Neurodegenerative tauopathies represent a heterogeneous group of central nervous system (CNS) diseases characterized by accumulation of insoluble neurofibrillary tangles of tau protein, synaptic dysfunction, neuroinflammation, and progressive neuronal loss, culminating in debilitating cognitive decline. In recent years, studies have attempted to elucidate potential mechanisms underlying the pathogenicity of tauopathies, with particular focus on preventative strategies that may target key initiating factors or events which occur before the onset of memory loss and neurofibrillary tangle deposits in the brain. Two such potential initiating events are neuroinflammatory activation and improper protein sorting via the endosomal-lysosomal trafficking network. This work describes two novel players in each biological system, the 5-lipoxygenase proinflammatory pathway and its relevance to the neuroinflammatory response as well as the endosomal retromer complex in protein recycling. Importantly, we investigate the contribution of these pathways in the development of tau accumulation and pathology, with the ultimate goal to demonstrate the therapeutic potential of these novel players in neurodegeneration. In current literature, there is great debate whether neuroinflammation functions as a primary or secondary pathogenic event in tauopathies. Furthermore, investigating novel pathways which activate inflammation in the CNS is an integral part of understanding their relevance to neurodegeneration. Recent studies implicate the proinflammatory 5-lipoxygenase (5LO) enzymatic pathway as a potential effector of neuroinflammation in Alzheimer’s disease (AD); however, little is known about the role of 5LO on tau pathology in the absence of amyloid beta. Thus, our work focused on investigating the contribution of the 5LO pathway in tauoapthy by implementing a genetic approach to modulate this enzyme in a P301S mouse model of tauopathy and in neuronal cells. First, we provide evidence for an age-dependent and region-specific upregulation of the 5LO pathway (protein, message and activity) in a transgenic mouse model of tauopathy. Additionally, global genetic deletion of 5LO in this mouse model results in significant memory improvement, reduces neuroinflammation in association with reduced tau phosphorylation at specific epitopes, and improves synaptic pathology. Utilizing the opposite approach by overexpressing 5LO using AAV2/1, we demonstrate that tau mice given AAV-5LO perform significantly worse on several cognitive assessments, display elevated tau pathology and neuroinflammation, and have greater synaptic pathology. Mechanistically, the effect of 5LO modulation on tau phosphorylation is dependent on the activity of kinase, cdk5, as confirmed in a neuronal cell line. Simultaneously, an equally important aspect of tauopathies is the inefficient sorting and degradation of accumulated proteins in the brain. Improper degradation of toxic proteins is considered an early event in pathogenesis, and thus, targeting this aspect of neurodegeneration has received considerable attention in recent years. One such sorting mechanism, the endosomal retromer complex, has been implicated in abnormal processing of amyloid precursor protein (APP) and accumulation of amyloid beta (Aβ) within endosomes. Most notably, a small pharmacological chaperone mitigated this retromer-dependent effect on Aβ in primary hippocampal neurons. Current studies have only recently focused on the relationship between the retromer complex and tau accumulation, thus our aim was to investigate the effects of retromer dysfunction on the development of the tauopathy phenotype. First, we assessed that core components of the retromer complex are down-regulated in two distinct human primary tauopathies in cortical and hippocampal brain regions. Furthermore, retromer core protein levels are reduced in an age-dependent and region-specific manner in P301S mice. To manipulate the retromer complex, first, using a genetic approach, we demonstrate that knockdown of VPS35 using shRNA AAV resulted in exacerbation of cognitive and motor learning deficits in P301S mice. This coincided with greater accumulation of pathological and phosphorylated tau, increased neuroinflammation, and elevated synaptic pathology. Second, utilizing TPT-260, a pharmacological stabilizer of VPS35, we demonstrate ameliorated behavioral performance, reduced tau pathology and neuroinflammation, and rescued synaptic pathology in P301S mice. Finally, using a neuronal cell line, we confirm the direct role of VPS35 on tau phosphorylation and accumulation using genetic and pharmacological manipulation of VPS35, the effect of which, is mediated by lysosomal protease, cathepsin D. Taken together, our data reveal a direct role of the 5LO proinflammatory pathway on tau phosphorylation as well as a VPS35-dependent effect on tau solubility and pathological accumulation. Importantly, this work highlights the relevance of investigating the mechanisms that underscore neuroinflammatory activation and improper protein sorting in tauopathies and the potential of targeting these pathways for therapeutic intervention in neurodegenerative diseases. / Biomedical Sciences

