Morphology of GNAT3‐immunoreactive chemosensory cells in the rat larynx

Abstract

The upper airways play important roles in respiratory defensive reflexes. Although solitary chemosensory cells and chemosensory cell clusters have been reported in the laryngeal mucosa of mammalian species, the distribution and cellular morphology of chemosensory cells remain unclear. In the present study, the distribution and morphology of solitary chemosensory cells and chemosensory cell clusters were examined by immunofluorescence for GNAT3 on whole‐mount preparations of the rat laryngeal mucosa. Electrophysiological experiments were performed to analyze the respiratory reflexes evoked by bitter stimuli to the laryngeal cavity. In the whole area of the laryngeal mucosa, the numbers of GNAT3‐immunoreactive solitary chemosensory cells and chemosensory clusters were 421.0 ± 20.3 and 62.7 ± 6.9, respectively. GNAT3‐immunoreactive solitary chemosensory cells were mainly distributed in the mucosa overlying epiglottic and arytenoid cartilage, and chemosensory clusters were mainly distributed on the edge of the epiglottis and aryepiglottic fold. GNAT3‐immunoreactive solitary chemosensory cells were slender with elongated processes or had a flask‐like/columnar shape. The number of GNAT3‐immunoreactive cells in chemosensory clusters was 6.1 ± 0.4, ranging between 2 and 14 cells. GNAT3‐immunoreactive cells in the cluster were variform and the tips of apical processes gathered at one point at the surface of the epithelium. The tips of apical cytoplasmic processes in solitary chemosensory cells and cells in the cluster were immunoreactive for espin, and faced the laryngeal cavity. Physiological experiments showed that the application of 10 mm quinine hydrochloride to the laryngeal cavity decreased respiratory frequency. The present results revealed the chemosensory field of the larynx and the morphological characteristics of the laryngeal chemosensory system for respiratory depression.

Chemical receptors of the arytenoid: A comparison of human and mouse

“…This finding is similar to cow, wherein SCCs were detected in the trachea and bronchi but not in the arytenoids . Conversely, in the rat, GNAT3‐immunoreactive SCCs were present throughout arytenoid tissue, although few were specifically located in the region investigated in the current work (i.e., at the tip of the corniculate process of the arytenoid cartilage) . Tizzano et al reported SCCs within the laryngeal epithelium, and specifically in the area of the arytenoids referred to as the hypoglossal region, which likely refers to the lingual face of the arytenoids.…”

“…The oropharynx and airways also contain scattered chemoresponsive cells (i.e., taste‐like cells) termed solitary chemosensory cells (SCCs), that express taste receptors. In rats, SCCs are reported to be densely packed in the vicinity of the epiglottis and arytenoids . Tizzano et al report that SCCs in mice occur primarily in the epiglottis and portions of the arytenoids, in epithelium innervated by the superior laryngeal nerve.…”

Morphology of GNAT3‐immunoreactive chemosensory cells in the nasal cavity and pharynx of the rat

“…Furthermore, Finger et al (2003) also reported synaptic specialization in the nasal solitary chemosensory cells and synaptic vesicles within the cells. In the larynx, nerve endings immunoreactive for P2X2/P2X3 purinoreceptors were also observed on solitary chemosensory cells (Masuda et al, 2019;Takahashi et al, 2016). Furthermore, numerous chemosensory cell clusters in the larynx were innervated by P2X3-immunoreactive nerve fibers (Masuda et al, 2019).…”

“…On the other hand, a stimulation of the nasal mucosa by denatonium benzoate, quinine hydrochloride (QHCl), or cycloheximide induced apnea (Tizzano & Finger, 2013). The perfusion of QHCl into the laryngeal cavity also induced ventilatory depression (Masuda et al, 2019). Thus, the chemosensory cells may participate in local immune system of the upper airway and/or involvement of bitter evoked autonomic reflex.…”

Solitary chemosensory cells are innervated by trigeminal nerve endings and autoregulated by cholinergic receptors

“…Earlier work demonstrated that murine SCCs release ACh subsequent to stimulation of their T2Rs 8 and that they coexpress nAChRs 11,12 . Although SCCs are intimately enveloped by nerve endings in murine nasal, trachea, and even laryngeal epithelium, 13 their survival is independent of neurogenic input. 14 The nAChR is a well‐known cholinergic neuroinflammatory target.…”