Figure 1

Ligation of the masseter tendon of the rat. a. Drawing of rat skull and masseter muscle. The tendon (TASM) attachment of the anterior superficial portion of the masseter muscle to the right maxillary bone and the site of ligation with two ligatures are shown (arrows). b. Hematoxylin and eosin staining illustrating histology of the masseter tendon in naive (top) and TASM-ligated rats (TL-2w). Naive rat exhibited normal organized collagen fibers and uniformly distributed tenocytes (T, also see b1). Arrows in TL-2w panel indicate site of ligation injury. Note the depressed region produced by ligature (arrows). Compared to the naive rat, adhesive bands of collagen fibers were formed at the level of ligation (stars). Disruption of major collagen fiber bundle was found (arrowhead). Clusters of purple stained inflammatory cells mixed with tenocytes were seen (circle). Scale = 0.2 mm. b1, b2. High power photomicrograph images showing examples of tenocytes in the normal tendon from a naive rat (b1) and examples of inflammatory cells are shown (b2). Mϕ, macrophage; M, monocyte; N, neutrophil. Scale = 0.02 mm. c. Comparison of body weight of the rats. Dashed line is adapted from Growth Chart of Harlan Sprague Dawley rat [20]. Note that the TL group had slowed growth at 12-16-week (4-8 weeks after injury) (p < 0.01, vs. naive rats). Error bars represent S.E.M.