Elucidating the Role of Injury-Induced Electric Fields (EFs) in Regulating the Astrocytic Response to Injury in the Mammalian Central Nervous System

Activating astrocytic α2A adrenoceptors in hippocampus reduces glutamate toxicity to attenuate sepsis-associated encephalopathy in mice

BACKGROUND

Glutamate metabolism disorder is an important mechanism of sepsis-associated encephalopathy (SAE). Astrocytes regulate glutamate metabolism. In septic mice, α2A adrenoceptor (α2A-AR) activation in the central nervous system provides neuroprotection. α2A-ARs are expressed abundantly in hippocampal astrocytes. This study was performed to determine whether hippocampal astrocytic α2A-AR activation confers neuroprotection against SAE and whether this protective effect is astrocyte specific and achieved by the modulation of glutamate metabolism.

METHODS

Male C57BL/6 mice with and without α2A-AR knockdown were subjected to cecal ligation and puncture (CLP). They were treated with intrahippocampal guanfacine (an α2A-AR agonist) or intraperitoneal dexmedetomidine in the presence or absence of dihydrokainic acid [DHK; a glutamate transporter 1 (GLT-1) antagonist] and/or UCPH-101 [a glutamate/aspartate transporter (GLAST) antagonist]. Hippocampal tissue was collected for the measurement of astrocyte reactivity, GLT-1 and GLAST expression, and glutamate receptor subunit 2B (GluN2B) phosphorylation. In vivo real-time extracellular glutamate concentrations in the hippocampus were measured by ultra-performance liquid chromatography tandem mass spectrometry combined with microdialysis, and in vivo real-time hippocampal glutamatergic neuron excitability was assessed by calcium imaging. The mice were subjected to the Barnes maze and fear conditioning tests to assess their learning and memory. Golgi staining was performed to assess changes in the hippocampal synaptic structure. In vitro, primary astrocytes with and without α2A-AR knockdown were stimulated with lipopolysaccharide (LPS) and treated with guanfacine or dexmedetomidine in the presence or absence of 8-bromo- cyclic adenosine monophosphate (8-Br-cAMP, a cAMP analog). LPS-treated primary and BV2 microglia were also treated with guanfacine or dexmedetomidine. Astrocyte reactivity, PKA catalytic subunit, GLT-1 an GLAST expression were determined in primary astrocytes. Interleukin-1β, interleukin-6 and tumor necrosis factor-alpha in the medium of microglia culture were measured.

RESULTS

CLP induced synaptic injury, impaired neurocognitive function, increased astrocyte reactivity and reduced GLT-1 and GLAST expression in the hippocampus of mice. The extracellular glutamate concentration, phosphorylation of GluN2B at Tyr-1472 and glutamatergic neuron excitability in the hippocampus were increased in the hippocampus of septic mice. Intraperitoneal dexmedetomidine or intrahippocampal guanfacine administration attenuated these effects. Hippocampal astrocytes expressed abundant α2A-ARs; expression was also detected in neurons but not microglia. Specific knockdown of α2A-ARs in hippocampal astrocytes and simultaneous intrahippocampal DHK and UCPH-101 administration blocked the neuroprotective effects of dexmedetomidine and guanfacine. Intrahippocampal administration of DHK or UCPH-101 alone had no such effect. In vitro, guanfacine or dexmedetomidine inhibited astrocyte reactivity, reduced PKA catalytic subunit expression, and increased GLT-1 and GLAST expression in primary astrocytes but not in primary astrocytes that received α2A-AR knockdown or were treated with 8-Br-cAMP. Guanfacine or dexmedetomidine inhibited microglial reactivity in BV2 but not primary microglia.

CONCLUSIONS

Our results suggest that neurocognitive protection against SAE after hippocampal α2A-AR activation is astrocyte specific. This protection may involve the inhibition of astrocyte reactivity and alleviation of glutamate neurotoxicity, thereby reducing synaptic injury. The cAMP/protein kinase A (PKA) signaling pathway is a potential cellular mechanism by which activating α2A-AR modulates astrocytic function.

