Evaluation of spasticity in experimental models of ischemic stroke

Strokes are one of the most common causes of lifelong physical impairment, with about 35% of the patients suffering from post-stroke spasticity (PSS). In contrast to the long and successful history of experimental stroke, rodent models of PSS are sparse and insufficiently characterized [275]. Motivated by this gap in stroke studies, this thesis focused on the development of a PSS mouse model and the long-term effects after strokes within the primary motor area (MOp), secondary motor area (MOs), and internal capsule. For longitudinal determination of PSS, sensorimotor behavioral tests, and equivalent to the measurement in the patient, electrophysiological measurements of the Hoffman reflex were performed. For this purpose, in addition to a longitudinal H-wave measurement, a novel direct nerve H-wave measurement was established in the mouse. For the quantitative determination of the PSS, the ratio of H- and M-wave as well as the rate-dependent depression were measured, which allow an objective measurement of PSS. The experiments revealed that a lesion within the MOp leads to motor deficits, without development of PSS, whereas a lesion within the MOs and internal capsule leads to mild and strong PSS, respectively, after 56 days. In the established internal capsule stroke model for the induction of PSS, an onset of PSS was detected electrophysiologically after 14 days. The sensorimotor deficit score correlated with the PSS measurement, i.e. animals with a PSS showed a reduced recovery of motor function. It was demonstrated that, in addition to the grid walk test, the cylinder test represents behavioral tests that still detect a motor deficit 56 days after a lesion and are sensitive to the motor deficits that occur in PSS. In addition to electrophysiolgical and sensorimotor changes, structural changes were also analyzed, which included examination of secondary neurodegeneration in addition to lesion description. Within the first 28 days after lesion within the MOp microglia/- macrophages were found mainly in the ipsilesional in subregions of the thalamus, which suggested a secondary neurodegeneration. Within the spinal cord, this aggregation of microglia/macrophages and thus evidence of selective secondary degeneration was particularly evident in the dorsal corticospinal tract, an important descending motor pathway. The knowledge gained will serve as a basis for further studies, which will include a precise characterization of secondary neurodegeneration at the spinal cord level and neuronal tracing to evaluate the influence of the cortico- as well as reticolospinal tracts

Microcephaly with a disproportionate hippocampal reduction, stem cell loss and neuronal lipid droplet symptoms in Trappc9 KO mice

Mutations of the humanTRAFFICKING PROTEIN PARTICLE COMPLEX SUBUNIT 9(TRAPPC9) cause a neurodevelopmental disorder characterised by microcephaly and intellectual disability. Trappc9 constitutes a subunit specific to the intracellular membrane-associated TrappII complex. The TrappII complex interacts with Rab11 and Rab18, the latter being specifically associated with lipid droplets (LDs). Here we used non-invasive imaging to characteriseTrappc9knock-out (KO) mice as a model of the human hereditary disorder. KOs developed postnatal microcephaly with many grey and white matter regions being affected.In vivoMRI identified a disproportionately stronger volume reduction in the hippocampus, which was associated with a significant loss of Sox2-positive neural stem and progenitor cells. Diffusion Tensor imaging indicated a reduced organisation or integrity of white matter areas.Trappc9KOs displayed behavioural abnormalities in several tests related to exploration, learning and memory. Trappc9-deficient primary hippocampal neurons accumulated a larger LD volume per cell following Oleic Acid stimulation, and the coating of LDs by Perilipin-2 was much reduced. Additionally,Trappc9KOs developed obesity, which was significantly more severe in females than in males. Our findings indicate that, beyond previously reported Rab11-related vesicle transport defects, dysfunctions in LD homeostasis might contribute to the neurobiological symptoms of Trappc9 deficiency.</jats:p

Microcephaly with a disproportionate hippocampal reduction, stem cell loss and neuronal lipid droplet symptoms in Trappc9 KO mice

Mutations of the human TRAFFICKING PROTEIN PARTICLE COMPLEX SUBUNIT 9 (TRAPPC9) cause a neurodevelopmental disorder characterised by microcephaly and intellectual disability. Trappc9 constitutes a subunit specific to the intracellular membrane-associated TrappII complex. The TrappII complex interacts with Rab11 and Rab18, the latter being specifically associated with lipid droplets (LDs). Here we used non-invasive imaging to characterise Trappc9 knock-out (KO) mice as a model of the human hereditary disorder. KOs developed postnatal microcephaly with many grey and white matter regions being affected. In vivo magnetic resonance imaging (MRI) identified a disproportionately stronger volume reduction in the hippocampus, which was associated with a significant loss of Sox2-positive neural stem and progenitor cells. Diffusion tensor imaging indicated a reduced organisation or integrity of white matter areas. Trappc9 KOs displayed behavioural abnormalities in several tests related to exploration, learning and memory. Trappc9-deficient primary hippocampal neurons accumulated a larger LD volume per cell following Oleic Acid stimulation, and the coating of LDs by Perilipin-2 was much reduced. Additionally, Trappc9 KOs developed obesity, which was significantly more severe in females than in males. Our findings indicate that, beyond previously reported Rab11-related vesicle transport defects, dysfunctions in LD homeostasis might contribute to the neurobiological symptoms of Trappc9 deficiency

Pursuit of precision medicine: Systems biology approaches in Alzheimer\u27s disease mouse models.

