Accumulating evidence suggests that inflammation plays an important role in the progression ofParkinson's disease (PD). Among many inflammatory factors found in the PD brain, cyclooxygenase(COX), especially the inducible isoform, COX-2, is believed to be the critical enzyme in theinflammatory response. Induction of COX-2 is also found in an experimental model of PD producedby administration of 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). To investigate whetherinhibition of COX-2 by valdecoxib or deficiency in COX-2 could prevent dopaminergic neuronaltoxicity and locomotor activity impairment, we injected MPTP into valdecoxib-treated C57BL/6N miceand COX-2 deficient mice, respectively. Both automated total distance and vertical activitymeasurements of the open-field test were significantly reduced in the vehicle-treated mice at two weekspost-MPTP injection. In contrast, valdecoxib treatment significantly attenuated these deficits.Similarly, COX-2 deficiency attenuated MPTP-induced loss of coordination on a rotarod assay.Valdecoxib or deficiency of COX-2 reduced microglial activation while preventing loss of tyrosinehydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNpc). The total number ofactivated microglia in the SNpc had a strong positive correlation with the level of COX-2 anddopaminergic neurodegeneration. The results of this study indicate that reducing the activity of COX-2can mitigate the progressive loss of dopaminergic neurons as well as the motor deficits caused byMPTP neurotoxicity, possibly by suppressing the activation of microglia in the SNpc.

Pas de résumé fourni. / No summary available.

Made available in DSpace on 2018-08-01T21:35:05Z (GMT). No. of bitstreams: 1 tese_12340_Dissertação_João Marcos Lira de Melo.pdf: 1377215 bytes, checksum: 6a580a7f42211627bcef208e1b7e259a (MD5) Previous issue date: 2018-03-18 / O ácido rosmarínico (AR) é o componente químico de plantas muito utilizadas no meio medicinal, como alecrim, salvia, entre outras. Sua capacidade antioxidante é estudada como uma via alternativa natural para o tratamento de diversas doenças, mas o seu efeito sobre o sistema renina angiotensina (SRA) no modelo de Parkinson no sistema nervoso central ainda é pouco conhecido. Diante disso, o presente estudo tem como objetivo averiguar a influência do AR sobre o SRA no tronco encefálico de camundongos da linhagem C57bl/6 afetados pela toxina MPTP. Os animais foram tratados com a toxina MPTP (30 mg/Kg) para indução da doença de Parkinson, sendo que um grupo recebeu a toxina e o outro além do MPTP foi administrado o AR na dose 20 mg/Kg, via oral por 14 dias. Animais controle foram divididos em um grupo CON, outro grupo recebeu somente AR na dose 20 mg/Kg (grupo AR). A avaliação do peso dos órgãos dos animais demonstrou alteração significativa no peso do fígado e alterações histomorfométricas nos rins. A expressão proteica das proteínas antioxidantes (SOD e catalase) não demonstrou diferenças significativas entres os grupos. Não foi observadas diferenças entres os grupos na expressão da ECA1. Observou-se uma redução significativa na expressão do receptor AT2 no grupo MPTP, e houve um aumento significativo no grupo MPTP/AR. Estes resultados mostram um efeito protetor antioxidante e regulador do AR sobre o SRA. Dessa forma os resultados evidenciam que o AR pode ser uma via de estudo promissora para a busca de novos meios de tratamentos para doenças que alteram o sistema renina angiotensina.

