Abstract
Purpose :
The ERG is usually viewed as a sequence of waves (a-wave, b-wave, etc.) that result from overlapping components (PI, PII, PIII). But the components can arise from more than one cellular source. For instance, PIII consists of fast PIII from photoreceptors (PR) and slow PIII from Muller cells (MC). In this study we dissected the ERG into three cellular constituents originating from PR, MC, or bipolar cells (BC). These three cells respond differently to steady and flickering light, and the purpose of this work was to investigate how this manifests in the ERG.
Methods :
Intraretinal recordings were made from isolated mouse (C57Bl/6J) retinae. Diffuse steady and flickering (1, 3 and 10 Hz) light of scotopic and photopic intensities was applied in both dark-and light-adapted conditions. Double-barreled glass microelectrodes were beveled so that there was 75-100 μm between the tips of the barrels. These permitted the spatial separation of PR responses from the proximal constituents of the ERG, originating from MC and BC. To isolate the MC constituent, neuronal post-PR activity was prevented by Co++. To isolate the BC constituent, the MC response was suppressed by Ba++.
Results :
All three constituents overlap each other. Extracellular PR responses in isolated mouse retina can reach 300-400 μV, making the b-wave of the ERG smaller than the BC-constituent at its maximum. The MC-constituent greatly participates in shaping the b-wave and also has some diminishing effect on b-wave amplitude. As expected, the PR response depended mostly on steady light. A difference attributable to flickering light was largest with low frequency (1 Hz) and at scotopic intensity. In the photopic range rods saturated and the faster cones were not numerous enough to contribute visibly to a PR constituent. The MC constituent followed PR responses with some delay. The BC constituent was evoked almost exclusively by flickering light, with larger responses at low frequency and with higher light intensities.
Conclusions :
These results enhance our understanding of mechanisms responsible for ERG generation in response to flicker. They also form a basis for optimal stimulation of the retina for investigation of light-induced metabolic changes, which are expected to be different in the distal and proximal parts of the retina.
This is a 2020 ARVO Annual Meeting abstract.