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H. Fong, L. Rife, T. Ogden; Low Amplitude Cone ERG Response of Light-adapted RGR Knockout Mice . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1868.
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Purpose: A normal steady-state level of 11-cis-retinal and rhodopsin in a light-adapted eye requires the presence of the retinal G protein-coupled receptor opsin (RGR). The aim of this work is to measure cone ERG responses of normal and RGR opsin knockout mice. We tested the hypothesis that loss of RGR will diminish cone pigments and cone function (cone ERG) in light-adapted RGR–/– mice in comparison with normal mice. Methods: Dark-adapted baseline ERGs were recorded from all animals prior to test procedures. Mice were pre-adapted for various times under constant fluorescent lighting at 70 foot-candles (fc) before the measurement of cone ERG b-wave amplitudes. To isolate the cone ERG response, a rod-desensitizing adapting field at 6 fc was applied throughout the period of stimuli presentation. The cones were stimulated with either a single flash or 10-Hz flickering via a Grass xenon flash at full intensity. Results: Dark-adapted RGR–/– and RGR+/+ mice (no pre-adaptation) showed no significant differences in b-wave amplitudes in response to flash or 10-Hz flicker stimuli. Under the 6-fc background lighting, there was a progressive increase in cone ERG amplitude over a period of 10-12 min in both strains; this behavior was similar to that reported previously for cone ERGs of humans and other vertebrates. In contrast, when the mice were pre-adapted 1-4 hr under constant light, cone ERG b-wave amplitudes from single-flash or 10-Hz flicker stimuli were significantly lower in RGR–/– mice than RGR+/+ wildtype controls. After the shift from 70-fc pre-adapting to 6-fc background light, wildtype mice demonstrated a recovery of the cone b-wave that plateaued by 12 min at an amplitude even higher than that obtained with dark-adapted mice. In comparison with RGR+/+ mice, the light-adapted RGR–/– mice had reproducibly lower b-wave amplitudes throughout the measurement period and a slower rate of cone ERG recovery under anesthesia. Conclusions: In the presence of light, the function of cone photoreceptors can be significantly impaired by the absence of RGR and disruption of normal retinoid processing in the RPE or Müller cells. The RGR opsin must participate, either directly or indirectly, in the complex mechanism of regeneration of cone pigments.
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