Filler-Enhanced Piezoelectricity of Poly-L-Lactide and Its Use as a Functional Ultrasound-Activated Biomaterial

Poly-L-lactide (PLLA) offers a unique possibility for processing into biocompatible, biodegradable, and implantable piezoelectric structures. With such properties, PLLA has potential to be used as an advanced tool for mimicking biophysical processes that naturally occur during the self-repair of wounds and damaged tissues, including electrostimulated regeneration. The piezoelectricity of PLLA strongly depends on the possibility of controlling its crystallinity and molecular orientation. Here, it is shown that modifying PLLA with a small amount (1 wt%) of crystalline filler particles with a high aspect ratio, which act as nucleating agents during drawing-induced crystallization, promotes the formation of highly crystalline and oriented PLLA structures. This increases their piezoelectricity, and the filler-modified PLLA films provide a 20-fold larger voltage output than nonmodified PLLA during ultrasound (US)-assisted activation. With 99% PLLA content, the ability of the films to produce reactive oxygen species (ROS) and increase the local temperature during interactions with US is shown to be very low. US-assisted piezostimulation of adherent cells directly attach to their surface (such as skin keratinocytes), stimulate cytoskeleton formation, and as a result cells elongate and orient themselves in a specific direction that align with the direction of PLLA film drawing and PLLA dipole orientation.

Effects of the radio electric asymmetric conveyer (REAC) on motor disorders: An integrative review

Introduction

The radio electric asymmetric conveyer (REAC) is a technology that has the purpose of restoring the cellular polarity triggering the rebalancing of the endogenous bioelectric field, which considering the neurological dysfunctions, affects the neural communication mechanisms. The studies published so far show that the REAC neuromodulation technology has positive effects in treating these dysfunctions, with the principles of endogenous bioelectricity as a basis to achieve these effects.

Objectives

This study aims to review the literature that explored the effects of REAC protocols on motor control and to identify which mechanisms would be involved.

Materials and methods

This integrative review considered studies that used REAC as a therapeutic intervention directed at human motor control and experimental research with animals that applied REAC to obtain effects related to motor behavior.

Results

Ten articles were included, eight clinical and two experimental studies. The clinical studies used the neuro postural optimization (NPO) protocol in 473 patients, of which 53 were healthy subjects, 91 were Alzheimer's disease patients, 128 were patients with atypical swallowing, 12 subjects with neurological diseases, and 189 were without the specification of disease. The experimental studies used the antalgic neuromodulation and neurodegeneration protocols in animal models.

Conclusion

The information integrated in this review made it possible to consider REAC technology a promising resource for treating motor control dysfunctions. It is possible to infer that the technology promotes functional optimization of neuronal circuits that may be related to more efficient strategies to perform motor tasks.

Electric Fields Induced in the Brain by Transcranial Electric Stimulation: A Review of In Vivo Recordings

Transcranial electrical stimulation (tES) techniques, such as direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), cause neurophysiological and behavioral modifications as responses to the electric field are induced in the brain. Estimations of such electric fields are based mainly on computational studies, and in vivo measurements have been used to expand the current knowledge. Here, we review the current tDCS- and tACS-induced electric fields estimations as they are recorded in humans and non-human primates using intracerebral electrodes. Direct currents and alternating currents were applied with heterogeneous protocols, and the recording procedures were characterized by a tentative methodology. However, for the clinical stimulation protocols, an injected current seems to reach the brain, even at deep structures. The stimulation parameters (e.g., intensity, frequency and phase), the electrodes’ positions and personal anatomy determine whether the intensities might be high enough to affect both neuronal and non-neuronal cell activity, also deep brain structures.

Engineering Tissues of the Central Nervous System: Interfacing Conductive Biomaterials with Neural Stem/Progenitor Cells

Conductive biomaterials provide an important control for engineering neural tissues, where electrical stimulation can potentially direct neural stem/progenitor cell (NS/PC) maturation into functional neuronal networks. It is anticipated that stem cell-based therapies to repair damaged central nervous system (CNS) tissues and ex vivo, "tissue chip" models of the CNS and its pathologies will each benefit from the development of biocompatible, biodegradable, and conductive biomaterials. Here, technological advances in conductive biomaterials are reviewed over the past two decades that may facilitate the development of engineered tissues with integrated physiological and electrical functionalities. First, one briefly introduces NS/PCs of the CNS. Then, the significance of incorporating microenvironmental cues, to which NS/PCs are naturally programmed to respond, into biomaterial scaffolds is discussed with a focus on electrical cues. Next, practical design considerations for conductive biomaterials are discussed followed by a review of studies evaluating how conductive biomaterials can be engineered to control NS/PC behavior by mimicking specific functionalities in the CNS microenvironment. Finally, steps researchers can take to move NS/PC-interfacing, conductive materials closer to clinical translation are discussed.

