Fine ultradian structures of mouse locomotion in response to light-dark reversal

Abstract

We have shown previously with image analysis technique that a minimum of 10 days is required for the locomotion pattern of mice to adjust to an abrupt change in the day-night cycle. In this experiment we further studied those fine temporal changes in the locomotion signal in particular in the ultradian band. Locomotor activity of mice (Strain C57, aged 8–10 weeks) was recorded using an image-based monitoring system developed in our laboratory. Individual animal was housed in a top-open cage kept within a sound-shielded, ventilation- and light-controlled chamber (12 h light and 12 h dark, LD) with unrestricted diet. Displacement of the animal body was frame-grabbed at 2-second intervals and pixels in the difference image of two consecutive frames were summed in order to index the extent of locomotion. To study their ability to synchronize locomotion with the external lighting conditions, the LD cycle was reversed by introducing a light-light (LL) or dark-dark (DD) transition on the 5th day. The subsequent locomotor activity was monitored for another 2 weeks. The locomotion signal was analyzed using the Wavelet transform and spliced into 7 frequency bands covering the circadian (1 cycle per day (cpd)) to the very high frequency rhythms (130 cpd). Results show that there is a consistent ‘merge-split’ phenomenon, we called ‘2-1-2’ pattern, within the frequency bands of 2–5 cpd. This can be used to as a sensitive index to time-course and distinguish the response to a LL versus a DD transition. We interpret such phenomenon as a result of interaction of the underlying multiple oscillators in the body. Supported in part by NSC87-2314-B6-96.