Parkinson's disease (PD) is a neurodegenerative Lewy body disorder characterized by severe motor deficits, followed by cognitive dysfunction with progression of the disease. Environmental exposure has been suggested as a possible contributor to the development of PD and this view is linked to the discovery of the nigrostriatal neurotoxin MPTP. MPTP can induce dopamine specific degeneration within the basal ganglia often resulting in motor deficits similar to PD. MPTP used in the C57BL/6 mouse is a widely used animal model of PD. The pyrethroid permethrin (PM), and the organophosphate chlorpyrifos (CPF), can produce changes in dopaminergic nigrostriatal neurons, the primary target of PD and MPTP-induced neurotoxicity. Such insecticide induced changes in the basal ganglia could exacerbate the onset or severity of PD. Chronic exposure to the metal manganese (Mn) can damage the globus pallidus (GP) of the BG, and produce motor deficits similar to PD. Since the GP is part of the BG circuitry essential for motor control, and is synaptically integrated with the nigrostriatal pathway, Mn may exacerbate MPTP-induced neurotoxicity. Because the BG is disynaptically linked to the mesocortical pathway, a dopaminergic pathway that is important for cognition, Mn induced damage in the BG could indirectly affect the mesocortical pathway as well. This study investigated the pesticides, permethrin and chlorpyrifos, and the heavy metal, manganese as possible environmental compounds that could exacerbate PD in the MPTP treated C57BL/6 mouse. The first part of this dissertation used immunohistochemistry to examine insecticide induced effets on MPTP-induced neurotoxicity in the dorsolateral striatum of the C57BL/6 mouse, the principal target of the nigrostriatal pathway. Tyrosine hydroxylase (TH) was used as a marker for loss of dopaminergic neuropil and glial fibrillary acidic protein (GFAP) was used as a marker of glial activation in the striatum. Three experiments assessed effects of 1) PM (200 mg/kg), 2) CPF (50 mg/kg) & 3) PM + CPF, on MPTP (30 mg/kg) neurotoxicity. Immunohistochemistry revealed a decrease in TH staining and an increase in GFAP staining with MPTP (30 mg/kg). A main effect increase in GFAP was observed for PM (200 mg/kg), but not for CPF (50 mg/kg) or PM+CPF. Insecticides, alone or combined, did not alter MPTP-induced toxicity. . However, the absence of the PM-induced increase in GFAP staining following combined insecticide treatment suggests a neuroprotective effect. The next set of experiments in this dissertation looked at the effect of Mn on MPTP-induced neurotoxicity in the nigrostriatal and mesocortical dopaminergic pathways of the C57BL/6 mouse. Inductively Coupled Plasma atomic emission spectrometry revealed striatal Mn levels were significantly increased with multiple dose 100, 50, and 25 mg/kg MnCl2. Administration of Mn (MnCl2 s.c., Days 1, 4, & 7) in the MPTP (20 mg/kg i.p., Day 8) treated C57BL/6 mouse revealed Mn and MPTP interactions for locomotor activity, grip strength, and repeated measures of learning. Mn attenuated the effect of MPTP on striatal DOPAC, and facilitated the effect of MPTP on cortical DA and DOPAC. Mn also attenuated the MPTP induced decrease in cortical DAT. While these data support the notion that insecticides can produce tissue damage in the nigrostriatal pathway, in this case, these insecticide induced changes were not found to be strong enough to facilitate PD-like tissue damage. While Mn did not always facilitate MPTP neurotoxicity in the mesocortical and nigrostriatal dopaminergic pathways, these results demonstrate Mn and MPTP can interact in a complex way to alter dopaminergic function as well as motor and cognitive behavior. Differences in brain uptake mechanisms and metabolism of Mn and MPTP, could explain why combined administration of Mn and MPTP differentially affect dopaminergic activity in the nigrostriatal and mesocortical pathways. / Ph. D.

