BDNF/TrkB Signaling Pathway In RACC Contributes To Bone Cancer Pain Related Aversion

BackgroundBone cancer pain(BCP)is a chronic pain caused by primary or metastatic bone tumors.Patients with BCP have changes in feeling,emotion,cognition and so on.Negative emotions such as anxiety and fear caused by pain not only aggravate pain,but also lead to serious consequences such as suicide.Studies have shown that 55%of patients with BCP lasting more than 6 months are accompanied by psychological disorders.Therefore,to explore the mechanism and prevention of BCP related negative emotions is of great significance for the treatment of BCP and related mental diseases.Rostral anterior cingulate cortex(rACC)is the key to pain aversion.Recent studies have found that there is emotion related glutamatergic synaptic transmission in rACC,and its changes contribute to the development of pain induced aversion.In addition,brain derived neurotrophic factor(BDNF)enhances glutamate transmission by binding to tropomyosin receptor kinase B(TrkB).Therefore,we speculate that rACC neurons may participate in the regulation of bone cancer pain and negative emotion through BDNF/TrkB signaling pathway.ObjectiveThe aim of this study was to explore the effect and influence of rACC neuron BDNF/TrkB pathway on the formation of cancer pain related aversion,by injecting breast cancer cells into the right tibia to establish a rat model of BCP.MethodsHealthy adult male Sprague-Dawley rats(200-220g)were selected and divided into blank control group(Naive),sham operation group(Sham)and bone cancer pain group(BCP).BCP rat model was established by injecting MRMT-1 breast cancer cells into right tibia.To ensure the model we established can respond to pain aversion in rats,the changes of paw withdrawal threshold(PWT)and place escape/avoidance paradigm(PEAP)were detected at different time points in each group,and selected the time point of stable pain emotions for follow-up research.The rACC of rats were damaged by injection of ibotenic acid(neuron damaging agent)into rACC.The quantitative and semiquantitative detection of relevant genes of BDNF/TrkB pathway were completed at the nucleic acid and protein level by qRT-PCR and Western blotting.The possible mechanism of BDNF/TrkB pathway involved in cancer pain aversion was verified by using various antagonists,and the effect of exogenous BDNF on emotion was explored by conditional place avoidance(CPA)experiment.Results(1)rACC plays an important role in the formation of BCP aversion:Compared with sham group,the PWT and time spent in the dark area of BCP rats were significantly reduced from the 7th day postoperatively,indicating that the BCP aversion model was successfully established.Compared with BCP rats without rACC damage,there was no significant change in PWT in BCP rats with rACC damage,and the time spent in the dark area was significantly prolonged,suggesting that rACC damage alleviated aversion,but had no effect on pain threshold.(2)BDNF/TrkB signaling pathway in rACC is involved in the formation of cancer pain aversion:Compared with sham group,BDNF mRNA content and protein expression in rACC of BCP rats increased significantly on the 7th day postoperatively.TrkB receptor blocker CTX-B alleviated the aversion of BCP rats without changing the PWT.Exogenous BDNF can induce avoidance behavior in BDNF-conditioned room after CPA experimental training.CTX-B pretreatment can improve avoidance behavior.(3)NR2B is involved in the formation of cancer pain aversion mediated by BDNF/TrkB in rACC:Compared with sham group,the content of NR2B mRNA in rACC of BCP rats increased significantly on the 7th day after operation.The specific antagonism of NR2B alleviated aversion in rats,but the PWT did not change.Specifically antagonizing BDNF/TrkB can inhibit the protein expression of NR2B in rACC of BCP rats.Specific antagonism of NR2B can improve the avoidance behavior of rats in BDNF induced CPA experiment.(4)ERK-CREB signaling is involved in the formation of cancer pain aversion mediated by BDNF in rACC:Compared with sham group,the expression of phosphorylated ERK(pERK)and phosphorylated CREB(pCREB)in rACC of BCP rats increased significantly,and could be inhibited by CTX-B,which indicating that BDNF/TrkB signaling pathway mediates the activation of ERK-CREB signalling.Specific blocking of ERK alleviated aversion in rats,but the PWT did not change.In addition,blocking of ERK can improve BDNF induced avoidance behavior in rats.Conclusion(1)BDNF/TrkB signaling pathway of rACC is involved in the generation of cancer pain related aversion:(2)BDNF/TrkB signaling pathway plays a role in the generation of cancer pain related aversion through NR2B and ERK-CREB signaling pathway.