Effect of intrathecal injection of magnesium sulfate on pain behavior in bone cancer pain mouse

Objective To investigate the effect of intrathecal injection of magnesium sulfate(MgSO4) on pain behavior in mouse with bone cancer pain. Methods 56 male 8-10 week old C3H/HeJ mice weighing 18-22 g were divided randomly into 7 groups(n=8): sham group(S group), control group(C group) and MgSO4 plus morphine treat groups(T1-T5 group). Group C and T mice were induced bone cancer pain models by intra-right-femur inoculation of osteolytic NCTC2472 cells while group S were injected of only α-MEM. On the 14d after inoculation, group S and C received intrathecal injection of artificial cerebrospinal fluid 5μl, while group T1-T5 received intrathecal injection of MgSO4 14.4μg, 43.2μg, 86.4μg, morphine 0.36μg, MgSO4 14.4μg-morphine 0.36μg, which were dissolved in 5μl artificial cerebrospinal fluid. Mice received pain behavior tests including quantification of spontaneous flinches, paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) at 0.5h before and 0.5h, 2h, 4h, 8h after administration. Results Treatment with MgSO4(14.4μg), morphine (0.36μg) have no effect on bone cancer pain, while treatment with MgSO4 (43.2μg, 86.4μg)can dose-dependently reverse quantification of spontaneous flinches, mechanical allodynia and thermal hyperalgesia which were induced by inoculation as well as MgSO4 14.4μg-morphine 0.36μg. At 0.5h after administration, the quantification of spontaneous flinches of the three groups((10.08±1.66), (7.35±1.36), (10.54±1.32)) were decreased when compared with control group (13.05±2.06), PWMT ((0.81±0.22) g; (1.33±0.19)g; (0.93±0.26)g), PWTL((10.57±1.53)s; (13.12±1.71)s; (11.46±1.83)s) were increased when compared with control group((0.42±0.23)g, (8.87±1.27)s)(P<0.05). The effect reached maximum level at 2h, lasted for at least 4h and disappeared at 8h. Conclusion Intrathecal injection MgSO4 can effectively attenuate bone cancer pain dose-dependently.At the same time MgSO4 can amplify the analgesic effect of subliminal morphine. Key words: Bone cancer pain; Magnesium sulfate; Morphine; Behavior; Mouse