The Role And Mechanism Of Hippocampal BDNF-TrkB Signaling Pathway In Nicotine Addiction

[Background] Tobacco epidemic is one of the world’s greatest public health threats,and tobacco is the leading cause of preventable death in the world.Nicotine(Nic)is the main psychoactive ingredient in tobacco,and the essence of tobacco addiction is nicotine addiction.Nicotine exposure leads to changes in the plasticity of brain nerve pathways,forming a strong and long-lasting memory of nicotine addiction,which makes nicotine addicts a continuous desire to smoke.Therefore,to clarify the mechanism of memory formation of nicotine addiction and to explore ways to eliminate the memory of nicotine addiction is the key to treating nicotine dependence and preventing relapse after smoking cessation.Brain-derived neurotrophic factor(BDNF)is one of the most abundant neurotrophic factors in the brain.BDNF not only affects the development and survival of neurons,but also plays a key role in the formation of learning and memory.BDNF binds to its high-affinity receptor tyrosine kinase receptor B(TrkB)and further activates a series of downstream signaling pathways to participate in learning and memory.Studies have shown that nicotine changed the brain BDNF levels,but the role of BDNF-TrkB signaling pathway in nicotine addiction memory is still unclear.This study mainly explored the role of the hippocampal BDNF-TrkB signaling pathway in the formation of nicotine addictive memory and its possible mechanism.[Methods] 1.In order to establish a mouse model of nicotine addiction,48 mice were divided into 4 groups randomly,namely the saline group(n=12),0.25mg/kg nicotine group(n=9),0.5mg/kg nicotine group(n=18),1mg/kg nicotine group(n=9),which were injected with saline or corresponding doses of nicotine,and were trained with conditioned place preference(CPP)to detect the effects of different doses of nicotine on the CPP behavior of mice;2.In order to explore the acute effects of nicotine on the BDNF-TrkB signaling pathway in different brain regions,9 mice were divided into 2 groups randomly,namely the saline group(n=4)and0.5mg/kg nicotine group(n=5),after acute nicotine treatment enzyme-linked immunosorbent assay and Western Blot(WB)were used to detect the expression of BDNF,TrkB and p-TrkB in different brain areas;3.To explore the chronic effects of nicotine on the BDNF-TrkB signaling pathway in different brain regions,14 mice were divided into14 groups randomly,namely the saline group(n=4),0.5mg/kg nicotine last injection 2h group(n=5)and 0.5 mg/kg nicotine last injection 24 h group(n=5),after chronic nicotine treatment,enzyme-linked immunosorbent assay and WB were used to detect the expression of BDNF,TrkB and p-TrkB in different brain areas;4.After injecting0.5mg/kg nicotine into mice,CPP training was carried out,detect CPP behavior to confirm the formation of nicotine addiction memory,and before the second test,the TrkB receptor blocker 0.5mg/kg ANA-12 was injected to detect the effect of blocking the BDNF-TrkB signaling pathway on the memory of nicotine addiction;5.In order to study the effect of chronic nicotine treatment on the Glu A1 subunit of AMPA receptor in the hippocampus(Hip),immunofluorescence was used to detect the expression of Glu A1 in the Hip of the three groups of mice treated with chronic nicotine;6.In order to study the effect of acute nicotine treatment on the downstream signaling pathway of BDNF-TrkB in Hip,WB was used to detect the expression of PI3 K,AKT,GSK3 B,MEK,ERK and CREB in the Hip of the two groups of mice treated with acute nicotine;7.To study the effect of chronic nicotine treatment on the downstream signaling pathway of BDNF-TrkB in Hip,WB was used to detect the expression of AKT,GSK3 B,MEK,ERK and CREB in the Hip of the three groups of mice treated with chronic nicotine,in order to clarify the possible mechanism of nicotine promoting the formation of addictive memory by activating the BDNF-TrkB signaling pathway.[Results] 1.The CPP score of the 0.5 mg/kg nicotine group was significantly higher than that of the saline group,indicating that 0.5mg/kg nicotine induced the formation of CPP in mice;2.Acute nicotine treatment had no effect on the expression of BDNF-TrkB signaling pathway in the nucleus accumbens(NAc)and prefrontal cortex(PFC),but it reduced the expression of BDNF protein in the Hip;3.Chronic nicotine treatment did not affect the expression of BDNF-TrkB signaling pathway in PFC,but it can significantly affect the expression of BDNF-TrkB in NAc and Hip.Among them,2h and 24 h after the last nicotine injection,the activity of the BDNF-TrkB pathway in NAc was significantly inhibited.However,2h after the last nicotine injection,the expression of BDNF-TrkB pathway in Hip was significantly increased,indicating that chronic nicotine treatment up-regulated the BDNF-TrkB signaling pathway in Hip;4.Intervention with 0.5mg/kg ANA-12 after the formation of CPP in mice,and it was found that the CPP score of the mice after the intervention was significantly lower than that before the intervention,indicating that the inhibitor of TrkB receptor ANA-12 can inhibit the expression of CPP in mice;5.24 h after the last nicotine injection,the expression of Glu A1 protein in the Hip CA1,CA3 and dentate gyrus(DG)increased;6 WB results showed that acute nicotine treatment did not affect the expression of BDNF-TrkB downstream signaling pathway proteins in Hip;7.2h after the last nicotine injection,the expression of AKT protein in Hip increased,indicating that nicotine may activate the AKT pathway downstream of BDNF-TrkB to up-regulate the expression of hippocampal Glu A1.[Conclusion] Nicotine can induce the formation of CPP by activating the BDNF-TrkB signaling pathway in the Hip,and its mechanism may be related to the activation of the downstream AKT signaling pathway and the up-regulation of Glu A1 expression in the Hip.