Effects of aging on the circadian rhythm of wheel-running activity in C57BL/6 mice

Jan 22, 1998The American journal of physiology

How aging changes daily activity patterns in C57BL/6 mice

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Abstract

Old C57BL/6J mice show a longer free-running period under constant darkness compared to adult mice.

Old mice displayed delayed activity onset after light offset and increased variability in activity onset compared to adult mice.
Following a phase advance of the light cycle, old mice took significantly longer to adjust their activity rhythm than adult mice.
There was a decline in daily wheel revolutions and a tendency for a shorter active phase in older mice.
Aging was associated with increased fragmentation of activity, characterized by shorter bursts of activity and longer rest periods.
No significant age difference was found in the maximum intensity of wheel-running activity.

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The effects of age on the circadian clock system have been extensively studied, mainly in two rodent species, the laboratory rat and the golden hamster. However, less information is available on how aging alters circadian rhythmicity in a commonly studied rodent animal model, the mouse. Therefore, in the present study we compared the rhythm of wheel-running activity in adult (6-9 mo) and old (19-22 mo) C57BL/6J mice maintained under different lighting conditions for a period of 4 mo. During this period, mice were subjected to phase advances and phase delays of the light-dark (LD) cycle and eventually to constant darkness (DD). In LD (12 h light, 12 h dark), old mice exhibited delayed activity onset relative to light offset and an increase in the variability of activity onset compared with adult mice. After a 4-h phase advance of the LD cycle, old mice took significantly longer to reentrain their activity rhythm when compared with adult animals. Old mice also demonstrated a decline in the number of wheel revolutions per day and a tendency toward a decrease in the length of the active phase. An increase in fragmentation of activity across the 24-h day was obvious in aging animals, with bouts of activity being shorter and longer rest periods intervening between them. No age difference was detected in the maximum intensity of wheel-running activity. In DD, the free-running period was significantly longer in old mice compared with adults. In view of the rapidly expanding importance of the laboratory mouse for molecular and genetic studies of the mammalian nervous system, the present results provide a basis at the phenotypic level to begin to apply genetic methods to the analysis of circadian rhythms and aging in mammals.

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Effects of aging on the circadian rhythm of wheel-running activity in C57BL/6 mice

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