Three-dimensional architectures of P2X2-/P2X3-immunoreactive afferent nerve terminals in the rat carotid body as revealed by confocal laser scanning microscopy

Abstract

We investigated the three-dimensional architectures of P2X2-/P2X3-immunoreactive nerve terminals in the rat carotid body using immunohistochemistry with confocal laser microscopy. Nerve endings immunoreactive for P2X2 and P2X3 were associated with clusters of type I cells, whereas some nerve endings were sparsely distributed in a few clusters. Most nerve endings surrounding type I cells were hederiform in shape and extended several flattened axon terminals, which were polygonal or pleomorphic in shape and contained P2X2-/P2X3-immunoreactive products. Three-dimensional reconstruction views revealed that some flattened nerve endings with P2X3 immunoreactivity formed arborized, sac- or goblet-like terminal structures and were attached to type I cells immunoreactive for tyrosine hydroxylase (TH). However, P2X3-immunoreactive axon terminals were sparsely distributed in type I cells immunoreactive for dopamine beta-hydroxylase. Multi-immunolabeling for P2X2, S100, and TH revealed that P2X2-immunoreactive axon terminals were attached to TH-immunoreactive type I cells on the inside of type II cells with S100 immunoreactivity. These results revealed the detailed morphology of P2X2-/P2X3-immunoreactive nerve terminals and suggest that sensory nerve endings may integrate chemosensory signals from clustered type I cells with their variform nerve terminals.

Vesicular nucleotide transporter‐immunoreactive type I cells associated with P2X3‐immunoreactive nerve endings in the rat carotid body

“…Intense immunoreactivity for TH has been observed in a few type I cells, while weak immunoreactivity has been observed in some cells and nerve fibers in the CB of rats under normoxic condition (Kato, Yamaguchi‐Yamada, & Yamamoto, ). Immunoreactivity for DBH has been observed in some type I cells and sympathetic nerve fibers in the CB (Kato et al, ; Yokoyama et al, ). Bassoon is a presynaptic active zone molecule (Schoch & Gundelfinger, ).…”

“…An immunoblotting analysis of this antibody showed a single band of ~60 kDa in homogenates of the rat carotid body and adrenal medulla (Kato et al, ). This antibody has also been used for immunohistochemical analyses of the rat nucleus of the solitary tract (Austgen et al, ) and the rat carotid body (Kato et al, ; Yokoyama et al, ).…”

“…On the other hand, another electron microscopic study has shown that up to half of type I cells are not innervated by axon terminals of sensory nerve endings in the rat CB (McDonald & Mitchell, ). In our previous study, P2X2/P2X3 purinoceptors‐expressing sensory nerve endings made contact with type I cells immunoreactive for tyrosine hydroxylase (TH), the rate‐limiting enzyme of catecholamine biosynthesis, whereas few endings were attached to cells immunoreactive for dopamine beta‐hydroxylase (DBH), the noradrenaline biosynthetic enzyme (Yokoyama, Saino, Nakamuta, Kusakabe, & Yamamoto, ). Thus, a specific subpopulation of type I cells may release ATP in order to activate sensory nerve endings in the CB.…”

Morphology of P2X3‐immunoreactive nerve endings in the rat tracheal mucosa

“…Moreover, brush cells may be regarded as the source of ATP because they are expected to release acetylcholine in response to luminal stimuli (Kummer, Lips, & Pfeil, 2008). neuroepithelial bodies (Brouns et al, 2000), intraganglionic laminar endings in the esophagus (Wang & Neuhuber, 2003), sensory endings around glomus cells in the carotid and aortic bodies (Piskuric et al, 2011;Prasad et al, 2001;Yokoyama et al, 2016), arterial baroreceptors (Song et al, 2012), and nerve endings in the taste buds (Ishida et al, 2009). However, in the tracheal P2X3-immunoreactive nerve ending, the P2X2-immunoreactivity was weak or not observed.…”

“…An immunoblotting analysis showed a 62-kDa band in HEK cells transfected with a plasmid encoding the P2X2-FLAG protein or mouse brain tissue (Chaumont et al, 2008). This antibody has also been used for immunohistochemical analyses of the mouse brain (Chaumont et al, 2008) and nerve endings in the peripheral nervous system (Takahashi et al 2016;Yokoyama, Saino, Nakamuta, Kusakabe, & Yamamoto, 2016).…”