Calcitonin gene-related peptide (CGRP)-immunoreactive nerves in the tracheal epithelium of rats: an immunohistochemical study by means of whole mount preparations.

The airway mucosa is known to be densely supplied with several types of peptidergic nerve fibers. The distribution of the nerve fibers in a large extent of the mucosa, however, has been difficult to visualize by observation of conventional thin sections. In the present study, whole mount preparations of the rat tracheal mucosa were designed to demonstrate calcitonin gene-related peptide (CGRP)-containing nerves which are most predominant among peptidergic nerves in the trachea. The mucosal sheet of the trachea was separated from the cartilaginous base by means of dispase, a protease, to be processed to immunohistochemistry for CGRP. In the cartilaginous portion, thick nerve bundles immunoreactive for CGRP ran transversely between the cartilage rings, sending terminal branches toward the epithelium. In the membranous portion, immunoreactive nerve bundles were thinner than those in the cartilaginous portion and ran longitudinally. A very dense nerve plexus of CGRP-immunoreactive fibers was demonstrated to extend in the basal part of the epithelium; every epithelial cell appeared to contact more than one nerve fiber. Immunohistochemistry of the whole mount preparations also clearly demonstrated the distribution and entire shape of broncho-pulmonary paraneurons scattered in the epithelium. Ultrastructurally, the CGRP-immunoreactive intraepithelial nerves were found to lack myelin and Schwann sheaths, and to run through the bases of the epithelial cells; they were most frequently surrounded by the cytoplasmic processes of the epithelial cells. The present study demonstrates that immunohistochemistry of whole mount preparations is a useful tool to morphologically analyze neuronal and paraneuronal distribution throughout the tracheal epithelium.