Glutamate-induced temporomandibular joint pain in healthy individuals is partially mediated by peripheral NMDA receptors.
OBJECTIVE
To determine if glutamate injected into the healthy temporomandibular joint (TMJ) evokes pain through peripheral N-methyl-D-aspartate (NMDA) receptors and if such pain is influenced by sex or sex steroid hormones.


METHODS
Sixteen healthy men and 36 healthy women were included and subjected to two randomized and double-blind intra-articular injections of the TMJ. Experimental TMJ pain was induced by injection of glutamate (1.0 mol/L) and NMDA block was achieved by co-injection of the NMDA antagonist ketamine (10 mmol/L). The TMJ pain intensity in the joint before and during a 25-minute postinjection period was continuously recorded on an electronic visual analog scale (0 to 10). Estradiol, progesterone, and testosterone levels in serum were analyzed.


RESULTS
Glutamate-induced pain showed a median (25/75 percentile) duration of 8.3 (5.2/12.2) minutes. The peak pain intensity was 6.1 (4.2/8.2), the time to peak was 50 (30/95) seconds, and the area under the curve was 59 (29/115) arbitrary units. The women reported higher maximum pain intensity than the men and shorter time to peak. The sex hormone levels were not significantly related to the glutamate-induced TMJ pain. NMDA block significantly reduced the glutamate-induced TMJ pain, mainly in the women. There were no significant correlations between sex hormone levels and the effects of NMDA block for any pain variable.


CONCLUSIONS
Glutamate evokes immediate pain in the healthy human TMJ that is partly mediated by peripheral NMDA receptors in the TMJ.
Alstergren
Per
P
Karolinska Institutet, Institute of Odontology, Box 4064, 141 04 Huddinge, Sweden. per.alstergren@ki.se
Ernberg
Malin
M
Nilsson
Mikael
M
Hajati
Anna-Kari
AK
Sessle
Barry J
BJ
Kopp
Sigvard
S
D000328:Adult; D019540:Area Under Curve; D004311:Double-Blind Method; D004958:Estradiol / Q000097:blood; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018846:Excitatory Amino Acids / Q000008:administration & dosage / Q000009:adverse effects*; D005157:Facial Pain / Q000139:chemically induced*; D005260:Female; D005500:Follow-Up Studies; D018698:Glutamic Acid / Q000008:administration & dosage / Q000009:adverse effects*; D012739:Gonadal Steroid Hormones / Q000097:blood; D006801:Humans; D007270:Injections, Intra-Articular; D007649:Ketamine / Q000494:pharmacology; D008297:Male; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology; D011374:Progesterone / Q000097:blood; D016059:Range of Motion, Articular / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000187:drug effects*; D012737:Sex Factors; D013705:Temporomandibular Joint Disorders / Q000139:chemically induced*; D013739:Testosterone / Q000097:blood; D055815:Young Adult
D018691:Excitatory Amino Acid Antagonists; D018846:Excitatory Amino Acids; D012739:Gonadal Steroid Hormones; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D013739:Testosterone; D011374:Progesterone; D004958:Estradiol; D007649:Ketamine