Polycomb repressive complex 2 is critical for mouse cortical glutamatergic neuron development.

The Polycomb Repressive Complex 2 (PRC2) regulates corticogenesis, yet the consequences of mutations to this epigenetic modifier in the mature brain are poorly defined. Importantly, PRC2 core genes are haploinsufficient and causative of several human neurodevelopmental disorders. To address the role of PRC2 in mature cortical structure and function, we conditionally deleted the PRC2 gene Eed from the developing mouse dorsal telencephalon. Adult homozygotes displayed smaller forebrain structures. Single-nucleus transcriptomics revealed that glutamatergic neurons were particularly affected, exhibiting dysregulated gene expression profiles, accompanied by aberrations in neuronal morphology and connectivity. Remarkably, homozygous mice performed well on challenging cognitive tasks. In contrast, while heterozygous mice did not exhibit clear anatomical or behavioral differences, they displayed dysregulation of neuronal genes and altered neuronal morphology that was strikingly different from homozygous phenotypes. Collectively, these data reveal how alterations to PRC2 function shape the mature brain and reveal a dose-specific role for PRC2 in determining glutamatergic neuron identity.

A cross-comparative analysis of in vivo versus ex vivo MRI indices in a mouse model of concussion.

BACKGROUND: We present a cross-sectional, case-matched, and pair-wise comparison of structural magnetic resonance imaging (MRI), diffusion tensor imaging (DTI), and neurite orientation dispersion and density imaging (NODDI) measures in vivo and ex vivo in a mouse model of concussion, thus aiming to establish the concordance of structural and diffusion imaging findings in living brain and after fixation. METHODS: We allocated 28 male mice aged 3-4 months to sham injury and concussion (CON) groups. CON mice had received a single concussive impact on day 0 and underwent MRI at day 2 (n = 9) or 7 (n = 10) post-impact, and sham control mice likewise underwent imaging at day 2 (n = 5) or 7 (n = 4). Immediately after the final scanning, we collected the perfusion-fixed brains, which were stored for imaging ex vivo 6-12 months later. We then compared the structural imaging, DTI, and NODDI results between different methods. RESULTS: In vivo to ex vivo structural and DTI/NODDI findings were in notably poor agreement regarding the effects of concussion on structural integrity of the brain. COMPARISON WITH EXISTING METHODS: ex vivo imaging was frequently done to study the effects of diseases and treatments, but our results showed that ex vivo and in vivo imaging can detect completely opposite and contradictory results. This is also the first study that compares in vivo and ex vivo NODDI. CONCLUSION: Our findings call for caution in extrapolating translational capabilities obtained ex vivo to physiological measurements in vivo. The divergent findings may reflect fixation artefacts and the contribution of the glymphatic system changes.

Multiparametric magnetic resonance imaging for detection of pathological changes in the central nervous system of a mouse model of multiple sclerosis in vivo.

Multiple sclerosis (MS) is an autoimmune disease involving demyelination and axonal damage in the central nervous system (CNS). In this study, we investigated pathological changes in the lumbar spinal cord of C57BL/6 mice induced with progressive experimental autoimmune encephalomyelitis (EAE) disease using 9.4-T magnetic resonance imaging (MRI). Multiparametric MRI measurements including MR spectroscopy, diffusion tensor imaging (DTI) and volumetric analyses were applied to detect metabolic changes in the CNS of EAE mice. Compared with healthy mice, EAE mice showed a significant reduction in N-acetyl aspartate and increases in choline, glycine, taurine and lactate. DTI revealed a significant reduction in fractional anisotropy and axial diffusivity and an increase in radial diffusivity in the lumbar spinal cord white matter (WM), while in the grey matter (GM), fractional anisotropy increased. High-resolution structural imaging also revealed lumbar spinal cord WM hypertrophy and GM atrophy. Importantly, these MRI changes were strongly correlated with EAE disease scoring and pathological changes in the lumbar (L2-L6), particularly WM demyelination lesions and aggregation of immune cells (microglia/macrophages and astrocytes) in this region. This study identified changes in MRI biomarker signatures that can be useful for evaluating the efficacy of novel drugs using EAE models in vivo.

