Date of Graduation
Fall 2025
Degree
Master of Science in Biology
Department
Biology
Committee Chair
Paul Durham
Abstract
Temporomandibular Disorders (TMD) are chronic orofacial pain conditions involving pain and dysfunction of the temporomandibular joint (TMJ) and the muscles of mastication. Hyperextension of the TMJ that occurs during yawning or during dental and orthodontic procedures or oral surgery can cause an intrinsic injury to the joint, muscle, ligaments, and tendons. This type of injury can lead to a chronic pain state involving activation and sensitization of neuronal cells of the trigeminal pathway that relays painful information from peripheral tissues to the central nervous system. Although females exhibit a higher prevalence of TMD, the underlying pathology for this phenomenon is not known. The goal of my study was to investigate changes in nociception (pain signaling) and protein expression in the spinal trigeminal nucleus in a preclinical TMD model caused by a single transient maximal TMJ opening (hyperextension). Mechanical nociception was determined on day 1 and day 14 post-hyperextension via von Frey filaments in young adult male and female Sprague Dawley rats. Female, but not male, rats exhibited enhanced nociception on day 1 and 14 post-hyperextension and exhibited guarding behavior of the TMJ, which is a protective mechanism to minimize further injury to the TMJ. Changes in protein expression in the spinal trigeminal nucleus were investigated by immunohistochemistry. On day 1, expression of the glutamate receptor NMDA, was significantly increased in females. On day 14, the pro-inflammatory protein CGRP and anti-nociceptive proteins GAD 65/67 were significantly decreased in females only. In contrast, expression of the receptor protein GABAB1 and the pro-inflammatory signaling protein P-p38 was significantly elevated. My findings provide evidence of sexual dimorphism in a novel TMD model in which sustained trigeminal sensitization was associated with enhanced expression of proteins that mediate trigeminal pain signaling while causing suppression of descending inhibitory pain signaling proteins.
Keywords
temporomandibular disorders, spinal trigeminal nucleus, sexual dimorphism, central sensitization, nociception, guarding behavior
Subject Categories
Life Sciences | Medicine and Health Sciences
Copyright
© Mikayla Scharnhorst
Recommended Citation
Scharnhorst, Mikayla, "TMJ Hyperextension Causes Sexually Dimorphic Changes in Nociception and Protein Expression in the Spinal Trigeminal Nucleus" (2025). Graduate Theses/Dissertations. 4138.
https://bearworks.missouristate.edu/theses/4138
