Experimental serotonin myopathy as an animal model of muscle degeneration and regeneration in muscular dystrophy.

Degenerating and regenerating muscle fibers, in serotonin-induced myopathy (SM) of rats, were investigated histochemically, immunohistochemically and electron microscopically with polyclonal antibodies against dystrophin, type IV collagen and laminin. The myopathy produced was characterized by grouping of degenerating and regenerating muscle fibers, and degeneration of capillary endothelial cells. Dystrophin disappeared in an early stage of muscle degeneration and reappeared in an early stage of regeneration. On the other hand, type IV collagen and laminin were well preserved throughout the degeneration and regeneration processes, even on the shrunk and wrinkled basement membrane of empty muscle fibers after phagocytosis. Muscle fiber regeneration was completed within each tube of the preserved basement membrane through the fusion of myoblasts derived from satellite cells of single necrotic fibers, myotubes already being visible on the 1st or 2nd day of regeneration on light microscopy. These small regenerating myotubes did not fuse with each other at all. The findings in the present experimental SM study are compatible with those in Duchenne muscular dystrophy, especially at the preclinical stage.