Validation of a microwave radar system for the monitoring of locomotor activity in mice

Abstract

BackgroundThe general or spontaneous motor activity of animals is a useful parameter in chronobiology. Modified motion detectors can be used to monitor locomotor activity rhythms. We modified a commercial microwave-based detection device and validated the device by recording circadian and ultradian rhythms.MethodsMovements were detected by microwave radar based on the Doppler effect. The equipment was designed to detect and record simultaneously 12 animals in separate cages. Radars were positioned at the bottom of aluminium bulkheads. Animal cages were positioned above the bulkheads. The radars were connected to a computer through a digital I/O board.ResultsThe apparatus was evaluated by several tests. The first test showed the ability of the apparatus to detect the exact frequency of the standard moving object. The second test demonstrated the stability over time of the sensitivity of the radars. The third was performed by simultaneous observations of video-recording of a mouse and radar signals. We found that the radars are particularly sensitive to activities that involve a displacement of the whole body, as compared to movement of only a part of the body. In the fourth test, we recorded the locomotor activity of Balb/c mice. The results were in agreement with published studies.ConclusionRadar detectors can provide automatic monitoring of an animal's locomotor activity in its home cage without perturbing the pattern of its normal behaviour or initiating the spurt of exploration occasioned by transfer to a novel environment. Recording inside breeding cages enables long-term studies with uninterrupted monitoring. The use of electromagnetic waves allows contactless detection and freedom from interference of external stimuli.

Pharmacological validation of a novel home cage activity counter in mice

“…In addition, as the camera needs to be able to track the animal at all times, special observation cages are needed. The same holds true for methods like ultrasonic systems, infrared sensors or microwave radar systems (Clarke and Smith, 1985;Pasquali et al, 2006;Young et al, 2000). These systems are in general very sensitive and well validated, but the experimental set-up is complex and often expensive.…”

Practical aspects of estimating energy components in rodents

“…Several devices exist for quantifying the level of spontaneous PA in rodents, such as photocell sensors (Nonogaki et al, 2003; Bjursell et al, 2008; Kotz et al, 2008), piezo-electric force transducers (Even et al, 1991, 1994), microwave radar systems (Brown et al, 1991; Pasquali et al, 2006) and video-tracking systems (Poirrier et al, 2006). A frequently used approach in commercially available metabolic chamber systems is to measure PA as the number of infrared beam interruptions.…”

Rodent Activity Detector (RAD), an Open Source Device for Measuring Activity in Rodent Home Cages

“…The presence of a running wheel is not always ideal as the wheel itself alters activity patterns and induces mice to move more (O'Neal et al, 2017), which may confound other factors that affect activity (Copes et al, 2015; de Carvalho et al, 2016; O'Neal et al, 2017). Other groups have used passive infrared (PIR) sensors (Tamborini et al, 1989; Brown et al (2016), capacitive sensors (Giles et al, 2018; Iannello, 2019; Pernold et al, 2019), and microwave based activity monitors (Pasquali et al, 2006; Genewsky et al, 2017) to measure home-cage activity. Here, we aimed to complement and enhance these existing methods by designing an easy to build, cost-effective, and open-source device.…”