Figure 5

Capsaicin alleviates the nociceptive hypersensitivity induced by peripheral inflammation or nerve injury. (A) Intraplantar injection of 100 μg capsaicin could reduce the mechanical allodynia 2 days after CFA injection (n = 12 for vehicle, n = 9 for 50 μg capsaicin treatment and n = 11 for 100 μg capsaicin treatment). The significant analgesic effect of 100 μg capsaicin began 2 h after capsaicin injection and maintained for 24 h, while 50 μg showed a shorter analgesic effect (p < 0.05 for 50 μg and p < 0.001 for 100 μg capsaicin versus vehicle group, ANOVA). (B) Whole-cell patch-clamp recording showed that puffing 2 μM capsaicin for 30 s, the action potential frequency was totally suppressed after 5 min washout in small DRG neurons dissociated from rats injected CFA for 2 days. ***p < 0.001, versus the same group of neurons before capsaicin treatment (n = 11). (C) Intraplantar injection of 100 μg capsaicin could mildly reduce mechanical allodynia 7 days after SNI (n = 8 for vehicle and n = 9 for capsaicin treatment) (p < 0.01 for 100 μg capsaicin versus vehicle group, ANOVA). (D) Whole-cell patch-clamp recording showed that treatment with 2 μM capsaicin for 30 s almost totally suppressed the action potential firing after 5 min washout in small DRG neurons dissociated from rats on post-SNI day 7. ***p < 0.001, versus the same group of neurons before capsaicin treatment (n = 17). Data are shown as mean ± SEM.