The Role Of Fractalkine/CX3CR1 In Pain Facilitation And Spinal Mechanisms In Rat Model Of Bone Cancer Pain

PartⅠChanges in Expression of Chemokine Receptor CX3CR1 in Dorsal Horn of Spinal Cord in A Rat Model of Bone Cancer PainObjective To investigate the Changes in expression of chemokine receptor CX3CR1 in dorsal horn of spinal cord in a rat model of bone cancer pain. Methods Fifty SD female rats weighing 150-180 g were randomly divided into 5 groups (n=10): control group (C); sham operation group (S): intra-tibial injection of 5μl Hank's solution; bone cancer 6 day group (B6); bone cancer 12 day group (B12); bone cancer 18 day group (B18), group B6,B12,B18: intra-tibial injection of 5μl Walker256 mammary gland carcinoma cells of rats (2x107cells/ml) respectively. The von Frey threshold and weight bearing difference between the 2 hind limb were measured before operation (baseline) and on day 6 , 12 and 18 after operation. The animals were killed on days 6,12 and 18 after operation. The lumbar 4~6 of the spinal cord was immediately removed.The CX3CR1 expression in the dorsal horn of the spinal cord was measured by Western blotting and immunohistochemistry. Results The mechanical pain thresholds and weight bearing of left hind limb were significantly decrease, weight bearing difference between the 2 hind limbs were increase, and expression of CX3CR1 in the spinal cord was remarkly increase in group B6,B12,B18 as compared with the groups C and S. As compared with group B6, the mechanical pain thresholds and weight bearing of left hind limb were significantly decrease, weight bearing difference between the 2 hind limbs were increase, and expression of CX3CR1 in the spinal cord was remarkly increase in group B12 and B18, but without significant differences between group B12 and B18. Conclusion The CX3CR1 in the spinal cord is involved in the mechanism of bone cancer pain in rats. PartⅡEffect of Intrathecal injection of anti-CX3CR1 neutralizing antibody in A Rat Model of Bone Cancer Pain and Its Spinal MechanismsObjective To observe the the effect of intrathecal injection of fractalkine receptor antagonist (neutralizing antibody against rat CX3C receptor-1; CX3CR1) in rat model of bone cancer pain. Moreover investigate its effective mechanism through the alteration of spinal glial in spinal cord. Methods A bone cancer pain model was established by inoculated Walker256 mammary gland carcinoma cells into the tibia medullary cavity. Fouty SD female rats were randomly divided into 5 groups (n=8each): groupⅠ(sham group); groupⅡ(model group); groupⅢ: sham group+anti-CX3CR1 intrathecal (IT); groupⅣ: model group+normal IgG IT; groupⅤ: model group+anti-CX3CR1 IT. Anti-CX3CR1 or normal IgG were injected IT during 10～12th day. Von Frey threshold were measured one day before and every 2 days after operation.On the 12th day after operation, rats were sacrificed after IT injection of either anti-CX3CR1 or normal IgG, the lumbar 4-6 spinal cord was removed. The expression of the spinal OX-42 (microglial marker) and GFAP (glia fibrillary acidic protein, astrocyte marker) immunostaining were detected by immunohistochemistry. Results On the 10th days after operation, there were no obvious differences in mechanical pain thresholds between groupsⅠandⅢ, groupsⅡandⅣ; there was significantly higher in groupⅤthan in groupⅣduring 2～8 h after injected IT CX3CR1. During 10~12th days after operation, von Frey threshold in groupsⅡa ndⅣwere significantly lower than in group I and groupⅢ(p<0.01), there was no significant difference between groupⅠand groupⅢ; groupⅤwas remarkly higher than in groupⅡand groupⅣ(p<0.01). The spinal expression of OX-42 and GFAP in groupsⅡo rⅣwere significantly increase compared with that in groupⅠorⅢ(p<0.01), groupⅤIT anti-CX3CR1 was significantly suppressed OX-42 and GFAP expression as compared to those in groupsⅡo rⅣ(p<0.01) . Conclusion Intrathecal injectctions of anti-CX3CR1 neutralizing antibody provides analgesia in the tibial cancer pain rats and inhibits the OX-42 and GFAF expression in the lumbar spinal dorsal horn,suggesting that fractalkine is involved in the bone cancer pain via activation of spinal microglia and astrocytes.