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Title
TOWARD PRECISION MEDICINE : EFFECTS OF THE COMMON VAL66MET BDNF VARIANT IN THE AGING BRAIN AND IMPLICATIONS FOR THE FUTURE OF PARKINSON’S DISEASE THERAPEUTICS
Creator
Mercado-Idziak, Natosha Marie
Date
2021
Collection
Electronic Theses & Dissertations
Description
The rs6265 (Val66Met) single nucleotide polymorphism in the gene for brain-derived neurotrophic factor (BDNF) is a common genetic variant that has been shown to alter therapeutic responses in patients with Parkinson’s disease (PD). Possession of the variant Met allele results in decreased activity-dependent release of BDNF by disrupting BDNF transport and sorting into synaptic vesicles. In the experiments detailed in this thesis, I examine the effects of the Val66Met SNP, and its interaction...
Show moreThe rs6265 (Val66Met) single nucleotide polymorphism in the gene for brain-derived neurotrophic factor (BDNF) is a common genetic variant that has been shown to alter therapeutic responses in patients with Parkinson’s disease (PD). Possession of the variant Met allele results in decreased activity-dependent release of BDNF by disrupting BDNF transport and sorting into synaptic vesicles. In the experiments detailed in this thesis, I examine the effects of the Val66Met SNP, and its interaction with aging, on therapeutic efficacy and the development of aberrant side-effects following primary dopamine (DA) neuron transplantation, a restorative experimental therapeutic approach for PD that is currently experiencing a robust revitalization following a decade-long worldwide moratorium. In particular, I hypothesized that rs6265-mediated dysfunctional BDNF signaling is an unrecognized contributor to the limited clinical benefit observed in a subpopulation of individuals with PD despite robust survival of grafted DA neurons and extensive integration into the host brain. I also hypothesized that this genetic variant contributes to the development of graft-induced dyskinesias (GID). To test these hypotheses, we generated a novel CRISPR knock-in rat model of the rs6265 BDNF SNP to investigate for the first time the influence of a common genetic polymorphism on graft survival, functional efficacy, and side-effect burden in subjects grafted with embryonic ventral mesencephalic DA neurons. In two sister studies, I compared these primary endpoints between wild-type (Val/Val) rats and those homozygous for the variant Met allele (Met/Met), in both young adult (8 m.o. at grafting) and middle-aged (15 m.o. at grafting) cohorts. In each study, rats were rendered unilaterally parkinsonian with intranigral 6-hydroxydopamine and primed with levodopa (12 mg/kg M-Fr) to induce stable expression of levodopa-induced dyskinesias (LID), the primary behavioral endpoint for assessing graft function. After levodopa priming, rats received an intrastriatal graft of embryonic ventral mesencephalic neurons (200,000 cells in young adult rats, 400,000 cells in middle-aged rats; E14 wild-type donors) or a sham graft. LID were evaluated for 9-10 weeks post-engraftment, and GID were assessed 24-48 hr prior to sacrifice. In young adult graft recipients, this research demonstrates that: 1) Met/Met rats display enhanced graft efficacy and paradoxically enriched graft-derived neurite outgrowth compared to Val/Val rats, and 2) the Met allele is strongly linked to GID development and this behavioral phenotype is correlated with neurochemical signatures of glutamatergic neurotransmission by grafted DA neurons. In middle-aged graft recipients, this research indicates that: 1) behavioral enhancement associated with the Met allele is maintained with advancing age, and 2) advanced age is associated with the induction of GID in rats of both genotypes despite the presence of widespread intrastriatal grafts. In this rapidly evolving era of precision medicine, understanding mechanisms underlying the beneficial versus detrimental impact of the Val66Met polymorphism, and/or its interaction with aging, will aid in the development of safe and optimized therapeutic approaches for remodeling the parkinsonian striatum.
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Title
PERTURBATION OF ASTROCYTIC KEAP1-NRF2-ARE PATHWAY AND GLUTAMATE TRANSPORTER EXPRESSION IN SPINAL ASTROCYTIC DEGENERATION
Creator
Wiwatratana, Duanghathai
Date
2021
Collection
Electronic Theses & Dissertations
Description
Several cellular mechanisms are known to be involved in methylmercury (MeHg) induced central nervous system (CNS) toxicity, including the dysregulation of intracellular Ca2+, redox, and glutamate homeostasis. However, the factors that make particular neurons susceptible to MeHg toxicity, and the latency period of neurological signs and symptoms, have not yet been clearly delineated. For example, the spinal dorsal root ganglia (DRG) is the primary target of MeHg. Mercury (Hg) granules are...
