Circadian rhythm dissociation induced by periodic feeding in rats with suprachiasmatic lesions.

Rats with lesions of the suprachiasmatic nucleus (SCN) were maintained in constant darkness and placed on restricted feeding schedules with 1 h access to food twice per day. When both schedules had a 24 h period and food access was spaced 12 h apart, all rats with SCN lesions displayed anticipatory activity to both feedings. In the first experiment, the period of one schedule was then changed to 25 h while the other continued with a period of 24 h. None of the rats with SCN lesions were able to anticipate both schedules simultaneously. In a second experiment, 24 h and 24.5 h schedules were used. Five of 6 rats with SCN lesions anticipated both schedules for at least 9 days and 2 of these anticipated both schedules for 48 days. This forced dissociation of activity into two components with different periods is consistent with the hypothesis that entrainment of activity by restricted food access is mediated by more than one circadian pacemaker.