Establishing motor disorder mouse models of Parkinson disease Comparison of 6-hydroxydompamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

At present, pathogenesis and mechanism of Parkinson disease （PD） are still unclear. Animal models of PD are essential tools in studies on etiology and therapy and should mimic the chronic pathological process, histological characteristics and motor behavior dysfunction. In recent years, transgenic mice have been widely utilized to study the mechanism of PD, and it has become imperative that a PD mouse model of motor behavioral dysfunction be established. OBJECTIVE： To compare the behavioral and histochemical characters of two neurotoxic mice model induced with 6-hydroxydopamine （6-OHDA） or 1-methyl-4-phenyl-1, 2, 3, 6 -tetrahydropyridine （MPTP）, and a better method to mimic Parkinson disease will be found out. DESIGN： Parallel experiment. SETTING： Laboratory of Molecular Genetics, Department of Medical Genetics, Shanghai Jiao Tohg University. MATERIALS： Sixty 129Sv/C57BL6J male wild mice, SPF grade, 8 - 12 weeks old, weighing 20 - 25 g, were provided by Experimental Animal Center, Shanghai Jiao Tong University. All the surgery operation was performed according to the rules of Shanghai Jiaotong University Animal Committee. METHODS： The experiment was carried out in the Laboratory of Molecular Genetics （National Key Laboratory）, Department of Medical Genetics, Shanghai Jiao Ttong University from March to August 2006. ①Thirty-two male mice were randomly divided into control group and drug treatment group with 16 mice in each group. Surgery was carried out and 6-OHDA was administrated to substantia nigra pars compacta （SNpc） and nigra-striatum pathway according to the different parameters with intoxication apparatus. Saline was injected to the other 16 mice according to the same paradigm. 1 mg/kg apomorphine was injected intraperitoneally 2 weeks later after surgery to induce the imbalanced rotation behavior for 40 minutes. ②Twenty-eight mice were randomly divided into 4 groups with 7 in each group, including low-dose, moderate-dose, high-dose groups and negative control group. Then, mice in the drug treatment group were injected intraperitoneally with 5, 10 and 15 mg/kg MPTP for 9 successive days. In addition, mice in the control group were injected with the same volume of saline for 9 days. Pole test and stride length test were utilized to detect coordinative behavioral dysfunction. Mice were sacrificed 20 days after MPTP treatment, and histochemical staining of tyrosine hydroxynase （TH） was used to observe the loss of dopaminergic neuron in SNpc. MAIN OUTCOME MEASURES： ① Success ratio of each model establishment method; ② inducible asymmetric cycle behavior test 2 weeks after 6-OHDA injection; ③behavioral dysfunction in pole test and stride length, morphological changes in brain tissue. RESULTS： Totally sixty mice were used in this experiment and 3 mice were excluded because of the hypersensitivity or the clumsy reaction in motor behavioral detection before MPTP treatment, therefore, data was analyzed with the rest 57 mice. ① Lethal ratio： Three out of 16 mice died in striatum injection group and 5 out of 16 mice died in nigro-striatal pathway group. No mouse died in MPTP treatment groups. ② Locomotor behavior： No dysfunction of locomotor was found in 6-OHDA treatment groups. However, several motor behavioral dysfunction were start to present at the 4th day of MPTP injection. ③ Asymmetric cycle behavior： No asymmetric cycle was induced successfully two weeks after 6-OHDA surgery. Mice show hypersensitive behavior 10 minutes after apomorphine injection, which lasted for about 20 minutes. ④ Pole test： From the 4^th day of MPTP treatment, mice started to display coordinate dysfunction, such as climbing down along the pole in spiral, moving slowly with hesitation. Some mice could not grab the pole and slide down along the pole at 4th day post injection. Comparing with 0 dose control group, all the threedrug treatment groups show significant different dysfunction from the 4th day to the 20th day post injection （P 〈 0.01）. ⑤ stride length test： Mice＇s stride length decreased, when treated with MPTP, and the mice in the high dose group displayed obviously. ⑥ Dopaminergic neuron stained with TH in nigra pars compacta： The results indicated that administrated MPTP （from low dose to high dose） by intraperitoneal cause chronic lesions on the dopaminergic neuron in the SNpc. CONCLUSION： PD mice models induced with 6-OHDA show high mortality ratio and no asymmetric cycle was found after apomorphine injection. However, injection of MPTP intraperitoneally can simulate the chronic pathway of PD, typical histological changes are found and stable motor behavioral dysfunctions are displayed.