The brain structure and the neural network features of the diurnal cuttlefish Sepia plangon.

Cuttlefish are known for their rapid changes of appearance enabling camouflage and con-specific communication for mating or agonistic display. However, interpretation of their sophisticated behaviors and responsible brain areas is based on the better-studied squid brain atlas. Here we present the first detailed description of the neuroanatomical features of a tropical and diurnal cuttlefish, Sepia plangon, coupled with observations on ontogenetic changes in its visual and learning centers using a suite of MRI-based techniques and histology. We then make comparisons to a loliginid squid, treating it as a 'baseline', and also to other cuttlefish species to help construct a connectivity map of the cuttlefish brain. Differences in brain anatomy and the previously unknown neural connections associated with camouflage, motor control and chemosensory function are described. These findings link brain heterogeneity to ecological niches and lifestyle, feeding hypotheses and evolutionary history, and provide a timely, new technology update to older literature.

Microstructural mapping of dentate gyrus pathology in Alzheimer's disease: A 16.4 Tesla MRI study.

The dentate gyrus (DG) is an integral portion of the hippocampal formation, and it is composed of three layers. Quantitative magnetic resonance (MR) imaging has the capability to map brain tissue microstructural properties which can be exploited to investigate neurodegeneration in Alzheimer's disease (AD). However, assessing subtle pathological changes within layers requires high resolution imaging and histological validation. In this study, we utilized a 16.4 Tesla scanner to acquire ex vivo multi-parameter quantitative MRI measures in human specimens across the layers of the DG. Using quantitative diffusion tensor imaging (DTI) and multi-parameter MR measurements acquired from AD (N = 4) and cognitively normal control (N = 6) tissues, we performed correlation analyses with histological measurements. Here, we found that quantitative MRI measures were significantly correlated with neurofilament and phosphorylated Tau density, suggesting sensitivity to layer-specific changes in the DG of AD tissues.

Comparative brain structure and visual processing in octopus from different habitats.

Octopods are masters of camouflage and solve complex tasks, and their cognitive ability is said to approach that of some small mammals. Despite intense interest and some research progress, much of our knowledge of octopus neuroanatomy and its links to behavior and ecology comes from one coastal species, the European common octopus, Octopus vulgaris. Octopod species are found in habitats including complex coral reefs and the relatively featureless mid-water. There they encounter different selection pressures, may be nocturnal or diurnal, and are mostly solitary or partially social. How these different ecologies and behavioral differences influence the octopus central nervous system (CNS) remains largely unknown. Here we present a phylogenetically informed comparison between diurnal and nocturnal coastal and a deep-sea species using brain imaging techniques. This study shows that characteristic neuroanatomical changes are linked to their habits and habitats. Enlargement and division of the optic lobe as well as structural foldings and complexity in the underlying CNS are linked to behavioral adaptation (diurnal versus nocturnal; social versus solitary) and ecological niche (reef versus deep sea), but phylogeny may play a part also. The difference between solitary and social life is mirrored within the brain including the formation of multiple compartments (gyri) in the vertical lobe, which is likened to the vertebrate cortex. These findings continue the case for convergence between cephalopod and vertebrate brain structure and function. Notably, within the current push toward comparisons of cognitive abilities, often with unashamed anthropomorphism at their root, these findings provide a firm grounding from which to work.

Neurogenic-dependent changes in hippocampal circuitry underlie the procognitive effect of exercise in aging mice.

We have shown that the improvement in hippocampal-based learning in aged mice following physical exercise observed is dependent on neurogenesis in the dentate gyrus (DG) and is regulated by changes in growth hormone levels. The changes in neurocircuitry, however, which may underlie this improvement, remain unclear. Using in vivo multimodal magnetic resonance imaging to track changes in aged mice exposed to exercise, we show the improved spatial learning is due to enhanced DG connectivity, particularly the strengthening of the DG-Cornu Ammonis 3 and the DG-medial entorhinal cortex connections in the dorsal hippocampus. Moreover, we provide evidence that these changes in circuitry are dependent on neurogenesis since they were abrogated by ablation of newborn neurons following exercise. These findings identify the specific changes in hippocampal circuitry that underlie the cognitive improvements resulting from physical activity and show that they are dependent on the activation of neurogenesis in aged animals.

