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S. Ueno, M. Kondo, Y. Niwa, H. Terasaki, Y. Miyake; "Push-Pull" Interplay between On-, Off-, and Photoreceptoral Components in the Primate Photoic ERG Contributes to the "Photopic Hill" . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1886.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: It is known that the amplitude of the photopic ERG b-wave increases with increasing stimulus intensities at lower stimulus levels, but it decreases at higher stimulus intensities ("photopic hill". Wali and Leguire, 1992). To study the mechanism for this unusual phenomenon, we investigated the photopic ERGs elicited by different stimulus intensities following intravitreous injection of various pharmacological agents in monkeys. Methods: Seven eyes of 5 adult monkeys (Macaca mutata and Macaca fascicularis) were studied. Stimuli were elicited by strong xenon strobe-flashes, and were reduced by ND filters in steps of 0.4 log unit. APB and PDA were used to block on- and off-bipolar activities, respectively, and NMDA and TTX to suppress inner retinal activities. Results: The intensity-response curve of the photopic ERG b-wave did not change significantly after the injection of TTX and/or NMDA, suggesting that the contribution of the inner retinal activities to the "photopic hill" is small. After APB, the positive wave was prolonged at the highest intensities, and a large, wide negative waveform remained at the highest intensities. After PDA, a sharp positive wave was seen at moderate intensities, but it became wide and decreased at the highest intensities. After APB+ PDA injection, the remaining negative photoreceptor component became deeper and wider with increasing intensities to the highest intensities. The postsynaptic on- and off-components were isolated by subtraction. At the highest intensities, a wide positive waveform derived from the ON-component was interfered by a wide, negative waveforms derived from the OFF- and photoreceptor components. Conclusions: These results suggest that a "push-pull" interplay between on-, off-, and photoreceptoral components at the highest stimulus intensities contribute to the "photopic hill".
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