Intramural nerves and interstitial cells revealed by the Champy-Maillet stain in the opossum esophagus.

The 3 layers of smooth muscle of the opossum esophagus exhibit distinctly different and characteristic functions in response to nerve stimulation. These behaviors might be related to differences in patterns of innervation. Serial sections, stained with osmic acid and zinc iodide, were examined from all parts of the esophagus to describe in full the innervation of opossum esophageal smooth muscle. Linear beaded structures identified as terminal nerves were abundant in all 3 layers of smooth muscle. They were aligned with muscle bundles in bundles of 1-5 in mucosal muscle and up to about 10 in the longitudinal layer of muscularis propria. In the circular layer of muscularis propria they were less dense and more arborized and they crossed the muscle obliquely to also innervate bipolar interstitial cells; these cells resembled type III interstitial cells of Cajal, were specific for the circular muscle layer and were uniformly distributed throughout the thickness of that layer. Their distribution density in the circular muscle was slightly greater, 8777/cm2 in the most caudad 1.5 cm of the esophagus (which encompasses the sphincter) than in the 6 cm above that level. Terminal nerves also innervated submucosal glands, vessels and the epithelium. Ganglion cells and nerve bundles in the submucous and myenteric plexuses were variably stained. Ganglia of the latter plexus contained intraganglionic laminar endings as described previously in other species. In the striated muscle there were nerves terminating in motor end-plates. Other leafy stellate cells resembling interstitial cells of Cajal of other types were stained, as were oval interstitial cells.