A doença de Parkinson (DP) é uma doença neurodegenerativa caracterizada pela progressiva depleção dos neurônios dopaminérgicos da substância negra (pars compacta). A DP não ocasiona apenas uma desordem motora, mas também pode provocar uma disautonomia cardiovascular. A DP com sintomas similares aos que ocorrem em humanos pode ser experimentalmente induzida em ratos e camundongos com a administração das neurotoxinas 1-metil-1-4-fenil-1,2,3,6-tetrahidropirimidina (MPTP), 6-hidroxidopamina (6-OHDA) e rotenona. Mais, na década de 90, camundongos transgênicos que expressam altos níveis de alfa-sinucleína mutante humana têm sido produzidos e utilizados para investigar a possível relação entre a agregação da proteína alfa-sinucleína e a DP, uma vez que em humanos, a alta expressão dessa proteína está relacionada ao desenvolvimento do parkinsonismo associado à desnervação cardíaca simpática. No entanto, a desnervação cardíaca e suas conseqüências no miocárdio na DP não estão claramente caracterizadas, pois na literatura os métodos quantitativos empregados para tal finalidade têm sua confiabilidade e acurácia questionáveis. Desta forma, avaliou-se, no modelo de indução neurotóxico (MPTP), o miocárdio de camundongos C57/BL aplicando-se métodos morfoquantitativos tridimensionais (estereológicos). Neste trabalho, observamos que o volume da parede ventricular, o volume e a densidade de volume do interstício cardíaco foram, respectivamente, 0,8%, 5,3% e 2,4% maior no grupo MPTP. O volume do lúmen ventricular, o volume ventricular, o volume das fibras musculares cardíacas e a sua densidade de volume foram, respectivamente, 11,7%, 0,9%, 2,3% e 1,7% maior no grupo controle. O número total de núcleos de cardiomiócitos foi 14,8% menor no grupo MPTP bem como o número total de cardiomiócitos que foi 19% menor também neste grupo. Houve diferença estatística significativa entre os grupos para o parâmetro número de cardiomiócitos. Não houve, porém, diferença estatística significativa para os outros parâmetros avaliados. / Parkinson´s disease (PD) is a neurodegenerative disorder mostly characterised by a profound reduction of dopamine in the striatum due to a dramatic loss of dopaminergic neurons in the substantia nigra (pars compacta). The disease is not only characterised by a motor disorder but also present cardiovascular dysautonomia. The disease has been chemically induced in rats and mice using neurotoxins such as 1-metyl-1-4-phenyl-1,2,3,6-tetrahydropyrimidina (MPTP), 6-OHDA and rotenone. In the nineties, transgenic α-synuclein mice have recently been used as a model of PD and alpha-synuclein aggregation, because the overexpression of this protein is related to the development of parkinsonism associated to the sympathetic cardiac denervation. Although, the cardiac denervation in PD and its consequences in myocardium is not well defined because the literature reports no reliable quantitative methods. Therefore, the myocardium of the C57/BL mice was investigated in the neurotoxin animal model (MPTP) applying tridimensional morphoquantitative methods (stereological). In this study, we observed an increase of 0,8%, 5,3% and 2,4% in ventricular wall volume, in cardiac interstitial volume and in cardiac interstitial volume density, respectively, in the MPTP group. The lumen ventricular volume, the ventricular volume, the cardiac muscle fibre and their volume density were, respectively, 11,7%, 0,9% , 2,3% and 1,7% larger in control group. The total number of cardiomyocyte nuclei was 14,8% lower in MPTP group as well as the total number of cardiomyocyte that was 19% lower for this group too. Significant difference was observed between the groups to the total number of cardiomyocyte. No significant difference, however, was detected for the others estimated parameters.

