Biology subjects

Vlachos, A.

Publications and source records attributed to Vlachos, A..

At least 37 records · Page 2Linked to original sources

bioRxiv2024

Regional Microglial Response in Enthorino-hippocampal Slice Cultures to Schaffer Collateral Lesion and Metalloproteinases Modulation.

Microglia and astrocytes are essential in sustaining physiological networks on the central nervous system, with their ability to remodel the extracellular matrix, being pivotal for synapse plasticity. Recent findings challenge the traditional view of homogenous glial populations in the brain, uncovering morphological, functional and molecular heterogeneity among glial cells. This diversity has significant implications for both physiological and pathological brain states. In the present study, we mechanically induced a Schaffer collateral lesion (SCL) in mouse enthorino-hippocampal slice cultures to investigate glial behavior, i.e., microglia and astrocytes, under metalloproteinases (MMPs) modulation in the lesioned area, CA3, and the denervated region, CA1. We observed distinct response patterns in microglia and astrocytes 3 days after the lesion. Notably, GFAP-expressing astrocytes showed no immediate changes post-SCL. Microglia responses varied depending on their anatomical location. The MMPs inhibitor GM6001 did not affect microglial reactions in CA3, while increasing the Iba1 cells numbers in CA1, underscoring the complexity of the hippocampal neuroglial network post-injury. These findings highlight the importance of understanding glial regionalization following neural injury and MMPs modulation, and pave the way for further research into glia-targeted therapeutic strategies for neurodegenerative disorders.

neuroscience↗

bioRxiv2023

Antiepileptic medication strengthens excitatory neurotransmission in pyramidal neurons of the adult human neocortex

Homeostatic synaptic plasticity serves to maintain neuronal function within a dynamic range upon perturbations in network activity. While coordinated structural and functional changes at synaptic sites play a crucial role in adaptive processes, the specific regulatory mechanisms and biological relevance of homeostatic plasticity in the human brain warrant further investigation. In this study, we investigated the effects of neural network silencing, achieved through pharmacological inhibition of voltage-gated sodium channels or glutamatergic neurotransmission - common targets of antiepileptic medication - on functional and structural properties of murine and human cortical tissue. Using mouse entorhino-hippocampal tissue cultures, acute neocortical slices of adult mice, and human brain tissue, we characterize homeostatic synaptic plasticity across models, brain regions, and species. Our findings demonstrate local homeostatic synaptic plasticity in the adult human neocortex, highlighting the potential effects of antiepileptic medication in brain regions unaffected by the primary diseases, which might represent a mechanism for neuropsychiatric effects linked to these medications and increased seizure susceptibility upon discontinuation of antiepileptic medication.

neuroscience↗

bioRxiv2023

Axon morphology and intrinsic cellular properties determine repetitive transcranial magnetic stimulation threshold for plasticity

Repetitive transcranial magnetic stimulation (rTMS) is a widely used therapeutic tool in neurology and psychiatry, but its cellular and molecular mechanisms are not fully understood. Standardizing stimulus parameters, specifically electric field strength and direction, is crucial in experimental and clinical settings. It enables meaningful comparisons across studies and facilitating the translation of findings into clinical practice. However, the impact of biophysical properties inherent to the stimulated neurons and networks on the outcome of rTMS protocols remains not well understood. Consequently, achieving standardization of biological effects across different brain regions and subjects poses a significant challenge. This study compared the effects of 10 Hz repetitive magnetic stimulation (rMS) in entorhino-hippocampal tissue cultures from mice and rats, providing insights into the impact of the same stimulation protocol on similar neuronal networks under standardized conditions. We observed the previously described plastic changes in excitatory and inhibitory synaptic strength of CA1 pyramidal neurons in both mouse and rat tissue cultures, but a higher stimulation intensity was required for the induction of rMS-induced synaptic plasticity in rat tissue cultures. Through systematic comparison of neuronal structural and functional properties and computational modeling, we found that morphological parameters of CA1 pyramidal neurons alone are insufficient to explain the observed differences between the groups. However, axon morphologies of individual cells played a significant role in determining activation thresholds. Notably, differences in intrinsic cellular properties were sufficient to account for the 10 % higher intensity required for the induction of synaptic plasticity in the rat tissue cultures. These findings demonstrate the critical importance of axon morphology and intrinsic cellular properties in predicting the plasticity effects of rTMS, carrying valuable implications for the development of computer models aimed at predicting and standardizing the biological effects of rTMS.

