Wanted dead or alive? The tradeoff between in-vivo versus ex-vivo MR brain imaging in the mouse

High-resolution MRI of the mouse brain is gaining prominence in estimating changes in neuroanatomy over time to understand both normal developmental as well as disease processes and mechanisms. These types of experiments, where a change in time is to be captured as accurately as possible using imaging, face multiple experimental design choices. Chief amongst these choices is whether to image ex-vivo, where superior resolution and contrast are available, or in-vivo, where resolution and contrast are lower but the animal can be followed longitudinally. Here we explore this tradeoff by first estimating the sources of variability in anatomical mouse MRI and then, using statistical simulations, provide power analyses of these experiment design choices

Time Course and Nature of Brain Atrophy in the MRL Mouse Model of Central Nervous System Lupus

Objective. Similar to patients with systemic lupus erythematosus, autoimmune MRL/lpr mice spontaneously develop behavioral deficits and pathologic changes in the brain. Given that the disease-associated brain atrophy in this model is not well understood, the present study was undertaken to determine the time course of morphometric changes in major brain structures of autoimmune MRL/lpr mice. Methods. Computerized planimetry and highresolution magnetic resonance imaging (MRI) were used to compare the areas and volumes of brain structures in cohorts of mice that differ in severity of lupus-like disease. Results. A thinner cerebral cortex and smaller cerebellum were observed in the MRL/lpr substrain, even before severe autoimmunity developed. With progression of the disease, the brain area of coronal sections became smaller and the growth of the hippocampus was retarded, which likely contributed to the increase in the ventricle area:brain area ratio. MRI revealed reduced volume across different brain regions, with the structures in the vicinity of the ventricular system particularly affected. The superior colliculus, periaqueductal gray matter, pons, and midbrain were among the regions most affected, whereas the volumes of the parietal-temporal lobe, parts of the cerebellum, and lateral ventricles in autoimmune MRL/lpr mice were comparable with values in congenic controls. Conclusion. These results suggest that morphologic alterations in the brains of MRL/lpr mice are a consequence of several factors, including spontaneous development of lupus-like disease. A periventricular pattern of parenchymal damage is consistent with the cerebrospinal fluid neurotoxicity, limbic system pathologic features, and deficits in emotional reactivity previously documented in this model. Neuropsychiatric (NP) manifestations are a common and serious complication of systemic lupus erythematosus (SLE). Contemporary imaging techniques have revealed various abnormalities in patients with SLE, including lesions in the periventricular and subcortical regions (1,2), hypoperfusion (3), and regional metabolic abnormalities (4). Brain atrophy is the most frequent observation (5) and is likely a consequence of widespread neuronal and glial damage (6). Consistent with these reports, recent studies on water diffusivity indicate a genuine loss of brain-tissue integrity in patients with NPSLE/central nervous system (CNS) lupus (7). However, the lack of understanding of CNS damage led to development of animal models of acute and chronic lupus and dissection of complex pathogenic circuits (8). MRL/MpJTnfrsf6 lpr (MRL/lpr) mice and MRL/ MpJϩ/ϩ (MRLϩ/ϩ) congenic control mice share more than 99.9% of their genome but differ in the onset of lupus-like manifestations. The 3-4-month difference in the time to onset allows discrimination of autoimmunityinduced functional and structural brain damage from epiphenomena associated with aging and with damage of vital peripheral organs (9). In addition to accelerated development of serologic signs of inflammation and autoimmunity, MRL/lpr mice develop, at an early stage, a constellation of behavioral deficits and neuropathologic changes, operationally termed autoimmune

