Distribution of catecholamine‐containing nerves on blood vessels of the rat trachea

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Abstract
This study was performed to determine the distribution of catecholamine‐containing sympathetic nerves on blood vessels of the rat trachea. The glyoxylic acid method was used to visualize catecholamine‐containing axons in tracheal whole mounts, and silicone vascular casts were used to elucidate the architecture of the vasculature. We also examined the relationship of these axons to the trachea's plexus of cholinergic nerves and ganglia, using tracheal whole mounts stained for acetylcholinesterase activity. We found that most catecholamine‐containing axons were associated with arterioles located between cartilaginous rings or in the posterior membrane. In both regions, catecholamine‐containing nerves were most abundant at the origin of terminal arterioles, which supplied the airway mucosa and smooth muscle. At the origin of these vessels, the fluorescent axons changed their orientation from longitudinal to circumferential. Few fluorescent axons were present beyond this region of the terminal arterioles, and none was found on capillaries or venules or on smooth muscle cells of the posterior membrane. Fluorescent axons were present in some tracheal ganglia but none enveloped neuronal cell bodies or had varicosities, and no ganglion cells had glyoxylic acid‐induced fluorescence. Catecholamine‐fluorescence was also present in clusters of small intensely fluorescent (SIF) cells, which were located in the adventitia of the posterior membrane and in the longitudinal nerve trunks which ran the length of the trachea. Pargyline pretreatment increased the fluorescence of axons and SIF cells but did not reveal a different distribution of these structures. We conclude that most catecholamine‐containing axons in the rat trachea innervate arterioles, particularly terminal arterioles, and presumably participate in the control of blood now to the airway wall. We obtained no evidence that such axons innervate the ganglia or smooth muscle of the rat trachea.