Mapping astrogliosis in the individual human brain using multidimensional MRI.

There are currently no non-invasive imaging methods available for astrogliosis assessment or mapping in the central nervous system despite its essential role in the response to many disease states, such as infarcts, neurodegenerative conditions, traumatic brain injury and infection. Multidimensional MRI is an increasingly employed imaging modality that maximizes the amount of encoded chemical and microstructural information by probing relaxation (T1 and T2) and diffusion mechanisms simultaneously. Here, we harness the exquisite sensitivity of this imagining modality to derive a signature of astrogliosis and disentangle it from normative brain at the individual level using machine learning. We investigated ex vivo cerebral cortical tissue specimens derived from seven subjects who sustained blast-induced injuries, which resulted in scar-border forming astrogliosis without being accompanied by other types of neuropathological abnormality, and from seven control brain donors. By performing a combined post-mortem radiology and histopathology correlation study we found that astrogliosis induces microstructural and chemical changes that are robustly detected with multidimensional MRI, and which can be attributed to astrogliosis because no axonal damage, demyelination or tauopathy were histologically observed in any of the cases in the study. Importantly, we showed that no one-dimensional T1, T2 or diffusion MRI measurement can disentangle the microscopic alterations caused by this neuropathology. Based on these findings, we developed a within-subject anomaly detection procedure that generates MRI-based astrogliosis biomarker maps ex vivo, which were significantly and strongly correlated with co-registered histological images of increased glial fibrillary acidic protein deposition (r = 0.856, P < 0.0001; r = 0.789, P < 0.0001; r = 0.793, P < 0.0001, for diffusion-T2, diffusion-T1 and T1-T2 multidimensional data sets, respectively). Our findings elucidate the underpinning of MRI signal response from astrogliosis, and the demonstrated high spatial sensitivity and specificity in detecting reactive astrocytes at the individual level, and if reproduced in vivo, will significantly impact neuroimaging studies of injury, disease, repair and aging, in which astrogliosis has so far been an invisible process radiologically.

Diffuse axonal injury has a characteristic multidimensional MRI signature in the human brain.

Axonal injury is a major contributor to the clinical symptomatology in patients with traumatic brain injury. Conventional neuroradiological tools, such as CT and MRI, are insensitive to diffuse axonal injury (DAI) caused by trauma. Diffusion tensor MRI parameters may change in DAI lesions; however, the nature of these changes is inconsistent. Multidimensional MRI is an emerging approach that combines T1, T2, and diffusion, and replaces voxel-averaged values with distributions, which allows selective isolation of specific potential abnormal components. By performing a combined post-mortem multidimensional MRI and histopathology study, we aimed to investigate T1-T2-diffusion changes linked to DAI and to define their histopathological correlates. Corpora callosa derived from eight subjects who had sustained traumatic brain injury, and three control brain donors underwent post-mortem ex vivo MRI at 7 T. Multidimensional, diffusion tensor, and quantitative T1 and T2 MRI data were acquired and processed. Following MRI acquisition, slices from the same tissue were tested for amyloid precursor protein (APP) immunoreactivity to define DAI severity. A robust image co-registration method was applied to accurately match MRI-derived parameters and histopathology, after which 12 regions of interest per tissue block were selected based on APP density, but blind to MRI. We identified abnormal multidimensional T1-T2, diffusion-T2, and diffusion-T1 components that are strongly associated with DAI and used them to generate axonal injury images. We found that compared to control white matter, mild and severe DAI lesions contained significantly larger abnormal T1-T2 component (P = 0.005 and P < 0.001, respectively), and significantly larger abnormal diffusion-T2 component (P = 0.005 and P < 0.001, respectively). Furthermore, within patients with traumatic brain injury the multidimensional MRI biomarkers differentiated normal-appearing white matter from mild and severe DAI lesions, with significantly larger abnormal T1-T2 and diffusion-T2 components (P = 0.003 and P < 0.001, respectively, for T1-T2; P = 0.022 and P < 0.001, respectively, for diffusion-T2). Conversely, none of the conventional quantitative MRI parameters were able to differentiate lesions and normal-appearing white matter. Lastly, we found that the abnormal T1-T2, diffusion-T1, and diffusion-T2 components and their axonal damage images were strongly correlated with quantitative APP staining (r = 0.876, P < 0.001; r = 0.727, P < 0.001; and r = 0.743, P < 0.001, respectively), while producing negligible intensities in grey matter and in normal-appearing white matter. These results suggest that multidimensional MRI may provide non-invasive biomarkers for detection of DAI, which is the pathological substrate for neurological disorders ranging from concussion to severe traumatic brain injury.

