Shunt fascicles in the gastric myenteric plexus in five species.

Thick nerve bundles, called shunt fascicles, lie in the myenteric plexus of the stomach in guinea pig, rabbit, cat, opossum, and cynomolgus monkey. They enter the stomach at the cardia, either as extensions of the esophageal myenteric plexus or of vagal branches to the caudal esophagus, and radiate toward the greater curvature. They bypass ganglia in the orad part of the stomach but give off branches to ganglia in more caudad parts. They are more abundant in the gastric fundus and body than in the antrum; they are infrequent along the greater curvature of the antrum. About 4% of the fibers they contain are myelinated. Arterioles and venules follow shunt fascicles and give rise to perifascicular capillary networks. Shunt fascicles are prominent in the cat, opossum, and monkey; they are short, thin, and sparse in the rabbit and guinea pig. They do not appear to be extensions of the direct vagal branches to the stomach but may be special nerve pathways from the esophagus to parts of the stomach.