ADAPTATION OF ROD AND CONE ELECTRORETINOGRAMS IN THE ABYSSINIAN CAT HEREDITARY ROD CONE DEGENERATION

1. The rod ERG was studied during and after recovery from a full field adapting light (4.5 log td) considered to bleach most of the rhodopsi n. At any stage in adaptation the dystrophic rod ERG was smaller and b -wave implicit time delayed compared to the normal. At equal response amplitudes, the b-wave implicit time was identical to normal. Sensitiv ity recovered at a similar rate but was one-tenth of normal. Rod b-wav e implicit time tracked the same dark adaptation function and when com pared at equal response amplitudes was identical in normal and dystrop hic cats. 2. The cone ERG was studied at different steady levels of ad aptation. Light adaptation decreased the sensitivity and implicit time of the cone ERG in normal and dystrophic cats. High levels of light a daptation were less effective in producing these effects in the dystro phic cat so that at 4 log td the cone ERG of the dystrophic was delaye d in implicit time compared to normals. At all levels the cone ERG (b- wave) of dystrophic and normal cats was 5-10 ms faster than the human cone ERG. 3. The results suggest that there is no defect in the kineti cs of dark adaptation or in the time-course of the transduction mechan ism in this Abyssinian mutant. The ERG defects can be explained by red uced light absorption of rods and cones.