Effects of sinomenine on expression of P2X3 receptor mRNA and cyclooxygenase-2 mRNA in spinal dorsal horns of rats with neuropathic pain

Objective To evaluate the effects of sinomenine on the expression of P2X3 receptor (P2X3R) mRNA and cyclooxygenase-2 (COX-2) mRNA in the spinal dorsal horns of rats with neuropathic pain (NP).Methods Fifty-four male Wistar rats,aged 6-8 weeks,weighing 180-220 g,were randomly assigned into 3 groups (n =18 each) using a random number table:sham operation group (group S),group NP and sinomenine (group SIN).The animals were anesthetized with 10％ chloral hydrate 350 mg/kg.NP was induced by chronic constrictive injury.In group SIN,sinomenine 40 mg/kg was intraperitoneally injected immediately after the end of operation once a day for 14 consecutive days,while the equal volume of normal saline was given in the same way in S and NP groups.The mechanical paw withdrawal threshold to yon Frey stimuli (MWT) and paw withdrawal latency to thermal nociceptive stimulus (TWL) were measured at 1 day before operation and 3,7 and 14 days after operation.The rats were sacrificed after measurement of pain threshold,and their lumbar segments (L4-6) of the spinal cord were immediately removed for determination of P2X3 R and COX-2 mRNA expression in the spinal cord (by real-time fluorescent quantitative PCR).Results Compared with group S,the MWT was significantly deceased,the TWL was shortened and the expression of P2X3R and COX-2 mRNA was up-regulated in NP and SIN groups.Compared with group NP,MWT and TWL were significantly increased,the TWL was prolonged and the expression of P2X3R and COX-2 mRNA was down-regulated in group SIN.Conclusion Sinomenine can mitigate NP in rats possibly through inhibiting the expression of P2X3R mRNA and COX-2 mRNA in the spinal dorsal horns. Key words: Sinomenine ;  Neuralgia;  Receptors, purinergic P2 ;  Cyclooxygenase 2 ;  Spinal cord