FIGURE 5.

The R838S⁺ rod ERG in the line 379 becomes strongly reduced by 6 months of age, whereas cones remain functional. A, waveforms of ERG in response to a standard 1.1 × 10³ R*/rod bright flash, recorded from dark-adapted (scotopic) wild type mice (black) and R838S⁺ (red) slower line 379 littermates at 6 months of age (same as in Fig. 4A), shown on the left. The waveforms of light-adapted (photopic) ERG, shown on the right, was recorded from the same pair of mice in response to 6 × 10⁵ R*/rod 505- and 365-nm flashes in a background of a constant light producing 33 × 10³ R*/rod/s. Note the remaining strong cone responses in comparison with the suppressed rod response in the R838S⁺ mouse. B and C, maximal amplitudes of the ERG. B, amplitudes of the dark-adapted (scotopic) a-wave (upper panel) and b-wave (lower panel) to a bright flash of 1.1 × 10³ R*/rod in the R838S⁺ (red symbols) mice become progressively suppressed by 6 months of age compared with the wild type littermates (black symbols); each symbol shows response from different animals, error bars, standard deviation per each age group. C, cones remain responsive as rod vision becomes severely impaired. Averaged S cone a-wave (open symbols) and b-wave (closed symbols) amplitudes to a 6 × 10⁵ R*/rod 365-nm flash at a constant 505-nm 33 × 10³ R*/rod/s background light in a combined group of 25 transgenic mice aged 4 to 6 months (red symbols) was not significantly different from 20 wild type (black symbols) littermates (34 ± 9 versus 35 ± 14 μV, respectively; p = 0.7), and the b-wave amplitude even appeared slightly elevated (172 ± 34 and 132 ± 42 μV; p < 0.002); dashed horizontal line, mean average for each group; error bars, standard deviation.