Un des rôles de la mitochondrie, qui possède son propre ADN (ADNmt), est la production de l'énergie nécessaire à la cellule, qu'elle synthétise sous forme d'ATP grâce aux oxydations phosphorylantes (OXPHOS). Ainsi, une altération du métabolisme énergétique mitochondrial peut provoquer l'apparition de pathologies mitochondriales dont, généralement, la sévérité est inversement proportionnelle à l'âge de début. De nombreuses études s'intéressent aux mécanismes d'apparition et de développement de ces maladies afin de mieux les comprendre et de pouvoir proposer des thérapies. Cependant, à ce jour, il est encore difficile de transformer l'ADNmt de façon ciblée (remaniement ou mutation). De plus, il existe encore peu de modèles animaux de pathologies mitochondriales qui permettraient de réaliser des études intégratives et d'essayer d'éventuelles molécules thérapeutiques. Dans le cadre de cette thèse, nous avons étudié deux types de modèles impliquant la modification du métabolisme mitochondrial. Dans un premier temps, nous nous sommes intéressés à la réalisation d'un modèle murin exprimant un grand nombre de caractéristiques du syndrome de Leigh, une maladie neurologique progressive. Pour cela nous avons utilisé une neurotoxine (MPTP) qui est connue pour sa toxicité envers les neurones dopaminergiques et aussi comme inhibiteur de la chaine respiratoire. Nous avons analysé l'activité de chaque complexe OXPHOS de différents tissus cérébraux et de tissus périphériques (cœur, foie, muscle et rein), prélevés sur des souris traitées et non-traitées. Nous avons retrouvé une inhibition des complexes III et/ou IV de la chaîne respiratoire dans le foie, le cortex, le striatum et le cervelet. Ces résultats, ajoutés à une neuro- dégénérescence accrue retrouvée dans une étude précédente, sont tous caractéristiques du syndrome de Leigh. Ces souris traitées par le MPTP semblent donc être un bon modèle pour l'étude de cette pathologie mitochondriale. Dans un second projet, nous nous sommes intéressés à l'effet des haplogroupes de l'ADNmt sur le métabolisme mitochondrial. En effet, bien qu'ils soient définis par des mutations neutres de l'ADNmt (polymorphismes), plusieurs études ont démontré des associations entre les haplogroupes et les pathologies, suggérant que les haplogroupes sont capables d'avoir un effet protecteur ou aggravant dans l'apparition d'une pathologie. Récemment, notre laboratoire a montré que certains haplogroupes avaient la capacité d'influencer le fonctionnement du métabolisme énergétique mitochondrial. Mon projet de recherche a donc consisté à mettre en place un modèle afin d'étudier les mécanismes cellulaires et moléculaires impliqués dans ce phénomène. Pour cela, nous avons recherché des haplogroupes d'intérêt dans la population française afin d'élaborer une collection de " cybrides " où chaque lignée de cellules possède un haplogroupe particulier mais un fonds génétique nucléaire commun à toutes les lignées. Nous avons caractérisé ces cybrides de manière biochimique (analyse de l'activité et des paramètres cinétiques de chaque complexe) et phénotypique (courbes de croissance). L'ensemble de ces résultats a été intégré dans un modèle informatique spécifiquement développé dans notre laboratoire pour modéliser la physiologie de la mitochondrie. Ce projet nous a permis de mettre en évidence l'influence des haplogroupes de l'ADNmt sur le métabolisme mitochondrial et de proposer une vision modulée des pathologies mitochondriales tant pour leur étude que pour leur diagnostic, en faisant ressortir la notion de médecine personnalisée. A l'avenir, il sera nécessaire de tenir compte du contexte génétique de l'ADNmt pour trouver de nouvelles stratégies ou de nouvelles cibles pour les thérapies des maladies mitochondriales. / The mitochondrion is an intracellular organelle responsible for the cellular energy production, by synthesizing ATP through the oxidative phosphorylation (OXPHOS). One of the characteristics of this organelle is that it has its own DNA (mtDNA) encoding for subunits of OXPHOS complexes. Any alterations of mitochondrial energy metabolism cause mitochondrial pathologies whose severity is generally inversely proportional to the age of onset. Some scientific studies are looking at the mechanisms of occurrence and development of these diseases in order to better understand them and to be able to offer therapies. However, there is