Localized membrane depolarizations and localized calcium influx during electric field-guided neurite growth

Electric field stimulation directs target-specific axon regeneration and partial restoration of vision after optic nerve crush injury

Failure of central nervous system (CNS) axons to regenerate after injury results in permanent disability. Several molecular neuro-protective and neuro-regenerative strategies have been proposed as potential treatments but do not provide the directional cues needed to direct target-specific axon regeneration. Here, we demonstrate that applying an external guidance cue in the form of electric field stimulation to adult rats after optic nerve crush injury was effective at directing long-distance, target-specific retinal ganglion cell (RGC) axon regeneration to native targets in the diencephalon. Stimulation was performed with asymmetric charged-balanced (ACB) waveforms that are safer than direct current and more effective than traditional, symmetric biphasic waveforms. In addition to partial anatomical restoration, ACB waveforms conferred partial restoration of visual function as measured by pattern electroretinogram recordings and local field potential recordings in the superior colliculus-and did so without the need for genetic manipulation. Our work suggests that exogenous electric field application can override cell-intrinsic and cell-extrinsic barriers to axon regeneration, and that electrical stimulation performed with specific ACB waveforms may be an effective strategy for directing anatomical and functional restoration after CNS injury.

An NIR-IIb emissive transmembrane voltage nano-indicator for the optical monitoring of electrophysiological activities in vivo

In vivo transmembrane-voltage detection reflected the electrophysiological activities of the biological system, which is crucial for the diagnosis of neuronal disease. Traditional implanted electrodes can only monitor limited regions and induce relatively large tissue damage. Despite emerging monitoring methods based on optical imaging have access to signal recording in a larger area, the recording wavelength of less than 1000 nm seriously weakens the detection depth and resolution in vivo. Herein, a Förster resonance energy transfer (FRET)-based nano-indicator, NaYbF4:Er@NaYF4@Cy7.5@DPPC (Cy7.5-ErNP) with emission in the near-infrared IIb biological window (NIR-IIb, 1500-1700 nm) is developed for transmembrane-voltage detection. Cy7.5 dye is found to be voltage-sensitive and is employed as the energy donor for the energy transfer to the lanthanide nanoparticle, NaYbF4:Er@NaYF4 (ErNP), which works as the acceptor to achieve electrophysiological signal responsive NIR-IIb luminescence. Benefiting from the high penetration and low scattering of NIR-IIb luminescence, the Cy7.5-ErNP enables both the visualization of action potential in vitro and monitoring of Mesial Temporal lobe epilepsy (mTLE) disease in vivo. This work presents a concept for leveraging the lanthanide luminescent nanoprobes to visualize electrophysiological activity in vivo, which facilitates the development of an optical nano-indicator for the diagnosis of neurological disorders.

The potential of graphene coatings as neural interfaces

Recent advances in nanotechnology design and fabrication have shaped the landscape for the development of ideal cell interfaces based on biomaterials. A holistic evaluation of the requirements for a cell interface is a highly complex task. Biocompatibility is a crucial requirement which is affected by the interface's properties, including elemental composition, morphology, and surface chemistry. This review explores the current state-of-the-art on graphene coatings produced by chemical vapor deposition (CVD) and applied as neural interfaces, detailing the key properties required to design an interface capable of physiologically interacting with neural cells. The interfaces are classified into substrates and scaffolds to differentiate the planar and three-dimensional environments where the cells can adhere and proliferate. The role of specific features such as mechanical properties, porosity and wettability are investigated. We further report on the specific brain-interface applications where CVD graphene paved the way to revolutionary advances in biomedicine. Future studies on the long-term effects of graphene-based materials in vivo will unlock even more potentially disruptive neuro-applications.

Quantification of Trophoblast Syncytialization by Fluorescent Membrane Labeling

Trophoblast fusion or syncytialization is a fundamental yet poorly understood process during placental development. Primary cultured cytotrophoblasts and human choriocarcinoma cell lines are commonly used to study trophoblast fusion mechanisms in vitro. Quantification of trophoblast fusion index is a key for the in vitro studies. In this chapter, we describe a new method to quantify fusion index, which is based on fluorescent labeling of the plasma membrane using Di-8-ANEPPS, a membrane potential dye. This method directly works on live cells, thereby is simple, economic, and reliable.

