Contribution of proximal retinal neurons to b- and d-waves of frog electroretinogram under different conditions of light adaptation.

The effects of pharmacological blockade of the proximal retinal activity by N-methyl-D-aspartate (NMDA) on the V-log I function of the ERG b- and d-waves were studied in dark and light adapted frog eyes. The effects of NMDA depended on the type of photoreceptor input. In rod-dominated ERG the b-wave amplitude was decreased by NMDA, but that of the d-wave remained unchanged. In cone-dominated ERG the b-wave amplitude was increased while the d-wave amplitude was decreased. Thus, the b/d amplitude ratio was decreased in rod-dominated, but increased in cone-dominated ERG. Our results imply that the b/d amplitude ratio would be changed in an opposite way in the rod- and cone-dominated ERG, when the function of the proximal retinal neurons is compromised.