Manual acupuncture inhibits mechanical hypersensitivity induced by spinal nerve ligation in rats

Manual acupuncture (MA) has presented analgesic activity against neuropathic pain in patients and animal models, yet a series of questions remain: Is MA effectiveness dependent of acupoint selection or combination? Is it equally efficient when treatment starts on the initial (acute) or sub-chronic phase of spinal nerve ligation (SNL)-induced neuropathy? Is MA effect related to the release of endogenous opioids? Does MA produce similar effects to gabapentin? To answer these questions rats submitted to the L5/L6 SNL injury were treated with unilateral MA (ST36 (Zusanli), SP6 (Sanyingjiao) or ST36+SP6 acupoint stimulation); or with gabapentin (30 mg/kg i.p., used as positive control). Both acupoints have been demonstrated to present analgesic activity and are used in clinical practice and basic science research. In addition, we investigated the influence of naloxone (1 mg/kg i.p., a nonselective opioid receptor antagonist) on MA treatment and also the effect of unilateral ST36+SP6 MA treatment beginning acutely (5 days) or sub-chronically (14 days) after SNL. Our results demonstrate that single or combined unilateral stimulation was able to reduce mechanical hypersensitivity with treatment beginning in both acute and sub-chronic phases of SNL-induced neuropathy; MA effect was blocked by naloxone, and finally; SP6+ST36 MA presented similar effect to gabapentin (30 mg/kg). In conclusion, our results demonstrate, for the first time, that unilateral MA (ST36, SP6 or ST36+SP6) reduces hypersensitivity induced by the SNL with effect dependent of the opioid system and comparable with the one obtained with gabapentin (used as positive control).