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- Genre: Masters Thesis
Description
The cerebellum predicts and corrects motor outputs based on sensory feedback for smoother and more precise movements, thus contributing to motor coordination and motor learning. One area of the cerebellum, the vestibulocerebellum, integrates vestibular and visual information to regulate balance, gaze stability, and spatial orientation. Highly concentrated within the granule cell layer of this region is a class of excitatory glutamatergic interneurons known as unipolar brush cells (UBCs) that receive input from mossy fibers and synapse onto multiple granule cells and other UBCs. They can be divided into ON and OFF subtypes based on their responses to synaptic stimulation. Prior research has implicated ON UBCs in motor dysfunction, but their role in motor coordination, balance, and motor learning is unclear. To test the hypothesis that ON UBCs contribute to motor coordination and balance, a transgenic mouse line (GRP-Cre) was used to express the GqDREADD (Gq designer receptors exclusively activated by designer drugs) hM3Dq in a subset of ON UBCs in the cerebellum to disrupt their electrical activity. In a second set of experiments, a Cre-dependent caspase 3 AAV (adeno-associated virus) viral vector was injected into the nodulus of the vestibulocerebellum of GRP-Cre mice to selectively ablate a subset of ON UBCs in the region and test whether they were necessary for motor learning. Motor coordination and balance were assessed using the rotor-rod and balance beam in young mice, and the forced swim test was used to assess vestibular function in older mice. Activity levels, anxiety, gross locomotion, and exploration in young mice were assessed using the open field. The results show that neither motor coordination and balance, nor motor learning, were impaired when the ON UBCs were disrupted or ablated in young mice. However, disruptions affected climbing behavior in older mice during the forced swim test, suggesting an age-dependent effect of ON UBCs on vestibular function.
ContributorsKizeev, Gabrielle (Author) / Balmer, Timothy (Thesis advisor) / Newbern, Jason (Committee member) / Velazquez, Ramon (Committee member) / Arizona State University (Publisher)
Created2023
Description
Cellular metabolism is an essential process required for tissue formation, energy production and systemic homeostasis and becomes dysregulated in many disease states. In the context of human cerebral cortex development, there’s a limited understanding of how metabolic pathways, such as glycolysis, impacts proliferation and differentiation of cortical cells. The technical challenges of studying primary in vivo cortical tissue at a cellular and molecular level led to the development of human pluripotent stem cell (PSC) derived cortical organoids. Cortical organoids are a highly tractable model system that can be used for high-throughput investigation of early stages of development and corresponding glycolytic programs. Through transplantation of cortical organoids into the developing mouse cortex, human cortical cells can also be studied in an in vivo environment that more closely resembles endogenous development where the impact of metabolism in typical developmental programs and disease states can be studied. While current data is preliminary, initial observations suggest that cortical populations increase glucose uptake over time and regulation of glucose uptake rates occur in cell type-specific manner. Additionally, mouse transplantation data suggests that glycolytic activity is downregulated post-transplantation, suggesting that the in vitro environment contributes metabolic state. The more dynamic range of metabolic states in vivo may impact the rate of differentiation and maturation in cellular populations in the transplant model. I hypothesize that the more endogenous-like regulation of glycolysis may impact the proliferative window and expansion of key progenitor cell types in the human brain, particularly the intermediate progenitor cells.
ContributorsMorales, Alexandria (Author) / Andrews, Madeline (Thesis advisor) / Newbern, Jason (Committee member) / Stabenfeldt, Sarah (Committee member) / Arizona State University (Publisher)
Created2023
Description
Autism spectrum disorder (ASD) is characterized by deficits in flexible cognition and social behavior. The most common atypical brain structure in ASD, the cerebellum, has multisynaptic connections through the cerebellar nuclei (CN) and thalamus to cognitive- and social-associated brain regions, yet formation and modulation of these pathways are not fully understood. Additionally, a CN output mechanism, perineuronal nets (PNNs), structure and function are undefined. PNNs are specialized extracellular matrix structures whose appearance is associated with the end of the critical period of plasticity and have been implicated in learning and neurodevelopmental disorders, but their role in the CN during development is unknown.To examine the role of CN on cognition, CN activity was increased or decreased in both male and female mice using Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) from postnatal day 21-35. Learning and reversal was analyzed using a pairwise visual discrimination task. Social behavior was assessed using a classic three-chamber assay and analyzed using SLEAP (Social Leap Estimates Animal Poses). A marker of critical periods, perineuronal nets (PNNs), was examined to understand relationships between neural development and behavior.
