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SLEEP AND TEMPERATURE REGULATION
Department of Physiology, Hokkaido University Graduate School of Medicine, Sapporo, Japan
Submitted 16 May 2006 ; accepted in final form 18 September 2006
Circadian rhythms in clock gene expressions in the suprachiasmatic nucleus (SCN) of CS mice and C57BL/6J mice were measured under a daily restricted feeding (RF) schedule in continuous darkness (DD), and entrainment of the SCN circadian pacemaker to RF was examined. After 23 wk under a light-dark cycle with free access to food, animals were released into DD and fed for 3 h at a fixed time of day for 34 wk. Subsequently, they returned to having free access to food for 23 wk. In CS mice, wheel-running rhythms entrained to RF with a stable phase relationship between the activity onset and feeding time, and the rhythms started to free run from the feeding time after the termination of RF. mPer1, mPer2, and mBMAL1 mRNA rhythms in the SCN showed a fixed phase relationship with feeding time, indicating that the circadian pacemaker in the SCN entrained to RF. On the other hand, in C57BL/6J mice, wheel-running rhythms free ran under RF, and clock gene expression rhythms in the SCN showed a stable phase relation not to feeding time but to the behavioral rhythms, indicating that the circadian pacemaker in the SCN did not entrain. These results indicate that the SCN circadian pacemaker of CS mice is entrainable to RF under DD and suggest that CS mice have a circadian clock system that can be reset by a signal associated with feeding time.
biological rhythm; food entrainment; clock gene; behavior; brain
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