The prevalence of milder forms of HIV-associated neurocognitive disorders (HAND) is rising despite combination antiretroviral therapy (cART). Efavirenz (EFV) is among the most commonly used antiretroviral drugs globally, but causes neurological symptoms that may interfere with adherence and reduce tolerability, and may have central nervous system (CNS) effects that contribute in part to HAND in patients on cART. Thus we evaluated a commonly used EFV containing regimen: EFV/zidovudine (AZT)/lamivudine (3TC) in murine N2a cells transfected with the human “Swedish” mutant form of amyloid precursor protein (SweAPP N2a cells) to assess for promotion of amyloid-beta (Aβ) production (Chapter 3). Treatment with EFV or the EFV containing regimen generated significantly increased soluble Aβ, and promoted increased β-secretase-1 (BACE-1) expression while 3TC, AZT, or, vehicle control did not significantly alter these endpoints. Further, EFV or the EFV containing regimen promoted significantly more mitochondrial stress in SweAPP N2a cells as compared to 3TC, AZT, or vehicle control. We next tested the EFV containing regimen in Aβ - producing Tg2576 mice combined or singly using clinically relevant doses. EFV or the EFV containing regimen promoted significantly more BACE-1 expression and soluble Aβ generation while 3TC, AZT, or vehicle control did not. Finally, microglial Aβ phagocytosis was significantly reduced by EFV or the EFV containing regimen but not by AZT, 3TC, or vehicle control alone. These data suggest the majority of Aβ promoting effects of this cART regimen are dependent upon EFV as it promotes both increased production, and decreased clearance of Aβ peptide. Further (Chapter 4), there is evidence that neural stem cells (NSCs) can migrate to sites of brain injury such as those caused by inflammation and oxidative stress, which are pathological features of HAND. Thus, reductions in NSCs may contribute to HAND pathogenesis. Since the HIV non-nucleoside reverse transcriptase inhibitor EFV has previously been associated with cognitive deficits and promotion of oxidative stress pathways, we examined its effect on NSCs in vitro as well as in C57BL/6J mice. Here we report that EFV induced a decrease in NSC proliferation in vitro as indicated by MTT assay, as well as BrdU and nestin immunocytochemistry. In addition, EFV decreased intracellular NSC adenosine triphosphate (ATP) stores and NSC mitochondrial membrane potential (MMP). Further, we found that EFV promoted increased lactate dehydrogenase (LDH) release, activation of p38 mitogen-activated protein kinase (MAPK), and increased Bax expression in cultured NSCs. Moreover, EFV reduced the quantity of proliferating NSCs in the subventricular zone (SVZ) of C57BL/6 mice as suggested by BrdU, and increased apoptosis as measured by active caspase-3 immunohistochemistry. If these in vitro and in vivo models translate to the clinical syndrome, then a pharmacological or cell-based therapy aimed at opposing EFV-mediated reductions in NSC proliferation may be beneficial to prevent or treat HAND in patients receiving EFV. 1 Portions of this abstract have been previously published (Brown LAM, et al., 2014; Jin, J, et al, 2016) and are utilized with permission of the publisher.1

Die Alzheimersche Erkrankung (AD) ist die häufigste Demenzerkrankung bei älteren Menschen in den westlichen Industriestaaten mit ständig wachsender Zahl der Erkrankten. Trotz angestrengter wissenschaftlicher und medizinischer Forschung ist u. a. noch keine Möglichkeit der klinischen Frühdiagnose dieser Erkrankung etabliert. In der vorliegenden Arbeit wurden am transgenen Mausmodell Tg2576 mit beta-Amyloidplaque-Pathologie cholinerge und adrenerge Parameter sowie Einfluss-größen des Energiestoffwechsels untersucht, um transgen-induzierte neuro-chemische bzw. neuromorphologische Veränderungen im Hirngewebe zu erkennen. Außerdem sollte die Möglichkeit einer ex vivo Markierung solcher Moleküle getestet werden, von denen eine besondere Bindungsaffinität an beta-Amyloidablagerungen bereits bekannt ist. Das Ziel der vorliegenden Arbeit war, diese Mauslinie weiterhin hinsichtlich ihres Modellcharakters für die Alzheimersche Erkrankung zu beschreiben und potenzielle Plaque-assoziierte Markermoleküle aufzufinden, die einen in vivo Nachweis der b-Amyloidablagerungen erlauben. Die so gewonnenen Erkenntnisse könnten zur Entwicklung neuer Strategien zur Frühdiagnostik der Alzheimerschen Erkrankung beitragen. Genutzt wurden dazu v. a. die biochemischen Methoden der Rezeptorautoradiografie und der Immunhistochemie sowie der in situ Hybridisierung als molekularbiologische Methode. Weiterhin wurde eine radiochemische Methode zur ex vivo Darstellung der Azetylcholinesterase getestet. Bei der Untersuchung des cholinergen Systems konnte eine signifikante Verringerung in der [3H]Hemicholinium-3-Bindung (als Marker des hoch affinen Cholintransporters) bei den fünf Monate alten transgenen Mäusen