Intraepithelial Vagal Sensory Nerve Terminals in Rat Pulmonary Neuroepithelial Bodies Express P2X₃ Receptors

Abstract

The neurotransmitters/modulators involved in the interaction between pulmonary neuroepithelial bodies (NEBs) and the vagal sensory component of their innervation have not yet been elucidated. Because P2X(3) purinoreceptors are known to be strongly expressed in peripheral sensory neurons, the aim of the present study was to examine the localization of nerve endings expressing P2X(3) purinoreceptors in the rat lung in general and those contacting pulmonary NEBs in particular. Most striking were intraepithelial arborizations of P2X(3) purinoceptor-immunoreactive (IR) nerve terminals, which in all cases appeared to ramify between calcitonin gene-related peptide (CGRP)- or calbindin D28k (CB)-labeled NEB cells. However, not all NEBs received nerve endings expressing P2X(3) receptors. Using CGRP and CB staining as markers for two different sensory components of the innervation of NEBs, it was revealed that P2X(3) receptor and CB immunoreactivity were colocalized, whereas CGRP-IR fibers clearly formed a different population. The disappearance of characteristic P2X(3) receptor-positive nerve fibers in contact with NEBs after infranodosal vagal crush and colocalization of tracer and P2X(3) receptor immunoreactivity in vagal nodose neuronal cell bodies in retrograde tracing experiments further supports our hypothesis that the P2X(3) receptor-IR nerve fibers contacting NEBs have their origin in the vagal sensory nodose ganglia. Combination of quinacrine accumulation in NEBs, suggestive of the presence of high concentrations of adenosine triphosphate (ATP) in their secretory vesicles, and P2X(3) receptor staining showed that the branching intraepithelial P2X(3) receptor-IR nerve terminals in rat lungs were exclusively associated with quinacrine-stained NEBs. We conclude that ATP might act as a neurotransmitter/neuromodulator in the vagal sensory innervation of NEBs via a P2X(3) receptor-mediated pathway. Further studies are necessary to determine whether the P2X(3) receptor-expressing neurons, specifically innervating NEBs in the rat lung, belong to a population of P2X(3) receptor-IR nociceptive vagal nodose neurons.

Mechanical stretch-induced serotonin release from pulmonary neuroendocrine cells: implications for lung development

“…The mechanical strain-induced 5-HT release could be analogous to well-characterized mechanosensitive release of ATP, a small molecule that acts as a neurotransmitter of mechanosensation in various tissues (4). Recent studies have indicated that purinergic mechanisms, including ATP release, may be involved in PNEC/NEB function, particularly the chemotransmission and modulation of hypoxia signaling via P2X 2-3 receptors expressed on NEB cells and on the nerves that innervate them (5,16). Reported candidates for ATP release pathways include ABC transporter proteins (e.g., CFTR, P-glycoprotein), hemi gap-junction channel, and exocytosis of ATP-containing vesicles (22).…”

Pathophysiology and Therapeutic Potential of Purinergic Signaling

“…It has been suggested that ventilator-induced lung injury may involve stretch-associated release of ATP from neuroepithelial cell bodies (Brouns et al, 2000(Brouns et al, , 2003Rich et al, 2003) and may therefore be a therapeutic target for this condition.…”

Quantification of Neuroepithelial Bodies and Their Innervation in Fawn-Hooded and Wistar Rat Lungs

“…These second primary antibodies were visualized using GAR-Fab-FITC (diluted 1:200, 1 h). TSAenhanced immunostaining for SP and for the P2X 3 receptor was performed according to previously described methods (11,16).…”

“…Especially the extensively innervated aggregates of neuroendocrine cells, called neuroepithelial bodies (NEBs), which are diffusely spread in the epithelium at all levels of the intrapulmonary airways but are preferentially located at airway bifurcation points in rat lungs (10), might be involved. Neuroendocrine cells are able to synthesize and release ATP (11), monoamine, and peptide transmitters, resulting in autocrine, paracrine, neurocrine, or endocrine effects. NEBs morphologically resemble known chemoreceptors, such as taste buds and carotid bodies, and are, among other possible functions, thought to represent "chemosensors."…”

“…17). An intraepithelial vagal sensory innervation of NEBs, with origin in the nodose ganglion (20), appeared to be myelinated and was characterized by a calbindin D28k (CB) immunostaining (16) and the expression of purinergic P2X 3 receptors (11). A second sensory, capsaicin-sensitive, and calcitonin gene-related peptide (CGRP)/Substance P (SP)-immunoreactive (IR) innervation of NEBs, was shown to have a nonvagal origin (16,20).…”