Structural alterations of the junctional region in extraocular muscle of dystrophic mice. II. Hypertrophy of the neuromuscular junctional apparatus.

The fine structure of end-plate abnormalities was studied in the Bar harbor C57Bl/6jdy2j dystrophic mouse. A marked increase in area and volume of junctional sarcoplasm was often apparent. Such hypertrophied end-plates were often penetrated by networks of axonal terminal branches. At times, pseudopod-like extensions of the junctional sarcoplasm encompassed and made protracted synaptic contact with the incoming axon. Such apparent remodeling of the neuromuscular apparatus might represent a compensatory cellular response to decreased impulse transmission efficiency, as might result from a flattening of the postjunctional folding seen on abnormal muscle fibers in these animals.