The Roles Of Thioredoxin-1 In Regulating Extinction And Reinstatement Of Conditioned Place Preference Induced By Environmental Toxicant Methamphetamine

Drug abuse result in drug addiction which expresses tolerance,dependence,abstinence relapse.Methamphetamine?METH?is a strongly addictive psychostimulant,which can act on central nervous system and cause severe mental dependence and addictive behavior.Long-term use of METH can seriously damage the body function,lead to mental disorders,damage family harmony and healthy social development.In addition,illegal synthesis and extensive use of METH can destroy water quality and soil,resulting in serious environmental pollution.Currently,the most difficult problem in the treatment of drug addiction is the high relapse rate even after long-term extinction.The main reason for drug relapse is the drug itself,drug-related clues and environment.Environmental stimulus and drug use process are repeatedly matched and become drug-related environmental clues.After long-term extinction,the organism will have a strong thirst for drugs when it contacts environmental cues again,which will lead to drug relapse.Therefore,eliminating or weakening the cognitive memory of drug-related clues,environment and drug itself will help to withdraw from drug addiction.The dopamine and glutamate system from ventral tegmental area?VTA?projecting to nucleus accumbens?NAc?and prefrontal cortex?PFC?play important roles in drug addiction.N-methyl-D-aspartic acid?NMDA?,extracellular signal-regulated kinase?ERK?and cAMP responsive element-binding protein?CREB?are involved in METH-CPP extinction and regulate the cues related with memory by interacting with dopamine receptor D1.Thioredoxin-1?Trx-1?is a redox regulating protein with an active site sequence,-Cys-Gly-Pro-Cys-,is widely distributed in tissues and organs.Trx-1 plays a cytoprotective role against cellular damage and environmental stress.Trx-1 can protect cells from oxidative stress damage caused by hydrogen peroxide?H₂O₂?,ultraviolet radiation by scavenging oxygen free radicals and hydroxyl free radicals.Our previous study has shown that the Trx-1 inducer,Geranylgeranylacetone?GGA?can protect mice against morphine-induced reward effect and withdrawal syndrome through upregulation of the Trx-1 expression.Trx-1 overexpression can resist METH-induced CPP in mice.The aims of this study is to explore the roles of Trx-1 in regulating METH addiction and the underling molecular mechanism.We studied the role of Trx-1 in METH-induced CPP expression,extinction,and reinstatement,as well as the possible molecular mechanisms through establishment of the METH-induced CPP expression,extinction,and reinstatement in mice and detected the effects of Trx-1 on the expressions of dopamine and glutamate signaling pathway,synaptic formation related molecules.The main results of this paper are as follows:?Overexpression of Trx-1 occluded the CPP induced by METH.The results of behavioral test showed that,there was no significant difference in locomotor activity between wild-type mice and Trx-1 transgenic mice.After establishment of METH-CPP,there was still no significant difference in locomotor activity between wild-type mice and Trx-1 transgenic mice.However,the CPP was significantly induced after conditioned training with METH in wild-type mice,but not in Trx-1 transgenic mice.These results indicate that overexpression of Trx-1 did not affect the locomotor activity of mice,but could resist the expression of CPP induced by METH.?Overexpression of Trx-1 blocked the expression of CPP induced by METH-priming in mice.The results of behavioral test showed that the behavioral sensitization was significantly induced by METH,while Trx-1 overexpression attenuated the activity of behavior sensitization.In addition,Trx-1 overexpression also inhibited the expression of CPP in Trx-1 transgenic mice as compared with the wild-type mice.Western blot analysis showed that the expression of Trx-1 in the NAc of wild-type mice was significantly induced by METH,while the increase of Trx-1 in the NAc was significantly inhibited by the overexpression of Trx-1.The present results showed that METH significantly increased the expression of NMDA receptor 2B subtype?GluN2b?in the NAc of wild-type mice,while Trx-1 overexpression significantly inhibited the increase of the GluN2b expression induced by METH.The results showed that METH significantly increased the activities of ERK and CREB in the NAc of wild type mice,while Trx-1 overexpression significantly inhibited the increases.These results suggest that Trx-1 may regulate the expression of CPP induced by METH-priming via inhibiting GluN2b,ERK and CREB.?Downregulation of Trx-1 in VTA delays CPP extinction induced by METH.The results of behavioral test showed that METH significantly induced the formation of CPP in mice.Trx-1siRNA in VTA significantly delayed the extinction time of CPP as compared with normal mice.Western blot analysis showed that the expression of Trx-1 in VTA of mice was significantly lower than that in control group?treated with saline?,and VTA Trx-1 siRNA significantly decreased Trx-1 expression and inhibited the decrease of Trx-1 expression after METH-CPP extinction.Western blot analysis showed that the expressions of TH and D1 in the VTA,NAc and PFC of mice were significantly lower than that in the control group.Interestingly,downregulation of Trx-1 in VTA reversed the decrease of TH and D1 expressions in the VTA,NAc and PFC caused by METH-CPP extinction.The current results showed that the activities of ERK and CREB in the VTA,NAc and PFC of mice were in accordance with the changes in the expression of TH and D1 after METH-CPP extinction.These results indicate that downregulation of Trx-1 in VTA may promote METH-CPP expression through promoting transduction of mesolimbic dopamine signal,thereby delays the extinction of METH-CPP.?Trx-1 downregulation in NAc promotes CPP reinstatement induced by METH.The results of behavioral test showed that,1.0mg/kg of METH significantly induced the reinstatement of METH-CPP in normal and NAc Trx-1 shRNA mice.0.5 mg/kg of METH significantly induced the reinstatement of METH-CPP in NAc Trx-1 shRNA mice but did not cause the reinstatement of METH-CPP in normal mice.These results indicate that the Trx-1 downregulation in NAc may enhance the sensitivity of mice to METH,which led to the low dose of METH to induce the reinstatement of CPP.Western blot analysis showed that the expressions of Trx-1 and GluN2b and the activities of ERK and CREB in the NAc of normal and NAc Trx-1 shRNA mice were significantly higher than those in the control group after reinstatement of 1.0 mg/kg of METH-induced CPP.The expressions of Trx-1 and GluN2b and the activities of ERK and CREB in the NAc of METH-treated mice has no significant difference as compared with the control mice after reinstatement of 0.5 mg/kg of METH-induced CPP,while Trx-1 and GluN2b expressions,and ERK and CREB activities in the NAc of METH-treated mice were significantly higher as compared with the saline-treated mice in Trx-1 shRNA group mice.Indicating that the downregulation of Trx-1 in NAc promoted the expressions of GluN2b and the increases of ERK and CREB activities in the NAc by METH-priming,thus CPP reinstatement induced by 0.5 mg/kg of METH in the NAc of Trx-1 shRNA mice may be enhanced.In conclusion,Trx-1 plays an important role in regulating METH-induced CPP formation,extinction and reinstatement.Trx-1 may inhibit the addiction induced by METH through regulating the mesolimbic dopamine and glutamate system.