A Bioresorbable and Conductive Scaffold Integrating Silicon Membranes for Peripheral Nerve Regeneration

Peripheral nerve injury represents one of the most common types of traumatic damage, severely impairing motor and sensory functions, and posttraumatic nerve regeneration remains a major challenge. Electrical cues are critical bioactive factors that promote nerve regrowth, and bioartificial scaffolds incorporating conductive materials to enhance the endogenous electrical field have been demonstrated to be effective. The utilization of fully biodegradable scaffolds can eliminate material residues, and circumvent the need for secondary retrieval procedures. Here, a fully bioresorbable and conductive nerve scaffold integrating N-type silicon (Si) membranes is proposed, which can deliver both structural guidance and electrical cues for the repair of nerve defects. The entire scaffold is fully biodegradable, and the introduction of N-type Si can significantly promote the proliferation and production of neurotrophic factors of Schwann cells and enhance the calcium activity of dorsal root ganglion (DRG) neurons. The conductive scaffolds enable accelerated nerve regeneration and motor functional recovery in rodents with sciatic nerve transection injuries. This work sheds light on the advancement of bioresorbable and electrically active materials to achieve desirable neural interfaces and improved therapeutic outcomes, offering essential strategies for regenerative medicine.

Simulating the Voltage-Dependent Fluorescence of Di-8-ANEPPS in a Lipid Membrane

Voltage-sensitive fluorescent dyes such as di-8-ANEPPS (di-8-aminonaphthylethylenepyridinium propylsulfonate) are powerful tools to study biological membranes. Its fluorescence is affected by changes in the membrane potential and other factors, requiring extensive calibration to extract meaningful quantitative results. The amphiphilic di-8-ANEPPS molecule is expected to bind at the membrane-solution interface. However, atomic-level information is sparse about its position and orientation in the membrane, especially in regards to how the latter dynamically fluctuates to affect the observed fluorescence. In the present work, molecular dynamics simulations of the ground and excited states of di-8-ANEPPS embedded in a DPPC membrane as represented by classical force fields were used to investigate how the fluorescence is affected by externally applied potential. The calculations reproduce the shifts in the wavelength of emission as a function of voltage that are observed experimentally, indicating that the approach can help better understand the various factors that can affect the fluorescence of membrane-bound dyes.

Modeling Electric Fields in Transcutaneous Spinal Direct Current Stimulation: A Clinical Perspective

Clinical findings suggest that transcutaneous spinal direct current stimulation (tsDCS) can modulate ascending sensitive, descending corticospinal, and segmental pathways in the spinal cord (SC). However, several aspects of the stimulation have not been completely understood, and realistic computational models based on MRI are the gold standard to predict the interaction between tsDCS-induced electric fields and anatomy. Here, we review the electric fields distribution in the SC during tsDCS as predicted by MRI-based realistic models, compare such knowledge with clinical findings, and define the role of computational knowledge in optimizing tsDCS protocols. tsDCS-induced electric fields are predicted to be safe and induce both transient and neuroplastic changes. This could support the possibility to explore new clinical applications, such as spinal cord injury. For the most applied protocol (2-3 mA for 20-30 min, active electrode over T10-T12 and the reference on the right shoulder), similar electric field intensities are generated in both ventral and dorsal horns of the SC at the same height. This was confirmed by human studies, in which both motor and sensitive effects were found. Lastly, electric fields are strongly dependent on anatomy and electrodes' placement. Regardless of the montage, inter-individual hotspots of higher values of electric fields were predicted, which could change when the subjects move from a position to another (e.g., from the supine to the lateral position). These characteristics underlines the need for individualized and patient-tailored MRI-based computational models to optimize the stimulation protocol. A detailed modeling approach of the electric field distribution might contribute to optimizing stimulation protocols, tailoring electrodes' configuration, intensities, and duration to the clinical outcome.

