Neural pathway from jaw-closing muscle spindles
Eating is vital to life – Enjoy eating until the end of one’s life is important in this aging society. Enjoy eating requires the neural mechanisms involving both pathways that convey oral and orofacial sensory information to the brain and those that command proper output for orofacial muscular movement. We aim for the elucidation of neural mechanisms in the central nervous system for this sensorimotor information processing.
Identification of the supratrigeminal nucleus receiving proprioceptive sensation from jaw-closing muscle spindles
The supratrigeminal nucleus (Su5) receives proprioceptive sensation from jaw-closing muscle spindles (JCMSs) via the trigeminal mesencephalic neurons. We identified the rat Su5 with cytoarchitecture and electrophysiology. This is the structural basis of the ascending projection via Su5 for jaw reflex and information processing of proprioceptive sensation from JCMSs. (Fujio et al., Neuroscience, 2016)
Ascending pathway of jaw-closing muscle-proprioception to the thalamus
We found that jaw-closing muscle-proprioception is mainly contralaterally transmitted to the caudo-ventromedial edge (VPMcvm) of ventral posteromedial thalamic nucleus (VPM) from the supratrigeminal nucleus (Su5). This result shows that the proprioceptive pathway from jaw-closing muscle spindles (JCMSs) differs from the other orofacial sensory afferent through distinct projections from the trigeminal nucleus to the thalamus. (Yoshida et al., Brain Struct Funct., 2017)
Thalamo-cortical pathway for jaw-closing muscle-proprioception
We showed that the jaw-closing muscle-proprioceptive afferent terminated largely in the dorsal part of the granular insular cortex rostroventrally adjacent to the rostralmost part of secondary somatosensory cortex (dGIrvs2), but it did not target the motor cortex. This result indicates the contribution of jaw-closing muscle-proprioception to the emotional brain function. (Sato et al., Neuroscience, 2017)
Proprioceptive afferent in the intralaminar thalamic nuclei
We found that the supratrigeminal nucleus (Su5) neurons projected bilaterally to the oval paracentral nucleus (OPC) of the intralaminar thalamic nuclei as well as the caudo-ventromedial edge of ventral posteromedial thalamic nucleus (VPMcvm). Understanding of this previously unrecognized pathway of proprioception ascending inputs from the brainstem to the thalamus may contribute to treatments of tourette syndrome patients.
Corticopetal pathways from the intralaminar thalamic nucleus (OPC)
We revealed that the rat OPC broadly projects to S1, S2 and GI including dGIrvs2 which receives JCMS proprioception from VPMcvm. This finding indicated that there exist divergent corticopetal pathways from the intralaminar thalamic nucleus, which process JCMS proprioception and that JCMS proprioception via the OPC may be involved in both discriminative and integrative process of orofacial sensations in those cerebral cortices. (Tsutsumi et al., Brain Struct Funct. 2021)
Ascending pathway of jaw-closing muscle-proprioception to the cerebellar cortex
We found that the JCMS proprioceptive information is delivered bilaterally to the cerebellar cortex (mainly in the simplex B, crus II and flocculus which are included the hemisphere of lobules VI, VII and X, respectively) via the Su5. Compared with the projection pattern from the external cuneate nucleus (ECu), which receives proprioceptive information from the neck and forelimb muscles, Su5 and ECu projected mainly to the hemisphere and vermis, respectively. This finding demonstrated that the projection pattern from the Su5 to the cerebellar cortex is distinct from that from the ECu, so proprioceptive inputs arising from orofacial and other body-part muscles are differentially processed in segregated domains of cerebellar functions. (Tsutsumi et al., Cerebellum., 2022)
Oral splint ameliorates tic symptoms in patients with tourette syndrome
An oral splint was shown to be therapeutically effective to ameliorate tic symptoms of tourette syndrome (TS) patients (Murakami et al., Mov Disord., 2019). The oral splint is expected to be applied for the treatment of TS patients, especially younger patients.