Augmented rod bipolar cell function in partial receptor loss: an ERG studyin P23H rhodopsin transgenic and aging normal rats

Physiological consequences of early stages of photoreceptor degeneration we re examined in heterozygous P23H rhodopsin transgenic (Tg) and in aging nor mal Sprague Dawley rats. Rod photoreceptor and rod bipolar (RB) cell functi on were estimated with maximum value and sensitivity parameters of P3 and P 2 components of the electroretinogram. In both Tg and aging normal rats, th e age-related rate of decline of P3 amplitude was steeper than that of the P2 amplitude. Tg rats showed greater than normal sensitivity of the rods. A new model of distal RB pathway connectivity suggested photoreceptor loss c ould not be the sole cause of physiological abnormalities; there was an add itional increase of post-receptoral sensitivity. We propose that changes at rod-RB synapses compensate for the partial loss of rod photoreceptors in s enescence and in early stages of retinal degeneration. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.