Hesperetin ameliorates ischemia/hypoxia‐induced myocardium injury via inhibition of oxidative stress, apoptosis, and regulation of Ca 2+ homeostasis

Ischemia/hypoxia (I/H)-induced myocardial injury has a large burden worldwide. Hesperetin (HSP) has a cardioprotective effect, but the molecular mechanism underlying this is not clearly established. Here, we focused on the protective mechanisms of HSP against I/H-induced myocardium injury. H9c2 cardiomyocytes were challenged with CoCl₂ for 22 h to imitate hypoxia after treatment groups received HSP for 4 h. The viability of H9c2 cardiomyocytes was evaluated, and cardiac function indices, reactive oxygen species, apoptosis, mitochondrial membrane potential (MMP), and intracellular Ca²⁺ concentration ([Ca²⁺ ]_i ) were measured. L-type Ca²⁺ current (I_Ca-L ), myocardial contraction, and Ca²⁺ transients in isolated ventricular myocytes were also recorded. We found that HSP significantly increased the cell viability, and MMP while significantly decreasing cardiac impairment, oxidative stress, apoptosis, and [Ca²⁺ ]_i caused by CoCl₂ . Furthermore, HSP markedly attenuated I_Ca-L , myocardial contraction, and Ca²⁺ transients in a concentration-dependent manner. Our findings suggest a protective mechanism of HSP on I/H-induced myocardium injury by restoring oxidative balance, inhibiting apoptosis, improving mitochondrial function, and reducing Ca²⁺ influx via L-type Ca²⁺ channels (LTCCs). These data provide a new direction for HSP applied research as a LTCC inhibitor against I/H-induced myocardium injury.

Membrane Dipole Potential: An Emerging Approach to Explore Membrane Organization and Function

Biological membranes are complex organized molecular assemblies of lipids and proteins that provide cells and membrane-bound intracellular organelles their individual identities by morphological compartmentalization. Membrane dipole potential originates from the electrostatic potential difference within the membrane due to the nonrandom arrangement (orientation) of amphiphile and solvent (water) dipoles at the membrane interface. In this Feature Article, we will focus on the measurement of dipole potential using electrochromic fluorescent probes and highlight interesting applications. In addition, we will focus on ratiometric fluorescence microscopic imaging technique to measure dipole potential in cellular membranes, a technique that can be used to address novel problems in cell biology which are otherwise difficult to address using available approaches. We envision that membrane dipole potential could turn out to be a convenient tool in exploring the complex interplay between membrane lipids and proteins and could provide novel insights in membrane organization and function.

Weak Electromagnetic Fields Accelerate Fusion of Myoblasts

Weak electromagnetic fields (WEF) alter Ca²⁺ handling in skeletal muscle myotubes. Owing to the involvement of Ca²⁺ in muscle development, we investigated whether WEF affects fusion of myoblasts in culture. Rat primary myoblast cultures were exposed to WEF (1.75 µT, 16 Hz) for up to six days. Under control conditions, cell fusion and creatine kinase (CK) activity increased in parallel and peaked at 4–6 days. WEF enhanced the extent of fusion after one and two days (by ~40%) vs. control, but not thereafter. Exposure to WEF also enhanced CK activity after two days (almost four-fold), but not afterwards. Incorporation of ³H-thymidine into DNA was enhanced by one-day exposure to WEF (~40%), indicating increased cell replication. Using the potentiometric fluorescent dye di-8-ANEPPS, we found that exposure of cells to 150 mM KCl resulted in depolarization of the cell membrane. However, prior exposure of cells to WEF for one day followed by addition of KCl resulted in hyperpolarization of the cell membrane. Acute exposure of cells to WEF also resulted in hyperpolarization of the cell membrane. Twenty-four hour incubation of myoblasts with gambogic acid, an inhibitor of the inward rectifying K⁺ channel 2.1 (K_ir2.1), did not affect cell fusion, WEF-mediated acceleration of fusion or hyperpolarization. These data demonstrate that WEF accelerates fusion of myoblasts, resulting in myotube formation. The WEF effect is associated with hyperpolarization but WEF does not appear to mediate its effects on fusion by activating K_ir2.1 channels.

