Fig. 8

Morphological adaptation of the NMJ after degenerative and regenerative damage. a In the NMJ of control muscles, the postsynaptic domain (green) exhibits a complex pretzel-like morphology, mostly covered by a single presynaptic axon terminal (blue), and 2 or 3 terminal Schwann cells (gray) covering the endplate. b After nerve resection (NMJ degeneration), the distal axon stump goes through Wallerian degeneration (circle), tSC extend projections outside of the synaptic region (middle panel), the postsynaptic domain become denervated, unstable, and fragmented (red), ectopic AChR aggregates appear along the muscle fiber, and muscle fibers suffer atrophy (middle and right panel). c After nerve crush injury (NMJ regeneration), the distal axon stump goes through Wallerian degeneration (circle) and the postsynaptic domain becomes denervated and unstable (left panel). Reinnervation results in a significant mono- and poly-innervated synapses (middle panel), while most postsynaptic domains become fragmented and do not recover the control values of stability (orange postsynaptic domain in the middle panel). Long after reinnervation, a significant proportion of NMJs are still poly-innervated (~ 30%). While postsynaptic domains recover their stability, most of them remain fragmented (right panel)