THE EFFECTS OF BOTULINUM TOXIN ON THE PATTERN OF INNERVATION OF SKELETAL MUSCLE IN THE MOUSE

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Abstract
Sublethal quantities of botulinum toxin were injected into the gastrocnemius and hamstring muscles of one leg in mice. Local paralysis and atrophy occurred and persisted for a few weeks. Histological examination showed no degeneration of nerve fibres or of motor nerve endings. Silver impregnations showed that during the period of muscle paralysis there was growth of motor nerve fibres from the terminal arborizations. Nerve fibre overgrowth was accompanied by elongation and abnormal configuration of sites of cholinesterase activity. As muscle function recovered the nerve fibre overgrowth receded and well‐formed though still abnormally shaped subneural apparatuses were seen. Nine months after the injection of the toxin, the pattern of innervation of the muscle was still abnormal.The growth of motor nerve fibres after the injection of botulinum toxin appears to be a response to the failure of neuromuscular transmission and is not analogous to regeneration of nerve fibres after trauma.