neuroscience↗

bioRxiv2023

On-chip brain slice stimulation: precise control of electric fields and tissue orientation

Non-invasive brain stimulation modalities, including transcranial direct current stimulation (tDCS), are widely used in neuroscience and clinical practice to modulate brain function and treat neuropsychiatric diseases. DC stimulation of ex vivo brain tissue slices has been a method used to understand mechanisms imparted by tDCS. However, delivering spatiotemporally uniform direct current electric fields (dcEFs) that have precisely engineered magnitudes and are also exempt from toxic electrochemical by-products are both significant limitations in conventional experimental setups. As a consequence, bioelectronic dose-response interrelations, the role of EF orientation, and the biomechanisms of prolonged or repeated stimulation over several days all remain not well understood. Here we developed a platform with fluidic, electrochemical, and magnetically-induced spatial control. Fluidically, the chamber geometrically confines precise dcEF delivery to the enclosed brain slice and allows for tissue recovery in order to monitor post-stimulation effects. Electrochemically, conducting hydrogel electrodes mitigate stimulation-induced faradaic reactions typical of commonly-used metal electrodes. Magnetically, we applied ferromagnetic substrates beneath the tissue and used an external permanent magnet to enable in situ rotational control in relation to the dcEF. By combining the microfluidic chamber with live-cell calcium imaging and electrophysiological recordings, we showcased the potential to study the acute and lasting effects of dcEFs with the potential of providing multi-session stimulation. This on-chip bioelectronic platform presents a modernized yet simple solution to electrically stimulate explanted tissue by offering more environmental control to users, which unlocks new opportunities to conduct thorough brain stimulation mechanistic investigations. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/536696v1_ufig1.gif" ALT="Figure 1"> View larger version (85K): org.highwire.dtl.DTLVardef@10bac4dorg.highwire.dtl.DTLVardef@15d1dd3org.highwire.dtl.DTLVardef@5119c8org.highwire.dtl.DTLVardef@73b554_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2023

Repetitive transcranial magnetic stimulation (rTMS) triggers dose-dependent homeostatic rewiring in recurrent neuronal networks

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive brain stimulation technique used to induce neuronal plasticity in healthy individuals and patients. Designing effective and reproducible rTMS protocols poses a major challenge in the field as the underlying biomechanisms remain elusive. Current clinical protocol designs are often based on studies reporting rTMS-induced long-term potentiation or depression of synaptic transmission. Herein, we employed computational modeling to explore the effects of rTMS on long-term structural plasticity and changes in network connectivity. We simulated a recurrent neuronal network with homeostatic structural plasticity between excitatory neurons, and demonstrated that this mechanism was sensitive to specific parameters of the stimulation protocol (i.e., frequency, intensity, and duration of stimulation). The feedback-inhibition initiated by network stimulation influenced the net stimulation outcome and hindered the rTMS-induced homeostatic structural plasticity, highlighting the role of inhibitory networks. These findings suggest a novel mechanism for the lasting effects of rTMS, i.e., rTMS-induced homeostatic structural plasticity, and highlight the importance of network inhibition in careful protocol design, standardization, and optimization of stimulation. Author summaryThe cellular and molecular mechanisms of clinically employed repetitive transcranial magnetic stimulation (rTMS) protocols remain not well understood. However, it is clear that stimulation outcomes depend heavily on protocol designs. Current protocol designs are mainly based on experimental studies that explored functional synaptic plasticity, such as long-term potentiation of excitatory neurotransmission. Using a computational approach, we sought to address the dose-dependent effects of rTMS on the structural remodeling of stimulated and non-stimulated connected networks. Our results suggest a new mechanism of action--activity-dependent homeostatic structural remodeling--through which rTMS may assert its lasting effects on neuronal networks. We showed that the effect of rTMS on structural plasticity critically depends on stimulation intensity, frequency, and duration and that recurrent inhibition can affect the outcome of rTMS-induced homeostatic structural plasticity. These findings emphasize the use of computational approaches for an optimized rTMS protocol design, which may support the development of more effective rTMS-based therapies.

