Postnatal developmental changes in the laryngeal chemosensory cell clusters of rats

Chemosensory cell clusters are taste bud-like sensory structures located in the pharyngo-laryngeal mucosa. These clusters are densely distributed at the entrance of lower airways to detect chemical stimuli and trigger respiratory reflexes; however, their postnatal development remains poorly understood. In this study, we examined postnatal changes in the morphology and distribution of chemosensory clusters in rat laryngeal whole-mount preparations using immunofluorescence for alpha-gustducin (GNAT3, a marker of type II taste cells) and synaptotagmin-1 (Syt1, a marker of type III taste cells). Chemosensory cell clusters were detected along the margin of the epiglottis on postnatal day 2 (PD2). Their numbers rapidly increased by PD7 (26 ± 4.5) and plateaued by postnatal week 3 (PW3, 84.0 ± 4.9), whereas the number of constituent cells continued to increase until PW8. Clusters at early stages (PD2-PD7) contained 2-3 spindle GNAT3-immunoreactive cells and round Syt1-immunoreactive cells. As the cluster matured, both cell types elongated longitudinally, extended the apical tip of their cytoplasmic processes to the epithelial surface, and GNAT3-immunoreactive cells developed branched cytoplasmic processes. P2X3-immunoreactive afferent nerve endings contacted GNAT3- and Syt1-immunoreactive cells throughout development. The results indicate the constant presence of chemosensory cell clusters in the laryngeal entrance and the establishment of neuronal connections as early as PD2. These clusters may be sentinel chemoreceptors at the entrance of the larynx. Because stabilization of chemosensory cell cluster numbers coincides with the weaning period, the postnatal development of these clusters may be associated with feeding behaviors in rats.