Show moreSeveral cellular mechanisms are known to be involved in methylmercury (MeHg) induced central nervous system (CNS) toxicity, including the dysregulation of intracellular Ca2+, redox, and glutamate homeostasis. However, the factors that make particular neurons susceptible to MeHg toxicity, and the latency period of neurological signs and symptoms, have not yet been clearly delineated. For example, the spinal dorsal root ganglia (DRG) is the primary target of MeHg. Mercury (Hg) granules are first detected in spinal cord motor neurons (SMNs) in the non-symptomatic phase, whereas Hg granules are detected in glia later, following with neurological symptoms (Møller-Madsen, 1991). This finding suggested that the latent period (non-symptomatic phase) is associated with Hg accumulation in neurons, while the symptomatic phase occurs following Hg accumulation in glia, and the susceptibility is not associated with Hg granule accumulation in cells (Møller-Madsen, 1991). Astrocytes generally provide glutathione (GSH) for neurons to detoxify toxic insult. In the spinal cord, MeHg might perturb the antioxidant pathway, Keap1-Nrf2-ARE pathway in the spinal cord astrocytes (SCAs) consequently contribute to DRG or SMN susceptibility to MeHg toxicity. In this study, the comparative responses of different SCAs maturity to a non-toxic MeHg concentration (0.1 μM) suggested that the fully mature SCAs (Day in vitro 30; DIV30), were more susceptible to MeHg than SCAs on DIV14. The perturbation of the Keap1-Nrf2-ARE pathway in SCAs (DIV 30) during exposure to sub-toxic MeHg concentration (0.50 μM) caused a biphasic increase in antioxidant genes such as Keap1, Nrf2, Gclc, Abcc1 mRNAs expression. The concomitant increase of glutamate transporter Slc7a11 encoded for the system Xc-, and Slc1a3 encoded for EAAT1, and Slc1a2 encoded for EAAT2 expression during MeHg exposure might suggest the cooperative expression or function of these glutamate transporters. This concomitant expression was further demonstrated in studies using Nrf2-knockout (Nrf2-KO) derived SCAs. The increase of basal Slc7a11 mRNA, was concurrent to the increase of basal Slc1a3 and Slc1a2 mRNA expressions in Nrf2-KO derived SCA. The function of time of MeHg exposure indicated that Nrf2-KO derived SCAs were more susceptible to MeHg than the wild-type (WT)-derived SCAs. The pronounced susceptibility of Nrf2-KO derived SCAs was mainly due to the loss of GSH) metabolism and transport genes Gclc, GPx1, GPx4, and Abcc1 mRNAs in this genotype. MeHg significantly reduced these mRNA expressions in both genotypes. However, not all Nrf2-ARE regulated genes were affected by MeHg in similar ways in these genotypes. For example, MeHg induced the increase of Slc7a11 mRNA expression in WT-derived SCAs, but it appears to cause the reduction of this mRNA expression in Nrf2 KO-derived SCAs. Administration of antioxidant N-acetyl-L-cystine (NAC) in pretreatment (NP), co-treatment (CO), and post-treatment of MeHg (MP) prevented the reduction of SCAs metabolic functions for over 160h. The mechanism of NAC action in preventing MeHg induced SCAs degeneration is primarily due to its thiol antioxidant property.In conclusion, this study suggests that age and genetic predisposition contribute to SCAs susceptibility to MeHg toxicity. The dysregulation of the antioxidant pathways and glutamate homeostasis in SCAs potentially contributes to SMNs or DRG susceptible to MeHg.
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Title
An examination of between- and within-subject effects of stress on emotional eating over 49 consecutive days in women
Creator
Fowler, Natasha
Date
2021
Collection
Electronic Theses & Dissertations
Description
Objective: Stress is associated with emotional eating (EE) in women cross-sectionally (between-subject). However, few studies have examined stress longitudinally limiting our understanding of how within-subject variations in stress level influence risk for EE over time and whether stress is in fact a risk factor or consequence of EE (within-subject). This study used an intensive, longitudinal study design to examine between- and within-subject effects of major life stress, daily stress impact...
Show moreObjective: Stress is associated with emotional eating (EE) in women cross-sectionally (between-subject). However, few studies have examined stress longitudinally limiting our understanding of how within-subject variations in stress level influence risk for EE over time and whether stress is in fact a risk factor or consequence of EE (within-subject). This study used an intensive, longitudinal study design to examine between- and within-subject effects of major life stress, daily stress impact, and cortisol on EE in women. Methods: An archival sample of 477 women aged 15-30 years recruited from the Michigan State University Twin Registry provided daily ratings of EE and stress impact for 49 consecutive days, along with self-reports of major life stress in the last 12 months and hair cortisol concentration (HCC), a longitudinal measure of cortisol secretion. Mixed linear models examined main and interactive effects of each stress variable on EE. Results: Both between- and within-subject analyses showed that daily stress more strongly predicted EE than major life stress. Specifically, women engaged in higher levels of EE when they experienced higher levels of daily stress impact relative to other women (between-subject) and their own daily stress levels (within-subject). There was a tendency for lower HCC to predict increased levels of EE (between-subject). Discussion: Findings confirm longitudinal associations between daily stress impact and cortisol with EE in women. Results also highlight the importance of within-subject shifts in a woman’s stress level in her risk for EE and suggest that stress management techniques may a be useful tool for treatment.
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Title
Heterogeneous Thalamic Reticular Nucleus Neurons and Their Functional Role in Thalamocortical Processing
Creator
Harding-Jackson, Laura
Date
2021
Collection
Electronic Theses & Dissertations
Description
The thalamic reticular nucleus (TRN) is an integral regulator of information flow between the thalamus and cortex. The TRN receives synaptic inputs from both cortical and thalamic regions and based upon this information it selectively inhibits thalamic activity. TRN neurons produce action potentials in two distinct modes: a fast, transient burst discharge from a hyperpolarized state, and a prolonged, tonic discharge from a relatively depolarized state. While previous studies have...
Show moreThe thalamic reticular nucleus (TRN) is an integral regulator of information flow between the thalamus and cortex. The TRN receives synaptic inputs from both cortical and thalamic regions and based upon this information it selectively inhibits thalamic activity. TRN neurons produce action potentials in two distinct modes: a fast, transient burst discharge from a hyperpolarized state, and a prolonged, tonic discharge from a relatively depolarized state. While previous studies have characterized burst discharge as a transient high frequency discharge (> 250 Hz), these electrophysiological studies reveal a highly variable range of burst frequencies (4- 342 Hz). In these studies, I aim to discover the mechanisms underlying these highly variable burst frequencies, as well as their functional role in thalamocortical processing.In chapter two, I found that bursts from TRN neurons with relatively higher frequency discharge (>100 Hz) contain more action potentials per burst. These neurons also have higher input resistances, broader action potentials, higher action potential thresholds, and larger somas. The amplitude of the T-type calcium channel-mediated low-threshold spike, which underlies the burst discharge, is positively correlated with both the burst discharge frequency and the number of action potentials per burst. I next investigated whether small conductance calcium-activated potassium channels (SK channels) could mediate the differences in burst firing rate and action potential number. Blocking SK channels increased the frequency and duration of the burst but did not increase the amplitude of the underlying T-type calcium current. Prior studies suggest that T-type calcium channels are distributed along the dendrites in TRN neurons with high frequency burst discharge. In chapter three, I examine the distribution of dendritic calcium activity within the lower frequency bursting neurons. While the calcium signal was lower in these neurons all along the dendrites, the calcium signal was evenly distributed across proximal, intermediate, and distal dendritic regions. Investigation of SK channel activity revealed significant location-specific effects. In lower frequency bursting neurons, SK channels had the greatest influence at proximal and distal locations. In higher frequency bursting neurons, SK channels had the greatest influence at proximal and intermediate dendritic locations. Heterogeneous TRN burst discharge frequencies may represent a diverse cell population with unique dendritic ion channel composition and distribution. These results may improve our understanding of the mechanisms of TRN neuron afferent synaptic integration as well as modulation of thalamocortical inhibition. In chapter four I investigate whether intrinsic properties of TRN neurons are altered in the Fmr1-KO mouse model of Fragile X Syndrome (FXS). Individuals with FXS experience a variety of comorbidities that could involve TRN function, such as altered sensory perceptions, sleep disorders, and epilepsy. Analysis of intrinsic cellular properties revealed no differences in TRN neuron properties. Further investigation of synaptic plasticity, which is an abnormal finding in several other brain regions in FXS, also revealed no pathology. These findings suggest that TRN dysfunction does not contribute to FXS pathology.
