Intrathecally administration of minocycline on mechanical allodynia and heat hyperalgesia induced by chronic constriction injury of the sciatic nerve in rats

Aim To observe the effect of intrathecal minocycline ,a microglial inhibitor,on mechanical allodynia and heat hyperalgesia induced by chronic constriction injury(CCI) of the sciatic nerve in rats. Methods Rats in all groups were intrathecally cathetered at 8 d before operation. Mechanical allodynia and heat hyperalgesia were evaluated by mechanical withdrawal threshold(MWT) and thermal withdrawal latency(TWL),respectively. In a preemptive treatment group,normal saline(10 μl) or minocycline (50 μg), beginning on 1 day before surgery, were administered twice daily for 3 days, the TWL and MWT were measured before surgery and on days 1,3,5,7 and 14 after surgery; in post-surgery treatment group,The effect of minocycline or saline on TWL and MWT was examined at 0.5,1,2,4,and 8 h after its intrathecal administration initiated on day 7 after surgery. Results CCI group formed steady mechanical allodynia and heat hyperalgeia from the first day after surgery to the end of this study. Preemptive administration of minocycline evidently increased the CCI rats MWT and TWL, on the contrary, initiation of minocycline treatment to rats after day 7 of nerve injury did not show any significant effect on the MWT and TWL compared with vehicle-treated nerve-injured rats. Conclusion Preemptive treatment with minocycline remarkably suppressed mechanical allodynia and heat hyperalgesia of rats following CCI,suggesting microglial activation is involved in the development of neuropathic pain induced by chronic constriction injury (CCI).