Exercise-induced hypoalgesia profiles for pain prediction in the trigeminal system

Abstract

Aim: This study aimed to evaluate the predictivity of exerciseinduced hypoalgesia (EIH) profile on pain severity produced by nerve injury in an animal model. Materials and methods: A total of 51 rats were divided according to the EIH model, which was evaluated by the percentage of withdrawal actions of 30 repetitive physical stimuli on the hind paw of the rat before and after 3 minutes of exercise on a treadmill, into high and low EIH. Left infraorbital nerve injury was then done on rats from high and low EIH groups. Pain assays as mechanical allodynia and mechanical hyperalgesia were evaluated in the ipsilateral and unaffected whisker pad before and 3, 10, and 17 days after the surgery. Results: Rats that were categorized as low EIH showed increased hypersensitivity and demonstrated significantly severe mechanical hyperalgesia in ipsilateral side 10 and 17 days after the surgery compared with the high EIH rats. Conclusion: The authors concluded that the pinprick behavioral assay (mechanical hyperalgesia) was able to predict chronic pain development in the area of the trigeminal nerve distribution using EIH profile measured at the hind paw of the rat.