Influence of picrotoxin and strychnine on the spectral sensitivity of the turtle ERG b‐ and d‐waves: II. Light adaptation

The ERG ON- (b-wave) and OFF-response (d-wave) to differently coloured stimuli was studied using a wide range of stimulus intensities in dark adapted turtle retina. The intensity-response curve of the b-wave showed saturation but that of the d-wave, decline in the high-intensity stimulus range. The curves of the relative spectral sensitivity of the ERG ON - and OFF-response were similar and showed a maximum in the longwave part of the spectrum. GABAergic blockade by 50 μmol L -1 picrotoxin caused an increase of the sensitivity. contrast sensitivity and the amplitude range of both ON- and OFF-responses without narrowing of the response dynamic range. In the range of lower stimulus intensities the ON-responses to blue stimuli and the OFF-responses to red stimuli were affected to a greater extent. An increased ERG b- and d-wave sensitivity was also observed during glycinergic blockade by 50 μmol L -1 strychnine. In the low intensity stimulus range the effect was maximal on the ON-responses to blue stimuli and on the OFF-responses to 570 nm stimuli. It was concluded that the GABA- and glycinergic systems in the retina equalize rather than make different the relative spectral sensitivities of the ON- and OFF-responses.