MORPHOLOGICAL-CHANGES OF NEUROMUSCULAR-JUNCTIONS IN THE DYSTROPHIC (DY) MOUSE - A SCANNING AND TRANSMISSION ELECTRON-MICROSCOPIC STUDY

Neuromuscular junctions in the extensor digitorum longus muscle of con trol and dystrophic (ny) mice at stages ranging from 30 to 120 postnat al days were examined by scanning and transmission electron microscopy (SEM and TEM), In control mice, the neuromuscular junctions consisted of thin ramifying nerve endings and of complex labyrinthine gutters w ith a great number of slit-like junctional folds, The subneural appara tuses of ny mice on the 30th and the 60th postnatal days were composed of undeveloped gutters or a number of cup-like depressions containing a few pit-like or slit-like junctional folds, Ln dystrophic neuromusu clar junctions on the 120th postnatal day, subneural apparatuses were classified into two types: one had a cluster of continuous cup-like de pressions with or without slit-like junctional folds, and the other co nsisted of discrete depressions containing slit-like junctional folds, Moreover, a small number of dystrophic muscle fibers were endowed wit h two subneural apparatuses which were 20 to 30 mu m away from each ot her. Small round pits (0.5-1.0 mu m in diameter) in some cup-like depr essions were occasionally protruded by short processes of terminal axo ns, The present findings suggest that the age-dependent postsynaptic s tructural changes of dystrophic dy mice induce a complex morphological reorganization of presynaptic nerve endings. This might help the nerv e endings compensate for the functional deterioration of dystrophic mu scle fibers.