Effect of a prolonged (4 h) remifentanil infusion at a constant rate of 120 mg/kg/h on nociceptive thresholds. (A) The thermal thresholds measured by plantar test (n = 8). (B) The mechanical thresholds determined by Randall-Selitto test (n = 11). The data are presented as the mean ± SEM. *P < 0.05 vs. baseline (one-way ANOVA followed by Dunnett’s test).