MECHANISM OF SYNAPSE DISASSEMBLY AT THE DEVELOPING NEUROMUSCULAR-JUNCTION

Throughout the developing nervous system of higher vertebrates, synapt ic connections are concurrently being established and eliminated. The consequence of this synaptic remodeling is that axons strengthen their connections with some targets while completely disconnecting from oth er postsynaptic cells. The transition from multiple to single axonal i nnervation of skeletal muscle fibers is the most accessible example of this developmental reorganization. In muscle, the elimination of axon al input appears to be driven by a protracted competition between diff erent axons co-innervating the same junction, with the muscle fiber as intermediary. Asynchronous synaptic activity may be the factor that d ifferentiates the competing inputs. In some circumstances, synapses ca n also be lost in ways that are independent of activity. Similarities between activity-dependent and activity-independent synapse eliminatio n provide insights into mechanisms underlying developmental synaptic r eorganization.