Characterization of sensory neuronal subtypes innervating mouse tongue

Abstract

The tongue is uniquely exposed to water-soluble environmental chemicals that may lead to injury or tumorigenesis. However, comparatively little research has focused on the molecular and functional organization of trigeminal ganglia (TG) afferent neurons innervating the tongue. The current study identified and characterized lingual sensory neurons based on a neuronal subtype classification previously characterized in the dorsal root ganglion (DRG) neurons. We employed immunohistochemistry on transgenic reporter mouse lines as well as single-cell PCR of known markers of neuronal subtypes to characterize neuronal subtypes innervating the tongue. Markers expressed in retrogradely labeled TG neurons were evaluated for the proportion of neurons expressing each marker, intensity of expression, and overlapping genes. We found that tongue-innervating sensory neurons primarily expressed CGRP, TRPV1, TrkC, 5HT3A and Parvalbumin. These markers correspond to peptidergic and a subgroup of non-peptidergic C-nociceptors, peptidergic A nociceptors, proprioceptors and myelinated low-threshold mechanoreceptors (LTMRs). Interestingly, as reported previously, we also found several differences between TG and DRG neurons indicating the need for single-cell sequencing of neuronal types based on tissue type within all TG as well as DRG neurons.

Depiction of Oral Tumor-Induced Trigeminal Afferent Responses Using Single-Fiber Electrophysiology

“…Recently, Prato et al ., demonstrated that mechanically-insensitive C-Fibers that express the marker CHRNA3 are converted to mechanosensitive neurons in the presence of NGF 38 . Interestingly, CHRNA3 is expressed in lingual neurons 39 and the majority of MIA fibers detected in our study were C-fibers (Table 1 ). Moreover, NGF is shown to be overexpressed and released by OSCC tumor contributing to oral cancer pain 12 .…”

“…In addition to the findings described above, use of tongue-nerve electrophysiology revealed three interesting observations about trigeminal afferent responses. First, C-LTMR fibers were identified in lingual sensory neurons, despite the presence of very low proportion of tyrosine hydroxylase or VGLUT3 expression (both being markers of C-LTMR in dorsal root ganglion (DRG) neurons as reported recently 39 – 41 . This reflects and emphasizes the differences between DRG neurons and trigeminal ganglia (TG) neurons.…”

“…Second, our data may also signal similarities between DRG and TG neurons. Calbindin, a marker of rapidly-adapting neurons 43 was identified in a very small proportion of lingual neurons 39 . This finding correlated with very few rapidly-adapting fibers that were identified in the tongue-nerve preparations.…”

Variable branching characteristics of peripheral taste neurons indicates differential convergence

“…If the measure was normally distributed, then differences were determined using a one-way analysis of variance with a Tukey's post hoc analysis. If they were not normally distributed differences across multiple groups were compared using a Kruskal-Wallis test, while two groups were compared using a (Wu, Arris et al 2018). Therefore, we used TrkB CreER :alkaline phosphatase (AP) mice to reconstruct single taste nerve axons innervating the tongue (Rutlin, Ho et al 2014).…”

Genetic Deletion of TrpV1 and TrpA1 Does not Alter Avoidance of or Patterns of Brainstem Activation to Citric Acid in Mice

“…Polymodal nociceptors respond to acidification as well as other potentially painful stimuli 42 (Bessou and Perl 1969). Many small caliber polymodal nociceptors that innervate the oral cavity 43 (Kichko, Neuhuber et al 2018, Wu, Arris et al 2018) express one or both of the pH-sensitive 44 transient receptor potential (Trp) channels, TrpA1 (Wang, Chang et al 2011) and TrpV1 45 (Tominaga, Caterina et al 1998). TrpA1 has been implicated especially in responsiveness to 46 weak acids capable of penetrating cell membranes to produce intracellular acidification (Wang,47 Chang et al 2011).…”