Fig. 7.

Effect of application of lidocaine to the subnucleus caudalis on the activity evoked in the ipsilateral jaw muscles by application of glutamate to the TMJ region. Line plots inA illustrate the activity evoked in the ipsilateral digastric and masseter muscles by three applications (solid arrow) of glutamate (2.5 μmol) to the TMJ region from two individual experiments. The second application of glutamate to the TMJ region was preceded by application of either normal saline or lidocaine over the subnucleus caudalis (solid line). Bar graphs indicate the mean ± SE (n = 5) for each application. Note that application of lidocaine, but not normal saline, to the brainstem reversibly blocked glutamate-evoked activity in the ipsilateral digastric and masseter muscles (asterisk, p < 0.05, Student’st test). This result indicates that application of glutamate to the TMJ region evokes activity in the jaw muscles by a reflex pathway through subnucleus caudalis.