Effect of CCI on mechanical pain thresholds in LEW, FIS and WIS rats. The paw withdrawal response to mechanical stimulation of the right hind paw was measured in Lewis (LEW), Fischer (FIS) and Wistar (WIS) rats before and after CCI surgery. For up to 14 days neuropathic pain behavior was less prominent in LEW than in FIS rats. In comparison with the control strain (WIS), LEW was less sensitive in the early phase after nerve injury (d4), whereas FIS showed enhanced sensitivity later on at day 14. Data are shown as mean ± s.e.m. Asterisks represent a significant difference between the LEW and the FIS strain for the individual time point (*p < 0.05, **p < 0.01, ***p < 0.001). #indicates a significant difference between LEW or FIS and WIS (#p < 0.05, ###p < 0.001).