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Title
Delineation of Delta FosB's in vivo redox sensitivity
Creator
Lynch, Haley Marie
Date
2021
Collection
Electronic Theses & Dissertations
Description
Many neurodegenerative diseases, including Alzheimer’s disease (AD), are driven by altered reduction/oxidation (redox) balance in the brain. Moreover, cognitive decline in AD is caused by neuronal dysfunction that precedes cell death, and this dysfunction is in part produced by altered gene expression. However, the mechanisms by which redox state controls gene expression in neurons are not well understood. Delta FosB is a neuronally enriched transcription factor critical for orchestrating...
Show moreMany neurodegenerative diseases, including Alzheimer’s disease (AD), are driven by altered reduction/oxidation (redox) balance in the brain. Moreover, cognitive decline in AD is caused by neuronal dysfunction that precedes cell death, and this dysfunction is in part produced by altered gene expression. However, the mechanisms by which redox state controls gene expression in neurons are not well understood. Delta FosB is a neuronally enriched transcription factor critical for orchestrating gene expression underlying memory, mood, and motivated behaviors and is dysregulated in AD. Delta FosB regulates gene expression by dimerizing with JunD to form activator protein 1 (AP-1) which binds the promoter regions of target genes to control transcription. In controlled in vitro conditions, AP-1 complex formation and DNA binding are modulated by redox-sensitive disulfide bonds and related redox-sensitive conformational changes in Delta FosB. Here, we show that the redox-dependence of the structure-function relationship of Fos-family proteins found in vitro is also conserved in Delta FosB in cells and in the mouse brain. Under oxidizing conditions, Delta FosB cysteine residues can form disulfide bridges, including at C222 and C172, which can stabilize its interaction with a partner protein; however, these conditions reduce complex binding to AP-1 consensus sequence DNA, specifically when C172 is oxidized. We present evidence that this effect occurs in cells and in mouse brain, altering Delta FosB target gene expression during redox stress. This evidence supports Delta FosB as an important mediator of oxidative stress-driven changes in gene expression seen in neurological conditions and implicates Delta FosB as a possible therapeutic target for intervention in diseases of oxidative stress like AD.
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Title
MIND-BODY STATE LITERACY : A PEDAGOGICAL APPROACH THAT USES MINDFULNESS AND BRAIN LITERACY TO SUPPORT LEARNING AND RELATIONAL NARRATIVE WORK
Creator
Schaefer, Erin Elizabeth
Date
2020
Collection
Electronic Theses & Dissertations
Description
Mind-Body State Literacy: A Pedagogical Approach that uses Mindfulness and Neuroscience to Support Learning and Relational Narrative Work describes the literacies necessary to develop the habits of minds presented in the Framework for Success in Postsecondary Writing: “curiosity, openness, engagement, creativity, persistence, responsibility, flexibility and metacognition” (WPA, NCTE, & NWP, 2011, par. 2). Such habits, because they deal with students’ openness in the learning process, are key...
Show moreMind-Body State Literacy: A Pedagogical Approach that uses Mindfulness and Neuroscience to Support Learning and Relational Narrative Work describes the literacies necessary to develop the habits of minds presented in the Framework for Success in Postsecondary Writing: “curiosity, openness, engagement, creativity, persistence, responsibility, flexibility and metacognition” (WPA, NCTE, & NWP, 2011, par. 2). Such habits, because they deal with students’ openness in the learning process, are key to students’ ability to receive a liberal education. I suggest that before instructors or students can develop these habits, they need to learn to develop an open mind-body state, defined as the ability to let one’s narrative incorporate other narratives/perspectives through listening. The Mind-Body State model is comprised of three facets: brainwaves, narratives, and emotions. The Mind-Body State Literacy (MBSL) approach suggests that students develop literacies related to these three facets, drawing primarily from mindfulness practices and philosophies the center the body and compassion. I anchor my presentation of the MBSL by suggesting why it might be especially relevant as students engage in personal narrative writing in the Rhetoric and Writing classroom.
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Title
Enteric glial modulation of immune activation during inflammatory stress
Creator
Chow, Aaron Kin Yeung
Date
2020
Collection
Electronic Theses & Dissertations
Description
Gastrointestinal (GI) disorders such as inflammatory bowel disease (IBD), irritable bowel syndrome, and other functional GI disorders are major health concerns and account for about $26.4 billion in yearly costs in the United States alone. Many of these GI disorders manifest symptoms such as GI dysmotility, intestinal secretion and absorption dysfunction, and abdominal pain. Inflammation plays a major role in the pathogenesis of these diseases, and current therapies for many GI disorders aim...
