Purpose To establish an ideal animal model of Parkinson’s disease (PD) in tree shrews, subcutaneous and intramuscular injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were used to observe the motor symptoms and brain histopathological changes in the tree shrews.
Methods The tree shrew PD model was induced by subcutaneous and intramuscular injections of 2 mg/kg MPTP, and the motor symptoms of PD were observed. A behavioral rating scale assessing tremor, posture, locomotion, gait, and balance was established for the tree shrew PD model with reference to the quantitative assessment criteria for Parkinson’s motor symptoms in non-human primates and patients; morphological changes in the midbrain of the tree shrews were observed by immunohistochemical staining of tyrosine hydroxylase (TH) and α-synuclein (α-syn). mRNA expression of TH and α-syn in the brain tissues of the tree shrew PD model was analyzed by qPCR.
Results Typical motor symptoms of PD appeared after the 3rd injection in the two injection methods, and the most obvious PD motor symptoms were found after the 4th injection, which were obviously weakened after the 7th injection and basically disappeared in the 15th injection. Immunohistochemical staining of TH and α-syn revealed that there was a decrease in the number of TH-positive nerve fibers in the substantia nigra and an abnormal increase in the number of α-syn in both the subcutaneous and intramuscular injections groups, demonstrating typical PD pathology. In the two injections groups, TH mRNA expression in the brain tissues was extremely significantly decreased and α-syn mRNA expression was extremely significantly increased.
Conclusion Repeated subcutaneous and intramuscular injections of 2 mg/kg MPTP both can induce consistent motor symptoms and lesions typical of PD in tree shrews, and both can be used to model PD in tree shrews.
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