Astrocyte reactivity in related brain regions in a mouse model of MPTP-induced Parkinson's disease

BACKGROUND: Severe injury to dopaminergic neuronal cell bodies and their axon terminals in the substantia nigra pars compacta (SNC) has been observed in both Parkinson's disease (PD) patients or in 1-methy-4-phenyl-1,2,3,6-tetrahydropyrindine(MPTP)-induced PD animal models, but only slight injury occurs in the adjacent ventral tegmental area (VTA). The mechanisms underlying this selective injury remain poorly understood. OBJECTIVE: To comparatively observe astrocyte reactivity in the SNC, caudate putamen (CPU), VTA, and frontal association cortex (FrA). DESIGN, TIME AND SETTING: A cellular and molecular biology, randomized, controlled experiment was performed at the Institute of Neurobiology, Department of Human Anatomy, Medical School of Nantong University, between December 2006 and September 2008. MATERIALS: A total of 80 healthy adult male C57BL/6 mice were included in this study. MPTP was purchased from Sigma, USA. METHODS: Mice were randomly divided into a model group (n = 64) and a sham-operated group (n = 16). PD was induced in the mice from the model group by intraperitoneal injection of 20 mg/kg MPTP, once every three hours, for a total of 4 times. MAIN OUTCOME MEASURES: Tyrosine hydroxylase (TH)-immunoreactive neurons and glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes were examined by dual immunofluorescence labeling. GFAP-immunoreactive astrocytes in the CPU and FrA were determined by immunofluorescent staining. GFAP mRNA expression in the SNC, CPU, VTA, and FrA was detected using real-time polymerase chain reaction. TH protein levels in the TH-immunoreactive axon terminals of the CPU and FrA were detected by Western blotting. RESULTS: Numbers of TH-immunoreactive neurons in the SNC, and TH protein level in the CPU, markedly decreased (by approximately 68%) 1 day after MPTP injection, and gradually increased at 3 days. Simultaneously, astrocyte reactivity was strengthened, in particular at 7 days. However, after MPTP injection, decreases in the numbers of TH-immunoreactive neurons in the VTA, and TH protein levels in the FrA, were less apparent (approximately 15%). Also, no obvious astrocyte reactivity was observed. CONCLUSION: In a mouse model of PD, astrocyte reactivity was apparent in the SNC and CPU, but not the VTA or FrA. In addition, astrocyte reactivity was greater in regions where injury to dopaminergic neurons was more severe.