Prox1 inhibits neurite outgrowth during central nervous system development

During central nervous system (CNS) development, proper and timely induction of neurite elongation is critical for generating functional, mature neurons, and neuronal networks. Despite the wealth of information on the action of extracellular cues, little is known about the intrinsic gene regulatory factors that control this developmental decision. Here, we report the identification of Prox1, a homeobox transcription factor, as a key player in inhibiting neurite elongation. Although Prox1 promotes acquisition of early neuronal identity and is expressed in nascent post-mitotic neurons, it is heavily down-regulated in the majority of terminally differentiated neurons, indicating a regulatory role in delaying neurite outgrowth in newly formed neurons. Consistently, we show that Prox1 is sufficient to inhibit neurite extension in mouse and human neuroblastoma cell lines. More importantly, Prox1 overexpression suppresses neurite elongation in primary neuronal cultures as well as in the developing mouse brain, while Prox1 knock-down promotes neurite outgrowth. Mechanistically, RNA-Seq analysis reveals that Prox1 affects critical pathways for neuronal maturation and neurite extension. Interestingly, Prox1 strongly inhibits many components of Ca2+ signaling pathway, an important mediator of neurite extension and neuronal maturation. In accordance, Prox1 represses Ca2+ entry upon KCl-mediated depolarization and reduces CREB phosphorylation. These observations suggest that Prox1 acts as a potent suppressor of neurite outgrowth by inhibiting Ca2+ signaling pathway. This action may provide the appropriate time window for nascent neurons to find the correct position in the CNS prior to initiation of neurites and axon elongation.

TRPV2 interacts with actin and reorganizes submembranous actin cytoskeleton

The understanding of molecules and their role in neurite initiation and/or extension is not only helpful to prevent different neurodegenerative diseases but also can be important in neuronal damage repair. In this work, we explored the role of transient receptor potential vanilloid 2 (TRPV2), a non-selective cation channel in the context of neurite functions. We confirm that functional TRPV2 is endogenously present in F11 cell line, a model system mimicking peripheral neuron. In F11 cells, TRPV2 localizes in specific subcellular regions enriched with filamentous actin, such as in growth cone, filopodia, lamellipodia and in neurites. TRPV2 regulates actin cytoskeleton and also interacts with soluble actin. Ectopic expression of TRPV2-GFP in F11 cell induces more primary and secondary neurites, confirming its role in neurite initiation, extension and branching events. TRPV2-mediated neuritogenesis is dependent on wildtype TRPV2 as cells expressing TRPV2 mutants reveal no neuritogenesis. These findings are relevant to understand the sprouting of new neurites, neuroregeneration and neuronal plasticity at the cellular, subcellular and molecular levels. Such understanding may have further implications in neurodegeneration and peripheral neuropathy.

Direct Current Electric Stimulation Alters the Frequency and the Distribution of Mitotic Cells in Planarians

Background: The use of direct current electric stimulation (DCS) is an effective strategy to treat disease and enhance body functionality. Thus, treatment with DCS is an attractive biomedical alternative, but the molecular underpinnings remain mostly unknown. The lack of experimental models to dissect the effects of DCS from molecular to organismal levels is an important caveat. Here, we introduce the planarian flatworm Schmidtea mediterranea as a tractable organism for in vivo studies of DCS. We developed an experimental method that facilitates the application of direct current electrical stimulation to the whole planarian body (pDCS). Materials and Methods: Planarian immobilization was achieved by combining treatment with anesthesia, agar embedding, and low temperature via a dedicated thermoelectric cooling unit. Electric currents for pDCS were delivered using pulled glass microelectrodes. The electric potential was supplied through a constant voltage power supply. pDCS was administered up to six hours, and behavioral and molecular effects were measured by using video recordings, immunohistochemistry, and gene expression analysis. Results: The behavioral immobilization effects are reversible, and pDCS resulted in a redistribution of mitotic cells along the mediolateral axis of the planarian body. The pDCS effects were dependent on the polarity of the electric field, which led to either increase in reductions in mitotic densities associated with the time of pDCS. The changes in mitotic cells were consistent with apparent redistribution in gene expression of the stem cell marker smedwi-1. Conclusion: The immobilization technique presented in this work facilitates studies aimed at dissecting the effects of exogenous electric stimulation in the adult body. Treatment with DCS can be administered for varying times, and the consequences evaluated at different levels, including animal behavior, cellular and transcriptional changes. Indeed, treatment with pDCS can alter cellular and transcriptional parameters depending on the polarity of the electric field and duration of the exposure.

