Ultrastructural localization of neuronal nitric oxide synthase-immunoreactivity in the rat ileum

The location of neuronal nitric oxide synthase-immunoreactivity (NOS-IR) in whole mount preparations of muscularis externa of rat ileum was determined by using pre-embedding electron microscope immunocytochemistry. Several neurons, nerve fibers and nerve endings in the myenteric plexus (MP) and nerve endings within the muscle layers were found to be NOS-IR. These nerve endings were especially numerous in the deep muscular plexus (DMP) and much closer to interstitial cells of Cajal (ICC) than to smooth muscle cells. Some of the ICC-MP were NOS-IR. These findings indicate that ICC-MP are apparently able to produce NO and ICC-DMP are the ileal ICC type very richly innervated by the NO releasing nerves.