The geriatric pain experience in mice: intact cutaneous thresholds but altered responses to tonic and chronic pain

Abstract Older individuals have an elevated risk for chronic pain as half of all individuals over 65 years old have at least one chronic pain condition. Unfortunately, relevant assessment tools and recommendations for chronic pain management targeting older adults are lacking. This study explores changes in response to pain between young (2-3-month-old) and geriatric (20-24-month-old) ages using mice. While cutaneous thresholds to brisk stimuli (von Frey and radiant heat assays) were not affected, behavioural responses to tonic stimuli (acetone and capsaicin assays) were more pronounced in geriatric animals. After nerve injury, geriatric mice present an altered neuropathic pain profile with hypersensitivity to mechanical stimuli but not acetone and an impairment in conditioned noxious stimuli avoidance. This altered behavioural response pattern was associated with an abnormal monoaminergic signature in the medial prefrontal cortex, suggesting decreased COMT function. We conclude that young and geriatric mice exhibit different behavioural and physiological responses to the experience of pain, suggesting that knowledge and practices must be adjusted for geriatric populations.