Thresholds for masking responses to light in three strains of retinally degenerate mice

Mutant mice with retinal degeneration (rd/rd) were given 1-h pulses of ligh t of varying brightness at times of the night when they would normally be a ctive. The mutant mice showed a significantly greater inhibition of locomot or activity to light (negative masking) than wildtype controls. Lack of imp airment, or even enhancement of negative masking suggests that this respons e may depend on sparing in retinally degenerate mice of the same receptor t ype that mediates clock resetting, because synchronization of the circadian system is known to be unimpaired in these mutants. With very dim light pul ses, mutants did not change their activity, but wildtypes actually became m ore active (positive masking). Positive and negative masking appear to depe nd on different sensory and central processes.