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M. W. Seeliger, M. Biel, M. Humphries, N. Tanimoto; A Model-Based Approach to Functional Rod-Cone Interaction in the Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2847. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the nature of rod-cone interaction in the retina based on functional studies in specifically altered mutant mice.
A model was generated that provides a prediction of flicker electroretinography (ERG) amplitudes of mixed rod and cone system origin. Dark-adapted, functionally cone- or rod-deficient (Cnga3-/- or rho-/-) knockout mice were used to determine the model parameters for a variety of conditions (i.e. flash intensities, static backgrounds, flicker frequencies) by restricting retinal input to one photoreceptor class. Mixed responses reflecting the result of rod and cone signal addition and/or interference were then estimated by a phase (latency)-dependent addition of two sine waves of different amplitude (as given by the model prediction for each system).These mixed response data were compared to wild-type mouse recordings to validate the predictions. In addition, the time course of adaptational changes was assessed during recovery from a 95% bleach and the results compared to the predictions.
The rod-cone interaction detected was dependent on 1) the amplitude of rod and cone signals and 2) their latency difference. If amplitudes were similar but there was no latency difference, they did simply add. Vice versa, if one amplitude was very small in comparison to the other, it did not matter if signals were out of phase. We found that rod-cone interaction was largest in the mesopic range, as rod signals were still not too much desensitized and cone signals were already substantial.The model was found to fit real flicker data fairly well. We were able to predict the amplitude changes associated with the recovery following a 95% bleach over time and to identify the role of rod-cone interaction in shaping the respective signal waveforms. Intriguingly, the "mesopic range" where interactions took place was subject to a left shift with time during recovery in good agreement with the model predictions.
Rod-cone interaction in the outer retina is largest when rod and cone signals are both of comparable size but differ in implicit time, which is usually the case in the mesopic range. The adaptational state alters the range where this happens due to the recovery differences between the two classes of photoreceptors.
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