Retinal Cx36 gap junctions in the inner and outer plexiform layers differentially control visual thresholds

Gap junctions are important components of signal communication in sensory systems. In the retina, connexin 36 (Cx36) gap junctions integrate visual signals over space and time. However, we do not understand how Cx36 gap junctions in the inner- and outer-retina govern visual thresholds under dim light conditions. Here we address this question using transgenic mouse models, an operant behavioral assay, and psychophysical modeling. Visual thresholds with Ganzfeld illumination decreased with flash durations <0.5 s, plateauing at ∼2 × 10^-4 ph/μm²/s with longer flashes. Removal of Cx36 in the outer retina lowered visual thresholds by 2.6-fold. However, removing Cx36 in both the inner and outer retina increased visual thresholds by 16.5-fold relative to controls. Further, we demonstrated that the visual thresholds of Cx36KO mice are rod-mediated, most likely via the OFF-rod pathway. We conclude that both inner- and outer-retinal Cx36 control visual thresholds under dim light conditions, but in distinct ways.