AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 6 927-R934, Copyright © 1983 by American Physiological Society
Light-dark masking of circadian temperature and activity rhythms in squirrel monkeys
P. H. Gander and M. C. Moore-Ede
In addition to the synchronizing effects of light-dark cycles on the
circadian timing system, light per se can have a direct masking effect on
the rhythmic variables monitored as indicators of the circadian system. To
evaluate the masking action of light on the rest-activity and body
temperature rhythms of squirrel monkeys (Saimiri sciureus), animals were
exposed to cycles of 2 h of light alternating with 2 h of darkness (LD
2:2). There was evidence of phase-dependent masking responses in both
rhythms, with the light-induced elevation of activity levels and
temperature greatest around the times of the circadian maxima of the
respective rhythms. The temporal distribution of activity was more strongly
affected by the masking action of the 2:2 cycle than was the temporal
pattern of temperature variation. The increase in activity observed during
lights on was evidently a major factor contributing to the corresponding
increase in temperature.