Interestingly, adolescent CN disruption did not alter task acquisition, yet correct choice reversal performance was dependent on DREADD manipulation and sex. CN inhibition improved reversal learning in males (5 days faster to criteria) and CN excitation improved female reversal learning (10 days faster to criteria) compared to controls. Analysis of social behavior revealed male social preference was abolished in CN manipulated groups, whereas females failed to demonstrate a social preference. Interestingly, CN manipulation in females regardless of direction, reduced PNN intensity, whereas in males only CN inhibition reduced PNN intensity. PNN intensity negatively correlated with reversal performance. CN PNN intensity showed no relation to social behavior. These data suggest chronic adolescent CN manipulation may have compensatory changes in PNN structure and CN output to improve reversal learning and PNN function was unrelated to social behavior. This study provides new evidence for CN in non-motor functions and sex-dependent differences in behavior and CN plasticity.
ContributorsLyle, Tristan (Author) / Verpeut, Jessica (Thesis advisor) / Sanabria, Federico (Committee member) / Newbern, Jason (Committee member) / Arizona State University (Publisher)
Created2024
Description
Following a traumatic brain injury (TBI) 5-50% of patients will develop post traumatic epilepsy (PTE). Pediatric patients are most susceptible with the highest incidence of PTE. Currently, we cannot prevent the development of PTE and knowledge of basic mechanisms are unknown. This has led to several shortcomings to the treatment of PTE, one of which is the use of anticonvulsant medication to the population of TBI patients that are not likely to develop PTE. The complication of identifying the two populations has been hindered by the ability to find a marker to the pathogenesis of PTE. The central hypothesis of this dissertation is that following TBI, the cortex undergoes distinct cellular and synaptic reorganization that facilitates cortical excitability and promotes seizure development. Chapter 2 of this dissertation details excitatory and inhibitory changes in the rat cortex after severe TBI. This dissertation aims to identify cortical changes to a single cell level after severe TBI using whole cell patch clamp and electroencephalogram electrophysiology. The work of this dissertation concluded that excitatory and inhibitory synaptic activity in cortical controlled impact (CCI) animals showed the development of distinct burst discharges that were not present in control animals. The results suggest that CCI induces early "silent" seizures that are detectable on EEG and correlate with changes to the synaptic excitability in the cortex. The synaptic changes and development of burst discharges may play an important role in synchronizing the network and promoting the development of PTE.
ContributorsNichols, Joshua (Author) / Anderson, Trent (Thesis advisor) / Neisewander, Janet (Thesis advisor) / Newbern, Jason (Committee member) / Arizona State University (Publisher)
Created2014
Description
The Erk/MAPK pathway plays a major role in cell growth, differentiation, and survival. Genetic mutations that cause dysregulation in this pathway can result in the development of Rasopathies, a group of several different syndromes including Noonan Syndrome, Costello Syndrome, and Neurofibromatosis Type-1. Since these mutations are germline and affect all cell types it is hard to differentiate the role that Erk/MAPK plays in each cell type. Previous research has shown that individual cell types utilize the Erk/MAPK pathway in different ways. For example, the morphological development of lower motor neuron axonal projections is Erk/MAPK-independent during embryogenesis, while nociceptive neuron projections require Erk/MAPK to innervate epidermal targets. Here, we tested whether Erk/MAPK played a role in the postnatal development of lower motor neurons during crucial periods of activity-dependent circuit modifications. We have generated Cre-dependent conditional Erk/MAPK mutant mice that exhibit either loss or gain of Erk/MAPK signaling specifically in ChAT:Cre expressing lower motor neurons. Importantly, we found that Erk/MAPK is necessary for the development of neuromuscular junction morphology by the second postnatal week. In contrast, we were unable to detect a significant difference in lower motor neuron development in Erk/MAPK gain-of-function mice. The data suggests that Erk/MAPK plays an important role in postnatal lower motor neuron development by regulating the morphological maturation of the neuromuscular junction.
