Time structure of locomotor activity in mice kept on different light - dark cycles

Objective. This study investigates how the shortening or lengthening of the circadian period of the environmental lighting schedule affects the circadian and extra-circadian structure of locomotor activity in mice, with particular focus on the circasemiseptan, circaseptan, and circadecadian components with anticipated periods of about 3.5, 7, and 10 days, respectively. Methods. The locomotor activity of mice kept on different light - dark (LD) cycles was automatically monitored around the clock for about five weeks. The data were analyzed by linear - nonlinear rhythmometry. Results. As anticipated, in LD12:12, a prominent circadian rhythm was observed, with a marked 12-hour component qualifying the circadian waveform. By comparison, in LD10:10 and in LD14:14, the circadian rhythm had a reduced amplitude and a period close to that of the environmental synchronizer. Extra-circadian variation was then also demonstrated. In conclusion, circadian lighting schedules affect a broader-than-circadian time structure of locomotor activity in mice.