Fig. 1

Mechanical static allodynia and hyperalgesia impairment 14 and 28 days after spinal nerve ligation. The mean behavioral score in response to five stimuli applied on the plantar surface of the ipsilateral (A1) and contralateral (B1) hind paw of naïve, sham, and spinal nerve-ligated (SNL) animals at day 0 (D0), day 14 (D14), and day 28 (D28) is plotted against the strength of the applied von Frey hair. Note that the curves of SNL at D14 and D28 for the ipsilateral hind paw are dramatically shifted to the left and to the top compared to D0 (A1). Bar histograms show mean nociceptive threshold (expressed as percentage of naïve values) of the ipsilateral hind paw at D14 (A2) and D28 (A3) and of the contralateral hind paw at D14 (B2) and D28 (B3) as well as the hyperalgesia score of the ipsilateral hind paw at D14 (A4) and D28 (A5) and of the contralateral hind paw at D14 (B4) and D28 (B5). The nociceptive threshold of the ipsilateral hind paw of the SNL rats at D14 and D28 was significantly reduced compared to the ones of the naïve and of the sham rats (A2: Kruskal-Wallis test H(2) = 44.45, p < 0.0001; A3: Kruskal-Wallis test H(2) = 33.79, p < 0.0001). For the contralateral hind paw, the nociceptive threshold of SNL rats was significantly increased at D14 compared to the one of the naïve rats (B2: Kruskal-Wallis test H(2) = 11.87, p = 0.0026) but not at D28 (B3: Kruskal-Wallis test H(2) = 3.95, p = 0.14). The hyperalgesia score (expressed as percentage of naïve values) of the ipsilateral hind paw of the SNL rats at D14 and D28 was significantly increased compared to the ones of the naïve and of the sham rats (A4: Kruskal-Wallis test H(2) = 37.34, p < 0.0001; A5: Kruskal-Wallis test H(2) = 18.30, p = 0.0001). Note that the hyperalgesia score of the ipsilateral hind paw of the sham rats is significantly higher than the one of the naïve rats at D14 (A4). No hyperalgesia was detected on the contralateral hind paw (B4: Kruskal-Wallis test H(2) = 5.36, p = 0.0683; B5: Kruskal-Wallis test H(2) = 1.328, p = 0.51). Post hoc test (Dunn’s multiple comparison test): *p < 0.05; **p < 0.01; ***p < 0.001