|
Objective:Parkinson’s disease is a late-onset, progressivemotor disease marked by selective degeneration of dopaminergicneurons of the substantia nigra and formation of fibrillarcytoplasmic inclusions, known as Lewy bodies, which containubiquitin and α-synuclein. The cause of commonly encounteredsporadic disesase is unknown, and the role of genetics in these casesis uncertain. Post mortem studies strongly implicate oxidativedamage and mitochondrial impairment in the pathogenesis of PD.Epidemiological studies have suggested that pesticide exposure isassociated with an increased risk of developing PD.An accurate in vivo experimental model of PD shouldreproduce the progressive, selective nigrostriatal dopaminergicdegeneration and Lewy body formation seen in PD, test therelevance of the systemic comples I defect, and explain thepotential involvement of pesticide exposure in development ofparkinsonism. Unfortunately, no current animal model incorporatesall of these features.Nowadays, Betarbet et al who use a commonpesticide-rotenone,have developed a new model of PD,which can fitall these requirements.A naturally occurring compound derivedfrom the roots of certain plant species, rotenone is commonly usedas an insecticide in vegetable gardens, and is also used to kill orsample fish populations in lakes and reservoirs. It is widelybelieved to be a safe, natural alternative to synthetic pesticides.Rotenone is also a well characterized , high-affinity,specificinhibitor of complex I, one of the five enzyme complexes of theinner mitochondrial membrane involved in oxidativephosphorylation. Because it is extremely hydrophobic, rotenonecrosses biological membranes easily, and it does not depend on thedopamine transporter for access to the cytoplasm. Therefore,rotenone-unlike MPTP-is well-suited to produce a systemicinhibition of complex I. As the experiment conditions is too strict,manufacture procedure is too complicated, and the death rate is toohigh, Betarbet’s model is in difficulty to spreading and utilizing. Todevelop a more accurate in vivo model of PD ,we refine themanufacture procedure and adopt i.h rotenone chronically,continuously and systemically on the back .During the procedure,we execute the rats at different time point to observe its ethologyand pathology alternations.Method: Ninety adult male Wistar rats weighted 300~320gwere randomly divided into three groups:animal model rotenone2mg/kg group(30 rats), animal model rotenone 1mg/kg group(50rats) and control group(10 rats).The rotenone was hypodermicinjected into the back of rats every other day for 8 weeks. Thecontrol group received the same amount of DMSO:PEG(1:1) only.During the procedure, we execute the rats at 2 weeks, 4 weeks, 6weeks, 8 weeks. We used microscope to observe the pathologicalchanges of substantia nigra compacta in each groups. And observedthe expression of α-synuclein in the substantia nigra pars compactaby immunohistochemical stain under optical microscope.Statisticalanalysis: Intra-animal comparisons were done using pairedstudent’s t-test, while comparisons between groups were done usingone factor analysis for variance, t-test.Results:Initial characterization fo this model focused ondelineating the biochemical, molecular and anatomical pathologyof rotenone-induced degeneration. Rotenone-treated animalsdeveloped motor and postural deficits characteristic of PD, theseverity of which depended on the extent of lesions. All animalswith a dopaminergic lesion because hypokinetic and had unsteadymovement and hunched posture, even after termination of therotenone infusion. Systemic partial inhibition of complex I resultedin progressive nigrostriatal dopaminergic degeneration.Immunocytochemistry of phenotypic markers for dopaminergicneurons(tyrosine hydroxylase, TH) gave identical results, indicatingdopaminergic degeneration. Depending on the dose and duration ofrotenone exposure, animals demonstrated varying degress of striataldopaminergic denervation.Although we didn’t find the Lewy body,we saw some nigral neurons that showed aggregatescontainingα-synuclein which contain of Lewy body.Conclusion: It is more likely to succeed to make animalmodels of PD using rotenone hypodermic injected into the backof the rats.After administration, the animal model rotenone 2mg/kggroup showed severe systemic symptoms, which cover up the PD’scharacters, and the dopaminergic neurons of the substantia nigrapars compacta degenerated and dead severely. This progress is notlike of the natural progress of PD. For the above reasons, we candraw this conclusion which rotenone 2mg/kg is not a reasonabledose.On the contrary, after administration for 3 weeks, the animalmodel rotenone 1mg/kg group showed typically PD’s symptoms,like rigidity, hypokinetic and hunched posture.If continuousadministration, these PD’s characters aggravated gradualness andcovered up the original symptoms. Immunocytochemistry ofphenotypic markers for dopaminergic neurons(tyrosine hydroxylase,TH) gave identical results, indicating dopaminergic degeneration.Depending on the dose and duration of rotenone exposure, animalsdemonstrated varying degress of striatal dopaminergic denervation.Although we didn’t find the Lewy body, we saw some nigralneurons that showed aggregates containingα-synuclein whichcontain of Lewy body.So we can draw a safety conclusion thatabnormal accumulation ofα-synuclein is linked to PD.We test thatchronic, systemic inhibition of complex I by the lipophilic pesticide,rotenone, causes highly selective nigrostriatal dopaminergicdegeneration that is associated behaviorally with hypokinesia andrigidity. Nigral neurons in rotenone-treated rats accumulate fibrillarcytoplasmic inclusions that contain α-synuclein. These resultsindicate that chronic exposure to a common pesticide can reproducethe anatomical, neurochemical, behavioral and neuropathologicalfeatures of PD.
|