ABSTRACT
Techniques for the histochemical demonstration of acetylcholinesterase (AChE) enabled studies on the distribution of presumed cholinergic nerves in the respiratory tract in which AChE-positive nerve fibers were found to form dense plexuses around blood vessels. A smaller number of neuropeptides has been demonstrated in the respiratory tract. Vasoactive intestinal peptide (VIP) is richly distributed in perivascular nerve fibers in the entire respiratory tract. In view of the specific toxic effect of capsaicin on certain sensory nerves the substance P (SP) fibers in the respiratory tract are thought to be peripheral ramifications of primary sensory neurones. In the respiratory tract, neuropeptide-Y (NPY)-containing nerve fibers are seen beneath the surface epithelium, in the smooth muscle, around seromucous glands, and around blood vessels. Blood vessels in the respiratory tract are supplied with several nerve populations containing different neuropeptides: VIP, SP, calcitonin gene-related peptide (CGRP), gastrin-releasing peptide, and NPY. VIP, SP, and CGRP are vasodilators, whereas NPY causes vasoconstriction.
