Negative and positive masking responses to light in retinal degenerate slow (rds/rds) mice during aging.

Bright light suppresses locomotor activity in mice (negative masking) but dim light augments activity (positive masking). Retinal degeneration slow mice (rds/rds) were tested for responses to light at 3 months, 1 and 2 years old. The suppressive effect of light increased between 1 and 2 years, but the positive response to dim lights was severely reduced at 1 year. No such effects occurred in aging wildtypes. The results indicate that enhancement of negative masking depends on the degree of degeneration of the classical photoreceptors, and that residual function in photoreceptors lacking outer segments is initially sufficient for positive masking.