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Masatoshi Nagaya, Shinji Ueno, Mineo Kondo, Takahisa Furukawa, Hiroko Terasaki; Reduction of ERG Amplitude during light adaptation in Pikachurin null-mutant mice. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5083.
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The amplitude of the b-wave of the ERG increases during light adaptation, and several studieshave suggested that this was caused byan increase in the cone photoreceptor responsesduring light adaptation. The Pikachurin null-mutant mice(Pika -/-) have a misalignment of the bipolar cell dendritic tips to the photoreceptor ribbon synapses which alters the post-receptoral responses.The purpose of this study was to determine the contribution of post-receptoral potentials to the increase in the b-waves during light adaptation.
Sixty Pika -/- and control C57 BL6J mice (WT)of 6 to 10-weeks of-age were studied. After at least 6 hours of dark-adaptation, animals were anesthesized and placed in a Ganzfeld bowl. ERGs were elicited by stroboscopic stimuli, and 20 to 30 ERGs were averaged with a repetition rate of 1 sec. The photopicstimulus intensity was 1.0 log cd-s/m2under 30 cd/m2 of background light. ERGs were recorded immediately after the beginning of light-adaptation and recorded periodically for 10 minutes during light adaptation. Six Pika -/- and 6 WT mice were injected DL-2-amino-4- phosphonobutyric acid(APB) intravitreally to block the post-receptoral ON bipolar cell components.
The amplitude of photopic b-waves of WT mice increased by30% during the first 3 minutes and increased to50% of the pre-light-adaptation amplitude after 7 minutes and reached a plateau. On the other hand, the amplitude ofthe b-wave ofPika -/-mice decreased by 20% in the first 3 minutes and reached plateau. After APB, the photopic b-waveswere severely decreased in both the Pika -/-and WT mice. The APB-sensitive component, i.e., the difference between original wave and post-APB wave,was increased during the first 10 minutes of light adaptation in WT mice but decreased inPika -/-mice.
The reduction of the b-waves inPika -/- mice during light-adaptationsuggeststhat not only the cone photoreceptor potentials but also the post-receptoral potentialscontribute to the ERG growth during the course of light adaptation.
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