im Vergleich zu deren nicht transgenen Wurfgeschwistern festgestellt werden. Es wird hier von einem modulatorischen Effekt des löslichen beta-Amyloids ausgegangen, da die jüngeren Tiere noch keine Plaqueablagerungen aufweisen, die Ursache solcher Veränderungen sein könnten. Beim vesikulären Azetylcholintransposter (VAChT) konnte eine signifikante Erhöhung in der [3H]Vesamicol-Bindung bei 17 Monate alten transgenen Mäusen im Vergleich zu nicht transgenen Geschwistertieren beobachtet werden, obwohl der gegenteilige Fall erwartet wurde. Das Ergebnis wird als Ausdruck einer erhöhten Vesikeldichte interpretiert. Die immunhistochemische Untersuchung der a4- und a7-Untereinheiten der nikoti-nischen Azetylcholinrezeptoren ergab, dass die beta-Amyloidplaqueablagerung keinen Einfluss auf morphologische Veränderungen der Neuronen hatte, die diese Rezep-toren tragen. Es gab keine Hinweise, dass solche Neuronen degenerieren. Hinsichtlich der untersuchten Parameter des Glukosestoffwechsels konnten keine Veränderungen zwischen transgenen Tieren und nicht transgenen Wurfgeschwistern festgestellt werden. Bei der Verteilung der Hirnkapillaren konnte eine verringerte Dichte in unmittelbarer Umgebung der b-Amyloidplaques, verglichen mit weiter entfernt liegenden Gebieten, ermittelt werden. Dieser Befund bedarf weiterer Unter-suchungen, da er Relevanz für die in vivo Diagnostik und Therapie besitzen könnte. Im Vergleich mit den zwar oft nicht einheitlichen Befunden bei Alzheimerpatienten wird deutlich, dass das Mausmodell Tg2576 als Modell der Alzheimerschen Erkrankung nicht alle Aspekte der Pathogenese simuliert. Übereinstimmungen ergeben sich bei dieser transgenen Maus hinsichtlich der beta-Amyloidproduktion und -ablagerung im Hirn und den auch beim Menschen vorkommenden entzündlichen Reaktion um die Plaques. Damit kann sie als geeignetes Modell zum Studium der Amyloidogenese und damit verbundener inflammatorischer Prozesse angesehen werden. / Alzheimer´s Disease (AD) is the most common form of dementia among the elderly in the Western world, with growing prevalence. In spite of intensive scientific and medical research, no possibility of early clinical diagnosis for this disease has yet been established. In this thesis cholinergic and adrenergic parameters, as well as energy metabolism, were studied in the transgenic mouse model Tg2576, to reveal transgene-induced neurochemical and neuromorphological changes in the brain tissue of these animals. Also, the ex vivo labelling of marker molecules with a known high affinity for beta-amyloid was to be tested. The objective was to further characterize the Tg2576 mouse strain as a model of AD, and to find plaque-associated marker molecules which could be used for the in vivo detection of b-amyloid plaques. Such findings could contribute to the development of new stategies for the early diagnosis of AD. Quantitative receptor autoradiography, immunohistochemistry and in situ hybridization were the main biochemical and molecular biological methods employed. Furthermore, a radiochemical method was used for ex vivo labelling of acetylcholinesterase. The 5 month-old transgenic mice, with no significant plaque load, demonstrated reduced [3H]hemicholinium-3 binding to choline uptake sites in anterior brain regions, as compared to non-transgenic littermates. This provides evidence of the modulatory effect of soluble beta-amyloid on high affinity choline uptake sites. However, a significant increase of [3H]vesamicol receptor binding to the vesicular acetylcholine transporter was detected in 17 month-old transgenic animals, as compared to non-transgenic mice. Even though the opposite was expected, the result could be interpreted as an elevated vesicle density. The immunhistochemical studies of a4 and a7 subunits of the nicotinic acetylcholine receptor revealed that neurons expressing these receptors do not undergo morphological changes in close proximity to beta-amyloid plaques. There was no sign of degeneration in these neurons. Concerning the examined parameters of glucose metabolism, no changes between transgenic animals and non-transgenic littermates were detected. This observation is in accordance with the data available in the literature, but in contrast to findings in AD patients. The density of brain capillaries in close vicinity of beta-amyloid plaques, compared to a more distant surrounding, is reduced. This finding needs further examination because it could be relevant for in vivo diagnosis and therapy. Comparing the transgenic Tg2576 mouse model to AD patients, it becomes apparent that the mouse model does not simulate all aspects of the pathogenesis of this disease. Consistent with the human disease this model is characterized by b-amyloid plaque production and deposition in the brain, as well as inflammatory processes around the plaques, which are also known in humans. Therefore, it represents a suitable model to study amyloidogenesis and inflammation.

