Thèse Médecine Paris, 1901, n°367.

Korsakoff's syndrome (KS) is characterized by the acute onset of a severe anterograde memory impairment and a less pronounced retrograde amnesia. In addition to deficits in memory, executive function, visuo-spatial abilities, and visuo-perception are impaired. The main structures involved in the neuropathology of KS are the mammillary bodies and the thalamus. It is generally assumed that KS is a stable amnesic condition, and little research has been done in studying the effects of aging on the syndrome. / A group of elderly KS patients were evaluated on a large battery of neuropsychological tests to examine general cognitive function, memory, attention, visuo-spatial ability, and executive function. Their performance was compared to age-matched Alzheimer's disease patients and healthy controls. Results showed that there is an interaction between age and KS, with exaggerated deficits seen in memory and executive function, as well as new deficits in semantic memory. / To better understand KS, the thesis provides a review focusing on human, English language studies published between the years 1995 and 2008. Updates on the current findings of treatment and prevention, genetics and prevalence, neuropathology, and neuropsychology including memory and frontal function are provided. In addition, comparison studies of KS to other neurological disorders are summarized.

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Doctor of Philosophy (PhD) / Proteomics is rapidly achieving recognition as a complimentary and perhaps superior approach to examine global changes in protein abundance in complex biological systems and the value of these techniques in neuropsychiatry is beginning to be acknowledged. Characterizing the brain’s regional proteomes provides a foundation for the detection of proteins that may be involved in disease-related processes. Firstly, optimal conditions were achieved for the application of two dimensional-gel electrophoresis (2D-GE)-based proteomics with postmortem human brain tissue. These optimized techniques were then applied to soluble fractions of adjacent grey and white matter of a single cytoarchitecturally defined area (Brodmann area 9; BA9) and of two adjacent regions of frontal white matter (BA9 and CC body) from healthy individuals. These normative proteomic comparisons highlighted the importance of correct tissue sampling, i.e. proper separation of regional white matter, as heterogeneity in the respective proteomes was demonstrated. Furthermore, they stressed the necessity for future molecular brain mapping studies. The main focus of this thesis however, was to examine the proteomes of brain regions specifically vulnerable to alcohol-induced damage underlying cognitive dysfunction. Alcoholic patients commonly experience mild to severe cognitive decline. It is postulated that cognitive dysfunction is caused by an alcohol-induced region selective brain damage, particularly to the prefrontal cortex. The cerebellum is increasingly recognized for its role in various aspects of cognition and alcohol–induced damage to the cerebellar vermis could indirectly affect neurocognitive functions attributed to the frontal lobe. We used a 2D-GE-based proteomics approach to compare protein abundance profiles of BA9 grey and white matter and the cerebellar vermis from human alcoholics (neurologically uncomplicated and alcoholics complicated with liver cirrhosis) and healthy control brains. Among the protein level changes observed are disturbances in the levels of a number of thiamine-dependent enzymes. A derangement in energy metabolism perhaps related to thiamine deficiency seems to be important in all regions analysed, even where there are no clinical or pathological findings of Wernicke-Korsakoff Syndrome. Evidence of oxidative changes was also seen in all regions and effects of liver dysfunction in the vermis found. However, overall, these results highlight the complexity of this disease process in that a number of different proteins from different cellular pathways appear to be affected. By identifying changes in protein abundance levels in the prefrontal grey and white matter and the cerebellar vermis, hypotheses may draw upon more mechanistic explanations as to how chronic ethanol consumption causes the structural and functional alterations associated with alcohol-related brain damage. Furthermore, by comparing these results, we may be able to isolate disturbances in molecular pathways specific to the brain damage caused by alcohol, severe liver dysfunction and thiamine deficiency.

