Inclusions composed of α-synuclein (α-syn), i.e., Lewy bodies (LBs) and Lewy neurites (LNs), define synucleinopathies including Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Here, we ...demonstrate that preformed fibrils generated from full-length and truncated recombinant α-syn enter primary neurons, probably by adsorptive-mediated endocytosis, and promote recruitment of soluble endogenous α-syn into insoluble PD-like LBs and LNs. Remarkably, endogenous α-syn was sufficient for formation of these aggregates, and overexpression of wild-type or mutant α-syn was not required. LN-like pathology first developed in axons and propagated to form LB-like inclusions in perikarya. Accumulation of pathologic α-syn led to selective decreases in synaptic proteins, progressive impairments in neuronal excitability and connectivity, and, eventually, neuron death. Thus, our data contribute important insights into the etiology and pathogenesis of PD-like α-syn inclusions and their impact on neuronal functions, and they provide a model for discovering therapeutics targeting pathologic α-syn-mediated neurodegeneration.
► Internalized preformed fibrils cause α-syn to form inclusions in primary neurons ► Higher concentrations of endogenous presynaptic α-syn enhance inclusion formation ► Aggregates form first in axons and propagate throughout the entire neuron ► Parkinson-like inclusion formation impairs neuronal function and viability
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Although concussion is now recognized as a major health issue, its non-lethal nature has limited characterization of the underlying pathophysiology. In particular, potential neuropathological changes ...have typically been inferred from non-invasive techniques or post-mortem examinations of severe traumatic brain injury (TBI). Here, we used a swine model of head rotational acceleration based on human concussion to examine blood–brain barrier (BBB) integrity after injury in association with diffuse axonal injury and glial responses. We then determined the potential clinical relevance of the swine concussion findings through comparisons with pathological changes in human severe TBI, where post-mortem examinations are possible. At 6–72 h post-injury in swine, we observed multifocal disruption of the BBB, demonstrated by extravasation of serum proteins, fibrinogen and immunoglobulin-G, in the absence of hemorrhage or other focal pathology. BBB disruption was observed in a stereotyped distribution consistent with biomechanical insult. Specifically, extravasated serum proteins were frequently observed at interfaces between regions of tissue with differing material properties, including the gray–white boundary, periventricular and subpial regions. In addition, there was substantial overlap of BBB disruption with regions of axonal pathology in the white matter. Acute perivascular cellular uptake of blood-borne proteins was observed to be prominent in astrocytes (GFAP-positive) and neurons (MAP-2-positive), but not microglia (IBA1-positive). Parallel examination of human severe TBI revealed similar patterns of serum extravasation and glial uptake of serum proteins, but to a much greater extent than in the swine model, attributed to the higher injury severity. These data suggest that BBB disruption represents a new and important pathological feature of concussion.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•We present an open-source software for semi-automated analysis of fluorescent calcium imaging.•FluoroSNNAP, Fluorescence Single Neuron and Network Analysis Package, enables automated segmentation ...and calcium transient event detections.•Calcium dynamics of single-cells can be used to phenotype neurons.•FluoroSNNAP enables global and local synchronization cluster analysis.•FluoroSNNAP determines functional connectivity and allows graphical visualization.
Recent advances in genetically engineered calcium and membrane potential indicators provide the potential to estimate the activation dynamics of individual neurons within larger, mesoscale networks (100s–1000+neurons). However, a fully integrated automated workflow for the analysis and visualization of neural microcircuits from high speed fluorescence imaging data is lacking.
Here we introduce FluoroSNNAP, Fluorescence Single Neuron and Network Analysis Package. FluoroSNNAP is an open-source, interactive software developed in MATLAB for automated quantification of numerous biologically relevant features of both the calcium dynamics of single-cells and network activity patterns. FluoroSNNAP integrates and improves upon existing tools for spike detection, synchronization analysis, and inference of functional connectivity, making it most useful to experimentalists with little or no programming knowledge.
We apply FluoroSNNAP to characterize the activity patterns of neuronal microcircuits undergoing developmental maturation in vitro. Separately, we highlight the utility of single-cell analysis for phenotyping a mixed population of neurons expressing a human mutant variant of the microtubule associated protein tau and wild-type tau.
We show the performance of semi-automated cell segmentation using spatiotemporal independent component analysis and significant improvement in detecting calcium transients using a template-based algorithm in comparison to peak-based or wavelet-based detection methods. Our software further enables automated analysis of microcircuits, which is an improvement over existing methods.