Pharmacokinetics of Single Domain Antibodies and Conjugated Nanoparticles Using a Hybrid near Infrared Method.

Iron oxide nanoparticles and single domain antibodies from camelids (VHHs) have been increasingly recognized for their potential uses for medical diagnosis and treatment. However, there have been relatively few detailed characterizations of their pharmacokinetics (PK). The aim of this study was to develop imaging methods and pharmacokinetic models to aid the future development of a novel family of brain MRI molecular contrast agents. An efficient near-infrared (NIR) imaging method was established to monitor VHH and VHH conjugated nanoparticle kinetics in mice using a hybrid approach: kinetics in blood were assessed by direct sampling, and kinetics in kidney, liver, and brain were assessed by serial in vivo NIR imaging. These studies were performed under "basal" circumstances in which the VHH constructs and VHH-conjugated nanoparticles do not substantially interact with targets nor cross the blood brain barrier. Using this approach, we constructed a five-compartment PK model that fits the data well for single VHHs, engineered VHH trimers, and iron oxide nanoparticles conjugated to VHH trimers. The establishment of the feasibility of these methods lays a foundation for future PK studies of candidate brain MRI molecular contrast agents.

Use of Repetitive Transcranial Magnetic Stimulation in the Treatment of Neuropsychiatric and Neurocognitive Symptoms Associated With Concussion in Military Populations.

BACKGROUND: Since the year 2000, over 342 000 military service members have experienced a concussion, often associated with chronic neuropsychiatric and neurocognitive symptoms. Repetitive transcranial magnetic stimulation (rTMS) protocols have been developed for many of these symptoms in the general population. OBJECTIVE: To conduct a scoping review of the literature on rTMS for neuropsychological and neurocognitive symptoms following concussion. METHODS: PubMed and Google Scholar search engines identified 9 articles, written in English, corresponding to the search terms TBI or concussion; and TMS or rTMS; and depression, PTSD, or cognition. Studies that were not therapeutic trials or case reports, did not have neuropsychiatric or neurocognitive primary outcome measures, or described samples where 80% or more of the cohort did not have a TBI were excluded. RESULTS: There were no reports of seizures nor difference in the frequency or quality of other adverse events as compared with the broader rTMS literature, supporting the safety of rTMS in this population. Support for the efficacy of rTMS for the treatment of neuropsychiatric and neurocognitive symptoms, in this population, is limited. CONCLUSIONS: Large-scale, innovative, neuroscience-informed protocols are recommended to elucidate the potential utility of rTMS for the complex neuropsychiatric and neurocognitive symptoms associated with military concussions.

Individualized Connectome-Targeted Transcranial Magnetic Stimulation for Neuropsychiatric Sequelae of Repetitive Traumatic Brain Injury in a Retired NFL Player.

