AJP - Regulatory, Integrative and Comparative Physiology, Vol 248, Issue 3 353-R362, Copyright © 1985 by American Physiological Society
Circadian sleep-wake cycle organization in squirrel monkeys
D. B. Wexler and M. C. Moore-Ede
To investigate the relationship between circadian rhythms of body
temperature and sleep-wake stages, four squirrel monkeys were prepared for
unrestrained monitoring of temperature, locomotor activity,
electroencephalogram, electroculogram, and electromyogram. Continuous
records for each animal were made for several 12-h light-dark (LD) cycles
and then after a few days in constant illumination (LL). All animals
maintained consolidated sleep-wake cycles and had a longer circadian period
(mean 24.7 h) in LL than in LD (mean 24.1 h). The increased period
reflected greater time per circadian cycle spent awake in LL (mean 14.0 h)
than in LD (mean 12.8 h). Total night NREM sleep was less in LL (mean 6.5
h) than in LD (mean 8.2 h). Sleep onset occurred at later phases in LL (187
+/- 6 degrees) than in LD (170 +/- 2 degrees). Because the circadian phase
measure of NREM sleep was unchanged between LD and LL conditions, the
difference in sleep onsets reflected balanced changes in NREM circadian
waveforms. Wake-up phases were the same in both conditions (mean 342
degrees). In summary, during free run squirrel monkeys maintain a stable
consolidated circadian sleep-wake cycle with a period greater than 24 h,
but they exhibit only minimal internal phase restructuring.