We expect the dissemination of this software will facilitate a comprehensive analysis of neuronal networks, promoting the rapid interrogation of circuits in health and disease.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Biomechanics of concussion Meaney, David F; Smith, Douglas H
Clinics in sports medicine
30, Issue:
1
Journal Article
Peer reviewed
Open access
The rising awareness of the long-term health problems associated with concussions re-emphasizes the need for understanding the mechanical etiology of concussions. This article reviews past studies ...defining the common mechanisms for mild traumatic brain injury and summarizes efforts to convert the external input to the head (force, acceleration, and velocity) into estimates of motions and deformations of the brain that occur during mild traumatic brain injury. Studies of how these mechanical conditions contribute to the cellular mechanisms of damage in mild traumatic brain injury are reviewed. Finally, future directions for improving understanding concussion biomechanics are discussed.
Until recently, mild traumatic brain injury (mTBI) or "concussion" was generally ignored as a major health issue. However, emerging evidence suggests that this injury is by no means mild, considering ...it induces persisting neurocognitive dysfunction in many individuals. Although little is known about the pathophysiological aspects of mTBI, there is growing opinion that diffuse axonal injury (DAI) may play a key role. To explore this possibility, we adapted a model of head rotational acceleration in swine to produce mTBI by scaling the mechanical loading conditions based on available biomechanical data on concussion thresholds in humans. Using these input parameters, head rotational acceleration was induced in either the axial plane (transverse to the brainstem; n=3), causing a 10- to 35-min loss of consciousness, or coronal plane (circumferential to the brainstem; n=2), which did not produce a sustained loss of consciousness. Seven days following injury, immunohistochemical analyses of the brains revealed that both planes of head rotation induced extensive axonal pathology throughout the white matter, characterized as swollen axonal bulbs or varicosities that were immunoreactive for accumulating neurofilament protein. However, the distribution of the axonal pathology was different between planes of head rotation. In particular, more swollen axonal profiles were observed in the brainstems of animals injured in the axial plane, suggesting an anatomic substrate for prolonged loss of consciousness in mTBI. Overall, these data support DAI as an important pathological feature of mTBI, and demonstrate that surprisingly overt axonal pathology may be present, even in cases without a sustained loss of consciousness.
•An interdisciplinary computational model coupling a finite element brain mechanics model with linked models of brain dynamics (Kuramoto oscillator) and vascular perfusion (Balloon-Windkessel) was ...developed to study the alterations in structural and functional network topology following head impacts.•Two injury mechanisms were investigated: (i) injury to the nodes (gray matter) led to decreases in the nodal oscillation frequency, (ii) damage to the edges (axonal connections) progressively decreased coupling among connected nodes.•Changes between the disrupted and healthy functional connectivity consistently correlated well with injury outcomes, regardless of injury mechanisms.•Lesion model for gray matter damage predicted increases in global efficiency and clustering coefficient with increases in injury risk, while disrupting axonal connections led to lower network efficiency and clustering.
The brain is a complex network consisting of neuron cell bodies in the gray matter and their axonal projections, forming the white matter tracts. These neurons are supported by an equally complex vascular network as well as glial cells. Traumatic brain injury (TBI) can lead to the disruption of the structural and functional brain networks due to disruption of both neuronal cell bodies in the gray matter as well as their projections and supporting cells. To explore how an impact can alter the function of brain networks, we integrated a finite element (FE) brain mechanics model with linked models of brain dynamics (Kuramoto oscillator) and vascular perfusion (Balloon-Windkessel) in this study. We used empirical resting-state functional magnetic resonance imaging (MRI) data to optimize the fit of our brain dynamics and perfusion models to clinical data. Results from the FE model were used to mimic injury in these optimized brain dynamics models: injury to the nodes (gray matter) led to a decrease in the nodal oscillation frequency, while damage to the edges (axonal connections/white matter) progressively decreased coupling among connected nodes. A total of 53 cases, including 33 non-injurious and 20 concussive head impacts experienced by professional American football players were simulated using this integrated model. We examined the correlation of injury outcomes with global measures of structural connectivity, neural dynamics, and functional connectivity of the brain networks when using different lesion methods. Results show that injurious head impacts cause significant alterations in global network topology regardless of lesion methods. Changes between the disrupted and healthy functional connectivity (measured by Pearson correlation) consistently correlated well with injury outcomes (AUC≥0.75), although the predictive performance is not significantly different (p>0.05) to that of traditional kinematic measures (angular acceleration). Intriguingly, our lesion model for gray matter damage predicted increases in global efficiency and clustering coefficient with increases in injury risk, while disrupting axonal connections led to lower network efficiency and clustering. When both injury mechanisms were combined into a single injury prediction model, the injury prediction performance depended on the thresholds used to determine neurodegeneration and mechanical tolerance for axonal injury. Together, these results point towards complex effects of mechanical trauma to the brain and provide a new framework for understanding brain injury at a causal mechanistic level and developing more effective diagnostic methods and therapeutic interventions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Traumatic brain injury (TBI) can lead to neurodegeneration in the