Show moreGastrointestinal (GI) disorders such as inflammatory bowel disease (IBD), irritable bowel syndrome, and other functional GI disorders are major health concerns and account for about $26.4 billion in yearly costs in the United States alone. Many of these GI disorders manifest symptoms such as GI dysmotility, intestinal secretion and absorption dysfunction, and abdominal pain. Inflammation plays a major role in the pathogenesis of these diseases, and current therapies for many GI disorders aim to regulate the activation and progression of the inflammatory cascade. However, due to a gap in knowledge in how the immune system is regulated within the GI tract, there remains a lack of effective treatments for these common GI disorders. Interactions between the nervous system and immune system point to neurons having important roles in immune modulation, but the mechanisms of neuro-immune regulation in the gut is not completely understood.The enteric nervous system (ENS) consists of enteric neurons and enteric glia arranged in plexuses embedded in the gut wall. This neural network is responsible for the normal secretomotor functioning of the GI tract, and the disruption of the ENS network alters GI functioning and underlies pathological GI symptoms. As part of the ENS, enteric glia work in tandem with enteric neurons to coordinate GI functions. In addition to their contributions to maintain normal secretomotor functioning of the GI tract, enteric glia are activated by immunomodulatory signals, they can secrete and respond to cytokines, can exert immunosuppressive effects, and share characteristics with antigen presenting cells. Therefore, we hypothesize that enteric glia play an active role in immune regulation in the ENS.In this dissertation, we specifically examine the role enteric glial cells play as an antigen presenting cell to regulate immune activation. Our results show that enteric glia have the machinery necessary to act as an antigen presenting cell and can express major histocompatibility complex (MHC) type II molecules during inflammatory stress to interact with T-lymphocytes. Enteric glial MHC II expression has functional relevance, as it modulates the activation in Th17 and Treg subtypes, but not Th1 or Th2 T-lymphocyte subtypes. Although MHC II molecules are typically associated with the expression of phagocytosed extracellular antigens, our results show that enteric glia do not readily phagocytose extracellular antigens. Instead, MHC II expression in enteric glia is mediated by autophagy. The activation of autophagic pathways is necessary, but not sufficient in eliciting enteric glial MHC II expression. Finally, although enteric glia regulate T-lymphocyte activation, cytokine levels at the whole organism or regional tissue levels remain unchanged, suggesting that enteric glial cytokine effects primarily operate at the local microenvironment level.Our findings provide support for enteric glial cells having an active role as an immunomodulator. Specifically, we show that enteric glia modulate T-lymphocyte activation via autophagy-mediated MHC II expression and propose a novel mechanism of neuro-immune modulation in the gut.
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Title
Biomaterial and genetic tools to influence neuronal network formation, excitability, and maturity at the electrode interface
Creator
Setien-Grafals, Monica B.
Date
2020
Collection
Electronic Theses & Dissertations
Description
Understanding brain function remains a grand challenge of our time. Likewise, when neurodegeneration occurs, repair efforts are limited due to the highly heterogeneous and interconnected nature of the cerebral cortex. The drive to better understand normal brain function and pathological states has intensified demand for new technologies which can interrogate the nervous system with enhanced spatiotemporal resolution. Implanted brain electrodes are being used and developed to provide a deeper...
Show moreUnderstanding brain function remains a grand challenge of our time. Likewise, when neurodegeneration occurs, repair efforts are limited due to the highly heterogeneous and interconnected nature of the cerebral cortex. The drive to better understand normal brain function and pathological states has intensified demand for new technologies which can interrogate the nervous system with enhanced spatiotemporal resolution. Implanted brain electrodes are being used and developed to provide a deeper understanding for neurological injury and neurodegeneration. However, issues with biological integration come into play and potentially interfere with signal stability over time. Here, this work provides innovative tools that can be used to interface and control the tissue-electrode interface. In particular, we are interested in exploring surface chemistries, genetic tools, and electrode materials which favor neural regeneration around implanted electrodes. The research presented in this dissertation describes the exploration of biomaterial and genetic tools for interfacing the tissue-electrode interface: (1) characterization of surface chemistries presented to differentiating neural progenitors, and an understanding of the conditions which promote neurite outgrowth and electrophysiological maturation, (2) a blue-light inducible gene expression system, which could potentially be used to control gene expression at the implanted electrode interface, and (3) testing the impacts of "next-generation" electrode materials, such as diamond, as candidates for neural interfacing. Chapter 2 uncovers the study of various common substrates and their effects on rat neural progenitor cells, which can be used to create unique morphologies. Chapter 3 explores the use of an optogenetic system from a bacterial transcription factor (EL222) that allows for blue light-dependent transcriptional activation. Here, we validated the use of EL222 for spatial patterning of fluorescent reporter genes and developed stable expression in HEK293 cells, which can be used long-term for developing approaches for light-driven regeneration of neural circuitry. Chapter 4 reveals material and genetic factors that can affect cell structure and function. Here, we report the results of an initial characterization of the biocompatibility of the novel diamond-based materials, including conductive boron-doped polycrystalline diamond (BDD) and insulating polycrystalline diamond (PCD). The results presented will inform the transfer of the novel diamond substrate materials to sensing applications in the in vivo environment, where we expect to leverage the positive performance characteristics of the diamond materials displayed in vitro. Taken together, these chapters offer significant development of material and biological tools and that will help manage and mitigate challenges presented at the tissue-electrode interface. Future directions aim at exploring synergistic effects of electrode material and optogenetic control for controlling excitability and identity of cells at the interface, effectively bridging the divide between electronics and tissue.
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Title
Early Axonal Tau Pathology in the Human Hippocampus and the Molecular Consequences of AT8 Tau Phosphorylation
Creator
Christensen, Kyle Robert
Date
2018
Collection
Electronic Theses & Dissertations
Description
Tau is a microtubule-associated protein that is classically thought to play a role in stabilizing microtubules and the pathological accumulation of tau protein is a hallmark of several diseases collectively known as tauopathies, including Alzheimer’s disease (AD). Despite the clear implications for tau playing a critical role in tauopathies, many questions regarding its deposition in disease and mechanisms of toxicity remain unanswered. This dissertation was aimed at addressing two key...
