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G. R. Rubin, M. S. Loop, T. W. Kraft; Comparisons Between ERG and Behaviorally Determined CFF in a Rodent Model of Retinal Degeneration. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2844. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The full-field corneal ERG is frequently used to estimate rod- or cone-driven function in rodent models of retinal degeneration. However, the relationship between ERG response amplitudes and visually guided behavior has been little studied for this model. A longitudinal comparison of ERG to behavioral responses in a light-damage model of retinal degeneration allows us to better understand the functional implications of electrophysiological changes.
All animals were handled according to the principles of the ARVO Statement for the Use of Animals in Vision Research. Flicker-ERG and behavioral responses to flicker were used to determine the critical flicker frequency (CFF) of Sprague-Daly albino rats under both scotopic and photopic conditions. Behavioral CFF was determined by two alternative forced choice psychophysical testing in a water maze. Dark- and light-adapted flash ERG b-waves were also measured. Data were collected before and after a 10-day period of low-intensity (280 lux) light-damage that was calibrated to decrease the outer nuclear layer by 50%. Control animals underwent sham light damage, but were maintained under regular cyclic lighting.
Dark adapted ERG flash responses were reduced by about 50% while CFF determined by flicker-ERG under scotopic conditions was only about 15% lower than control animals on R6, 6 days after light-damage. Behavioral CFF measured under scotopic and photopic conditions was reduced about 15%. Neither the photopic flicker ERG nor the light-adapted flash ERG were significantly different from controls at R6. All CFF values fully recovered by R20, 20 days after light damage. Dark-adapted flash ERG also recovered by R20.
Flash ERG b-wave amplitudes were severely reduced after light damage in contrast to CFF as measured by ERG or behavior. While reduction of b-wave amplitude mirrors rod loss initially, the relative maintenance of a near threshold flicker signal suggests that different mechanisms are responsible for meditating these separate functions. The recovery of b-wave and flicker sensitivity reveals a plasticity of retinal circuits following injury. These positive changes may be clinically meaningful.
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