Electric field stimulation for tissue engineering applications

Electric fields are involved in numerous physiological processes, including directional embryonic development and wound healing following injury. To study these processes in vitro and/or to harness electric field stimulation as a biophysical environmental cue for organised tissue engineering strategies various electric field stimulation systems have been developed. These systems are overall similar in design and have been shown to influence morphology, orientation, migration and phenotype of several different cell types. This review discusses different electric field stimulation setups and their effect on cell response.

Recent Advances in the Regenerative Approaches for Traumatic Spinal Cord Injury: Materials Perspective

Spinal cord injury (SCI) is a devastating health condition that may lead to permanent disabilities and death. Understanding the pathophysiological perspectives of traumatic SCI is essential to define mechanisms that can help in designing recovery strategies. Since central nervous system tissues are notorious for their deficient ability to heal, efforts have been made to identify solutions to aid in restoration of the spinal cord tissues and thus its function. The two main approaches proposed to address this issue are neuroprotection and neuro-regeneration. Neuroprotection involves administering drugs to restore the injured microenvironment to normal after SCI. As for the neuro-regeneration approach, it focuses on axonal sprouting for functional recovery of the injured neural tissues and damaged axons. Despite the progress made in the field, neural regeneration treatment after SCI is still unsatisfactory owing to the disorganized way of axonal growth and extension. Nanomedicine and tissue engineering are considered promising therapeutic approaches that enhance axonal growth and directionality through implanting or injecting of the biomaterial scaffolds. One of these recent approaches is nanofibrous scaffolds that are used to provide physical support to maintain directional axonal growth in the lesion site. Furthermore, these preferable tissue-engineered substrates can afford axonal regeneration by mimicking the extracellular matrix of the neural tissues in terms of biological, chemical, and architectural characteristics. In this review, we discuss the regenerative approach using nanofibrous scaffolds with a focus on their fabrication methods and their properties that define their functionality performed to heal the neural tissue efficiently.

Percutaneous Bioelectric Current Stimulation for Chronic Cluster Headache - A Possible Transformative Approach to Cluster Headache

Background

Cluster headache (CH) is considered to be a catastrophic disease presenting the most severe human pain condition. Available pharmacological treatments are hampered by unwanted side effects, and there is an urgent need for non-pharmacological treatment alternatives. We present a novel therapeutic approach for chronic CH, having evolved from an episodic CH, using a non-invasive percutaneous bioelectric current stimulation (PBCS), which generates static electric fields in the range of the naturally occurring electric potentials.

Patients and Methods

This study employed a retrospective data analysis of 20 cases of chronic cluster headache (CCH) patients, four of those having had cluster-related surgery (SPG, ONS). All patients were treated with PBCS between 2014 and 2018. Data of these patients were analyzed with respect to frequency of CH attacks and triptan application and followed up for one (20 cases) or two (12 cases) years.

Results

Four weeks after the first PBCS treatment, cluster headache attacks were reduced from 2.8 to 1.7 per day and triptan application decreased from 2.5 to 1.5 times/day. Six non-responders, 4 of which had pre-CH surgery, did not show any reaction to PBCS, while 14 responders improved within 4 weeks from 2.2 to 0.7 attacks/day and 2.0 to 0.4 triptan applications/day. A 50% or greater reduction of attack frequency was observed in 10 patients after 4 weeks and in 11 patients after 12 weeks. One year after the first treatment, 13/20 patients experienced a reduction of attack frequency of 50% or more, while remarkably 10 patients were completely free of attack. After 2 years, 8 of 12 patients experienced a reduction of attack frequency of 50% or more and 7 of those were completely symptom-free. No serious adverse effects were observed.

Conclusion

PBCS is a promising transformative treatment approach for CCH patients. Drug consumption was reduced significantly, and the CCH may revert back to an episodic cluster headache with increasingly long times of remission. Responders can be clearly differentiated from non-responders. The data support the need for randomized controlled trials.

