Time course of pain-related behaviour in repeatedly injected animals. Thresholds for primary mechanical hyperalgesia assessed at the ipsilateral knee joint were reduced in all blood or blood compartment injected animals compared to those injected with saline (A), arrows indicate the injections for all displayed data), while secondary hyperalgesia obtained from the contralateral knee joint did not show differences between groups (B). The relative weight resting on the injected hindlimb was slightly, yet non-significantly reduced in all groups receiving blood or blood components (C). The guarding score indicating pain- and inflammation-related gait disturbances was significantly increased in all groups, but most prominently in those animals receiving whole blood injections (D). Knee joint histology from different time points is displayed in (E) to (H). For comparison, a naïve joint without injections is shown in (E), while joints that received three, five or eight injections, displaying increasing signs of inflammatory changes in the joint space and in surrounding tissues, are shown in (F), (G) and (H), respectively. Pictures in the lower panel are magnifications of the indicated inset in the upper panel. Arrows indicate the (mild) inflammatory changes and intra-articular blood cells. Scale bars are 500 μm. Data are presented as means ± SEM. Data of those animals receiving saline in lithium-heparin which were included in the statistical analysis are not displayed in the figure for clarity. * P <0.05; ** P <0.01; *** P <0.001. BL, baseline; SEM, standard error of the mean; WB, whole blood.
Boettger et al. Arthritis Research & Therapy 2013 15:R148 doi:10.1186/ar4331