Background & Aims
Both lack of exercise and social interaction have been linked to increased pain experience. Sedentary individuals, who often become socially isolated, are more likely to develop heightened pain symptoms, anxiety and depression, while individuals with chronic pain who have reduced social connectedness report higher pain. Physical activity has become a first-line treatment in rehabilitation settings for joint pain patients; it improves disease symptoms and elevates mood, thus improving the overall mental and physical wellbeing of individuals. However, whether the improvement in well-being in these patients is only due to increased exercise and whether increased social interactions may be a contributing factor is difficult to determine. Here, we used a pre-clinical model of joint pain to tease out the contribution of physical exercise and enriched environment with social interactions in the recovery from joint pain.
Methods
Experimental, but not control, adult male C57/Bl6J mice had access to a running wheel in their home cage for two weeks before the initiation of joint pain through intraarticular injection of monosodium iodoacetate. We tested 3 experimental set-ups: set-up (a): enriched environment in IVC cages housing 4 mice; set-up (b): running wheels for mice single-housed in IVC cages; set-up (c): running wheels for single-housed mice that could hear, see, and smell companions. Control mice were single- or group-housed, with a range of environmental enrichment provided, as appropriate. Wheel recording apparatus allowed us to monitor how much the mice were running. Open field and sucrose preference test were used to quantify anxiety- and depressive-like behaviours, while mechanical allodynia was assessed with von Frey filaments.
Results
We found grouped housed mice in an enriched environment never developed comorbid anxiety- and depressive-like behaviours following joint pain induction, in contrast to single housed mice. However, even when group-housed in an enriched environment, mice never recovered from the joint pain induced mechanical hypersensitivity. Mechanical hypersensitivity was only reduced by wheel running and only if mice could feel the presence of another companion (set-up c). Overall, access to a running wheel. without companionship, did not improve any of the negative behaviour associated with joint pain.
Conclusions
Together, our findings demonstrate that improvements in the sensory or the emotional comorbidities associated with joint pain can be differentially achieved through changes in housing. Our results suggest that great care must be taken when designing pre-clinical experiments concerning animal housing set-up and also that clinical studies investigating the impact of exercise on persistent pain should record any measure of social interactions, when possible, as these have significant impact on well-being.
References
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