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B. Lei, B. Chang; Detect Rod- and Cone-driven Signals with Scotopic Flicker Electroretinogram (ERG) in Mice . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1902.
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Purpose: Recently, dark adapted flicker electroretinogram (ERG) has been used to assess retinal sensitivity and monitor the therapeutic effects in retinal degeneration animal models. The characteristics of the scotopic flicker ERGs, however, are not defined. In mice, we found the 10 Hz dark-adapted flicker ERG intensity ? response amplitude curve consisted of two phases: one peak at middle stimulus intensity and one peak at high intensity. This study is to demonstrate that the two phases are driven by different photoreceptors, i.e. rods and cones respectively. Methods: Six 1 ~ 2 month old C57BL/6 normal mice and 6 age matched C57BL/6J-cpfl1 (cone photoreceptor function loss 1, a model of human congenital achromatopsia) mice were used in this study. Dark- and light-adapted Ganzfeld ERGs were recorded. Scotopic and photopic 10 Hz flicker ERGs were measured with an intensity range of 6.5 log unit (step 0.2 ~ 0.5), and the maximum stimulus intensity is 0.66 log cd*s/m2. In photopic ERG, a steady white background light of 1.6 log cd/m2 was used to saturate rod function. Results: In normal mice, the scotopic 10 Hz flicker responses elicited at middle intensity were different from that elicited at high intensity in waveforms, characteristics of latency, phase (time to peak) and harmonic components, suggesting different cellular origin. In cpfl1 mice which did not possess cone function, the scotopic 10 Hz flicker ERG showed the first peak at middle intensity as in C57BL/6 mice, while no responses were recorded at high intensity. Conclusions: Scotopic flicker ERG provides an effective way in evaluating rod and cone function in mice. Since light adaptation is not needed in this protocol, it may reflect cone function more accurately.
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