<div><b>Rationale:</b> Focal cortical dysplasia (FCD) is a neurodevelopmental disorder that is associated with abnormal cortical development and is one of the most common drug-resistant epilepsies. The mechanistic target of rapamycin (mTOR) pathway is a highly complex pathway </div><div>associated with cell proliferation, synaptic plasticity, neuroinflammation, and cortical development. Hyperactivation of this pathway has also been implicated in hyperexcitability, seizures, and accumulation of beta-amyloid (Aβ) plaques and neurofibrillary tangles (NFT) through hyperphosphorylation of tau. Interestingly, Aβ and hyperphosphorylated tau have been reported in both rodent models and human patients of temporal lobe epilepsy (TLE) and FCD however, the mechanisms through which this occurs are still yet to be defined. Therefore, to identify the possible link between Aβ and tau pathology in FCD, we determined the spatial distribution and protein levels of Aβ and phosphorylated tau (p-tau) along with mTOR signaling </div><div>molecules. We hypothesized that there would be presence of Aβ and tau pathology as well as an increase in Aβ and p-tau protein levels that would be correlated with hyperactivation of the mTOR and GSK3 signaling pathways in tissue biopsies from human FCD patients compared to brain tissues from non-epileptic (NE) individuals.</div><div><br></div><div><b>Methods:</b> Cortical brain samples surgically resected from patients with FCD were used and compared to NE samples surgically resected from glioblastoma patients with no history of seizures or epilepsy. Immunostaining was used to determine the distribution of phosphorylation of S6 (p-S6), a marker for mTOR activation, and NeuN, a marker for neurons, along with Aβ and p-tau. Additionally, western blotting (WB) was used to determine the levels of mTOR signaling through p-S6 and GSK3 (p-GSK) along with Aβ and p-tau.</div><div><br></div><div><b>Results:</b> We found cortical dyslamination, mTOR activation, p-tau, and Aβ accumulation in cortices of patients with FCD with drug-resistant epilepsy. However, we did not find a </div><div>significant difference in the protein levels of p-S6 (p = 0.422), p-GSK3 (p = 0.947), p-tau (p = 0.649), and Aβ (p = 0.852) in cortical tissue homogenates derived from FCD patients when compared to those of NE samples. Additionally, we did not find sex differences in the protein </div><div>levels of p-S6 (p = 0.401), p-GSK3 (p = 0.331), p-tau (p = 0.935), and Aβ (p = 0.526). There was no significant correlation between age and p-S6 (p = 0.920), age and p-GSK3 (p = 0.089), age and p-tau (p = 0.956), and age and Aβ (p = 0.889). Moreover, there was no significant correlation between mTOR activation (p-S6), Aβ (p = 0.586) and p-tau (p = 0.059) nor GSK3 activation (p-GSK3), Aβ (p = 0.326), and p-tau (p = 0.715). Lastly, there was no significant correlation within the mTOR and GSK3 pathway activation within the same patients (p = 0.602).</div><div><br></div><div><b>Conclusion:</b> These data suggest that mTOR hyperactivation occurs alongside the presence of Aβ and tau pathology. However, several unknown factors such as medical and medication history may be altering the expression or suppression of these proteins. Additionally, there may be alternative pathways that crosstalk with mTOR signaling therefore influencing Aβ and tau pathology in FCD patients with drug-resistant epilepsy. Further investigation will need to be conducted to understand the detailed mechanisms through which Aβ and tau pathology occur in </div><div>FCD.</div>

