The Effect of Glutamate-Evoked Masseter Muscle Pain on the Human Jaw-Stretch Reflex Differs in Men and Women

Aims: 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 glutumate-evoked pain inten-sity 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. Conclusion: These results suggest that there is a significant sex-related difference in human jaw-stretch reflex responses and their modulation by painful stim-uli. 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.

glutamate; jaw-stretch reflex; masticatory muscle; sex differences; trigeminal pain mechanisms

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