This article is written by Professor Brun Ulfhake (together with Dr Karin Pernold and Dr Eric Rullman), principal investigator at the Division Clinical Physiology, Department of Laboratory Medicine, Karolinska Institute, Sweden, and it represents a milestone in the approach to assessing laboratory mice locomotion activity.
More specifically, by using 14–19 months of cumulative 24/7 home-cage activity recorded with Tecniplast’s DVC® system, researchers discovered a highly significant circannual oscillation in spontaneous activity of male and female C57BL/6 mice held under constant conditions. The periodicity of this hitherto not recognized oscillation is in the range of 2–4 months (the average estimate was 97 days across cohorts of cages). It off-sets responses to environmental stimuli and co-varies with the feeding behavior but does not significantly alter the preference for being active during the dark hours. The absence of coordination of this rhythmicity between cages with mice or seasons of the year suggests that the oscillation of physical activity is generated by a free-running intrinsic oscillator devoid of an external timer. Due to the magnitude of this rhythmic variation, it may be a serious confounder in experiments on mice if left.
The authors introduced another possible application of the Home Cage Monitoring system (DVC®) when analyzing data in the frequency range, which opens up to potentially revolutionary consequences to be taken into account when approaching laboratory mice locomotion activity assessment.