Fig. 5. The line and scatter plots show the effect of substance injection on masseter muscle blood flow. Baseline blood flow was determined approximately 5 min before injection of substances at time 0. Isotonic saline (squares), which was injected into the right masseter muscle, did not significantly affect muscle blood flow in any of the experiments. Injection of glutamate (A ) or dextrose (B ) into the left masseter muscle significantly increased blood flow. (C ) Coinjection of kynurenate with glutamate into the left masseter muscle attenuated glutamate-induced increased blood flow. (D ) Coinjection of lidocaine (74 mm) with glutamate also attenuated glutamate-induced increased blood flow. (E ) Coinjection of lidocaine (74 mm) with dextrose into the left masseter muscle substantially decreased dextrose-induced increased blood flow. Bars = SD; *P < 0.05, repeated-measures analysis of variance, Dunnett method.