Control of behavioral circadian rhythms for nesting and wheel running in mice

In Experiment 1 a circadian rhythm for nest-building behavior is demonstrated in 10 males from a genetically heterogeneous stock of Mus musculus. In Experiment 2, this circadian rhythm in nesting and that for wheel running activity were monitored simultaneously in an additional sample of five males from the same stock. Under a 16:8 LD photoperiod, mice displayed a 24-hr periodicity for both behaviors but a phase difference in peak behavioral intensities of approximately two and one-half hours. After ten days of exposure to constant light both rhythms persisted, but with no detectable difference in phase. The altered phase relationship under constant light suggests a difference in control of the circadian periodicities of these two behaviors. In Experiment 3, 5 additional males were subjected to a 10-hr shift in photoperiod to further examine control of these rhythms as well as those in food and water consumption. All four circadian rhythms re-entrained within four days. Thus, their entrainment mechanisms are functionally similar in spite of the differences in control suggested in Experiment 2.