Nerve plexuses in the trachea and extrapulmonary bronchi of the rat

Intrinsic nerve plexuses of the rat trachea and extrapulmonary bronchi were examined by immunohistochemistry. Three nerve plexuses-peritracheal and peribronchial, intramuscular, and submucosal-were found in the wall of the trachea and bronchi. Nerve cell bodies were located in the peritracheal and peribronchial nerve plexuses. They occurred singly or formed ganglia in the plexus, and regional differences in cell numbers were found in the cervical and thoracic portions of the trachea and in the extrapulmonary bronchia. In total, 83.5 +/- 28.3 ganglia (mean +/- SD, 57-131, n=5) and 749.8 +/- 221.1 nerve cell bodies (540-1,080, n=5) were found in the nerve plexus. The mean densities of ganglia were 0.31, 0.97 and 1.15/mm(3), and the mean densities of the nerve cell bodies were 1.82, 9.26 and 11.54/mm(2) in the cervical region, thoracic region of trachea, and extrapulmonary bronchi, respectively. Almost all nerve cell bodies in ganglia were positive for choline acetyltransferase and neuropeptide Y (NPY), and a few cells were positive for vasoactive intestinal peptide (VIP). In addition, in cholinergic nerves, a few nerve fibers in the smooth muscles were positive for substance P (SP), calcitonin gene-related peptide (CGRP), and VIP, and a moderate number of fibers were positive for NPY. Tyrosine hydroxylase-immunoreactive nerve fibers were observed around blood vessels and within nerve bundles in the tunica adventitia. In the epithelium, nerve fibers were positive for SP and CGRP. Our results indicate that postganglionic neurons form three layers of cholinergic plexuses in the rat trachea and extrapulmonary bronchi, and that all of these possess intrinsic and extrinsic peptidergic innervation.