Objective To explore the effects of prophylactic inoculation of optimized hα-synuclein(hα-syn) DNA vaccine on the dopaminergic neurons suffering from acute neurotoxin injury.Methods The optimized DNA vaccine,designated as pVAX1-IL-4/SYN-B,was prepared.The C57BL mice were grouped as pVAX1-IL-4/SYN-B group,pVAX1 group and PBS group.Animals in each group received 3 times of 50μl injection of plasmid pVAX1-IL-4/SYN-B,plasmid pVAX1 or PBS,respectively,in the anterior tibial muscle of either posterior limb.Two weeks after the last injection,all the mice were then given intraperitoneal injection of 20mg/kg MPTP with an attempt to reproduce the model of Parkinson’s disease(PD) 4 times with a 2h interval.The changes in behavior of mice were observed when the model was being reproduced to verify if the model was reproduced.Mice were sacrificed at 1st,3rd and 7th day(6 each) after the last injection of MPTP.The expression of COX-2 mRNA at each time point was detected by RT-PCR,and the expressive changes in COX-2 and CD11b(representing the activated state of microglia) were detected with immunohistochemistry assay.Results The PD mouse model was successfully reproduced.The number of positive COX-2 and CD11b cells was remarkably decreased in pVAX1-IL-4/SYN-B group than in pVAX1 group and PBS group,while no significant difference was found between the latter 2 groups(P > 0.05).The results of RT-PCR showed that COX-2 mRNA expression in all the 3 groups at the 1st,3rd and 7th day after last injection of MPTP was slight on the 1st day,peak value appeared on the 3rd day,and it then declined on the 7th day.At each time point,the COX-2 mRNA expression in pVAX1-IL-4/SYN-B group(0.28±0.07,0.59±0.07 and 0.45±0.05 at day 1,3 and 7) was significantly lower(P < 0.01) than that in pVAX1 group(0.43±0.05,0.74±0.15 and 0.61±0.10) and in PBS group(0.41±0.02,0.73±0.13 and 0.60±0.01),while no difference was found between the latter 2 groups(P > 0.05).Conclusion Prophylactic inoculation of optimized hα-syn DNA vaccine may inhibit the expression of COX-2 and the activation of microglia,showing a protective effect on dopaminergic neurons.