Organization and development of the S-cone system

National Eye Institute

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Abstract

Here we present a thorough accounting of the S-cone specific wiring in the OPL of the cone-dominant thirteen-lined ground squirrel (13-LGS), using multiple convergent lines of anatomical and physiological evidence. We find the only S-cone specific bipolar cell to be the canonical ON SCBC, and find no evidence that an OFF SCBC is a core component of S-cone circuitry in the 13-LGS retina, indicating that its SCA is likely to be the main substrate for S-OFF signaling (Chen & Li, 2012; Sher & DeVries, 2012). Other BCs either make indiscriminate contacts with M- and S-cones or avoid S-cones. Further, we show that indeed, the H2 cell lacks contacts with M-cones entirely and is only modulated by S-cone isolating light stimuli. Finally, aided by high-resolution serial block-face electron microscopy (SBEM), we show that interestingly, H1 cell axons avoid S-cones entirely although they contact all cones with their dendritic field regardless of type. Combined, these findings identify the 13-LGS S-cone circuit as a particularly privileged chromatically sensitive circuit whose study promises to be valuable for understanding the so-called primordial S-cone system.