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A. V. Kolesnikov, V. J. Kefalov; Effects of Aging on the Function of Mouse Rod Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1667.
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© ARVO (1962-2015); The Authors (2016-present)
The performance of our visual system deteriorates with age. Considering the dramatic effects of loss of vision on quality of life at old age, surprisingly little is known about the changes that occur in the retina and, more specifically, in photoreceptors with age. To establish the mouse as a model for studying the age-induced physiological changes in photoreceptors, and in an effort to understand the mechanisms that underlie age-related deterioration of vision, we sought to characterize how mouse rod photoreceptor function is altered by age. More specifically, we were interested in investigating a possible link between deterioration of photoreceptor performance with age and a gradual depletion of chromophore in those cells.
Using a suction electrode, membrane current was recorded from the outer segments of single mouse rod photoreceptors. We compared dark current amplitude, flash sensitivity, time to peak, and integration time of rods from 3-month and 24-month old mice.
We found that aging significantly alters the function of rod photoreceptors in mouse. Specifically, comparing rod photoresponses from 3-month and 24-month old mice, we found that the mean saturating response, which represents the dark current, was reduced from 14.4 pA to 11.3 pA. In addition, the mean flash intensity required to reproduce half-saturating response increased from 105 photons µm-2 to 146 photons µm-2 indicating a significant decrease in flash sensitivity of rods from the old animals. Aging also accelerated the kinetics of the flash response: time to peak decreased from 189 ms to 145 ms, and integration time (time integral of the normalized flash response) decreased from 327 ms to 225 ms.
We find that aging significantly affects the physiological properties of mouse rods. Our results demonstrate that the mouse can be a useful model for studying the age-induced functional changes in mammalian rod photoreceptors. The observed reduction in dark current, decrease in sensitivity, and acceleration of the flash response are similar to the effects of bleaching adaptation in photoreceptors. Thus, the observed age-induced changes in mouse rod function are consistent with a gradual depletion of chromophore and accumulation of free opsin in aged photoreceptors.
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