Vertical ground reaction force measurements and video measurements provide comparable estimates of distance moved by mice during artificial light and dark periods

Abstract

Video-based measures of spontaneous activity of rodents are of interest in studying, e.g. physiology. However, video-based tracking methods typically require light. The purpose of the present study was to develop a video based method for tracking movements of mice during a dark period. The method was applied in comparing the dark and light period activities of mice. Ten male mice were used in the present study. The activity of the animals was monitored simultaneously with video and ground reaction force (GRF) recordings during consecutive 12h periods of artificial light and dark. Texture based background subtraction method was used to track the mouse from the video recording, while the weighted mean of vertical GRFs measured from four rectangularly arranged strain gauges was used for the GRF based tracking. The association between distance calculated from video and from vertical GRF data was r=0.99 (p<0.001). No difference between methods was observed (difference 0 (95% limits of agreement −1.2–1.2)km) after adjusting the distances calculated with the GRF method with the least squares method fit. The mean distances moved by mice during artificial light period were 4.9 (SD 2.4) and 6.4 (2.8)km measured with the GRF and video methods, respectively. The corresponding values for the dark period were higher: 7.7 (4.0) (p=0.012) and 10.0 (4.3)km (p=0.007). In conclusion, the video based method appeared to be feasible in estimating the distance moved by a mouse during the dark period.