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Ex vivo analysis of presymptomatic spinal cord of ALS mice by Ultra-High Field MRI diffusion. a Scheme representing MRI cross-sections from different spinal cord segments (cervical, thoracic, and lumbar) used for analysis. b T2w representative MR images from individual spinal cords scans showing the white matter (WM) ROIs in the WM anterolateral funiculus (white dotted line) from each spinal cord segment (YFP vs. G93A-SOD1 mice) Scale bar = 1 mm. Abbreviations: WM: white matter. YFP: yellow fluorescent protein
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Background
Amyotrophic lateral sclerosis (ALS) is a disease characterized by a progressive degeneration of motor neurons leading to paralysis. Our previous MRI diffusion tensor imaging studies detected early white matter changes in the spinal cords of mice carrying the G93A-SOD1 mutation. Here, we extend those studies using ultra-high field MRI (17...
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... water displacement probability dens- ity function [30] was used to estimate white matter tracts. White matter regions-of-interest (ROIs), defined within slices at the top and bottom of each of spinal cord seg- ments (cervical, thoracic, and lumbar), were manually outlined following the anterolateral distribution of the white matter on each slice (Fig. 1) using ImageJ software (NIH, ...
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... clinical and animal diffusion imaging studies ALS SCs have shown that regional changes in parameters were more affected at the distal than proximal regions [14,33]. Hence, we centered our MRI diffusion studies on the an- terolateral white matter funiculi of three SC regions (cer- vical, thoracic and lumbar segments) (Fig. 1a). Manual segmentation of WM ROIs across diffusion maps from five SC slices were considered in this analysis, (Fig. 1b). Two time-points were considered; a presymptomatic stage (P80) and a symptomatic stage (P120). At presymptomatic stages (P80), we observed a significant reduction of FA in the cer- vical region (p < 0.05) in the YFP, ...
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... in parameters were more affected at the distal than proximal regions [14,33]. Hence, we centered our MRI diffusion studies on the an- terolateral white matter funiculi of three SC regions (cer- vical, thoracic and lumbar segments) (Fig. 1a). Manual segmentation of WM ROIs across diffusion maps from five SC slices were considered in this analysis, (Fig. 1b). Two time-points were considered; a presymptomatic stage (P80) and a symptomatic stage (P120). At presymptomatic stages (P80), we observed a significant reduction of FA in the cer- vical region (p < 0.05) in the YFP, G93A-SOD1 mice (YFP mice =0.60 +/-0.01 versus YFP, G93A-SOD1 mice = 0.57 +/-0.01) (-6.6%) as well as in the thoracic ...
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... cord from an ALS mouse model. The com- bination of higher signal to noise ratios (SNR) available at higher magnetic fields [53,54], and the histological detail provided by an ALS transgenic mice expressing a neuronal specific endogenous fluorescent protein (YFP), enhanced the detection of early changes in DTI parameters and WM microstructure (Figs. 1b and 4a). Thus, we have iden- tified presymptomatic changes in MRI diffusion are based on alterations in of morphological axonal features, such as a reduction in axonal areas and increase in axonal density (Fig. ...
Citations
... These techniques provide unique ways for exploring microstructural alterations in the brain and offer noninvasive opportunities to monitor the progression of neurodegenerative disorders. 21,22 Furthermore, dMRI tractography enables the visualisation of WM structures within the zebrafish brain, thereby enabling the precise examination of these anatomical structures. 23 To elucidate the precise involvement of TLR2 in regulating normal neurological functions and neuroinflammatory processes, we employed TLR2 knockout (KO) (tlr2 À/À ) zebrafish as a model organism. ...
... 65 An increase in potential biomarkers of oedema such as aquaporin 4 (AQP4), which regulate brain water and CSF water movement, have been detected in models of neurodegeneration disease. 21 It is intriguing that an increase in cortical thickness in asymptomatic mutation carriers was reported along with a substantial reduction in the mean diffusivity, almost a decade prior to the predicted clinical onset, 48 a finding that parallels the alterations in cerebral volume and reduced diffusivity in the current study. In the present work, zebrafish were subjected to formalin fixation to mitigate degradation processes during analysis. ...
