| BACKGROUNDExtensive research has shown that ?-synuclein(?-syn),a small acidic protine,is composed by 140 amino acids and widely expressed in the nerve cells of the brain.Overexpression and abnormal aggregation of ?-synuclein in the lewy bodies and synapses of neurons in the substantia nigra,is a significant marker of the pathological changes of Parkinson's disease.Under pathological conditions,structural changes lead to misfolding,followed by fibrosis and eventually formation of insoluble fibrous aggregates,which induced mitochondrial dysfunction,lysosomal autophagy and thus leading to apoptosis of nerve cells.Another major characteristic of Parkinson's disease is the continuous activation of N-methyl-D-aspartate receptor(NMDA receptor).Ketamine(Ket)is a non-competitive antagonist of NMDA receptors,which has an inhibitory effect on the over-activation of NMDA receptors.It has reported that ketamine has an inhibitory effect on motor symptoms of Parkinson's disease,but the basic research that either ketamine has influence over ?-syn expression or not,has not been found.AIMIn this study,we are going to explore the effects of ketamine on the behavioral and the expression of synaptic protein ?-syn in a mouse model of Parkinson's disease,and revealing the pathway by which ketamine can change the abnormal expression of ?-syn.METHODSForty-eight healthy male mice were randomly divided into three groups for the experiment.The three groups were the control group(NaCl group),the model group(MPTP group)and the experinental group(MPTP+Ket group).The Parkinson's disease mouse model was prepared by intraperitoneal injection of neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP)with the dose of 25 mg/Kg.The dose of MPTP and ketamine was given for continuous seven days with single injection of each drug every day and ketamine was always injected after half an hour of MPTP adminitration.Rotarod experiment and gait analysis system were used to evaluate the behavioral differences among the animals in three groups.Immunohistochemical(DAB)staining was used to observe the changes in the number of dopaminergic neurons in the substantia nigra.Immunofluorescence staining was used to observe the changes of expression and distribution of ?-syn in the nigrostriatal region and western blot was used to detect the expression of ?-syn,tyrosine hydroxylase(TH)and the changes of the proteins realate to autophagy,such as LC3,Atg 4D,Atg 5 and Beclin 1 in substantia nigra and striatum region.RESULTSAccording to the results of the behavioral experiments,ketamine changed the phenomenon that the number of laps and the step length of the mice were reduced in MPTP group,indicating that the coordination ability of the mice was improved after Ketamine treatment.The results of DAB staining indicated that the decreas in the number of dopaminergic neurons in substantia nigra was reversed by ketamine,and the immunofluorescence staining results showed that the fluorescence intensity of ?-syn in nigrostriatal region was decreased in MPTP+Ket group than that in MPTP group.Western blot results also confirmed that the expression of TH protein in the nigrostriatal region of the MPTP+Ket group was increased compared with that in MPTP group,while the expression of ?-syn was decreased,and the expression of autophagy-related proteins in the striatum of the mice was relatively decreased.These results suggest that ketamine has a neuroprotective effect on a mouce model of Parkinson's disease induced by MPTP.CONCLUSIONKetamine inhibited the level of ?-syn oligomers in the nigrostriatal region of the Parkinson's disease mice,reduced the nonfunctional autophagy in the striatum and the neuronal apoptosis caused by accumulation of autophagosomes,thus indicating a neuroprotective effect of ketamine on the neurotoxicity induced by MPTP. |
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