradient of the intracellular calcium concentration in photoreceptors, which is resulted in the localization of the ionic channels on the cell membrane and the intracellular calcium regulating systems.Based on these studies, we have developed a quantitative model of the outer retina, which is essential toward better understanding of the outer plexiform layr. We proposed ionic current models of photoreceptor, horizontal cell and bipolar cell. The models provide a detailed understanding of the functional role of the ionic currents which generate the electrical responses in outer retinal cells. We also discussed how the function of the retinal outer plexiform layr could be studied by constructing a network model from the ionic current based single cell models. Less