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Naoyuki Tanimoto, Vithiyanjali Sothilingam, Peter Humphries, Shigetada Nakanishi, Martin Biel, Mathias W. Seeliger; Flicker ERG Frequency Series at the ISCEV Standard Flash Intensity in Mice. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2463.
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© ARVO (1962-2015); The Authors (2016-present)
Electroretinography (ERG) is indispensable for the functional evaluation of the retina. For clinical use, there is a minimum standard issued by the International Society for Clinical Electrophysiology of Vision (ISCEV) that includes responses to scotopic and photopic single flash and flicker recordings. In rodents, there is yet no formal standard, and most groups use single flash ERGs in their experimental work. Here, we validate a scotopic flicker ERG paradigm in mice as a tool for further diagnostic differentiation of phenotypes.
For this work, wild-type and transgenic mice with specific functional properties (Cnga3-/-, pure rod function; rho-/-, pure cone function; mGluR6-/-, postsynaptic deficits in photoreceptor to ON-bipolar cell signal transmission) were examined in vivo with Ganzfeld ERG. Steady-state responses to trains of flashes for a fixed intensity (0.5 log cd s/m2; the ISCEV standard flash (SF) intensity; Marmor et al., 2004) with varying frequency (0.5, 1, 2, 3, 5, 7, 10, 12, 15, 18, 20 and 30 Hz) were obtained under dark-adapted conditions.
In wild-type mice, low frequency flicker responses were composed of components that correlate with a- and b-wave and oscillatory potentials in single flash ERG. Generally, these components merged and became smaller with increasing stimulus frequency. In Cnga3-/- mice featuring rod-only responses, the flicker ERG became rapidly attenuated with increasing stimulus frequency and vanished at about 5 Hz in this setting. In contrast, there was no perceivable difference in responses between wild-type and cone-only rho-/- mice at higher frequencies, suggesting that any response to ISCEV SF flicker at 5 Hz and above is entirely cone-driven. In mGluR6-/- mice that feature OFF system signals only, responses in the intermediate frequency range (5-15 Hz) were smaller than those in rho-/- mice. However, there was no obvious difference at higher frequencies than 15 Hz, suggesting that any response to ISCEV SF flicker at 15 Hz and above is entirely driven by the cone OFF system, and in the intermediate range (5-15 Hz) is cone ON system dominated.
We found that in the scotopic flicker ERG frequency series using ISCEV SF stimuli, the frequency range up to 3 Hz is dominated by rod system activity, that between 5-15 Hz by cone ON system activity, and that above 15 Hz by cone OFF system activity. This novel diagnostic tool thus provides a quick overview of the functionality of the rod and the cone ON and OFF systems within a single recording session.
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