Fig. 3.  The effect of ketamine (A ), norketamine (B ), and traxoprodil (C ) on mechanical allodynia in the spared nerve injury model of the ipsilateral paw. Squares  represent data from placebo-treated animals; circles , animals treated with N -methyl-d-aspartic acid receptor antagonists; triangles , sham-operated animals. Vertical gray bar  depicts treatment period. On the y-axis, the force used on injured paw with von Frey filaments to induce withdrawal response. Values are presented as mean ± SEM.