Objective To investigate the expression of miR-16 in spinal cord and the effects of miR-16 mimics on the pain behavior and the expression of its target gene BDNF during the development and maintenance of bone cancer pain.Methods The bone cancer pain model rats were developed by intra-tibia inoculation of Walker 256 mammary gland cells.Before inoculation and 3,5,7,10,14 d after inoculation,the samples of spinal cord L4～6 lumbar enlargement were collected to detect the expression of miR-16 using real-time PCR.Mice in group BM and group BN were intrathcal injected of miR-16 mimics and its negative control products on 10 d,11 d,12 d after inoculation.Paw withdrawal mechanical threshold (PWMT) was measured using von Frey hair mechanical stimulation.The expression of BDNF was detected using western-blot on 14 d after behavior tests.Results Compared with the base level and the level in group S,the significant decrease of miR-16 expression was observed at 5 d～14dingroupT (5d (0.91±0.04),7 d (0.77±0.01),10 d (0.73±0.03),14d (0.42±0.08)) (all P＜ 0.05).Compared with SH group,PWMT was significantly decreased in BC and BP groups at 5 d～ 14 d (P＜0.05),and in group BM at 5 d～ 10 d(P＜0.05).Compared with BP group,PWMT was significantly higher in BM group at 10～12 d(P＜0.05).Compared with SH group,the expression of BDNF was significantly increased in BN and BP groups((2.78±0.31),(2.34±0.23)) (all P＜0.01).Compared with BP group,the expression of BDNF was significantly decreased in BM group (1.42±0.16) (P＜0.01).Conclusion miR-16 is downregulated in spinal cord of bone cancer pain rats,while intrathcal injection of miR-16 mimics can attenuate the pain behaviors in a rat model of bone cancer pain and decrease the expression of BDNF.miR-16 may modulate bone cancer pain through BDNF.

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.