Influence of picrotoxin on the retinal sensitivity at different levels of background illumination.

The intensity-response function of the b-wave of the ERG in the retina of the turtle (Emys orbicularis) was investigated at two different background illuminations--0.01 and 10 lx, before and after blockade of the GABA-ergic transmission by 0.4 mmol/l picrotoxin (PT). A shift of the curve to the left along the intensity axis at both backgrounds was observed after PT treatment. The region where the b-wave amplitude was linear function of the logarithm of the stimulus intensity was also considerably narrowed. The registered experimental data fitted in well with the Naka-Rushton equation. The participation of GABA-ergic neurones in the processes of light adaptation and gain control in the retina is discussed.