Related Experiment Video
Updated: Aug 7, 2026
Light/dark Transition Test for Mice
Published on: November 13, 2006
Thresholds for masking responses to light in three strains of retinally degenerate mice
N Mrosovsky1, R G Foster, P A Salmon
1Department of Zoology, University of Toronto, Ontario, Canada. mro@zoo.utoronto.ca
Abstract:
Mutant mice with retinal degeneration (rd/rd) were given 1-h pulses of light of varying brightness at times of the night when they would normally be active. The mutant mice showed a significantly greater inhibition of locomotor activity to light (negative masking) than wildtype controls. Lack of impairment, or even enhancement of negative masking suggests that this response may depend on sparing in retinally degenerate mice of the same receptor type that mediates clock resetting, because synchronization of the circadian system is known to be unimpaired in these mutants. With very dim light pulses, mutants did not change their activity, but wildtypes actually became more active (positive masking). Positive and negative masking appear to depend on different sensory and central processes.
Insights
Retinal degeneration in mutant mice (rd/rd) caused greater light-induced activity inhibition (negative masking) than wildtypes. This suggests spared retinal receptors may mediate this response, differing from positive masking.
Area of Science:
- Neuroscience
- Chronobiology
- Vision Science
Background:
- Retinal degeneration (rd/rd) mouse models exhibit progressive photoreceptor loss.
- Circadian rhythms regulate daily activity patterns, influenced by light cues.
- Light can modulate locomotor activity through masking effects.
Purpose of the Study:
- To investigate the impact of retinal degeneration on light-induced masking of locomotor activity.
- To compare negative and positive masking responses in rd/rd mice and wildtype controls.
- To explore the sensory and neural mechanisms underlying differential masking effects.
Main Methods:
- rd/rd mutant mice and wildtype littermates were exposed to 1-hour light pulses during their active phase.
- Light pulses varied in intensity to assess dose-dependent effects on locomotor activity.
- Locomotor activity was continuously monitored and analyzed for changes in response to light stimuli.
Main Results:
- Mutant rd/rd mice exhibited significantly enhanced negative masking (activity inhibition) compared to wildtype controls.
- Wildtype mice showed positive masking (increased activity) in response to very dim light pulses, while rd/rd mice did not.
- These findings suggest distinct neural pathways mediate positive and negative masking.
Conclusions:
- The enhanced negative masking in rd/rd mice may involve spared retinal photoreceptors crucial for clock resetting.
- Differential responses to light intensity indicate separate sensory and central processing for positive and negative masking.
- These results provide insights into the functional consequences of retinal degeneration on circadian behaviors.
