The effect of aerobic exercise training in animal model of widespread chronic pain

Abstract

Therapeutic exercises are routinely used to manage chronic musculoskeletal pain conditions, and yet neuromuscular mechanisms of exercise-induced analgesia are poorly understood. It is well recognized that physical training modulates selective neurotrophins, and recently a positive correlation between neurotrophin-3 (NT-3) and pain reduction has been explored. The primary goal of this study was to demonstrate the effect of aerobic exercise training on mechanical sensation and NT-3 in an animal model of widespread chronic pain. Animals were assigned to either exercise or sedentary group. After 4 weeks of exercise training (daily treadmill running, 13-15 m/min, 25 minutes), half animals from each group were randomly given 2 injections of acidic solution into the right gastrocnemius muscle to induce widespread pain. All animals in exercise group continued with exercise training for 2 more weeks. Daily running scores were recorded and used to determine their ability to achieve the required level of training. Using a standard method with von Frey monofilament, behavior analysis was assessed periodically to monitor mechanical sensitivity. The levels of skeletal muscle NT-3 mRNA expression were analyzed using real time RT-PCR. The results indicated that animals were able to sustain the same level of exercise training after the acid injections. Furthermore, exercise training decreased ipsilateral mechanical hyperalgesia induced by acid injections. However, no statistically significant increase in skeletal muscle NT-3 mRNA expression was noted as a result of exercise training. Our results suggest that exercise may be beneficial in this model of chronic pain; however the relationship between exercise, NT-3, and analgesia remains unclear.