Show moreTau is a microtubule-associated protein that is classically thought to play a role in stabilizing microtubules and the pathological accumulation of tau protein is a hallmark of several diseases collectively known as tauopathies, including Alzheimer’s disease (AD). Despite the clear implications for tau playing a critical role in tauopathies, many questions regarding its deposition in disease and mechanisms of toxicity remain unanswered. This dissertation was aimed at addressing two key questions in the field. 1) Does tau deposition occur first in the axons of affected neurons before proceeding to the somatodendritic compartment? 2) Does pathological modification of tau cause abnormalities in the ability of tau to modulate protein phosphatase 1 (PP1)? A long-held hypothesis on the progressive deposition of tau pathology in AD is that pathological tau accumulates first in axons of neurons and then progresses back into the cell bodies to form neurofibrillary tangles, however, studies have not directly analyzed this relationship in human tissue. In the early phases of tau deposition, both AT8 phosphorylation and exposure of the amino terminus of tau occur in tauopathies, and these modifications are linked to mechanisms of synaptic and axonal dysfunction. Here, the hippocampus of 44 well-characterized human samples from cases ranging between non-demented and mild cognitively impaired were examined for AT8 phosphorylation, amino terminus exposure, and amyloid- (Aβ) pathology in the axons and neuronal cell bodies within strata containing the CA3-Schaffer collateral and dentate granule-mossy fiber pathways. We show that tau pathology first appears in the axonal compartment of affected neurons in the absence of observable tau pathology in the corresponding cell bodies and independent of the presence of Aβ pathologies. Using the axonal marker, SMI-312, we confirmed that the majority of tau pathology-positive neuropil threads were axonal in origin. These results support the hypothesis that AT8 phosphorylation and PAD exposure are early pathological events and that the deposition of tau pathology occurs first in the axonal compartment prior to observable pathology in the cell bodies of affected neuronal pathways. The functional implications of AT8 and PAD-exposed tau deposition early in the axons of affected neurons is important because of a recently identified mechanism where these pathogenic forms of tau activate a PP1-dependent signaling pathway and lead to disruption of axonal functions. However, the connection between tau and PP1 was not defined. Here, we performed detailed studies on the interaction between tau and PP1 and subsequent effects on PP1 activity. Wild-type tau interacts with and activates PP1α and γ, but shows little to no interaction with PP1β, and this effect depends primarily on the microtubule binding repeats in tau. Additionally, AT8 tau increased the interactions with and activity of PP1γ, while deletion of PAD in the presence of AT8 reduced this interaction. These results suggest that tau’s function likely extends beyond stabilizing microtubules to include regulation of PP1 signaling cascades, and disease-associated tau phosphorylation may alter this function. Collectively, this work suggests forms of pathological tau, such as AT8 phospho-tau, that alter PP1 signaling and disrupt axonal function deposit in the axons of affected hippocampal neurons early during disease pathogenesis and prior to their appearance in the somatodendritic compartment of neurons.
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Title
Altered Metabotropic Glutamate Receptor Function in the Neocortex of a Fragile X Mouse
Creator
Fenn, Jacqueline Ann
Date
2017
Collection
Electronic Theses & Dissertations
Description
Fragile X Syndrome (FXS) is the leading cause of inherited intellectual disability. It is characterized by a wide array of symptoms, including cognitive impairments, attention deficit and hyperactivity disorder (ADHD), hypersensitivity to sensory stimuli, autistic features, mood lability, and seizures. Since the creation of the Fmr1 KO mouse more than 20 years ago, a wealth of studies have uncovered a role for group I metabotropic glutamate receptors (mGluRs) in mediating many FXS phenotypes,...
Show moreFragile X Syndrome (FXS) is the leading cause of inherited intellectual disability. It is characterized by a wide array of symptoms, including cognitive impairments, attention deficit and hyperactivity disorder (ADHD), hypersensitivity to sensory stimuli, autistic features, mood lability, and seizures. Since the creation of the Fmr1 KO mouse more than 20 years ago, a wealth of studies have uncovered a role for group I metabotropic glutamate receptors (mGluRs) in mediating many FXS phenotypes, leading to development of "The mGluR Theory of Fragile X". However, studies supporting this theory have focused on impairments in the hippocampus, amygdala, and other structures of the allocortex. The isocortex remains largely uninvestigated, despite its major role in sensory integration, attentional processes, and executive function. MgluRs are also highly expressed in the neocortex, where they can modulate neuronal excitability and synaptic transmission. Using electrophysiological methods, I investigated the role of group I and group II mGluRs in modulating neocortical circuits in primary visual cortex. Humans with FXS show severe visual-motor deficits, and perform poorly on global motion tasks. Autopsy studies also reveal abnormal dendritic spine morphologies in layer 5/6 of the visual neocortex, and this is substantiated in the Fmr1 KO mouse. Using whole cell patch clamp recordings of different neuron subtypes in layer 5/6 of primary visual cortex, I found that Fmr1 KO layer 5/6 somatostatin expressing neurons (SST+) have a significant decrease in input resistance compared to wild type (WT), indicating that they are less intrinsically excitable than WT SST+ neurons. Further, I show that activation of group II mGluRs leads to disinhibition of excitatory pyramidal neurons. I also discover that suppression of GABAergic transmission by group II mGluRs is normal in the Fmr1 KO, leading to my hypothesis that increased disinhibition of pyramidal neurons by group II mGluRs is due to their altered modulation of fast glutamatergic transmission onto layer 5/6 interneurons in the Fmr1 KO mouse. Using recordings from fluorescently labeled interneurons in layer 5/6 visual neocortex, I discover that group II mGluR-mediated suppression of fast excitatory glutamatergic transmission onto inhibitory neurons is exaggerated in the Fmr1 KO mouse. I show that this effect is cell specific, as it only occurs in SST+ interneurons and not parvalbumin expressing interneurons. Finally, I show that this deficit in excitatory drive onto SST+ interneurons is mediated by presynaptic mGluRs, and that these defects are specific to layer 5/6 visual neocortex. Both the decreased excitability of SST+ interneurons and exaggerated group II-mGluR mediated suppression of excitatory drive onto these cells would lead to neocortical circuit hyperexcitability in the Fmr1 KO mouse. A hyperexcitable neocortical circuit would be anticipated to negatively impact sensory integration, a requirement for both stimulus encoding and attentional processes. Lastly, a hyperexcitable neocortical network could give rise to epileptiform activity. The results of these studies are fascinating, as group II mGluRs have not previously been implicated in studies of the neocortical pathogenesis in the Fmr1 KO mouse. This investigation also showed that group I mGluR-mediated modulation of membrane excitability and fast synaptic transmission is unaltered in the Fmr1 KO mouse, suggesting that "The mGluR theory of Fragile X" may in fact be more or less valid contingent on the brain region under investigation. It is my hope that these circuit studies will inform scientific investigations on autism spectrum disorders and epilepsy syndromes, as both show high comorbidity in individuals with FXS.
