AJP - Regulatory, Integrative and Comparative Physiology, Vol 234, Issue 3 110-R114, Copyright © 1978 by American Physiological Society
Circadian rhythms in blinded rats: correlation between pineal and activity cycles
C. R. Pohl and F. P. Gibbs
The rat pineal gland exhibits diurnal rhythms in levels of
N-acetyltransferase activity and its substrate serotonin. We attempted to
demonstrate the endogenous nature of these changes by measuring the pineal
enzyme and its substrate in rats blinded for 37 and 60 days. In order to
determine the proper sampling times for these one-time, terminal
measurements, the running activity rhythm of each rat was monitored
continuously and the animals were killed at either midrest or midrun.
Circadian changes of pineal N-acetyltransferase and serotonin were
demonstrated, with enzyme levels high and substrate content low during
midrun. Absolute values during each activity phase were similar to those of
control rats entrained to a light cycle (LD 12:12). Levels of the pineal
constituents were unrelated to local time. These results suggest that rats
blinded for up to 60 days maintain their free-running pineal rhythms with
undamped amplitudes and in synchronization with the activity rhythm.
