Abstract: Objective · To investigate the mechanism of spinal chemokine C-C motif receptor 2 (CCR2)-mediated maintenance of bone cancer pain (BCP) in rats. Methods · Fifty-four SD rats were divided into BCP group, sham operation group, BCP+INCB3344 (CCR2 specific antagonist) group, and BCP+vehicle control group. Walker256 breast cancer cells were injected into the tibia medullary cavity of rats in the BCP group to establish the BCP model, while the rats in the sham operation group were injected with the same amount of saline. The rats in the BCP+INCB3344 group received intrathecal injection of INCB3344 on the 14th day after the establishment of BCP model, while the BCP+vehicle control group rats were injected with the same amount of vehicle. The mechanical pain thresholds of BCP group rats and sham operation group rats were measured to judge the success of BCP model. The s of CCR2 in the dorsal horn of spinal cord in the sham operation group rats and the BCP group rats were detectedWestern blotting. The effects of intrathecal administration of INCB3344 on the mechanical pain threshold of BCP rats were observedmechanical pain behavior test. Whole-cell patch-clamp recordings were used to investigate the differences of spontaneous excitatory postsynaptic currents (sEPSCs), α-amino-3-hydroxy-5-methyl-4-isoxazole-propionicacid (AMPA) and N-methyl-D-aspartic acid (NMDA)-induced currents of spinal substantia gelatinosa (SG) neurons of rats in the BCP group, the BCP+INCB3344 group and the BCP+vehicle control group. Results · Compared with the sham operation group, the mechanical pain threshold of BCP group rats reduced significantly on the 14th day after operation (P0.000), and the of CCR2 in ipsilateral spinal cord of BCP group rats increased significantly (P0.009). After intrathecal injection of INCB3344 for 4 h, the mechanical pain threshold of BCP+INCB3344 group rats was significantly increased (P0.002). The frequency and amplitude of sEPSCs and the amplitude of AMPA and NMDA-induced currents in SG neurons of BCP group rats were significantly higher than those of the sham operation group rats (all P0.000), while intrathecal administration of INCB3344 could significantly inhibit the above-mentioned indices in the BCP+INCB3344 group (all PP0.001) and amplitude (P0.020) of sEPSCs in SG neurons in BCP rats. Conclusion · CCR2 expressing in the spinal cord mediates the enhancement of excitatory synaptic transmission efficacy in the spinal dorsal horn of BCP ratsenhancing the functions of AMPA and NMDA receptors, which may be an important mechanism for the maintenance of BCP.

Key words: chemokine C-C motif receptor 2 (CCR2), bone cancer pain (BCP), spinal cord, spontaneous excitatory postsynaptic currents (sEPSCs), substantia gelatinosa (SG)