Pulmonary neuroepithelial bodies are innervated by vagal afferent nerves: an investigation with in vivo anterograde DiI tracing and confocal microscopy.

Abstract

The pulmonary airway and alveolar epithelia contain distinctly innervated clusters of basally granulated cells: the neuroepithelial bodies. In the past, morphological criteria and the results of selective vagotomy have led to the interpretation that their innervation is sensory. Consequently, they are regarded as receptor organs. As a further test of this hypothesis, the present investigation set out to label vagal sensory nerve fibres to the lungs by anterograde neural tracing, and to establish the relationship between these fibres and the neuroepithelial bodies. A fluorescent neural tracer was injected unilaterally into the left or right nodose ganglion of adult rats. After suitable survival times, thick frozen sections of lung tissue were studied with laser scan confocal microscopy. Sensory nerve fibres were seen to run in the airway walls and occasionally penetrated the epithelium, where they formed complex terminals. The resulting intraepithelial sensory end organs showed a close morphological resemblance to the neuroepithelial bodies. Subsequently, electron microscopic investigation of such identified structures revealed the typical ultrastructural characteristics of neuroepithelial bodies: corpuscular cells containing dense cored secretory vesicles and contacted by mitochondria-rich nerve endings. We conclude that anterograde tracing of sensory nerves from the nodose ganglion confirms the receptor nature of the pulmonary neuroepithelial bodies, which may correspond to a subpopulation of the irritant and C-fibre receptors.