Abstract: Objective To investigate the neuron-protective effects of copolymer-1(Copolymer-1,Cop-1) on dopaminergic neurons in the continuous low-dose 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP) induced C57BL/6J mouse model of Parkinson's disease.Methods The C57BL/6J mice were randomly divided into 6 groups:group 1,MPTP model,group 2,in which MPTP was injected before the Cop-1 immunization,group 3,MPTP was injected immediately after the Cop-1 immunization,group 4,Cop-1 immunization was performed before MPTP injection,group 5,Cop-1 immunization and group 6,normal control group.The mice except for group 5 and 6 received one i.p.injection of MPTP(5 mg.kg-1) every day.After continuous injection for 24 days,all mice were sacrificed after the day of last MPTP injection.The dopaminergic neurons were analyzed quantitatively using immunohistocheministry of tyrosine hydroxylase(TH) and stereological counts,high performance liquid chromatography(HPLC) was used for analysis of striatal dopamine and its metabolites content,HE staining was used for spleen sections.Spleens of the mice of groups 1-4 were separated and Cop-1 sensitized lymphocytes were cultured.Results Compared with normal control group,the animals of,groups 1-4 showed toxins accumulation in the spleen,but HE staining was not significantly different among the groups.Compared with Cop-1 immunization group,there were also a large number of Cop-1 sensitized lymphocytes in other three Cop-1 immunization groups.Stereological counts revealed that MPTP caused a 65.13% loss of TH-positive neurons in substantia nigra(SN) compared with saline controls.Similar results were observed in MPTP-injected mice that received MPTP injection before Cop-1 immunization,immediately after Cop-1 immunization or Cop-1 immunization was performed before MPTP injection.The results of HPLC determination of striatal dopamine and its metabolites showed that,compared with the control group,MPTP model group dopamine and its metabolites were significantly reduced.The levels of dopamine and its metabolites were similar among groups 2-4,but were significantly higher than those of group 1(P<0.05).Conclusion Our data suggest that in the C57BL/6J mouse model,continuous low-dose MPTP injection did not show obvious destructive effects on the spleen,an organ of the immune system.Direct immunization with Cop-1 could be effective against MPTP toxicity,and protect DA neurons in the substantia nigra.

Key words: Parkinson's disease, copolymer-1, immunity, injured spleen