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C Friedburg, F Ståhlberg, HM Mayser, E Zrenner, M Biel, MW Seeliger; Rod Photoreceptor Light Adaptation in a Mouse Model of Achromatopsia Investigated With Paired-Flash ERGs . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1839.
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Purpose: To characterise the rod photoreceptor response and its changes with background illumination in cone cyclic nucleotide-gated channel (CNG3) knockout micea, a model for achromatopsia in which cones are completely unresponsive. Methods: Ganzfeld electroretinograms (ERGs) were recorded simultaneously from both eyes of anaesthetized CNG3 -/- mice under pupil dilatation. We employed the paired-flash techniqueb in which the level of circulating current in the rod outer segment at a particular time after a white test flash was estimated from the size of the a-wave recorded in response to an intense white probe flash of 160 scot cd m-2. Results: Classical signs of rod light adaptation were observed. A steady background I. suppressed the circulating current, approximately described by the Michaelis-Menten (or Naka-Rushton) relation with a halfsaturation at an intensity of ∼0.4 cd m-2; II. accelerated the time course of the photoreceptor response to a dim test flash with the time to peak decreasing from ∼120 ms in the dark to ∼80 ms on a 1 cd m-2 background; III. reduced flash sensitivity measured at about the peak of the response for a range of test flash intensities. The reduction approximately obeyed Weber's Law; IV. accelerated the recovery from saturation after a probe flash. Recovery to 90% of the original response was achieved within 20 s on a 1 cd m-2 background compared with 35 s in the dark. Conclusion: Paired-flash ERGs in CNG3-/- mice demonstrated classical signs of normal rod light adaptation supporting earlier reportsa that rod function in CNG3-/- mice is unaltered by the absence of functional cones. [a] Biel M, Seeliger MW, Pfeifer A, et al. (1999). Selective loss of cone function in mice lacking the cyclic nucleotide-gated channel CNG3. Proc Natl Acad Sci USA 96: 7553-7557. [b] Pepperberg DR, Birch DG and Hood DC (1997): Photoresponses of human rods in vivo derived from paired-flash electroretinograms. Vis Neurosci 14: 73-82.
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