Abstract
Objective: To establish an adequate experimental model of the chronic muscle pain. Methods: A total of 24 male rats were allocated to four groups. Eccentric exercise [EEG], exercise under ischemia [EIG], 3% λ-carrageenan injection [CIG; 0.1 ml, i.m.] and acidic saline (pH 4) [AIG; 0.1 ml, i.m.] groups. These procedures were done to the gastrocnemius [GS] muscle and pain thresholds were measured by von Frey filament testing [VFT] and Randall-Selitto test [RST] over the GS muscle for 6 weeks after the conditioning stimulation. Results: In the EEG, the threshold of RST of exercised side were the lowest on the 1st day after exercise and returned on 7th day. No influence was observed in the contralateral side. In the EIG, however, the lowest thresholds appeared 2 days after the stimulation and it prolonged for 21 days. The VFT thresholds were not changed significantly in the EEG and EIG. On the other hand, in the CIG and AIG, the thresholds of VFT were the lowest on the 1st day after the injection and then returned to the baseline on the 4th week. However, the thresholds of RST were not changed. Conclusion: In the present study, repeated eccentric exercise under the ischemic condition induced the elongation of the muscular hyperalgesia for three weeks and no cutaneous hyperalgesia was observed. On the contrary, the other procedures of chemical injections induced long-lasting cutaneous hyperalgesia, but no change was detected by the RST. These results suggest that the eccentric exercise under the ischemic condition might to be a useful experimental model of the chronic muscle pain. [Jpn J Physiol 55 Suppl:S164 (2005)]
