The three-dimensional distribution of nerves along the entire intrapulmonary airway tree of the adult rat and the anatomical relationship between nerves and neuroepithelial bodies

Using airway microdissection and three-dimensional confocal microscopy techniques in combination with the immunomarkers protein gene product (PGP) 9.5 and calcitonin gene-related peptide (CGRP), we defined the distribution of small afferent nerves fibers and all nerves throughout the intrapulmonary airways, along with the distribution of airway neuroendocrine cells and neuroepithelial bodies. We found (i) the presence of CGRP-and PGP 9.5-positive structures along the entire intrapulmonary airway tree of adult rats, (ii) decreasing nerve density from more proximal to more distal generations of conducting airways, (iii) the presence of nerve fibers in terminal bronchioles, (iv) the asymmetrical distribution of nerves within a single generation of intrapulmonary airway with regard to associated vessels, (v) the frequent interchange of single nerve fibers across epithelial and sub-epithelial compartments without termination, and (vi) a definably intimate relationship between afferent nerves and neuroepithelial bodies (NEBs) (i.e., 58% of NEBs studied were observed to have nerve fibers coursing through them, indicating direct connections). We conclude that the distribution of nervous elements (nerve fibers and neuroendocrine cells) within the intrapulmonary airways is highly heterogeneous, varying between airway levels and locally within a specific airway level.