NEUROMUSCULAR-JUNCTIONS OF LONGITUDINAL AND CIRCULAR MUSCLE-FIBERS OFTHE GUINEA-PIG ESOPHAGUS AND THEIR RELATION TO MYENTERIC PLEXUS

The structure of the neuromuscular junctions (NMJs) and their relation to the myenteric plexus were studied by zinc iodide-osmic acid (ZIG) staining and by scanning electron microscopy in the guinea-pig esophag us, The esophageal muscle coat consisted of the inner circular and out er longitudinal striated muscle fibers. The myenteric plexus was locat ed between the two muscle layers along its whole length and was charac terized by a loose and irregular network. It was demonstrated that unm yelinated nerve fibers form NMJs with the muscle fibers of both layers , The NMJs in the longitudinal muscle can be classified as 'plate' typ e, whereas those of the circular muscle resemble the 'grape' type, The different NMJs in the two muscle layers probably correspond to differ ent contractile properties, The whole-mount preparations with ZIO stai ning also demonstrated that some NMJs receive minute branches from the myenteric plexus. Therefore, it is likely that the myenteric plexus i s involved in the control of striated muscles of the guinea-pig esopha gus.