Thesis (Ph. D.)--University of Missouri--Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves : 176-210). Also available on the Internet.

Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted.

Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted.

A epilepsia do lobo temporal (ELT) é o tipo mais comum de epilepsia em adultos. Estudos experimentais têm descrito aumento da geração de espécies reativas de oxigênio (EROs) na morte neuronal relacionada à excitotoxicidade, presente em muitas doenças neurodegenerativas, incluindo a epilepsia. O objetivo deste estudo foi avaliar a participação das EROs e da NADPH oxidase na morte neuronal no hipocampo de ratos submetidos ao modelo de ELT induzido pela pilocarpina (PILO). Os métodos utilizados foram a dihidroetidina (DHE) para determinar a geração de EROs, Fluoro-Jade B (detecta a degeneração de neurônios) e o tratamento com apocinina (APO), um antioxidante e inibidor da NADPH oxidase durante 7 dias prévios à injeção de PILO. Ratos machos Wistar adultos (n=5/grupo) foram submetidos à indução do status epilepticus (SE) e sacrificados após diferentes períodos (3, 6, 12 e 24 horas do início do SE). O giro denteado (GD) apresentou morte neuronal e aumento da geração de EROs em todos os períodos avaliados após indução de SE. Na região CA1, foi observada morte neuronal após 24 horas e aumento da geração em 6 e 24 horas. Na região CA3 morte neuronal e geração de EROs foram observadas após 24 horas do início do SE. O tratamento com APO diminuiu os níveis de EROs e morte neuronal em todas as regiões avaliadas. Nossos resultados indicam que o estresse oxidativo contribui para a morte neuronal durante o SE induzido por PILO. Além disso, pode-se sugerir que a NADPH oxidase está envolvida nesse processo, uma vez que o tratamento com APO diminuiu a neurodegeneração presente neste modelo de epilepsia / Temporal lobe epilepsy (TLE) is the most frequent form of epilepsy in adults. Experimental data have described an increase of reactive species oxygen (ROS) generation in relation to the neuronal death related to excitotoxicity, which occurs in many neurodegenerative diseases, including epilepsy. The aim of this study was to evaluate the participation of ROS generated by NADPH oxidase in the cell death observed in the hippocampus of rats submitted to the pilocarpine (PILO) model of TLE. Dihydroethidium (DHE) oxidation and Fluoro-Jade B assays were peformed in order to detect ROS generation and neurodegeneration, respectively. Moreover, treatment of rats with apocynin (APO), an antioxidant and NADPH oxidase inhibitor, was also performed for 7 days prior to induction of status epilepticus (SE). Male Wistar rats (n=5/group) were submitted to PILO injection for SE induction and sacrificed after different periods (3, 6, 12 and 24 hours after SE establishment). The dentate gyrus (DG) present clear neurodegeneration, as well as an increase of ROS generation, in all analysed periods. In the CA1 area neuronal death was observed at 24h and ROS generation after 6h and 24h after SE establishment. In the CA3 area neuronal death and ROS generation were detected 24h after SE induction. APO treatment was effective in decreasing both ROS production and neurodegeneration in all three hipocampal areas. These results reinforce the idea that oxidative stress contributes to the neuronal death ensuing after SE induced by pilocarpine. In addition, as the APO treatment decreased neurodegeneration present in this epilepsy model, we suggest an involvement of ROS generated by NADPH oxidase in TLE

