Effects of partial receptor cell loss on the electroretinogram of chimaeric mice

A series of chimaeric mice were produced by aggregating morulae from rd/rd and normal (+/+) mice. In the retina of chimaeric mice, produced by aggregating morulae of these two genotypes, loss of rd/rd photoreceptor cells results in a patchy distribution of the surviving normal receptor cells. The number of remaining receptor cells vary between individual chimaeras. The inner retinal layers in the chimaeras, as well as in the two parental genotypes remain intact. Electroretinograms were recorded from 16 chimaeric mice, and various parameters were compared with the amount of visual cells present as estimated by the average thickness of the outer nuclear layer. The amplitudes of the a- and b-wave, showed a linear reduction with decreasing thickness of the outer nuclear layer thickness. However, threshold of the b-wave increased only when the thickness of the outer nuclear layer fell to about 25% of the normal thickness while the time-to-peak of the waves did not change appreciably among the chimaeric individuals. These results suggest that the changes in the electroretinogram of the chimaeric individuals are related to the amount of visual cells present in the retina.