Fluorescent localization of catecholamine stores in the rat lung

To localize the stores of catecholamines present, normal rat lungs were examined with a histochemical fluorescence technique. Comparison was made with sections from animals infused with methylene blue to demonstrate the autonomic innervation usually observed. An extensive network of fine fluorescent fibers was seen in the mucosa of the entire bronchial tree. Coarse interstitial fibers adjacent to bronchi represented the largest monoamine stores observed, and communicated by delicate fibers with both the musculature and mucosa. Arterial fluorescence was less prominent, and a continuous subendothelial layer of coarse fluorescent material communicated with finer fibers in the muscular walls. The extensive fluorescent fibrous network visualized with the present method, demonstrating fine details of innervation, suggested an intimate relation between the bronchi and pulmonary arteries.