Effects of bright light on age-related changes in the locomotor activity of Syrian hamsters.
Syrian hamsters display age-related changes in the expression of circadian rhythms and in responsiveness of the circadian system to photic and non-photic 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 < or = 0.01) and activity rhythm amplitude (P < or = 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.
Labyak
S E
SE
Department of Neurobiology and Physiology, Northwestern University, Evanston 60208-3520, USA.
Turek
F W
FW
Wallen
E P
EP
Zee
P C
PC
D000375:Aging; D000818:Animals; D001522:Behavior, Animal / Q000528:radiation effects; D002940:Circadian Rhythm / Q000528:radiation effects; D006224:Cricetinae; D004307:Dose-Response Relationship, Radiation; D008027:Light; D008647:Mesocricetus / Q000502:physiology*; D009043:Motor Activity / Q000528:radiation effects*