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H. Maeda, S.M. Saszik, L.J. Frishman; Postreceptoral Contributions to the A-Wave of the Photopic Flash ERG of the Mouse Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1891.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine the extent to which postreceptoral signals contribute to the photopic flash ERG of the mouse. Methods: Ganzfeld ERGs were recorded from adult C57/BL6 mice anesthetized with ketamine (56 mg/kg) and xylazine (5.6 mg/kg). Recordings were made between DTL fiber electrodes placed under contact lenses on the eyes. Stimuli were brief LED flashes (λmax 513nm; 0.4-2.2 log sc td s) and xenon photostrobe flashes (2.5-3.5 log sc td s). A rod-suppressing background of 2.5 log sc Td was used, and mice were adapted to the background for 15 minutes before recordings. The following pharmacological agents were injected intravitreally: PDA (cis-2,3-piperidine-dicarboxylic acid, 3-5 mM) to block transmission to hyperpolarizing 2nd order and all 3rd order neurons, NMDA (N-methyl-D-aspartic acid, 3 mM) to suppress activity of 3rd order neurons, or TTX (tetrodotoxin; 3-4 µM) to block Na+-dependent spikes. ERGs also were recorded after ganglion cells were lesioned by optic nerve crush (ONC; 14-28 days post crush). Results: PDA significantly reduced the amplitude of the a-wave at all stimulus energies. For a-waves measured 15 ms after the flash, the postreceptoral component removed by PDA was 60% of the control response to the LED stimulus, and about 45% of the control response to the xenon strobe, whereas responses up to about 8 ms after flash were not affected by PDA. NMDA removed only a small portion of the a-wave at 15 ms, and TTX and ONC had little or no effect. PDA also eliminated the majority of the oscillatory potentials (OPs) and the photopic negative response (PhNR). NMDA reduced but did not eliminate these components, and TTX and ONC both had smaller effects on OPs than NMDA, and did not remove the PhNR. Conclusions: Postreceptoral neurons make a significant contribution to the photopic a-wave of the mouse ERG. Ganglion cells and spiking activity of inner retinal neurons do not make substantial negative-going contributions to the a-wave or PhNR, and only small contributions to the OPs.
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