Fig. 4.

Digastric muscle activity evoked by repeated applications of EAA receptor agonists to the TMJ region.A, Line plots illustrate the activity evoked in the ipsilateral digastric muscle by three applications (solid arrow) each of glutamate (2.5 μmol), NMDA, AMPA, and kainate (0.5 μmol) in four individual experiments. Relative EMG activity was calculated by normalizing each EMG area bin to the mean of baseline EMG activity before the first injection. B, Bar graphs indicate the mean ± SE (n = 6) for each of the three trials. Note that for glutamate, NMDA, and AMPA, repeated application evoked activity of equal magnitude when compared with the first response (p > 0.05, repeated measures ANOVA). However, the magnitude of digastric muscle responses to repeated applications of kainate progressively decreased (p < 0.05, repeated measures ANOVA), suggesting that a process of desensitization may be occurring.