neuroscience↗

bioRxiv2023

Interplay between homeostatic synaptic scaling and homeostatic structural plasticity maintains the robust firing rate of neural networks

AbstractCritical network states and neural plasticity are essential for flexible behavior in dynamic envi-ronments, allowing for efficient information processing and experience-dependent learning. Synaptic-weight-based Hebbian plasticity and homeostatic synaptic scaling were considered the key mechanisms in enabling memory while stabilizing network dynamics. However, the role of structural plasticity as a homeostatic mechanism is less consistently reported, especially under activity inhibition, leading to an incomplete understanding of its functional impact. In this study, we combined live-cell microscopy of eGPF-labeled neurons in organotypic entorhinal-hippocampal tissue cultures with computational modeling to investigate the response of spine-number-based structural plasticity to activity perturba-tions and its interaction with homeostatic synaptic scaling. Tracking individual dendritic segments, we demonstrated that inhibiting excitatory neurotransmission does not monotonically regulate den-dritic spine density. Specifically, inhibition of AMPA receptors with a low concentration of 2,3-dioxo-6-nitro-7-sulfamoyl-benzo[f]quinoxaline (NBQX, 200 nM) significantly increased spine density, while complete AMPA receptors blockade with 50 {micro}M NBQX reduced spine density. Motivated by these findings, we developed network simulations incorporating a bi-phasic structural plasticity rule governing activity-dependent synapse formation. We showed that this biphasic rule maintained neu-ral activity homeostasis under stimulation and permitted either synapse formation or synapse loss, depending on the degree of activity deprivation. Homeostatic synaptic scaling affected the recurrent connectivity, modulated the network activity, and influenced the outcome of structural plasticity. Specifically, it reduced stimulation-triggered synapse loss by downscaling synaptic weights and res-cued silencing-induced synapse loss by upscaling recurrent inputs, thus reactivating silent neurons. Our interaction between these mechanisms offers an explanation for divergent findings in the existing literature. In summary, calcium-based synaptic scaling and homeostatic structural plasticity rules compete and compensate for one another, ensuring efficient and robust control of firing rate home-ostasis. Significance StatementO_LIThis work combined systematic computer simulations and in vitro experiments to explore the in-terplay between homeostatic structural plasticity and synaptic scaling under conditions of activity deprivation. C_LIO_LIWe identified a non-monotonic relationship between neural activity and spine numbers, where par-tial inhibition of synaptic transmissions increased spine density, while complete inhibition reduced it. C_LIO_LIPartial inhibition led to increased spine sizes across all initial spine sizes, whereas complete inhibition selectively increased the size of relatively large spines. C_LIO_LIA biphasic, spine-number-based homeostatic structural plasticity (HSP) rule reconciled previously divergent experimental findings regarding activity-dependent changes in spine density. C_LIO_LIUsing an engineering and complex systems framework, we proposed that the biphasic HSP rule incorporates a negative feedback mechanism and acts as a redundant and heterogeneous mechanism alongside the synaptic-weight-based homeostatic synaptic scaling (HSS) rule. C_LIO_LIBy comparing simulation and experimental results, we demonstrated the necessity of HSP-HSS interplay in maintaining firing rate homeostasis. C_LIO_LIBoth plasticity rules are driven by intracellular calcium concentration, which reflects cumulative neural activity. Thus, we propose that integral feedback control is critical in firing rate homeostasis. C_LI

