PROJECT SUMMARY/ABSTRACT The signals of rods and cones set the fundamental limits of visual discrimination, which ultimately determine our ability to detect objects in the world around us. Normal photoreceptor function is essential for vision; degeneration of rods and cones produces blindness. Although research during the last 40 years has clarified many features of photoreceptor function and dysfunction, most of this work has been done on rods, even though cones respond over a much wider range of intensities and are more important in visual perception, particularly for the ability of the visual system to detect change and motion. The principal aim of this proposal is to exploit an important technical advance which, for the first time, has made possible the routine recording of both voltage and current light responses from intact mouse cones. Although cones in other mammalian species including primates have been investigated, mouse has the particular advantage that mutant strains are available. These strains make possible (1) more accurate voltage clamping of photoreceptors by removal of photoreceptor gap junctions, (2) deletion of particular conductance mechanisms to test their effects on signal modulation and degeneration, and (3) physiological recording from degenerating cones in strains particularly amenable to analysis. With these techniques, we are proposing to learn how cone inner-segment conductances modulate outer-segment currents to generate voltage responses and increase temporal discrimination. Recordings will be made from Cx36-/- mutant mice lacking connexin-36 gap junctions, and from Cx36-/- mice also lacking one of the inner-segment conductances, in order to explain how these conductances interact with outer-segment currents to produce the waveform of voltage responses. We will use a combination of white noise and chirp stimuli to investigate the temporal characteristics of cone responses, in order to assess the importance of inner-segment conductances to the frequency response of the cone. We will use mathematical modeling to explain the effects of each of the inner-segment conductances on the waveform of the voltage response and on temporal sensitivity. Our ultimate goal is to understand how inner-segment conductances shape the voltage response and determine the sensitivity of cones to changing illumination. We will use these same techniques to investigate how cone function is altered during degeneration. We are proposing to record from cones at several stages during degeneration in both rd10 and Cngb1-/- mice, whose cones degenerate at different rates. In this way, we hope to study cone single-cell physiology as they begin losing their outer segments, and then later from single "dormant" cell bodies after outer segments are lost. We will also investigate the effect of deletion of inner-segment conductances on the rate of cone degeneration, and the effect of these deletions on the physiology of the degenerating cells.