Figure 4

Effect of noxious electrical and formalin stimulation-induced DNIC on the tail-flick latency. (A, B) Halothane-anaesthetized rats were grouped into sham needles (C), E10 (10× twitch intensity), E20, and E50 (> 50×) electrical stimulation of the right ST36 acupoint. Changes in tail-flick latencies were compared by the "maximal possible effect". Control rats exhibited consistent tail-flick latencies without anesthetic influence. The electrical stimuli produced intensity-dependent analgesia on the tail reflex and showed maximal DNIC effects within the stimulation period. Notably, E50 elicited a strong and long analgesic effect (B). (C, D) A high-dose formalin injection (Fm20) caused a distinct DNIC pattern from E50 stimulation in tail-flick suppression. However, total pain summation (area under the curve) indicated no statistical difference between E50 and Fm20 (D). The horizontal thick bar indicates the electrical stimulating period. Rat numbers: C = 11, E10 = 10, E20 = 11, E50 = 9, Fm20 = 10. * p < 0.05, *** p < 0.001 vs. C; ⁺⁺ p < 0.01, ⁺⁺⁺ p < 0.001 vs. E10; ^# p < 0.05, ^### p < 0.001 vs. E20; one-way ANOVA with Bonferroni's post hoc test.