Mutual influence of rats having different circadian rhythm of adrenocortical activity

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Abstract
The possibility of a mutual influence between male adult rats having different circadian adrenocortical rhythms was studied under 2 different lighting conditions. Intact and optic-enucleated rats were housed together in the same cage in various ratios of intact to blinded rats. Twenty-four or forty-eight hour patterns of plasma corticosterone levels were determined individually at 4 h intervals. Under diurnal light-dark alternation, the circadian periodicity of the intact rats always synchronized with light, whereas single blinded rats in cages with 3 intact rats demonstrated free-running rhythms throughout the experimental period of 15 wk. Under constant light the circadian rhythm free-ran in both intact and blinded rats for the 1st 2 wk. A phase reversal of the rhythm was observed in the intact rats at the end of the 2nd wk, and between 5 and 8 wk after blinding in the blinded rats. The circadian adrenocortical rhythms in intact and blinded rats are not entrained to each other, even when the 2 types of rats live together in the same age.

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