Alzheimer\u27s disease (AD) is a complex disease that is mediated by numerous factors and manifests in various forms. A systems biology approach to studying AD involves analyses of various body systems, biological scales, environmental elements, and clinical outcomes to understand the genotype to phenotype relationship that potentially drives AD development. Currently, there are many research investigations probing how modifiable and nonmodifiable factors impact AD symptom presentation. This review specifically focuses on how imaging modalities can be integrated into systems biology approaches using model mouse populations to link brain level functional and structural changes to disease onset and progression. Combining imaging and omics data promotes the classification of AD into subtypes and paves the way for precision medicine solutions to prevent and treat AD

DETECTING BRAIN-WIDE INTRINSIC CONNECTIVITY NETWORKS USING fMRI IN MICE

Functional neuroimaging methods in mice are essential for unraveling complex neuronal networks that underlie maladaptive behavior in neurological disorder models. By using fMRI to detect intrinsic connectivity networks in mice, we can examine large scale alteration in brain activity and functional connectivity to establish causal associations in brain network changes. The work presented in this dissertation is organized into five chapters. Chapter 1 provides the necessary background required to understand how functional neuroimaging tools such as fMRI detect signal changes attributed to spontaneous neuronal activity of intrinsic connectivity networks in mice. Chapter 2 describes the development of our isotropic fMRI acquisition sequence in mice and semi-automated pipeline for mouse fMRI data. Naïve mouse fMRI scans were used to validated the pipeline by reliably and reproducibly extracting intrinsic connectivity networks. Chapter 3 establishes the development and validation of a novel superparamagenetic iron-oxide nanoparticle to enhance fMRI signal sensitivity. Chapter 4 studies the effects norepinephrine released by locus coeruleus neurons on the default mode network in mice. Norepinephrine release selectively enhanced neuronal activity and connectivity in the Frontal module of the default mode network by suppressing information flow from the Retrosplenial-Hippocampal to the Association modules. Chapter 5 addresses the implications of our findings and addresses the limitations and future studies that can be conducted to expand on this research.Doctor of Philosoph

Molecular mechanisms underlying cerebral small vessel disease associated with mutations in COL4A1

Cerebral small vessel diseases (cSVDs) are the leading cause of stroke and vascular dementia, but the underlying pathogenic mechanisms are unknown. Humans and mice with autosomal dominant mutations in the collagen-encoding gene COL4A1 present with brain pathology that typifies cSVD. Data in this thesis reveals divergent pathogenic mechanisms in two Col4a1 mutant mouse models and offers viable therapeutic strategies for treating related cSVDs. Col4a1G1344D cSVD was associated with the loss of myogenic tone due to blunted pressure-induced smooth muscle cell (SMC) depolarization. Dysregulation of membrane potential was linked to impaired Ca2+-dependent activation of transient receptor potential melastatin 4 (TRPM4) channels caused by disruption in sarcoplasmic reticulum (SR) Ca2+ signaling. Deficits were prevented by treating mice with 4-phenylbutyrate, a compound that promotes the trafficking of misfolded proteins from the SR, suggesting accumulation of mutant collagen in the SR contributes to the pathogenesis. The fundamental defect in Col4a1G394V cSVD was the depletion of phosphatidylinositol 4,5 bisphosphate (PIP2), a necessary cofactor for TRPM4 and inwardly-rectifying K+ (KIR) channels, in vascular SMCs and endothelial cells. This caused a loss of myogenic tone and neurovascular coupling contributing to cSVD. PIP2 depletion was linked to increased phosphoinositide 3-kinase (PI3K) activity acting downstream of transforming growth factor-beta (TGF-β) receptors. Restoring PIP2 by blocking PI3K or TGF-β receptors restored myogenic tone, neurovascular coupling, and memory function. Differences in pathogenic mechanisms between mutations within the same gene highlight the diverse causes and the need for specific treatments of cSVDs

Processing Pipeline for Atlas-Based Imaging Data Analysis of Structural and Functional Mouse Brain MRI (AIDAmri)

Magnetic resonance imaging (MRI) is a key technology in multimodal animal studies of brain connectivity and disease pathology. In vivo MRI provides non-invasive, whole brain macroscopic images containing structural and functional information, thereby complementing invasive in vivo high-resolution microscopy and ex vivo molecular techniques. Brain mapping, the correlation of corresponding regions between multiple brains in a standard brain atlas system, is widely used in human MRI. For small animal MRI, however, there is no scientific consensus on pre-processing strategies and atlas-based neuroinformatics. Thus, it remains difficult to compare and validate results from different pre-clinical studies which were processed using custom-made code or individual adjustments of clinical MRI software and without a standard brain reference atlas. Here, we describe AIDAmri, a novel Atlas-based Imaging Data Analysis pipeline to process structural and functional mouse brain data including anatomical MRI, fiber tracking using diffusion tensor imaging (DTI) and functional connectivity analysis using resting-state functional MRI (rs-fMRI). The AIDAmri pipeline includes automated pre-processing steps, such as raw data conversion, skull-stripping and bias-field correction as well as image registration with the Allen Mouse Brain Reference Atlas (ARA). Following a modular structure developed in Python scripting language, the pipeline integrates established and newly developed algorithms. Each processing step was optimized for efficient data processing requiring minimal user-input and user programming skills. The raw data is analyzed and results transferred to the ARA coordinate system in order to allow an efficient and highly-accurate region-based analysis. AIDAmri is intended to fill the gap of a missing open-access and cross-platform toolbox for the most relevant mouse brain MRI sequences thereby facilitating data processing in large cohorts and multi-center studies