Effects of intrathecal injection rapamycin on neuropathic pain behaviors in mice

Objective To investigate the effects of continuously intrathecal injection rapamycin on neuro pathic pain behaviors in mice.Methods 48 male adult C57/BL6 mice received intrathecal catheter implantation successfully and without motor dysfunction and serious weight loss,were choosed and randomly divided into shamoperation group ( sham,n =24) and chronic constriction injury model group ( CCI,n =24 ).After operation,each group randomly divided into 3 group again.Group I did nothing,group Ⅱ intrathecally injected rapamycin 1 μg/5μlon day 1 to 6 after operation,group Ⅲ intrathecally injected 20％ DMSO 5μl on the same time ( sham,CCI,sham +R,sham + V,CCI + R,CCI + V,n =8 ).Bilateral mechanical paw withdrawal threshold (WMT) and thermal paw withdrawal latency(TWL) were tested on day 1 before CCI and day 1,3,5,7,10,14,17,21,28 after operation.Results Compared with sham group,both WMT and TWL (7d,MWT:( 1.02 ±0.12)g vs (0.42 ±0.12)g,F=51.01,P＜0.05;TWL:(7.03 ±0.71 )s vs (3.26 ±0.66)s,F=38.27,P＜0.05) were significantly decreased after CCI on the ipsilateral side.When intrathecally injected Rapamycin 1 μg/5 μl on day 1 ～6 after CCI,the mechanical allodynia relieved obviously ( 7 d,M WT:( 0.42 ± 0.18 ) g vs ( 0.86 ± 0.25 ) g,F =6.56,P ＜ 0.05 ),and at least continued to 10 d.On the contrary,the effects of rapamycin on thermal hyperalgesia just showed a trend of inhibition,there was no statistic meaning.In addition,the sham group and contralateral pain behaviors did not change (P＞ 0.05 ).Conclusion Rapamycin can relieve the neuropathic pain behaviors in mice after CCI,mainly the mechanical allodynia,but not thermal hyperalgesia. Key words: Rapamycin ;  Neuropathic pain;  Mechanical alloclynia;  Thermal hyperalgesia