Objective To observe the effect of electroacupuncture(EA) on the expression of lumbar spinal κ-opioid receptor(KOR) and Toll-like receptor 4(TLR4) in microglia in neuropathic pain rats

so as to explore the role of cross-talk between KOR and TLK4 in EA-induced alleviation of chronic neuropathic pain. Methods Wistar male rats were randomized into control

model

EA and EA plus KOR inhibitor(EA+inhibitor) groups(n=18 in each group). The neuropathic pain model was established in rats by ligature of the right sciatic nerve. EA was applied at bilateral “Zusanli”(ST36) and “Yanglingquan”(GB34) for 30 min

once daily for 5 days. JDTic dihydrochloride(a KOR inhibitor) was administrated by intraperitoneal injection before EA intervention. The difference value of paw withdrawal thermal latency(PWLD) of the bilateral hind-limbs was used as the thermal pain reaction level. At the end of experiments

the rat's lumbar spinal cord(L2—L4) was taken for detecting the expression of CD68 mRNA(a marker of the activated microglia) and Iba-1(a marker for the activated and resting microglia) immunoactivity

and dynorphin content

and KOR mRNA and TLR4 protein(in immunomagnetic microbead method separated microglia) by using fluorescence quantitative PCR

immunofluorescence

radioimmunoassay and Western blot

separately. Results Compared with the control group

a strong thermal hyperalgesia was induced

the expression levels of Iba-1 and CD68 mRNA in the spinal cord

TLR4 protein of the spinal microglia were significantly increased(P<0.01) in the model group. The microglia were characterized by somatic hypertrophy and thickened branches in the model group. After EA intervention

the PWLD

the expression of Iba-1

CD68 mRNA and TLR4 protein of the microglia were significantly decreased(P<0.05)

while the content of spinal dynorphin and the expression of KOR mRNA of the microglia increased in the EA group relative to the model group(P<0.05). The hypertrophic microglia shrinked slightly in the EA group. After injection of KOR inhibitor

the PWLD and expression levels of Iba-1

CD68 mRNA and TLR4 protein were significantly increased(P<0.05)

and the expression of KOR mRNA was significantly decreased(P<0.05) in the EA+inhibitor group in comparison with the EA group. Conclusion The analgesia effect of EA may partly mediated by spinal microglial KOR and the activation of KOR of microglia may be a target for inhibition of microglial TLR4-induced pro-inflammatory signaling.