Plexus muscularis profundus and associated interstitial cells. I. Light microscopical studies of mouse small intestine.

The zinc iodide/osmic acid (ZIO) method was used in a modification that selectively stained nerves and associated interstitial cells of Cajal (ICC) of muscularis externa. Due to its selectivity the method allowed a detailed stereoscopical analysis of whole mounts with respect to the topography and morphology of these elements. The method thus assisted and expanded our ultrastructural studies. The ZIO staining allowed a distinction of four morphologically different interstitial cell types (ICC-I-IV) confined to four compartments. The stained components were: (1) A rich plexus of highly ramified interstitial cells (ICC-II) in the subserous layer. (2) Auerbach's plexus with an associated extensive plexus of interstitial cells (ICC-I) in close contact with tertiary fasciculi. (3) Nerve fasciculi of the outer division of the circular muscle layer. These formed a nerve plexus in a well-defined plane in the outermost cell layers (plexus muscularis superficialis), with few fasciculi located internal to this plexus. A few bipolar interstitial cells (ICC-IV) were associated with nerve fasciculi of this region. (4) A nerve plexus located in the region between the two subdivisions of the circular muscle, plexus muscularis profundus (PMP). PMP was revealed throughout the small intestine as a continuous network of elongated, circularly oriented meshes. The pattern of connections between PMP and the other enteric plexuses was studied stereoscopically. Ganglion cells intrinsic to PMP occurred widely scattered. Interstitial cells associated with PMP (ICC-III) were arranged in a plexiform manner; their morphology and relations to nerves were investigated in great detail. A selective innervation of ICC-III via axons of PMP was strongly supported.