no tool that can transform mtDNA in a targeted way by mutation or DNA rearrangement. Moreover, there are still few animal models of mitochondrial pathology that would allow integrative studies on the one hand, and on the other hand, to try out possible therapeutic molecules. In this thesis, we studied two types of models involving the modification of mitochondrial metabolism either by chemical treatment or by the use of mutations found in individuals. In a first part, we were interested in the realization of mouse model with a large number of characteristics of the Leigh syndrome, a progressive neurological disease characterized by neuropathological lesions associating a damage of the brain stem and the basal ganglia. For this study, we have used the 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP) neurotoxin, known for its toxicity to dopamine neurons and also as an inhibitor of mitochondrial respiratory chain. We analyzed the activity of the OXPHOS complexes I to IV on brain tissues (cerebelum, cortex, striatum and substancia nigra) and peripheral tissues (heart, liver, muscle and kidney) from treated and untreated mice. Inhibition of complexes III and/or IV in the liver, cortex, striatum and cerebellum was found. These results, combined with an increased neurodegeneration found in a previous study, are all characteristics of Leigh Syndrome. Mice treated with MPTP seem to be a good model for this mitochondrial pathology. In the second project, we looked at the effect of mtDNA haplogroups (haplotypes grouping) on mitochondrial metabolism. Although, haplogroups are defined by neutral mutations of mtDNA (polymorphism), several studies have shown associations between haplogroups and some pathologies suggesting that haplogroups are able to have a protective effect or being a risk factor in the pathology development. Recently, our laboratory has confirmed that some haplogroups may not be neutral and have the ability to influence the mitochondrial energy metabolism functioning. Therefore, my research project consisted of setting up a model to study these cellular and molecular mechanisms. We looked for haplogroups of interest in the population in order to elaborate a cellular collection where each cell line has a particular haplogroup but with a common nuclear genetic background in all the cell lines. This collection was obtained by cybride constructions. We characterized these cybrides biochemically by analyzing the activity of each complex, determining kinetic parameters (KM and Vmax) and titration specific respiratory chain inhibitors. Concomitantly, we defined cell parameters via growth curves. All these results were integrated into a computer model specifically developed in our laboratory to model mitochondrial processes. This project gives us some evidence of the mtDNA haplogroups' influence on mitochondrial metabolism and to propose a modulated vision of mitochondrial pathologies for their study and their diagnosis, highlighting the notion of personalized medicine. As each haplogroup modulates in the different way the mitochondrial metabolism, each individual could have a personal response to the same mutation or pathology. In future, the mtDNA genetics background should be taken into account to find new strategies or new targets for the therapies of mitochondrial diseases.

A doença de Parkinson (DP) é uma doença neurodegenerativa caracterizada pela progressiva depleção dos neurônios dopaminérgicos da substância negra (pars compacta). A DP não ocasiona apenas uma desordem motora, mas também pode provocar uma disautonomia cardiovascular. A DP com sintomas similares aos que ocorrem em humanos pode ser experimentalmente induzida em ratos e camundongos com a administração das neurotoxinas 1-metil-1-4-fenil-1,2,3,6-tetrahidropirimidina (MPTP), 6-hidroxidopamina (6-OHDA) e rotenona. Mais, na década de 90, camundongos transgênicos que expressam altos níveis de alfa-sinucleína mutante humana têm sido produzidos e utilizados para investigar a possível relação entre a agregação da proteína alfa-sinucleína e a DP, uma vez que em humanos, a alta expressão dessa proteína está relacionada ao desenvolvimento do parkinsonismo associado à desnervação cardíaca simpática. No entanto, a desnervação cardíaca e suas conseqüências no miocárdio na DP não estão claramente caracterizadas, pois na literatura os métodos quantitativos empregados para