Role of spinal mTOR/S6K1/Gli1 signaling pathway in chronic morphine tolerance in mice / 中华麻醉学杂志

ABSTRACT

Objective:To evaluate the role of spinal mammlian target of rapamycin (mTOR)/ribosomal S6 kinase 1 (S6K1)/glioma associated oncogene homolog 1 (Gli1) signaling pathway in chronic morphine tolerance in mice.Methods:Healthy male Kunming mice, aged 8-10 weeks, weighing 23-25 g, were used in the study.The experiment was performed in two parts.Experiment I Fifty mice were randomly assigned into 2 groups: normal saline group (group S, n=10) and morphine group (group M, n=40). In M and S groups, morphine and normal saline 10 mg/kg were injected subcutaneously, respectively, twice a day for 7 consecutive days.The thermal pain threshold (TPT) was measured and the maximum analgesic effect percentage (MPE) was calculated at 1 day before administration and 30 min after the last administration every day.Ten mice in each group were randomly selected and sacrificed after measurement of TPT at 1, 3, 5 and 7 days after administration in group M and after the last measurement of TPT in group S, and the lumbar segment (L 4-6) of the spinal cord was removed.Experiment Ⅱ Forty mice were randomly divided into 4 groups ( n=10 each): KU-0063794+ morphine group (group KU+ M), dimethyl sulfoxide (DMSO)+ morphine group (group DM+ M), morphine+ KU-0063794 group (group M+ KU) and morphine + DMSO group (group M+ DM). Morphine 10 mg/kg was injected subcutaneously twice a day for 7 consecutive days in 4 groups.At 1-3 days of morphine injection, mTOR specific inhibitor KU-0063794 200μl (1 μg/μl) and 10% DMSO 200 μl was injected intraperitoneally in KU+ M group and DM+ M group at 30 min before administration twice a day.At 5-7 days of morphine injection, KU-0063794 200μl (1 μg/μl) or 10% DMSO 200 μl was injected intraperitoneally in group M+ KU or group M+ DM at 30min before administration, respectively, twice a day.TPT was measured and MPE was calculated at 1 day before morphine injection and at 30 min after the last administration every day.The animals were sacrificed after the last measurement of TPT, and the lumbar segment (L 4-6) of the spinal cord was removed for determination of the expression of spinal mTOR, phosphorylated mTOR (p-mTOR), S6K1, phosphorylated S6K1 (p-S6K1) and Gli1 (using Western blot). Results:Experiment Ⅰ Compared with group S, MPE was significantly increased at each time point after administration at 3, 5 and 7 days after administration, expression of spinal p-mTOR, p-S6K1 and Gli1 was significantly down-regulated ( P<0.05), and no significant change was found in mTOR and S6K1 in group M ( P>0.05). Experiment Ⅱ Compared with group DM+ M, MPE was significantly decreased at 3-7 days after morphine injection, expression of p-mTOR, p-S6K1 and Gli1 in spinal cord was down-regulated ( P<0.05), and no significant change was found in expression of mTOR and S6K1 in group KU+ M ( P>0.05). Compared with group M+ DM, MPE was significantly increased at 6-7 days after morphine injection, expression of p-mTOR, p-S6K1 and Gli1 in spinal cord was down-regulated ( P<0.05), and no significant change was found in mTOR and S6K1 in group M+ KU ( P>0.05). Conclution:Spinal mTOR/S6K1/Gli1 signaling pathway is involved in the development and maintenance of chronic morphine tolerance in mice.