Open-access quantitative MRI data of the spinal cord and reproducibility across participants, sites and manufacturers.

In a companion paper by Cohen-Adad et al. we introduce the spine generic quantitative MRI protocol that provides valuable metrics for assessing spinal cord macrostructural and microstructural integrity. This protocol was used to acquire a single subject dataset across 19 centers and a multi-subject dataset across 42 centers (for a total of 260 participants), spanning the three main MRI manufacturers: GE, Philips and Siemens. Both datasets are publicly available via git-annex. Data were analysed using the Spinal Cord Toolbox to produce normative values as well as inter/intra-site and inter/intra-manufacturer statistics. Reproducibility for the spine generic protocol was high across sites and manufacturers, with an average inter-site coefficient of variation of less than 5% for all the metrics. Full documentation and results can be found at https://spine-generic.rtfd.io/ . The datasets and analysis pipeline will help pave the way towards accessible and reproducible quantitative MRI in the spinal cord.

Generic acquisition protocol for quantitative MRI of the spinal cord.

Quantitative spinal cord (SC) magnetic resonance imaging (MRI) presents many challenges, including a lack of standardized imaging protocols. Here we present a prospectively harmonized quantitative MRI protocol, which we refer to as the spine generic protocol, for users of 3T MRI systems from the three main manufacturers: GE, Philips and Siemens. The protocol provides guidance for assessing SC macrostructural and microstructural integrity: T1-weighted and T2-weighted imaging for SC cross-sectional area computation, multi-echo gradient echo for gray matter cross-sectional area, and magnetization transfer and diffusion weighted imaging for assessing white matter microstructure. In a companion paper from the same authors, the spine generic protocol was used to acquire data across 42 centers in 260 healthy subjects. The key details of the spine generic protocol are also available in an open-access document that can be found at https://github.com/spine-generic/protocols . The protocol will serve as a starting point for researchers and clinicians implementing new SC imaging initiatives so that, in the future, inclusion of the SC in neuroimaging protocols will be more common. The protocol could be implemented by any trained MR technician or by a researcher/clinician familiar with MRI acquisition.

Elp2 mutations perturb the epitranscriptome and lead to a complex neurodevelopmental phenotype.

Intellectual disability (ID) and autism spectrum disorder (ASD) are the most common neurodevelopmental disorders and are characterized by substantial impairment in intellectual and adaptive functioning, with their genetic and molecular basis remaining largely unknown. Here, we identify biallelic variants in the gene encoding one of the Elongator complex subunits, ELP2, in patients with ID and ASD. Modelling the variants in mice recapitulates the patient features, with brain imaging and tractography analysis revealing microcephaly, loss of white matter tract integrity and an aberrant functional connectome. We show that the Elp2 mutations negatively impact the activity of the complex and its function in translation via tRNA modification. Further, we elucidate that the mutations perturb protein homeostasis leading to impaired neurogenesis, myelin loss and neurodegeneration. Collectively, our data demonstrate an unexpected role for tRNA modification in the pathogenesis of monogenic ID and ASD and define Elp2 as a key regulator of brain development.

Homologous laminar organization of the mouse and human subiculum.

The subiculum is the major output component of the hippocampal formation and one of the major brain structures most affected by Alzheimer's disease. Our previous work revealed a hidden laminar architecture within the mouse subiculum. However, the rotation of the hippocampal longitudinal axis across species makes it unclear how the laminar organization is represented in human subiculum. Using in situ hybridization data from the Allen Human Brain Atlas, we demonstrate that the human subiculum also contains complementary laminar gene expression patterns similar to the mouse. In addition, we provide evidence that the molecular domain boundaries in human subiculum correspond to microstructural differences observed in high resolution MRI and fiber density imaging. Finally, we show both similarities and differences in the gene expression profile of subiculum pyramidal cells within homologous lamina. Overall, we present a new 3D model of the anatomical organization of human subiculum and its evolution from the mouse.

