Coupling between feeding- and light-entrainable circadian pacemakers in the rat

Activity of the rat can be entrained to LD cycles (light-entrainable rhythm = LER) and to periodic food access (feeding-entrainable rhythm = FER) and these responses appear to be mediated by separate circadian pacemaking systems. The purpose of this study was to explore interactions between these systems. In Experiment I, after entrainment of activity to a LD cycle and to restricted feeding, the LD cycle was phase delayed by 4 hr and rats were food deprived for 3 days. Delaying transients were observed in both the LER and FER although food was no longer a Zeitgeber. In Experiment II, food was scheduled at 3 different phases of the LD cycle. Food access was then phase delayed by 8 hr and rats were placed in DD. When the new food access fell into the subjective day, the phase of the LER was not affected but transients in the FER persisted for up to 18 days, 3 to 5 times longer than reported for rats with suprachiasmatic nucleus lesions. When the new food access fell into the early subjective night, the "free-running" LER was phase advanced by over 3 hr but no delaying transients in the FER were observed. When the new food access fell into the late subjective night, the LER was not phase advanced but its period remained close to 24 hr and no delaying transients in the FER were observed. In Experiment III, food was presented at two phases of the LD cycle and restricted feeding was continued in DD without phase shifts.(ABSTRACT TRUNCATED AT 250 WORDS)