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Restricted Daytime Feeding Attenuates Reentrainment of the Circadian Melatonin Rhythm after an 8-h Phase Advance of the Light-Dark Cycle

Netherlands Institute for Brain Research, Meibergdreef 33, 1105 AZ Amsterdam, the Netherlands

S. Barassin

Neurobiologie des Fonctions Rythmiques et Saisonnières, UMR-CNRS 7518, Université Louis Pasteur, 12, rue de l'Université, Strasbourg, France

J. J. van Heerikhuize

J. van der Vliet

R. M. Buijs

Netherlands Institute for Brain Research, Meibergdreef 33, 1105 AZ Amsterdam, the Netherlands

It is well established that in the absence of photic cues, the circadian rhythms of rodents can be readily phase-shifted and entrained by various nonphotic stimuli that induce increased levels of locomotor activity (i.e., benzodiazepines, a new running wheel, and limited food access). In the presence of an entraining light-dark (LD) cycle, however, the entraining effects of nonphotic stimuli on (parts of) the circadian oscillator are far less clear. Yet, an interesting finding is that appropriately timed exercise after a phase shift can accelerate the entrainment of circadian rhythms to the new LD cycle in both rodents and humans. The present study investigated whether restricted daytime feeding (RF) (1) induces a phase shift of the melatonin rhythm under entrained LD conditions and (2) accelerates resynchronization of circadian rhythms after an 8-h phase advance. Animals were adapted to RF with 2-h food access at the projected time of the new dark onset. Before and at several time points after the 8-h phase advance, nocturnal melatonin profiles were measured in RF animals and animals on ad libitum feeding (AL). In LD-entrained conditions, RF did not cause any significant changes in the nocturnal melatonin profile as compared to AL. Unexpectedly, after the 8-h phase advance, RF animals resynchronized more slowly to the new LD cycle than AL animals. These results indicate that prior entrainment to a nonphotic stimulus such as RF may "phase lock" the circadian oscillator and in that way hinder resynchronization after a phase shift.

Key Words: phase shift • microdialysis • suprachiasmatic nucleus • food intake • hormonal rhythm

Journal of Biological Rhythms, Vol. 15, No. 1, 57-66 (2000)
DOI: 10.1177/074873040001500107


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