Semi-Automatic segmentation of multiple mouse embryos in MR images

<p>Abstract</p> <p>Background</p> <p>The motivation behind this paper is to aid the automatic phenotyping of mouse embryos, wherein multiple embryos embedded within a single tube were scanned using Magnetic Resonance Imaging (MRI).</p> <p>Results</p> <p>Our algorithm, a modified version of the simplex deformable model of Delingette, addresses various issues with deformable models including initialization and inability to adapt to boundary concavities. In addition, it proposes a novel technique for automatic collision detection of multiple objects which are being segmented simultaneously, hence avoiding major leaks into adjacent neighbouring structures. We address the initialization problem by introducing balloon forces which expand the initial spherical models close to the true boundaries of the embryos. This results in models which are less sensitive to initial minimum of two fold after each stage of deformation. To determine collision during segmentation, our unique collision detection algorithm finds the intersection between binary masks created from the deformed models after every few iterations of the deformation and modifies the segmentation parameters accordingly hence avoiding collision.</p> <p>We have segmented six tubes of three dimensional MR images of multiple mouse embryos using our modified deformable model algorithm. We have then validated the results of the our semi-automatic segmentation versus manual segmentation of the same embryos. Our Validation shows that except paws and tails we have been able to segment the mouse embryos with minor error.</p> <p>Conclusions</p> <p>This paper describes our novel multiple object segmentation technique with collision detection using a modified deformable model algorithm. Further, it presents the results of segmenting magnetic resonance images of up to 32 mouse embryos stacked in one gel filled test tube and creating 32 individual masks.</p

White matter injury predicts disrupted functional connectivity and microstructure in very preterm born neonates

© 2018 The Authors Objective: To determine whether the spatial extent and location of early-identified punctate white matter injury (WMI) is associated with regionally-specific disruptions in thalamocortical-connectivity in very-preterm born neonates. Methods: 37 very-preterm born neonates (median gestational age: 28.1 weeks; interquartile range [IQR]: 27–30) underwent early MRI (median age 32.9 weeks; IQR: 32–35), and WMI was identified in 13 (35%) neonates. Structural T1-weighted, resting-state functional Magnetic Resonance Imaging (rs-fMRI, n = 34) and Diffusion Tensor Imaging (DTI, n = 31) sequences were acquired using 3 T-MRI. A probabilistic map of WMI was developed for the 13 neonates demonstrating brain injury. A neonatal atlas was applied to the WMI maps, rs-fMRI and DTI analyses to extract volumetric, functional and microstructural data from regionally-specific brain areas. Associations of thalamocortical-network strength and alterations in fractional anisotropy (FA, a measure of white-matter microstructure) with WMI volume were assessed in general linear models, adjusting for age at scan and cerebral volumes. Results: WMI volume in the superior (β = −0.007; p =.02) and posterior corona radiata (β = −0.01; p =.01), posterior thalamic radiations (β = −0.01; p =.005) and superior longitudinal fasciculus (β = −0.02; p =.001) was associated with reduced connectivity strength between thalamus and parietal resting-state networks. WMI volume in the left (β = −0.02; p =.02) and right superior corona radiata (β = −0.03; p =.008), left posterior corona radiata (β = −0.03; p =.01), corpus callosum (β = −0.11; p \u3c.0001) and right superior longitudinal fasciculus (β = −0.02; p =.02) was associated with functional connectivity strength between thalamic and sensorimotor networks. Increased WMI volume was also associated with decreased FA values in the corpus callosum (β = −0.004, p =.015). Conclusions: Regionally-specific alterations in early functional and structural network complexity resulting from WMI may underlie impaired outcomes

A new mouse model of ATR-X syndrome carrying a common patient mutation exhibits neurological and morphological defects