Toll‐like receptor 2 (TLR2) belongs to the TLR protein family that plays an important role in the immune and inflammation response system. While TLR2 is predominantly expressed in immune cells, its expression has also been detected in the brain, specifically in microglia and astrocytes. Recent studies indicate that genomic deletion of TLR2 can result in impaired neurobehavioural function. It is currently not clear if the genomic deletion of TLR2 leads to any alterations in the microstructural features of the brain. In the current study, we noninvasively assess microstructural changes in the brain of TLR2‐deficient ( tlr2 −/− ) zebrafish using state‐of‐the art magnetic resonance imaging (MRI) methods at ultrahigh magnetic field strength (17.6 T). A significant increase in cortical thickness and an overall trend towards increased brain volumes were observed in young tlr2 −/− zebrafish. An elevated T 2 relaxation time and significantly reduced apparent diffusion coefficient ( ADC ) unveil brain‐wide microstructural alterations, potentially indicative of cytotoxic oedema and astrogliosis in the tlr2 −/− zebrafish. Multicomponent analysis of the ADC diffusivity signal by the phasor approach shows an increase in the slow ADC component associated with restricted diffusion. Diffusion tensor imaging and diffusion kurtosis imaging analysis revealed diminished diffusivity and enhanced kurtosis in various white matter tracks in tlr2 −/− compared with control zebrafish, identifying the microstructural underpinnings associated with compromised white matter integrity and axonal degeneration. Taken together, our findings demonstrate that the genomic deletion of TLR2 results in severe alterations to the microstructural features of the zebrafish brain. This study also highlights the potential of ultrahigh field diffusion MRI techniques in discerning exceptionally fine microstructural details within the small zebrafish brain, offering potential for investigating microstructural changes in zebrafish models of various brain diseases.
... This result is different from that reported in the dogs in this study where AD showed a decreasing trend toward the posterior cervical spinal cord and an increasing trend toward the upper thoracic spinal cord. Furthermore, FA values in the spinal cord of mice and rats are almost the same in the cervical and thoracic spinal cord, which differs from that in dogs and humans [14,15]. These findings suggest that normal variation in DTI parameters differs in varying degrees among species due to anatomical and histological differences. ...
This study aimed to determine the characteristics and reference values of each vertebra in the cervicothoracic region by performing diffusion tensor imaging (DTI) scans and analyzing DTI parameters in normal Beagle dogs. In five adult Beagles under anesthetic maintenance, DTI was performed using a 1.5-T magnetic resonance imaging (MRI) scanner. Axial DTI was performed using three overlapping slabs to cover the cervical and thoracic spinal cords. After post-processing, DTI parameters were calculated along the entire spinal cord. Among DTI parameters, fractional anisotropy, relative anisotropy, and axonal diffusivity significantly decreased in the caudal direction. However, the apparent diffusion coefficient, radial diffusivity, and mean diffusivity values were not significantly correlated with vertebral levels. We provide evidence for the existence of segment-dependent DTI parameters in the canine cervical spinal cord. Therefore, comparisons of DTI parameters between lesions at different vertebral levels should be avoided unless normative data are available. Furthermore, the DTI data obtained in this study may contribute to the development of a clinical reference for spinal cord evaluation in dogs using DTI parameters.
... dMRI is among the foremost innovative imaging techniques, capable of providing distinct information on neuronal tissue microstructure and composition (Gatto et al., 2018). As such, tissue-specific metrics derived from dMRI continue to prove to be of high interest to the neuroimaging community. ...
The global phenomenon of increased life expectancies in humans is attributable to advances in medical care. The incidence of neurodegenerative diseases (NDDs) goes hand-in-hand with having a larger aging population. Non-invasive imaging techniques provide opportunities to monitor the progression of NDDs and assess treatment response. The development of novel methodologies, especially those over the past few decades, lead to new knowledge and more insightful measurements of brain changes. In particular, medical imaging techniques have become forerunners in translation and routine adoption for clinical practice. In this Research Topic, we explore new insights brought by technological advances such as high-density EEG recordings, novel biomarkers derived from relaxometry and diffusion MRI, AI-powered image analysis for microbleed detection, and translatability of animal models of brain and spine injury.
... This could reinforce the theory that micro diffusivity changes captured by MD are more related to extracellular compartment anomalies that could be an independent finding of axonal degeneration not detected by the tractography reconstructions. Another possible explanation could reside in the difference between the voxel size and biological ultrastructure scales, which makes it extremely challenging to detect early WM changes, even with high magnetic fields (Gatto et al., 2018;Gatto et al., 2019). Therefore, partial volume effects need to be considered when diffusion MRI and other imaging techniques need to be compared (Alexander et al., 2001). ...
Background
Progressive supranuclear palsy (PSP) is a 4-repeat tauopathy with neurodegeneration typically observed in the superior cerebellar peduncle (SCP) and dentatorubrothalamic tracts (DRTT). However, it is unclear how these tracts are differentially affected in different clinical variants of PSP.
