Effect of triiodothyronine on the maxilla and masseter muscles of the rat stomatognathic system. M.V. Mariúba, F. Goulart-Silva, S. Bordin and M.T. Nunes. Braz J Med Biol Res 2011; 44: 694-699.

Figure 3. Effect of triiodothyronine (T3) on masseter muscle fiber types. Serial cross-sections of the masseter muscle from sham-operated (SO), thyroidectomized (Tx), sham-operated T3-treated (SO T3), and Tx rats chronically treated with T3 (Tx T3) illustrating the histochemical stains for myosin ATPase activity. The amount of T3 used was 5 μg/100 g body weight, for 15 days. Fiber types are identified as type I and II based on myosin ATPase histochemistry using different pre-incubation at different pH, namely 4.3 (Panel A) and 10.3 (Panel B). Type II fibers show myosin ATPase activity at alkaline pH (alkaline-resistant fibers: dark fibers) and absence of it at acid pH (acid-labile fibers: light fibers). Five animals per group were used. Bars = 100 μm.