OBJECTIVE: The recent advent of individualized resting-state network mapping (RSNM) has revealed substantial interindividual variability in anatomical localization of brain networks identified by using resting-state functional MRI (rsfMRI). RSNM enables personalized targeting of focal neuromodulation techniques such as repetitive transcranial magnetic stimulation (rTMS). rTMS is believed to exert antidepressant efficacy by modulating connectivity between the stimulation site, the default mode network (DMN), and the subgenual anterior cingulate cortex (sgACC). Personalized rTMS may be particularly useful after repetitive traumatic brain injury (TBI), which is associated with neurodegenerative tauopathy in medial temporal limbic structures. These degenerative changes are believed to be related to treatment-resistant neurobehavioral disturbances observed in many retired athletes. METHODS: The authors describe a case in which RSNM was successfully used to target rTMS to treat these neuropsychiatric disturbances in a retired NFL defensive lineman whose symptoms were not responsive to conventional treatments. RSNM was used to identify left-right dorsolateral prefrontal rTMS targets with maximal difference between dorsal attention network and DMN correlations. These targets were spatially distinct from those identified by prior methods. Twenty sessions of left-sided excitatory and right-sided inhibitory rTMS were administered at these targets. RESULTS: Treatment led to improvement in Montgomery-Åsberg Depression Rating Scale (72%), cognitive testing, and headache scales scores. Compared with healthy individuals and subjects with TBI-associated depression, baseline rsfMRI revealed substantially elevated DMN connectivity with the medial temporal lobe (MTL). Serial rsfMRI scans revealed gradual improvement in MTL-DMN connectivity and stimulation site connectivity with sgACC. CONCLUSIONS: These results highlight the possibility of individualized neuromodulation and biomarker-based monitoring for neuropsychiatric sequelae of repetitive TBI.

Traumatic brain injury in the prodromal period of Parkinson's disease: A large epidemiological study using medicare data.

OBJECTIVE: Studies suggest a greater risk of Parkinson's disease (PD) after traumatic brain injury (TBI), but it is possible that the risk of TBI is greater in the prodromal period of PD. We aimed to examine the time-to-TBI in PD patients in their prodromal period compared to population-based controls. METHODS: We identified 89,790 incident PD cases and 118,095 comparable controls aged > 65 years in 2009 using Medicare claims data. Using data from the preceding 5 years, we compared time-to-TBI in PD patients in their prodromal period to controls. We estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for TBI in a Cox regression, while adjusting for age, sex, race/ethnicity, modified Charlson comorbidity index, smoking, and alcohol use. RESULTS: Risk of TBI was greater in PD patients in their prodromal period across all age and sex groups, with HRs consistently increasing with proximity to PD diagnosis. HRs ranged from 1.64 (95% CI, 1.52, 1.77) 5 years preceding diagnosis to 3.93 (95% CI, 3.74, 4.13) in the year before. The interaction between PD, TBI, and time was primarily observed for TBI attributed to falls. Motor dysfunction and cognitive impairment, suggested by corresponding International Classification of Diseases, Ninth Revision codes, partially mediated the PD-TBI association. INTERPRETATION: There is a strong association between PD and a recent TBI in the prodromal period of PD. This association strengthens as PD diagnosis approaches and may be a result of undetected nonmotor and motor symptoms, but confirmation will be required. Ann Neurol 2017;82:744-754.

Astrocytic degeneration in chronic traumatic encephalopathy.

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repeated head traumas. Using immunohistochemistry for glial fibrillary acidic protein as a marker, plus automated quantitative analysis, we examined the characteristics and extent of astrogliosis present in stage III and IV CTE, along with Alzheimer's disease (AD), and frontotemporal dementia (FTD) cases. Astrogliosis in CTE patients was more diffuse compared to that of AD and FTD patients, which was concentrated in the sulcal depths. Of 14 patients with CTE, 10 exhibited signs of a degenerating astrocyte pathology, characterized by beaded, broken astrocytic processes. This astrocytic degeneration was typically found to be diffuse throughout the white matter, although two cases demonstrated astrocytic degeneration in the gray matter. The degeneration was also observed in 2 of 3 AD and 2 of 3 FTD brains, with overall similar characteristics across diseases. There was minimal to no astrocytic degeneration in six age-matched controls with no neurodegenerative disease. We found that the extent of the white matter astrocytic degeneration was strongly correlated with the level of overall astrogliosis in both the white and gray matter. However, astrocytic degeneration was not correlated with the overall extent of tau pathology. Specifically, there was no correlation between levels of p-tau in the sulcal depths and astrocytic degeneration in the white matter adjacent to the sulcal depths. Thus, astrocytic degeneration and overall astrogliosis appear to represent distinct pathological features of CTE. Further investigation into these astroglial pathologies could provide new insights into underlying disease mechanisms and represent a potential target for in vivo assessment of CTE as well as other neurodegenerative disorders.

