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G. A. Williams, J. A. Fenwick, G. H. Jacobs; Effects of Aging on Cone-Based Vision in the Mouse. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1285.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the possibility of changes in photopic visual sensitivity, cone ERGs, cone photoreceptor numbers, and cone opsin expression in the mouse as a function of age.
Subjects were C57BL/6 mice ranging in age from 32 to 954 days housed under dim, cyclic illumination (51 lux; 12:12). Increment thresholds were measured in a behavioral discrimination test under lighting conditions designed to assess cone-based vision. ERGs were recorded using stimulus and adaptation conditions appropriate for recording signals originating from each of the two types of cone photopigment of the mouse retina (UVS, max = 359 nm; MWS, max = 509 nm). Quantitative PCR using primers designed against the mouse cone opsin genes was performed to examine cone opsin mRNA expression. To assess cone photoreceptor numbers opsin antibody labeling was performed on whole-mounted retinas using antibodies that selectively label each of the mouse cone opsin types.
A total of 13 photopic threshold measurements were repeatedly made on one subject over a period of time extending from 107 to 753 days of age. Cone-based thresholds of this subject showed no significant change over this time span. ERG V-log I functions were obtained from 30 mice (ages 66-826 days) and fitted with Naka-Rushton functions. MWS and UVS cone Vmax values measured for normal mice declined significantly (on average, by about 50%) as a function of age. The ½ saturation constants, k, obtained from signals originating from absorption in UVS cone photopigments increased slightly as a function of age while those from MWS cone photopigments remained effectively unchanged. Results from PCR experiments showed no significant age-related changes in cone opsin mRNA transcript levels. Likewise, there were no age-related changes in total cone density or in the densities of cones expressing either MWS or UVS photopigment.
Sensitivity thresholds measured under moderate photopic levels were unchanged over a period that corresponds to about the average life-span for C57BL/6 mice. Across this same time period mice show large declines in ERG Vmax values. This change is similar to that documented for people tested at various ages. The decline in ERG voltage does not predict behavioral sensitivity. Results from PCR and labeling experiments show that reductions in ERG voltages in mice are not due to reduced cone densities or reductions in mRNA transcript levels.
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