title: The effect of glutamate-evoked masseter muscle pain on the human jaw-stretch reflex differs in men and women.
abstract: OBJECTIVE
  To compare jaw-stretch reflex responses in male and female subjects and to determine whether injection of glutamate into the masseter muscle facilitates these responses in both sexes.
  
  
  METHODS
  Jaw-stretch reflex responses were evoked with a muscle stretcher, and pain intensity was scored by 11 men and 13 women before and after the injection of glutamate (1.0 mol/L, 0.2 ml) into the masseter muscle. The subjects rated glutamate-evoked pain intensity on a visual analog scale.
  
  
  RESULTS
  Baseline jaw-stretch reflex responses were larger and glutamate injections into the masseter muscle were significantly more painful in women than in men, however, glutamate significantly facilitated jaw-stretch reflex responses in men but not in women.
  
  
  CONCLUSIONS
  These results suggest that there is a significant sex-related difference in human jaw-stretch reflex responses and their modulation by painful stimuli. Since one possible function of facilitated jaw-stretch reflex responses during jaw muscle pain may be to reduce jaw mobility and thus protect against further exacerbation of an existing injury, the finding of a sex-related difference in modulation of jaw-stretch reflex responses may prove to be important in clarifying why the prevalence of temporomandibular disorders is greater in women than in men.
authors.affiliation: Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, Canada.
authors.forename: Brian E
authors.initials: BE
authors.lastname: Cairns
authors.forename: Kelun
authors.initials: K
authors.lastname: Wang
authors.forename: James W
authors.initials: JW
authors.lastname: Hu
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Sessle
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen
authors.forename: Peter
authors.initials: P
authors.lastname: Svensson
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004576:Electromyography; D005260:Female; D018698:Glutamic Acid / Q000008:administration & dosage*; D006801:Humans; D007273:Injections, Intramuscular; D008297:Male; D008406:Masseter Muscle / Q000187:drug effects*; D010147:Pain Measurement; D012026:Reflex, Stretch / Q000187:drug effects*; D012727:Sex Characteristics; D018709:Statistics, Nonparametric
chemical_list: D018698:Glutamic Acid