VISUAL AND CIRCADIAN RESPONSES TO LIGHT IN AGED RETINALLY DEGENERATE MICE

The progression of photoreceptor degeneration in retinally degenerate (rd) mice commences early in postnatal development resulting in the co mplete loss of rods by 60-70 days of age followed by the more protract ed loss of cones. We have previously shown that rd mice 80 days of age are capable of phase shifting their circadian locomotor rhythms in re sponse to brief pulses of light and these animals show the same sensit ivity as wild-type (+/+) controls. If surviving cones mediate these ci rcadian responses, then one would expect the sensitivity of the circad ian system in rd mice to decline with age and parallel the loss of con es. We demonstrate that aging rd mice (80-767 days of age) remain capa ble of photically regulating circadian locomotor rhythms in a manner i ndistinguishable from +/+ mice. Circadian responses to light do not pa rallel cone cell degeneration in rd mice. In contrast to the circadian responses to light, old (> 210 days of age) rd mice show no visually- evoked behavioral or electroretinogram (ERG) responses.