Presence of VIP fibers of sensory origin in the rat trachea.

The presence of vasoactive intestinal peptide (VIP) immunoreactive nerve fibers (LI) in the respiratory tract of mammals is well documented. These fibers are known to originate from parasympathetic postganglionic neurons and to be associated with blood vessels, submucosal glands, and with smooth muscle. We found that, in addition to this, the epithelial layer of the rat trachea also contains VIP-LI fibers. Vagotomy or ligation of the cervical portion of the vagus nerve resulted respectively in a decrease of VIP-LI fibers within the epithelium or in the accumulation of VIP in axons proximal to the site of transection or ligation, whereas no changes were seen in other parts of the trachea. On the other hand, capsaicin pretreatment also caused similar changes to the surgical procedures. These findings indicate that VIP-LI fibers in the tracheal epithelium of the rat are supplied by the sensory ganglia of the vagus nerve.