SYNAPTIC SEGREGATION AT THE DEVELOPING NEUROMUSCULAR-JUNCTION

Throughout the developing nervous system, competition between axons ca uses the permanent removal of some synaptic connections. In mouse neur omuscular junctions at birth, terminal branches of different axons are intermingled. However, during the several weeks after birth, these br anches progressively segregated into nonoverlapping compartments befor e the complete withdrawal of all but one axon. Segregation was caused by selective branch atrophy, detachment, and withdrawal; the axon bran ches that were nearest to the competitor's branches were removed befor e the more distant branches were removed. This progression suggests th at the signals that mediate the competitive removal of synapses must d ecrease in potency over short distances.