Intrathecal injection of IL-1ra and ketamine for chronic neuropathic pain model in rats

objective To observe the effect of intrathecal injection of IL-1ra and ketamine for chronic constriction injury (CCI)in rats. Methods 40 male SD rats were randomly divided into 5 groups: Sham operation group;CCI group; IL-1ra group;ketamine group; IL-1ra and ketamine group. Thermal withdrawal latency (TWL) and mechanical withdrawal threshold(MWT) of 2 h pre -drug and 2,4,6 h after injected drugs at day 21 in rats were performed by Hargreave's thermal radiation apparatus and von Frey's method of micro filament, respectively. The rats were killed after the behavior test was finished. The expression of p-ERK was measured in the spinal cord by immunohistochemical analysis and western blot method. Results The group of combined injection IL-1rα and ketamine produced significantly more potent analgesia compared with that of CCI group. MWT(7.1±2.2 )and TWL ( 13.5 ±3.6)were increased from 2 hours to 6 hours after intrathecal injection of IL-1rα and ketamine(P<0.01 ). The expressions of p-ERK and the number of positive cells in the combined injection group were significantly lower than that of CCI group (P<0.01). The effect of IL-1ra and ketamine in lower dosages is tendency enhanced than that of higher dosage alone. Conclusion The combined injection of IL-lra and ketamine in lower dosage can produce synergistic abirritation in chronic pain. Key words: Ketamine; IL-1ra; Neuropathic pain; Spinal cord; p-ERK; Rat