The Effects Of Dopamine On Remyelination After Cuprizone-induced Demyelination In Mice

Background and purposeSchizophrenia is a severe mental disorder affecting about 1% of the population worldwide.Oligodendrocyte damage theory and dopamine(DA)theory are two popular ones among the multiple theories about schizophrenia.Oligodendrocytes(OLs)abnormality may decrease myelin integrity in white matter thus contributing to some symptoms of schizophrenia.Drugs that change DA level in brain can induce psychotic symptoms and decrease myelin basic protein(MBP)level.However,the relationship between the OLs and DA has rarely been studied.We aim to explore the possible effect of DA on myelination and oligodendrocytes maturation in white matter of the brain.Materials and methods6-week-old male C57BL/6J mice were randomly divided into 4 groups: Control group(CNT),cuprizone group(CPZ),cuprizone-vehicle group(CPZ-VEH),cuprizone-tolcapone group(CPZ-TL).We established a demyelination model by feeding mice with CPZ-containing food for 4 weeks and a remyelination model by stoping CPZ exposure to allow remyelination for three weeks.During the remyelination period,mice received intraperitoneal injection once a day of tolcapone(TL),which is an inhibitor of catecholamine-o-methy transferase(COMT)and able to change DA levels in the brain.The body weight of mice was scaled once a week during the experimental period.On day 28 or 51,the behavior tests of open field,puzzle box,and social interaction were performed with the mice,followed by immunohistochemical staining with the antibody against MBP,Western blot measurement of MBP protein levels in PFC and CPU regions,DA level assessment by ELISA,m RNA expression levels of DA receptors(D2R,D3R)by RT-q PCR,and evaluation of OLs development by immunofluorescent staining with brain tissue of mice.ResultsBody weight: Two-way ANOVA analysis results showed that the interaction between time and CPZ exposure had statistical significance.One-way ANOVA analysis results showed that time significantly affected the weight of mice in the CNT and CPZ group,which means that the animal weight increased with age.The post-hoc comparison showed that the weight of mice in the CPZ group was significantly lower than those in the CNT group on the day 14,21,and 28.During the recovery period,the interaction between time and TL administration did not have a statistical significance.One-way ANOVA analysis results showed that mice in the CPZ-VEH group and CPZ-TL group did not gain weight with age.The post-hoc comparison showed that there was no statistical difference in weight of mice between the CPZ-VEH group and CPZ-TL group at the same time point.Behavioral tests: After 28 days of CPZ exposure,compared with the CNT group,the CD/TD ratio of the mice in the CPZ group was significantly reduced in the open field test;the time spent in the T7 test of the puzzle box experiment was significantly reduced;in the social interaction test,there was a significant difference between E session and C session in the CNT group,but there was no statistical difference between those in the CPZ group.Three weeks after CPZ withdrawal,compared with CPZ-VEH group,the CD/TD ratio and CD in the CPZ-TL group were significantly reduced in the open field test;the time spent in the T3 and T4 of the puzzle box test was significantly reduced;in the social interaction test,there was a significant difference between E session and C session in the CPZ-VEH group,but there was no statistical difference between those in the CPZ-TL group.DA levels: In ELISA,after 28 days of CPZ exposure,there was no significant difference in DA level between the CPZ and CNT group.Three weeks after CPZ withdrawal,compared with the CPZ-VEH group,the CPZ-TL group had significantly higher DA level in the PFC region,and significantly lower DA level in the CPU region.RT-q PCR test showed that there was no statistical difference in the m RNA expression of D2R/D3 R.Remyelination: After 28 days of CPZ exposure,compared with the CNT group,IHC test showed that the optical density × positive staining area(IOD)of MBP in mice’s brain was significantly reduced in PFC and CPU regions,and the WB test results indicated a significant decrease in the expression of MBP protein levels.Three weeks after CPZ withdrawal,compared with CPZ-VEH group,IHC test showed that the IOD value of MBP in PFC and CPU regions was significantly reduced,and the results of the WB showed that MBP protein levels were significantly reduced in the CPU region.OLs development: Three weeks after CPZ withdrawal,compared with the CPZ-VEH group,the number of APC-positive cells was significantly reduced in CPU region,while the number of NG2-positive cells was significantly increased in the CPZ-TL group in PFC and CPU regions by IF.ConclusionCPZ exposure can cause behavioral changes and demyelination in the brain of mice.Three weeks after CPZ withdrawal,the behavioral changes of the mice gradually returned to normal,accompanied by the process of remyelination.During this recovery period,by injecting TL intraperitoneally,DA levels were increased in the PFC region,but decreased in the CPU region,and mouse’s short-term,long-term memory and social behavior were damaged at the same time.It is worth noting that this treatment inhibited the maturation process of the OLs cell lines in PFC and CPU regions,thereby inhibiting the remyelination process of these two brain regions after CPZ withdrawal.However,TL did not significantly affect the expression levels of D2 R and D3 R m RNA.These results proved for the first time that the DA level of brain can inhibit the maturation of OLs cell lines and myelination process whether DA level is too high or too low,thus integrating the DA theory of schizophrenia and the theory of oligodendrocyte damage and deepening our understanding of the pathophysiology of schizophrenia.