The contribution of cone responses to rat electroretinograms

The contribution of rods and cones to the scotopic electroretinogram (ERG) of small animals is unclear, with a recent report suggesting that the mouse has no cone a-wave. The present study considered the contribution of cones to the ERG of the rat. Dark-adapted Long Evans rats (n = 4) had ERG signals collected following a single flash, which stimulated rods and cones (mixed response), or a twin-fash paradigm (short interstimulus interval, 1 s), which isolated cone responses. Rod signals were derived by digital subtraction of the cone signal from the mixed rod/cone ERG. The rat a-wave was found to be dominated by rod responses but cone responses contributed substantially (45%) to post-receptoral waveforms (b-wave) at higher light levels.