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C. Dong, W.A. Hare; Retinal Mechanisms That Underlie Generation of the Erg Oscillatory Potential (op) in the Rabbit Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1889.
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Purpose: The OP is a transretinal field potential believed to be generated by light-elicited activity of inner retinal neurons, particularly amacrine cells. It is a sensitive, non-invasive tool for detecting early functional disturbance in retinal diseases such as diabetic retinopathy. In order to enhance the utility of the OP as a tool for evaluation of retinal function under normal and disease conditions we investigated the neural mechanisms that underlie OP generation in the rabbit. Methods: ERG signals, elicited by a Grass PS-33 Plus Visual Stimulator, were recorded from anesthetized, adult pigmented rabbits which were dark-adapted for 5 min. Averaged responses to 10 stimulus repetitions were used for analysis. The inter-flash interval was 10 sec. The OPs and b-waves were band-filtered between 100-1000 Hz and 0.1-1000 Hz, respectively, and were digitized at 5 KHz. All test compounds were applied by intravitreal injection. Results: A bright light flash (16x) elicited a stereotypic OP that consisted of 6 clearly identifiable negative (N1-6) and positive (P1-6) peaks. Blocking transmission between photoreceptors (PRs) and ON bipolar cells with APB eliminated the b-wave and the later OP wavelets (N4P4-N6P6), attenuated significantly the intermediate ones (N2P2-N3P3), but had no effect on the early wavelets (N1P1). Application of non-NMDA glutamate receptor antagonists (PDA or CNQX) that blocked transmission between PRs and OFF bipolar cells and also between bipolar cells and 3rd order neurons attenuated the amplitude and slowed the kinetics of the b-wave, but had an effect on the OP that was very similar to that of APB. The selective GABAa (but not glycine) receptor antagonist attenuated significantly the amplitude of N2P2-N6P6 and shifted their phases, but had no effect on N1P1. Blocking voltage-gated Na+ channels with TTX eliminated N4P4-N6P6, attenuated slightly N2P2-N3P3, but had no effect on N1P1. N1P1 were affected only by the treatments that impair PR function. Conclusions: The rabbit OPs can be divided into early (N1P1), intermediate (N2P2-N3P3), and later (N4P4-N6P6) subgroups that appear to be generated mainly by PRs, direct (action potential independent), and long-range (action potential dependent) interactions between ON, but not OFF, bipolar cells and 3rd order neurons, respectively. GABAa inhibition plays substantially more important role than glycine inhibition in generation of intermediate and later OPs.
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