Comparison between 2D and 3D MEDIC for human cervical spinal cord MRI at 3T.

INTRODUCTION: High-resolution magnetic resonance imaging (MRI) of the cervical spinal cord is important to provide accurate diagnosis and pathological assessment of injuries. MEDIC (Multiple Echo Data Image Combination) sequences have been used in clinical MRI; however, a comparison of the performance of 2D and 3D MEDIC for cervical spinal cord imaging has not been reported. The aim of this study is to compare axial 2D and 3D MEDIC for the visualisation of the grey matter (GM) and white matter (WM) of the human cervical spinal cord. METHODS: Eight healthy participants were scanned using Siemens Prismafit 3T MRI. T2*-weighted gradient spoiled 2D and 3D MEDIC sequences were acquired at 0.4 × 0.4 × 3.0 and 0.3 × 0.3 × 3.0 mm resolutions, with the acquisition times of 6 and 7 min, respectively. Quantitative analyses of the images were made based on the image signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and non-uniformity (NU). Two independent radiologists (CS and FN), each provided Likert scoring assessments of anatomical visibility of the GM and WM structures and image clarity for all samples. RESULTS: Quantitative evaluation showed that 3D MEDIC provided higher SNR, higher CNR and lower NU than 2D MEDIC. However, 2D MEDIC provided better anatomical visibility for the GM, WM and CSF, and higher image clarity (lower artefacts) compared to 3D MEDIC. CONCLUSIONS: 2D MEDIC provides better information for depicting the internal structures of the cervical spinal cord compared to 3D MEDIC.

Abnormal Behavior and Cortical Connectivity Deficits in Mice Lacking Usp9x.

Genetic association studies have identified many factors associated with neurodevelopmental disorders such as autism spectrum disorder (ASD). However, the way these genes shape neuroanatomical structure and connectivity is poorly understood. Recent research has focused on proteins that act as points of convergence for multiple factors, as these may provide greater insight into understanding the biology of neurodevelopmental disorders. USP9X, a deubiquitylating enzyme that regulates the stability of many ASD-related proteins, is one such point of convergence. Loss of function variants in human USP9X lead to brain malformations, which manifest as a neurodevelopmental syndrome that frequently includes ASD, but the underlying structural and connectomic abnormalities giving rise to patient symptoms is unknown. Here, we analyzed forebrain-specific Usp9x knockout mice (Usp9x-/y) to address this knowledge gap. Usp9x-/y mice displayed abnormal communication and social interaction behaviors. Moreover, the absence of Usp9x culminated in reductions to the size of multiple brain regions. Diffusion tensor magnetic resonance imaging revealed deficits in all three major forebrain commissures, as well as long-range hypoconnectivity between cortical and subcortical regions. These data identify USP9X as a key regulator of brain formation and function, and provide insights into the neurodevelopmental syndrome arising as a consequence of USP9X mutations in patients.

GABAa receptor density alterations revealed in a mouse model of early moderate prenatal ethanol exposure using [18F]AH114726.

INTRODUCTION: Prenatal ethanol exposure (PEE) has been shown to alter the level and function of receptors in the brain, one of which is GABAa receptors (GABAaR), the major inhibitory ligand gated ion channels that mediate neuronal inhibition. High dose PEE in animals resulted in the upregulation of GABAaR, but the effects of low and moderate dose PEE at early gestation have not been investigated. This study aimed at examining GABAaR density in the adult mouse brain following PEE during a period equivalent to the first 3 to 4 weeks in human gestation. It was hypothesized that early moderate PEE would cause alterations in brain GABAaR levels in the adult offspring. METHODS: C57BL/6J mice were given 10% v/v ethanol during the first 8 gestational days. Male offspring were studied using in-vivo Positron Emission Tomography (PET)/Magnetic Resonance Imaging (MRI), biodistribution, in-vitro autoradiography using [18F]AH114726, a novel flumazenil analogue with a high affinity for the benzodiazepine-binding site, and validated using immunohistochemistry. RESULTS: In vivo PET and biodistribution did not detect alteration in brain tracer uptake. In vitro radiotracer studies detected significantly reduced GABAaR in the olfactory bulbs. Immunohistochemistry detected reduced GABAaR in the cerebral cortex, cerebellum and hippocampus, while Nissl staining showed that cell density was significantly higher in the striatum following PEE. CONCLUSION: Early moderate PEE may induce long-term alterations in the GABAaR system that persisted into adulthood.

