Abstract
Synchronization of an internal clock (entrainment) and a direct response to light (masking) are complementary ways of restricting activity of an animal to day or night. The protein CLOCK has an important role in the oscillatory mechanism of mammalian pacemakers. Our data show that it is also involved in masking responses. Mice with the Clock/Clock mutation reduced their wheel running less than wildtypes when given 1-h light pulses of light (2–1,600 lx) in the night. With dimmer lights (<2 lx), there were no significant differences between mutant and wildtype mice. Impaired masking responses to light in Clock/Clock mice were confirmed in tests with ultradian light–dark cycles (3.5:3.5 h and 1:1 h). Tests with pulses of light longer than 1 h revealed that, although the mutants responded more slowly to light, they sustained the suppression of activity over the course of the 3-h tests better than wildtypes.
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Abbreviations
- SCN:
-
Suprachiasmatic nucleus
- LD:
-
Light–dark
- DD:
-
Constant darkness
- PBS:
-
Phosphate buffer saline
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Acknowledgements
We thank Martha Vitaterna for providing us with mice and advice, and Peggy Salmon for taking on the breeding and screening and helping with the analysis. Hsi-Wen Liao, Zinta Zommers, and Leslie Wong also assisted with the experiments. King-Wai Yau kindly made facilities available for immunocytochemistry. These experiments comply with the guidelines of the Canadian Council on Animal Care. Support came from the Canadian Institutes of Health Research.
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Redlin, U., Hattar, S. & Mrosovsky, N. The circadian Clock mutant mouse: impaired masking response to light. J Comp Physiol A 191, 51–59 (2005). https://doi.org/10.1007/s00359-004-0570-z
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DOI: https://doi.org/10.1007/s00359-004-0570-z