Quantitative validation of a nonlinear histology-MRI coregistration method using generalized Q-sampling imaging in complex human cortical white matter.

Advanced diffusion MRI methods have recently been proposed for detection of pathologies such as traumatic axonal injury and chronic traumatic encephalopathy which commonly affect complex cortical brain regions. However, radiological-pathological correlations in human brain tissue that detail the relationship between the multi-component diffusion signal and underlying pathology are lacking. We present a nonlinear voxel based two dimensional coregistration method that is useful for matching diffusion signals to quantitative metrics of high resolution histological images. When validated in ex vivo human cortical tissue at a 250×250×500 µm spatial resolution, the method proved robust in correlations between generalized q-sampling imaging and histologically based white matter fiber orientations, with r=0.94 for the primary fiber direction and r=0.88 for secondary fiber direction in each voxel. Importantly, however, the correlation was substantially worse with reduced spatial resolution or with fiber orientations derived using a diffusion tensor model. Furthermore, we have detailed a quantitative histological metric of white matter fiber integrity termed power coherence capable of distinguishing architecturally complex but intact white matter from disrupted white matter regions. These methods may allow for more sensitive and specific radiological-pathological correlations of neurodegenerative diseases affecting complex gray and white matter.

Axonal disruption in white matter underlying cortical sulcus tau pathology in chronic traumatic encephalopathy.

Chronic traumatic encephalopathy (CTE) is a progressive degenerative disorder associated with repetitive traumatic brain injury. One of the primary defining neuropathological lesions in CTE, based on the first consensus conference, is the accumulation of hyperphosphorylated tau in gray matter sulcal depths. Post-mortem CTE studies have also reported myelin loss, axonal injury and white matter degeneration. Currently, the diagnosis of CTE is restricted to post-mortem neuropathological analysis. We hypothesized that high spatial resolution advanced diffusion MRI might be useful for detecting white matter microstructural changes directly adjacent to gray matter tau pathology. To test this hypothesis, formalin-fixed post-mortem tissue blocks from the superior frontal cortex of ten individuals with an established diagnosis of CTE were obtained from the Veterans Affairs-Boston University-Concussion Legacy Foundation brain bank. Advanced diffusion MRI data was acquired using an 11.74 T MRI scanner at Washington University with 250 × 250 × 500 µm3 spatial resolution. Diffusion tensor imaging, diffusion kurtosis imaging and generalized q-sampling imaging analyses were performed in a blinded fashion. Following MRI acquisition, tissue sections were tested for phosphorylated tau immunoreactivity in gray matter sulcal depths. Axonal disruption in underlying white matter was assessed using two-dimensional Fourier transform analysis of myelin black gold staining. A robust image co-registration method was applied to accurately quantify the relationship between diffusion MRI parameters and histopathology. We found that white matter underlying sulci with high levels of tau pathology had substantially impaired myelin black gold Fourier transform power coherence, indicating axonal microstructural disruption (r = -0.55, p = 0.0015). Using diffusion tensor MRI, we found that fractional anisotropy (FA) was modestly (r = 0.53) but significantly (p = 0.0012) correlated with axonal disruption, where lower FA was associated with greater axonal disruption in white matter directly adjacent to hyperphosphorylated tau positive sulci. In summary, our findings indicate that axonal disruption and tau pathology are closely associated, and high spatial resolution ex vivo diffusion MRI has the potential to detect microstructural alterations observed in CTE tissue. Future studies will be required to determine whether this approach can be applied to living people.

Alzheimer's Toxic Amyloid Beta Oligomers: Unwelcome Visitors to the Na/K ATPase alpha3 Docking Station.

