Effect of tetramethylpyzine on expression of GAP-43 mRNA in dorsal root ganglion in a rat model of neuropathic pain

Objective To evaluate the effect of tetramethylpyzine on the expression of growth associated protein-43 (GAP-43) mRNA in the dorsal root ganglion in a rat model of neuropathic pain (NP).Methods Fiftyfour male Wistar rats,weighing 180-220 g,aged 6-8 weeks,were randomly assigned into 3 groups (n =18 each) using a random number table:sham operation group (group S),NP group and tetramethylpyzine group (group TMP).NP was induced by chronic constrictive injury in anesthetized rats in NP and TMP groups.The sciatic nerve was exposed and 4 loose ligatures were placed on the right sciatic nerve at 1 mm intervals with 4-0 silk thread.In group S,the right sciatic nerve was only exposed but not ligated.In group TMP,tetramethypylrazine 100 mg· kg-1 · d-1 was injected intraperitoneally for 14 consecutive days starting from the end of operation,while the equal volume of normal saline was administered instead of tetramethylpyrazine in S and NP groups.Mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were measured at 1 day before operation (T0,baseline) and 3,7 and 14 days after operation (T1-3).The animals were then sacrificed after measurement of pain threshold at T1-3.The L4-6 segments of dorsal root ganglions on the injured side were removed for determination of the expression of GAP-43 mRNA using real-time fluorescent PCR.Results Compared with group S,MWT and TWL were significantly decreased,and the expression of GAP-43 mRNA was up-regulated in NP and TMP groups (P ＜ 0.05).Compared with group NP,MWT and TML were significantly increased,and the expression of GAP43 mRNA was down-regulated in group TMP (P ＜ 0.05).Conclusion The mechanism by which tetramethylpyrazine attenuates NP may be related to inhibition of the expression of GAP-43 mRNA in the dorsal root ganglion of rats. Key words: TETRAMETHYLPYRAZINE ;  Neuralgia;  GAP-43 protein ;  Ganglia, spinal