<p>Lead (Pb) is one of the most harmful and most abundant neurotoxins in the environment. Despite the extensive movement made to eradicate toxic levels of Pb in the environment, children, predominately in lower socioeconomic areas, are still exposed to varying levels of Pb. Human studies suggest that Pb exposure leads to altered drug consumption in adults by altering underlying neural mechanisms, specifically dopamine (DA) activity. However, there is limited research on this at blood Pb levels below 10 μg/dL, levels often seen in children growing up in neighborhoods located in old industrial and urban areas. To model how early-life low-level Pb exposure effects DA-dependent behaviors associated with addiction in adulthood, we used C57BL/6J mice. Litters were weaned at PND 21 and assigned to either a three-week history of 30 parts per million (ppm) Lead (IV) Acetate exposure or a control condition of 0 ppm Pb in DI drinking water. After the Pb exposure period, mice were switched to regular tap water until they reached adulthood. Afterward, separate animals were tested in one of three experiments: two-bottle choice alcohol preference drinking, alcohol-induced behavioral sensitization (EBS), and cocaine-induced behavioral sensitization (CBS). In experiment 1, our hypothesis was met, and both male and female mice with a prior Pb exposure displayed significantly higher alcohol intake and preference scores over the three-week period than control mice. In experiment 2, there were no differences in EBS and no evidence of EBS in any of the groups. However, there was an increased acute response to 2.0 g/kg EtOH in the Pb-exposed chronic group as compared to the control animals. Lastly, in experiment 3, Pb-exposed animals in the chronic cocaine group were more sensitive to the effects of cocaine (10 mg/kg) across days than the controls, both the acute cocaine groups and both saline control groups. Thus, with these experiments, we concluded that low levels of developmental Pb exposure might be targeting DA in the reward pathway, which is essential for alcohol intake and drug sensitization.</p>

<p>Magnetic resonance spectroscopy (MRS) is a non-invasive diagnostic technique that provides unique information about the biochemical composition of the human body. By excluding the overwhelming signals from water and fat, clinically relevant biomarkers such as lactate, N-acetyl aspartate, choline, creatine, glutamate/glutamine (Glx), gamma-aminobutyric acid (GABA), glutathione, and myoinositol can be reliably quantified. MRS has diverse applications in investigating the metabolic window of a wide range of biochemical processes. </p> <p>Here, we have utilized MRS to better understand chemical changes associated with neurological disorders and treatment response. We have investigated neurometabolic imbalances in brain regions related to post-traumatic stress disorder (PTSD). MRS was applied to better understand the neurobiological processes of hyperbaric oxygen therapy in military veterans with clinically diagnosed traumatic brain injury and/or PTSD.</p>

<p>A C. elegans model of nicotine use and aversion resistance following chronic low-dose nicotine pretreatment. Model was then applied to various receptor knockouts  (acr-5, acr-15, acr-16, dop-1, and dop-2) to determine the role of these receptors in aversion resistance. </p>

<p dir="ltr">Localizing movements in the external space is crucial for animals to navigate safely, find food, avoid predators, and interact with their surroundings. Efficient localization during body movements requires the brain to distinguish between externally generated movements and self-generated ones. This involves integrating external stimulation with a continuous estimate of one's body position, to isolate external motion by suppressing sensations arising from self-motion.</p><p dir="ltr">To explore the neural mechanisms underlying object localization during active touch, we focused on the mouse superior colliculus (SC), which harbors multiple egocentric maps of sensorimotor space. Our studies revealed that SC neurons exhibit a rapidly adapting tactile response during externally generated touch. The response is significantly attenuated during self-generated touch, thus enhancing the ability to distinguish between external and self-induced tactile stimuli. Additionally, the direction of external motion is precisely encoded in the firing rates of these tactile-responsive neurons, indicating a specialized localization mechanism within the SC.</p><p dir="ltr">In scenarios devoid of external stimuli, SC neural activity accurately reflects the kinematics of self-motion, such as whisker position and locomotion speed, capturing past, present, and future body positions. Half of the neurons that encode self-motion also respond to external tactile stimuli. This dual functionality suggests that these neurons not only track self-motion but also engage in the processing of external tactile information. The magnitude of the external tactile response in these neurons is modulated by the state of self-motion upon touch. These results suggest that SC neurons integrate internal estimates of body movements with external tactile inputs to compute the egocentric distance of objects.</p>