neuroscience↗

bioRxiv2023

Mechanisms of Premotor-Motor Cortex Interactions during Goal Directed Behavior

Deciphering the neural code underlying goal-directed behavior is a long-term mission in neuroscience1,2. Neurons exhibiting preparation and movement-related activity are intermingled in the premotor and motor cortices3,4, thus concealing the neural code of planned movements. We employed a combination of electrophysiology, pathway-specific optogenetics, phototagging, and inverse reinforcement learning (RL) to elucidate the role of defined neuronal subpopulations in the rat rostral and caudal forelimb areas (RFA and CFA), which correspond to the premotor and motor cortical areas. The inverse RL enabled the functional dissection of spatially intermingled neuronal subpopulations, complementing our pathway-specific optogenetic manipulations and unveiling differential functions of the preparation and movement subpopulations projecting from RFA to CFA. Our results show that the projecting preparation subpopulation suppresses movements, whereas the projecting movement subpopulation promotes actions. We found the influence of RFA on CFA to be adaptable, with the projection either inhibiting or exciting neurons in the superficial and deep CFA layers, depending on context and task phase. These complex interactions between RFA and CFA likely involve the differential recruitment of inhibitory interneurons in the CFA, which is supported by our electron microscopy analysis of the connectivity between these regions. We provide here unprecedented mechanistic insights into how the premotor and primary motor cortices are functionally and structurally interlinked with the potential to advance neuroprosthetics. Graphical abstractThis study provides mechanistic insights into the interactions between the rostral forelimb area (RFA) and the caudal forelimb area (CFA). Specifically, we provide evidence for a differential impact of RFA on CFA depending on the task phase and the targeted CFA layers. RFA contains at least two spatially intermingled subpopulations - one related to movement preparation and one to movement execution. Both subpopulations project to CFA. Here we investigated the impact of these two subpopulations on the activity of the local CFA circuit as well as on the behavior in different contexts. When rats were not involved in a task, the effect of RFA was mainly excitatory in the deep CFA layers, while the superficial layers remained unaffected. This can be interpreted as a non-selective activation of the deep CFA neurons enabling a variety of spontaneous movements. During the preparation phase before a movement, the RFA had an opposite impact on the superficial and deep layers: while the superficial CFA layers were excited by RFA input, the deeper layers were mostly inhibited, minimizing movements and enabling continued holding of a lever. During the movement phase, the inhibitory effect on neurons in the deep CFA layers was counterbalanced by excitation, thus enabling a selected conduction of movements. The opposing effects during preparation and movement phase on CFA deep layers were correlated with increased firing rates of the RFA preparation and movement subpopulations, respectively, making it likely that the inhibition resulted from increased activities of these subpopulation specifically. With an electron microcopy approach we demonstrate that inhibitory and excitatory CFA neurons are directly targeted by RFA, thus providing a mechanism for the bidirectional control of CFA activity. Please note that the depicted impact of RFA on excitatory or inhibitory CFA neurons refers to net effects in this figure, not to the targeting of individual neurons. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=109 SRC="FIGDIR/small/524944v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@4de2d5org.highwire.dtl.DTLVardef@167164forg.highwire.dtl.DTLVardef@e9d298org.highwire.dtl.DTLVardef@101320b_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2022

Synaptopodin-associated ribosomal hubs regulate lesion-induced homeostatic plasticity at hippocampal mossy fiber synapses

