The effects of electroacupuncture on glutamic acid and expression of NMD receptor on spinal cord of neuropathic pain model rats with chronic constriction injury of the sciatic nerve

Objective To investigate the effect of electroacupuncture(EA) on hyperalgia and glutamic acid (Glu) and expression of NMDA receptor in rats with neuropathic pain. Methods SD rats, healthy and male, were tested the base mechanical pain threshold by dynamic plantar aesthesiometer. After removed the rats with high or low pain threshold, randomly divided into sham operation group ( n = 16 ) and model group ( n = 32) with chronic constriction injury of the sciatic nerve(CCI). After the CCI model of rats was established, the rats divided into model group( n= 16) and EA group( n= 16) continusly. The CCI rats were treated by EA (2Hz, onset 1mA, enhance 1mA each 10 min) on Huan tiao ( GB 30) and Wei zhong ( BL 40) , and the effects of EA was observed by tested the mechanical and thermal pain thresholds. The contents of Glu in spinal cord was tested by HPLC with OPA derivatized, and the expressions of Glu positive neurons, the NR1 and NR2B receptor subunits were measured by immunohistochemistry. Results At 10th day, the mechanical and thermal pain thresholds were reduced on CCI rats markedly, and showed (12.10 ±2.25)g and ( 10.09 ± 1.23) s respectively. There were significantly difference compared with the sham operation group (P<0.01).The contents of Glu was significantly increased (23.66 ±4.37)μmol/mg, and the expressions of Glu positive neurons was reduced markedly in spinal cord(0.16 ±0.01 ) , the significant difference was existed. The expressions of NR1 also increased in spinal cord (0.12 ±0:03) , and existed significantly difference compared with the sham operation group (P < 0.05). After CCI rats treated by 2Hz EA, 7 day, the contents of Glu, the expressions of Glu positive neurons, and NR1 subunits were all significantly reversed in rats with CCI(P<0.01, P<0.05). Same times, the behavior of pain was improved. Conclusion EA could efficaciously inhibited releasing of Glu, and adjusted the function and the conditions of NMDA receptor in related segment of spinal cord. It is the analgesia mechanisms of EA on neuropathic pain in spinal cord. Key words: Neuropathic pain; Electroacupuncture; Spinal cord; Glu; NMDAR