This thesis is broken into four chapters. The first two chapters summarize two separate lines of investigation into the role of a putative neurotoxin in the pathogenesis of Huntington's Disease (HD). The third chapter outlines an investigation of the putative role of beta-N-methylamino-L-alanine (BMAA) in the pathogenesis of amyotrophic lateral sclerosis (ALS), while the final chapter details a post-mortem investigation of the contents of biogenic amines and amino acids in the brain of a man who died of a familial form of parkinsonism. Chapter I is a description of a chromatographic technique developed to isolate quinolinic acid (QA), an endogenous compound implicated in the pathogenesis of HD, from deproteinized human sera. A cation exchange column was used to selectively isolate QA, which was eluted with 10 mM HCl. The eluted fractions were analyzed by UV spectrometry to isolate and quantify QA. Once the fractions corresponding the elution of authentic QA were isolated, concentrated and the excess HCl removed, the fractions were added to growing fetal rat striatal explant cultures as an assay of neurotoxicity. Since HD involves the selective degeneration of GABAergic neurons in the striatum, the activity of glutamic acid decarboxylase, the final enzyme in the synthesis of GABA, was used to determine the viability of the cultures. Unfortunately, the method was confounded by the contamination of all effluents by compounds originating from the cation exchange resin, which were discovered to be neurotoxic to the striatal cultures, and as a result the investigation had to be abandoned. Chapter II describes an investigation designed to further characterize the nature of neurotoxicity observed in the sera obtained from patients with HD (Perry et al. 1987). Compounds with the capacity to selectively stimulate neurons at the N-methyl-D-aspartate (NMDA) receptor have been implicated in a variety of neurodegenerative disorders, including HD. Selective antagonists at the NMDA receptor have been shown to protect neurons from the degenerative effects of such "excitotoxins". The investigation described used MK-801, a potent noncompetitive NMDA antagonist, in an attempt to protect fetal rat striatal cultures from the neurodegenerative effects of the sera obtained from HD patients. The results obtained were equivocal. No evidence was obtained to support a role of the NMDA receptor in the mediation of the neurotoxicity, and in addition the neurodegenerative effects of HD sera were not reproduced in the present investigation. A variety of possible explanations for the apparent discrepancy are suggested. Chapter III describes an experiment intended to produce an animal model of ALS based on the observations by Spencer et al. 1987 that chronic oral administration of BMAA in monkeys produced the histological and behavioural characteristics of this disease. In the present investigation synthetic D,L-BMAA was given by gavage to mice over an eleven week period. Since BMAA is known to act at the NMDA receptor, a subset of the mice were also given MK-801 in an effort to protect them from any deleterious effects based on the action of BMAA at this receptor. The animals were sacrificed at the end of the experiment, and biochemical analyses were performed on the striata and cortices of the animals. In addition, neuropathological studies were performed on the spinal cords, basal ganglia and related structures. The results indicated no biochemical or neuropathological abnormality as a result of BMAA administration. Chapter IV describes a post-mortem investigation of a man who was a member of a well described pedigree which carries an autosomal dominant form of parkinsonism. The object of the investigation was to determine post-mortem levels of dopamine, noradrenaline, serotonin and their metabolites, in addition to amino acids in various regions of brain. Although conflicting evidence was obtained during life, neuropathological findings and the present neurochemical analyses confirm the degeneration of the nigrostriatal dopaminergic tract, characteristic of parkinsonism, in this man. / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate

Glia, whose name derives from the original Greek word, meaning “glue,” have long been understood to be cells that play an important functional role in the nutritive and structural support of the central nervous system, yet their full involvement has been historically undervalued. Despite the strong evidence that glial reactions to cellular debris govern the health of the nervous system, the specific properties of damaged axonal debris and the mechanisms by which glia sense them, morphologically adapt to their presence, and initiate phagocytosis for clearance, have remained poorly understood. The work presented in this thesis was aimed at addressing this fundamental gap in our understanding of the role for glia in neurodegenerative processes. I demonstrate that the cellular machinery responsible for the phagocytosis of apoptotic cell corpses is well conserved from worms to mammals. Draper is a key component of the glial response machinery and I am able to show here, for the first time, that it signals through Drosophila Shark, a non-receptor tyrosine kinase similar to mammalian Syk and Zap-70. Shark binds Draper through an immunoreceptor tyrosine-based activation motif (ITAM) in the Draper intracellular domain. I show that Shark activity is essential for Draper-mediated signaling events in vivo, including the recruitment of glial membranes to axons undergoing Wallerian degeneration. I further show that the Src family kinase (SFK) Src42A can markedly increase Draper phosphorylation and is essential for glial phagocytic activity. Therefore I propose that ligand-dependent Draper receptor activation initiates the Src42A-dependent tyrosine phosphorylation of Draper, the association of Shark and the subsequent downstream activation of the Draper pathway. I observed that these Draper-Src42A-Shark interactions are strikingly similar to mammalian immunoreceptor-SFK-Syk signaling events in myeloid and lymphoid cells. Thus, Draper appears to be an ancient immunoreceptor with an extracellular domain tuned to modified-self antigens and an intracellular domain that promotes phagocytosis through an ITAM domain-SFK-Syk-mediated signaling cascade. I have further identified the Drosophila guanine-nucleotide exchange factor (GEF) complex Crk/Mbc/dCed-12, and the small GTPase Rac1 as novel modulators of glial clearance of axonal debris. I am able to demonstrate that Crk/Mbc/dCed-12 and Rac1 function in a non-redundant fashion with the Draper pathway to promote a distinct step in the clearance of axonal debris. Whereas Draper signaling is required early during glial responses, promoting glial activation and extension of glial membranes to degenerating axons, the Crk/Mbc/dCed-12 complex functions at later stages of glial response, promoting the actual phagocytosis of axonal debris. Finally, many interesting mutants have been identified in primary screens for genes active in neurons that are required for axon fragmentation or clearance by glia, and genes potentially active in glia that orchestrate clearance of fragmented axons. The further characterization of these genes will likely unlock the mystery surrounding “eat me” and “find me” cues hypothesized to be released or exposed by neurons undergoing degeneration. Illuminating these important glial pathways could lead to a novel therapeutic approach to brain trauma or other neurodegenerative conditions by providing a druggable means of inducing early attenuation of the glial response to injury down to levels less damaging to the brain. Taken together, my combined work identifies new components of the glial engulfment machinery and shows that glial activation, phagocytosis of axonal debris, and the termination of glial responses to injury are genetically separable events mediated by distinct signaling pathways.

