Topographic comparison of subneural apparatuses at neuromuscular junctions in normal and dystrophic (mdx) mice: a...

The differences in the morphodifferentiation of subneural apparatuses (SNAs) at neuromuscular junctions (NMJs) in the extensor digitorum longus muscle of normal and dystrophic (mdx) mice were examined by scanning electron microscopy. In normal mice, primitive shallow cup-like synaptic troughs present at birth had developed to anastomosing grooves containing both pit-like and slit-like junctional folds (JFs) during the 2nd postnatal week. At the 35th day, the SNAs had developed to almost the adult forms, consisting of labyrinthine synaptic grooves with exclusively slit-like JFs. In the mdx mice, the SNAs showed transformation similar to those in the normal mice until the 35th postnatal day. After this period, SNAs with a number of cup-like depressions occurred and increased in number. These morphological changes seemed to be found on regenerating muscle fibers after necrosis, probably indicating the remodelling of their NMJs.