<div><p>Parkinson’s disease (PD) is a devastating neurodegenerative disorder that affects 10 million people worldwide and is characterized by pronounced motor symptoms. Dementia with Lewy Bodies (DLB) involves both cognitive and motor deficits and affects ~1 million people in the United States. To date there is no cure for PD or DLB, and current treatments address only a subset of the symptoms that define these diseases. PD and DLB are ‘synucleinopathies’, defined as disorders involving the accumulation in patients’ brains of Lewy bodies. Lewy bodies are cellular inclusions that consist largely of aggregated species of alpha-synuclein (aSyn), a presynaptic protein that exists as both cytosolic and membrane-bound forms. Pathophysiological findings suggest that aggregated aSyn is involved in neurodegeneration in PD and DLB. However, mechanisms by which aSyn forms neurotoxic aggregates, and neurotoxic processes that distinguish different synucleinopathies such as PD and DLB, are poorly understood. To address these gaps, we have (i) designed a protocol to establish a primary cell culture model that can recapitulate key neuropathological features of PD, (ii) examined effects of expressing aSyn variants in a rat model of PD, and (iii) examined the expression profiles of neuroprotective genes in PD and DLB brain specimens.</p><p> </p><p>In the first part of my thesis, I describe the development of an optimized protocol to prepare primary midbrain and cortical cultures from rat embryonic brains for the study of PD and other synucleinopathies. The establishment of cellular models that simulate specific aspects of neuropathology can enable the characterization of molecular perturbations that lead to dopaminergic (DA) neuronal death. Our primary midbrain mixed culture model provides an outstanding opportunity to explore therapeutic strategies to rescue DA neurons from toxicity elicited by a range of PD-related insults. In addition, our primary cortical mixed cultures can be used to model cortical neuropathology in various CNS disorders including synucleinopathies.</p><p> </p><p>A number of mutations in the gene that codes for aSyn are associated with familial, early-onset forms of PD. A major goal of my thesis research is to characterize neurotoxic effects of a recently discovered familial substitution, A53E. This mutant was chosen based on the rationale that the introduction of a negatively charged residue at position 53 could potentially interfere with aSyn-membrane interactions and favor A53E aggregation, as we described for other familial aSyn mutants. For the first time, we have reproduced the neurotoxicity of A53E seen in human patients by expressing the mutant protein in rat midbrain. Rats injected unilaterally in the substantia nigra (SN) with rAAV encoding A53E and another familial mutant, A53T, but not rAAV encoding WT aSyn or a vector-control (‘stuffer’) virus, exhibited a significant motor impairment. Immunohistochemical analysis at 14 weeks after the viral injection revealed that brain sections from aSyn-expressing rats exhibit key features reminiscent of neuropathology in human PD, including nigral dopaminergic neuron loss (confirmed by unbiased stereology), striatal terminal depletion, and aSyn inclusion formation. In addition, it was determined that WT aSyn and the A53E and A53T mutants invaded the non-injected substantia nigra, implying that expressed aSyn protein can spread throughout the brain in the rat rAAV-aSyn model. These results yield insights into the molecular basis for the neurotoxicity of A53E and shed light on a potential role for membrane-induced aSyn aggregation in PD pathogenesis in vivo, thus setting the stage for developing therapies to slow neurodegeneration in the brains of familial and idiopathic PD patients. </p><p> </p><p>aSyn neurotoxicity varies with the expression of neuroprotective proteins, and misfolded aSyn affects cellular functions and gene expression. These observations suggest that differential gene expression patterns can inform us about similarities and differences in pathogenic mechanisms of different synucleinopathy disorders. A third phase of my thesis research was aimed at determining the expression levels of a panel of candidate neuroprotective genes in post-mortem brain samples from DLB and PD patients and age-matched controls (5 individuals in each group). mRNAs encoding the following proteins were quantified via qRT-PCR in homogenates prepared from the frontal cortex and the BA24 region encompassing the cingulate gyrus: DJ-1, a protein with antioxidant and chaperone activities; PGC1α, a master regulator of mitochondrial biogenesis and oxidative metabolism; MsrA, an antioxidant enzyme responsible for repairing oxidatively damaged proteins; and ATP13A2, a lysosomal protein involved in autophagy. In addition to yielding new insights into differential gene expression patterns in cortex versus cingulate gyrus, the data revealed differences in mRNA expression levels in DLB versus non-DLB cortical tissue. Although levels of all four neuroprotective mRNAs were increased (or showed a trend towards being increased) in DLB cortex, Western blot analysis revealed that only the DJ-1 and PGC1α proteins showed a trend towards being up-regulated, whereas levels of ATP13A2 and MsrA were unchanged. These findings suggest that there is a failure to induce cellular antioxidant responses and lysosomal autophagy at the protein level in DLB cortex, and in turn this failure could contribute to neuropathology. Interestingly, analysis of the same panel of neuroprotective genes in PD cortical samples did not show significant differences in mRNA or protein levels compared to control samples, suggesting that different neuroprotective mechanisms are induced in DLB versus PD cortex. These studies shed light on brain-region specific changes in gene expression associated with different synucleinopathy disorders, and they set the stage for developing new diagnostic tests and therapeutic strategies.</p></div><br>

