Synapse disassembly at the neuromuscular junction

During the early postnatal life of mammals (and analogouslyin other terrestrial vertebrates) the number of motor axons innervating individual muscle fibers undergoes a dramatic change: whereas at birth virtually all muscle fibers are innervated by multiple motor axons, several weeks later every muscle fiber is innervated by one axon. This transition is caused by a competitive interaction between the terminal branches of multiple axons co-innervating the same muscle fiber at the same junction. The muscle fiber seems to be the intermediary in the interaction by selectively initiating changes in the postsynaptic membrane (including loss of AchRs) at the sites occupied by one axon. The postsynaptic changes are soon followed by withdrawal of the overlying nerve terminals. The muscle seems to be able to distinguish the sites occupied by the different axons by virtue of their different activity patterns. These results may help inform on the ways in which experience alters synaptic connections throughout the developing nervous system and in the adult brain.