Feasibility of establishing model of Parkinson disease by injecting 6-hydroxydopamine at different parts of the nigrostriatal pathway in the brain of rats

BACKGROUND： Previous researches found that animal models with Parkinson disease （PD） could be established by injecting 6-hydroxydopamine （6-OHDA） into medial forebrain bundle （MFB）, substantia nigra compacta （SNC） and caudate-putamen complex （CPU） of the nigrostriatal pathway. OBJECTIVE ： To compare behavioral, biochemica 6-OHDA injections in the areas of MFB, SNC and DESIGN： Controlled observational study and histological properties of these rats undergoing the CPU respectively. SEI-IING： Department of Neurology, First Affiliated Hospital of Guangxi Medical University MATERIALS： A total of 64 adult female SD rats weighing 180-230 g were provided by the Animal Experimental Center of Guangxi Medical University. 6-OHDA （Sigma Company, USA）; Brain solid positioner （Standard model 51600, Stoelting Co., IL, USA）; rotational monitoring of little animal （type QL-1, USA）; high liquid chromatography （HLC, Waters Company）. METHOOS： The experiment was carried out in the Medical Experimental Center of Guangxi Medical University from February to December 2005. ① According to digital table, 64 SD rats were divided into MFB group, SNC group, CPU group and control group with 16 in each group. On the basis of the brain atlas of Paxinos, rats in the first three groups were injected with 5 μL 6-OHDA into right MFB （0 mm of line of incisor tooth, A/P 4.4 mm, L/R 1.2 mm, ON -7.8 mm）, SNC （line of incisor tooth just equal to horizon, A/P -4.8 mm, L/R 1.6 mm, ON -7.8 mm） and CPU （0 mm of line of incisor tooth, A/P 1.2 mm, L/R 2.7 mm, ON -5.4 mm）, respectively. The rats in control group were injected with 5 μL ascorbic acid solution （2 g/L）. One week after operation, 0.1 g/L apomorphine （Apo, 0.05 mg/kg） was subcutaneously injected into neck and then rotational behavior induced by Apo was recorded once a week for 8 weeks. The PD models were considered successful only when rotational times more than or equal to 7 times per minute. Eight weeks after operation, micro-perfusion was used to obtain micro-perfusate in bilateral CPU and contents of 3,4-dihydroxyphenylacetic acid （3,4-DOPAC） and homovanillic acid （HVA） were also measured. In addition, amount of tyrosine hydroxylase positive cells （TH＊） in SNC was counted with immuno- histochemical staining. MAIN OUTCOME MEASURES ： ① Successful rate of PD models; ② contents of dopamine and its metabolite in MFB, SNC and CPU groups and TH＊ amount. RESULTS： All 64 SD rats were involved in the final analysis. ③ Successful rate and rotational behavior： One week after operation, there were 6 successful models both in SNC and MFB groups; in the 2^nd week, there were 6 both in SNC and MFB groups and 1 in CPU group; in the 3^nd week, there were 1 in MFB group and 3 in CPU group; in the 4^nd week, there were 3 in CPU group. Otherwise, no successful case was found out in the next 3 weeks. Abnormal rotational behavior was not observed in control group. Four weeks after operation, successful rates were 81% （13/16） in MFB group, 75% （12/16） in SNC group and 44% （7/16） in CPU group.② Contents of 3, 4-DOPAC and HVA： Eight weeks after operation, contents in the SNC area of the injured side were lower than those on non-lesion side （P 〈 0.01）.③Changes of TH＋ amount： Eight weeks after operation, TH＋ amount in the SNC area of the lesion side was lower than that on non-lesion side （P 〈 0.01 ）. CONCLUSION： Injecting 6-OHDA into MFB, SNC and CPU can damage dopaminergic cells and establish successful PD models.

Dysfunction of synaptic endocytic trafficking in Parkinson's disease

Parkinson's disease is characterized by the selective degeneration of dopamine neurons in the nigrostriatal pathway and dopamine deficiency in the striatum.The precise reasons behind the specific degeneration of these dopamine neurons remain largely elusive.Genetic investigations have identified over 20 causative PARK genes and 90 genomic risk loci associated with both familial and sporadic Parkinson's disease.Notably,several of these genes are linked to the synaptic vesicle recycling process,particularly the clathrinmediated endocytosis pathway.This suggests that impaired synaptic vesicle recycling might represent an early feature of Parkinson's disease,followed by axonal degeneration and the eventual loss of dopamine cell bodies in the midbrain via a"dying back"mechanism.Recently,several new animal and cellular models with Parkinson's disease-linked mutations affecting the endocytic pathway have been created and extensively characterized.These models faithfully recapitulate certain Parkinson's disease-like features at the animal,circuit,and cellular levels,and exhibit defects in synaptic membrane trafficking,further supporting the findings from human genetics and clinical studies.In this review,we will first summarize the cellular and molecular findings from the models of two Parkinson's disease-linked clathrin uncoating proteins:auxilin(DNAJC6/PARK19)and synaptojanin 1(SYNJ1/PARK20).The mouse models carrying these two PARK gene mutations phenocopy each other with specific dopamine terminal pathology and display a potent synergistic effect.Subsequently,we will delve into the involvement of several clathrin-mediated endocytosis-related proteins(GAK,endophilin A1,SAC2/INPP5 F,synaptotagmin-11),identified as Parkinson's disease risk factors through genome-wide association studies,in Parkinson's disease pathogenesis.We will also explore the direct or indirect roles of some common Parkinson's disease-linked proteins(alpha-synuclein(PARK1/4),Parkin(PARK2),and LRRK2(PARK8))in synaptic endocytic trafficking.Additionally,we will discuss the emerging novel functions of these endocytic proteins in downstream membrane traffic pathways,particularly autophagy.Given that synaptic dysfunction is considered as an early event in Parkinson's disease,a deeper understanding of the cellular mechanisms underlying synaptic vesicle endocytic trafficking may unveil novel to rgets for early diagnosis and the development of interventional therapies for Parkinson's disease.Future research should aim to elucidate why generalized synaptic endocytic dysfunction leads to the selective degeneration of nigrostriatal dopamine neurons in Parkinson's disease.