Charge-Balanced Electrical Stimulation Can Modulate Neural Precursor Cell Migration in the Presence of Endogenous Electric Fields in Mouse Brains

Electric fields (EFs) can direct cell migration and are crucial during development and tissue repair. We previously reported neural precursor cells (NPCs) are electrosensitive cells that can undergo rapid and directed migration towards the cathode using charge-balanced electrical stimulation in vitro. Here, we investigate the ability of electrical stimulation to direct neural precursor migration in mouse brains in vivo. To visualize migration, fluorescent adult murine neural precursors were transplanted onto the corpus callosum of adult male mice and intracortical platinum wire electrodes were implanted medial (cathode) and lateral (anode) to the injection site. We applied a charge-balanced biphasic monopolar stimulation waveform for three sessions per day, for 3 or 6 d. Irrespective of stimulation, the transplanted neural precursors had a propensity to migrate laterally along the corpus callosum, and applied stimulation affected that migration. Further investigation revealed an endogenous EF along the corpus callosum that correlated with the lateral migration, suggesting that the applied EF would need to overcome endogenous cues. There was no difference in transplanted cell differentiation and proliferation, or inflammatory cell numbers near the electrode leads and injection site comparing stimulated and implanted non-stimulated brains. Our results support that endogenous and applied EFs are important considerations for designing cell therapies for tissue repair in vivo.

Steered migration and changed morphology of human astrocytes by an applied electric field

Direct current electric field (DC EF) plays a role in influencing the biological behaviors and functions of cells. We hypothesize that human astrocytes (HAs) could also be influenced in EF. Astrocytes, an important type of nerve cells with a high proportion quantitatively, are generally activated and largely decide the brain repair results after brain injury. So far, no electrotaxis study on HAs has been performed. We here obtained HAs derived from brain trauma patients. After purification and identification, HAs were seeded in the EF chamber and recorded in a time-lapse image system. LY294002 and U0126 were then used to probe the role of PI3K or ERK signaling pathway on cellular behaviors. The results showed that HAs could be guided to migrate to the anode in DC EFs, in a voltage-dependent manner. The HAs displayed elongated cell bodies and reoriented perpendicularly to the EF in morphology. When treated with LY294002 or U0126, alternation of parameters such as cellular verticality, track speed, displacement speed, long axis, vertical length and circularity were inhibited partly as expected, while the EF-induced directedness was not terminated even at a high drug dosage which was not consistent with previous electrotaxis studies. In conclusion, applied EFs steered the patient-derived HAs directional migration and changed morphology, in which PI3K and ERK pathways at least partially participate. The characteristics of HAs to EF stimulation may be involved in wound healing and neural regeneration, which could be utilized as a novel treatment strategy in brain injury.

Percutaneous direct current stimulation - a new electroceutical solution for severe neurological pain and soft tissue injuries

There is a high medical need to improve the effectiveness of the treatment of pain and traumatic soft tissue injuries. In this context, electrostimulating devices have been used with only sporadic success. There is also much evidence of endogenous electrical signals that play key roles in regulating the development and regeneration of many tissues. Transepithelial potential gradients are one source of the direct current (DC) electrical signals that stimulate and guide the migration of inflammatory cells, epithelial cells, fibroblasts and mesenchymal stem cells to achieve effective wound healing. Up to now, this electrophysiological knowledge has not been adequately translated into a clinical treatment. Here, we present a mobile, handheld electroceutical smart device based on a microcontroller, an analog front end and a battery, which generates DC electric fields (EFs), mimicking and modulating the patient’s own physiological electrical signals. The electrical stimulation is applied to percutaneous metal probes, which are located close to the inflamed or injured tissue of the patient. The treatment can be used in an ambulatory or stationary environment. It shows unexpectedly, highly effective treatment for certain severe neurological pain conditions, as well as traumatic soft tissue injuries (muscle/ligament ruptures, joint sprains). Without EF intervention, these conditions, respectively, are either virtually incurable or take several months to heal. We present three cases – severe chronic cluster headache, acute massive muscle rupture of the rectus femoris and an acute ankle sprain with a ruptured anterior talofibular ligament – to demonstrate clinical effectiveness and discuss the fundamental differences between mimicking DC simulation and conventional transcutaneous electric nerve stimulation (TENS) or TENS-like implanted devices as used for peripheral nerve cord, spinal cord or dorsal root stimulation.

Growing Neural PC-12 Cell on Crosslinked Silica Aerogels Increases Neurite Extension in the Presence of an Electric Field

Externally applied electrical stimulation (ES) has been shown to enhance the nerve regeneration process and to influence the directionality of neurite outgrowth. In addition, the physical and chemical properties of the substrate used for nerve-cell regeneration is critical in fostering regeneration. Previously, we have shown that polyurea-crosslinked silica aerogels (PCSA) exert a positive influence on the extension of neurites by PC-12 cells, a cell-line model widely used to study neurite extension and electrical excitability. In this work, we have examined how an externally applied electric field (EF) influences the extension of neurites in PC-12 cells grown on two substrates: collagen-coated dishes versus collagen-coated crosslinked silica aerogels. The externally applied direct current (DC) bias was applied in vitro using a custom-designed chamber containing polydimethysiloxane (PDMS) embedded copper electrodes to create an electric field across the substrate for the cultured PC-12 cells. Results suggest orientation preference towards the anode, and, on average, longer neurites in the presence of the applied DC bias than with 0 V DC bias. In addition, neurite length was increased in cells grown on silica-crosslinked aerogel when compared to cells grown on regular petri-dishes. These results further support the notion that PCSA is a promising material for nerve regeneration.

