Entrainment of activity to multiple feeding times in rats with suprachiasmatic lesions

Entrainment of wheel running to two or three food access times per day was investigated in rats with SCN lesions. When two feeding times (1.5 hr each) were presented 8 hr apart, all rats entrained to both. Anticipatory activity (AA) to the second feeding time was greatly diminished when the interval was reduced to 5 hr. An 8 hr phase delay of one feeding time resulted in delaying transients and a concomitant reduction of AA to the unshifted schedule. Seven rats were maintained on 3 feeding times (1 hr each) per day at 6-6-12 hr intervals, followed by 8-8-8 hr intervals. Six rats displayed some AA to two of three access times, but no rat anticipated all 3 access times simultaneously. AA occasionally shifted from one access time to another. In all conditions, entrainment was much less stable compared to single access times. Typically, the instabilities in AA were suggestive of transients, i.e., a temporary loss of entrainment. The results appear most consistent with a model consisting of 2 internally coupled pacemakers that are entrained by feeding.