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Masatoshi Nagaya, Shinji Ueno, Mineo Kondo, Takahisa Furukawa, Hiroko Terasaki; Photoreceptor and post-photoreceptoral contribution to reduction of photopic b-wave ERG in light-adapted Pikachurin null-mutant mice. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6184.
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© ARVO (1962-2015); The Authors (2016-present)
The amplitude of the b-wave of the ERG increases during light-adaptation, but the mechanism for this increase has not been determined. 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. We have shown that the photopic b-wave did not increase but decreased during light-adaptation in Pika -/- mice (ARVO 2013). The purpose of this study was to determine the cellular components that cause the decrease in the b-waves during light-adaptation in Pika -/- mice .
Pika -/- and control C57 BL6J mice (WT) of 8 to 12-weeks of-age were studied. After at least 6 hours of dark-adaptation, animals were anesthetized 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 photopic stimulus intensity was 1.0 log cd-s/m2 under 30 cd/m2 of background light. ERGs were recorded immediately after the beginning of light-adaptation and recorded periodically for 10 minutes during the light-adaptation. Eleven Pika -/- and 11 WT mice were injected toDL-2-amino-4- phosphonobutyric acid (APB) and cis-2, 3-piperidine-dicarboxylic acid (PDA) intravitreally to block the post-receptoral ON and OFF bipolar cell components. The post-receptoral contributions were calculated by subtracting the ERGs after APB+PDA injection from ERGs after PBS injection.
The amplitude of photopic b-waves of WT mice increased by 50% of the pre-light-adaptation amplitude after 10 minutes of light-adaptation. On the other hand, the amplitude of the b-wave of Pika -/-mice decreased by 20%. After the APB+PDA intravitreal injection, which blocked the post receptor potentials, only the a-wave remained in both Pika -/- and WT mice. In both types of animals, the a-waves increased by 30% during the 10 minutes of light-adaptation. The post-receptoral contribution, i.e., the difference between the PBS-treated eyes and APB+PDA-treated eyes, increased by 70% in WT mice and decreased by 30% in Pika -/-mice.
Our results suggest that the reduction of the b-wave amplitudes in Pika -/- mice during light-adaptation was caused mainly by a reduction of the post-receptoral potentials.
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