title: Phase-shifting effects of dusklike and dawnlike light pulses on the circadian activity rhythms of Syrian hamsters.
abstract: This study tested whether light pulses with a dusklike offset or a dawnlike onset caused phase shifts of different sizes in the circadian wheel-running activity of Syrian hamsters, Mesocricetus auratus. Six experiments were conducted, each with 30 hamsters; the hamsters received first one type of pulse and then the other type a few weeks later, allowing a paired comparison. The six experiments represented the combination of two maximum light intensities (150 and 250 lux) and three zeitgeber times (ZTs) at which the pulses were given (ZT13.5, ZT14.5, and ZT20). Pulses were 30 minutes long, a relatively short duration to minimize circadian time effects. Aschoff's type II method of measuring phase shifts was used. In none of the six experiments did a two-tailed paired t test detect a significant difference in the size of phase shifts caused by dusklike versus dawnlike pulses. A three-way analysis of variance (ANOVA) on the combined data from all six experiments (with pulse type, pulse intensity, and ZT as factors) also failed to detect a significant effect of pulse type. Statistical power was calculated and found to be reasonably good. These negative results are in line with those of a previous study in which a different methodology was used.
authors.affiliation: Département de Biologie, Université de Moncton, NB, Canada. reebss@umoncton.ca
authors.forename: S G
authors.initials: SG
authors.lastname: Reebs
authors.forename: R
authors.initials: R
authors.lastname: Cormier
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002940:Circadian Rhythm; D006224:Cricetinae; D008027:Light; D008297:Male; D008647:Mesocricetus; D013997:Time Factors