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M.W. Seeliger, M. Biel, P. Humphries, C. Friedburg; Rod and Cone–Specific Components of the ERG b–wave Revealed by Paired–Flash Paradigm . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2253.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To study rod and cone contribution in a paired–flash paradigm using functionally specific knockout mice. Methods: ERGs were recorded with a Toennies Multiliner Vision Ganzfeld setup (Jaeger/Toennies, Hoechberg, Germany) to which an additional high–intensity flash (mecablitz 60 CT–4, Metz, Zirndorf, Germany) was added. For a paired–flash stimulation, the test flash from the Multiliner Vision was followed after a given interval by the probe flash from the mecablitz unit as trigered by a programmable delay unit. To verify the effect on rod and cone system we compared ERG responses in wild type mice with those of Rho–/– mice, lacking rod function, and with CNGa3–/– mice, lacking cone function. Results: Consistent with previous findings, a test flash intensity of approx. 10 mcds/m² elicited no visible response in the cone system but a maximal b–wave response in the rod system. In addition to the changes observed for the different intervals in the initial "a–wave"–response to the probe flash the probe "b–wave" was suppressed in the CNGa3–/– mice and began to recover about 200 ms after the test flash. No such changes were observed in the Rho–/– mice which do not detect the first flash. Conclusions: Bright flashes have been used to temporarily suppress rod function in ERG recordings before. Using mice with specific defects of either rod or cone system allows the amount of suppression to be visualized. Our data reveals that moderate flashes that do not cause a response in the mouse cone system may be used to elicit rod b–wave responses large enough to lead into saturation for up to 200 ms after the flash. Therefore, responses during this intervall are cone driven. Using this test flash intensity a double–flash paradigm can be used to obtain repetitive measurements of rod and cone contributions to the ERG without the limits of a full light adaptation.
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