Reinnervation of original synaptic sites on muscle fiber basement membrane after disruption of the muscle cells.

Abstract

Regenerating axons form new synapses precisely at sites of original synapses in denervated skeletal muscle. To determine what role the muscle cell plays in this phenomenon, the reinnervation of frog [Rana pipiens] muscle was studied at intervals after crushing the nerve and damaging the muscle fibers. Damaged muscle fibers degenerated and were phagocytized, but their basement membrane persisted and acted as a scaffold for regenerating muscle cells. Specializations of the basement membrane served to mark original synaptic sites after nerve and muscle degenerated. Regenerating axons entered the region of damage and formed functional synapses with regenerating myofibers. The new nerve terminals were found almost exclusively at the original synaptic sites, demonstrating that the integrity of the original postsynaptic cell is not necessary for topographically precise reinnervation of denervated muscle.