Effects of aging on entrainment and rate of resynchronization of circadian locomotor activity.
The phase angle of entrainment of the circadian rhythm of the locomotor activity rhythm to a light-dark (LD) cycle was examined in young (2-5 mo old) and middle-aged (13-16 mo old) hamsters. An age-related phase advance in the onset of locomotor activity relative to lights off was seen during stable entrainment to a 14:10-h LD cycle. In addition, the effects of age on the rate of reentrainment of the circadian rhythm of locomotor activity were examined by subjecting young and middle-aged hamsters to either an 8-h advance or delay shift of the LD cycle. Middle-aged hamsters resynchronized more rapidly after a phase advance of the LD cycle than did young hamsters, whereas young hamsters were able to phase delay more rapidly than middle-aged hamsters. The age-related phase advance of activity onset under entrained conditions, and the alteration of responses in middle-aged hamsters reentraining to a phase-shifted LD cycle, may be due to the shortening of the free-running period of the circadian rhythm of locomotor activity with advancing age that has previously been observed in this species.
Zee
P C
PC
Department of Neurology, Northwestern University, Chicago, Illinois 60611.
Rosenberg
R S
RS
Turek
F W
FW
D000375:Aging / Q000502:physiology*; D000818:Animals; D002940:Circadian Rhythm; D006224:Cricetinae; D008124:Locomotion / Q000502:physiology*; D008297:Male; D008647:Mesocricetus; D009043:Motor Activity / Q000502:physiology*; D017440:Photoperiod; D051381:Rats