Neurological diseases can lead to the denervation of brain regions caused by demyelination, traumatic injury or cell death. Nevertheless, the molecular and structural mechanisms underlying lesion-induced reorganization of denervated brain regions are a matter of ongoing investigation. In order to address this issue, we performed an entorhinal cortex lesion (ECL) in mouse organotypic entorhino-hippocampal tissue cultures of both sexes and studied denervation-induced plasticity of mossy fiber synapses, which connect dentate granule cells (dGCs) with CA3 pyramidal cells (CA3-PCs) and play important roles in spatial learning. Partial denervation caused a strengthening of excitatory neurotransmission in dGCs, in CA3-PCs, and their direct synaptic connections as revealed by paired recordings (GC-to-CA3). These functional changes were accompanied by ultrastructural reorganization of mossy fiber synapses, which regularly contain the plasticity-related protein synaptopodin and the spine apparatus organelle. We demonstrate that the spine apparatus organelle and its integral protein synaptopodin are associated with ribosomes in close proximity to synaptic sites and unravel a synaptopodin-related transcriptome. Notably, synaptopodin-deficient tissue preparations that lack the spine apparatus organelle, failed to express lesion-induced synaptic adjustments. Hence, synaptopodin and the spine apparatus organelle play a crucial role in regulating lesion-induced synaptic plasticity at hippocampal mossy fiber synapses.

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bioRxiv2022

The amyloid precursor protein regulates synaptic transmission at medial perforant path synapses

The perforant path provides the main cortical excitatory input to the hippocampus. Due to its important role in information processing and coding, entorhinal projections to the dentate gyrus have been studied in considerable detail. Nevertheless, a characterization of synaptic transmission between individual connected pairs of entorhinal stellate cells and dentate granule cells is still pending. Here, we have used organotypic entorhino-hippocampal tissue cultures, in which the entorhino-dentate (EC-GC) projection is present and EC-GC pairs can be studied using whole-cell patch clamp recordings. Using cultures of wildtype mice, the properties of EC-GC synapses formed by afferents from the lateral and medial entorhinal cortex were compared and differences in short-term plasticity were revealed. Since the perforant path is severely affected in Alzheimers disease, we used cultures of APP-deficient mice to address the role of the amyloid-precursor protein (APP) at this synapse. APP-deficiency caused alterations in excitatory neurotransmission at medial perforant path synapses that were accompanied by transcriptomic and ultrastructural changes. Moreover, the deletion of pre- but not postsynaptic APP through the local injection of Cre-expressing AAVs in conditional APPflox/flox tissue cultures increased the efficacy of neurotransmission at perforant path synapses. Together, these data suggest a physiological role for presynaptic APP at medial perforant path synapses, which may be adversely affected under conditions of altered APP processing.

neuroscience↗

bioRxiv2022

Tumor necrosis factor α modulates excitatory and inhibitory neurotransmission in a concentration-dependent manner

Microglia, the brains resident immune cells, have been implicated in important brain functions, such as synaptic transmission and plasticity. The pro-inflammatory cytokine tumor necrosis factor (TNF), which is produced and secreted by microglia, has been linked to the expression of synaptic plasticity in neurons. However, the role of TNF-mediated activation of microglia has not been addressed in this context. Here, we assessed concentration-dependent effects of TNF on the balance of synaptic excitation/inhibition and the activation of microglia using mouse organotypic entorhino-hippocampal tissue cultures. We found that low concentrations of TNF enhanced excitatory synaptic strength while not affecting inhibitory neurotransmission. At higher concentrations, TNF increased inhibitory neurotransmission without affecting excitatory synaptic strength. Both low and high concentrations of TNF induced the synaptic accumulation of GluA1-containing AMPA receptors, suggesting that a high concentration of TNF exerts a homeostatic effect on excitatory neurotransmission that prevents synaptic strengthening. Consistent with this, high, but not low, concentrations of TNF activated microglia. Moreover, high concentrations of TNF enhanced excitatory neurotransmission in microglia-depleted tissue cultures. These findings extend our knowledge on the role of TNF on synaptic plasticity by demonstrating concentration-dependent effects on excitatory and inhibitory neurotransmission. They reveal a TNF-mediated negative feedback mechanism on excitatory neurotransmission that is dependent on the activation of microglia, thereby emphasizing their role as gatekeepers of TNF-mediated plasticity and homeostasis.

