Figure 1.

Behavioral assessment of hyperalgesia after peripheral inflammation with complete Freund’s adjuvant (CFA). Rats were unilaterally injected with 150 μL of 1:1 saline:CFA emulsion and behavioral characterization of several sensory modalities was performed. (A) Inflammation caused significant edema lasting at least 28 days; **, P < .01; 2-way ANOVA followed by Holm-šidák. (B) Thermal sensitivity was evaluated using radiant thermal stimuli. Significantly reduced withdrawal latencies occurred for the inflamed paw which resolved completely by 14 days. (C) Mechanical sensitivity was recorded as the threshold response to von Frey filament testing. Inflammation reduced mechanical force necessary to induce withdrawal and this effect largely resolved after 28 days. (D) Evoked guarding behavior was stimulated by plantar pinprick. No guarding occurred at baseline, but in inflamed animals prolonged guarding lasted at least 21 days. (E) Spontaneous guarding behavior and weight bearing was assessed by observation of the animals while standing on a wire mesh grid. Behavioral scores were assigned in 6 consecutive 10-second epochs. 0, normal weight bearing; 1, partial weight bearing; 2, no weight bearing; 3, spontaneous nocifensive behavior (licking, quivering, or excessive guarding). Animals showed significantly more spontaneous guarding on the inflamed paw for at least 2 weeks. Error bars show standard error of the mean (A, B) or standard deviation (C, D). Significance testing was performed using 2-way ANOVA (A, B), multiple Mann-Whitney U-tests (C, E), or exact binomial test (D). For all results, Holm-šidák corrections were made to account for multiple comparisons; *, P < .05; **, P < .01.