EVIDENCE THAT EXCITATORY AMINO-ACID RECEPTORS WITHIN THE TEMPOROMANDIBULAR-JOINT REGION ARE INVOLVED IN THE REFLEX ACTIVATION OF THE JAW MUSCLES

Mle have previously shown that injection of the inflammatory irritant and small-fiber excitant mustard oil (MO) into the temporomandibular j oint (TMJ) region can reflexively induce a prolonged increase in the a ctivity of both digastric and masseter muscles in rats. It is possible that peripheral excitatory amino acid (EAA) receptors play a role in this effect, because MO-evoked increases in jaw muscle activity are at tenuated by preapplication of the noncompetitive NMDA receptor antagon ist MK-801 into the TMJ region. In the present study the EAA receptor agonists glutamate, NMDA, kainate, and AMPA were applied locally to th e TMJ region, Jaw muscle responses similar to those evoked by MO appli cation to the TMJ region were achieved with glutamate, NMDA, AMPA, and kainate. Repeated application of glutamate, NMDA, or AMPA at interval s of 30 min evoked responses in the ipsilateral jaw muscles that were of comparable magnitude, cc-application of the NMDA receptor antagonis t DL-2-amino-5-phosphonovalerate (0.5 mu mol) significantly reduced th e magnitude of the glutamate- and NMDA-evoked ipsilateral jaw muscle r esponses without affecting responses evoked by AMPA. In contrast, co-a pplication of the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxal ine-2,3-dione (1 nmol) significantly reduced the magnitude of the glut amate- and AMPA-evoked ipsilateral jaw muscle responses without affect ing responses evoked by NMDA. This evidence suggests that both NMDA an d non-NMDA EAA receptor types are located within the TMJ region and ma y contribute to jaw muscle activity that can be reflexively evoked fro m the TMJ region.