The Effect And Mechanism Of Brain Low Iron Content On Morphine Addiction Memory

Drug dependence(addiction)is a chronic brain disorder in which repeated use of addictive substances such as opioids can lead to uncontrolled craving and drug-seeking behavior and symptoms of physical and psychological dependence following withdrawal.Notably,only about 20 percent of people who repeatedly ingested opioids eventually developed opioid dependence,which clearly indicates that there is a significant individual susceptibility to opioid dependence,and research on its mechanism and treatment strategies remains an urgent and practical need.Once addiction occurs,it will never be forgotten,indicating that learning and memory functions play an important role in this process.For example,the association between contextual memory and reward memory can form strong and lasting memories,which is one of the neurobiological mechanisms of drug dependence.Therefore,mechanism studying of the storage and retrieval of information related to contextual and reward memory is particularly important for the mechanism research and treatment strategies development of drug dependence.Recently,more and more attention has been paid to the relationship between abnormal iron metabolism and drug dependence.Clinical studies have found that cocaine-addicted individuals showed excess iron accumulation in the globus pallidus,which strongly correlated with duration of cocaine use,and mild iron deficiency in the periphery,which was associated with low iron levels in the red nucleus.This suggests that cocaine addiction leads to disrupted iron regulation.Our previous studies showed that Clk1+/-mutation significantly suppressed METH-induced conditioned place preference,accompanied by increased expression of dopamine transporter(DAT)in plasma membrane of striatum and hippocampus.Notably,significantly decreased iron content in striatum and hippocampus was evident in both Clk1+/-mutant Mice.The decreased iron content was attributed to increased expression of iron exporter ferroportin 1(FPN1)that was associated with elevated expression of hypoxia-inducible factor-1α(HIF-1α)in response to Clk1 deficiency in vivo.These results suggest that iron plays a key role in the formation of methamphetamine conditioned location preference disorder in Clk1+/-mice,and that the susceptibility to drug dependence may be regulated by iron content in the brain.And then our research found that morphine conditioned place preference(mCPP)and morphine conditioned place aversion(mCPA)were impaired in low iron feeding mice.Based on previous work in our laboratory,this study focused on the effect of iron content on learning and memory after morphine exposure.mCPA,mCPP was used to detect negative addictive memory induced by urge withdrawal and positive addictive memory induced by morphine exposure,respectively.Morris water maze(MWM)was used to detect spatial memory,contextual fear conditioning(CFC)was used to detect contextual fear memory,and These types of learning and memory are closely related to the function of the dorsal hippocampus CA1.We first explored the effect of low iron content on basal cognitive ability,anxiety and depression-like behavior in mice.Openfield spontaneous activity,novel object recognition,and forced swimming were used to test normal and low-iron diet mice,and no difference was found in behavioral indicators of these tests between the two groups.In order to further explore the effect of iron content on mCPA and mCPP memory formation,we give normal feeding conditions for 21 days after low-iron modeling to test whether the damage of low-iron diet on mCPA and mCPP can be saved.After 5 days of increased dose of morphine exposure,followed by naloxone to hasten withdrawal,animals were randomly placed in conditioned place test boxes A or B for CPA modeling.Animal avoidance of box A or B was detected 24 hours later as mCPA test.It was found that the CPA memory was formed in the morphine group compared with the saline group.No mCPA memory was formed in the morphine group with low iron or supplemented iron diet compared with their saline group.Consistent with this,mCPP memory was formed in the normal diet morphine group compared with the saline group,but not in the other groups.These results indicate that although low iron content can inhibit the formation of mCPA and mCPP memory,iron supplementation has no effect on the recovery of established mCPA and mCPP memory impairment,suggesting that once the memory impairment is formed,even if additional iron supplementation cannot restore the damaged memory.We then explored whether low-iron content affects memory maintenance or extinction after mCPP memory has been formed.The results showed that there was no significant difference in the preference scores between the low iron diet morphine group and the normal diet morphine group,suggesting that low iron content does not affect the extinction of mCPP memory after the formation of mCPP.Interestingly,we found that low iron content impairs morphine-mediated spatial and contextual fear learning and memory retrieval.These results suggest that low iron diet can lower the iron content in hippocampus and striatum regions,and thus impair morphine-mediated learning and memory.All these learning and memory are closely related to the dorsal hippocampal CA1,so the dorsal hippocampal CA1 may be a key brain region in the effect of low iron content.To further verify this finding,a direct injection of deferiprone(DFP)(iron chelating agent approved by FDA in 2011)into the dorsal hippocampal CA1 was performed.Results showed that DFP administration to bilateral hippocampus CA1 reduced the total distance of spontaneous activity and effectively inhibited mCPP memory formation.To sum up,some new findings were obtained in this study.Low iron content impaired learning and memory after morphine exposure,including spatial memory,contextual fear memory,CPA negative memory and CPP positive memory.Among them,the dorsal hippocampal CA1 may be the key brain region,because direct injection of DFP into the dorsal hippocampal CA1 can reduce the total distance of spontaneous activity and lead to impairment of mCPP memory.These results suggest that brain low iron content may interfere with dopamine function in the dorsal hippocampal CA1 and thus impair learning and memory under opioid exposure,which may be one of the mechanisms of low iron content inhibiting addictive behaviors.These findings provide new evidence for understanding the neural mechanism of iron metabolism affecting opioid addiction and developing new approaches for addiction prevention and treatment related to iron metabolism,which has certain scientific significance and application value.