Double-flash responses in different retinal layers

Stimulating the isolated arterially perfused cat eye with two consecutive flashes (double flashes) we have studied the reduction of the 2nd response recorded from outer (isolated PIII component of the ERG), middle (b-wave) and inner (optic nerve response, ONR) retinal layers. The spectral sensitivity of the mechanism that reduces the amplitude of the 2nd response, determined by a constant threshold of 20% amplitude reduction of the b-wave, could be matched by a 500 nm pigment absorption function. For a given stimulus irradiance the response reduction was largest in the b-wave and smaller in the PIII and ONR. The injection of the dopamine antagonist fluphenazine, which presumably does not influence rod receptor function, changes the ratio between the two b-wave double-flash responses. These data indicate that the reduction of the 2nd response is produced by a rod driven mechanism that has a receptoral as well as a postreceptoral component. The ONR data indicate that mechanisms in the inner retina counteract the amplitude reduction of the 2nd flash, thereby stabilizing the retinal output.