Journal of Comparative Physiology A

, Volume 165, Issue 6, pp 811–818 | Cite as

Running activity mediates the phase-advancing effects of dark pulses on hamster circadian rhythms

  • Stéphan G. Reebs
  • Robert J. Lavery
  • N. Mrosovsky


Pulses of darkness can phase-shift the circadian activity rhythms of hamsters,Mesocricetus auratus, kept in constant light. Dark pulses under these conditions alter photic input to the circadian system, but they also commonly trigger wheel-running activity. This paper investigates the contribution of running activity to the phase-shifting effects of dark pulses. A first experiment showed that running activity by itself can phaseshift rhythms in constant light. Hamsters were induced to run by being confined to a novel wheel for 3–5 h. When this was done at circadian times (CT) 0, 6, and 9, the mean steady-state phase-shifts were 0.6 h, 3.5 h, and 2.3 h, respectively. The latter two values are at least as large as those previously obtained with dark pulses of similar durations and circadian phases. A second experiment showed that restricting the activity of hamsters during 3-h dark pulses at CT 9 reduces the amplitude of the phase-shifts. Unrestrained animals phase-advanced by 1.1 h, but this shift was halved in animals whose wheel was locked, and completely abolished in animals confined to nest boxes during the dark pulse. Activity restriction in itself (without dark pulses) had only minimal phase-delaying effects on free-running rhythms when given between ca. CT 10 and CT 13. These results support the idea that, in hamsters at least, dark pulses affect the circadian system mostly by altering behavioural states rather than by altering photic input to the internal clock.


Circadian Rhythm Activity Rhythm Behavioural State Constant Light Circadian System 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



circadian time


constant darkness




constant light


phase response curve


period of rhythm


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Copyright information

© Springer-Verlag 1989

Authors and Affiliations

  • Stéphan G. Reebs
    • 1
  • Robert J. Lavery
    • 2
  • N. Mrosovsky
    • 1
    • 2
    • 3
  1. 1.Department of ZoologyUniversity of TorontoTorontoCanada
  2. 2.Department of PsychologyUniversity of TorontoTorontoCanada
  3. 3.Department of PhysiologyUniversity of TorontoTorontoCanada

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