Altered β-Cell Calcium Dynamics via Electric Field Exposure

Electric field stimulation has long been investigated with results supporting its therapeutic potential; however, its effects on insulin secreting cells has yet to be fully elucidated. Herein we explored the effects of physiological direct current (DC) electric field stimulation on the intracellular calcium dynamics of mouse derived βTC-6 insulinoma cells. This electrical stimulation resulted in an elevation in intracellular calcium along with a rise in calcium spiking activity. Further investigation indicated that the rise in intracellular calcium was mediated by an influx of calcium via L-type voltage gated calcium channels. Additionally, the effects of the electric field stimulation were able to induce insulin secretion in the absence of glucose stimulation. Given these results, DC electric field stimulation could be used as a non-invasive tool to modulate intracellular calcium dynamics and insulin secretion of β-cells for therapeutic application.

Ratiometric widefield imaging with spectrally balanced detection

Ratiometric imaging is an invaluable tool for quantitative microscopy, allowing for robust detection of FRET, anisotropy, and spectral shifts of nano-scale optical probes in response to local physical and chemical variations such as local pH, ion composition, and electric potential. In this paper, we propose and demonstrate a scheme for widefield ratiometric imaging that allows for continuous tuning of the cutoff wavelength between its two spectral channels. This scheme is based on angle-tuning the image splitting dichroic beamsplitter, similar to previous works on tunable interference filters. This configuration allows for ratiometric imaging of spectrally heterogeneous samples, which require spectral tunability of the detection path in order to achieve good spectrally balanced ratiometric detection.

A simple and robust fluorescent labeling method to quantify trophoblast fusion

Trophoblast fusion into syncytiotrophoblasts is a specialized yet enigmatic cellular process, which is essential for placental development and function. To facilitate mechanistic understanding of this critical process, here we re-purposed a widely used fluorescent membrane potential dye, Di-8-ANEPPS, to stably label the plasma membrane of live BeWo trophoblast cells. Compared to the methods currently available to quantify trophoblast fusion, our new fluorescent labeling method is simple, economical, robust and versatile, enabling quick and accurate quantification of fusion index in living cells.

Fluorescence Approaches to Image and Quantify the Demarcation Membrane System in Living Megakaryocytes

The demarcation membrane system (DMS) develops to provide additional surface membrane for the process of platelet production. The DMS is an invagination of the plasma membrane that can extend throughout the extranuclear volume of mature megakaryocytes and its lumen is continuous with the extracellular solution. DMS ultrastructure in fixed samples has been extensively studied using transmission electron microscopy (TEM) and more recently with focused ion beam scanning EM. In addition, whole cell patch clamp membrane capacitance provides a direct measurement of DMS content in living megakaryocytes. However, fluorescence methods to image and quantify the DMS in living megakaryocytes provide several advantages. For example, confocal fluorescence microscopy is easier to use compared to EM or electrophysiological methods and the required equipment is more readily available. In addition, use of living cells avoids artifacts known to occur during the fixation, dehydration, or embedding steps used to prepare EM samples. Here we describe the use of styryl dyes such as FM 1-43 or di-8-ANEPPS and impermeant fluorescent indicators of the extracellular space as simple approaches for imaging and quantification of the DMS.

Anodal Transcranial Direct Current Stimulation Enhances Survival and Integration of Dopaminergic Cell Transplants in a Rat Parkinson Model