Serial MRI studies over 12 months using manual and atlas-based region of interest in patients with amyotrophic lateral sclerosis.

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by loss of upper and lower motor neurons. There is a need for an imaging biomarker to track disease progression. Previously, magnetic resonance imaging (MRI) has shown loss of grey and white matter in the brain of patients with ALS compared to controls. We performed serial diffusion tractography imaging (DTI) study of patients with ALS looking for changes over time. METHODS: On all subjects (n = 15), we performed three MRI studies at 6 month intervals. DTI changes were assessed with tract-based spatial statistics (TBSS) and region of interest (ROI) studies. Cortic-spinal tract (CST) was selected for our ROI at the upper level; the posterior limb of internal capsule (PLIC), and a lower level in the pons. RESULTS: There was no significant change in DTI measures over 12 months of observation. Better correlation of manual and atlas-based ROI methods was found in the posterior limb of the internal capsule than the pons. CONCLUSION: While previous DTI studies showed significant differences between ALS subjects and controls, within individual subjects there is little evidence of progression over 12 months. This suggests that DTI is not a suitable biomarker to assess disease progression in ALS.

Toward an MRI-Based Mesoscale Connectome of the Squid Brain.

Using high-resolution diffusion magnetic resonance imaging (dMRI) and a suite of old and new staining techniques, the beginnings of a multi-scale connectome map of the squid brain is erected. The first of its kind for a cephalopod, this includes the confirmation of 281 known connections with the addition of 145 previously undescribed pathways. These and other features suggest a suite of functional attributes, including (1) retinotopic organization through the optic lobes and into other brain areas well beyond that previously recognized, (2) a level of complexity and sub-division in the basal lobe supporting ideas of convergence with the vertebrate basal ganglia, and (3) differential lobe-dependent growth rates that mirror complexity and transitions in ontogeny.

Magnetic Resonance Imaging and Micro-Computed Tomography reveal brain morphological abnormalities in a mouse model of early moderate prenatal ethanol exposure.

BACKGROUND: This study investigated the effects of early moderate prenatal ethanol exposure (PEE) on the brain in a mouse model that mimics a scenario in humans, whereby moderate daily drinking ceases after a woman becomes aware of her pregnancy. METHODS: C57BL/6J pregnant mice were given 10% v/v ethanol from gestational day 0-8 in the drinking water. The male offspring were used for imaging. Anatomical and diffusion Magnetic Resonance Imaging were performed in vivo at postnatal day 28 (P28, adolescence) and P80 (adulthood). Micro-Computed Tomography was performed on fixed whole heads at P80. Tensor-based morphometry (TBM) was applied to detect alterations in brain structure and voxel-based morphometry (VBM) for skull morphology. Diffusion tensor and neurite orientation dispersion and density imaging models were used to detect microstructural changes. Neurofilament (NF) immunohistochemistry was used to validate findings by in vivo diffusion MRI. RESULTS: TBM showed that PEE mice exhibited a significantly smaller third ventricle at P28 (family-wise error rate (FWE), p < 0.05). All other macro-structural alterations did not survive FWE corrections but when displayed with an uncorrected p < 0.005 showed multiple regional volume reductions and expansions, more prominently in the right hemisphere. PEE-induced gross volume changes included a bigger thalamus, hypothalamus and ventricles at P28, and bigger total brain volumes at both P28 and P80 (2-sample t-tests). Disproportionately smaller olfactory bulbs following PEE were revealed at both time-points. No alterations in diffusion parameters were detected, but PEE animals exhibited reduced NF positive staining in the thalamus and striatum and greater bone density in various skull regions. CONCLUSION: Our results show that early moderate PEE can cause alterations in the brain that are detectable during development and adulthood.