Electrophysiological experiments on the mechanism and accuracy of neuromuscular specificity in the axolotl.

The supracoracoideus muscle of the axolotl shoulder girdle is innervated by two nerves, the supracoracoideus nerve (SC) supplying most of the muscle and the posterior supracoracoideus (PSC) supplying the posterior corner. All the muscle fibres are multiply innervated and at the border between the two innervations many muscle fibres, when penetrated by a microelectrode, show junction potentials from both nerves. In such cases one junction potential is often very small, below the threshold for exciting muscle contraction, the other large and effective at exciting the muscle. If the SC nerve is cut, the territory of the PSC nerve expands over several weeks. Upon regrowth of the cut nerve it reinnervates its old muscle fibres and removes the previous foreign innervation, the borderline between the two nerve territories being established exactly as before. This depends upon two processes, sprouting of nerves and a competitive repression of transmission from nerves ending on foreign muscle fibres.