Alzheimer's disease (AD) is a neurodegenerative disorder that manifests in the form of deficiencies in cognitive processes such as memory and learning. The pathological features of AD include hyperphosphorylated tau proteins that form neurofibrillary tangles as well as senile plaques composed primarily of the peptide β-amyloid (Aβ). When present in high concentrations in the brain, Aβ inhibits certain subtypes of neuronal nicotinic acetylcholine receptors (nAChRs) in the hippocampus. The effects of Aβ in the hippocampus have proven to be neurotoxic, resulting in reduced functionality of nAChRs and the subsequent death of neurons in the cholinergic pathway. The early stages of AD are characterized by reduction of nAChR density and by degeneration of the cholinergic neurons that provide input to the hippocampus. Because the hippocampus plays a critical role in memory formation and other cognitive processes, dysfunction in this brain region results in significant cognitive deficiencies. Understanding the interaction between Aβ and the structurally and functionally diverse nAChR subtypes and possible downstream effects in signaling cascades that might result from that interaction are important steps in comprehending AD pathogenesis. Comprehension of this interaction and factors that might influence it could lead to the development of pharmaceutical agents useful in the treatment of AD.

Alzheimer’s disease (AD) and Parkinson’s disease (PD) are defined by neurodegeneration and accumulations of misfolded proteins that spread through the brain in a well characterized manner. In AD these accumulations consist mainly of β-amyloid (Aβ) and tau, while in PD, α-synuclein (α-syn) make up the characteristic lewy pathology.     The general aim of this thesis was to investigate mechanisms associated with neurotoxic peptide activity by Aβ, tau and α-syn in relation to cellular degradation and transfer with a cell-to-cell transfer model system.    We found that intercellular transfer of oligomeric Aβ occurs independently of isoform. However, the amount of transfer correlates with each isoforms ability to resist degradation or cellular clearance. The Aβ1-42 isoform showed particular resistance to clearance, which resulted in higher levels of cell-to-cell transfer of the isoform and lysosomal stress caused by accumulation.    As Aβ accumulations can inhibit the proteasomal degradation we investigated how reduced proteasomal degradation affected neuron-like cells. We found increased levels of phosphorylated tau protein, disturbed microtubule stability and impaired neuritic transport after reduced proteasomal activity. These changes was partly linked to c-Jun and ERK 1/2 kinase activity.    We could also show that α-syn transferred from cell-to-cell in our model system, with a higher degree of transfer for the larger oligomer and fibrillar species. Similar to Aβ, α-syn mainly colocalized with lysosomes, before and after transfer.     Lastly, we have developed our cell-to-cell transfer system into a model suitable for high throughput screening (HTS). The type of cells have been upgraded from SH-SY5Y cells to induced pluripotent stem cells (iPSCs), with a differentiation profile more similar to mature neurons. The next step will be screening a small molecular library for substances with inhibitory effect on cell-to-cell transfer of Aβ peptides.     The importance of the degradative systems in maintaining protein homeostasis and prevent toxic accumulations in general is well known. Our findings shows the importance of these systems for neurodegenerative diseases and also highlight the link between degradation and cell-to-cell transfer. To restore or enhance the degradative systems would be an interesting avenue to treat neurodegenerative diseases. Another way would be to inhibit the transfer of misfolded protein aggregates. By using the HTS model we developed, a candidate substance with good inhibitory effect on transfer can hopefully be found.