tal finalidade têm sua confiabilidade e acurácia questionáveis. Desta forma, avaliou-se, no modelo de indução neurotóxico (MPTP), o miocárdio de camundongos C57/BL aplicando-se métodos morfoquantitativos tridimensionais (estereológicos). Neste trabalho, observamos que o volume da parede ventricular, o volume e a densidade de volume do interstício cardíaco foram, respectivamente, 0,8%, 5,3% e 2,4% maior no grupo MPTP. O volume do lúmen ventricular, o volume ventricular, o volume das fibras musculares cardíacas e a sua densidade de volume foram, respectivamente, 11,7%, 0,9%, 2,3% e 1,7% maior no grupo controle. O número total de núcleos de cardiomiócitos foi 14,8% menor no grupo MPTP bem como o número total de cardiomiócitos que foi 19% menor também neste grupo. Houve diferença estatística significativa entre os grupos para o parâmetro número de cardiomiócitos. Não houve, porém, diferença estatística significativa para os outros parâmetros avaliados. / Parkinson´s disease (PD) is a neurodegenerative disorder mostly characterised by a profound reduction of dopamine in the striatum due to a dramatic loss of dopaminergic neurons in the substantia nigra (pars compacta). The disease is not only characterised by a motor disorder but also present cardiovascular dysautonomia. The disease has been chemically induced in rats and mice using neurotoxins such as 1-metyl-1-4-phenyl-1,2,3,6-tetrahydropyrimidina (MPTP), 6-OHDA and rotenone. In the nineties, transgenic α-synuclein mice have recently been used as a model of PD and alpha-synuclein aggregation, because the overexpression of this protein is related to the development of parkinsonism associated to the sympathetic cardiac denervation. Although, the cardiac denervation in PD and its consequences in myocardium is not well defined because the literature reports no reliable quantitative methods. Therefore, the myocardium of the C57/BL mice was investigated in the neurotoxin animal model (MPTP) applying tridimensional morphoquantitative methods (stereological). In this study, we observed an increase of 0,8%, 5,3% and 2,4% in ventricular wall volume, in cardiac interstitial volume and in cardiac interstitial volume density, respectively, in the MPTP group. The lumen ventricular volume, the ventricular volume, the cardiac muscle fibre and their volume density were, respectively, 11,7%, 0,9% , 2,3% and 1,7% larger in control group. The total number of cardiomyocyte nuclei was 14,8% lower in MPTP group as well as the total number of cardiomyocyte that was 19% lower for this group too. Significant difference was observed between the groups to the total number of cardiomyocyte. No significant difference, however, was detected for the others estimated parameters.

Parkinson’s disease is the second common neurodegenerative disease and is most frequently diagnosed in individuals over 60. There are no available medications that can prevent or restore the loss of neurons that correspond to motor impairments in patients. Identifying novel therapeutic compounds that are capable of slowing and reversing the extensive neurodegeneration that occurs in PD remains an important goal of the field. While basic research has identified potential therapeutic agents, studies often use young model organisms to demonstrate efficacy of the target compound. This approach ignores the impact of the aged CNS on the disease process, and likely contributes to high failure rates of translation in clinical trials. Here we investigate the capacity for astaxanthin (AXT), a xanthophyll carotenoid, to attenuate the neurotoxicity to MPTP, a toxin routinely used to establish parkinsonian symptoms in mice. We show that AXT reduces MPTP induced neurotoxicity in young, but less effective in the aged animals. While AXT is an interesting neuroprotective capacity, there are also multiple reports that indicate AXT may preserve cognitive function in the context of neurodegeneration and neural injury, the impact of AXT under physiological conditions and in the aged CNS has been largely uninvestigated. We also evaluate the effect of AXT on cognitive function in young and aged mice. Here, we show that AXT supplementation can modulate neural plasticity is associated with improved performance in cognitive behavioral tasks. This diet effect was observed in both young and aged mice, suggesting a novel and direct mechanism of action in synaptic function.

