Nociceptive behaviour. Nociception induced by movement and loading in control and collagenase-injected rats evaluated by the Knee-Bend and CatWalk tests. Knee-Bend score (A-C) is presented for both ipsilateral and contralateral knees of saline-injected control rats (A), and rats injected with 250 U (B) or 500 U (C) of collagenase. CatWalk data (D, E) are expressed as the percentage of total ipsilateral paw print intensity (%TIPPI). Collagenase-injected animals present increased movement- and loading-induced nociception. The number of animals per group at each time-point is indicated below the graphs. An initial number of 24 animals was used in each group. Animals were then sacrificed at different time-points for histopathology (one, two, four and six weeks; n = 6 per dose and per time-point). Mean ± SEM, two-way ANOVA followed by Bonferroni post-hoc test for comparisons between groups at each time-point. #P <0.05, ###P <0.001, for comparisons between control and the 250 U collagenase group; *P <0.05, ***P <0.001, for comparisons between control and the 500 U collagenase group.