Effects of electroacupuncture on the mechanical allodynia in the rat model of neuropathic pain.

The analgesic effects of acupuncture on the mechanical allodynia in the rat model of neuropathic pain have not yet been studied. The aim of the present study is: first, to determine if electroacupuncture (EA) or morphine attenuates the mechanical allodynia; and secondly, to examine if the EA effect may be mediated by endogenous opioids. To produce neuropathic pain, the right superior caudal trunk was resected between the S3 and S4 spinal nerves. Twenty-one days after the neuropathic surgery, low frequency EA stimulation (2 Hz, 0.3 ms, 0.07 mA) delivered to Houxi (S13) for 30 min relieved significantly the signs of mechanical allodynia. Intraperitoneal (i.p.) morphine (0.5 or 1.5 mg/kg) also relieved the signs of mechanical allodynia in a dose-dependent manner. In addition, the antiallodynic effect of Houxi EA was blocked by pretreatment with naloxone (2 mg/kg, i.p.). However, combined application of EA and morphine did not show an obvious synergistic effect. These results suggest that low frequency EA or morphine can relieve the mechanical allodynia signs and the EA effect can be mediated by endogenous opioid systems.