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

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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