ELECTRORETINOGRAPHIC STUDY OF THE C57BL 6-MI(VIT)/MI(VIT) MOUSE MODELOF RETINAL DEGENERATION/

Purpose. The C57BL/6-mi(vit)/mi(vit) mouse model of retinal degenerati on is characterized by slow progressive loss of photoreceptor cells, c oncomitant loss of rhodopsin, and uneven pigmentation of the retinal p igment epithelium. The purpose of this study was to determine how thes e alterations affected the electroretinogram (ERG). Methods. Scotopic ERGs were measured in two litters of mi(vit)/mi(vit) mice beginning at 4 weeks and continued in the same animals at 2-week intervals through 18 weeks. Results. The mean of the maximum b-wave amplitude (V-max) a t 4 weeks was 234 +/- 14 mu V in mi(vit)/mi(vit) mice, which did not d iffer significantly from controls (266 +/- 26 mu V). With increasing a ge, all components of the ERG decreased and by 12 weeks, the mean of t he V-max had decreased to 170 mu V At 18 weeks, the mean V-max was 75 mu V, and the b- to a-wave ratio was still > 1.0. Comparison of these physiologic data to previously reported morphologic and biochemical da ta showed a high correlation between the b-wave amplitude and the numb er of photoreceptor cell nuclei (r = 0.9772) as well as the b-wave amp litude and rhodopsin levels (r = 0.9019). Conclusions. The loss of all components of the ERG and the lack of a negative-type ERG suggested t hat the primary cells altered in the mi(vit)/mi(vit) mouse were the ph otoreceptors. The high correlations between the ERG amplitude and the number of photoreceptor nuclei indicate that the V-max of the ERG is a good measure of the degree of photoreceptor loss.