DISTRIBUTION OF NADPH DIAPHORASE IN INTRAMURAL PLEXUSES OF CAT AND OPOSSUM ESOPHAGUS

Nonadrenergic noncholinergic (NANC) nerves, releasing nitric oxide (NO), regulate peristalsis in esophageal smooth muscle. The NADPH diaphorase reaction identifies nitric oxide synthase (NOS). NO-synthesizing (NANC) nerves should be more abundant in esophageal smooth muscle than in striated muscle. We used NADPH diaphorase histochemistry in whole-mounts of the esophagus of cat (predominantly striated muscle) and opossum (predominantly smooth muscle) to compare striated and smooth muscle regions. In the opossum myenteric plexus, 90% of nerve cells were stained, with two populations, dark-staining and light-staining cells. Dark cells constituted 35-51% of stained cells with no difference between striated muscle and smooth muscle regions. In the cat myenteric plexus, 50% of cells were unstained in the striated muscle segment, but only 10% in the smooth muscle segment. Stained cells constituted two populations, dark cells and light cells, dark cells making up 48-60% of stained cells in both striated and smooth muscle segments, with no difference between segments. Both dark cells and light cells lay in clusters in opossum, but not in cat. Dark cells showed no selectivity for large or small ganglia of myenteric plexus in either region in opossum. Many more NADPH diaphorase positive nerve fibers lay in the circular smooth muscle layer than in the other layers. They were not found in striated muscle. Interstitial cells of Cajal in the circular layer of smooth muscle were also positive. In the submucosal plexus of opossum, all cells were stained, 10% being dark cells in both striated and smooth muscle segments. The cat has almost no nerve cells in the submucosal plexus. The similarity of the myenteric plexus in striated muscle and smooth muscle regions of the esophagus suggests that NADPH diaphorase positive nerves have other functions besides regulation of smooth muscle. Also, a positive reaction may not dictate that NO is the sole transmitter released.