MIA Induced TMJOA in Rat Figure 4. Time-dependent radiographic changes in condylar subchondral bone and nociceptive responses following MIA injection (0.5 mg/joint). A. Representative images of the condyle by MicroCT scanning with a sagittal section view demonstrated. (a). Control condyle showed intact subchondral bone with a smooth, continuous surface. (b). Regional loss of surface bone (arrowhead) occurred in the frontal bevel of the condyle by 1 week. (c). Multiple erosions of subchondral bone (arrowhead) were observed by 2 weeks. (d). Erosion in the subchondral bone grew deeper and was much more extensive with obvious defects (arrowhead) and osteophyte formation (arrow) by 4 weeks. (e and f). Sclerotic changes (dotted arrow) and osteophytes (arrow) were evident by 8 weeks and 12 weeks. (Bar = 300 mm) B. Changes in animal nociceptive response after MIA injection into TMJ. The HWT was significantly decreased in the first 3 weeks after MIA injection, but gradually recovered to control levels from 4 weeks post-injection. All data were presented as mean 6 SEM. (n = 3; **P,0.01; *P,0.05). doi:10.1371/journal.pone.0045036.g004 Discussion In this study, we provided multi-level data to show that a comprehensive rat model of TMJOA could be successfully established through MIA injection into the upper compartment of the TMJ. First, electron microscopy showed that the intermediate zone of the disc loosened to facilitate the diffusion of MIA into the lower compartment. Second, histopathologic analysis illustrated that typical OA-like lesions in the TMJ, including degenerative changes in the condyle, disc, and temporal fossa, as well as synovitis, were induced by MIA in a dose- and time-dependent manner. Third, subchondral bone destruction, which is characteristic of the early stage of OA, and sclerosis, which is seen during the later stage of OA, were observed by MicroCT scanning. Fourth, the molecular analysis revealed that chondrocytic apoptosis and the imbalance between the anabolism and catabolism of cartilage and subchondral bone might account for the advanced condylar destruction following MIA induction. Fifth, nociceptive responses increased in the early stages corre- sponding to the presence of synovitis. To the best of our knowledge, this is the first report to demonstrate that MIA can effectively induce typical OA-like lesions in the TMJ of a rodent species. PLOS ONE | www.plosone.org 7 September 2012 | Volume 7 | Issue 9 | e45036