Stress can disrupt a variety of cognitive processes, including learning and memory. Previous studies in rodents have demonstrated that central infusions of the stress-neuropeptide, corticotropin releasing factor (CRF), can disrupt mnemonic processes. However, where CRF is working within the brain to regulate cognition is largely underexplored. A candidate region for direct CRF regulation is the medial septum (MS), because this forebrain cholinergic nucleus is critical for spatial learning and CRF receptors are found on cholinergic neurons therein. We assessed whether administering CRF directly into the MS impaired spatial learning in male and female rats. We infused different doses of CRF or the vehicle, artificial cerebral spinal fluid, into the MS prior to testing on an object location task, which tests spatial learning, and a novel object recognition task, which does not test spatial learning. On the object location task, we found that, overall; CRF in the MS reduced time spent exploring the displaced object compared to the familiar object, suggesting that this manipulation impairs spatial reference learning. In addition, males were more sensitive to this effect than females, such that a low dose of CRF in the MS that had no effect in females disrupted object location learning in males. In the novel object recognition task, the CRF in the MS did not decrease preference for the novel object in either sex, suggesting that the effects of CRF in the MS are specific to spatial learning, which requires an intact hippocampus. Next, we assessed the receptor subtype involved by pretreating with a CRFR1 antagonist, prior to testing the effects of the high dose of CRF in the MS on spatial learning. We found that the CRFR1 antagonist recovered the spatial learning deficits similarly in both sexes. Lastly, we examined the influence of circulating ovarian hormones in regulating sensitivity of the MS to CRF by accessing estrous cycle stage, as well as, conducting ovariectomy and sham ovariectomy. We did not find an influence of ovarian hormones using any of these manipulations, suggesting that these hormones do not play a protective role against the impairing effects of CRF in the MS on spatial learning. Collectively, these studies reveal that CRF in the MS selectively impairs spatial learning, especially in males, highlighting an unexplored mechanism by which stress can regulate cognition. Clinically, these findings suggest that drugs which block the effects of CRF represent a viable therapeutic option to treat cognitive deficits that characterize certain stress-related psychiatric disorders. / Psychology

Aging increases the risk of both cardiovascular disease and dementia. Incidence of dementia such as Alzheimer’s Disease increases with aging. Dementia and cardiovascular diseases have not been associated, but ongoing research points to possible correlation between them. The aim of this study was to investigate whether there is a causal relationship between aging, neuroinflammation, cerebral microbleeds, and vascular dementia in a wild-type C57BL/6 mouse model. Microbleeds were found to be worse in aged mice compared to young adult mice by using Prussian Blue staining histology.[1] Immunohistochemistry assays on microglia were used to determine inflammation status. Novel Object Recognition (NOR) test and locomotor activity tests were used to assess animal behavior and cognitive ability. The current study aimed at eventually developing a possible treatment for cognitive ability decline and cardiovascular damage by targeting inflammation. This study also suggested a possible mechanism for the cause of cerebral microbleeds. / 2024-05-23T00:00:00Z