The stomach is a digestive organ in the gastrointestinal tract that regulates food intake and paces digestion of nutrients and fluids. The emptying and motility patterns of the stomach are crucial rate-determining processes in maintaining energy homeostasis in the body. Dysregulation of gastric functions often leads to distressing conditions such as gastroesophageal reflux diseases, functional dyspepsia, gastroparesis and obesity. Gastric disorders affect more than 60 million people in the US, producing significant medical and economic burden. These diseases are often chronic and greatly compromise quality of life. As the causes of these diseases remain largely unknown, effects of current pharmacological, dietary, or surgical treatments are often dismal. In this regard, neuromodulation of peripheral nerves emerges as a promising electroceutical therapy for remedying gastric disorders. However, therapeutic effects were shown to be modest, largely due to the inability to validate or calibrate the efficacy and stability of neuromodulation methods with appropriate physiological readouts. To address these problems, here I developed a non-invasive, repeatable online high-resolution magnetic resonance imaging protocol, empowered with advanced image processing algorithms, to track gastric emptying, antral motility, pyloric motility, intestinal filling and absorption in a rat model. The protocol can be used to guide tuning and optimization of stimulation parameters of neuromodulation without perturbing ongoing and spontaneous physiology. The proposed technology and findings are expected to pave the way for the use of gastric MRI to evaluate the efficacy of therapeutics in treating gastric disorders under both preclinical and clinical settings.

