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. 2010 Mar 19;17(1):19. doi: 10.1186/1423-0127-17-19

Figure 1.

Figure 1

Weighted pain score [24,25]of a formalin injection in the hind limb. (A) An i.m. injection of 100 μl of 5% (Fm5), 10% (Fm10), or 20% (Fm20) formalin in the anterior tibial muscle induced dose-dependent pain scores and a biphasic pain pattern similar to that of a subcutaneous plantar injection (2%, 50 μl, Fp). The Fm20 group had a lower pain score in the early phase and fewer flinch responses for the entire period compared to the Fp group. However, the Fp and Fm20 groups had similar highest pain scores in the late phase. (B) The Fm20 group showed no statistical difference in the cumulative pain score from that of the Fp group, indicating the muscular injection with 100 μl of 20% formalin resulted in a strong noxious reaction. Rat numbers: Fp = 9, Fm5 = 7, Fm10 = 6, Fm20 = 7. ** p < 0.01 vs. Fp; + p < 0.05, ++ p < 0.01 vs. Fm5; one-way ANOVA with Bonferroni's post hoc test.