| Type | MGI:General | Description | distal lumbrical muscles -- mainly composed of fast-fatigable (FF) motor units -- show severely disorganized NMJs with little innervation of acetylcholine receptors (AChR) and marked endplate fragmentation; AChR clusters are fragmented with many small clusters that lack the typical pretzel morphology seen in wild-type clusters at 3 months of age, lumbrical NMJs show: (i) a complete absence of any presynaptic elements, (ii) occasional motor axons in the vicinity of some AChR clusters or (iii) apparently innervated endplate fragments with a severe presynaptic sprouting phenotype endplate fragmentation and presynaptic sprouting is consistent with presynaptic degeneration extensor digitorum longus (EDL), a fast-twitch muscle, shows marked NMJ denervation with >50% of all postsynaptic AChR clusters uninnervated; however, EDL pathology is less severe than the endplate fragmentation seen in distal lumbrical muscles |