ContributorsSmith, Colton (Author) / Newbern, Jason (Thesis advisor) / Neisewander, Janet (Committee member) / Hamm, Thomas (Committee member) / Arizona State University (Publisher)
Created2017
Description
Of the 2.87 million traumatic brain injuries (TBI) sustained yearly in the United States, 75% are diffuse injuries. A single TBI can have acute and chronic influences on the neuroendocrine system leading to hypothalamic-pituitary-adrenal axis (HPA) dysregulation and increased affective disorders. Preliminary data indicate TBI causes neuroinflammation in the hippocampus, likely due to axonal damage, and in the paraventricular nucleus of the hypothalamus (PVN), where no axonal damage is apparent. Mechanisms regulating neuroinflammation in the PVN are unknown. Furthermore, chronic stress causes HPA dysregulation and glucocorticoid receptor (GR)-mediated neuroinflammation in the PVN. The goal of this project was to evaluate neuroinflammation in the HPA axis and determine if GR levels change at 7 days post-injury (DPI).
Adult male and female Sprague Dawley rats were subjected to midline fluid percussion injury. At 7 DPI, half of each brain was post-fixed for immunohistochemistry (IBA-1) and half biopsied for gene/protein analysis. IBA-1 staining was analyzed for microglia activation via skeleton analysis in the hypothalamus and hippocampus. Extracted RNA and protein were used to quantify mRNA expression and protein levels for GRs. Data indicate increased microglia cell number and decreased endpoints/cell and process length in the PVN of males, but not females. In the dentate gyrus, both males and females have an increased microglia cell number after TBI, but there is also an interaction between sex and injury in microglia presentation, where males exhibit a more robust effect than females. Both sexes have significant decreases of endpoints/cell and process length. In both regions, GR protein levels decreased for injured males, but in the hippocampus, GR levels increased for injured females. Data indicate that diffuse TBI causes alterations in microglia morphology and GR levels in the hypothalamus and hippocampus at 7 DPI, providing a potential mechanism for HPA axis dysregulation at a sub-acute time point.
Adult male and female Sprague Dawley rats were subjected to midline fluid percussion injury. At 7 DPI, half of each brain was post-fixed for immunohistochemistry (IBA-1) and half biopsied for gene/protein analysis. IBA-1 staining was analyzed for microglia activation via skeleton analysis in the hypothalamus and hippocampus. Extracted RNA and protein were used to quantify mRNA expression and protein levels for GRs. Data indicate increased microglia cell number and decreased endpoints/cell and process length in the PVN of males, but not females. In the dentate gyrus, both males and females have an increased microglia cell number after TBI, but there is also an interaction between sex and injury in microglia presentation, where males exhibit a more robust effect than females. Both sexes have significant decreases of endpoints/cell and process length. In both regions, GR protein levels decreased for injured males, but in the hippocampus, GR levels increased for injured females. Data indicate that diffuse TBI causes alterations in microglia morphology and GR levels in the hypothalamus and hippocampus at 7 DPI, providing a potential mechanism for HPA axis dysregulation at a sub-acute time point.
ContributorsRidgway, Samantha (Author) / Thomas, Theresa C (Thesis advisor) / Newbern, Jason (Thesis advisor) / Bimonte-Nelson, Heather A. (Committee member) / Arizona State University (Publisher)
Created2019
Description
LKB1/STK11 is a serine/threonine kinase first identified in C.elegans as a gene important for cell polarity and proliferation. Mutations in LKB1 are the primary cause of Peutz-Jegher’s cancer syndrome, an autosomal dominantly inherited disease, in which patients are predisposed to benign and malignant tumors. Past studies have focused on defining LKB1 functions in various tissue types, for example LKB1 regulates axonal polarization and dendritic arborization by activating downstream substrates in excitatory neurons of the developing neocortex. However, the implications of LKB1, specifically in the developing cortical inhibitory GABAergic interneurons is unknown. LKB1 deletion was achieved by using Cre-lox technology to induce LKB1 loss in cells localized in the medial ganglionic eminence (MGE) that express Nkx2.1 and generate cortical GABAergic neurons. In this research study it is suggested that LKB1 plays a role in GABAergic interneuron specification by specifically regulating the expression of parvalbumin during the development of fast-spiking interneurons. Preliminary evidence suggest LKB1 also modulates the number of Nkx2.1-derived oligodendrocytes in the cortex. By utilizing a GABAergic neuron specific LKB1 deletion mutant, we confirmed that the loss of parvalbumin expression was due to a GABAergic neuron autonomous function for LKB1. These data provide new insight into the cell specific functions of LKB1 in the developing brain.
ContributorsSebastian, Rebecca (Author) / Newbern, Jason (Thesis advisor) / Neisewander, Janet (Committee member) / Gipson-Reichardt, Cassandra (Committee member) / Arizona State University (Publisher)
Created2019