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Transient circadian internal desynchronization after light-dark phase shift in monkeys.

M C Moore-Ede, D A Kass, J A Herd

    The American Journal of Physiology
    |January 1, 1977
    PubMed
    Summary
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    Squirrel monkeys exhibit robust circadian rhythms in behavior and physiology. These rhythms can desynchronize and resynchronize with environmental light-dark cycles, indicating a complex internal timing system.

    Area of Science:

    • Chronobiology
    • Primate Physiology
    • Animal Behavior

    Background:

    • Squirrel monkeys (Saimiri sciureus) display prominent 24-hour rhythms in feeding, drinking, activity, body temperature, and urinary excretion under a standard light-dark cycle.
    • Circadian rhythms are endogenous biological processes that regulate physiological and behavioral patterns over approximately 24 hours.

    Purpose of the Study:

    • To investigate the dependency of circadian rhythms on the light-dark cycle in squirrel monkeys.
    • To determine the effectiveness of light-dark cycles as a zeitgeber (time cue) for resynchronizing physiological and behavioral rhythms.
    • To explore the potential for multiple, independently oscillating units within the squirrel monkey's circadian timing system.

    Main Methods:

    • Four conscious squirrel monkeys were acclimatized to a 12-hour light-12-hour dark (LD 12:12) cycle.

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  • Monkeys were exposed to extended periods of darkness (36 hours) followed by light (36 hours) to assess rhythm persistence.
  • The light-dark cycle was abruptly phase-delayed by 8 hours to evaluate resynchronization rates of various rhythms.

    • Main Results:

    • Circadian rhythms persisted even when independent of the light-dark cycle, suggesting endogenous control.
    • Light-dark cycles effectively acted as a zeitgeber, inducing resynchronization of all monitored rhythms.
    • Behavioral and body temperature rhythms (feeding, drinking, activity) resynchronized approximately 90% within 2 days, while urinary rhythms took approximately 5 days for 90% resynchronization.

    Conclusions:

    • The squirrel monkey's circadian timing system appears to comprise multiple spontaneously oscillating units.
    • These internal oscillators can become transiently uncoupled when environmental time cues (light-dark cycles) are perturbed.
    • Differential resynchronization rates suggest distinct mechanisms governing behavioral and urinary circadian rhythms in this species.