Effect of electroacupuncture on the expression of Iba-1 in spinal dorsal horn and hippocampus of chronic pain rats with knee osteoarthritis

Abstract

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. 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 μL) 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 27th 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. 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). 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.