Doctor of Philosophy (PhD) / Proteomics is rapidly achieving recognition as a complimentary and perhaps superior approach to examine global changes in protein abundance in complex biological systems and the value of these techniques in neuropsychiatry is beginning to be acknowledged. Characterizing the brain’s regional proteomes provides a foundation for the detection of proteins that may be involved in disease-related processes. Firstly, optimal conditions were achieved for the application of two dimensional-gel electrophoresis (2D-GE)-based proteomics with postmortem human brain tissue. These optimized techniques were then applied to soluble fractions of adjacent grey and white matter of a single cytoarchitecturally defined area (Brodmann area 9; BA9) and of two adjacent regions of frontal white matter (BA9 and CC body) from healthy individuals. These normative proteomic comparisons highlighted the importance of correct tissue sampling, i.e. proper separation of regional white matter, as heterogeneity in the respective proteomes was demonstrated. Furthermore, they stressed the necessity for future molecular brain mapping studies. The main focus of this thesis however, was to examine the proteomes of brain regions specifically vulnerable to alcohol-induced damage underlying cognitive dysfunction. Alcoholic patients commonly experience mild to severe cognitive decline. It is postulated that cognitive dysfunction is caused by an alcohol-induced region selective brain damage, particularly to the prefrontal cortex. The cerebellum is increasingly recognized for its role in various aspects of cognition and alcohol–induced damage to the cerebellar vermis could indirectly affect neurocognitive functions attributed to the frontal lobe. We used a 2D-GE-based proteomics approach to compare protein abundance profiles of BA9 grey and white matter and the cerebellar vermis from human alcoholics (neurologically uncomplicated and alcoholics complicated with liver cirrhosis) and healthy control brains. Among the protein level changes observed are disturbances in the levels of a number of thiamine-dependent enzymes. A derangement in energy metabolism perhaps related to thiamine deficiency seems to be important in all regions analysed, even where there are no clinical or pathological findings of Wernicke-Korsakoff Syndrome. Evidence of oxidative changes was also seen in all regions and effects of liver dysfunction in the vermis found. However, overall, these results highlight the complexity of this disease process in that a number of different proteins from different cellular pathways appear to be affected. By identifying changes in protein abundance levels in the prefrontal grey and white matter and the cerebellar vermis, hypotheses may draw upon more mechanistic explanations as to how chronic ethanol consumption causes the structural and functional alterations associated with alcohol-related brain damage. Furthermore, by comparing these results, we may be able to isolate disturbances in molecular pathways specific to the brain damage caused by alcohol, severe liver dysfunction and thiamine deficiency.

Thesis (Ph. D.)--State University of New York at Binghamton, Department of Psychology, Behavioral Neuroscience, 2008. / Includes bibliographical references.

Thesis (M.A.)--State University of New York at Binghamton, Department of Psychology, 2005. / Includes bibliographical references.

Thesis (M.S.)--State University of New York at Binghamton, Department of Psychology, 2009. / Includes bibliographical references.

