Date on Master's Thesis/Doctoral Dissertation

12-2025

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Anatomical Sciences and Neurobiology

Degree Program

Anatomical Sciences and Neurobiology, PhD

Committee Chair

Krimm, Robin

Committee Member

Breza, Joseph

Committee Member

Samuelsen, Chad

Committee Member

Lundy, Robert

Committee Member

Petruska, Jeffrey

Author's Keywords

mechanosensation; trigeminal; touch; tongue; LTMR; taste bud

Abstract

Mechanosensory innervation of the oral cavity enables us to detect the texture and location of the foods we consume. Our goal was to find a genetic identifier for a mechanoreceptive subtype. Toward this goal, we examined neurons expressing the neurotrophin receptor TrkC, parvalbumin (Pvalb), and the glutamate transporter Vglut3. Because different papilla types contribute to food detection in different ways, we examined the innervation patterns of these neuron subtypes. We found that Pvalb+ and Vglut3+ neurons were fungiform papilla specific, where TrkC innervated both papilla types. We examined the anatomy of the three genetic populations, finding that the Pvalb+ neurons consistently displayed “basket-like” axonal endings surrounding taste buds within fungiform papillae. While TrkC+ and Vglut3+ neurons had a varied structure indicative of multiple morphological subtypes. The Vglut3+ axonal endings displayed the greatest degree of morphological variability. Collectively, these data show that Pvalb+ is more likely a genetic identifier for a single myelinated mechanoreceptor innervating fungiform papillae than the other two labels. We next examined individual tongue-innervating Pvalb+ neurons using axon reconstructions, optotagging and electrophysiology. Pvalb+ neurons were myelinated, expressed neurofilaments in the terminals and had relatively fast conduction velocities. Specifically, while the full population of LTMRs had a wide range of conduction velocities, all the Pvalb+ neurons fell into the A-fast category. Axon reconstructions demonstrated that Pvalb+ neurons have small receptive fields, that innervate one or two fungiform papillae. The Pvalb+ population consisted entirely of rapidly-adapting neurons, whereas the full population of LTMRs contained both rapidly-adapting and slowly-adapting LTMRs. Unlike slowly adapting neurons, Pvalb+ neurons did not increase their spike rates in response to increasing forces. However, Pvalb+ neuron latency to force stimulation decreased with increasing forces, indicating that Pvalb+ neurons may code for force through their latency. Lastly, when we examined Pvalb+ neuron responses to brush stimulation, we found that they are highly sensitive to brush stimulation. These findings indicate that Pvalb+ neurons that innervate the tongue are an A-fast, rapidly-adapting LTMR subtype with a small receptive field that responds to movements across the lingual surface.

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