Toxic amyloid beta oligomers (AßOs) are known to accumulate in Alzheimer's disease (AD) and in animal models of AD. Their structure is heterogeneous, and they are found in both intracellular and extracellular milieu. When given to CNS cultures or injected ICV into non-human primates and other non-transgenic animals, AßOs have been found to cause impaired synaptic plasticity, loss of memory function, tau hyperphosphorylation and tangle formation, synapse elimination, oxidative and ER stress, inflammatory microglial activation, and selective nerve cell death. Memory loss and pathology in transgenic models are prevented by AßO antibodies, while Aducanumab, an antibody that targets AßOs as well as fibrillar Aß, has provided cognitive benefit to humans in early clinical trials. AßOs have now been investigated in more than 3000 studies and are widely thought to be the major toxic form of Aß. Although much has been learned about the downstream mechanisms of AßO action, a major gap concerns the earliest steps: How do AßOs initially interact with surface membranes to generate neuron-damaging transmembrane events? Findings from Ohnishi et al (PNAS 2005) combined with new results presented here are consistent with the hypothesis that AßOs act as neurotoxins because they attach to particular membrane protein docks containing Na/K ATPase-α3, where they inhibit ATPase activity and pathologically restructure dock composition and topology in a manner leading to excessive Ca++ build-up. Better understanding of the mechanism that makes attachment of AßOs to vulnerable neurons a neurotoxic phenomenon should open the door to therapeutics and diagnostics targeting the first step of a complex pathway that leads to neural damage and dementia.

Experimental subarachnoid haemorrhage results in multifocal axonal injury.

The great majority of acute brain injury results from trauma or from disorders of the cerebrovasculature, i.e. ischaemic stroke or haemorrhage. These injuries are characterized by an initial insult that triggers a cascade of injurious cellular processes. The nature of these processes in spontaneous intracranial haemorrhage is poorly understood. Subarachnoid haemorrhage, a particularly deadly form of intracranial haemorrhage, shares key pathophysiological features with traumatic brain injury including exposure to a sudden pressure pulse. Here we provide evidence that axonal injury, a signature characteristic of traumatic brain injury, is also a prominent feature of experimental subarachnoid haemorrhage. Using histological markers of membrane disruption and cytoskeletal injury validated in analyses of traumatic brain injury, we show that axonal injury also occurs following subarachnoid haemorrhage in an animal model. Consistent with the higher prevalence of global as opposed to focal deficits after subarachnoid haemorrhage and traumatic brain injury in humans, axonal injury in this model is observed in a multifocal pattern not limited to the immediate vicinity of the ruptured artery. Ultrastructural analysis further reveals characteristic axonal membrane and cytoskeletal changes similar to those associated with traumatic axonal injury. Diffusion tensor imaging, a translational imaging technique previously validated in traumatic axonal injury, from these same specimens demonstrates decrements in anisotropy that correlate with histological axonal injury and functional outcomes. These radiological indicators identify a fibre orientation-dependent gradient of axonal injury consistent with a barotraumatic mechanism. Although traumatic and haemorrhagic acute brain injury are generally considered separately, these data suggest that a signature pathology of traumatic brain injury-axonal injury-is also a functionally significant feature of subarachnoid haemorrhage, raising the prospect of common diagnostic, prognostic, and therapeutic approaches to these conditions.

Acute post-traumatic stress symptoms and age predict outcome in military blast concussion.

High rates of adverse outcomes have been reported following blast-related concussive traumatic brain injury in US military personnel, but the extent to which such adverse outcomes can be predicted acutely after injury is unknown. We performed a prospective, observational study of US military personnel with blast-related concussive traumatic brain injury (n = 38) and controls (n = 34) enrolled between March and September 2012. Importantly all subjects returned to duty and did not require evacuation. Subjects were evaluated acutely 0-7 days after injury at two sites in Afghanistan and again 6-12 months later in the United States. Acute assessments revealed heightened post-concussive, post-traumatic stress, and depressive symptoms along with worse cognitive performance in subjects with traumatic brain injury. At 6-12 months follow-up, 63% of subjects with traumatic brain injury and 20% of controls had moderate overall disability. Subjects with traumatic brain injury showed more severe neurobehavioural, post-traumatic stress and depression symptoms along with more frequent cognitive performance deficits and more substantial headache impairment than control subjects. Logistic regression modelling using only acute measures identified that a diagnosis of traumatic brain injury, older age, and more severe post-traumatic stress symptoms provided a good prediction of later adverse global outcomes (area under the receiver-operating characteristic curve = 0.84). Thus, US military personnel with concussive blast-related traumatic brain injury in Afghanistan who returned to duty still fared quite poorly on many clinical outcome measures 6-12 months after injury. Poor global outcome seems to be largely driven by psychological health measures, age, and traumatic brain injury status. The effects of early interventions and longer term implications of these findings are unknown.

