Innervation of the rat lung. Acetylcholinesterase‐containing nerves of the bronchial tree

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Abstract
The innervation to the bronchial tree of the rqt was studied using silver impregnation and methylene blue staining in conjunction with histochemical demonstration of acetylcholinesterase and one‐micron sections of osmium‐bed, plastic‐embedded material. Innervation to the bronchial structures enters the lung along two pathways: (1) in bundles of nerves along the bronchi (peribronchial bundles), and (2) as nerve bundles associated with bronchial arteries (periarterial bundles) to innervate bronchial arteries and respiratory passageways. Fibers within the peribronchial bundles and associated nerve cells contain acetylcholinesterase. Varicose nerve plexuses associated with bronchial muscle (intermuscular nerves) are acetylcholinesterase‐positive, as are the submucosal nerves. Submucosal nerves are of two types. One type originates directly from the peribronchial bundles after passing through the muscularis without innervating it. These nerves extend circumferentially and longitudinally with respect to the bronchiole. The second submucosal nerve type originates from the intermuscular nerve plexus. These nerves have a radial orientation within the bronchial submucosa and reach the mucosa. It is concluded that the intermuscular nerves are postganglionic parasympathetics. The two types of submucosal nerves are thought to perform different functions.