Neuromuscular Junction Architectures following Muscle Injury.

The purpose of this study was to investigate the temporal changes taking place in the neuromuscular junction during muscle damage by histochemistry. Bupivacaine (BPVC; 200 μl, 0. 5% dilution) was injected in the rat hindlimb to induce extensor digitorum longus muscle damage. The morphology of the neuromuscular junction was monitored over 10 days (12 h and 1, 2, 3, 4, 6, and 10 days after injection) in longitudinal serial sections.Skeletal muscle fiber damage was detected early after BPVC injection. Opaque and necrotized fibers were first observed on day 2 and day 4, respectively. Regarding the neuromuscular junction, the nerve ending and the area of the motor end plate degenerated gradually, reaching a maximum on day 4 and day 6, respectively.The terminal arborization was reduced to a minimum on day 4. Finally, morphological regeneration started on day 6.These data suggest that BPVC causes a rapid degeneration of motor nerve endings and motor end plates in skeletal muscles, raising the possibility that exercise-induced skeletal muscle damage influences the somatic nervous syste