Adaptation

In normal eyes, the amplitude of the b-wave of the photopic ERGs increases during light ad-aptation, but the mechanism causing this increase has not been fully determined. The pur-pose of this study was to evaluate the contribution of receptoral and post-receptoral components of the retina to this phenomenon. To accomplish this, we examined the ERGs during light adaptation in Pikachurin null-mutant (Pika-/-) mice, which have a misalignment of the bipolar cell dendritic tips to the photoreceptor ribbon synapses. After dark-adaptation, photopic ERGs were recorded from Pika-/- and wild type (WT) mice during the first 9 min-utes of light adaptation. In some of the mice, post-receptoral components were blocked pharmacologically. The photopic b-waves of WT mice increased by 50 % during the 9 min of light adaptation as previously reported. On the other hand, the b-waves of the Pika-/- mice decreased by 20 % during the same time period. After blocking post-receptoral components, the b-waves were abolished from the WT mice, and the ERGs resembled those of the Pika-/- mice. The extracted post-receptoral component increased during light adaptation in the WTmice, but decreased for the first 3 minutes to a plateau in Pika-/- mice. We conclude that the normal synaptic connection between photoreceptor and retinal ON bipolar cells, which is controlled by pikachurin, is required for the ERGs to increase during light-adapta-tion. The contributions of post-receptoral components are essential for the photopic b-wave increase during the light adaptation