Effect of electroacupuncture on P2X3 receptor expression in spinal cord of rats with neuropathic pain

Objective To investigate the effect of electroacupuncture(EA) on P2X3 receptor expression in the spinal cord of rats with neuropathic pain (NP).Methods Sixty healthy male Sprague Dawley (SD) rats weighing 180 g-220 g were randomly divided into 6 groups (n=10 each):sham operation group (Sham group),CCI group,CCI+2Hz-Acupoint-EA (LEA group),CCI+ 15Hz-Acupoint-EA (HEA group),CCI +2Hz-Nonacupoint-EA (NA-LEA group); CCI + 15Hz-Nonacupoint-EA (NA-HEA group).Chronic constriction injury (CCI) was induced by exposing the right sciatic nerve and placing 4 ligatures on the sciatic nerve at 1 mm intervals with 4-0 silk thread.In sham operation group the right sciatic nerve was exposed but not ligated.Electrical stimulation at acupoints was performed at Zusanli (ST36) and Yanlingquan (GB34) once a day from 4th day after CCI to the successive 6 days (30 mir/d).Nonacupoints were performed 5 mm nearby the acupoints of Yanglingquan and Zusanli.EA variables were set as alternating strings of continues frequency (2 Hz or 15 Hz),and the intensity was adjusted to induce moderate muscle contract of the hindlimb (≤1.5 mA).The thermal withdrawal latency(TWL) was measured using hot plate test and mechanical withdrawal threshold (MWT) with von Frey filaments was measured for injured ipsilateral paw the day before and at the 3rd,5th,7th days after operation (T0-4).The right lumbar segment (L4-6) of spinal cord was removed on the 10th day after induction of CCI for determination of the protein and mRNA expression of P2X3 in the spinal cordl using western-blotting and reverse transcription-polymerase chain reaction (RT-PCR),respectively.Results In comparison with sham group,after CCI,MWT and TWL decreased significantly and P2X3protein and mRNA levels were significantly increased in all other groups (P＜0.05).Compared with group CCI,MWT and TWL increased at T2-4 and the protein and mRNA level of P2X3 expression decreased significantly in LEA and HEA group (P＜0.05).MWT and TWL was significantly higher and P2X3 protein and mRNA expression were lower in group LEA than those in group HEA (P＜0.05).Condusions Down-regulation of P2X3 receptor expression in spinal cord is involved in the mechanism of analgesic effects of electroacupuncture on neuropathic pain. Key words: Electroacupuncture;  Neuropathic pain;  Spinal cord;  Purinergic receptor P2