Effects of sinomenine on expression of glutamate transporter-1 mRNA and glutamate aspartate transporter mRNA in spinal cord of rats with neuropathic pain

Objective To evaluate the effectsof sinomenine on the expression of glutamate transporter-1 (GLT-1) mRNA and glutamate aspartate transporter (GLAST) mRNA in the spinal cord of rats with neuropathic pain (NP).Methods Seventy-two male Wistar rats,weighing 180-220 g,aged 6-8 weeks,were divided into 3 groups (n =24 each) using a random number table:sham operation group (group S); NP group; sinomenine group (group SIN).The animals were anesthetized with intraperitoneal 10％ chloral hydrate 350 mg/kg.NP was induced by chronic constrictive injury.The right sciatic nerve was exposed and 4 loose ligatures were placed on the sciatic nerve at 1 mm intervals with 4-0 silk thread.In group S,the right sciatic nerves were only exposed,but not ligated.In group SIN,sinomenine injection 40 mg/kg was injected intraperitoneally once a day starting from the end of operation until 1 day before the animals were sacrificed,while the equal volume of normal saline was given instead in S and NP groups.Mechanical paw withdrawal threshold to von Frey stimuli (MWT) and paw withdrawal latency to thermal nociceptive stimulus (TWL) were measured at 1 day before operation and 1,3,7 and 14 days after operation (T1-4).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 GLT-1 mRNA and GLAST mRNA expression in the spinal dorsal horn (by real-time fluorescent quantitative PCR).Results Compared with group S,MWT was significantly decreased and TWL was shortened at T1-4 in NP and SIN groups,the expression of GLT-1 mRNA and GLAST mRNA was up-regulated at T1.2 in group NP,and the expression of GLT-1 mRNA and GLAST mRNA was up-regulated at T1-3 in group SIN.Compared with group NP,MWT was significantly increased,TWL was prolonged,and the expression of GLT-1 mRNA and GLAST mRNA was up-regulated at T1.3 in group SIN.Conclusion Sinomenine can mitigate NP in rats and up-regulation of GLT-1 mRNA and GLAST mRNA expression is involved in the mechanism. Key words: Sinomenium;  Neuralgia;  Glutamate plasma membrane transport proteins;  Spinal cord