Inflammation of temporomandibular joint increases neural activity in rat vestibular nucleus

To determine whether the vestibular nuclei are affected by inflammation of temporomandibular joint (TMJ) region, we studied vestibular nucleus neural activity using two experimental groups: (1) normal saline 0.1 cm³ injection at right TMJ region, (2) 10% formalin 0.1 cm³ injection at right TMJ region. Neural activity after 24 hours was assessed by immunohistochemical staining with free-floating section at the level of interaural −1.30 mm to −2.00 mm for c-Fos. In inflammation group, formalin injection produced a bilateral increase in c-Fos at vestibular nucleus with ipsilesional side higher activity. In control group, expression of c-Fos protein was also observed in the vestibular nucleus (VN), especially MVN. But stain intensity of Fos-positive neurons was much weaker and mean number of c-Fos positive cells was fewer than inflammation group. This result suggests that there is a close neural connection between TMJ and vestibular nucleus, especially in case of inflammation.