Objectives
To determine whether diffusion tractography of the SCP and DRTT can differentiate autopsy-confirmed PSP with Richardson’s syndrome (PSP-RS) and PSP with predominant speech/language disorder (PSP-SL).
Methods
We studied 22 autopsy-confirmed PSP patients that included 12 with PSP-RS and 10 with PSP-SL. We compared these two groups to 11 patients with autopsy-confirmed Alzheimer’s disease with SL problems, i.e., logopenic progressive aphasia (AD-LPA) (disease controls) and 10 healthy controls. Whole brain tractography was performed to identify the SCP and DRTT, as well as the frontal aslant tract and superior longitudinal fasciculus. We assessed fractional anisotropy and mean diffusivity for each tract. Hierarchical linear modeling was used for statistical comparisons, and correlations were assessed with clinical disease severity, ocular motor impairment, and parkinsonism. DRTT connectomics matrix analysis was also performed across groups.
Results
The SCP showed decreased fractional anisotropy for PSP-RS and PSP-SL and increased mean diffusivity in PSP-RS, compared to controls and AD-LPA. Right DRTT fibers showed lower fractional anisotropy in PSP-RS and PSP-SL compared to controls and AD-LPA, with PSP-RS also showing lower values compared to PSP-SL. Reductions in connectivity were observed in infratentorial DRTT regions in PSP-RS vs cortical regions in PSP-SL. PSP-SL showed greater abnormalities in the frontal aslant tract and superior longitudinal fasciculus compared to controls, PSP-RS, and AD-LPA. Significant correlations were observed between ocular motor impairment and SCP in PSP-RS (p=0.042), and DRTT in PSP-SL (p=0.022). In PSP-SL, the PSP Rating Scale correlated with the SCP (p=0.045) and DRTT (p=0.008), and the Unified Parkinson’s Disease Rating Scale correlated with the DRTT (p=0.014).
Conclusions
Degeneration of the SCP and DRTT are diagnostic features of both PSP-RS and PSP-SL and associations with clinical metrics validate the role of these tracts in PSP-related clinical features, particularly in PSP-SL.
... Further, in vivo studies in mammalian tissue using endogenous fluorescent axonal labels have been an additional strategy to unveil the relationships between the dMRI signals and WM microstructures. Such experimental strategy has been adopted to provide quantitative tissue validation of advanced dMRI biophysical model metrics (Sato et al 2017), or to study the sensitivity of dMRI metrics for early detection of presymptomatic degenerative neurological diseases (Gatto et al 2018a, Gatto et al 2018b. ...
Diffusion MRI (dMRI) tractography is currently the only imaging technique that allows for non-invasive delineation and visualisation of white matter (WM) tracts in vivo prompting rapid advances in related fields of brain MRI research in recent years. One of its major clinical applications is for pre-surgery planning and intraoperative image guidance in neurosurgery, where knowledge about the location of WM tracts nearby the surgical target can be helpful to guide surgical resection and optimise surgical outcomes. Surgical injuries to these WM tracts can lead to permanent neurological and functional deficits, making the accuracy of tractography reconstructions paramount. The quality of dMRI tractography is influenced by many modifiable factors, ranging from MRI data acquisition through to the post-processing of the tractography output, with the potential of error propagation based on decisions made at each and subsequent processing steps. Research over the last 25 years has significantly improved the anatomical accuracy of tractography. An updated review about tractography methodology in the context of neurosurgery is now timely given the thriving research activities in dMRI, to ensure more appropriate applications in the clinical neurosurgical realm. This article aims to review the dMRI physics, and tractography methodologies, highlighting recent advances to provide the key concepts of tractography-informed neurosurgery, with a focus on the general considerations, the current state of practice, technical challenges, potential advances, and future demands to this field.
... Other factors accounting for reduced branching by miR-124 upregulation may derive from miR-146a downregulation and its known influence on the cytoskeleton actin through ROCK1 [68]. Considering that axonal deterioration is one of the earliest events of MN degeneration [69] alterations in neuritic tree in mSOD1 MNs and by miR-124 upregulation may then precede neurodegeneration in ALS mice [67]. Reasons for miR-124 detrimental effects, in contrast with studies suggesting benefits, may reside on the functional differences of MNs relatively to neurons. ...