neuroscience↗

bioRxiv2021

The GluN2A subunit of the NMDA receptor modulates the rate of functional maturation in parvalbumin-positive interneurons

N-methyl-D-aspartate receptors (NMDARs) comprise a family of ligand-gated ionotropic glutamate receptors that mediate a calcium-permeable component to fast excitatory neurotransmission. NMDARs are heterotetrameric assemblies of two obligate GluN1 subunits (encoded by the GRIN1 gene) and two GluN2 subunits (encoded by the GRIN2A-GRIN2D genes). Sequencing data shows that 43% (297/679) of all currently known NMDAR disease-associated genetic variants are within the GRIN2A gene, which encodes the GluN2A subunit. Here, we show that unlike missense GRIN2A variants, individuals affected with disease-associated null GRIN2A variants demonstrate a transient period of seizure susceptibility that begins during infancy and diminishes near adolescence. To explore this new clinical finding at that circuit and cellular level, we conducted studies using Grin2a+/- and Grin2a-/-mice at various stages during neurodevelopment. We show increased circuit excitability and CA1 pyramidal cell output in juvenile mice of both Grin2a+/- and Grin2a-/- mice. These alterations in somatic spiking are not due to global upregulation other GRIN genes (including Grin2b) nor can they be attributed to perturbations in the intrinsic excitability or action-potential firing properties of CA1 pyramidal cells. Deeper evaluation of the developing CA1 circuit led us to uncover age- and Grin2a gene dosing-dependent transient delays in the electrophysiological maturation programs of PV interneurons. Overall, we report that Grin2a+/+ mice reach electrophysiological maturation between the neonatal and juvenile neurodevelopmental timepoints, with Grin2a+/- mice not reaching electrophysiological maturation until preadolescence, and Grin2a-/- not reaching electrophysiological maturation until adulthood. Overall, these data may represent a molecular mechanism describing the transient nature of seizure burden in disease-associated null GRIN2A patients.

neuroscience↗

bioRxiv2021

Microglia mediate synaptic plasticity induced by 10 Hz repetitive magnetic stimulation

Microglia--the resident immune cells of the central nervous system--sense the activity of neurons and regulate physiological brain functions. They have been implicated in the pathology of brain diseases associated with alterations in neural excitability and plasticity. However, experimental and therapeutic approaches that modulate microglia function in a brain-region-specific manner have not been established. In this study, we tested for the effects of repetitive transcranial magnetic stimulation (rTMS), a clinically employed non-invasive brain stimulation technique, on microglia-mediated synaptic plasticity. 10 Hz electromagnetic stimulation triggered a release of plasticity-promoting cytokines from the microglia in organotypic brain tissue cultures, while no changes in microglial morphology or microglia dynamics were observed. Indeed, substitution of tumor necrosis factor alpha (TNF) and interleukin 6 (IL6) preserved synaptic plasticity induced by 10 Hz stimulation in the absence of microglia. Consistent with these findings, in vivo depletion of microglia abolished rTMS-induced changes in neurotransmission in the medial prefrontal cortex (mPFC) of anesthetized mice. We conclude that rTMS affects neural excitability and plasticity by modulating the release of cytokines from microglia.

neuroscience↗

bioRxiv2021

All-trans retinoic acid induces synaptopodin-dependent metaplasticity in mouse dentate granule cells

