title: Effects of inflammatory irritant application to the rat temporomandibular joint on jaw and neck muscle activity.
abstract: An electromyographic (EMG) study was carried out in 40 anaesthetized rats to determine if the activity of jaw and neck muscles could be influenced by injection of the small-fibre excitant and inflammatory irritant mustard oil into the region of the temporomandibular joint (TMJ). Injection of a vehicle (mineral oil, 20 microliters) did not produce any significant change in EMG activity. In contrast, injection of mustard oil (20 microliters, 20%) evoked increases in EMG activity in the jaw muscles but not in the neck muscles. The increased EMG activity evoked by mustard oil was reflected in 1 or 2 phases of increased activity. The early EMG increase occurred soon after the mustard oil injection (mean latency +/- SD: 3.5 +/- 2.3 sec), peaked within 1 min, and then subsided (mean duration: 7.5 +/- 5.2 min). The later EMG increase occurred at 14.6 +/- 10.0 min after the mustard oil injection and lasted 14.3 +/- 12.3 min. These excitatory effects of mustard oil on the EMG activity of jaw muscles appear to have a reflex basis since they could be abolished by pre-administration of local anaesthetic into the TMJ region. These results document that TMJ injection of mustard oil results in a sustained and reversible activation of jaw muscles that may be related to the reported clinical occurrence of increased muscle activity associated with trauma to the TMJ.
authors.affiliation: Faculty of Dentistry, University of Toronto, Toronto, Ont. M5G 1G6 Canada Canadian Memorial Chiropractic College, Toronto, Ont. M4G 3E6 Canada.
authors.forename: X-M
authors.initials: XM
authors.lastname: Yu
authors.forename: B J
authors.initials: BJ
authors.lastname: Sessle
authors.forename: H
authors.initials: H
authors.lastname: Vernon
authors.forename: J W
authors.initials: JW
authors.lastname: Hu
mesh_terms: D000818:Animals; D004576:Electromyography; D005260:Female; D007249:Inflammation / Q000139:chemically induced; D007267:Injections; D007509:Irritants / Q000494:pharmacology*; D007568:Jaw; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects; D009149:Mustard Plant; D009334:Neck Muscles / Q000187:drug effects; D010936:Plant Extracts / Q000494:pharmacology*; D010938:Plant Oils; D010946:Plants, Medicinal; D051381:Rats; D017207:Rats, Sprague-Dawley; D013705:Temporomandibular Joint Disorders / Q000139:chemically induced*
chemical_list: D007509:Irritants; D010936:Plant Extracts; D010938:Plant Oils; D008012:Lidocaine; C027793:mustard oil