Figure 8. ipRGCs with distinct types of intrinsic light response exhibit similar synaptically driven photoresponses.

Upper panel: raster plots of two representative ipRGCs with distinct kinetics of melanopsin-driven intrinsic photoresponse, apparently corresponding to two types defined by Tu et al., (2005) in adult mice. Type II cell (blue) has long onset latency and shorter post-stimulus discharge; Type III has short latency and prolonged afterdischarge. Stimulus was a 60 sec light step (yellow bar; 480 nm, ∼6×10¹² photons/cm²·s). Recordings were performed under synaptic blockade. Lower panel: intensity-response series of the same two cells, but without synaptic blockade. The light stimuli were one second flashes 500 nm flashes ascending in intensity within the series. Both cells showed the same irradiance-response properties, with thresholds approximately 0.02 Rh*/rod/s.