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 offsetor a dawnlike onset caused phase shifts of different sizes in the circadianwheel-running activity of Syrian hamsters, Mesocricetusauratus. Six experiments were conducted, each with 30 hamsters;the hamsters received first one type of pulse and then the other type a fewweeks later, allowing a paired comparison. The six experiments representedthe combination of two maximum light intensities (150 and 250 lux) and threezeitgeber times (ZTs) at which the pulses were given (ZT13.5, ZT14.5, andZT20). Pulses were 30 minutes long, a relatively short duration to minimizecircadian time effects. Aschoff's type II method of measuring phase shiftswas used. In none of the six experiments did a two-tailed paired t test detect a significant difference in the sizeof phase shifts caused by dusklike versus dawnlike pulses. A three-way analysisof variance (ANOVA) on the combined data from all six experiments (with pulsetype, pulse intensity, and ZT as factors) also failed to detect a significanteffect of pulse type. Statistical power was calculated and found to be reasonablygood. These negative results are in line with those of a previous study inwhich a different methodology was used. (ChronobiologyInternational, 18(3), 413–421, 2001)

• Circadian activity rhythm
• Dawn
• Dusk
• Hamster
• Phase shift
• Twilight