Entrainment of circadian rhythms by feeding schedules in rats with suprachiasmatic lesions

Abstract

Rats with lesions of the suprachiasmatic nucleus (SCN) and controls were maintained in constant light and exposed to a restricted feeding schedule at 23- and 24-hr intervals, as well as to a 12-hr phase shift in the feeding schedule. Despite the absence of circadian periodicity in activity or drinking in ad lib. conditions, rats with SCN lesions showed anticipatory wheel running to both feeding schedules, comparable to sham-operated rats. Following the 12-hr phase shift, transients qualitatively similar to those seen following phase shifts in the light—dark cycle were observed. During a 3-day period of total food deprivation following prolonged entrainment to a 24-hr feeding schedule, wheel running persisted with a near 24-hr periodicity while return to ad lib. conditions resulted in a rapid desynchronization of activity. These results indicate that anticipatory wheel running in rats with SCN lesions is based on endogenous circadian oscillators which are entrainable by feeding schedules in the circadian range. Apparently such oscillators free run under certain conditions (food deprivation) but become rapidly desynchronized in others (ad lib. feeding). The evidence strongly supports a multioscillator model of the circadian system in mammals.