Histological study of masseter muscle in a mouse muscular dystrophy model (mdx mouse).
Histological changes in the masseter muscle were observed over time in mdx mice, a muscular dystrophy model. It was found that marked necrosis occurs about the time of weaning at around 4 weeks of age; then the tissue actively regenerates at 8 weeks and stabilizes as regenerated muscle with centronuclei at 15 weeks old. This study examined the centronucleus in regenerated muscle. The process from necrosis to regeneration in muscle fibers occurs a little later in the masseter muscle than in other limbic muscles. Regenerated muscles observed around 15 weeks after birth showed a moth-eaten appearance. Transmission Electron Microscope (TEM) observation of transverse sections of muscle fibers revealed that myofibrils surrounded lost regions in the area showing a moth-eaten appearance. Thus, some defensive mechanism may affect the ability of muscle fibers to maintain a function close to normal in mdx mice even though the muscle fibers develop muscular dystrophy. The function of the masseter muscle drastically changes from sucking to mastication behavior at around 4 weeks, and this was considered to influence the morphological changes in the muscle tissue. The moth-eaten appearance seen at 15 weeks may represent an appropriate myofibril reconstruction preventing invasion of the lost regions.
Abe
S
S
Oral Health Science Center and Department of Anatomy, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan.
Kasahara
N
N
Amano
M
M
Yoshii
M
M
Watanabe
H
H
Ide
Y
Y
D000375:Aging / Q000473:pathology; D000818:Animals; D002467:Cell Nucleus / Q000648:ultrastructure; D004195:Disease Models, Animal; D008406:Masseter Muscle / Q000473:pathology*; D008409:Mastication / Q000502:physiology; D051379:Mice; D018101:Mice, Inbred mdx; D008854:Microscopy, Electron; D018485:Muscle Fibers, Skeletal / Q000648:ultrastructure; D009136:Muscular Dystrophies / Q000473:pathology*; D009210:Myofibrils / Q000648:ultrastructure; D009336:Necrosis; D012038:Regeneration / Q000502:physiology; D013391:Sucking Behavior / Q000502:physiology; D014886:Weaning