This project aims to complete our studies of the principal factors governing the transfer of signal from photoreceptors to bipolar cells. Specifically, we aim to identify the synaptic mechanism underlying the spatial organization of the receptive field of the bipolar cell, to identify the mechanism responsible for the bandpass filtering across the rod/bipolar cell synapse and to establish what aspects of the responses of receptor and bipolar cell responses are important in the encoding of intensity. We plan to extend our work from the dark-adapted state to include the effects of light adaptation. To do this we must first study the effects of background illumination on the sensitivity and kinetics of rod and cone responses.
Our aim i s to use that information to evaluate the effects of adaptation on the mechanisms of synaptic transfer. Specifically we shall evaluate the effects of backgrounds upon transsynaptic gain, on temporal filtering and upon the spatial organization of receptive fields. These analyses will be carried out at the levels of the receptor/bipolar cell synapse and the bipolar/ganglion cell synapse. We shall use intracellular recording techniques in intact retinae and patch-clamp recording methods applied to enzymatically dissociated cells in vitro in a coordinated and complementary way. We also plan to study the role of [Ca2+](in) in the mechanism of light adaptation of rods using a unique method for the measurement of intracellular calcium levels in rod outer segments developed in our laboratory. Those measurements will be coordinated with simultaneous measurements of transmembrane currents made with the suction pipette technique. This project should add considerably to our understanding of the processes of signal transfer and information processing not only in the retina but in the nervous system generally. The studies of Ca should contribute to an overall picture of the processes that contribute to photoreceptor adaptation. The project should add important information to our knowledge of visual function and may contribute to an understanding of certain clinical disorders involving low-vision loss.
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