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Restoration of Circadian Rhythmicity in Circadian Clock-Deficient Mice in Constant Light

Max-Planck Institute of Experimental Endocrinology, Hannover, Germany

Robert Dallmann

Institut für Zoologie, Tierärztliche Hochschule Hannover, Germany, Department of Zoology, University of Toronto, Ontario, Canada

Stephan Steinlechner

Institut für Zoologie, Tierärztliche Hochschule Hannover, Germany

Urs Albrecht

Institute of Biochemistry, University of Fribourg, Switzerland

Gregor Eichele

Max-Planck Institute of Experimental Endocrinology, Hannover, Germany

Henrik Oster

Max-Planck Institute of Experimental Endocrinology, Hannover, Germany, henrik.oster{at}mpihan.mpg.de

In mammals, circadian rhythms in behavior and physiology are controlled by a central pacemaker, the SCN, and subordinated clocks throughout the body. On the molecular level, these clocks are based on transcriptional/translational feedback loops involving a set of clock genes that regulate their own transcription. Among the components driving the mammalian circadian clock are the Period 1 and 2 (Per1 and Per2) and Cryptochrome 1 and 2 (Cry1 and Cry2) genes. In the present study, the authors characterize the behavioral and molecular rhythms of Per2/Cry1 double mutant mice under 3 different lighting conditions. In an LD cycle, the activity of these animals is masked by light, while in DD, the mutants lose circadian rhythmicity but exhibit strong ultradian rhythms. In LL of higher intensity, circadian rhythms are restored on the behavioral level with a drastically shortened endogenous period. Furthermore, both in the SCN and in the periphery, clock gene rhythms are restored. Based on these observations and also on the fact that light-mediated induction of Per gene expression is preserved in these mutants, the authors propose a mechanism by which endogenous ultradian rhythms may relay timed light exposure to the SCN, leading to a reinitiation of self-sustained circadian rhythms in LL.

Key Words: circadian • constant light • corticosterone • cry • kidney • per • SCN • ultradian

Journal of Biological Rhythms, Vol. 21, No. 3, 169-176 (2006)
DOI: 10.1177/0748730406288040


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