title: Aging and photoperiod affect entrainment and quantitative aspects of locomotor behavior in Syrian hamsters.
abstract: Aging affects the regulation of diurnal and circadian rhythmicity. We tested the hypothesis that the age-related difference in the phase angle of entrainment of the locomotor activity rhythm to a light-dark (LD) cycle would be greater under LD 6:18 than LD 14:10. We also analyzed changes in quantitative aspects of wheel-running behavior according to age group. Young (9-wk-old), middle-aged (11- to 12-mo-old), and old (15- to 17-mo-old) male golden hamsters were entrained to a 14:10 LD cycle followed by re-entrainment to a 6:18 LD cycle. Fourteen days after the start of locomotor recording in LD 14:10 and again after 27 days in LD 6:18, the phase of activity onset, the total number of wheel revolutions performed per day, the peak intensity of wheel-running activity, the duration of the active period, and the level of fragmentation of locomotor activity were quantitated. We also studied the temporal distribution of the largest bout of wheel-running activity among the age groups in both photoperiods. Short days induced testicular regression at a similar rate among young, middle-aged, and old hamsters. The data are discussed in terms of the effects of age on overall circadian organization in the seasonally changing environment.
authors.affiliation: Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208-3520, USA.
authors.forename: K
authors.initials: K
authors.lastname: Scarbrough
authors.forename: S
authors.initials: S
authors.lastname: Losee-Olson
authors.forename: E P
authors.initials: EP
authors.lastname: Wallen
authors.forename: F W
authors.initials: FW
authors.lastname: Turek
mesh_terms: D000375:Aging / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D002940:Circadian Rhythm; D006224:Cricetinae; D003624:Darkness; D008027:Light; D008297:Male; D008647:Mesocricetus; D009043:Motor Activity; D013997:Time Factors