GABAergic control on the intensity-response function of ERG waves under different background illumination

The effect of GABAergic blockade on the intensity-response function of frog ERG waves was investigated under two levels of background illumination in the mesopic and photopic range. GABAergic blockade by picrotoxin shifted the intensity-response curves to the left along the intensity axis and increased their slope under both backgrounds. The maximal gain (dV/dI) and contrast gain (dV/dlog I) of the mechanisms responsible for the ERG wave generation were also increased after GABAergic blockade. The intensity range in which the amplitude of the response was a linear function of the logarithm of the stimulus intensity was very restricted. GABAergic blockade influenced also the rapid transitory processes, which determined the steady-state amplitude of the ERG b-wave after a considerable change of the stimulus contrast. The adaptational effect of the background illumination on the intensity-response function of the ERG waves was not principally changed after GABAergic blockade. The possible neuronal mechanisms of the observed picrotoxin effects are discussed.