[Dedifferentiation and remodeling of motor endplates following experimental localized lesions of muscle fibers].

Local anaesthetics, cardiotoxin and mechanical injuries may cause necrosis of muscle fibres while leaving the motor nerve fibres and their terminals intact. With local injuries to mouse muscles carried out by freezing or cutting we made a point of preserving both the nerve terminals and the muscle fibre portions on which these terminals were located. It was thus possible to follow the changes induced at endplates by these lesions. Within two or three days of the freezing or cutting, the muscle fibres underwent very different degrees of regression of the contractile material and T-system. The neuromuscular junctions also underwent changes, principally affecting their postsynaptic portion, in particular the folds of the subneural apparatus. After dedifferentiation of subsynaptic areas, we observed sprouting of the nerve terminal on muscle fibres which survived the amputation of one end and formed actively new myofibrils. This sprouting restored synaptic connections at the original sites, but with new structural features and correlative changes in the distribution of cholinergic receptors and cholinesterases. It is probable that after a phase of involution followed by a phase of recovery, the injured muscle fibres triggered off the nerve terminal sprouting which led to the remodelling of the endplates.