抄録
DOMS is commonly observed after unaccustomed, strenuous exercise. Eccentric exercise (ECC) has been widely used in human and animal studies of DOMS, many of which have found histological, ultrastructural, biochemical, and physical changes. In contrast existence of mechanical hyperalgesia in exercised muscle was not known in animal models. In our previous experiment, we demonstrated the existence of tenderness by behavioral pain tests and by c-Fos protein expression in the spinal dorsal horn after ECC in rats. To further confirm existence of tenderness, we examined whether morphine, most potent analgesics, suppressed the increased expression of c-Fos. All experiments were done under anesthesia with pentobarbital. ECC was applied by electrical stimulation of the peroneal nerve while the extensor digitorum longus muscle (EDL) was being stretched. Two days later one group of animals received morphine (10 mg/kg, i.p.) and another group received saline. Thereafter compression (160 g, 60 times) was applied to the EDL. Two hours later animals were perfused and fixed, and c-Fos expression in the spinal dorsal horn was examined. Morphine treatment clearly decreased the number of c-Fos-immunoreactive neurons in the dorsal horn at L4 (from 25.5±4.4 cells/section in saline group to 5.4±0.6 cells/section in morphine group, p<0.01). This result further supports the hypothesis that the muscle was hyperalgesic to mechanical stimulation after ECC. [Jpn J Physiol 55 Suppl:S227 (2005)]
