Glycinergic and GABAergic control of intensity-response function of frog ERG waves under different conditions of light stimulation

The effect of glycinergic blockade by strychnine and GABAergic blockade by picrotoxin on the intensity-response function and time course of ERG b- and d-wave was investigated in dark and light adapted frog eyecups as well as in chromatically adapted eyecups, in which the responses were predominantly mediated by one photoreceptor type. Both of the blockers markedly increase d the maximal response amplitude and thus increased the contrast gain of th e mechanisms generating ERG waves. Strychnine but not picrotoxin narrowed t he dynamic range of the b-wave in all eyecups. The glycine and GABAergic co ntrol on retinal sensitivity however, depended on photoreceptor input. The b-wave sensitivity was increased to the greatest extent when green rods med iated the response; it was slightly increased when the response was mediate d by red cones and was not changed at all when red rods mediated the b-wave . On the other hand the d-wave sensitivity was enhanced regardless of photo receptor input so that it became equal (dark) or even greater (light adapte d eyes) than that of the b-wave. Strychnine shortened but picrotoxin increa sed the implicit time of the b-wave and both the blockers markedly slowed t he d-wave time course. Thus the blockers considerably diminished or fully e liminated the initial difference in time course between the ON and OFF resp onse. The glycine- and GABAergic blockade did not principally alter the lig ht adaptation process expressed in decreasing retinal sensitivity, narrowin g the dynamic range and speeding the time course of the responses with incr easing background illumination.