Restorative therapy concepts, such as cell based therapies aim to restitute impaired neurotransmission in neurodegenerative diseases. New strategies to enhance grafted cell survival and integration are still needed to improve functional recovery. Anodal direct current stimulation (DCS) promotes neuronal activity and secretion of the trophic factor BDNF in the motor cortex. Transcranial DCS applied to the motor cortex transiently improves motor symptoms in Parkinson’s disease (PD) patients. In this proof-of-concept study, we combine cell based therapy and noninvasive neuromodulation to assess whether neurotrophic support via transcranial DCS would enhance the restitution of striatal neurotransmission by fetal dopaminergic transplants in a rat Parkinson model. Transcranial DCS was applied daily for 20 min on 14 consecutive days following striatal transplantation of fetal ventral mesencephalic (fVM) cells derived from transgenic rat embryos ubiquitously expressing GFP. Anodal but not cathodal transcranial DCS significantly enhanced graft survival and dopaminergic reinnervation of the surrounding striatal tissue relative to sham stimulation. Behavioral recovery was more pronounced following anodal transcranial DCS, and behavioral effects correlated with the degree of striatal innervation. Our results suggest anodal transcranial DCS may help advance cell-based restorative therapies in neurodegenerative diseases. In particular, such an assistive approach may be beneficial for the already established cell transplantation therapy in PD.

Chiro-Optical Modulation for NURR1 Production from Stem Cells

Nuclear receptor related 1 (NURR1) is an essential protein for maintenance of dopaminergic neurons in adult midbrain of which deficiency leads to Parkinson's disease. To enhance the NURR1 production of neural cells, various approaches are under investigation. Here we report that NURR1 is highly expressed in stem cells by exposure to an L-polarized blue light emitting diode (LED). Compared to stem cells cultured in the absence of a LED, under polarized green and red LEDs, the stem cells exposed to a polarized blue LED significantly enhanced neuronal biomarkers such as neurofilament M (NFM) and neuron specific enolase (NSE) at both mRNA and protein levels. In particular, NURR1 was selectively enhanced by the stem cells exposed to the L-polarized blue LED. Stem cells exposed to the L-polarized blue LED increased mitochondrial ATP and intracellular calcium ions, which support neuronal differentiation of the stem cells. This study suggests that chiro-optical treatments by using polarized light with a specific wavelength can be used for engineering of stem cells with enhanced specific biochemicals, which may open a new method for a specific disease.

The use of electric, magnetic, and electromagnetic field for directed cell migration and adhesion in regenerative medicine

Directed cell migration and adhesion is essential to embryonic development, tissue formation and wound healing. For decades it has been reported that electric field (EF), magnetic field (MF) and electromagnetic field (EMF) can play important roles in determining cell differentiation, migration, adhesion, and evenwound healing. Combinations of these techniques have revealed new and exciting explanations for how cells move and adhere to surfaces; how the migration of multiple cells are coordinated and regulated; how cellsinteract with neighboring cells, and also to changes in their microenvironment. In some cells, speed and direction are voltage dependent. Data suggests that the use of EF, MF and EMF could advance techniques in regenerative medicine, tissue engineering and wound healing. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 33:5-16, 2017.

Kcnh2 and Kcnj8 interactively regulate skin wound healing and regeneration

Previous studies indicate that ion channels are mediators of bioelectricity promoting wound closure/regeneration in nonmammalian, lower vertebrate systems. The role of ion channels however in regeneration of wounds in mammalian systems that do not regenerate as adults is not yet defined. Using a mammalian model system that allows us to determine differentially expressed genes when skin regenerates and when skin does not regenerate after wound induction, we identified two potassium channels, kcnh2 and kcnj8, to be (1) differentially expressed between the two states and (2) highly expressed after wound induction at the nonregenerative state. We also found that kcnh2 small molecule inhibitor enhanced wound healing while kcnj8 small molecule inhibitor did not. In contrast, kcnj8 activator accelerated wound healing and even augmented the effect of kcnh2 inhibition. These results provide evidence for the first time that potassium channels may mediate skin wound healing and regeneration interactively.

Glia: A Neglected Player in Non-invasive Direct Current Brain Stimulation

Non-invasive electrical brain stimulation by application of direct current (DCS) promotes plasticity in neuronal networks in vitro and in in vivo. This effect has been mainly attributed to the direct modulation of neurons. Glia represents approximately 50% of cells in the brain. Glial cells are electrically active and participate in synaptic plasticity. Despite of that, effects of DCS on glial structures and on interaction with neurons are only sparsely investigated. In this perspectives article we review the current literature, present own dose response data and provide a framework for future research from two points of view: first, the direct effects of DCS on glia and second, the contribution of glia to DCS related neuronal plasticity.

