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Entrainment of split circadian activity rhythms in hamsters
1Long Island Research Institute, State University of New York, Stony Brook 11794.
Journal of Biological Rhythms
|January 1, 1985
Summary
Hamster circadian rhythms split under constant light can re-entrain to light-dark cycles. These split rhythms, driven by two coupled oscillator populations, respond similarly to light cues, suggesting a dual-oscillator model for circadian pacemakers.
Area of Science:
- Chronobiology
- Animal Behavior
- Neuroscience
Background:
- Circadian rhythms regulate daily physiological and behavioral patterns.
- Constant illumination (LL) can disrupt circadian rhythms, leading to splitting of activity patterns in hamsters.
- Understanding the underlying mechanisms of circadian rhythm splitting is crucial for comprehending pacemaker organization.
Purpose of the Study:
- To investigate the entrainment patterns of split circadian rhythms in hamsters exposed to light-dark (LD) cycles.
- To determine if the two components of a split rhythm respond differently to LD cycles.
- To provide further evidence for the dual-oscillator model of circadian pacemakers.
Main Methods:
- Hamsters with split circadian rhythms from LL exposure were subjected to LD cycles with varying periods (24.00, 24.23, 24.72 hr) and 2-hr dark segments.
- Control hamsters with nonsplit rhythms were also studied.
- Following entrainment, some animals were returned to LL, and LD cycles were reapplied with altered dark segment timing to assess component response.
Main Results:
- In all split rhythm cases, at least one component entrained to the LD cycle.
- The second component either free-ran or entrained with a stable phase angle (6-14.5 hr) relative to dark onset.
- Both split components responded similarly to the dark segments, regardless of whether the LD cycle period was shorter or longer than the split rhythm period.
Conclusions:
- The results support a model where split circadian rhythms in hamsters arise from two mutually coupled oscillator populations with similar properties.
- These findings suggest a bidirectional phase response curve for the split rhythm components.
- The dual-oscillator organization may also underlie normal circadian rhythms, with dissociation occurring under specific conditions like moderate LL intensity.