Fig. 2

Induction of mechanical allodynia in WT and σ2R^−/− mice. Chronic constriction injure (CCI) of the sciatic nerve caused neuropathic pain in mice. The paw withdrawal thresholds of the contralateral and ipsilateral paw of the wild-type (WT; left panel) and knockout (KO; right panel) mice were measured before (indicated as 0) and 1, 4, 7, and 12 days after surgery. The force (in grams) at which the mice withdrew their paws in response to von Frey hair stimulation was determined as an index of mechanical allodynia. All data are presented as the mean ± SEM of six mice. * Indicates significantly different compared to the nociceptive threshold of the sham-operated control group on day 0 (7th after surgery); p < 0.05. Lower panels: the effect of the σ1R antagonist S1RA on the mechanical allodynia displayed by WT and σ2R^−/− mice. Antiallodynic compound was administered icv 7 days after surgery, and the nociceptive threshold was evaluated at the indicated post-injection intervals (in minutes). The dashed line indicates the typical nociceptive threshold obtained of the contralateral paw. * Indicates significantly different compared to the ipsilateral paw; all data were analyzed by pairwise Holm-Sidak multiple comparison tests following ANOVA; p < 0.05