Histochemical and electron microscopic observations were made on normal and denervated masseter muscles of mice to elucidate differences of characteristics between the masticatory muscles and other skeletal muscles.
The three types of muscle fibers were classified by means of Succinic dehydrogenase (SDH) reaction. In masseter muscles of normal adult mice, the three types of fibers, that is, high SDH activity fibers, intermediate SDH activity fibers and low SDH activity fibers, were recognized. More oxidative fibers in the deep portion of masseter muscles were found than that in the superior portion, which suggests that each portion has its own functional role.
It is generally believed that denervation gradually causes atrophy in skeletal muscles. On the other hand, denervated masseter muscles of mice clearly showed different reactions which had two phases. In the first phase right after denervation, many masseter muscle fibers were degenerated, necrosed and regenerated. A few weeks later, in the second phase, muscle fibers remained immature, denervation atrophy was occurred, and dense connective tissue was proliferated.
The other side of nondenervated masseter muscle was not influenced by denervated ones.