AJP - Regulatory, Integrative and Comparative Physiology, Vol 235, Issue 5 243-R249, Copyright © 1978 by American Physiological Society
Internal synchronization among several circadian rhythms in rats under constant light
K. I. Honma and T. Hiroshige
Three biological rhythms (locomotor activity, body temperature, and plasma
corticosterone) were measured simultaneously in individual rats under
light-dark cycles and continuous light. Spontaneous locomotor activity was
recorded on an Animex and body temperature was telemetrically monitored
throughout the experiments. Blood samples were obtained serially at 2-h
intervals on the experimental days. Phase angles of these rhythms were
calculated by a least-squares spectrum analysis. Under light-dark cycles,
the acrophases of locomotor activity, body temperature, and plasma
corticosterone were found at 0029, 0106, and 1940 h, respectively. When
rats were exposed to 200 lx continuous light, locomotor activity and body
temperature showed free-running rhythms with a period of 25.2 h on the
average. Plasma corticosterone levels determined at 12 days after exposure
to continuous light exhibited a circadian rhythm with the acrophase shifted
to 0720. The acrophases of locomotor activity and body temperature,
determined simultaneously on the same day, were found to be located at 1303
and 1358 h, respectively. Phase-angle differences among the three rhythms
on the 12th day of continuous light were essentially the same with those
under the light-dark cycle. These results suggest that circadian rhythms of
locomotor activity, body temperature, and plasma corticosterone are most
probably coupled to a common internal oscillator in the rat.
