Figure 3.

Morphine-induced exacerbation of pain behaviour is not accompanied by greater joint pathology at 14 or 21 days after model induction A. AUC analysis of pain behaviour time course from study 2 (see Fig. 1B for timeline) confirmed the morphine-induced exacerbation of MIA-induced changes in weight-bearing asymmetry (A and C) and PWTs (B and D) at day 21. % change in weight-bearing asymmetry or log(PWTs) was calculated by comparing AUC data from each group with saline/saline–treated animals, with 0% representing no difference in value. Data are presented as mean ± SEM, n = 6/group. **P < 0.01, ****P < 0.0001. One-way ANOVA with the Tukey multiple comparison post hoc test. (E). At D14, mean combined cartilage damage scores were higher for both the saline/MIA and morphine/MIA groups compared with the saline/saline group, *P < 0.05 vs saline/saline, Kruskal-Wallis test with the Dunn multiple comparison post hoc test. (F) Similarly, mean combined cartilage damage scores were higher for both the saline/MIA and morphine/MIA groups compared with the saline/saline and morphine/saline groups at D21 (P < 0.05 vs saline-treated controls, 2-way ANOVA with the Tukey multiple comparison post hoc test), with no significant difference between saline/MIA and morphine/MIA at either D14 or D21. ANOVA, analysis of variance; AUC, area under the curve; MIA, monosodium iodoacetate; PWT, paw withdrawal threshold.