Neuronal networks within the brain exhibit an extraordinary complexity, laying the groundwork for behavioral and cognitive processing. External cues profoundly impact critical functions like learning and motor control by gating environmental information to the brain. Dynamic modulation of neural connectivity in response to external cues underscores the brain's adaptability and plasticity, while network dysfunction leads to neurological disorders. High-performance neural activity indicators have facilitated the study of neuronal networks at single-cell level during behavior. In this dissertation, we employed calcium imaging and local field potential (LFP) recordings complemented by customized algorithms, to investigate the influence of external cues on neural network dynamics during learning and locomotion. In the first study, we examined how sensory cue dependent learning relates to the dynamic changes of hippocampal neuronal networks. We performed calcium imaging of hippocampal CA1 neurons in mice during trace eye-blink conditioning and subsequent extinction learning. We examined cellular and network changes using both conventional data analytical approaches and a novel co-activity-based network approach algorithm to monitor trial-by-trial evolution of population responses. Our findings revealed that unique pairs of neurons are differentially activated leading to distinct network patterns encoding the two types of learning, although the connectivity density of the network remained constant. These results underline the hippocampus’s role in encoding behaviorally relevant external cues. In parallel, to understand the role of sensory cues on motor behavior, we investigated the impact of sensory cues on neural network dynamics and locomotion in the dorsal striatum, a brain region critical for motor control. Focusing on beta (10–30 Hz) rhythms, known for their significance in motor circuits, we examined how beta-frequency sensory stimulation impacts motor circuit regulation during stepping. We delivered audiovisual stimulation at 10 Hz or 145 Hz in mice voluntarily locomoting and conducted multimodal analysis using calcium imaging and LFP. Our findings indicate that sensory stimulation enhances locomotion and desynchronizes the striatal network. Notably, only 10 Hz stimulation effectively entrains striatal LFPs, improves stepping rhythmicity, and enhances the coupling between stepping and striatal LFP delta and beta oscillations. These results underscore the therapeutic potential of non-invasive beta-frequency sensory stimulation for improving gait.Overall, this dissertation sheds light on the neural mechanisms in sensory driven learning and locomotion, from single-cell to network levels. These insights offer avenues for developing therapeutic strategies by targeted modulation of specific network features. Moreover, this work provides a robust toolkit for studying neural network dynamics in response to external cues, deepening our understanding of brain function and dysfunction and revealing the complex orchestration of neural activity that drives adaptive behavior.

Spinal cord injuries (SCIs) can cause lower urinary tract (LUT) dysfunction, specifically neurogenic bladder, which affects 70%–84% of SCI patients. The current treatment options are limited and may trigger medical complications, leading to a significant decrease in quality of life. Therefore, restoring LUT function is a high priority for individuals living with SCI disabilities. The use of electrical spinal cord stimulation (ESCS) has been shown to be effective in restoring lost functions in some individuals with neurological impairments of this system. The objective of this thesis research project was to explore the investigation of different electrical stimulation modalities as a clinical or experimental treatment for bladder dysfunction, resulting from SCI-related LUT dysfunction. This paper aimed to provide a comprehensive outline of the intricate anatomy, neuroanatomy, and physiology of the LUT, highlighting how disruptions to these systems might result in LUT dysfunctions after clinical SCI. The strengths and limitations of each ESCS modality were systematically analyzed, with particular attention given to efficacy evaluation and the issues of side effects and safety. Overall, the findings suggest that ESCS, which is an established clinical therapy for managing chronic neuropathic pain, has demonstrated the potential to be repurposed to provide a safe, sustainable, and impactful treatment for bladder abnormalities in individuals with SCI. However, because of the limited knowledge about the LUT-specific mechanisms of ESCS action, more research investments are required before stimulation parameters including the appropriate timing and electrode location can be further improved to maximize ESCS-mediated improvement of LUT function after SCI.

BACKGROUND: Despite advances in healthcare technology and resources, patient survival after cardiac arrest is still very low. Patients who do initially survive cardiac arrest are still at high risk from potentially fatal neurological or other organ injuries (Laver et al., 2004). After initial treatment, clinical care of unresponsive cardiac arrest patients relies heavily on neuroprognostication to assess the extent of brain injury and help form outcome predictions. If neuroprognosis evaluates a patient outcome to be very poor, withdrawal of life-sustaining therapy is likely to occur. These factors make the improvement of neuroprognostication an important challenge in the healthcare industry. METHODS: Our retrospective study constructed and analyzed qualitative and quantitative models of patient neurological outcomes based on diffusion-weighted images (DWI). The patient cohorts included 204 patient post-cardiac arrest comatose targeted temperature management (TTM) patients, as well as a 48-patient non-cardiac arrest control group. Magnetic resonance imaging (MRI) reports were qualitatively assessed for the presence of anoxic injury, while MRI images were quantitatively assessed via their apparent diffusion coefficients (ADC). Models were then constructed based on this data using logistic regression. RESULTS: Our results indicated that ADC values differed most in cortical regions and that cortical regions quantitatively predicted good patient neurological outcomes superior to all other regions, with only the occipital lobe model having significantly higher predictive value than the qualitative models. We also saw that qualitative models predicted good neurological outcomes with a higher specificity but lower sensitivity than quantitative models. The qualitative and quantitative models showed substantial agreement in most regions, with the qualitative model having a higher positive and lower negative predictive value for good outcomes compared to the quantitative models. DISCUSSION: We saw a large concentration of anoxic injury in cortical regions, with these regions predicting good patient outcomes better than all others. Generally, the qualitative and quantitative models had the same predictive value across all regions except the occipital lobe. The difference between qualitative and quantitative models seems to provide evidence of a self-fulfilling prophecy in post-cardiac arrest care. Further directions for this project include modeling with the addition of other prognostic tests to form a more valuable predictive model.

