Abstract
DOMS is commonly observed after unaccustomed, strenuous exercise. It usually reaches a peak 24 to 48 hours after exercise. The mechanism for DOMS is not clear yet. 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 eccentric contraction (ECC), which is known to induce DOMS more effectively, in young rats (8 w). To know if there is any change in DOMS in aged rats, we examined mechanical threshold of extensor digitorum longus muscle (EDL) and c-Fos expression of dorsal horn in the aged rats (130-139 w) after ECC. The mechanical threshold started to significantly decrease 1 day after ECC and remained decreased up to 5 days after ECC. It finally returned to the pre-ECC value 7 days after ECC. It became clear that DOMS continued for a longer period than the young (8 week-old) rats, in which DOMS lasted between 1 and 3 days after ECC. In the aged rats, the compression (160 g, 60 times) was applied to the EDL 3 days after ECC. Two hours later animals were perfused and fixed, and c-Fos expression in the dorsal horn was examined. c-Fos-immunoreactive neurons in the superficial dorsal horn at L4 increased significantly in not only at L4 but also in L5 spinal segment. This distribution is wider than that in the young rats (in L4 only). This result suggested that pain information from the muscle in aged rats was transmitted to the wider level of spinal cord than young rats. [J Physiol Sci. 2006;56 Suppl:S236]
