OBJECTIVE: The purpose of this study was to evaluate the short- and long-term effects of exercise on neuropathic pain. METHOD: Pain responses between rats in the exercise and control groups were compared to evaluate the effects of exercise in neuropathic pain. Materials consisted of 30 male Sprague-Dawley rats (8 weeks old, 180~200 g), which were divided into an exercise group (n=15) and a control group (n=15). Neuropathic pain was produced by partially injuring the nerve innervating the tail. Running exercise was given on a Rota-rod treadmill exercise machine for 3 weeks (3.1 Km/day, 6 cycle of 9 minutes exercise and 1 minute rest). Behavioral reactions to mechanical allodynia were checked using a von Frey hairs of 2.0 g (19.6 mN) bending force at 10 minutes, 1 hour and 24 hours post-exercise to evaluate the short term effects of exercise. Behavioral reactions to mechanical and thermal allodynia with 4 degrees C or 40 degrees C were evaluated 7, 14, 21 and 28 days following exercise. RESULT: The exercise group exhibited less tail-flick frequencies to mechanical stimulation from 58.8+/-6.8% to 41.1+/-5.4%, 37.6+/-13.2% at 1 and 24 hours post-exercise compared to the control group, but there was no significant difference between the groups at weeks 1 through 4. In the exercise group, the decrease of tail-flick frequencies were blocked by naloxone (2 mg/kg i.p.). It is suggested that long-lasting muscle exercise (e.g. running) which influences central endorphin mechanisms giving analgetic effects. CONCLUSION: The results of this study support the hypothesis that the exercise can reduce neuropathic pain in the acute stage.
Animals ; Endorphins ; Hair ; Humans ; Hyperalgesia ; Male ; Models, Theoretical* ; Naloxone ; Neuralgia* ; Peripheral Nervous System Diseases* ; Rats ; Rats, Sprague-Dawley ; Running ; Tail