Low intensity transcranial electric stimulation: Safety, ethical, legal regulatory and application guidelines

Low intensity transcranial electrical stimulation (TES) in humans, encompassing transcranial direct current (tDCS), transcutaneous spinal Direct Current Stimulation (tsDCS), transcranial alternating current (tACS), and transcranial random noise (tRNS) stimulation or their combinations, appears to be safe. No serious adverse events (SAEs) have been reported so far in over 18,000 sessions administered to healthy subjects, neurological and psychiatric patients, as summarized here. Moderate adverse events (AEs), as defined by the necessity to intervene, are rare, and include skin burns with tDCS due to suboptimal electrode-skin contact. Very rarely mania or hypomania was induced in patients with depression (11 documented cases), yet a causal relationship is difficult to prove because of the low incidence rate and limited numbers of subjects in controlled trials. Mild AEs (MAEs) include headache and fatigue following stimulation as well as prickling and burning sensations occurring during tDCS at peak-to-baseline intensities of 1-2mA and during tACS at higher peak-to-peak intensities above 2mA. The prevalence of published AEs is different in studies specifically assessing AEs vs. those not assessing them, being higher in the former. AEs are frequently reported by individuals receiving placebo stimulation. The profile of AEs in terms of frequency, magnitude and type is comparable in healthy and clinical populations, and this is also the case for more vulnerable populations, such as children, elderly persons, or pregnant women. Combined interventions (e.g., co-application of drugs, electrophysiological measurements, neuroimaging) were not associated with further safety issues. Safety is established for low-intensity 'conventional' TES defined as <4mA, up to 60min duration per day. Animal studies and modeling evidence indicate that brain injury could occur at predicted current densities in the brain of 6.3-13A/m2 that are over an order of magnitude above those produced by tDCS in humans. Using AC stimulation fewer AEs were reported compared to DC. In specific paradigms with amplitudes of up to 10mA, frequencies in the kHz range appear to be safe. In this paper we provide structured interviews and recommend their use in future controlled studies, in particular when trying to extend the parameters applied. We also discuss recent regulatory issues, reporting practices and ethical issues. These recommendations achieved consensus in a meeting, which took place in Göttingen, Germany, on September 6-7, 2016 and were refined thereafter by email correspondence.

Environmental Factors That Influence Stem Cell Migration: An "Electric Field"

Environmental Stimulus of Electric Fields on Stem Cell Migration. The movement of cells in response to electric potential gradients is called galvanotaxis. In vivo galvanotaxis, powered by endogenous electric fields (EFs), plays a critical role during development and wound healing. This review aims to provide a perspective on how stem cells transduce EFs into directed migration and an understanding of the current literature relating to the mechanisms by which cells sense and transduce EFs. We will comment on potential EF-based regenerative medicine therapeutics.

Endogenous bioelectric fields: a putative regulator of wound repair and regeneration in the central nervous system

Studies on a variety of highly regenerative tissues, including the central nervous system (CNS) in non-mammalian vertebrates, have consistently demonstrated that tissue damage induces the formation of an ionic current at the site of injury. These injury currents generate electric fields (EF) that are 100-fold increased in intensity over that measured for uninjured tissue. In vitro and in vivo experiments have convincingly demonstrated that these electric fields (by their orientation, intensity and duration) can drive the migration, proliferation and differentiation of a host of cell types. These cellular behaviors are all necessary to facilitate regeneration as blocking these EFs at the site of injury inhibits tissue repair while enhancing their intensity promotes repair. Consequently, injury-induced currents, and the EFs they produce, represent a potent and crucial signal to drive tissue regeneration and repair. In this review, we will discuss how injury currents are generated, how cells detect these currents and what cellular responses they can induce. Additionally, we will describe the growing evidence suggesting that EFs play a key role in regulating the cellular response to injury and may be a therapeutic target for inducing regeneration in the mammalian CNS.