Evaluating home-cage-activity metrics for detecting postprocedural pain in a plantar incision mouse model
Detection of postoperative pain in mice is challenging, and there is a need for unbiased, automated methods. Home-cage monitoring systems are promising, but their ability to detect mild pain remains unclear. We evaluated whether home-cage activity measures can be used to detect pain-related changes in a plantar incision model of postoperative pain. First, we confirmed the presence of local hypersensitivity using von Frey filaments on 48 C57BL/6JRj mice (24 males, 24 females). Subsequently, we pair-housed 64 mice (32 males, 32 females) and allocated them to receive either a 4 mm plantar incision on the hind paw under anaesthesia, or anaesthesia alone. Baseline locomotion and voluntary wheel-running activity were recorded over five days, followed by four days of postprocedural monitoring in the home cages. Both procedure groups (incision and anaesthesia-only) showed reduced locomotion and running wheel activity relative to baseline. However, activity measures did not differ between incised and anaesthesia-only mice, and we detected no sex-related effects. Under these conditions, home cage activity measures did not reliably discriminate pain-related behavioural changes in the model, despite the model showing local mechanical hypersensitivity in the von Frey test. Together, these findings indicate that, given the mild and localised nature of the plantar incision mouse model, commonly used home-cage metrics cannot yet reliably detect subtle pain-related behavioural changes.