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

Highlights

• Baseline cutaneous thresholds are not different between young and geriatric mice.

• Geriatric mice are hyperreactive to tonic pain stimuli.

• Nerve-injured geriatric mice are hypersensitive to mechanical but not cooling stimuli.

• Geriatric mice display decreased aversive responses to chronic pain.

• Geriatric mice display altered supraspinal plasticity during 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 months old) and geriatric (20–24 months old) ages using mice. Although cutaneous thresholds to brisk stimuli (von Frey and radiant heat assays) were not affected, behavioral 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 behavioral 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 behavioral and physiological responses to the experience of pain, suggesting that knowledge and practices must be adjusted for geriatric populations.