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Title
Pathology at the neuromuscular junction in mouse models of spinal bulbar muscular atrophy
Creator
Poort, Jessica Erin
Date
2014
Collection
Electronic Theses & Dissertations
Description
Spinal bulbar muscular atrophy (SBMA) is a progressive, late onset neuromuscular disease that results in muscle weakness and atrophy, as well as motoneuron death in men. While pathology at the neuromuscular junction (NMJ) is noted in numerous neurodegenerative diseases, disease-related changes at the NMJ in SBMA have not been explored. Characterizing such changes is not only important for determining whether the NMJ has any role in the functional changes underlying motor dysfunction, but also...
Show moreSpinal bulbar muscular atrophy (SBMA) is a progressive, late onset neuromuscular disease that results in muscle weakness and atrophy, as well as motoneuron death in men. While pathology at the neuromuscular junction (NMJ) is noted in numerous neurodegenerative diseases, disease-related changes at the NMJ in SBMA have not been explored. Characterizing such changes is not only important for determining whether the NMJ has any role in the functional changes underlying motor dysfunction, but also in determining how such potential pathology at the NMJ develops as disease progresses. If for example, pathology emerges first at the NMJ followed by motoneuron death, then the NMJ offers future promise as a therapeutic target for preventing or reversing symptoms of SBMA before motoneurons are lost. We evaluated three different mouse models of SBMA, one overexpressing a wildtype androgen receptor (AR) exclusively in muscle fibers (so called "myogenic" model), a second which expressed the endogenous AR gene with the first exon of the human mutant AR gene "knocked in" (the so called "knock-in" model), and a final model that broadly expresses a full length human AR transgene harboring the SBMA mutation (the so called "97Q" model). Using both confocal microscopy and electron microscopy, I found that all three mouse models show a pathological fragmentation of the NMJ suggestive of functionally weakened synapses. Other changes at the neuromuscular synapse suggesting decreases in synaptic strength that were found in some but not all models include a decline in the number of docked vesicles ready for release in nerve terminals, a widening of synaptic clefts, simplified postsynaptic folds, and an abnormal accumulation of synaptic vesicle and neurofilament proteins. Retrograde axonal transport of endosomes was also characterized in the 97Q model using live imaging confocal microscopy. Despite previously published data, I found no evidence for a disease-related defect in retrograde transport in the 97Q model. The strikingly abnormal morphology of NMJs in all three models raises the possibility that synaptic function is impaired. Such synaptic dysfunction may contribute to or underlie the impairments in motor function associated with SBMA.
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Title
Masking : the acute effects of light on the brain and behavior
Creator
Shuboni, Dorela Doris
Date
2013
Collection
Electronic Theses & Dissertations
Description
Masking of behavior by external stimuli works with the circadian system to ensure that animals are active during the correct time-of-day. Light for diurnal and nocturnal species produces different masking responses, enhancing activity for diurnal species and suppressing activity for nocturnal species. Few studies have examined the neural mechanisms of masking; none these experiments use animals active during the day. The first experiment of this dissertation uses the protein of the immediate...
Show moreMasking of behavior by external stimuli works with the circadian system to ensure that animals are active during the correct time-of-day. Light for diurnal and nocturnal species produces different masking responses, enhancing activity for diurnal species and suppressing activity for nocturnal species. Few studies have examined the neural mechanisms of masking; none these experiments use animals active during the day. The first experiment of this dissertation uses the protein of the immediate-early gene cFOS to compare activation of brain regions to light between nocturnal mice and diurnal grass rats during a time-point where they showed a distinct behavioral dichotomy in response. Grass rats showed a consistent increase in activation in areas that receive retinal innervation or were related to sleep/arousal, while mice showed either no difference or a decrease in activation with the exception of the SCN. This study demonstrates the differences in behavioral and neurological responses to masking pulse of light between a nocturnal and diurnal rodent species.We next examined the functional role of the ventral subparaventricular zone (vSPZ) on masking to light in the grass rat. The vSPZ uniquely responded to light in diurnal grass rats, receives direct retinal innervation from the eye and after ablation showed a possible alteration in masking. Schwartz et al. (2009)showed that grass rats with damage to the vSPZ had bouts of arrhythmia in LD conditions, indicating that the masking system may be altered. In Chapter 3, we tested the functional for of the region by bilateral lesioning the vSPZ and directly testing the effects of light on masking. Animals with complete ablations still increased activity in response to light in two different masking protocols. In Chapter 4, we examined another brain structure that could have played a role in masking, the pineal gland. Melatonin is a hormone produced by the pineal gland that plays a role in circadian rhythms and seasonality. The expression of melatonin is sensitive to light exposure, additionally, the presence of the hormone also feedbacks and influences the effects of light on the brain. Additionally, pinealectomy in rats alters the behavior profile of activity in LD conditions. Removal of the pineal gland in the grass rats did not influence the ability of animals to mask to light or the animal's circadian rhythm of activity.In summary, the work presented in this dissertation demonstrates the immediately impact of light on behavior and the possible brain regions that may play a functional role in the masking response. We established that two neural structures when ablated or removed do not impact the grass rat's ability to respond to light with an increase in activity. Here we broaden the scope of research into the neural mechanisms of masking to include a diurnal species, beginning the journey toward understanding the neural changes needed for a species to transition between temporal niches.
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Title
Nanoengineered tissue scaffolds for regenerative medicine in neural cell systems
Creator
Tiryaki, Volkan Mujdat
Date
2013
Collection
Electronic Theses & Dissertations
Description
Central nervous system (CNS) injuries present one of the most challenging problems. Regeneration in the mammal CNS is often limited because the injured axons cannot regenerate beyond the lesion. Implantation of a scaffolding material is one of the possible approaches to this problem. Recent implantations by our collaborative research group using electrospun polyamide nanofibrillar scaffolds have shown promising results in vitro and in vivo. The physical properties of the tissue scaffolds have...
