EPITHELIAL INNERVATION OF LOWER RESPIRATORY-TRACT OF CAT

Abstract

This morphologic study was undertaken to determine the ultrastructure, concentration and association of intra-epithelial nerve fibers with epithelial cells which line the airways of the cat. The study is particularly relevant as physiological studies have indicated a close relationship of airway irritant receptors with epithelium. Eight adult cats, of clean stock, were used and the following 4 airway levels investigated: lower trachea; main carina; hilar axial pathway of left lower lobe and a distal airway (i.e., small lateral bronchus 0.5-0.7 mm in diameter). Epithelia were examined by EM in such a way that the numbers of intra-epithelial nerve fibers occurring in 85 .mu.m lengths of epithelium could be counted. Intra-epithelial nerve fibers appeared as electron-lucent profiles with neurotubules and, often, mitochondria. They were invariably without myelin, Schwann cell or basement membrane. About 80% of the profiles lacked neurosecretory vesicles: the rest usually had clear vesicles of varying diameter. The highest concentration of nerve fibers was found at the main carina when about 90% were in the basal zone of the epithelium and 10% near to the airway lumen. At this site, the axon to cell ratio was 1:3. No particular cell type was preferentially innervated. The morphology of these fibers or endings suggests they probably subserve a sensory function, but this hypothesis requires experimental confirmation.