Estudos demonstram que a indução do estresse oxidativo pelo peptídeo beta amiloide (A?) exerce um importante papel no desencadeamento da excitotoxicidade neuronal o que pode resultar no desenvolvimento de doenças neurodegenerativas. A formação do peptídeo A? se deve a alterações na proteína precursora de amiloide (APP) que é clivada para a formação do peptídeo A?. Por sua vez, os mecanismos de ação do A? no S.N.C. ocorrem através da sinalização do receptor NMDA (N-metil D-aspartato) receptor este que quando ativado pelo glutamato exerce importante papel fisiológico no S.N.C., visto que apresenta atividade ionotrópica que permite o influxo de Na+ e Ca2+ para as células neuronais, auxiliando nos processos de formação da memória e aprendizagem. Entretanto, apesar do seu papel fisiológico, a ativação excessiva do receptor NMDA é fortemente correlacionada com lesões no S.N.C. decorrente da excessiva permeabilidade do íon Ca2+ para o citosol das células neuronais. Com isso as concentrações de glutamato na fenda sináptica são estritamente controladas para que não haja ativação excessiva dos receptores com atividade glutamatérgica, como o receptor NMDA. Estudos indicam que o transporte de glutamina/glutamato através da barreira hematoencefálica é menor do que de outros aminoácidos, sendo que cerca de 25% a 30% do transporte de aminoácidos dos vasos sanguíneos para o cérebro através da barreira hematoencefálica é ocupado pelo aminoácido leucina, sendo este um grande responsável pela síntese de glutamato/glutamina no S.N.C. Com isso, estudos tem demonstrado que dietas enriquecidas com aminoácidos de cadeia ramificada, dentre eles a leucina, é responsável por alterar o metabolismo do glutamato e aumentar a susceptibilidade à excitotoxicidade de células neurais. A fim de testar esta hipótese utilizamos um modelo de cultura de células de neuroblastoma humano e realizamos o tratamento com diferentes concentrações de aminoácido leucina associado com o tratamento de peptídeo beta-amilóide. Realizamos as analises de citotoxicidade (LDH), viabilidade celular (MTT) e apoptose celular por citometria de fluxo (marcação com PE Anexina V e 7-AAD). Nossos resultados indicam que houve diferenças apenas entre o controle em relação aos demais grupos de tratamento / Studies demonstrate that induction of oxidative stress by beta amyloid peptide (A?) plays an important role in triggering neuronal excitotoxicity which can result in the development of neurodegenerative diseases. The formation of A? peptide are due to changes in the amyloid precursor protein (APP) which is cleaved to form the peptide A?. On the other hand, the mechanisms of action of A? in the C.N.S. occur through signaling of the NMDA (N-methyl-D-aspartate) receptor that when activated by glutamate plays an important physiological role in the C.N.S., as has inotropic activity that allows the influx of Na+ and Ca2+ into the neuronal cells, assisting in procedures of memory formation and learning. However, despite its physiological role, the excessive activation of the NMDA receptor is strongly correlated with C.N.S. lesions due to excess permeability of Ca2+ ions into the cytosol of neuronal cells. Thus the concentrations of glutamate in the synaptic cleft are strictly controlled so that there is excessive activation of receptors with glutamatergic activity, as the NMDA receptor. Studies indicate that the transport of glutamine/glutamate across the blood brain barrier is lower than that of other amino acids, of which about 25% to 30% of the amino acid transport blood vessels to the brain through the blood brain barrier is occupied by leucine this being one largely responsible for the synthesis of glutamate/glutamine in the C.N.S. Thus, studies have shown that diets enriched in branched chain amino acids, including leucine, are responsible for altering the metabolism of glutamate and excitotoxic increase susceptibility to neural cells. To test this hypothesis we used a cell culture model of human neuroblastoma and carry out the treatment with different concentrations of leucine associated with the processing of amyloid-beta peptide. We performed analysis of cytotoxicity (LDH), cell viability (MTT assay) and apoptosis using flow cytometry (Annexin V staining with PE and 7-AAD). Our results indicate that there were differences only between the control compared to the other treatment groups

The disturbances and abnormalities occurring in the components of the Acetylcholine (ACh) neurocycle are considered one of the main features of cholinergic sicknesses like Parkinson’s and Alzheimer’s diseases. A fundamental understanding of the ACh neurocycle is therefore very critical in order to design drugs that keep the ACh concentrations in the normal physiological range. In this dissertation, a novel two-enzyme-two-compartment model is proposed in order to explore the bifurcation, dynamics, and chaotic characteristics of the ACh neurocycle. The model takes into consideration the physiological events of the choline uptake into the presynaptic neuron and the ACh release in the postsynaptic neuron. In order to approach more realistic behavior, two complete kinetic mechanisms for enzymatic processes pH-dependent are built: the first mechanism is for the hydrolysis reaction catalyzed by the acetylcholinesterase (AChE) and the