Show moreCentral nervous system (CNS) injuries present one of the most challenging problems. Regeneration in the mammal CNS is often limited because the injured axons cannot regenerate beyond the lesion. Implantation of a scaffolding material is one of the possible approaches to this problem. Recent implantations by our collaborative research group using electrospun polyamide nanofibrillar scaffolds have shown promising results in vitro and in vivo. The physical properties of the tissue scaffolds have been neglected for many years, and it has only recently been recognized that significant aspects include nanophysical properties such as nanopatterning, surface roughness, local elasticity, surface polarity, surface charge, and growth factor presentation as well as the better-known biochemical cues.The properties of: surface polarity, surface roughness, local elasticity and local work of adhesion were investigated in this thesis. The physical and nanophysical properties of the cell culture environments were evaluated using contact angle and atomic force microscopy (AFM) measurements. A new capability, scanning probe recognition microscopy (SPRM), was also used to characterize the surface roughness of nanofibrillar scaffolds. The corresponding morphological and protein expression responses of rat model cerebral cortical astrocytes to the polyamide nanofibrillar scaffolds versus comparative culture surfaces were investigated by AFM and immunocytochemistry. Astrocyte morphological responses were imaged using AFM and phalloidin staining for F-actin. Activation of the corresponding Rho GTPase regulators was investigated using immunolabeling with Cdc42, Rac1, and RhoA. The results supported the hypothesis that the extracellular environment can trigger preferential activation of members of the Rho GTPase family, with demonstrable morphological consequences for cerebral cortical astrocytes. Astrocytes have a special role in the formation of the glial scar in response to traumatic injury. The glial scar biomechanically and biochemically blocks axon regeneration, resulting in paralysis. Astrocytes involved in glial scar formation become reactive, with development of specific morphologies and inhibitory protein expressions. Dibutyryl cyclic adenosine monophosphate (dBcAMP) was used to induce astrocyte reactivity. The directive importance of nanophysical properties for the morphological and protein expression responses of dBcAMP-stimulated cerebral cortical astrocytes was investigated by immunocytochemistry, Western blotting, and AFM. Nanofibrillar scaffold properties were shown to reduce immunoreactivity responses, while PLL Aclar properties were shown to induce responses reminiscent of glial scar formation. Comparison of the responses for dBcAMP-treated reactive-like and untreated astrocytes indicated that the most influential directive nanophysical cues may differ in wound-healing versus untreated situations.Finally, a new cell shape index (CSI) analysis system was developed using volumetric AFM height images of cells cultured on different substrates. The new CSI revealed quantitative cell spreading information not included in the conventional CSI. The system includes a floating feature selection algorithm for cell segmentation that uses a total of 28 different textural features derived from two models: the gray level co-occurance matrix and local statistics texture features. The quantitative morphometry of untreated and dBcAMP-treated cerebral cortical astrocytes was investigated using the new and conventional CSI, and the results showed that quantitative astrocyte spreading and stellation behavior was induced by variations in nanophysical properties.
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Title
The role of parkin in the recovery of central dopamine neurons from acute neurotoxicant exposure
Creator
Benskey, Matthew John
Date
2013
Collection
Electronic Theses & Dissertations
Description
Parkinson Disease (PD) pathology is associated with the selective degeneration of nigrostriatal dopamine (NSDA) neurons, while the tuberoinfundibular DA (TIDA) neurons of the hypothalamus remain intact. The same pattern of selective degeneration has been observed following exposure to 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyradine (MPTP), a mitochondrial complex I inhibitor which recapitulates many of the molecular pathologies associated with PD. The purpose of this dissertation is to...
Show moreParkinson Disease (PD) pathology is associated with the selective degeneration of nigrostriatal dopamine (NSDA) neurons, while the tuberoinfundibular DA (TIDA) neurons of the hypothalamus remain intact. The same pattern of selective degeneration has been observed following exposure to 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyradine (MPTP), a mitochondrial complex I inhibitor which recapitulates many of the molecular pathologies associated with PD. The purpose of this dissertation is to identify early molecular events that underlie TIDA neuron recovery from toxicant exposure and adapt these mechanisms in an attempt to rescue NSDA neurons from toxicity. NSDA neurons show loss of axon terminal DA concentrations following acute (20mg/kg; s.c.) and chronic (10 x 20mg/kg; s.c. over 35 days) MPTP administration and exhibit cell death following chronic MPTP administration. In contrast, TIDA neurons show no loss of axon terminal DA concentrations or cell death following acute or chronic MPTP exposure. The recovery of TIDA neurons is independent of extrinsic factors such as decreased toxicant exposure or hormonal activation. TIDA neuron recovery is associated with an increase in the PD-associated proteins, parkin and ubiquitin carboxy-terminal hydrolase L-1 (UCHL-1) within the arcuate nucleus (ARC) 24 h following MPTP. Additionally, parkin protein concentrations remain elevated in the ARC for up to 22 days following chronic MPTP administration. In contrast, the susceptibility of NSDA neurons is associated with decreased expression of both parkin and UCH-L1. The high correlation between the presence of the parkin protein and the recovery of DA neurons from MPTP toxicity is consistent with a role of parkin in DA neuron survival. In order to determine if parkin is necessary and sufficient in the recovery of TIDA neurons following MPTP, recombinant adeno-associated viral (rAAV) vectors containing parkin shRNA or a scrambled shRNA were created. Mice received stereotaxic ARC injections of rAAV containing either parkin shRNA or scrambled shRNA (250nl/side; 3.5x1013vg/ml), or remained naïve to surgery, and were administered a single injection of MPTP (20mg/kg; s.c.) 30 days following rAAV surgery. Twenty-four h post-MPTP, TIDA neurons were able to recover axon terminal DA concentrations following MPTP in control and scrambled shRNA treated animals. However, axon terminal DA was significantly reduced 24 hr following MPTP exposure following knockdown of parkin in TIDA neurons. To determine if parkin overexpression would protect NSDA neurons from MPTP toxicity, mice received unilateral stereotaxic injection of rAAV containing parkin into the substantia nigra (SN) (500nl; 3.4x1013vg/ml) and were administered a single injection of MPTP (20mg/kg; s.c.) 30 days following rAAV surgery. Twenty-four hours post-MPTP, parkin overexpression was unable to rescue MPTP-induced loss of DA in the striatum (ST), but did rescue MPTP-induced loss of tyrosine hydroxylase (TH) in the SN and ST. These findings are consistent with the following conclusions: 1) TIDA neuronal recovery from acute MPTP exposure is independent of extrinsic factors and is mediated by an intrinsic ability to increase expression of neuroprotective proteins, 2) The ability of TIDA neurons to up-regulate parkin is at least partially responsible for recovery of axon terminal DA following MPTP, 3) toxicant-induced loss of parkin contributes to MPTP toxicity within NSDA neurons.
