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Updated: Jun 14, 2026
Direct-Coupled Electroretinogram (DC-ERG) for Recording the Light-Evoked Electrical Responses of the Mouse Retinal Pigment Epithelium
Published on: July 14, 2020
Retinal ON- and OFF-pathway dysfunction due to HCN channel inhibition evaluated using dark and light adapted flicker
Naohisa Umeya1, Toru Usui1, Izuru Miyawaki1
1Preclinical Research Unit, Research and Development Division, Sumitomo Pharma Co. Ltd., 3-1-98 Kasugade-naka, Konohana-ku, Osaka, 554-0022, Japan.
Abstract:
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channel inhibitors that induce visual abnormalities such as phosphenes in humans are believed to disrupt the feedback mechanisms of retinal photoreceptor cells and cause dysfunction of the ON and OFF pathways in the retina. However, this hypothesis is based mainly on studies using HCN channel-knockout mice. In this study, we evaluated whether the retinal ON and OFF pathway defects could be detected in animals treated with HCN channel inhibitors by dark-adapted and light-adapted flicker electroretinography (ERG). Ivabradine, an HCN channel inhibitor, was administered subcutaneously to Long-Evans rats at 4-40 mg/kg as a single dose, and dark- and light-adapted flicker ERGs were measured at frequencies ranging from 1 to 30 Hz. In dark-adapted flicker ERGs, waveforms including rod photoreceptor components in the low frequency range and rod ON pathway and cone ON and OFF pathway components in the intermediate- and high-frequency range were changed, and the amplitude of the waveforms were attenuated. These inhibitions of cone ON and OFF pathways were considered, based on the results of the light-adapted flicker ERGs, to have been influenced by interference with rod-driven signals via gap junctions. This study is the first report to demonstrate inhibition of ON and OFF pathway signaling in animals treated with an HCN channel inhibitor. Our findings also suggest that dark- and light-adapted flicker ERGs across a range of frequencies may be a useful tool for detecting retinal dysfunction caused by compounds inducing visual abnormalities.
Insights
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channel inhibitors disrupt retinal pathways. This study shows dark- and light-adapted flicker electroretinography (ERG) can detect these ON and OFF pathway defects in rats treated with ivabradine.
Area of Science:
- Ophthalmology
- Neuroscience
- Pharmacology
Background:
- Hyperpolarization-activated cyclic nucleotide-gated (HCN) channel inhibitors are linked to visual abnormalities.
- Previous hypotheses on retinal pathway disruption were mainly based on knockout mouse studies.
- The precise impact of HCN channel inhibitors on retinal ON and OFF pathways requires further investigation in vivo.
Purpose of the Study:
- To evaluate the detectability of retinal ON and OFF pathway defects in animals treated with HCN channel inhibitors.
- To investigate the effects of ivabradine, an HCN channel inhibitor, on retinal function using electroretinography.
- To establish flicker ERG as a potential tool for detecting drug-induced retinal dysfunction.
Main Methods:
- Long-Evans rats were administered varying doses of ivabradine subcutaneously.
- Dark-adapted and light-adapted flicker electroretinography (ERG) were performed across a range of frequencies (1-30 Hz).
- Changes in waveform components and amplitudes were analyzed to assess pathway function.
Main Results:
- Treatment with ivabradine altered waveforms in dark-adapted flicker ERGs, affecting rod photoreceptor, rod ON, and cone ON/OFF pathways.
- Waveform amplitudes were attenuated across different frequency ranges.
- Light-adapted flicker ERGs suggested that cone pathway inhibition was influenced by rod-driven signal interference via gap junctions.
Conclusions:
- This study provides the first evidence of ON and OFF pathway signaling inhibition in animals treated with an HCN channel inhibitor.
- Retinal ON and OFF pathway defects induced by HCN channel inhibitors can be detected using flicker ERG.
- Dark- and light-adapted flicker ERGs across multiple frequencies are a valuable method for identifying retinal dysfunction caused by compounds inducing visual abnormalities.
