Figure 7.

Remifentanil and fentanyl induced a long-lasting reduction in mechanical hindpaw response thresholds. The mean response thresholds to probing with von Frey filaments are plotted at different time points. Animals received a 1 h infusion into the jugular vein (black bars) under deep anesthesia. A, Response thresholds from remifentanil-treated animals (dosing as in Fig. 1A) were significantly reduced compared with baseline at all time points after the infusion. Response threshold for vehicle-treated group (3.4 mg·kg⁻¹·h⁻¹ glycine infusion) remained stable compared with pre-drug level. B, Fentanyl-treated animals (dosing as in Fig. 1B) showed significantly lower thresholds compared with predrug responses at all time points after the infusion. The saline-treated group showed no significant changes after infusion compared with baseline. **p < 0.01, *** p < 0.001.