Abstract
The objective of the present study was to compare the effect of electroacupuncture (EA) and carprofen (CP) on postoperative incisional pain using the plantar incision (PI) model in rats. A 1-cm longitudinal incision was made through skin, fascia and muscles of a hind paw of male Wistar rats and the development of mechanical and thermal hypersensitivity was determined over 4 days using the von Frey and Hargreaves methods, respectively. Based on the experimental treatments received on the third postoperative day, the animals were divided into the following groups: PI+CP (CP, 2 mg/kg, po); PI+EAST36 (100-Hz EA applied bilaterally at the Zusanli point (ST36)); PI+EANP (EA applied to a non-acupoint region); PI+IMMO (immobilization only); PI (vehicle). In the von Frey test, the PI+EAST36 group had higher withdrawal force thresholds in response to mechanical stimuli than the PI, PI+IMMO and PI+EANP groups at several times studied. Furthermore, the PI+EAST36 group showed paw withdrawal thresholds in response to mechanical stimuli that were similar to those of the PI+CP group. In the Hargreaves test, all groups had latencies higher than those observed with PI. The PI+EAST36 group was similar to the PI+IMMO, PI+EANP and PI+CP groups. We conclude that 100-Hz EA at the ST36 point, but not at non-acupoints, can reduce mechanical nociception in the rat model of incisional pain, and its effectiveness is comparable to that of carprofen.
Highlights
Postoperative incisional pain is simultaneously a unique and common form of acute pain
The post hoc Student-Newman-Keuls test showed that the plantar incision (PI)+EAST36, PI+CP, PI+EANP, and PI+IMMO groups were similar and had thermally stimulated paw withdrawal latencies that were significantly higher than those of the PI group at 6, 9, 12, and 24 h after treatment (P < 0.001 for all time points), except for the PI+CP group that was similar to the PI group at 9 h (Figure 1)
The PI+EAST36 and PI+CP groups were similar and showed higher paw withdrawal thresholds at 6, 9, and 12 h after treatment compared to the PI, PI+IMMO and PI+EANP groups
Summary
Postoperative incisional pain is simultaneously a unique and common form of acute pain. Different pathophysiological mechanisms are responsible for the pain caused by inflammation, nerve injury or incision This explains why many treatment strategies are effective only against specific types of pain [3]. An animal model used to study postoperative pain is a 1-cm incision through the skin and muscle of the plantar surface of the rat hind paw [4]. This experimental model is characterized by spontaneous pain, mechanical allodynia and thermal hyperalgesia that lasts for several days, and which corresponds with the time course of postoperative incisional pain in patients [5].
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