Abstract
Osteoarthritis (OA) is an age-related involutional degenerative joint disease. OA attacks the knee joint particularly, and is associated with chronic pain. Intra-articular injection of mono-iodoacetate (MIA) has been used for the development of experimental pain-related OA model of osteoarthritis. Usually young rats (less than 7 weeks) were used in this model as MIA acts as metabolic inhibitor of the chondrocytes, and no report of the MIA model in the adult and aged rats was found expect no insert age in the papers until now.The objective of this study was to investigate the difference of pain related behaviors (lifting hindpaw) between the young (7w) and adult (over 24 month) rats in the MIA (60mg/ml, 50 μl) model of OA. The pain-related behaviors were evoked using von Frey hairs (2-17g) and electrically rotating brush and counted the number of lifting among 10 trials. The surface skin temperature at the knee joint were measured, as an index of joint inflammationIn pain-related behaviors, the young rats showed more frequent lifting of the hind-paw to intense von Frey filament compared with those of the adults 14 days after injection. The baseline temperature of skin surface in the young rat was lower than that of adult, and it clearly increased over 10 days after the MIA injection in the young rats. On the other hand, no clear influence was observed in the adults.These results suggest that the young rat is more suitable for the MIA injection model for studying the OA and its associated pain-related behaviors. [J Physiol Sci. 2006;56 Suppl:S207]
