Our overall objective is to understand how electrical signals are initiated, transmitted, and processed through the vertebrate retina, culminating in ganglion cell impulse discharges that accurately encode the visual stimulus in the domains of space, time, intensity and color. Though notable progress has been made on these problems in recent years, much work is required to understand the detailed underlying physiology. This includes transduction and transmission in the photoreceptor, determination of the detailed physiological circuits by which retinal cells are interconnected, the nature of signal transmission of these interconnections, and the functional significance of these interconnections. The results should provide a more detailed explanation of various aspects of human psychophysics, such as the mechanisms underlying neural adaptation. The results should also provide a rational basis for diagnosis and treatment of retinal disorders resulting from dysfunctions of signal initiation or transmission. Much of the work on photoreceptor physiology and signal transmission will be conducted in lower vertebrates. Stringent efforts will also be made to conduct systematic intracellular studies in rods, cones, and second-order cells of mammalian retinas, using an arterially perfused isolated eyecup preparation. Our newly developed techniques for pulling ultrafine electrodes with short tips, and for advancing these electrodes by short high-speed steps, will be used to obtain high quality and stable intracellular recordings. When required, Procion yellow will be injected for histological identification of cells. Experiments with two separate electrodes in two adjacent histologically identified cells will be used to study the existence and nature of cellular interconnections.