Research papersGlutamate-evoked pain and mechanical allodynia in the human masseter muscleSvensson, Petera,b,c,∗; Cairns, Brian Ed; Wang, Kelunb; Hu, James We; Graven-Nielsen, Thomasb; Arendt-Nielsen, Larsb; Sessle, Barry JeAuthor Information aDepartment of Clinical Oral Physiology, Dental School, Aarhus University, DK-8000 Aarhus C, Denmark bOrofacial Pain Laboratory, Center for Sensory–Motor Interaction, Aalborg University, DK-9220 Aalborg, Denmark cDepartment of Maxillofacial Surgery, Aalborg Hospital, DK-9000 Aalborg, Denmark dDepartment of Anesthesia, Harvard Medical School/Children's Hospital, Boston, MA 02115, USA eFaculty of Dentistry, The University of Toronto, Toronto, Ontario, Canada M5G 1G6 ∗Corresponding author. Tel.: +45-8942-4191; fax: +45-8619-5665 E-mail: [email protected] Submitted August 13, 2001; revised February 19, 2002; accepted March 14, 2002. Pain: February 2003 - Volume 101 - Issue 3 - p 221-227 doi: 10.1016/S0304-3959(02)00079-9 Buy Metrics 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, 1.0 M 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 1.0 M 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 1.0 M may reflect allodynia to mechanical stimuli. This process of sensitization was not gender-dependent. The present results suggest that injection of 1.0 M glutamate into the masseter muscle may provide a useful experimental method to test sensitization and efficacy of peripheral EAA receptor antagonists in human subjects. © 2003 Lippincott Williams & Wilkins, Inc.