(249) Modulators of Burn Injury-Related Pain in Mice: The Search for Modulators in the Transition from Acute to Chronic Pain

Acute pain is prevalent following burn injury and can transition to chronic pain in over 50% of patients. Prolonged acute pain is an important component that leads to chronic pain. Our research investigates burn injury-related pain and searches for risk factors that influence acute-to-chronic pain transitions. The present work tests whether dietary intervention, genetic background or pre-injury stress affects thermal and mechanical hypersensitivity associated with 2° burn of the mouse hindpaw. Under Avertin anesthesia, (200 µL/10g body weight), the paw of the mouse was placed on a metal block with a surface temperature of 65°C for 15 seconds. A 5-g weighted pouch was placed on the dorsum of the paw to maintain pressure between the heel and the heat source. A visible scar is evident 5-7 days after the injury. Mechanical and thermal thresholds were assessed at baseline, and at 1, 3, 7, 14, 21, 28, and 33 days post-burn injury. Our results reveal that mice which undergo a burn develop significant ipsilateral thermal hypersensitivity and mechanical allodynia that resolves to baseline thresholds by 12 days (thermal) or 30 days (mechanical). Consumption of the high-fat diet did not alter the severity or duration of burn-induced thermal or mechanical hypersensitivity. At sacrifice, mice with a burn injury had a significant increase in degranulated epidermal mast cells (p=0.036). Ongoing experiments are comparing the response of A/J inbred mice that exhibit an anxious phenotype to hindpaw burn injury. Also, repeated foot shock stress in mice induces chronic stress and exacerbates cutaneous and visceral pain. Additional experiments are testing whether A/J mice exposed to foot shock stress for 10 continuous days and undergo burn injury have altered severity or duration of altered thermal and mechanical thresholds. Results from these new studies will be presented and compared to previous findings associated with dietary interventions.