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. 2022 Jan 27;163(10):1999–2013. doi: 10.1097/j.pain.0000000000002596

Figure 2.

Figure 2.

Lysophosphatidylcholine injections into mouse ankle joints produce long-lasting pain-like behaviors associated with anxiety-related behaviors. (A) Timeline of the experimental procedures used. (B) Effect of intra-articular ankle injections of LPC16:0 (10 nmol), CFA or vehicle (Veh) on mechanical allodynia in male mice. Ipsilateral mechanical paw withdrawal threshold was assessed using the up and down method with von Frey filament from D1 to D28. Results are expressed as 50% mechanical threshold (n = 8-16 mice per group; ****P < 0.0001 for Veh vs CFA; ###P < 0.001 and ####P < 0.0001 for Veh vs LPC16:0; &&P < 0.01 and &&&&P < 0.0001 for CFA vs LPC16:0; 2-way ANOVA followed by a Tukey post hoc test). (C) Effect of intra-articular injections of LPC16:0 (10 nmol), CFA or vehicle on weight-bearing in male mice. Results are expressed as the weight ratio between the ipsilateral and contralateral hind paws (n = 8 mice per group; ****P < 0.0001 for Veh vs CFA; ###P < 0.001 and ####P < 0.0001 for Veh vs LPC16:0; &&P < 0.01, &&&P < 0.001, and &&&&P < 0.0001 for CFA vs LPC16:0; 2-way ANOVA followed by a Tukey post hoc test). (D) The autotaxin inhibitor S32826 (ATXi) was co-injected at the dose of 10 nmol with LPC16:0 (10 nmol, I1) and mechanical paw withdrawal thresholds were assessed from 30 to 240 minutes post injection (n = 8 mice per group, *P < 0.05 and ****P < 0.0001, 2-way ANOVA followed by a Tukey post hoc test). (E) S32826 was injected at D10, ie, after the 2 injections of LPC16:0 (10 nmol) 5 days apart (I1/I2), in the same ankle joint, and mechanical paw withdrawal thresholds were assessed at 30 and 60 minutes post injection (n = 8 per group, *P < 0.05 and ****P < 0.0001, 2-way ANOVA followed by a Tukey post hoc test). (F–G) Effect of intra-articular injections of LPC16:0 (10 nmol), CFA or vehicle on the time spent in the center of an open field test at D20 (F) and on the time spent in the open arms in the elevated plus maze test at D23 (G). The open field and elevated plus maze test lasted 5 minutes and the time spent in the center and the open arms, respectively, was automatically calculated using Ethovision XT 13 (Noldus). One-way ANOVA followed by Tukey post hoc tests with **P < 0.01, ***P < 0.001, and ***P < 0.0001 (n = 8 mice per group). ANOVA, analysis of variance; CFA, complete Freund adjuvant; LPC, lysophosphatidylcholine.