The vitamin A derivative all-trans retinoic acid (atRA) is a key mediator of synaptic plasticity. Depending on the brain region studied, distinct effects of atRA on excitatory and inhibitory neurotransmission have been reported. However, it remains unclear how atRA mediates brain region-specific effects on synaptic transmission and plasticity. Here, we used intraperitoneal injections of atRA (10 mg/kg) in adult male C57BL/6J mice to study the effects of atRA on excitatory and inhibitory neurotransmission in the mouse fascia dentata. In contrast to what has been reported in other brain regions, no major changes in synaptic transmission were observed in the ventral and dorsal hippocampus 6 hours after atRA administration. Likewise, no evidence for changes in the intrinsic properties of hippocampal dentate granule cells was obtained in the atRA-treated group. Moreover, hippocampal transcriptome analysis revealed no essential changes upon atRA treatment. In light of these findings, we tested for the metaplastic effects of atRA, i.e., for its ability to modulate synaptic plasticity expression in the absence of major changes in baseline synaptic transmission. Indeed, in vivo long-term potentiation (LTP) experiments demonstrated that systemic atRA treatment improves the ability of dentate granule cells to express LTP. The plasticity-promoting effects of atRA were not observed in synaptopodin-deficient mice, thus extending our previous results on the relevance of synaptopodin in atRA-mediated synaptic strengthening in the mouse prefrontal cortex. Taken together, our data show that atRA mediates synaptopodin-dependent metaplasticity in mouse dentate granule cells.

neuroscience↗

bioRxiv2020

Neural inflammation alters synaptic plasticity probed by 10 Hz repetitive magnetic stimulation

Systemic inflammation is associated with alterations in complex brain functions such as learning and memory. However, diagnostic approaches to functionally assess and quantify inflammation-associated alterations in synaptic plasticity are not well-established. In previous work, we demonstrated that bacterial lipopolysaccharide (LPS)-induced systemic inflammation alters the ability of hippocampal neurons to express synaptic plasticity, i.e., the long-term potentiation (LTP) of excitatory neurotransmission. Here, we tested whether synaptic plasticity induced by repetitive magnetic stimulation (rMS), a non-invasive brain stimulation technique used in clinical practice, is affected by LPS-induced inflammation. Specifically, we explored brain tissue cultures to learn more about the direct effects of LPS on neural tissue, and we tested for the plasticity-restoring effects of the anti-inflammatory cytokine interleukin 10 (IL10). As shown previously, 10 Hz repetitive magnetic stimulation (rMS) of organotypic entorhino-hippocampal tissue cultures induced a robust increase in excitatory neurotransmission onto CA1 pyramidal neurons. Furthermore, LPS-treated tissue cultures did not express rMS-induced synaptic plasticity. Live-cell microscopy in tissue cultures prepared from a novel transgenic reporter mouse line [C57BL6-Tg(TNFa-eGFP)] confirms that ex vivo LPS administration triggers microglial tumor necrosis factor alpha (TNF) expression, which is ameliorated in the presence of IL10. Consistent with this observation, IL10 hampers the LPS-induced increase in TNF, IL6, IL1{beta}, and IFN{gamma} and restores the ability of neurons to express rMS-induced synaptic plasticity in the presence of LPS. These findings establish organotypic tissue cultures as a suitable model for studying inflammation-induced alterations in synaptic plasticity, thus providing a biological basis for the diagnostic use of transcranial magnetic stimulation in the context of brain inflammation.

neuroscience↗

bioRxiv2020

Selecting stimulation intensity in repetitive transcranial magnetic stimulation studies: A systematic review between 1991 and 2020

BackgroundRepetitive transcranial magnetic stimulation (rTMS) is an increasingly used, non-invasive brain stimulation technique in neuroscience research and clinical practice with a broad spectrum of suggested applications. Among other parameters, the choice of stimulus intensity and intracranial electric field strength substantially impact rTMS outcome. This review provides a systematic overview of the intensity selection approaches and stimulation intensities used in human rTMS studies. We also examined whether studies report sufficient information to reproduce stimulus intensities in basic science research models. Methods. We performed a systematic review by focusing on original studies published between 1991 and 2020. We included conventional (e.g., 1 Hz or 10 Hz) and patterned protocols (e.g., continuous or intermittent theta burst stimulation). We identified 3,784 articles in total, and we manually processed a representative portion (20%) of randomly selected articles. Results. The majority of the analyzed studies (90% of entries) used the motor threshold (MT) approach and stimulation intensities from 80 to 120% of the MT. For continuous and intermittent theta burst stimulation, the most frequent stimulation intensity was 80% of the active MT. Most studies (92% of entries) did not report sufficient information to reproduce the stimulation intensity. Only a minority of studies (1.03% of entries) estimated the rTMS-induced electric field strengths. Conclusion. We formulate easy-to-follow recommendations to help scientists and clinicians report relevant information on stimulation intensity. Future standardized reporting guidelines may facilitate the use of basic science approaches aiming at better understanding the molecular, cellular, and neuronal mechanisms of rTMS.