injured circuitry, either through primary structural damage to the neuron or secondary effects that disrupt key cellular processes. ...Moreover, traumatic injuries can preferentially impact subpopulations of neurons, but the functional network effects of these targeted degeneration profiles remain unclear. Although isolating the consequences of complex injury dynamics and long-term recovery of the circuit can be difficult to control experimentally, computational networks can be a powerful tool to analyze the consequences of injury. Here, we use the Izhikevich spiking neuron model to create networks representative of cortical tissue. After an initial settling period with spike-timing-dependent plasticity (STDP), networks developed rhythmic oscillations similar to those seen in vivo. As neurons were sequentially removed from the network, population activity rate and oscillation dynamics were significantly reduced. In a successive period of network restructuring with STDP, network activity levels returned to baseline for some injury levels and oscillation dynamics significantly improved. We next explored the role that specific neurons have in the creation and termination of oscillation dynamics. We determined that oscillations initiate from activation of low firing rate neurons with limited structural inputs. To terminate oscillations, high activity excitatory neurons with strong input connectivity activate downstream inhibitory circuitry. Finally, we confirm the excitatory neuron population role through targeted neurodegeneration. These results suggest targeted neurodegeneration can play a key role in the oscillation dynamics after injury.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Small clusters comprising hundreds to thousands of neurons are an important level of brain architecture that correlates single neuronal properties to fulfill brain function, but the specific ...mechanisms through which this scaling occurs are not well understood. In this study, we developed an
experimental platform of small neuronal circuits (islands) to probe the importance of structural properties for their development, physiology, and response to microtrauma.
Primary cortical neurons were plated on a substrate patterned to promote attachment in clusters of hundreds of cells (islands), transduced with GCaMP6f, allowed to mature until 10-13 days
(DIV), and monitored with Ca
as a non-invasive proxy for electrical activity. We adjusted two structural factors-island size and cellular density-to evaluate their role in guiding spontaneous activity and network formation in neuronal islands.
We found cellular density, but not island size, regulates of circuit activity and network function in this system. Low cellular density islands can achieve many states of activity, while high cellular density biases islands towards a limited regime characterized by low rates of activity and high synchronization, a property we summarized as "flexibility." The injury severity required for an island to lose activity in 50% of its population was significantly higher in low-density, high flexibility islands.
Together, these studies demonstrate flexible living cortical circuits are more resilient to microtrauma, providing the first evidence that initial circuit state may be a key factor to consider when evaluating the consequences of trauma to the cortex.
We examine the role of structural autapses, when a neuron synapses onto itself, in driving network-wide bursting behavior. Using a simple spiking model of neuronal activity, we study how autaptic ...connections affect activity patterns, and evaluate if controllability significantly affects changes in bursting from autaptic connections. Adding more autaptic connections to excitatory neurons increased the number of spiking events and the number of network-wide bursts. We observed excitatory synapses contributed more to bursting behavior than inhibitory synapses. We evaluated if neurons with high average controllability, predicted to push the network into easily achievable states, affected bursting behavior differently than neurons with high modal controllability, thought to influence the network into difficult to reach states. Results show autaptic connections to excitatory neurons with high average controllability led to higher burst frequencies than adding the same number of self-looping connections to neurons with high modal controllability. The number of autapses required to induce bursting was lowered by adding autapses to high degree excitatory neurons. These results suggest a role of autaptic connections in controlling network-wide bursts in diverse cortical and subcortical regions of mammalian brain. Moreover, they open up new avenues for the study of dynamic neurophysiological correlates of structural controllability.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Patients who suffer from traumatic brain injury (TBI) often complain of learning and memory problems. Their symptoms are principally mediated by the hippocampus and the ability to adapt to stimulus, ...also known as neural plasticity. Therefore, one plausible injury mechanism is plasticity impairment, which currently lacks comprehensive investigation across TBI research. For these studies, we used a computational network model of the hippocampus that includes the dentate gyrus, CA3, and CA1 with neuron-scale resolution. We simulated mild injury through weakened spike-timing-dependent plasticity (STDP), which modulates synaptic weights according to causal spike timing. In preliminary work, we found functional deficits consisting of decreased firing rate and broadband power in areas CA3 and CA1 after STDP impairment. To address structural changes with these studies, we applied modularity analysis to evaluate how STDP impairment modifies community structure in the hippocampal network. We also studied the emergent function of network-based learning and found that impaired networks could acquire conditioned responses after training, but the magnitude of the response was significantly lower. Furthermore, we examined pattern separation, a prerequisite of learning, by entraining two overlapping patterns. Contrary to our initial hypothesis, impaired networks did not exhibit deficits in pattern separation with either population- or rate-based coding. Collectively, these results demonstrate how a mechanism of injury that operates at the synapse regulates circuit function.
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