اثر دوره هاي مختلف فعاليت بدني بر درد حاد و مزمن در حضور و غياب نالوكسان

There exist some evidences that physical activity through increasing opioid level could have beneficial effects in some diseases. In the present study, the effect of naloxone and various periods of physical activity on the acute and chronic pain were investigated using formalin test model. For this purpose, 84 NMRI adult male rats weighing 200-280 g were used. Physical activity (for 15 minutes, daily) was induced in different groups by rotating treadmill for 1, 2, and 4 weeks. In addition, naloxone (3 mg/kg, i.p.) as an antagonist of opioids was used in groups with no activity and after different periods of physical activity. Response time for licking and biting behavior at two phases of the test (0-5 min as the acute pain and 25-45 min as the chronic pain) was measured after subcutaneous injection of formalin into dorsal paw of the rats. The results showed that physical activity at weeksl, 2, and 4 decreases the response time in acute and chronic phases of the model in a time-dependent manner, especially for chronic pain. In addition, naloxone (3 mg/kg) increased response time in acute and chronic pains in the presence of physical activity, but this effect was less in relation to the absence of physical activity. These results suggest that part of physical activity-induced analgesia may be mediated through opioid system and the role of other neurochemical systems could not be ignored in this respect.