Restricted daytime feeding attenuates reentrainment of the circadian melatonin rhythm after an 8-h phase advance of the light-dark cycle.
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.
Kalsbeek
A
A
Netherlands Institute for Brain Research, Amsterdam.
Barassin
S
S
van Heerikhuize
J J
JJ
van der Vliet
J
J
Buijs
R M
RM
D000818:Animals; D001923:Brain Chemistry / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D005508:Food Deprivation / Q000502:physiology*; D008027:Light; D008297:Male; D008550:Melatonin / Q000097:blood*; D017551:Microdialysis; D015999:Multivariate Analysis; D051381:Rats; D017208:Rats, Wistar
D008550:Melatonin