title: Influence of sex on reflex jaw muscle activity evoked from the rat temporomandibular joint.
abstract: Injection of glutamate into the rat temporomandibular joint (TMJ) evoked a concentration-dependent increase in jaw muscle activity. We investigated whether there are sex-related differences in glutamate-evoked jaw muscle activity that are mediated by sex hormones and whether prior injection of glutamate into the TMJ alters the magnitude of jaw muscle activity evoked by a subsequent injection of the algesic and inflammatory compound mustard oil (MO) into the TMJ. The magnitude of glutamate-evoked digastric and masseter muscle activity was significantly greater in female than male rats when 1000 mM glutamate was injected into the TMJ. Gonadectomy significantly reduced the magnitude of glutamate-evoked digastric muscle activity in female rats. Treatment of gonadectomized female rats with estrogen (20 microg/day) increased the magnitude of glutamate-evoked digastric muscle activity. Glutamate-evoked jaw muscle activity in gonadectomized and estrogen-treated gonadectomized males was not significantly different from intact males. Prior injection of glutamate over a concentration range of 10-1000 mM significantly increased digastric muscle activity evoked by MO injection into the TMJ 30 min later. In contrast, MO-evoked masseter muscle activity was significantly increased by prior injection of 250 mM glutamate only. There were, however, no sex-related differences in the enhancement of MO-evoked jaw muscle activity by prior injection of glutamate. These findings indicate that there are sex-related differences in glutamate-evoked jaw muscle activity that are dependent on female sex hormones, and increased glutamate concentrations sensitize the TMJ to noxious chemical stimuli.
authors.affiliation: Department of Oral Physiology, Faculty of Dentistry, The University of Toronto, 124 Edward Street, Toronto, ON, Canada.
authors.forename: Brian E
authors.initials: BE
authors.lastname: Cairns
authors.forename: Yiin
authors.initials: Y
authors.lastname: Sim
authors.forename: David A
authors.initials: DA
authors.lastname: Bereiter
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Sessle
authors.forename: James W
authors.initials: JW
authors.lastname: Hu
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D004967:Estrogens / Q000378:metabolism / Q000494:pharmacology; D030762:Estrous Cycle / Q000502:physiology; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology; D012739:Gonadal Steroid Hormones / Q000378:metabolism*; D008297:Male; D008410:Masticatory Muscles / Q000294:innervation* / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009619:Nociceptors / Q000187:drug effects / Q000378:metabolism*; D010146:Pain / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D012727:Sex Characteristics; D013704:Temporomandibular Joint / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D013705:Temporomandibular Joint Disorders / Q000378:metabolism / Q000503:physiopathology
chemical_list: D004967:Estrogens; D012739:Gonadal Steroid Hormones; D018698:Glutamic Acid