ATRX is a chromatin remodelling ATPase that is involved in transcriptional regulation, DNA damage repair and heterochromatin maintenance. It has been widely studied for its role in ALT-positive cancers, but its role in neurological function remains elusive. Hypomorphic mutations in the X-linked ATRX gene cause a rare form of intellectual disability combined with alpha-thalassemia called ATR-X syndrome in hemizygous males. Clinical features also include facial dysmorphism, microcephaly, short stature, musculoskeletal defects and genital abnormalities. Since complete deletion of ATRX in mice results in early embryonic lethality, the field has largely relied on conditional knockout models to assess the role of ATRX in multiple tissues. Given that null alleles are not found in patients, a more patient-relevant model was needed. Here, we have produced and characterised the first patient mutation knock-in model of ATR-X syndrome, carrying the most common causative mutation, R246C. This is one of a cluster of missense mutations located in the chromatin binding domain and disrupts its function. The knock-in mice recapitulate several aspects of the patient disorder, including craniofacial defects, microcephaly, reduced body size and impaired neurological function. They provide a powerful model for understanding the molecular mechanisms underlying ATR-X syndrome and for testing potential therapeutic strategies

Review Article MR technology for biological studies in mice

ABSTRACT: Mouse models are crucial for the study of genetic factors and processes that influence human disease. In addition to tools for measuring genetic expression and establishing genotype, tools to accurately and comparatively assess mouse phenotype are essential in order to characterize pathology and make comparisons with human disease. MRI provides a powerful means of evaluating various anatomical and functional changes and hence is growing in popularity as a phenotypic readout for biomedical research studies. To accommodate the large numbers of mice needed in most biological studies, mouse MRI must offer high-throughput image acquisition and efficient image analysis. This article reviews the technology of multiple-mouse MRI, a method that images multiple mice or specimens simultaneously as a means of enabling high-throughput studies. Aspects of image acquisition and computational analysis in multiple-mouse studies are also described

A Mouse Model of Heritable Cerebrovascular Disease

The study of animal models of heritable cerebrovascular diseases can improve our understanding of disease mechanisms, identify candidate genes for related human disorders, and provide experimental models for preclinical trials. Here we describe a spontaneous mouse mutation that results in reproducible, adult-onset, progressive, focal ischemia in the brain. The pathology is not the result of hemorrhage, embolism, or an anatomical abnormality in the cerebral vasculature. The mutation maps as a single site recessive locus to mouse Chromosome 9 at 105 Mb, a region of shared synteny with human chromosome 3q22. The genetic interval, defined by recombination mapping, contains seven protein-coding genes and one processed transcript, none of which are changed in their expression level, splicing, or sequence in affected mice. Targeted resequencing of the entire interval did not reveal any provocative changes; thus, the causative molecular lesion has not been identified

Altered Neurocircuitry in the Dopamine Transporter Knockout Mouse Brain

The plasma membrane transporters for the monoamine neurotransmitters dopamine, serotonin, and norepinephrine modulate the dynamics of these monoamine neurotransmitters. Thus, activity of these transporters has significant consequences for monoamine activity throughout the brain and for a number of neurological and psychiatric disorders. Gene knockout (KO) mice that reduce or eliminate expression of each of these monoamine transporters have provided a wealth of new information about the function of these proteins at molecular, physiological and behavioral levels. In the present work we use the unique properties of magnetic resonance imaging (MRI) to probe the effects of altered dopaminergic dynamics on meso-scale neuronal circuitry and overall brain morphology, since changes at these levels of organization might help to account for some of the extensive pharmacological and behavioral differences observed in dopamine transporter (DAT) KO mice. Despite the smaller size of these animals, voxel-wise statistical comparison of high resolution structural MR images indicated little morphological change as a consequence of DAT KO. Likewise, proton magnetic resonance spectra recorded in the striatum indicated no significant changes in detectable metabolite concentrations between DAT KO and wild-type (WT) mice. In contrast, alterations in the circuitry from the prefrontal cortex to the mesocortical limbic system, an important brain component intimately tied to function of mesolimbic/mesocortical dopamine reward pathways, were revealed by manganese-enhanced MRI (MEMRI). Analysis of co-registered MEMRI images taken over the 26 hours after introduction of Mn^(2+) into the prefrontal cortex indicated that DAT KO mice have a truncated Mn^(2+) distribution within this circuitry with little accumulation beyond the thalamus or contralateral to the injection site. By contrast, WT littermates exhibit Mn^(2+) transport into more posterior midbrain nuclei and contralateral mesolimbic structures at 26 hr post-injection. Thus, DAT KO mice appear, at this level of anatomic resolution, to have preserved cortico-striatal-thalamic connectivity but diminished robustness of reward-modulating circuitry distal to the thalamus. This is in contradistinction to the state of this circuitry in serotonin transporter KO mice where we observed more robust connectivity in more posterior brain regions using methods identical to those employed here

