Document Detail

Nonphotic entrainment in a diurnal mammal, the European ground squirrel (Spermophilus citellus).
MedLine Citation:
PMID:  10511008     Owner:  NLM     Status:  MEDLINE    
Entrainment by nonphotic, activity-inducing stimuli has been investigated in detail in nocturnal rodents, but little is known about nonphotic entrainment in diurnal animals. Comparative studies would offer the opportunity to distinguish between two possibilities. (1) If nonphotic phase shifts depend on the phase of the activity cycle, the phase response curve (PRC) should be about 180 degrees out of phase in nocturnal and diurnal mammals. (2) If nonphotic phase shifts depend on the phase of the pacemaker, the two PRCs should be in phase. We used the diurnal European ground squirrel (Spermophilus citellus) in a nonphotic entrainment experiment to distinguish between the two possibilities. Ten European ground squirrels were kept under dim red light (<1 lux) and 20 +/- 1 degrees C. During the entrainment phase of the experiment, the animals were confined every 23.5 h (T) to a running wheel for 3 h. The circadian rhythms of 6 squirrels entrained, 2 continued to free run, and 2 possibly entrained but displayed arrhythmicity during the experiment. In a second experiment, a photic pulse was used in a similar protocol. Five out of 9 squirrels entrained, 1 did not entrain, and 3 yielded ambiguous results. During stable entrainment, the phase-advancing nonphotic pulses coincided with the end of the subjective day, while phase-advancing light pulses coincided with the start of the subjective day: mean psi(nonphotic) = 11.4 h; mean psi(photic) = 0.9 h (psi defined as the difference between the onset of activity and the start of the pulse). The data for nonphotic entrainment correspond well with those from similar experiments with nocturnal Syrian hamsters where psi(nonphotic) varied from 8.09 to 11.34 h. This indicates that the circadian phase response to a nonphotic activity-inducing stimulus depends on the phase of the pacemaker rather than on the phase of the activity cycle.
R A Hut; N Mrosovsky; S Daan
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of biological rhythms     Volume:  14     ISSN:  0748-7304     ISO Abbreviation:  J. Biol. Rhythms     Publication Date:  1999 Oct 
Date Detail:
Created Date:  1999-11-02     Completed Date:  1999-11-02     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  8700115     Medline TA:  J Biol Rhythms     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  409-19     Citation Subset:  IM    
Zoological Laboratory, University of Groningen, The Netherlands.
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MeSH Terms
Activity Cycles / physiology
Circadian Rhythm / physiology*,  radiation effects
Motor Activity / physiology
Sciuridae / physiology*

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