Anti-hyperalgesic effect of electroacupuncture in a model of post-incisional pain in rats

Abstract

Electroacupuncture has been proposed to be a low cost and practical method that allows effective pain management with minimal collateral effects. In this study we have examined the effect of electroacupuncture against the hyperalgesia developed in a model of postincisional pain in rats. A 1-cm longitudinal incision was made through the skin and fascia of the plantar region of the animal hind paw. Mechanical hyperalgesia in the incision was evaluated 135 min after the surgery with von Frey filaments. The tension threshold was reduced from 75 g (upper limit of the test) to 1.36 ± 0.36 g (mean ± SEM) in control rats. It is shown that a 15-min period of electroacupuncture applied 120 min after surgery to the Zusanli (ST36) and Sanyinjiao (SP6) points, but not to non-acupoints, produces a significant and long-lasting reduction of the mechanical hyperalgesia induced by the surgical incision of the plantar surface of the ipsilateral hind paw. The tension threshold was reduced from 75 to 27.6 ± 4.2 g in animals soon after the end of electroacupuncture. The mechanical threshold in this group was about 64% less than in control. Electroacupuncture was ineffective in rats treated 10 min earlier with naloxone (1 mg/kg, ip), thus confirming the involvement of opioid mechanisms in the antinociceptive effects of such procedure. The results indicate that post-incisional pain is a useful model for studying the antihyperalgesic properties of electroacupuncture in laboratory animals.

High-frequency electroacupuncture versus carprofen in an incisional pain model in rats

“…These results are consistent with those of Oliveira and Prado (11), who reported that 15 min of EA at 4 Hz at the Zusanli (ST36) and Sanyinjiao (SP6) acupoints reduced mechanical hyperalgesia in the same pain model. Both studies provide positive results, although there are important differences in the experimental protocols: the frequency of electric stimulation (100 Hz vs 4 Hz), combination of points (ST36 vs ST36 + SP6), time of stimulation (20 vs 15 min), type of restraint (immobilization vs light halothane anesthesia), and time after surgery when the stimulus was applied (third day vs 2 h).…”

“…In the present study, all treatments were applied on the third day after surgery when the mechanism of hypersensitivity is well established, and mechanical and thermal hyperalgesia is maximal (5). Oliveira and Prado (11) studied the effect of EA in the early stages of hyperalgesia (2 h after the surgery) when sensitization mechanisms are being generated (4). Due to the positive results of both studies (with EA performed either 2 h or on the 3rd day after surgery), we can speculate that EA at acupoints possibly reduces the mechanisms responsible for the generation and maintenance of induced hyperalgesia in the incisional pain model.…”

“…The effect of acupuncture on postoperative pain has been studied clinically and experimentally. Although clinical results have been contradictory (9), experimental data clearly demonstrate that EA can produce potent analgesic effects in models of acute or chronic inflammatory pain (10,11). Oliveira and Prado (11) have shown that a 15-min period of low-frequency EA applied 120 min after surgery to the Zusanli (ST36) and Sanyinjiao (SP6) points, but not to non-acupoints, can reduce mechanical hyperalgesia in the plantar incisional (PI) pain model.…”

“…Although clinical results have been contradictory (9), experimental data clearly demonstrate that EA can produce potent analgesic effects in models of acute or chronic inflammatory pain (10,11). Oliveira and Prado (11) have shown that a 15-min period of low-frequency EA applied 120 min after surgery to the Zusanli (ST36) and Sanyinjiao (SP6) points, but not to non-acupoints, can reduce mechanical hyperalgesia in the plantar incisional (PI) pain model. In the present study, we assessed the efficacy of high-frequency EA applied on the third day after surgery in reducing mechanical and thermal hyperalgesia induced by PI in rats, and compared it to the anti-inflammatory drug CP, commonly prescribed to relieve postoperative pain.…”

Electroacupuncture analgesia in dogs: is there a difference between uni- and bi-lateral stimulation?

“…1986). In a similar study, EA at the acupoints ST36 and SP6 produced analgesia in the hind limbs of rats (Oliveira & Prado 2000). These differences may be produced by the pain inhibitory system activated in each situation (Bossut et al.…”