Changes in muscularis externa of rat small intestine after myenteric ablation with benzalkonium chloride: electron microscopic and morphometric study.

The influence of the intrinsic innervation on the muscularis externa of the rat small intestine was studied by chemical ablation of the myenteric plexus with benzalkonium chloride (BAC). The resulting severe hypertrophy (cell hypertrophy of 96-133% and hyperplasia) differs from working hypertrophy by the distribution and degree of muscle thickening and by characteristics of the extracellular matrix: narrowing of muscle interspaces of 43%; lack of increased collagen; changes in the ratio of interstitial cells of Cajal (ICCs) to fibroblasts from 1.6:1 to 0.8:1 with no numerical decrease in either type of cell; decreased interconnections of ICCs to muscles and nerves due to deformed ICCs; a 197% increase in vascularization (capillaries, venules) and lymphatics in both muscle layers and in the myenteric plexus cleft, possibly initiated by release of fibroblast growth factor from myelin fragmentation after nerve damage; and increased macrophages, plasma cells, monocytes and mast cells in the myenteric plexus cleft. These all signify the neural influence on the morphodifferentiation of the muscularis externa in concert with the extracellular matrix components.