Figure 8. The increase in nocifensive behaviour induced by a unilateral injection of acid saline is bilateral and is prevented if antagonists of glutamatergic receptors are administered together with the acid solution, but not if they are injected into the contralateral muscle.

Animals received two injections (arrows) of either normal (A) or acidic saline (B) into one of their masseter muscles. von Frey filament 5.18 (load = 15 g) was applied 10× on each side and the number of withdrawals was counted. Means and standard errors are shown. C: Ionotropic glutamate receptor antagonists (APV: 50mM and DNQX: 1mM) were added to the 2^nd injection. D: Metabotropic glutamate receptor antagonists MPEP and MCPG (1mM each) were added to the 2^nd injection. E: DNQX and APV were given contralaterally to the acid saline injection. F: MPEP and MCPG were given contralaterally to the acid saline injection. *, #: significantly different from their respective mean baseline (B1–B3) response.