1. Using the portable HMsERG unit for assessment of retinal function in
mouse models for hereditary retinal disease
Kristina Narfström1, Naoyuki Tanimoto2, Mathias W. Seeliger2
1Section for Comparative Ophthalmology, College of Veterinary Medicine and Department of Ophthalmology, Mason Eye Institute,
University of Missouri-Columbia, Columbia, USA, and 2Ocular Neurodegeneration Research Group, Centre for Ophthalmology,
Institute for Ophthalmic Research, Tübingen, Germany
Results: The ERG waveforms and their changes with intensity and frequency were remarkably similar when results of intensity and flicker series using the two ERG units were compared. The absolute scotopic and photopic ERG amplitudes for the HMsERG were, however, found to be lower than those obtained with the Toennies equipment, relatively more so for rod than for cone responses, presumably due to the LED light emission spectrum that undergoes a dip at the peak sensitivity for (murine) rods.
Conclusion: The HMsERG unit can be used to reliably obtain low intensity, high intensity responses and flicker ERG series, with waveforms that are comparable to those obtained with a conventional table-top Ganzfeld ERG system. Conformity may be further improved by refinements of the LED emission spectrum. The portable HMsERG appears to be a useful tool in phenotypic characterization of retinal disease processes in rodents in various laboratory settings.
References
Purpose: Previous studies in dogs and cats have shown efficacy of the handheld multispecies ERG (HMsERG) unit in the early diagnosis of hereditary retinal disease processes. We wanted to evaluate if the HMsERG was a reliable tool to use also in conjunction with phenotypic characterization of hereditary retinal disease processes in mouse models.
Materials and Methods
Animals and anesthesia: In this study, we used wildtype (C57Bl/6) and functionally rod- (Cnga3-/-, cone CNG channel deficient) or cone-specific (Rho-/-, rod opsin knockout) mice. Mice were dark-adapted overnight before the experiments. Anesthesia was induced by subcutaneous injection of ketamine (66.7 mg/kg body weight) and xylazine (11.7 mg/kg body weight). The pupils were dilated with tropicamide eye drops (Mydriaticum Stulln, Pharma Stulln, Stulln, Germany).
ERG recording systems: Conventional table-top full-field Xenon flash ERG equipment (Toennies Multiliner Vision, Viasys Healthcare, Hoechberg, Germany) was used in comparison to the HMsERG (RetVet Corp, Columbia, MO), which includes a mini-Ganzfeld stimulator utilizing white LED's for both stimulation and background light. The disposable stainless needle electrodes were stuck into the forehead and the back near the tail as a reference and a ground electrode, respectively. ERG signals were recorded through gold ring electrodes placed on the surface of cornea.
ERG protocols: ERG recordings were preformed under dark-adapted (scotopic) and light-adapted (photopic) conditions. Light adaptation was accomplished with a background illumination of 30 cd/m2 starting 10 minutes before recording. Scotopic and photopic single flash intensity series (scotopic: -4 to 1.5 log cd*s/m2, and photopic: -2 to 1.5 log cd*s/m2), flicker frequency series (0.5 to 30 Hz, at intensities of -2, 0.5, and 1.0 log cd*s/m2), and scotopic 6 Hz flicker intensity series (-5 to 1.3 log cd*s/m2) were performed. Band-pass filter cut-off frequencies were 0.3 and 300 Hz.