<p>Nerve injury induces up-regulation of the chaperone protein clusterin in affected neurons and adjacent astrocytes but the functional significance of this response is unclear. We find that motor neuron survival is significantly greater in clusterin(+/+) compared to (-/-) mice. These results suggest that endogenous expression of clusterin is neuroprotective after nerve injury. However, motor neuron survival in clusterin overexpressing mice was not different from that in wildtype mice. In contrast, treatment of neuronal cultures with clusterin-TAT recombinant protein is neuroprotective, including a positive effect on neuronal network complexity.</p><p>Since extracellular clusterin complexes are endocytosed after binding to various receptors, we examined the expression of known clusterin binding receptors in the spinal cord. We find that megalin is expressed in the nuclei of two cell populations in the mouse spinal cord: i) oligodendrocytes in late postnatal and adult spinal cord white matter, and ii) transiently (E11-15) in a population of immature astrocytes in the dorsal spinal cord. We find no correlation between clusterin and megalin in the intact or injured spinal cord. However, intranuclear localization of megalin, suggesting signalling properties, is supported by the co-localization with γ-secretase, the enzyme responsible for endodomain cleavage of megalin. Megalin deficient mice display a pronounced deformation of the dorsal part of spinal cord, an almost complete absence of oligodendroglial progenitor cells, and a marked reduction in the population of mature astrocytes at later prenatal developmental stages.</p><p>Taken together, our findings indicate that megalin is a novel signalling molecule for distinct populations of glial cells in the pre- and postnatal spinal cord. The functional role(s) of megalin is unknown. However, its expression patterns and cellular localization suggest that megalin regulates differentiation of oligodendrocytes and astrocytes in the prenatal spinal cord, as well as the function of myelinating oligodendrocytes in the postnatal spinal cord.</p>

Nerve injury induces up-regulation of the chaperone protein clusterin in affected neurons and adjacent astrocytes but the functional significance of this response is unclear. We find that motor neuron survival is significantly greater in clusterin(+/+) compared to (-/-) mice. These results suggest that endogenous expression of clusterin is neuroprotective after nerve injury. However, motor neuron survival in clusterin overexpressing mice was not different from that in wildtype mice. In contrast, treatment of neuronal cultures with clusterin-TAT recombinant protein is neuroprotective, including a positive effect on neuronal network complexity. Since extracellular clusterin complexes are endocytosed after binding to various receptors, we examined the expression of known clusterin binding receptors in the spinal cord. We find that megalin is expressed in the nuclei of two cell populations in the mouse spinal cord: i) oligodendrocytes in late postnatal and adult spinal cord white matter, and ii) transiently (E11-15) in a population of immature astrocytes in the dorsal spinal cord. We find no correlation between clusterin and megalin in the intact or injured spinal cord. However, intranuclear localization of megalin, suggesting signalling properties, is supported by the co-localization with γ-secretase, the enzyme responsible for endodomain cleavage of megalin. Megalin deficient mice display a pronounced deformation of the dorsal part of spinal cord, an almost complete absence of oligodendroglial progenitor cells, and a marked reduction in the population of mature astrocytes at later prenatal developmental stages. Taken together, our findings indicate that megalin is a novel signalling molecule for distinct populations of glial cells in the pre- and postnatal spinal cord. The functional role(s) of megalin is unknown. However, its expression patterns and cellular localization suggest that megalin regulates differentiation of oligodendrocytes and astrocytes in the prenatal spinal cord, as well as the function of myelinating oligodendrocytes in the postnatal spinal cord.

Axonal and synaptic degeneration is a hallmark of peripheral neuropathy, brain injury, and neurodegenerative disease. Axonal degeneration has been proposed to be mediated by an active autodestruction program, akin to apoptotic cell death; however, loss-of-function mutations capable of potently blocking axon self-destruction have not been described. Using a forward genetic screen in Drosophila, we identified that loss of the Toll receptor adaptor dSarm (sterile a/Armadillo/Toll-Interleukin receptor homology domain protein) cell-autonomously suppresses Wallerian degeneration for weeks after axotomy. Severed mouse Sarm1 null axons exhibit remarkable long-term survival both in vivo and in vitro, indicating that Sarm1 prodegenerative signaling is conserved in mammals. Our results provide direct evidence that axons actively promote their own destruction after injury and identify dSarm/Sarm1 as a member of an ancient axon death signaling pathway. This death signaling pathway can be activated without injury by loss of the N-terminal self-inhibitory domain, resulting in spontaneous neurodegeneration. To investigate the role of axon self-destruction in disease, we assessed the effects of Sarm1 loss on neurodegeneration in the SOD1-G93A model of amyotrophic lateral sclerosis (ALS), a lethal condition resulting in progressive motor neuron death and paralysis. Loss of Sarm1 potently protects motor axons and synapses from degeneration, but only extends animal survival by 10%. Thus, there appears to be at least two driving forces in place during ALS disease progression: (1) Sarm1 mediated axon death, and (2) cell body destruction via some unknown mechanism.

Dissertation (Ph.D.)--University of South Florida, 2007. / Title from PDF of title page. Document formatted into pages; contains 187 pages. Includes vita. Includes bibliographical references.