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Title
Directed information for complex network analysis from multivariate time series
Creator
Liu, Ying
Date
2012
Collection
Electronic Theses & Dissertations
Description
Complex networks, ranging from gene regulatory networks in biology to social networks in sociology, havereceived growing attention from the scientific community. The analysis of complex networks employs techniquesfrom graph theory, machine learning and signal processing. In recent years, complex network analysis tools havebeen applied to neuroscience and neuroimaging studies to have a better understanding of the human brain. In thisthesis, we focus on inferring and analyzing the complex...
Show moreComplex networks, ranging from gene regulatory networks in biology to social networks in sociology, havereceived growing attention from the scientific community. The analysis of complex networks employs techniquesfrom graph theory, machine learning and signal processing. In recent years, complex network analysis tools havebeen applied to neuroscience and neuroimaging studies to have a better understanding of the human brain. In thisthesis, we focus on inferring and analyzing the complex functional brain networks underlying multichannelelectroencephalogram (EEG) recordings. Understanding this complex network requires the development of a measureto quantify the relationship between multivariate time series, algorithms to reconstruct the network based on thepairwise relationships, and identification of functional modules within the network.Functional and effective connectivity are two widely studiedapproaches to quantify the connectivity between two recordings.Unlike functional connectivity which only quantifies the statisticaldependencies between two processes by measures such as crosscorrelation, phase synchrony, and mutual information (MI), effectiveconnectivity quantifies the influence one node exerts on anothernode. Directed information (DI) measure is one of the approachesthat has been recently proposed to capture the causal relationshipsbetween two time series. Two major challenges remain with theapplication of DI to multivariate data, which include thecomputational complexity of computing DI with increasing signallength and the accuracy of estimation from limited realizations ofthe data. Expressions that can simplify the computation of theoriginal definition of DI while still quantifying the causalityrelationship are needed. In addition, the advantage of DI overconventionally causality measures such as Granger causality has notbeen fully investigated. In this thesis, we propose time-laggeddirected information and modified directed information to addressthe issue of computational complexity, and compare the performanceof this model free measure with model based measures (e.g. Grangercausality) for different realistic signal models.Once the pairwise DI between two random processes is computed,another problem is to infer the underlying structure of the complexnetwork with minimal false positive detection. We propose to useconditional directed information (CDI) proposed by Kramer to addressthis issue, and introduce the time-lagged conditional directedinformation and modified conditional directed information to lowerthe computational complexity of CDI. Three network inferencealgorithms are presented to infer directed acyclic networks whichcan quantify the causality and also detect the indirect couplingssimultaneously from multivariate data.One last challenge in the study of complex networks, specifically in neuroscience applications, is to identifythe functional modules from multichannel, multiple subject recordings. Most research on community detection inthis area so far has focused on finding the association matrix based on functional connectivity, instead ofeffective connectivity, thus not capturing the causality in the network. In addition, in order to find a modularstructure that best describes all of the subjects in a group, a group analysis strategy is needed. In thisthesis, we propose a multi-subject hierarchical community detection algorithm suitable for a group of weightedand asymmetric (directed) networks representing effective connectivity, and apply the algorithm to multichannelelectroencephalogram (EEG) data.
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Title
Sexual dimorphisms and androgen influence in medial posterodorsal amygdala astrocytes
Creator
Johnson, Ryan T.
Date
2011
Collection
Electronic Theses & Dissertations
Description
The amygdala is a highly interconnected brain region involved in fear, anxiety, social and reproductive behaviors. In humans and laboratory species the amygdala exhibits sexual dimorphisms in neuroanatomy and function both in juveniles and adults. In rodents, the medial posterodorsal amygdala (MePD) is particularly sexually dimorphic and gonadal hormone sensitive, and while neurons have been examined in this region, few reports have examined the potential influence of gonadal hormones on...
Show moreThe amygdala is a highly interconnected brain region involved in fear, anxiety, social and reproductive behaviors. In humans and laboratory species the amygdala exhibits sexual dimorphisms in neuroanatomy and function both in juveniles and adults. In rodents, the medial posterodorsal amygdala (MePD) is particularly sexually dimorphic and gonadal hormone sensitive, and while neurons have been examined in this region, few reports have examined the potential influence of gonadal hormones on other cellular components of the MePD. Astrocytes are a subtype of glia involved in synapse formation and known to be plastic and dynamic cells sensitive to gonadal hormone influence in several brain regions. My dissertation reveals sexual dimorphisms in the number of astrocytes in the juvenile rat MePD and that this sexual dimorphism remains present in adult animals. I also found sex differences in the arbor complexity of astrocytes in adults that are not present prior to puberty. Astrocytes also respond to changes in circulating hormone levels in adulthood. Furthermore, while the sex difference in astrocyte numbers in juvenile animals is androgen receptor-independent, the sex differences found in adult astrocyte numbers and arbor complexity are both androgen receptor-dependent. Finally, I provide evidence that astrocytes in the MePD contain androgen receptors, suggesting that androgens may act directly on these cells. The influence of gonadal hormones on astrocytes in the MePD is likely an important part of pubertal development and has implications for our understanding of the cellular organization of the amygdala and its function.
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Title
Neural mechanisms of female zebra finch mate choice : the role of the auditory perception sites, the social behavior network, and the reward system
Creator
Svec, Lace Ann
Date
2009
Collection
Electronic Theses & Dissertations