The lateral habenula (LHb) is a bilateral brain structure implicated in action selection, reward processing, and motivation. The LHb projects to the ventral tegmental area (VTA) and dorsal raphe nucleus (DNR), and is thus involved in both dopaminergic and serotonergic pathways. Recent single-cell transcriptomic profiling of the LHb has revealed that it consists of four neuronal subtypes that are localized into four subregions. These have been designated as the HbX, lateral, oval/medial, and marginal subregions of the LHb. Each subregion is marked by non-overlapping genes. Cre mouse lines can be used as a tool to target these genes and thus manipulate these subtypes. This project utilizes fluorescence in situ hybridization (FISH) to genetically characterize the Sst-Cre mouse line to target the HbX subtype and the Kcnc1-Cre mouse line to target the marginal subtype. Investigating the specific effects of these subtypes can lead to a more comprehensive understanding of LHb function and dysfunction.

This literature review compares synapse degeneration in Alzheimer's disease (AD), Amyotrophic Lateral Sclerosis (ALS), Parkinson's disease (PD), and Huntington's disease (HD). Synapse degeneration is a typical pathogenic characteristic of various neurodegenerative diseases, and it contributes to the progression of cognitive and motor impairment. This review summarizes current research on the molecular causes of synapse degeneration as well as the distinctive characteristics of each illness that contribute to synapse loss. The comparative analysis further uncovers certain similarities in synapse degeneration between these diseases, such as abnormal protein aggregation and decreased mitochondrial function, and underlying mechanistic contributions, but also exposes distinctions in the affected brain circuits and patterns of synaptic susceptibility. Lastly, the conclusion of this review will explore potential treatment options that may target synapse degeneration in various disorders and emphasizes the need for more research to understand the complicated interaction between synapse degeneration and other neuropathological characteristics.