miRNA(miR)-124 is an important regulator of neurogenesis, but its upregulation in SOD1G93A motor neurons (mSOD1 MNs) was shown to associate with neurodegeneration and microglia activation. We used pre-miR-124 in wild-type (WT) MNs and anti-miR-124 in mSOD1 MNs to characterize the miR-124 pathological role. miR-124 overexpression in WT MNs produced a miRNA profile like that of mSOD1 MNs (high miR-125b; low miR-146a and miR-21), and similarly led to early apoptosis. Alterations in mSOD1 MNs were abrogated with anti-miR-124 and changes in their miRNAs mostly recapitulated by their secretome. Normalization of miR-124 levels in mSOD1 MNs prevented the dysregulation of neurite network, mitochondria dynamics, axonal transport, and synaptic signaling. Same alterations were observed in WT MNs after pre-miR-124 transfection. Secretome from mSOD1 MNs triggered spinal microglia activation, which was unno-ticed with that from anti-miR-124-modulated cells. Secretome from such modulated MNs, when added to SC organotypic cultures from mSOD1 mice in the early symptomatic stage, also coun-teracted the pathology associated to GFAP decrease, PSD-95 and CX3CL1-CX3CR1 signaling im-pairment, neuro-immune homeostatic imbalance, and enhanced miR-124 expression levels. Data suggest that miR-124 is implicated in MN degeneration and paracrine-mediated pathogenicity. We propose miR-124 as a new therapeutic target and a promising ALS biomarker in patient sub-populations.
... Advancements in MRI techniques have opened a new window of preclinical microstructural exploration in neuroanatomical regions particularly susceptible to HD ( Shim et al., 2019 ). Current improvements in gradient fields and imaging resolution have been able to non-invasively capture features, with improved accuracy in vivo and ex vivo at the early stages of neurodegenerative diseases ( Gatto et al., 2018a ;Gatto et al., 2018b ;Muller et al., 2020 ). The development of new diffusion MRI techniques has opened a new realm with a great number of parameters associated with microstructural anomalies in HD ( Rosas et al., 2006 ). ...
... Astrocytes undergo a series of morphological and functional changes (overall described as astrogliosis) mainly characterized by swelling of the cell body, presence of larger and thicker processes, as well as increasing GFAPexpression ( Pirici et al., 2009 ). Also, this cell type expresses AQP-4 channels and thus their role in water uptake as has been described for other NDDs ( Gatto et al., 2018a ). Specifically, in HD, astrocytes show inclusions of mutant HTT (mHTT) proteins that have been related to alterations of its components ( Cisbani and Cicchetti, 2012 ;Shin et al., 2005 ). ...
... Overall, UHFD-MRI is an exceptional tool to study structural neurodegenerative features in preclinical HD models ( Gatto et al., 2018a ) ( Fig. 12 ). However, the link between multiple macrostructural, microstructural, and neurochemical events are complex and still not well-understood. ...
Diffusion MRI (dMRI) has been able to detect early structural changes related to neurological symptoms present in Huntington's disease (HD). However, there is still a knowledge gap to interpret the biological significance at early neuropathological stages. The purpose of this study is two-fold: (i) establish if the combination of Ultra-High Field Diffusion MRI (UHFD-MRI) techniques can add a more comprehensive analysis of the early microstructural changes observed in HD, and (ii) evaluate if early changes in dMRI microstructural parameters can be linked to cellular biomarkers of neuroinflammation. Using an ultra-high field magnet (16.7T), diffusion tensor imaging (DTI), and neurite orientation dispersion and density imaging (NODDI) techniques were applied to fixed ex-vivo brains of a preclinical model of HD (R6/1 mice). Fractional anisotropy (FA) was decreased in deep and superficial grey matter (GM) as well as white matter (WM) brain regions with well-known early HD microstructure and connectivity pathology. NODDI parameters associated with the intracellular and extracellular compartment, such as intracellular ventricular fraction (ICVF), orientation dispersion index (ODI), and isotropic volume fractions (IsoVF) were altered in R6/1 mice GM. Further, histological studies in these areas showed that glia cell markers associated with neuroinflammation (GFAP & Iba1) were consistent with the dMRI findings. dMRI can be used to extract non-invasive information of neuropathological events present in the early stages of HD. The combination of multiple imaging techniques represents a better approach to understand the neuropathological process allowing the early diagnosis and neuromonitoring of patients affected by HD.
... The effects of neuroprotective compounds can be measured in experimental biological systems using noninvasive imaging methods (Gatto et al., 2015). In that regard, the growing use of structural diffusion magnetic resonance imaging (dMRI) technologies and the increasing development of high magnetic fields (Gatto et al., 2018) have been some of the rapidly evolving features of this technology,and one of the most promising tools in neurosciences, particularly applied to (in vivo) NP research . Recently, to address some of the limitations associated with monoexponential diffusion models like diffusion tensor imaging (DTI) , new sequences have been developed to explore inhomogeneous biological media (GM brain tissue) utilizing alternative non-Gaussian diffusion models (Gatto et al., 2019). ...
