Motor End-Plate Fine Structure of Red and White Muscles in Experimental Autoimmune Myasthenia Gravis

SUMMARY Neuromuscular junction ultrastructure in rat forelimb digit extensor muscle (FDE), extensor digitorum longus (EDL) and soleus (SOL) was quantitatively investigated in experimental autoim-mune myasthenia gravis (EAMG). Experimental animals were immunized with highly purified Narke Japonica acetylcholine receptor protein plus complete Freund's adjuvant and B. pertussis vaccine : control animals received only adjuvant and vaccine. Between day 7 and 11 (acute phase) mononuclear cells infiltrated those regions of muscle where the end-plates were located and there was intense destruction of postsynaptic regions and most postsynaptic regions were splitted away from the underlying muscle fibers in FDE and EDL. In contrast, most postsynaptic folds were not detached from the underlying muscle fibers in SOL. Subsequently, between day 30 to 33 (chronic phase) morphometric analysis revealed that the postsynaptic regions of FDE and EDL were simpler and destructed more intensely than those of SOL. These results indicate that the intensity of destruction of the postsynaptic region in EAMG is apparently different between type I fibers and type II fibers both in acute phase and chronic phase.