Bouts of rest and physical activity in C57BL/6J mice

The objective was to exploit the raw data output from a scalable home cage (type IIL IVC) monitoring (HCM) system (DVC(R)), to characterize pattern of undisrupted rest and physical activity (PA) of C57BL/6J mice. The systems tracking algorithm show that mice in isolation spend 67% of the time in bouts of long rest ([≥]40s) and 59 % of the time was interpreted as sleep. Twenty percent is physical activity (PA), split equally between local movements and locomotion. Decomposition revealed that a day contains [~]6500 discrete bouts of short and long rest, local and locomotor movements. Mice travel [~]330m per day, mainly during the dark hours, while travelling speed is similar through the light-dark cycle. Locomotor bouts are usually 1m. Tracking revealed also fits of abnormal behaviour. The starting positions of the bouts showed no preference for the rear over the front of the cage floor, while there was a strong bias for the peripheral (75%) over the central floor area. The composition of bouts has a characteristic circadian pattern, however, intrusive husbandry routines increased bout fragmentation by [~]40%. Extracting electrode activations density (EAD) from the raw data yielded results close to those obtained with the tracking algorithm, with 59% of time in long rest (0.95) and the data agreed in [~]96% of the file time. Thus, albeit EAD being less informative it may serve as a proxy for PA and rest, enabling monitoring group housed mice. The data show that a change in housing density from one to two, and up to three mice had the same effect size on EAD ([~]2) with no difference between sexes. The EAD deviated significantly from this stepwise increase with 4 mice per cage, suggesting a crowdedness stress inducing sex specific adaptations. We conclude that informative metrics on rest and PA can be automatically extracted from the raw data flow in near-real time (< 1 hrs). These metrics relay useful longitudinal information to those that use or care for the animals.