The Angiopoietin-Tie2 axis contributes to placental vascular disruption and adverse birth outcomes in malaria in pregnancy

BACKGROUND Malaria during pregnancy is a major contributor to the global burden of adverse birth outcomes including fetal growth restriction, preterm birth, and fetal loss. Recent evidence supports a role for angiogenic dysregulation and perturbations to placental vascular development in the pathobiology of malaria in pregnancy. The Angiopoietin-Tie2 axis is critical for placental vascularization and remodeling. We hypothesized that disruption of this pathway would contribute to malaria-induced adverse birth outcomes. METHODS Using samples from a previously conducted prospective cohort study of pregnant women in Malawi, we measured circulating levels of angiopoietin-1 (Angpt-1) and Angpt-2 by Luminex (n=1392). We used a preclinical model of malaria in pregnancy (Plasmodium berghei ANKA [PbA] in pregnant BALB/c mice), genetic disruption of Angpt-1 (Angpt1 mice), and micro-CT analysis of placental vasculature to test the hypothesis that disruptions to the Angpt-Tie2 axis by malaria during pregnancy would result in aberrant placental vasculature and adverse birth outcomes. FINDINGS Decreased circulating levels of Angpt-1 and an increased ratio of Angpt-2/Angpt-1 across pregnancy were associated with malaria in pregnancy. In the preclinical model, PbA infection recapitulated disruptions to the Angiopoietin-Tie2 axis resulting in reduced fetal growth and viability. Malaria decreased placental Angpt-1 and Tie2 expression and acted synergistically with reduced Angpt-1 in heterozygous dams (Angpt1), to worsen birth outcomes by impeding vascular remodeling required for placental function. INTERPRETATION Collectively, these data support a mechanistic role for the Angpt-Tie2 axis in malaria in pregnancy, including a potential protective role for Angpt-1 in mitigating infection-associated adverse birth outcomes. FUNDING This work was supported by the Canadian Institutes of Health Research (CIHR), Canada Research Chair, and Toronto General Research Institute Postdoctoral Fellowship Award. The parent trial was supported by the European & Developing Countries Clinical Trials Partnership and the Malaria in Pregnancy Consortium, which was funded by the Bill & Melinda Gates Foundation. The funders had no role in design, analysis, or reporting of these studies

Infant Brain Atlases from Neonates to 1- and 2-Year-Olds

Background: Studies for infants are usually hindered by the insufficient image contrast, especially for neonates. Prior knowledge, in the form of atlas, can provide additional guidance for the data processing such as spatial normalization, label propagation, and tissue segmentation. Although it is highly desired, there is currently no such infant atlas which caters for all these applications. The reason may be largely due to the dramatic early brain development, image processing difficulties, and the need of a large sample size. Methodology: To this end, after several years of subject recruitment and data acquisition, we have collected a unique longitudinal dataset, involving 95 normal infants (56 males and 39 females) with MRI scanned at 3 ages, i.e., neonate, 1-yearold, and 2-year-old. State-of-the-art MR image segmentation and registration techniques were employed, to construct which include the templates (grayscale average images), tissue probability maps (TPMs), and brain parcellation maps (i.e., meaningful anatomical regions of interest) for each age group. In addition, the longitudinal correspondences between agespecific atlases were also obtained. Experiments of typical infant applications validated that the proposed atlas outperformed other atlases and is hence very useful for infant-related studies. Conclusions: We expect that the proposed infant 0–1–2 brain atlases would be significantly conducive to structural and functional studies of the infant brains. These atlases are publicly available in our website