Objective To observe the effect of different intensities of manual acupuncture(MA)stimulation on mechanical pain thresholds(PTs)and the expression of phosphorylated extracellular signal-regulated kinases(p-ERK)in lumbar spinal dorsal horn regions in rats with neuropathic mirror-image pain

so as to explore its mechanisms underlying analgesia.MethodsForty male SD rats were equally and randomly divided into control

spinal nerve ligation(SNL)model

mild MA-stimulation

and strong MA-stimulation groups.Neuropathological pain model was established by ligature of the spinal nerve(L 5).Three days after the SNL

bilateral"Huantiao"(GB 30)were stimulated by rotating the thin(0.22mm×13mm)or thick(0.3mm×13mm)filiform needles at a frequencies of 60times/min or 180times/min and at an angle of 180°or 360°for 2min for rats in the mild and strong MA-stimulation groups

respectively

followed by remaining the needle in place for 30min.The mechanical PTs were measured before and after SNL.The expression of p-ERK protein in bilateral dorsal horn regions of the lumbar spinal cord(L 4-L 6)was detected by Western blot.Results In comparison with the control group

the mechanical PTs were significantly decreased beginning from the 3rd day on after SNL on the affected side and from the 7th day on after SNL on the healthy hindpaw(P<0.05)

simultaneously

p-ERK protein expression levels of dorsal horn regions on both sides of the spinal cord were considerably up-regulated on the 12th day(P<0.05).Compared with the model group

the PTs of the affected hindpaw and the healthy hindpaw were significantly increased on the 7th and 12th day in the strong MA-stimulation group(P<0.05

P<0.01)

whereas pERK expression levels in the bilateral spinal dorsal horn regions were obviously down-regulated in the strong MA-stimulation group(P<0.05).No significant differences were found between the model and mild MA-stimulation groups in the PTs of bilateral hindpaws and p-ERK expression levels of the bilateral spinal dorsal horn regions(P>0.05)except the PTs of the healthy hindpaw on 7th day(P<0.05).Conclusion Strong MA-stimulation can alleviate neuropathic mirror-image pain in SNL rats

which is closely related to its effect in down-regulating the expression of p-ERK in the bilateral spinal dorsal horn regions.