neuroscience↗

bioRxiv2020

Multi-scale Modeling Toolbox for Single Neuron and Subcellular Activity under (repetitive) Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation (TMS) is a non-invasive brain stimulation technique widely used in research and clinical applications. However, its mechanism of action and the neural response to TMS are still poorly understood. Multi-scale modeling can complement experimental research and provide a framework between the physical input parameters and the subcellular neural effects of TMS. At the macroscopic level, sophisticated numerical models exist to estimate the induced electric fields in whole-brain volume conductor models. However, multi-scale computational modeling approaches to predict TMS cellular and subcellular responses, crucial to understanding TMS plasticity inducing protocols, are not available so far. Here, we develop a multi-scale Neuron Modeling for TMS toolbox (NeMo-TMS) that enables researchers to easily generate accurate neuron models from morphological reconstructions, couple them to the external electric fields induced by TMS, and to simulate the cellular and subcellular responses of the neurons. Both single-pulse and rTMS protocols can be simulated and results visualized in 3D. We openly share our toolbox and provide example scripts and datasets for the user to explore. NeMo-TMS toolbox (https://github.com/OpitzLab/NeMo-TMS) allows researchers a previously not available level of detail and precision in realistically modeling the physical and physiological effects of TMS.

neuroscience↗

bioRxiv2020

All-Trans Retinoic Acid induces synaptic plasticity in human cortical neurons

A defining feature of the brain is its ability to adapt structural and functional properties of synaptic contacts in an experience-dependent manner. In the human cortex direct experimental evidence for synaptic plasticity is currently missing. Here, we probed plasticity in human cortical slices using the vitamin A derivative all-trans retinoic acid, which has been suggested as medication for the treatment of neuropsychiatric disorders, e.g., Alzheimers disease. Our experiments demonstrate coordinated structural and functional changes of excitatory synapses of superficial (layer 2/3) pyramidal neurons in the presence of all-trans retinoic acid. This synaptic adaptation is accompanied by ultrastructural remodeling of the calcium-storing spine apparatus organelle and requires mRNA-translation. We conclude that all-trans retinoic acid is a potent mediator of synaptic plasticity in the adult human cortex.

neuroscience↗

bioRxiv2020

Amyloid-beta mediates homeostatic synaptic plasticity

The physiological role of the amyloid-precursor protein (APP) is insufficiently understood. Recent work has implicated APP in the regulation of synaptic plasticity. Substantial evidence exists for a role of APP and its secreted ectodomain APPs in Hebbian plasticity. Here, we addressed the relevance of APP in homeostatic synaptic plasticity using organotypic tissue cultures of APP-/- mice. In the absence of APP, dentate granule cells failed to strengthen their excitatory synapses homeostatically. Homeostatic plasticity is rescued by amyloid-{beta} (A{beta}) and not by APPs, and it is neither observed in APP+/+ tissue treated with {beta}- or {gamma}-secretase inhibitors nor in synaptopodin-deficient cultures lacking the Ca2+-dependent molecular machinery of the spine apparatus. Together, these results suggest a role of APP processing via the amyloidogenic pathway in homeostatic synaptic plasticity, representing a function of relevance for brain physiology as well as for brain states associated with increased A{beta} levels.

neuroscience↗