IADR Abstract Archives
Mapping the Innervation of the Temporomandibular Joint
Objectives: The objectives of these studies are to 1) provide insight into normal innervation, 2) provide a basis for understanding how the innervation changes in TMD, and 3) determine if it contributes to chronic pain and could be targeted to prevent it.
Methods: We set out to define the types of somatosensory neurons that innervate the temporalis, a masticatory muscle used in the closure of the jaw. We performed retrograde capture of somatosensory neurons by injecting a CTB conjugate into the temporalis to retrogradely label associated sensory neurons. Three days post injection, TGs were harvested, flash-frozen, and cryosectioned. TG sections were stained using multi-round, multi-plex in situ hybridization for 8 diagnostic markers to enable subsequent machine learning-based classification of sensory neurons.
Results: A subset of sensory neurons were strongly labeled following CTB injection into the temporalis. We identified and classified a total of 433 neurons based on their predicted transcriptomic class and putative functions. Most temporalis sensory neurons were mechanoreceptors (C3~7%, C4~34%, C5~3%, C6~19% and C13~5%). The remaining neurons represented thermoreceptor cool sensing and noxious heat/pain-sensing neurons (C1/2~13% and C7/9/10~12% respectively), itch sensing (C11/12~4%), or heat/chemical noxious sensation (C8~3%). Importantly, we determined that nociceptors represent a substantial (~37%) portion of all neurons. When compared to the innervation of the masseter, another muscle involved in jaw closure, we observed that while there is a similar portion of neurons that we determined to be nociceptive, there is variability within other innervating sensory neuron classes.
Conclusions: We have demonstrated that CTB labeling and ISH-based classification represent a robust tool for identifying and distinguishing TG somatosensory neurons that innervate TMJ-associated muscles. Further work will determine how individual subsets of muscle-associated nociceptors contribute to joint pain. We are working to combine MRI with our classification to target smaller TMJ structures and evaluate associated somatosensory innervation.
Methods: We set out to define the types of somatosensory neurons that innervate the temporalis, a masticatory muscle used in the closure of the jaw. We performed retrograde capture of somatosensory neurons by injecting a CTB conjugate into the temporalis to retrogradely label associated sensory neurons. Three days post injection, TGs were harvested, flash-frozen, and cryosectioned. TG sections were stained using multi-round, multi-plex in situ hybridization for 8 diagnostic markers to enable subsequent machine learning-based classification of sensory neurons.
Results: A subset of sensory neurons were strongly labeled following CTB injection into the temporalis. We identified and classified a total of 433 neurons based on their predicted transcriptomic class and putative functions. Most temporalis sensory neurons were mechanoreceptors (C3~7%, C4~34%, C5~3%, C6~19% and C13~5%). The remaining neurons represented thermoreceptor cool sensing and noxious heat/pain-sensing neurons (C1/2~13% and C7/9/10~12% respectively), itch sensing (C11/12~4%), or heat/chemical noxious sensation (C8~3%). Importantly, we determined that nociceptors represent a substantial (~37%) portion of all neurons. When compared to the innervation of the masseter, another muscle involved in jaw closure, we observed that while there is a similar portion of neurons that we determined to be nociceptive, there is variability within other innervating sensory neuron classes.
Conclusions: We have demonstrated that CTB labeling and ISH-based classification represent a robust tool for identifying and distinguishing TG somatosensory neurons that innervate TMJ-associated muscles. Further work will determine how individual subsets of muscle-associated nociceptors contribute to joint pain. We are working to combine MRI with our classification to target smaller TMJ structures and evaluate associated somatosensory innervation.