Effect Of Combined Injection Of Ketamine And Clonidine On P2X₄ Receptor MRNA In Spinal Cord Of The Rats With Neuropathic Pain

Objective: The aim of this paper is to observe the effect of combined intraperitoneal injection of ketamine and clonidine on the expression of P2X₄ receptor in spinal cord for chronic constriction injury (CCI) in rats and to explore the therapeutic effects of Ketamine and Clonidine on the neuropathic pain and the effects of potential mechanism of neuropathic pain induced by P2X₄ receptor, which may provide theoretical basis for treatment.Methods: Eighty male SD rats weighing 180～220g were randomly divided into 5 groups as follows (n=16 each): sham operation group (S), neuropathic pain group (NP), ketamine group (K), clonidine group (CL) and combined group (KC). In group S, the right sciatic nerves were exposed but not ligated, and in other groups four ligatures were placed around the right sciatic nerve according to the methods of Bennett. From the third day after operation, 10 mg/kg ketamine (2 mL), 1 mg/kg clonidine (2 mL) and 5 mg/kg ketamine + 0.5 mg/kg clonidine (2 mL) were injection intraperitoneally into K, CL, KC group respectively and normal saline 2mL was injection into S and NP group once a day. Mechanical and thermal pain threshold were measured by paw withdrawal latencies to von Frey hair and radiant heat stimulation at 1 d before operation and 3, 7, 14, 21 d after operation. Four animals were killed at 1 d before operation and 7, 14 and 21 d after the pain threshold was measured in all groups respectively and the L_4～5 segment of the spinal cord was removed. Reversal transcript-polymerase chain reaction (RT-PCR) was used to evaluate the transcription of P2X₄ receptor.Results: PWML and PWTL of group NP, K, CL and KC were markedly reduced at 3d after operation than those before operation and group S (P>0.05). PWTL was dropped most significantly at 3d; however, PWML was dropped most significantly at 7d after operation (P<0.05). PWTL and PWML of group K, CL, KC at 7d, 14d, 21d after operation were increased compared with group NP(P<0.05), and the most remarkable effect was at the 21d after operation. PWTL and PWML of group KC was significantly higher than group K and CL (P<0.05). The expression of P2X₄ mRNA in group NP, K, CL, KC at 7d, 14d, 21d after operation was increased compared with group S (P<0.05). The expression of P2X₄ mRNA in group K, CL, KC was decreased compared with group NP (P<0.05). The reduction of group KC was more obviously than other groups (P<0.05).Conclusion: Ketamine and clonidine all has evident analgesic effects. The combined injection of ketamine and clonidine can reduce hyperalgesia and the underlying mechanism was correlated with the expression of P2X₄ receptor in the spinal cord.