<p>Although long known for their damaging effects to cell components and contribution to aging, cancer, and neurodegeneration, reactive oxygen species (ROS) have recently been found to have beneficial roles, such as mediating intracellular signaling and triggering regenerative inflammatory responses. While excessive ROS causes oxidative stress and cellular damage, an optimum ROS level is crucial for proper cell functioning, growth, and proliferation. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) is a major source of cellular ROS that has been linked to neuronal polarity, axonal growth, and nervous system development. However, the precise role of Nox-derived ROS in axonal regeneration after injury has remained unclear. Here, we tested a role for neuronal Nox in neurite regeneration following mechanical transection in cultured neurons. Using a novel hydrogen peroxide (H2O2)-sensing dye, <em>p</em>-bispinacolatoboron-5’-phenylpyridylthiazole (BPPT), we found that H2O2 -levels are elevated in regenerating growth cones following injury. Increased Nox2 co-localization with p40phox in the growth cone central domain suggests Nox2 activation after injury. Inhibiting Nox with pharmacological Nox inhibitor, celastrol, or reducing ROS with the chemical antioxidant N-acetyl-L-cysteine, reduced neurite regeneration rate. Higher level of H2O2 had negative effects on neurite outgrowth and regeneration. Growth cones treated with celastrol had reduced F-actin content in the growth cone periphery and T domain. Pharmacological inhibition of Nox also caused reduced activity of Src2, a redox modifiable protein that regulates actin organization and dynamics in the growth cone. Using a zebrafish larval spinal cord injury model, we found that pharmacological inhibition of Nox affects swimming behavior indicating impaired spinal cord regeneration due to the inhibition of Nox. Taken together, these findings indicate that the level of neuronal Nox-derived ROS is critical for neurite regeneration following injury. Identification of Nox downstream effectors in the growth cone is the next goal of this project to better understand the signaling pathway of Nox involved in neurite regeneration.</p>

<p>Human pluripotent stem cells (hPSCs) are an attractive tool for the study of different neurodegenerative diseases due to their potential to form any cell type of the body. Due to their versatility and self-renewal capacity, they have different applications such as disease modeling, high throughput drug screening and transplantation. Different animal models have helped answer broader questions related to the physiological functioning of various pathways and the phenotypic effects of a particular neurodegenerative disease. However, due to the lack of success recapitulating some targets identified from animal models into successful clinical trials, there is a need for a direct translational disease model. Since their advent, hPSCs have helped understand various disease effectors and underlying mechanisms using genetic engineering techniques, omics studies and reductionist approaches for the recognition of candidate molecules or pathways required to answer questions related to neurodevelopment, neurodegeneration and neuroregeneration. Due to the simplified approach that iPSC models can provide, some <em>in vitro</em> approaches are being developed using microphysiological systems (MPS) that could answer complex physiological questions. MPS encompass all the different <em>in vitro</em> systems that could help better mimic certain physiological systems that tend to not be mimicked by <em>in vivo</em> models. In this dissertation, efforts have been directed to disease model as well as to understand the intrinsic as well as extrinsic cues using two different MPS. First, we have used hPSCs with Alzheimer’s disease (AD)-related mutations to differentiate into retinal organoids and identify AD related phenotypes for future studies to identify retinal AD biomarkers. Using 5 month old retinal organoids from AD cell lines as well as controls, we could identify retinal AD phenotypes such as an increase in Aβ42:Aβ40 ratio along with increase in pTau:Tau. Nanostring analyses also helped in identification of potential target genes that are modulated in retinal AD that were related to synaptic dysfunction.  Thus, using retinal organoids for the identification of retinal AD phenotypes could help delve deeper into the identification of future potential biomarkers in the retina of AD patients, with the potential to serve as a means for early identification and intervention for patients. The next MPS we used to serve to explore non-cell autonomous effects associated with glaucoma to explore the neurovascular unit. Previous studies have demonstrated the degeneration of RGCs in glaucoma due to a point mutation OPTN(E50K) that leads to the degeneration of RGCs both at morphological and functional levels. Thus, using the previous studies as a basis, we wanted to further unravel the impact of this mutation using the different cell types of the neurovascular unit such as endothelial cells, astrocytes and RGCs. Interestingly, we observed the barrier properties being impacted by the mutation present in both RGCs and astrocytes demonstrated through TEER, permeability and transcellular transport changes. We also identified a potential factor TGFβ2 that was observed to be overproduced by the OPTN E50K astrocytes to demonstrate similar effects with the exogenous addition of TGFβ2 on the barrier. Furthermore, the inhibition of TGFβ2 helped rescue some of the barrier dysfunction phenotypes. Thus, TGFβ2 inhibition can be used as a potential candidate that can be used to further study its impact in <em>in vivo</em> models and how that can be used in translational applications. Thus, MPS systems have a lot of applications that can help answer different physiologically relevant questions that are hard to approach using <em>in vivo</em> models and the further development of these systems to accentuate the aspects of neural development and how it goes awry in different neurodegenerative diseases.  </p>