other is for the synthesis reaction catalyzed by the cholineacetyltransferase (ChAT). The effects of hydrogen ion feed concentrations, AChE activity, ChAT activity, feed ACh concentrations, feed choline concentrations, and feed acetate concentrations as bifurcation parameters, on the system performance are studied. It was found that hydrogen ions play an important role, where they create potential differences through the plasma membranes. The concentrations of ACh, choline and acetate in compartments 1 and 2 are affected by the activity of AChE through a certain range of their concentrations, where the activity of AChE is inhibited completely after reaching certain values. A detailed bifurcation analysis over a wide range of parameters is carried out in order to uncover some important features of the system, such as hysteresis, multiplicity, Hopf bifurcation, period doubling, chaotic characteristics, and other complex dynamics. The effects of the feed choline concentrations and the feed acetate concentrations as bifurcation parameters are studied in this dissertation. It is found that the feed choline concentrations play an important role and have a direct effect on the ACh neurocycle through a certain important range of the parameters. However, the feed acetate concentrations have less effect. It is concluded from the results that the feed choline is a more important factor than the feed acetate in ACh processes. The effects of ChAT activity and the choline recycle ratio as bifurcation parameters, on the system performance are investigated. It was found that as the ChAT activity increases, ACh concentrations in compartments 1 and 2 increase continuously. The effect of the choline recycle ratio shows that choline reuptake plays a very critical role in the synthesis of ACh in compartment 1, where it supplies the choline as a substrate for the synthesis reaction by ChAT. The concentrations of ACh, choline and acetate in compartments 1 and 2 are affected by the choline recycle ratio through a certain range of the choline recycle ratio; then, they become constant as the choline recycle ratio increases further. It is concluded from our results that choline uptake is the rate limiting step in the ACh processes in both compartments in comparison to ChAT activity. Based on partial dissociation of the acetic acid in compartments 1, and 2 of the ACh cholinergic system, the two-parameter continuation technique has been applied to investigate the pH range to be closer to physiological ranges of pH values. In addition, static/dynamic solutions of the ACh cholinergic neurocycle system based on feed choline concentration as the main bifurcation parameter in both compartments have been investigated. The findings of the above studies are related to the real phenomena occurring in the neurons, like periodic stimulation of neural cells and non-regular functioning of ACh receptors. It was found that ACh, choline, acetate, and pH exist inside the physiological range associated with taking into consideration the partial dissociation of the acetic acid. The disturbances and irregularities (chaotic attractors) occurring in the ACh cholinergic system may be good indications of cholinergic diseases such as Alzheimer’s and Parkinson’s diseases. The results have been compared to the results of physiological experiments and other published models. As there is strong evidence that cholinergic brain diseases like Alzheimer’s disease and Parkinson’s disease are related to the concentration of ACh, the present findings are useful for uncovering some of the characteristics of these diseases and encouraging more physiological research.

The disturbances and abnormalities occurring in the components of the Acetylcholine (ACh) neurocycle are considered one of the main features of cholinergic sicknesses like Parkinson’s and Alzheimer’s diseases. A fundamental understanding of the ACh neurocycle is therefore very critical in order to design drugs that keep the ACh concentrations in the normal physiological range. In this dissertation, a novel two-enzyme-two-compartment model is proposed in order to explore the bifurcation, dynamics, and chaotic characteristics of the ACh neurocycle. The model takes into consideration the physiological events of the choline uptake into the presynaptic neuron and the ACh release in the postsynaptic neuron. In order to approach more realistic behavior, two complete kinetic mechanisms for enzymatic processes pH-dependent are built: the first mechanism is for the hydrolysis reaction catalyzed by the acetylcholinesterase (AChE) and the other is for the synthesis reaction catalyzed by the cholineacetyltransferase (ChAT). The effects of hydrogen ion feed concentrations, AChE activity, ChAT activity, feed ACh concentrations, feed choline concentrations, and feed acetate concentrations as bifurcation parameters, on the system performance are studied. It was found that hydrogen ions play an important role, where they create potential differences through the plasma membranes. The concentrations of ACh, choline and acetate in compartments 1 and 2 are affected by the activity of AChE through a certain range of their concentrations, where the activity of AChE is inhibited completely after reaching certain values. A detailed bifurcation analysis over a wide range of