Measurement Method Influences the Interpreted Effect of Oral Gavage on Murine Circadian Activity

Historically, the primary method for measuring murine circadian activity in vivo has been monitoring voluntary wheel running. Recently, passive infrared (PIR) motion sensors have emerged as an alternative that is not reliant on voluntary behaviour. While research has examined the differences between the two methods for measuring circadian parameters, little focus has been placed on how these techniques may confound the assessment of therapeutic interventions. Here, we show that wheel running activity is disproportionately affected by daily oral gavage of saline compared to sham gavage treatment. In contrast, PIR-monitored activity indicates little difference between the two treatments. Both PIR and running-wheel-measured activity show a reduction in circadian amplitude and an increase in intradaily variability during both types of gavage, likely reflecting the stress of daily gavage, though the mice showed no weight loss. This finding indicates that pre- and post-intervention comparisons will misattribute gavage effects to the intervention unless appropriate sham and vehicle controls are included. More broadly, the choice of circadian measurement technique fundamentally shapes the interpretation of pharmacological interventions and must be considered in experimental design.