Quantitative assessments of traumatic axonal injury in human brain: concordance of microdialysis and advanced MRI.

Axonal injury is a major contributor to adverse outcomes following brain trauma. However, the extent of axonal injury cannot currently be assessed reliably in living humans. Here, we used two experimental methods with distinct noise sources and limitations in the same cohort of 15 patients with severe traumatic brain injury to assess axonal injury. One hundred kilodalton cut-off microdialysis catheters were implanted at a median time of 17 h (13-29 h) after injury in normal appearing (on computed tomography scan) frontal white matter in all patients, and samples were collected for at least 72 h. Multiple analytes, such as the metabolic markers glucose, lactate, pyruvate, glutamate and tau and amyloid-ß proteins, were measured every 1-2 h in the microdialysis samples. Diffusion tensor magnetic resonance imaging scans at 3 T were performed 2-9 weeks after injury in 11 patients. Stability of diffusion tensor imaging findings was verified by repeat scans 1-3 years later in seven patients. An additional four patients were scanned only at 1-3 years after injury. Imaging abnormalities were assessed based on comparisons with five healthy control subjects for each patient, matched by age and sex (32 controls in total). No safety concerns arose during either microdialysis or scanning. We found that acute microdialysis measurements of the axonal cytoskeletal protein tau in the brain extracellular space correlated well with diffusion tensor magnetic resonance imaging-based measurements of reduced brain white matter integrity in the 1-cm radius white matter-masked region near the microdialysis catheter insertion sites. Specifically, we found a significant inverse correlation between microdialysis measured levels of tau 13-36 h after injury and anisotropy reductions in comparison with healthy controls (Spearman's r = -0.64, P = 0.006). Anisotropy reductions near microdialysis catheter insertion sites were highly correlated with reductions in multiple additional white matter regions. We interpret this result to mean that both microdialysis and diffusion tensor magnetic resonance imaging accurately reflect the same pathophysiological process: traumatic axonal injury. This cross-validation increases confidence in both methods for the clinical assessment of axonal injury. However, neither microdialysis nor diffusion tensor magnetic resonance imaging have been validated versus post-mortem histology in humans. Furthermore, future work will be required to determine the prognostic significance of these assessments of traumatic axonal injury when combined with other clinical and radiological measures.

The pathophysiology of repetitive concussive traumatic brain injury in experimental models; new developments and open questions.

In recent years, there has been an increasing interest in the pathophysiology of repetitive concussive traumatic brain injury (rcTBI) in large part due to the association with dramatic cases of progressive neurological deterioration in professional athletes, military personnel, and others. However, our understanding of the pathophysiology of rcTBI is less advanced than for more severe brain injuries. Most prominently, the mechanisms underlying traumatic axonal injury, microglial activation, amyloid-beta accumulation, and progressive tau pathology are not yet known. In addition, the role of injury to dendritic spine cytoskeletal structures, vascular reactivity impairments, and microthrombi are intriguing and subjects of ongoing inquiry. Methods for quantitative analysis of axonal injury, dendritic injury, and synaptic loss need to be refined for the field to move forward in a rigorous fashion. We and others are attempting to develop translational approaches to assess these specific pathophysiological events in both animals and humans to facilitate clinically relevant pharmacodynamic assessments of candidate therapeutics. In this article, we review and discuss several of the recent experimental results from our lab and others. We include new initial data describing the difficulty in modeling progressive tau pathology in experimental rcTBI, and results demonstrating that sertraline can alleviate social interaction deficits and depressive-like behaviors following experimental rcTBI plus foot shock stress. Furthermore, we propose a discrete set of open, experimentally tractable questions that may serve as a framework for future investigations. In addition, we also raise several important questions that are less experimentally tractable at this time, in hopes that they may stimulate future methodological developments to address them. This article is part of a Special Issue entitled "Traumatic Brain Injury".

