Fig. 5.

Effects of opioid receptor antagonists on the analgesic effect of 2-Hz SCS. A1, A2 CTOP (3 and 10 μg), an MOR-specific antagonist, significantly attenuates the analgesic effect. B1, B2 NTI (3 and 10 mg/kg), a DOR-specific antagonist, does not affect the analgesic effect. C1, C2 Nor–BNI (5.74 and 22.96 μg), a KOR-specific antagonist, significantly reduces the analgesic effect. Pre-SCS, 50% PWT at 0 min in A1, B1, and C1; Dur-SCS, mean 50% PWT at 15 and 30 min in A1, B1, and C1; Post-SCS, 50% PWT at 60 min in A1, B1, and C1. Repeated ANOVA with Dunnett's multiple comparisons test; *P < 0.05, **P <0.01, ***P < 0.001 vs Pre-SCS; ^#P < 0.05, ^##P < 0.01, ^###P < 0.001 vs Dur-SCS in the SCS + Veh group. CTOP, D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH₂; NTI, naltrindole; Nor-BNI, nor-binaltorphimine.