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Am J Physiol Regul Integr Comp Physiol 274: R830-R839, 1998;
0363-6119/98 $5.00
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Vol. 274, Issue 3, R830-R839, March 1998

Effects of bright light on age-related changes in the locomotor activity of Syrian hamsters

Susan E. Labyak1,2, Fred W. Turek1, Edward P. Wallen3, and Phyllis C. Zee1,4

1 Department of Neurobiology and Physiology and Center for Circadian Biology and Medicine, Northwestern University, Evanston 60208-3520; 4 Department of Neurology, Northwestern University, Chicago, Illinois 60611; 2 Department of Psychiatry and Human Behavior, Brown University, Providence 02915; and 3 Department of Biological Sciences, University of Wisconsin at Parkside, Kenosha, Wisconsin 53140

Syrian hamsters display age-related changes in the expression of circadian rhythms and in responsiveness of the circadian system to photic and nonphotic stimuli. This study characterized the effects of age on the locomotor activity rhythm of middle-aged and old hamsters and evaluated the effects of strengthening the entraining light signal. Compared with young (4.5 mo) animals, middle-aged (11.25 mo) and old (16 mo) animals displayed increased daily bouts of activity (P < 0.001) and reduced total daily activity and activity rhythm amplitude (P < 0.05) in 14:10-h light-dark cycles. After the light intensity was increased from 300 to 1,500 lx during the light cycle, middle-aged hamsters demonstrated decreased daily activity bouts (P < 0.05) and increased total daily activity (P <=  0.01) and activity rhythm amplitude (P <=  0.001) compared with controls maintained in 300 lx. The pattern of changes in the activity rhythm of old experimental animals was similar to trends observed in middle-aged experimental hamsters, although not as robust. Thus age-related changes in the activity rhythm are occurring by middle age in hamsters, and the provision of stronger entraining signals may lead to more stable circadian organization.

aging; circadian activity rhythm


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