RNA-sequencing reveals oligodendrocyte and neuronal transcripts in microglia relevant to central nervous system disease.

Expression profiling of distinct central nervous system (CNS) cell populations has been employed to facilitate disease classification and to provide insights into the molecular basis of brain pathology. One important cell type implicated in a wide variety of CNS disease states is the resident brain macrophage (microglia). In these studies, microglia are often isolated from dissociated brain tissue by flow sorting procedures [fluorescence-activated cell sorting (FACS)] or from postnatal glial cultures by mechanic isolation. Given the highly dynamic and state-dependent functions of these cells, the use of FACS or short-term culture methods may not accurately capture the biology of brain microglia. In the current study, we performed RNA-sequencing using Cx3cr1(+/GFP) labeled microglia isolated from the brainstem of 6-week-old mice to compare the transcriptomes of FACS-sorted versus laser capture microdissection (LCM). While both isolation techniques resulted in a large number of shared (common) transcripts, we identified transcripts unique to FACS-isolated and LCM-captured microglia. In particular, ∼50% of these LCM-isolated microglial transcripts represented genes typically associated with neurons and glia. While these transcripts clearly localized to microglia using complementary methods, they were not translated into protein. Following the induction of murine experimental autoimmune encephalomyelitis, increased oligodendrocyte and neuronal transcripts were detected in microglia, while only the myelin basic protein oligodendrocyte transcript was increased in microglia after traumatic brain injury. Collectively, these findings have implications for the design and interpretation of microglia transcriptome-based investigations.

Disrupted modular organization of resting-state cortical functional connectivity in U.S. military personnel following concussive 'mild' blast-related traumatic brain injury.

Blast-related traumatic brain injury (TBI) has been one of the "signature injuries" of the wars in Iraq and Afghanistan. However, neuroimaging studies in concussive 'mild' blast-related TBI have been challenging due to the absence of abnormalities in computed tomography or conventional magnetic resonance imaging (MRI) and the heterogeneity of the blast-related injury mechanisms. The goal of this study was to address these challenges utilizing single-subject, module-based graph theoretic analysis of resting-state functional MRI (fMRI) data. We acquired 20min of resting-state fMRI in 63 U.S. military personnel clinically diagnosed with concussive blast-related TBI and 21 U.S. military controls who had blast exposures but no diagnosis of TBI. All subjects underwent an initial scan within 90days post-injury and 65 subjects underwent a follow-up scan 6 to 12months later. A second independent cohort of 40 U.S. military personnel with concussive blast-related TBI served as a validation dataset. The second independent cohort underwent an initial scan within 30days post-injury. 75% of the scans were of good quality, with exclusions primarily due to excessive subject motion. Network analysis of the subset of these subjects in the first cohort with good quality scans revealed spatially localized reductions in the participation coefficient, a measure of between-module connectivity, in the TBI patients relative to the controls at the time of the initial scan. These group differences were less prominent on the follow-up scans. The 15 brain areas with the most prominent reductions in the participation coefficient were next used as regions of interest (ROIs) for single-subject analyses. In the first TBI cohort, more subjects than would be expected by chance (27/47 versus 2/47 expected, p<0.0001) had 3 or more brain regions with abnormally low between-module connectivity relative to the controls on the initial scans. On the follow-up scans, more subjects than expected by chance (5/37, p=0.044) but fewer subjects than on the initial scans had 3 or more brain regions with abnormally low between-module connectivity. Analysis of the second TBI cohort validation dataset with no free parameters provided a partial replication; again more subjects than expected by chance (8/31, p=0.006) had 3 or more brain regions with abnormally low between-module connectivity on the initial scans, but the numbers were not significant (2/27, p=0.276) on the follow-up scans. A single-subject, multivariate analysis by probabilistic principal component analysis of the between-module connectivity in the 15 identified ROIs, showed that 31/47 subjects in the first TBI cohort were found to be abnormal relative to the controls on the initial scans. In the second TBI cohort, 9/31 patients were found to be abnormal in identical multivariate analysis with no free parameters. Again, there were not substantial differences on the follow-up scans. Taken together, these results indicate that single-subject, module-based graph theoretic analysis of resting-state fMRI provides potentially useful information for concussive blast-related TBI if high quality scans can be obtained. The underlying biological mechanisms and consequences of disrupted between-module connectivity are unknown, thus further studies are required.