Neural cell adhesion molecule 2 promotes the formation of filopodia and neurite branching by inducing submembrane increases in Ca2+ levels

Changes in expression of the neural cell adhesion molecule 2 (NCAM2) have been proposed to contribute to neurodevelopmental disorders in humans. The role of NCAM2 in neuronal differentiation remains, however, poorly understood. Using genetically encoded Ca(2+) reporters, we show that clustering of NCAM2 at the cell surface of mouse cortical neurons induces submembrane [Ca(2+)] spikes, which depend on the L-type voltage-dependent Ca(2+) channels (VDCCs) and require activation of the protein tyrosine kinase c-Src. We also demonstrate that clustering of NCAM2 induces L-type VDCC- and c-Src-dependent activation of CaMKII. NCAM2-dependent submembrane [Ca(2+)] spikes colocalize with the bases of filopodia. NCAM2 activation increases the density of filopodia along neurites and neurite branching and outgrowth in an L-type VDCC-, c-Src-, and CaMKII-dependent manner. Our results therefore indicate that NCAM2 promotes the formation of filopodia and neurite branching by inducing Ca(2+) influx and CaMKII activation. Changes in NCAM2 expression in Down syndrome and autistic patients may therefore contribute to abnormal neurite branching observed in these disorders.

The morphological and molecular changes of brain cells exposed to direct current electric field stimulation

BACKGROUND

The application of low-intensity direct current electric fields has been experimentally used in the clinic to treat a number of brain disorders, predominantly using transcranial direct current stimulation approaches. However, the cellular and molecular changes induced by such treatment remain largely unknown.

METHODS

Here, we tested various intensities of direct current electric fields (0, 25, 50, and 100V/m) in a well-controlled in vitro environment in order to investigate the responses of neurons, microglia, and astrocytes to this type of stimulation. This included morphological assessments of the cells, viability, as well as shape and fiber outgrowth relative to the orientation of the direct current electric field. We also undertook enzyme-linked immunosorbent assays and western immunoblotting to identify which molecular pathways were affected by direct current electric fields.

RESULTS

In response to direct current electric field, neurons developed an elongated cell body shape with neurite outgrowth that was associated with a significant increase in growth associated protein-43. Fetal midbrain dopaminergic explants grown in a collagen gel matrix also showed a reorientation of their neurites towards the cathode. BV2 microglial cells adopted distinct morphological changes with an increase in cyclooxygenase-2 expression, but these were dependent on whether they had already been activated with lipopolysaccharide. Finally, astrocytes displayed elongated cell bodies with cellular filopodia that were oriented perpendicularly to the direct current electric field.

CONCLUSION

We show that cells of the central nervous system can respond to direct current electric fields both in terms of their morphological shape and molecular expression of certain proteins, and this in turn can help us to begin understand the mechanisms underlying the clinical benefits of direct current electric field.

Cellular and molecular mechanisms of action of transcranial direct current stimulation: evidence from in vitro and in vivo models

Transcranial direct current stimulation is a noninvasive technique that has been experimentally tested for a number of psychiatric and neurological conditions. Preliminary observations suggest that this approach can indeed influence a number of cellular and molecular pathways that may be disease relevant. However, the mechanisms of action underlying its beneficial effects are largely unknown and need to be better understood to allow this therapy to be used optimally. In this review, we summarize the physiological responses observed in vitro and in vivo, with a particular emphasis on cellular and molecular cascades associated with inflammation, angiogenesis, neurogenesis, and neuroplasticity recruited by direct current stimulation, a topic that has been largely neglected in the literature. A better understanding of the neural responses to transcranial direct current stimulation is critical if this therapy is to be used in large-scale clinical trials with a view of being routinely offered to patients suffering from various conditions affecting the central nervous system.

