Phase Shifting the Hamster Circadian Clock by 15-Minute Dark Pulses

The mammalian circadian pacemaker can be phase shifted by exposure to a period of darkness interrupting otherwise continuous light. Circadian phase shifting by dark pulses was interpreted originally as reflecting a photic mirrorimage mechanism, but more recent observations suggest that dark pulseind...

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Bibliographic Details
Published in:Journal of biological rhythms 2002-06, Vol.17 (3), p.238-247
Main Authors: Rosenwasser, Alan M., Dwyer, Suzanne M.
Format: Article
Language:English
Subjects:
Animals
Biological Clocks - physiology
Circadian rhythm
Circadian Rhythm - physiology
Cricetinae - physiology
Darkness
Experiments
Male
Mesocricetus
Photic Stimulation
Restraint, Physical
Rodents
Time Factors
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Summary:The mammalian circadian pacemaker can be phase shifted by exposure to a period of darkness interrupting otherwise continuous light. Circadian phase shifting by dark pulses was interpreted originally as reflecting a photic mirrorimage mechanism, but more recent observations suggest that dark pulseinduced phase shifting may be mediated by a nonphotic, behavioral state-dependent mechanism. The authors recently presented evidence indicating that the dark-pulse phase response curve (PRC) is in fact a complex function, reflecting both photic mirror image and nonphotic mechanisms at different phases of the circadian cycle. Previous studies of dark pulse-induced phase shifting have universally employed relatively long (2 to 6 h) pulses, which complicates PRC analysis due to the extended segment of the underlying PRC spanned by such a long pulse. The present study was therefore designed to examine the phaseshifting effects of brief 15-min dark pulses presented at both mid-subjective day and subjective dusk, and to explore the possible activity dependence of these effects by using physical restraint to prevent evoked locomotor activity. The results indicate that 15-min dark pulses are effective phase-shifting stimuli at both midday and dusk. Furthermore, as with longer dark pulses, phase shifting by 15-min dark pulses is completely blocked by physical restraint during subjective day but combines in a simple additive manner with the independent phaseshifting effect of restraint at subjective dusk.
ISSN:0748-7304
1552-4531
DOI:10.1177/07430402017003007