Complex Correlations Between Desmin Content, Myofiber Types, and Innervation Patterns in the Human Extraocular Muscles

PURPOSE. To investigate whether the distribution of intermediate filament protein desmin is related to the different patterns of innervation in the human extraocular muscles (EOMs). METHODS. EOM samples were analyzed with immunohistochemistry using antibodies against desmin, vimentin, different myosin heavy chain (MyHC) isoforms, and fetal and adult acetylcholine receptor (AChR) subunits. Neuromuscular junctions (NMJs) were identified with alpha-bungarotoxin or with antibodies against neurofilament and synaptophysin. RESULTS. Desmin was present in the vast majority of myofibers, but it was weakly present or absent in a limited area in the close vicinity of the single en plaque NMJs in less than half of these myofibers. Desmin was either present or lacking in MyHCsto/I myofibers displaying multiple en grappe endings but present in MyHCsto/I myofibers receiving spiral nerve endings. In MyHCeom myofibers displaying multiterminal en plaque endings, desmin was either present or absent irrespective of AChR subunits or EOM layer. Vimentin did not substitute for the lack of desmin. CONCLUSIONS. The results indicate that the human EOMs have a more complex cytoskeletal organization than other muscles and suggest additional signalling mechanisms from the NMJs to the myofibers.