The effect of IL-10 on orofacial hyperalgesia associated with cutaneous inflammation. CFA was injected into the skin site overlying the right masseter muscle (S-CFA). At 24 h after CFA (time 0), there were significant decreases in the EF50 values ipsilateral to CFA injection (A, C), confirming the development of inflammatory hyperalgesia. There was no hyperalgesia developed at the contralateral site (B, D). IL-10 (1.0 ng) 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. The attenuation of hyperalgesia was observed as a significant increase in EF50s after injection of IL-10. Injection of IL-10 into the Vi/Vc transition zone (A) did not attenuate cutaneous hyperalgesia. Injection of IL-10 into the caudal Vc (C) attenuated hyperalgesia, compared to saline (vehicle)-injected rats. 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 < 0.01). (ANOVA with repeated-measures and post hoc tests).