title: Decreased face primary motor cortex (face-M1) excitability induced by noxious stimulation of the rat molar tooth pulp is dependent on the functional integrity of face-M1 astrocytes.
abstract: Acute inflammatory dental pain is a prevalent condition often associated with limited jaw movements. Mustard oil (MO, a small-fiber excitant/inflammatory irritant) application to the rat molar tooth pulp induces increased excitability (i.e., central sensitization) of trigeminal medullary dorsal horn (MDH) nociceptive neurons that can be modulated by MDH application of the astrocytic inhibitor methionine sulfoximine (MSO). The objectives of the study were to determine whether MO application to the rat right maxillary first molar tooth pulp affects left face-M1 excitability manifested as altered intracortical microstimulation thresholds for evoking electromyographic activity in the right anterior digastric (RAD, jaw-opening muscle), and whether MSO application to face-M1 can modulate this MO effect. Under Ketamine general anesthesia, Sprague-Dawley male rats had a microelectrode positioned at a low-threshold (≤30 μA) face-M1 site. Then MO (n = 16) or control solution (n = 16) was applied to the previously exposed tooth pulp, and RAD threshold was monitored for 15 min. MSO (0.1 mM, n = 8) or saline (n = 8) was then applied to the face-M1, and RAD thresholds were monitored every 15 min for 120 min. ANOVA followed by post hoc Bonferroni was used to analyze data (p < 0.05). Within 15 min of MO (but not control) pulp application, RAD thresholds increased significantly (p < 0.001) as compared to baseline. One hour following MSO (but not saline) application to the face-M1, RAD thresholds decreased significantly (p = 0.005) toward baseline. These novel findings suggest that acute inflammatory dental pain is associated with decreased face-M1 excitability that may be dependent on the functional integrity of face-M1 astrocytes and related to mechanisms underlying limited jaw movements in acute orofacial pain conditions.
authors.affiliation: Department of Oral Physiology, Faculty of Dentistry, University of Toronto, 124 Edward St., Toronto, ON, M5G 1G6, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Awamleh
authors.forename: H
authors.initials: H
authors.lastname: Pun
authors.forename: J-C
authors.initials: JC
authors.lastname: Lee
authors.forename: L
authors.initials: L
authors.lastname: Avivi-Arber
mesh_terms: D000344:Afferent Pathways / Q000503:physiopathology; D000704:Analysis of Variance; D000818:Animals; D003782:Dental Pulp / Q000294:innervation*; D004558:Electric Stimulation / Q000009:adverse effects; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000187:drug effects / Q000502:physiology*; D005152:Facial Muscles / Q000187:drug effects / Q000294:innervation*; D008297:Male; D009044:Motor Cortex / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D009149:Mustard Plant / Q000633:toxicity; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology; D017288:Pain Threshold; D010938:Plant Oils / Q000633:toxicity; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D010938:Plant Oils; C027793:mustard oil