Analgesia effects of intrathecally coadministered dexamethasone and Alt inhibitors on chronic dorsal root ganglion compression-induced pain in mouse

Objective To investigate the analgesic effects of intrathecal dexamethasone injection on pain induced by chronic compression of dorsal root ganglion in mouse.Methods Using rat model of radicular pain induced by chronic compression of dorsal root ganglion ( CCD), 40 male SD rats successfully received intrathecal catheter implantation and without motor dysfunction were randomly divided into 5 groups:Sham-operation group ( Sham group, n = 8 ), Control group ( CCD group, n = 8), Dexamethasone group ( D group, n = 8), Akt inhibitor V group (A group, n = 8 ) and Dexamethasone plus Akt inhibitor Ⅳ group (DA group, n = 8 ).Rats in D group, A group or DA group were intrathecally treated with dexamethasone (100μg/kg) ,Akt inhibitor Ⅳ (0.6μg/10μl) or dexamethasone ( 100 μg/kg) plus Akt inhibitor Ⅳ (0.6 μg/10 μl) on Day 3,13 after CCD respectively, while rats in C and Sham group received Vehicle (10% DMSO).Paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) were tested on 3 d before and 3 d,4 d,7 d,10 d,13 d,14 d and 15 d after operation.Results Compared with Sham group,both PWMT (P＜0.01) and PWTL (P＜0.01) were significantly decreased after CCD surgery on the ipsilateral side.After dexamethasone and Akt inhibitor were respectively intrathecally injected at 3 postoperative day,PWMT (7.33 ± 1.03 ) g, (5.67 ± 1.03 ) g, (2.67 ± 1.03 ) g (P ＜0.01 ) ,PWTL( 16.47 ±0.46)s, ( 14.48 ±0.84) s, ( 10.82 ±2.21 ) s(P＜0.01 ) ,then decreased gradually,and intrathecally injected again at 13 postoperative day, PWMT ( 7.33 ± 1.03 ) g, ( 5.67 ± 1.03 ) g, (2.33 ± 0.81 ) g (P ＜0.01 ), PWTL( 16.44 ±0.90) s, ( 14.01 ±0.82)s, ( 10.22 ± 1.28)s (P＜0.01).Coadministration dexamethasone and Akt inhibitor exhibit significant synergies, postoperative 4 d PWMT( 10.83 ± 2.04)g, (2.67 ± 1.03 )g (P ＜0.01),PWTL(19.11 ±2.01)s,(10.82 ±2.21)s (P＜0.01);14 d PWMT (7 ±0.82)g,(2.33 ±0.81)g (P ＜ 0.01 ), PWTL( 17.16 ± 1.14)s, ( 10.22 ± 1.28 ) s (P ＜ 0.01 ).Conclusion Intrathecal high-dose dexamethas one or PKB / Akt inhibitors can effectively improve pain behavior response induced by chronic compression of dorsal root ganglia,combination of these two drugs could generate significant synergies, and the effection is more obvious, more durable. Key words: Glucocorticoid ;  PKB/Akt ;  Neuropathic pain ;