The effect of IL-10 on orofacial hyperalgesia associated with masseter inflammation. CFA was injected into the right masseter muscle (M-CFA). At 24 h after CFA, there were significant decreases in the EF50 values at both ipsilateral and contralateral sites, confirming the development of hyperalgesia. IL-10 was injected into the Vi/Vc (A, B) or caudal Vc (C, D) in a volume of 500 nl after establishing behavioral hyperalgesia at 24 h after CFA (time 0). The attenuation of hyperalgesia was observed as a significant increase in EF50s after injection of IL-10. Note that injection of IL-10 into the Vi/Vc transition zone produced bilateral attenuation of hyperalgesia (A, B), injection of IL-10 into the caudal Vc only attenuated hyperalgesia ipsilaterally (C), and injection of IL-10 into either Vi/Vc or Vc did not produce an effect in non-inflamed (Naive) rats. Asterisks denote significant differences between the post-CFA (time 0) and after 1.0 ng IL-10 microinjection (p < 0.05). Pound sign denotes significant difference between the post-CFA (time 0) and after 0.1 ng IL-10 microinjection (p < 0.05). (ANOVA with repeated-measures and post hoc tests).