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M.W. Seeliger, N. Pereyra–Muñoz, E. Fahl, M. Biel, N. Tanimoto; Rod Flicker ERG in Mice . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4734.
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Dark–adapted flicker ERG in mice (Seeliger et al., Nat Genet 2001) has become an established method particularly for the evaluation of rod sensitivity. However, the dependence of this response on light intensity and flash frequency has not been addressed in detail. Here, we assess the changes evoked by variation of these parameters in actual recordings and reveal their nature on the basis of respective models.
C57/Bl6 control and functionally cone–deficient Cnga3–/– knockout mice were examined in this study. Following overnight dark adaptation, scotopic flicker ERG series were recorded for flash frequencies from 0.75 to 24 Hz, and intensities from 10–5 to 20 cd*s/m² (Cnga3–/– mice were used at higher intensities to ensure pure rod function). Functional testing was performed with Ganzfeld electroretinography (ERG; Jaeger/Toennies, Multiliner Vision, Hoechberg, Germany) under scotopic conditions. The study was performed in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Visual Research.
For each frequency, there was a monotonic rise of flicker amplitude with intensity up to a maximum value at about 10 mcd*s/m². The absolute value of that maximum decreased with frequency and vanished at around 15–20 Hz. A further increase in intensity led to a monotonic reduction of amplitude down to zero, which was at low frequencies preceded by a plateau at the maximum value. The intensity at the onset of the drop and at which zero amplitude was reached was inversely related to flicker frequency. The results were in good agreement with modeled data.
The impact of frequency and intensity on scotopic flicker ERG was described. At low light intensities, the absolute amplitude and the flicker fusion frequency was apparently limited by the timing properties of the rod outer segment. At high light intensities, the flash–to–flash interaction gained importance and could be well modeled by an equivalent background step increasing with intensity.
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