L’excitotoxicité est un mécanisme physiopathologique majeur impliqué dans la pathogenèse de la déficience en thiamine (DT). Dans les régions cérébrales vulnérables à la DT, on observe une mort cellulaire induite par excitotoxicité dont l’origine semble être la conséquence d’une perturbation du métabolisme énergétique mitochondrial, d’une dépolarisation membranaire soutenue et d’une diminution de l’absorption du glutamate par les astrocytes suite à la diminution de l’expression des transporteurs EAAT1 et EAAT2. Il est clairement établi que le glutamate joue un rôle central dans l’excitotoxicité lors de la DT. Ainsi, la mise en évidence des mécanismes impliqués dans la diminution de l’expression des transporteurs du glutamate est essentielle à la compréhension de la physiopathologie de la DT. L’objectif de cette thèse consiste en l’étude de la régulation des transporteurs astrocytaires du glutamate et la mise au point de stratégies thérapeutiques ciblant la pathogenèse de l’excitotoxicité lors de l’encéphalopathie consécutive à la DT. Les principaux résultats de cette thèse démontrent des perturbations des transporteurs du glutamate à la fois dans des modèles animaux de DT et dans des astrocytes en culture soumis à une DT. La DT se caractérise par la perte du variant d’épissage GLT-1b codant pour un transporteur du glutamate dans le thalamus et le colliculus inférieur, les régions cérébrales affectées lors d’une DT, en l’absence de modification des niveaux d’ARNm. Ces résultats suggèrent une régulation post-transcriptionnelle de l’expression des transporteurs du glutamate en condition de DT. Les études basées sur l’utilisation d’inhibiteurs spécifiques des facteurs de transcription NFkB et de l’enzyme nucléaire poly(ADP)ribose polymérase-1 (PARP-1) démontrent que la régulation de l’expression du transporteur GLT-1 est sous le contrôle de voies de signalisation NFkB dépendantes de PARP-1. Cette étude démontre une augmentation de l’activation de PARP-1 et de NFkB dans les régions vulnérables chez le rat soumis à une DT et en culture d’astrocytes DT. L’inhibition pharmacologique du facteur de transcription NFkB par le PDTC induit une augmentation des niveaux d’expression de GLT-1, tandis que l’inhibition de PARP-1 par le DPQ conduit à l’inhibition de l’hyperactivation de NFkB observée lors de DT. L’ensemble de ces résultats met en évidence un nouveau mécanisme de régulation des transporteurs du glutamate par l’activation de PARP-1. L’accumulation de lactate est une caractéristique de la DT. Un traitement avec le milieu de culture d’astrocytes en condition de DT sur des cultures d’astrocytes naïfs induit une diminution de l’expression de GLT-1 ainsi qu’une inhibition de la capacité d’absorption du glutamate par les astrocytes naïfs. En revanche, l’administration de lactate exogène ne modifie pas le niveau d’expression protéique de GLT-1. Ainsi, des facteurs solubles autres que le lactate sont sécrétés par des astrocytes en condition de perturbation métabolique et peuvent potentiellement réguler l’activité des transporteurs du glutamate et contribuer à la pathogenèse du syncytium astroglial. En outre, la ceftriaxone, un antibiotique de la famille des β-lactamines, augmente de façon différentielle l’expression du variant-d’épissage GLT-1 dans le colliculus inférieur chez le rat DT et en culture d’astrocytes DT. Ces résultats suggèrent que la ceftriaxone peut constituer une avenue thérapeutique dans la régulation de l’activité des transporteurs du glutamate lors de DT. Pour conclure, la mort cellulaire d’origine excitotoxique lors de DT survient en conséquence d’une dysfonction mitochondriale associée à une perturbation du métabolisme énergétique cérébral. La modification de l’expression des transporteurs du gluatamate est sous le contrôle des voies de signalisation NFkB dépendantes du facteur PARP-1. De plus, l’inhibition métabolique et l’augmentation des sécrétions de lactate observées lors de DT peuvent également constituer un autre mécanisme physiopathologique expliquant la diminution d’expression des transporteurs de glutamate. Enfin, la ceftriaxone pourrait représenter une stratégie thérapeutique potentielle dans le traitement de la régulation de l’expression des transporteurs du glutamate et de la perte neuronale associés à l’excitotoxicité observée lors de DT. / Excitotoxicity has been implicated as a major pathophysiological mechanism in the pathogenesis of thiamine deficiency (TD). Excitotoxic-mediated cell death is localized in areas of focal vulnerability in TD and may occur as a consequence of impairment in mitochondrial energy metabolism, sustained cell membrane depolarization and decreased uptake of glutamate by astrocytes due to the loss of excitatory amino acid transporters, (EAAT1 and EAAT2). Over the years, a number of studies have identified glutamate as being a major contributor to excitotoxicity in the pathophysiology of TD. Thus, downregulation of astrocytic glutamate transporters resulting in excitotoxicity is a key feature of TD and understanding the regulation of these transporters is essential to understanding the pathophysiology of the disorder. The objective of the present thesis project was to examine the underlying basis of astrocytic glutamate transporter regulation during TD encephalopathy. Major findings of the studies presented in this thesis project provide evidence for glutamate transporter abnormalities in TD animal models and astrocyte cultures exposed to TD. TD results in the loss of the glutamate transporter splice variant-1b (GLT-1b) in vulnerable areas of brain, i.e. thalamus and inferior colliculus, with no significant alteration in the mRNA levels of the transporters, suggesting that glutamate transporter regulation under conditions of TD is a posttranscriptional event. Studies using a specific inhibitor of the transcription factor, Nuclear factor-kappa B (NF-κB) and a nuclear enzyme poly (ADP)ribose polymerase-1 (PARP-1) provided evidence for the regulation of GLT-1 by PARP-1 dependent NF-κB signalling pathways. The major findings of this study suggested an increase in the activation of PARP-1 and NF-κB molecule in the vulnerable areas of TD rat brain and TD astrocyte cultures. Pharmacological inhibition of NF-κB showed an increase in the levels of GLT-1, while inhibition of PARP-1 using a specific PARP-1 inhibitor, DPQ inhibited the increased activation of NF-κB that was observed during TD. Overall results of this finding provided evidence for a mechanism involving PARP-1 activation in the regulation of glutamate transporters. Given the increased lactate accumulation as a classical feature of TD, we studied the effect of soluble factors produced by astrocytes on glutamate transporter function. Treatment of naïve astrocyte cultures with TD conditioned media resulted in decreased levels of GLT-1 and inhibition of glutamate uptake capacity concomitant with a loss of mitochondrial membrane potential. Administration of exogenous lactic acid produced a similar reduction in glutamate uptake to that resulting from conditioned media. However, lactic acid treatment did not result in a change in GLT-1 protein levels. In addition, the pro-inflammatory cytokine TNF-α was shown to be increased in astrocytes treated with TD along with elevated levels of the phospho-IκB fragment, indicative of increased activation of NFκB. Inhibition of NFκB led to an amelioration of the decrease in GLT-1 that occurs in TD, along with recovery of glutamate uptake. Thus, soluble factors released from astrocytes under conditions of metabolic impairment such as lactate and TNF-α impairment appear to exert a regulatory influence on glutamate transporter function. Ceftriaxone, a β-lactam antibiotic, has the ability to differentially stimulate GLT-1b (splice-variant) expression in the inferior colliculus in TD rats and under in vitro conditions with TD astrocyte cultures. Thus, ceftriaxone may be a potential therapeutic strategy in the regulation of glutamate transporter function during TD. In summary, excitotoxic cell death in TD occurs as a consequence of mitochondrial dysfunction associated with cerebral energy impairment and abnormal glutamate transporter status. A major underlying mechanism for glutamate transporter abnormalities is mediated by PARP-1 dependent NF-κB signaling pathways. In addition, metabolic inhibition with substantial production of lactate and TNF-α may be perhaps another mechanism responsible for glutamate transporter downregulation in TD.

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