Role of spinal microglial C-C chemokine receptor type 2 in maintenance of bone cancer pain in rats

Objective To evaluate the role of spinal microglial C-C chemokine receptor type 2 (CCR2) in the maintenance of bone cancer pain (BCP) in rats.Methods Fifty unmated female Sprague-Dawley rats,aged 2 months,weighing 160-180 g,were randomly divided into 5 groups (n =10 each):sham operation group (group Ⅰ),sham operation + RS102895 (CCR2 antagonist) group (group Ⅱ),BCP group (group Ⅲ),BCP + dimethylsulfoxide (DMSO) group (group Ⅳ),and BCP + RS102895 group (group Ⅴ).The rats were anesthetized with intraperitoneal chloral hydrate.BCP was induced by intra-tibial inoculation of 1 × 105 Walker 256 mammary gland carcinoma cells into the medullary cavity of the left tibial metaphysis.On 10-12 days after operation,3 μg/μl RS102895 10 μd was injected intrathecally once a day in Ⅱ and Ⅴ groups,10％ DMSO 10 μl was injected intrathecally once a day in Ⅳ group,and normal saline 10 μl was injected intrathecally once a day in Ⅰ and Ⅲ groups.Mechanical paw withdrawal threshold was measured at 1 day before operation and 3,6,9,10,11 and 12 days after operation.After measurement of pain threshold at day 12 after operation,the lumbar segments (L4-6) of the spinal cord were removed for determination of the level of ox-42 (spinal microglial activation marker) (by immuno-histochemistry) and contents of IL1-β,IL-6 and TNF-α (by ELISA).Results Compared with group Ⅰ,mechanical paw withdrawal threshold was significantly decreased at 6-12 days after operation,the number of ox-42 positive cells and contents of IL1-β,IL-6 and TNF-α were increased in Ⅲ,Ⅳ and Ⅴ groups,and no significant change was found in the parameters mentioned above in group Ⅱ.Compared with group Ⅲ,mechanical paw withdrawal threshold was significantly increased at 10-12 days after operation,the number of ox-42 positive cells and contents of IL1-β,IL-6 and TNF-α were decreased in group Ⅴ,and no significant change was found in the parameters mentioned above in group Ⅳ.Conclusion Spinal microglial CCR2 is involved in the maintenance of BCP via activating microglia and promoting the release of inflammatory cytokines of rats. Key words: Bone neoplasms ;  Pain ;  Receptors, CCR2 ;  Microglia ;  Spinal cord