Parkinson’s disease (PD) is characterized by the progressive loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNc). Mechanisms regulating this neurodegeneration, however, are unclear. Evidence from PD pathology and models of PD, indicate mitochondrial disfunction triggers several death signalling pathways. Accordingly, in vivo and in vitro mitochondrial stress models of PD were employed to explore the role of two divergent molecular influences on dopaminergic neuronal survival. We examined neuroinflammatory and death signalling pathways arising from MPTP-induced mitochondrial stress. Interferon-gamma (IFN-ɣ) is a cytokine known to activate cellular components of inflammation, including microglia of the central nervous system (CNS). Results of a screen for cytokines in PD patient plasma revealed elevated levels of IFN-ɣ, suggesting a correlation between IFN-ɣ and PD associated DA cell death. In an MPTP mouse model of PD, germline deletion of IFN-ɣ improved survival of DA neurons and the nigrostriatal system, along with a reduction in microglia activation. Employing a survival co-culture system of neurons and microglia, it was found that neutralizing IFN-ɣ reduced DA cell loss induced by the mitochondrial complex I inhibitor, rotenone. DA cell death required localized microglia, activated through the IFN-ɣ-receptor (IFN-ɣ-R), with DA survival inversely proportional to IFN-ɣ expression, found to be up-regulated following rotenone. Investigation of the calpain-Cdk5-MEF2 signalling pathway in the MPTP model of DA cell death, motivated an examination of the nuclear orphan receptor, Nur77, following a review of potential MEF2 regulatory targets. MPTP induced a reduction in Nur77 mRNA from basal ii levels in SNc tissue, further regulated by ectopic Nur77 expression. These results strengthened our new model of MEF2 Nur77 regulation in DA neurons. In MPP+/MPTP DA survival experiments, loss in germline Nur77 expression presented an elevation in DA neuronal death both in vitro and in vivo, with a greater impairment in the nigrostriatal circuitry in comparison with normal expressing animals and cells. Dopaminergic supersensitivity related to Nur77 deficiency was attenuated with the ectopic expression of AV-Nur77 in vivo. These opposing mediators of survival yield new mechanisms by which DA neurons die, suggesting a mutitargeting approach to halt the progression of DA cell death.

Attention deficit hyperactivity disorder (ADHD) is a neurobehavioral disorder that affects 11% of children in the US alo­ne. Methylphenidate (MPH) is the most commonly prescribed drug for the treatment of ADHD. Given the fact that ADHD symptoms persist in up to 50% of patients, many children receive MPH from childhood to early adulthood. Unfortunately, most of the scientific literature focuses on the short-term consequences of MPH, even though individuals are taking MPH for many years. MPH acts by blocking dopamine (DA) transporters and norepinephrine transporters, preventing the reuptake of these catecholamines following release. Previous research has shown that long-term exposure to MPH causes dopaminergic neurons within the nigrostriatal pathway to be more sensitive to the Parkinsonian toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We hypothesize that oxidative stress caused by the spontaneous oxidation of the excess DA in the synaptic cleft is what’s rendering dopaminergic neurons within the nigrostriatal pathway to be more sensitive to MPTP. Adolescent male Swiss-Webster mice were divided into three cohorts and administered either saline (control), 1 mg/kg MPH (normal dose) or 10 mg/kg (abusive dose) via intraperitoneal (IP) injections for 12 weeks. Mice were injected twice daily, Monday through Friday, mimicking a school-week dosing schedule. After 12 weeks, all animals received a drug washout period of 7 days. Then, half of each cohort was treated with MPTP (4 x 20mg/kg, every 2 hours), while the other half was administered 4 injections of sterile saline. Seven days after MPTP or saline treatment, the mice were sacrificed, brains were removed, and the substantia nigra (SN) and striatum (STR) were collected. Oxidative stress related to increased DA levels was determined using the glutathione assay to measure glutathione (GSH) content and near-infrared fluorescence dot blots to measure free and protein-bound ortho-quinones. GSH is an important antioxidant and thus its depletion would be indicative of oxidative stress. Additionally, since DA may be oxidized to a quinone, increases in free and protein-bound ortho-quinones also indicate oxidative stress. Interestingly, we observed a significant decrease in GSH as the dose of MPH increased with both saline and MPTP samples. Furthermore, there was a significant increase in quinones as the dose of MPH increased. In conclusion, it appears that long-term exposure to MPH sensitizes dopaminergic neurons within the nigrostriatal pathway to oxidative stress, rendering them vulnerable to further insults, such as MPTP exposure. As such, these studies provide insight into the risks of long-term psychostimulant exposure.