Objective To observe the effect of electroacupuncture(EA) on pain-ralated behaviors

morphology of hippocampus

concentrations of inflammatory cytokines and expression of ionized calcium binding adapter molecule 1(Iba-1) in dorsal horn of the spinal cord and the hippocampus

and brain-derived neurotrophic factor(BDNF) in hippocampus of rats with knee osteoarthritis(KOA)

so as to explore the mechanism of EA in improving chronic pain of KOA. Methods Forty SD rats were randomly divided into blank group

saline group

model group and EA group

with 10 rats in each group. Monosodium iodoacetate(MIA

80 mg/mL

50 SymbolmApL) was injected into the left knee joint cavity of rats in the model group and EA group to establish the chronic pain model of KOA

while the same volume of normal saline was injected into the left knee joint cavity of rats in the saline group. Rats in the EA group received EA stimulation(2 Hz/100 Hz

1-2 mA) at left “Yanglingquan”(GB34) and “Neixiyan”(EX-LE4) for 15 min

14 d after MIA injection. The treatment was given once daily

5 d as 1 session and 2 sessions of treatment were required. Methanical withdrawl threshold(MWT) and weight-bearing capacity tests on left hind limbs were carried out 1 d before

7 d

14 d

20 d and 26 d after MIA injection. At the 27

(th)

day

rats were sacrificed and HE staining was used to observe the morphology of hippocampal CA1 area. Concentrations of interleukin(IL)-1β and tumor necrosis factor(TNF)-α in the left L3-L5 spinal dorsal horn and hippocampal CA1 area were detected by ELISA

the expressions of Iba-1 in the spinal dorsal horn and hippo-campal CA1 area were detected by immunofluorescence

and the expression of BDNF in left hippocampal CA1 area was detected by Western blot. Results The HE staining results of the hippocampal CA1 area showed reduced number of neurons

unclear cell contour and boundary between nucleus and cytoplasm

and nuclear pyknosis in the model group

which was relatively milder in the EA group. Compared with the blank group

MWT and weight-bearing capacity of rats' left hind limbs

and expression of BDNF protein in hippocampal CA1 area were significantly decreased(P

<

0.01)

while the contents of IL-1β and TNF-α

the expression of Iba-1 in spinal dorsal horn and hippocampal CA1 area were significantly increased(P

<

0.01) in the model group. In comparison with the model group

MWT and weight-bearing capacity of rats' left hind limbs

and protein expression of BDNF in hippocampal CA1 area were significantly increased(P

<

0.01)

while the contents of IL-1β and TNF-α

and the expression of Iba-1 protein in spinal dorsal horn and hippocampal CA1 area were significantly decreased after EA intervention(P

<

0.01). Conclusion EA at GB34 and EX-LE4 can alleviate the pain-related behaviors of KOA rats. The mechanism might be related to the inhibition of inflammatory reaction mediated by microglia in spinal dorsal horn and hippocampus

and the up-regulation of BDNF expression in hippocampus.