<p><b>Purpose:</b> Children with speech sound disorder (SSD) mispronounce more speech sounds than is typical for their age and a growing body of research suggests that a deficit in speech perception abilities contributes to development of the disorder. However, little work has been done to characterize the neurophysiological processes indexing speech perception deficits in SSD. The primary aim of the current study was to compare the neural activity underlying speech perception in young children with SSD and typical development (TD).</p><p><b>Method</b>: Twenty-eight children ages 4;1-6;0 participated in the current study. Event-related potentials (ERPs) were recorded while children completed a speech perception task which included phonetic (speech sound) and lexical (meaning) matches and mismatches. Groups were compared on their judgment accuracy for matches and mismatches as well as the mean amplitude of the Phonological Mapping Negativity (PMN) and N400 ERP components.</p><p><b>Results</b>: Children with SSD demonstrated lower judgment accuracy across the phonetic and lexical conditions compared to peers with TD. The ERPs elicited by lexical matches and mismatches did not distinguish the groups. However, in the phonetic condition, the SSD group exhibited a more consistent left lateralized PMN effect and a delayed N400 effect over frontal sites compared to the TD group.</p><p><b>Conclusions</b>: These findings provide some of the first evidence of a delay in the neurophysiological processing of phonological information for young children with SSD compared to their peers with TD. This delay was not present for the processing of lexical information, indicating a unique difference between children with SSD and TD related to speech perception of phonetic errors.</p>

<p>This thesis aims to investigate how one fundamental component of the inner-ear (cochlear) response to all sounds, the temporal fine structure (TFS), is used by the auditory system in everyday hearing. Although it is well known that neurons in the cochlea encode the TFS through exquisite phase locking, how this initial/peripheral temporal code contributes to everyday hearing and how its degradation contributes to perceptual deficits are foundational questions in auditory neuroscience and clinical audiology that remain unresolved despite extensive prior research. This is largely because the conventional approach to studying the role of TFS involves performing perceptual experiments with acoustic manipulations of stimuli (such as sub-band vocoding), rather than direct physiological or behavioral measurements of TFS coding, and hence is intrinsically limited. The present thesis addresses these gaps in three parts: 1) developing assays that can quantify TFS coding at the individual level 2) comparing individual differences in TFS coding to differences in speech-in-noise perception across a range of real-world listening conditions, and 3) developing deep neural network (DNN) models of speech separation/enhancement to complement the individual-difference approach. By comparing behavioral and electroencephalogram (EEG)-based measures, Part 1 of this work identified a robust test battery that measures TFS processing in individual humans. Using this battery, Part 2 subdivided a large sample of listeners (N=200) into groups with “good” and “poor” TFS sensitivity. A comparison of speech-in-noise scores under a range of listening conditions between the groups revealed that good TFS coding reduces the negative impact of reverberation on speech intelligibility, and leads to reduced reaction times suggesting lessened listening effort. These results raise the possibility that cochlear implant (CI) sound coding strategies could be improved by attempting to provide usable TFS information, and that these individualized TFS assays can also help predict listening outcomes in reverberant, real-world listening environments. Finally, the DNN models (Part 3) introduced significant improvements in speech quality and intelligibility, as evidenced by all acoustic evaluation metrics and test results from CI listeners (N=8). These models can be incorporated as “front-end” noise-reduction algorithms in hearing assistive devices, as well as complement other approaches by serving as a research tool to help generate and rapidly sub-select the most viable hypotheses about the role of TFS coding in complex listening scenarios.</p>