Changes in motor nerve terminals during bupivacaine-induced postsynaptic deprivation.

The local anaesthetic agent bupivacaine induces a rapid degeneration of muscle cells when injected in the sternocleidomastoid muscle of the adult rat with no damage to intramuscular nerves. Nevertheless, silver impregnation and electron microscopy reveal a sequence of retraction and sprouting of the motor nerve endings during the period of the bupivacaine-induced muscle cell deprivation by necrosis. These morphological changes seem to be qualitatively similar to the retraction and growth phenomena described as forming part of the remodelling process affecting normal untreated neuromuscular junctions of the adult amphibia and mammals. The results are discussed in the context of the regulatory mechanisms governing the maintenance of motor nerve terminals.