parameters is carried out in order to uncover some important features of the system, such as hysteresis, multiplicity, Hopf bifurcation, period doubling, chaotic characteristics, and other complex dynamics. The effects of the feed choline concentrations and the feed acetate concentrations as bifurcation parameters are studied in this dissertation. It is found that the feed choline concentrations play an important role and have a direct effect on the ACh neurocycle through a certain important range of the parameters. However, the feed acetate concentrations have less effect. It is concluded from the results that the feed choline is a more important factor than the feed acetate in ACh processes. The effects of ChAT activity and the choline recycle ratio as bifurcation parameters, on the system performance are investigated. It was found that as the ChAT activity increases, ACh concentrations in compartments 1 and 2 increase continuously. The effect of the choline recycle ratio shows that choline reuptake plays a very critical role in the synthesis of ACh in compartment 1, where it supplies the choline as a substrate for the synthesis reaction by ChAT. The concentrations of ACh, choline and acetate in compartments 1 and 2 are affected by the choline recycle ratio through a certain range of the choline recycle ratio; then, they become constant as the choline recycle ratio increases further. It is concluded from our results that choline uptake is the rate limiting step in the ACh processes in both compartments in comparison to ChAT activity. Based on partial dissociation of the acetic acid in compartments 1, and 2 of the ACh cholinergic system, the two-parameter continuation technique has been applied to investigate the pH range to be closer to physiological ranges of pH values. In addition, static/dynamic solutions of the ACh cholinergic neurocycle system based on feed choline concentration as the main bifurcation parameter in both compartments have been investigated. The findings of the above studies are related to the real phenomena occurring in the neurons, like periodic stimulation of neural cells and non-regular functioning of ACh receptors. It was found that ACh, choline, acetate, and pH exist inside the physiological range associated with taking into consideration the partial dissociation of the acetic acid. The disturbances and irregularities (chaotic attractors) occurring in the ACh cholinergic system may be good indications of cholinergic diseases such as Alzheimer’s and Parkinson’s diseases. The results have been compared to the results of physiological experiments and other published models. As there is strong evidence that cholinergic brain diseases like Alzheimer’s disease and Parkinson’s disease are related to the concentration of ACh, the present findings are useful for uncovering some of the characteristics of these diseases and encouraging more physiological research.

Correlations between neuropsychiatric symptoms and beta-amyloid (Aβ) burden in specific brain regions in living Alzheimer’s disease (AD) patients remain to be elucidated. Ten mild AD patients underwent MR and [11C]SB-13 PET imaging. Neuropsychiatric symptoms were quantified with the Neuropsychiatric Inventory (NPI). NPI-depression/dysphoria, -apathy, -agitation/aggression, -anxiety, and -appetite/eating disorders scores were hypothesized to correlate with Aβ burden in particular brain regions. Pearson’s correlation coefficient revealed that depression/dysphoria scores positively correlated (p<0.05) with standardized uptake values (SUVs) from left medial temporal lobe (r=0.67), and agitation/aggression correlated with SUVs from bilateral anterior cingulate (right, r=0.71; left, r=0.78), temporal (right, r=0.71; left, r=0.75), parietal (right, r=0.77; left, r=0.81), and dorsolateral prefrontal cortex (right, r=0.74; left, r=0.73). However, NPI scores did not significantly correlate with better estimates of Aβ burden that use the cerebellum as reference region. Overall, our results confirm the lack of association between Aβ burden and neuropsychiatric symptoms reported in autopsy studies.

Correlations between neuropsychiatric symptoms and beta-amyloid (Aβ) burden in specific brain regions in living Alzheimer’s disease (AD) patients remain to be elucidated. Ten mild AD patients underwent MR and [11C]SB-13 PET imaging. Neuropsychiatric symptoms were quantified with the Neuropsychiatric Inventory (NPI). NPI-depression/dysphoria, -apathy, -agitation/aggression, -anxiety, and -appetite/eating disorders scores were hypothesized to correlate with Aβ burden in particular brain regions. Pearson’s correlation coefficient revealed that depression/dysphoria scores positively correlated (p<0.05) with standardized uptake values (SUVs) from left medial temporal lobe (r=0.67), and agitation/aggression correlated with SUVs from bilateral anterior cingulate (right, r=0.71; left, r=0.78), temporal (right, r=0.71; left, r=0.75), parietal (right, r=0.77; left, r=0.81), and dorsolateral prefrontal cortex (right, r=0.74; left, r=0.73). However, NPI scores did not significantly correlate with better estimates of Aβ burden that use the cerebellum as reference region. Overall, our results confirm the lack of association between Aβ burden and neuropsychiatric symptoms reported in autopsy studies.