Detection of blast-related traumatic brain injury in U.S. military personnel.

BACKGROUND: Blast-related traumatic brain injuries have been common in the Iraq and Afghanistan wars, but fundamental questions about the nature of these injuries remain unanswered. METHODS: We tested the hypothesis that blast-related traumatic brain injury causes traumatic axonal injury, using diffusion tensor imaging (DTI), an advanced form of magnetic resonance imaging that is sensitive to axonal injury. The subjects were 63 U.S. military personnel who had a clinical diagnosis of mild, uncomplicated traumatic brain injury. They were evacuated from the field to the Landstuhl Regional Medical Center in Landstuhl, Germany, where they underwent DTI scanning within 90 days after the injury. All the subjects had primary blast exposure plus another, blast-related mechanism of injury (e.g., being struck by a blunt object or injured in a fall or motor vehicle crash). Controls consisted of 21 military personnel who had blast exposure and other injuries but no clinical diagnosis of traumatic brain injury. RESULTS: Abnormalities revealed on DTI were consistent with traumatic axonal injury in many of the subjects with traumatic brain injury. None had detectable intracranial injury on computed tomography. As compared with DTI scans in controls, the scans in the subjects with traumatic brain injury showed marked abnormalities in the middle cerebellar peduncles (P<0.001), in cingulum bundles (P=0.002), and in the right orbitofrontal white matter (P=0.007). In 18 of the 63 subjects with traumatic brain injury, a significantly greater number of abnormalities were found on DTI than would be expected by chance (P<0.001). Follow-up DTI scans in 47 subjects with traumatic brain injury 6 to 12 months after enrollment showed persistent abnormalities that were consistent with evolving injuries. CONCLUSIONS: DTI findings in U.S. military personnel support the hypothesis that blast-related mild traumatic brain injury can involve axonal injury. However, the contribution of primary blast exposure as compared with that of other types of injury could not be determined directly, since none of the subjects with traumatic brain injury had isolated primary blast injury. Furthermore, many of these subjects did not have abnormalities on DTI. Thus, traumatic brain injury remains a clinical diagnosis. (Funded by the Congressionally Directed Medical Research Program and the National Institutes of Health; ClinicalTrials.gov number, NCT00785304.).

Amyloid-ß oligomerization in Alzheimer dementia versus high-pathology controls.

OBJECTIVE: Although amyloid-beta (Aß) peptide deposition into insoluble plaques is a pathological hallmark of Alzheimer disease; soluble oligomeric Aß has been hypothesized to more directly underlie impaired learning and memory in dementia of the Alzheimer type. However, the lack of a sensitive, specific, and quantitative assay for Aß oligomers has hampered rigorous tests of this hypothesis. METHODS: We developed a plate-based single molecule counting fluorescence immunoassay for oligomeric Aß sensitive to low pg/ml concentrations of synthetic Aß dimers using the same Aß-specific monoclonal antibody to both capture and detect Aß. The Aß oligomer assay does not recognize monomeric Aß, amyloid precursor protein, or other non-Aß peptide oligomers. RESULTS: Aß oligomers were detected in aqueous cortical lysates from patients with dementia of the Alzheimer type and nondemented patients with Aß plaque pathology. However, Aß oligomer concentrations in demented patients' lysates were tightly correlated with Aß plaque coverage (r = 0.88), but this relationship was weaker in those from nondemented patients (r = 0.30) despite equivalent Aß plaque pathology. The ratio of Aß oligomer levels to plaque density fully distinguished demented from nondemented patients, with no overlap between groups in this derived variable. Other Aß and plaque measures did not distinguish demented from nondemented patients. Aß oligomers were not detected in cerebrospinal fluid with this assay. INTERPRETATION: The results raise the intriguing hypothesis that the linkage between plaques and oligomers may be a key pathophysiological event underlying dementia of the Alzheimer type. This Aß oligomer assay may be useful for many tests of the oligomer hypothesis.