BACKGROUND: Two major populations of kisspeptin-expressing neurons in the hypothalamus synapse onto the gonadotropin-releasing hormone (GnRH) neurons to control the secretion of GnRH and, therefore, the luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The first population is found in the anteroventral periventricular nucleus of the hypothalamus (Kiss1AVPV/PeN) and is characteristic of the female brain. The Kiss1AVPV/PeN population functions as the LH surge generator in females, stimulating a large peak in LH release (called LH surge) mid-cycle to trigger ovulation, by mediating the positive feedback of sex steroids on the hypothalamic-pituitary-gonadal (HPG) axis. The second population is in the arcuate nucleus of the hypothalamus (ARC), where Kisspeptin neurons also co-express Neurokinin B and Dynorphin A (thereafter named KNDy neurons) and act as the pulse generator for GnRH/LH release, essential to normal reproductive function. KNDy neurons mediate the negative feedback of sex steroids on the HPG axis and relay information about the hormonal and neuroendocrine milieu (including metabolic cues) to the reproductive system. In addition to expressing three neuropeptides, KNDy neurons are also glutamatergic, but the role of this fast excitatory amino acid transmitter within KNDy neurons is still unclear. Current research into the potential role of glutamatergic signaling from KNDy neurons, while limited, has found that KNDy neurons send glutamatergic input to (1) Kiss1AVPV/PeN neurons, to (2) other KNDy neurons, and to (3) first-order homeostatic neurons regulating feeding behavior within the ARC. The majority of these findings were based on optogenetic activation of KNDy neurons, an artificial stimulation technique useful for tracing neural connections but unreliable for deducing the functional connection and role of such signaling pathways physiologically. OBJECTIVE: The aim of this study is to expand on existing optogenetic and electrophysiological studies by using viral CRISPR/Cas9 gene editing technology to examine the physiological impact of glutamatergic signal loss from KNDy neurons (GlutamateKNDy) on reproductive function in vivo. METHODS: Adult female Kiss1-cre het mice underwent stereotaxic injections of a cre-dependent CRISPR/SaCas9 virus targeting either Slc17a6 (the gene encoding Vglut2, a transporter necessary for glutamate neurotransmitter release), or Rosa-26 as a control. Using this method, we generated mice with a KNDy neuron specific deletion of glutamate release (Vglut2KD) and the impact on reproductive axis function was evaluated. Estrous cycles were tracked for four weeks before, and twelve weeks following Slc17a6 deletion from KNDy neurons. LH pulsatile release parameters were evaluated 10 weeks after viral injections and the females were submitted to an LH surge induced protocol to evaluate potential impairment to the LH surge driving ovulation. Body weight on a regular diet was also followed in the Vglut2KD and the control females to assess for potential significant metabolic impairments. RESULTS: Loss of glutamatergic signaling from KNDy neurons did not alter estrous cyclicity. Pulsatile LH release was not significantly altered but the frequency and amplitude of LH pulses tended to decrease in the Vglut2KD females as compared to controls. The induced LH surge protocol revealed a significant impairment to the surge mode of LH release in Vglut2KD females. Vglut2KD mice had no significant changes in body weight following Slc17a6 deletion from KNDy neurons. CONCLUSION: Glutamatergic signaling from KNDy neurons is not necessary to maintain normal pulsatile release of GnRH/LH, or estrous cyclicity, but is critical to the LH surge. This aligns with findings of transgenic Vglut2KO females with regular estrous cycles1 and of optogenetic stimulation of glutamate release from KNDy neurons onto the AVPV, generating a surge-like peak in circulating LH2. The lack of impairment to the pulse mode of LH release contradicts the recent hypothesis that glutamatergic stimulation from KNDy neurons serves as the basis of the population synchronization and pulsatility3. Further research is necessary to determine other potential sources of the noted stochastic glutamate stimulation of the KNDy network.

Some individually housed laboratory monkeys spontaneously develop self-injurious behavior (SIB). In rhesus macaques, this pathology usually takes the form of intense self-directed biting that, on occasion, can result in wounding severe enough to require veterinary treatment. Little is known about the underlying pathophysiology of SIB in socially reared monkeys. Most investigations of SIB have focused on monkeys that were reared in total social isolation, a form of deprivation that results in numerous abnormalities besides SIB. The objective of this dissertation was to characterize and identify the underlying pathophysiology of SIB in a group of socially reared, individually housed rhesus monkeys. Central monoamine systems, hypothalamic-pituitary-adrenal (HPA) and gonadal HPG) axes, and sympatho-adrenomedullary system (SAMS) activity were compared in monkeys with a veterinary record of self-inflicted wounding (SIB group) to that of control monkeys with similar rearing histories and ages (Control group). In addition to our focus on wounding, we examined the pathophysiology of SIB as it relates to the frequency of self-directed biting. Monkeys with SIB did not differ in their basal central monoamine activity from controls. Likewise, no group differences in basal gonadal or SAMS activity were found. However, monkeys with SIB did show persistently lower plasma cortisol levels following the stress of restraint and venipuncture, but not in 24-h urine samples collected under stress-free conditions. It was concluded that monkeys with SIB are hyporesponsive to the mild stress of blood sampling. Hypersensitivity in HPA negative feedback or reduced adrenocortical sensitivity were assessed as possible mechanisms for the observed attenuated stress response. Monkeys with SIB did not differ from controls in their response to a low dose of dexamethasone or to pharmacological challenge with ACTH. In contrast, when the relationship between HPA dysregulation and self-directed biting was assessed, significant negative correlations between self-biting and cortisol were found in post-stress blood samples and in response to ACTH, but not in 24-h urine samples. These data suggest that monkeys with high rates of self-biting show a blunted HPA response to stress. The role of early psychological and/or physical trauma as possible factors in the development of SUB and HPA dysregulation are discussed.