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Joined 2026-09-21 Message
Incoming links: House mouse
Circadian rhythm Created 2026-10-13 Updated 2026-10-14
A circadian rhythm is an endogenous biological oscillation with a period near 24 hours, persisting without a repeating external signal. A circadian clock times biological activities and anticipates daily changes without continual external instructions. A free-running circadian rhythm reveals its intrinsic period; entrainment of circadian rhythm coordinates it with an external cycle.[ref]
Overview of Circadian Rhythms by Martha Hotz Vitaterna and others. Vitaterna, Takahashi and Turek (2001), Overview of Circadian Rhythms, pp. 85–86, Biological Rhythms and Basic Properties of Circadian Rhythms
In 1994, Martha Hotz Vitaterna and colleagues screened offspring of mutagen-treated C57BL/6J mice (the house mouse). Each mouse lived in a cage with a running wheel, inside a ventilated, light-tight chamber with timer-controlled lighting. Wheel revolutions were recorded electronically or on an event recorder. The initial screen used 14:10 LD for the first 41 animals and 12:12 LD thereafter; LD denotes hours of light and darkness. Transfer to constant darkness, DD, omitted the next scheduled lights-on; recording continued for at least three weeks. The first 41 animals also received brief light pulses, so those records were not uninterrupted DD.[ref]
Mutagenesis and Mapping of a Mouse Gene, Clock, Essential for Circadian Behavior by Martha Hotz Vitaterna and others. Vitaterna and others (1994), Mutagenesis and Mapping of a Mouse Gene, Clock, Essential for Circadian Behavior, Figure 1 and References and Notes 6–10
The subsequent-generation comparison in Figure 2 used 12:12 LD before DD. Animals without the Clock mutation and with mutant genotypes supplied the comparison: the B6 examples in panels A–C had initial DD periods of 23.6, 24.8 and 27.1 hours, respectively; the homozygote later lost its sustained circadian rhythm. Total activity remained comparable across genotypes in the interstrain comparison. The mutation therefore altered timing, beyond merely reducing running. Wheel activity is a behavioral readout; it does not directly measure every circadian clock or establish a human period.[ref]
Mutagenesis and Mapping of a Mouse Gene, Clock, Essential for Circadian Behavior by Martha Hotz Vitaterna and others. Figure 2A–C; Table 2 and discussion of activity counts and loss of rhythmicity; References and Notes 10 and 14
Daily activity under LD alone cannot establish entrainment of circadian rhythm. Light can directly change activity without resetting the circadian clock: masking of circadian rhythm. Removing the light cycle helps distinguish these effects; they can coexist.[ref]
Overview of Circadian Rhythms by Martha Hotz Vitaterna and others. p. 92, glossary entries Entrainment, Free running and Masking
In an experiment, other repeating inputs must also be controlled: a nominally dark room with daily handling is not automatically an environment without timing cues. Clock mutation (mouse) 2026-10-14