Role of chemokine CXCL12 in spinal cord in development of bone cancer pain in rats: relationship with microglial activation

Objective To evaluate the role of chemokine CXCL12 in the spinal cord in the development of bone cancer pain (BCP) in rats and the relationship with microglial activation.Methods Thirty-two female Sprague-Dawley rats,weighing 180-220 g,were equally randomized into 4 groups (n =8 each) using a random number table:sham operation group (group S),BCP group (group B),BCP + CXCL12 neutralizing antibody group (group BC),and BCP + IgG control antibody group (group BI).BCP was induced by injecting Walker 256 mammary gland cancer cell suspension (4 × 105 cells/ml) 5 μl into the bone marrow of the right tibia of rats anesthetized with chloral hydrate in B,BC and BI groups,while the equal volume of normal saline was injected instead in group S.On 12,13 and 14 days after injection of mammary gland cancer cells,CXCL12 neutralizing antibody 10 μg/15 μl was intrathecally injected once a day in group BC,while IgG control antibody 10 μg/15 μl was intrathecally injected once a day in group BI.Before injection of mammary gland cancer cells (T0) and on 3,5,7,10,12 and 14 days after injection of mammary gland cancer cells (T16),paw withdrawal threshold to mechanical stimulation (PWMT) was measured.The rats were then sacrificed and L4,5 segments of the spinal cord were removed for determination of Iba-1 (pan-microglial marker) expression in spinal dorsal horn using immunofluorescence after PWMT measurement at T6.Results Compared with S group,PMWT was significantly decreased at T2-6,and Iba-1 expression was up-regulated at T6 in B,BC and BI groups (P ＜ 0.01).Compared with B group,PMWT was significantly increased at T5,6 and Iba-1 expression was down-regulated at T6 in BC group (P ＜ 0.01).Conclusion Chemokine CXCL12 in the spinal cord is involved in the development of BCP,and microglial activation is involved in the mechanism. Key words: Bone neoplasms;  Pain;  Spinal cord;  Chemokine CXCL12;  Microglia