Neuroplasticity (NP) has been defined as the neurobiological ability of the central nervous system to adjust its physiological functions in response to a continuously changing environment. Although this concept can be also extrapolated to changes in different molecular pathways at the unicellular level, in multicellular organ isms NP leads to the formation of new neural connections, rewiring cortical and subcortical circuits to adapt and survive. NP has been accepted as a sound theoretical basis for some therapies such as re
habilitation after stroke (Asakawa et al., 2017), transcranial magnetic stimulation (Kim et al., 2020), and deep brain stimulation (Asakawa et al., 2019). In the last decades, several discoveries and technical advances across multiple scientific areas have gained new insights on the theme of cortical plasticity. Thus, harnessing the potential of this endogenous biological self-repairing process and restoring brain functionality in the context of acute and chronic neurological diseases has been one of the key promises for translational therapeutic strategies. In this research topic, we intended to recapitulate some of the most recently molecular, technological, and modern medical approaches in the field of cortical plasticity. Hence, seven articles from different perspectives were in cluded in the special issue "Exploration of mechanisms in cortical plasticity''.
... evaluation FA decreased with more severe lesions whereas the MD results remained similar across groups. Direct spinal cord histopathological correlation with in vivo DTI metrics has previously only been performed in rodent models of ALS and has never been described in studies of spontaneous ALS in humans.39,40 Our study is the first to directly compare histopathology with DTI metrics in a spontaneous ALS model and provides preliminary evidence for future research to validate these methods.Diffusion tensor imaging is an advanced MRI technique that increasingly has been incorporated into clinical evaluations of humans with neurological disease.41 ...
Background
Degenerative myelopathy (DM) in dogs is a progressive neurodegenerative condition that causes white matter spinal cord lesions. These lesions are undetectable on standard magnetic resonance imaging (MRI), limiting diagnosis and monitoring of the disease. Spinal cord lesions cause disruption to the structural integrity of the axons causing water diffusion to become more random and less anisotropic. These changes are detectable by the technique of diffusion tensor imaging (DTI) which is highly sensitive to diffusion alterations secondary to white matter lesion development.
Objective
Perform spinal DTI on cohorts of dogs with and without DM to identify if lesions caused by DM will cause a detectable alteration in spinal cord diffusivity that correlates with neurological status.
Animals
Thirteen dogs with DM and 13 aged‐matched controls.
Methods
All animals underwent MRI with DTI of the entire spine. Diffusivity parameters fractional anisotropy (FA) and mean diffusivity (MD) were measured at each vertebral level and statistically compared between groups.
Results
Dogs with DM had significant decreases in FA within the regions of the spinal cord that had high expected lesion load. Decreases in FA were most significant in dogs with severe forms of the disease and correlated with neurological grade.
Conclusions and Clinical Importance
Findings suggest that FA has the potential to be a biomarker for spinal cord lesion development in DM and could play an important role in improving diagnosis and monitoring of this condition.
... Some of them are related to changes in axonal structure or possibly to structures part of myelinproducing cells. Despite these incredible capabilities, the possibility of DTI to dissect NP-related events at the sub voxel level is substantially limited due to: a) the significantly lower resolution compared with standard optical imaging techniques, b) the assumption of homogenous diffusivity along the voxel, and c) the limited histological co-registration and neuropathological validation (Gatto et al., 2018), all of them still a topic for further investigations and development (Gatto et al., 2020a). Although the use of DTI has been growing exponentially in the neuroscience field (Mori and Zhang, 2006), the interpretations of each diffusivity indices and their biological significance should be held with extreme caution due to a significant amount of limitations. ...
... Although in vivo MRI, animal imaging is an excellent tool to acquire images at high-resolution in physiologically intact mechanisms, it still needs to be biologically validated further to add more solid ground in NP translational research (Gatto et al., 2018). Unfortunately, a limited amount of work has been done to apply this MRI technology to strictly explore potential neuro repair strategies or modulation of neuroplasticity mechanisms in NDDs preclinical models (Table S3). ...
Advances in the understanding of genetic and molecular mechanisms and imaging technologies have opened a new window of research possibilities to address dynamic processes associated with neuroplasticity in physiologically intact models of neurodegenerative diseases. This review aims to: (i) establish the most relevant molecular mechanisms, as well as cellular and structural biomarkers in the study of neuroplasticity; (ii) introduce different neurodegenerative diseases in animal models that contribute to our knowledge of neuroplasticity; and (iii) illustrate the capabilities and limitations of current diffusion magnetic resonance imaging techniques to study cortical plasticity, as well as the use of alternative diffusion models.
