Regulation of Rest, Rather Than Activity, Underlies Day-Night Activity Differences in Mice

Abstract

The suprachiasmatic nucleus (SCN), which serves as the central pacemaker in mammals, regulates the 24-h rhythm in behavioral activity. However, it is currently unclear whether and how bouts of activity and rest are regulated within the 24-h cycle (i.e., over ultradian time scales). Therefore, we used passive infrared sensors to measure temporal behavior in mice housed under either a light-dark (LD) cycle or continuous darkness (DD). We found that a probabilistic Markov model captures the ultradian changes in the behavioral state over a 24-h cycle. In this model, the animal's behavioral state in the next time interval is determined solely by the animal's current behavioral state and by the "toss" of a proverbial "biased coin." We found that the bias of this "coin" is regulated by light input and by the phase of the clock. Moreover, the bias of this "coin" for an animal is related to the average length of rest and activity bouts in that animal. In LD conditions, the average length of rest bouts was greater during the day compared to during the night, whereas the average length of activity bouts was greater during the night compared to during the day. Importantly, we also found that day-night changes in the rest bout lengths were significantly greater than day-night changes in the activity bout lengths. Finally, in DD conditions, the activity and rest bouts also differed between subjective night and subjective day, albeit to a lesser extent compared to LD conditions. The ultradian regulation represented by the model does not result in ultradian rhythms, although some weak ultradian rhythms are present in the data. The persistent differences in bout length over the circadian cycle following loss of the external LD cycle indicate that the central pacemaker plays a role in regulating rest and activity bouts on an ultradian time scale.

PyRodentTracks: flexible computer vision and RFID based system for multiple rodent tracking and behavioral assessment

“…While small homecages can present some challenges, accuracy is still high and PRT has not only demonstrated capabilities to chronically track multiple mice from minutes to days, but also detect underlying animal phenotypes (stroke). Consistent with other studies, chronic recordings in the modified home-cage revealed diurnal locomotor activity patterns in mice (Ananthasubramaniam and Meijer, 2020; Wang et al, 2019). Specifically, mice showed higher levels of distance traveled, turns made, travel speed, and duration being active at night compared to day cycles.…”

“…A total of 4 cages each containing 3 mice were recorded for three days using the modified home-cage illustrated in Fig 3A . The effects of day/night cycle (lights on and lights off) on dependent outcomes such as distance traveled, active duration, average speed, wide angle turn count, sharp angle turn count, and average acceleration along with anxiety measures such as duration spent in the center, interacting with one or two mice were determined using an MANOVA (Seibenhener and Wooten, 2015). As expected, mouse activity levels follow a reverse circadian rhythm (Ananthasubramaniam and Meijer, 2020).…”

Deletion of AMPA receptor GluA1 subunit gene (Gria1) causes circadian rhythm disruption and aberrant responses to environmental cues

“…GluA1 knockouts’ extended active period but reduced total wheel-running activity may seem paradoxical, but it could be related to changes in overall circadian parameters, for example reduced robustness of the ~24-h rhythm; it could also be the result of altered microstructure of activity and rest [ 69 ], such as changes in activity/sleep bout length due to activity/sleep fragmentation. These possibilities were thoroughly investigated below.…”