Figure 1.

Pharmacological isolation of ipRGCs. Raw voltage traces from a rat whole mount retina preparation recorded simultaneously from ten electrodes of a multielectrode array under three different conditions. Most electrodes recorded spikes originating from more than one cell. Left and middle columns: Spike responses to a dim flash (−6 log I) recorded either in control Ames’ medium (left) or after 15 min in a pharmacological cocktail that blocks rod and cone signaling to ganglion cells (middle). Timing of light stimulus is indicated by the step below the traces and by the light background behind the traces. The brisk light-evoked responses evident in control conditions (left) are blocked by the cocktail at this light intensity (middle), suggesting that they are mediated by extrinsic input from retinal networks driven by rods and cones. Some spontaneous spiking persists. Right column: in the same cocktail, a light stimulus of 1000-fold higher intensity (−3 log I) evoked spiking in several channels (arrows). These exhibited the long onset latency and persistent post-stimulus discharge typical of melanopsin-mediated intrinsic responses.