title: Glutamate-evoked pain and mechanical allodynia in the human masseter muscle.
abstract: The present study examined the effect of peripheral administration of the excitatory amino acid (EAA) glutamate on the intensity of perceived pain and pressure pain thresholds (PPTs) in healthy young women (n=17) and men (n=18). Two injections separated by 25 min of 0.2 ml, 1.0M glutamate into the masseter muscle produced significantly higher scores of pain on 0-10 cm visual analogue scales (VAS) in women than in men (analysis of variance, ANOVA: P<0.001). There was no significant difference between the VAS scores for the first and the second injections in either men or women. The PPTs determined in the masseter muscle were significantly reduced following the first injection and further significantly reduced after the second injection (ANOVA: P<0.001). Furthermore, the PPTs were reduced to a similar extent in both women and men (maximum 44-56%), suggesting that gender did not influence the process of sensitization. There were no significant difference in VAS scores or PPTs between women taking oral contraceptives (n=9) and those who did not (n=8) (ANOVAs: P=0.709, P=0.153). It is concluded that the VAS scores produced by intramuscular administration of 1.0M glutamate may reflect a gender-dependent activation of nociceptive pathways which, in part, may be mediated through peripheral EAA receptors. The reduction of PPTs in the masseter muscle following administration of glutamate in a concentration of 1.0M may reflect allodynia to mechanical stimuli. This process of sensitization was not gender-dependent. The present results suggest that injection of 1.0M glutamate into the masseter muscle may provide a useful experimental method to test sensitization and efficacy of peripheral EAA receptor antagonists in human subjects.
authors.affiliation: Department of Clinical Oral Physiology, Dental School, Aarhus University, DK-8000 Aarhus C, Denmark Orofacial Pain Laboratory, Center for Sensory-Motor Interaction, Aalborg University, DK-9220 Aalborg, Denmark Department of Maxillofacial Surgery, Aalborg Hospital, DK-9000 Aalborg, Denmark Department of Anesthesia, Harvard Medical School/Children's Hospital, Boston, MA 02115, USA Faculty of Dentistry, The University of Toronto, Toronto, Ontario, Canada M5G 1G6.
authors.forename: Peter
authors.initials: P
authors.lastname: Svensson
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: Thomas
authors.initials: T
authors.lastname: Graven-Nielsen
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Sessle
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D018846:Excitatory Amino Acids; D005260:Female; D018698:Glutamic Acid; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000503:physiopathology*; D010146:Pain / Q000139:chemically induced / Q000145:classification / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D010812:Physical Stimulation; D011930:Reaction Time; D012727:Sex Characteristics; D013997:Time Factors
chemical_list: D018846:Excitatory Amino Acids; D018698:Glutamic Acid