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C. Joselevitch, M. Kamermans; Interaction Between Rod and Cone Inputs in Mixed-Input Bipolar Cells of the Goldfish Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3230.
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© ARVO (1962-2015); The Authors (2016-present)
Mixed-input bipolar cells (MBCs) contact both rods and cones. Although the morphology of the different MBC subtypes has been described, insight in the interaction between rods and cones at the bipolar cell level is scarce. The aim of this study was to characterize this interaction in the different physiological types of MBCs.
Voltage- and current-clamp recordings of cone, horizontal cell and MBC light responses were obtained from goldfish retinal slices. Intensity-response relations were fit with Hill functions and spectral and absolute sensitivities were analyzed in order to obtain an estimate of the relative contribution of rod and cone inputs to MBCs.
MBCs were classified as depolarizing (ON MBCs), hyperpolarizing (OFF MBCs) or having a combination of the two types of response (opponent MBCs) after center stimulation. The relative contributions of rod and cone inputs to these cells varied. ON MBCs are rod-dominated, having the highest sensitivity and the smallest dynamic range. OFF MBCs, on the other hand, have a more balanced rod-cone input ratio. This extends their dynamic range and decreases their sensitivity. Finally, opponent MBCs seem to be mostly cone-dominated, although some rod input is present. The antagonistic photoreceptor inputs form a push-pull system that makes opponent MBCs very sensitive to changes in light intensity.
Due to their different rod-cone input ratios, the three classes of MBC seem to be optimized for transmitting information at different light levels. Not only do they differ in absolute sensitivity, but also in dynamic ranges, which suggest that they might have distinct contrast sensitivities. The organization of MBCs into three classes with different dynamic ranges and absolute sensitivities might be a strategy to transmit information about all visual aspects most efficiently, given the sustained nature of BC responses and their limited voltage range.
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