The distribution of myelinated nerve fibers in the mature opossum esophagus.

J Auton Nerv Syst 35(3):227-35 (1991) PMID 1720798

Myelination of nerve fibers could be important in establishing normal esophageal peristalsis. We therefore examined the general distribution and the age of appearance of myelinated nerve fibers in the smooth-muscle part of the esophagus of the American opossum. Tissues stained with thionein and Sudan black B were examined by light microscopy. Other tissues were prepared for electron microscopy and examined in the light microscope in Toluidine blue stained sections as well as at electron microscopy. In mature animals (weight greater than 2.0 kg, age greater than or equal to 1 year), myelinated nerve fibers, oriented mainly craniocaudally, were most abundant at the striated muscle-smooth muscle junction, and declined in density distally along the organ. They were nearly absent at the esophagogastric junction. They were more abundant in the stomach just below the esophagogastric junction. The myelinated nerve fibers commonly lay within sheathed fascicles that had the appearance of peripheral nerves, like the shunt fascicles of the stomach and colon. In immature animals myelinated fibers did not appear until a weight of about 1 kg was reached, 50 days after weaning and about 150 days after birth. Since the younger animals are presumably swallowing normally, myelination of the extrinsic nerves is not essential for esophageal motor function.