Transient circadian internal desynchronization after light-dark phase shift in monkeys MARTIN C. MOORE-EDE, DAVID A. KASS, AND J. ALAN HERD Department of Physiology, Harvard Medical School, and Department of Surgery, Harvard Medical School at the Peter Bent Brigham Hospital, Boston 02115; and Department of Psychiatry, Harvard Medical School at the New England Regional Primate Research Center, Southboro, Massachusetts 01772 MOORE-EDE, MARTIN C., DAVID A. KASS, AND J. ALAN HERD. Transient circadian internal desynchronization after light-dark phase shift in monkeys. Am. J. Physiol. 232(l): R31-R37, 1977 or Am. J. Physiol: Regulatory Integrative Comp. Physiol. l(1): R31-R37, 1977. -In four conscious chair- acclimatized squirrel monkeys (Saimiri sciureus) studied with lights on (600 lx) from 0800 to 2000 h daily (LD 12:12), prominent 24-h rhythms in feeding, drinking, activity, body temperature, and urinary potassium, sodium, and water ex- cretion were seen. When the monkeys were subjected to 36 h of darkness followed by 36 h of light each variable demonstrated a circadian rhythm which was not passively dependent on the light-dark cycle. After the 24-h light-dark cycle was abruptly phase-delayed by 8 h, all the rhythms resynchronized with the new light-dark cycle phase, demonstrating that light-dark cycles are an effective zeitgeber. However, the resynchroniza- tion of the rhythms of feeding, drinking, activity, and body temperature was 90% complete within approximately 2 days while the 90% resynchronization of the urinary rhythms took approximately 5 days. These results suggest that the circadian timing system in S. sciureus may consist of several sponta- neously oscillating units which can become transiently uncou- pled during pertubations of environmental time cues. circadian rhythms; squirrel monkey; light-dark cycle; zeitge- ber phase shift ENDOGENOUS CIRCADIAN OSCILLATIONS in physiological variables have been demonstrated in organisms ranging from unicellular algae (14) to man (8). There is now considerable evidence to suggest that these physiologi- cal rhythms are generated by autonomous oscillators within the organism (21, 25). These circadian oscillators are normally synchronized by environmental time cues (“zeitgebers”), such as the light-dark cycle, but in the absence of such cues, the oscillating system demon- strates free-running periods which are usually different from 24 h. Any conclusion as to the organization and physiology of these circadian oscillators must be compatible with an important phenomenon known as “internal synchro- nization.” It has been demonstrated in both unicellular (20) and multicellular (2, 3, 6, 12) organisms that when circadian rhythms in several physiological variables are monitored simultaneously in an individual animal they are usually found to have identical periods. This has been observed whether the organism is synchronized by environmental time cues or has its circadian rhythms free-running under constant conditions. Such internal synchronization either demands that within an orga- nism there must be only one oscillator or “clock” on which all endogenous circadian rhythms are passively dependent, or, if there is more than one oscillator, then the various oscillators must be normally synchronized with one another. This paper reports studies in which we have manipu- lated environmental time cues to determine the extent of the coupling between seven behavioral and physiolog- ical variables that show circadian rhythmicity in the squirrel monkey. If constant internal phase relation- ships were maintained between the various circadian rhythms throughout these pertubations then this might suggest that all the rhythms were passively dependent on a single circadian oscillator. On the other hand if certain oscillating functions responded more rapidly than others to pertubations in environmental time cues, so that transient circadian internal desynchronization was observed, then this would suggest the possibility that the circadian timing system in the squirrel monkey is composed of multiple potentially independent oscilla- tors. MATERIALS AND METHODS The studies were performed using four adult male squirrel monkeys (Saimiri sciureus) weighing 600-900 g. For periods of up to 3 wk, continuous urine collections were obtained from unanesthetized monkeys, condi- tioned to sit in a specially designed metabolism chair. Environmental illumination, temperature, and audi- tory stimuli were controlled by conducting experiments within an isolation chamber. Once the monkeys were conditioned, they tolerated studies lasting 2-3 wk and showed no ill effects or loss of agility on return to their cages. While in the metabolism chair they behaved normally and maintained body weight. Metabolism chair. The design of this chair was based on the squirrel monkey chairs used in the behavioral experiments of Kelleher and Morse (17). The monkey sat on a bar and was restrained by a Plexiglas sheet which served as a table around its waist. The space between the table and the monkey was sealed by a soft R31 by 10.220.33.2 on November 8, 2016 http://ajpregu.physiology.org/ Downloaded from