Rat embryonic hippocampus and induced pluripotent stem cell derived cultured neurons recover from laser-induced subaxotomy

Axonal injury and stress have long been thought to play a pathogenic role in a variety of neurodegenerative diseases. However, a model for studying single-cell axonal injury in mammalian cells and the processes of repair has not been established. The purpose of this study was to examine the response of neuronal growth cones to laser-induced axonal damage in cultures of embryonic rat hippocampal neurons and induced pluripotent stem cell (iPSC) derived human neurons. A 532-nm pulsed [Formula: see text] picosecond laser was focused to a diffraction limited spot at a precise location on an axon using a laser energy/power that did not rupture the cell membrane (subaxotomy). Subsequent time series images were taken to follow axonal recovery and growth cone dynamics. After laser subaxotomy, axons thinned at the damage site and initiated a dynamic cytoskeletal remodeling process to restore axonal thickness. The growth cone was observed to play a role in the repair process in both hippocampal and iPSC-derived neurons. Immunofluorescence staining confirmed structural tubulin damage and revealed initial phases of actin-based cytoskeletal remodeling at the damage site. The results of this study indicate that there is a repeatable and cross-species repair response of axons and growth cones after laser-induced damage.

Design and Use of Organic Voltage Sensitive Dyes

The chemistry and the physics of voltage sensitive dyes (VSDs) should be understood and appreciated as a prerequisite for their optimal application to problems in neuroscience cardiology. This chapter provides a basic understanding of the properties of the large variety of available organic VSDs. The mechanisms by which the dyes respond to voltage guides the best set up of the optics for recording or imaging electrophysiological activity. The physical and chemical properties of the dyes can be tuned to optimize delivery to and staining of the cells in different experimental preparations. The aim of this chapter is to arm the experimentalists who use the dyes with enough information and data to be able to intelligently choose the best dye for their specific requirements.

Monitoring membrane potential with second-harmonic generation

This protocol describes the nonlinear optical phenomenon known as second-harmonic generation (SHG) and discusses its special attributes for imaging membrane-potential changes in single cells and multicellular preparations. Undifferentiated N1E-115 mouse neuroblastoma cells are used as a model cellular system for membrane electrophysiology. Styryl and naphthylstyryl dyes, also known as hemicyanines, are a class of electrochromic membrane-staining probes that have been used to monitor membrane potential by fluorescence; they also produce SHG images of cell membranes with SHG intensities that are sensitive to voltage. These experiments allow for the precise characterization of the voltage sensitivity of SHG and identification of the optimal wavelength for the incident laser fundamental light. This protocol presents the steps for the culture, staining, patching, and imaging of cells. The details of the imaging system and the measurements obtained are discussed, as are the prospects of this technology for imaging membrane potential changes in neuronal preparations.

Influence of electrotaxis on cell behaviour

Understanding the mechanism of cell migration and interaction with the microenvironment is not only of critical significance to the function and biology of cells, but also has extreme relevance and impact on physiological processes and diseases such as morphogenesis, wound healing, neuron guidance, and cancer metastasis.

Cell adhesion and intracellular calcium signaling in neurons

Cell adhesion molecules (CAMs) play indispensable roles in the developing and mature brain by regulating neuronal migration and differentiation, neurite outgrowth, axonal fasciculation, synapse formation and synaptic plasticity. CAM-mediated changes in neuronal behavior depend on a number of intracellular signaling cascades including changes in various second messengers, among which CAM-dependent changes in intracellular Ca²⁺ levels play a prominent role. Ca²⁺ is an essential secondary intracellular signaling molecule that regulates fundamental cellular functions in various cell types, including neurons. We present a systematic review of the studies reporting changes in intracellular Ca²⁺ levels in response to activation of the immunoglobulin superfamily CAMs, cadherins and integrins in neurons. We also analyze current experimental evidence on the Ca²⁺ sources and channels involved in intracellular Ca²⁺ increases mediated by CAMs of these families, and systematically review the role of the voltage-dependent Ca²⁺ channels (VDCCs) in neurite outgrowth induced by activation of these CAMs. Molecular mechanisms linking CAMs to VDCCs and intracellular Ca²⁺ stores in neurons are discussed.

Confocal imaging of transmembrane voltage by SEER of di-8-ANEPPS

Imaging, optical mapping, and optical multisite recording of transmembrane potential (V_m) are essential for studying excitable cells and systems. The naphthylstyryl voltage-sensitive dyes, including di-8-ANEPPS, shift both their fluorescence excitation and emission spectra upon changes in V_m. Accordingly, they have been used for monitoring V_m in nonratioing and both emission and excitation ratioing modes. Their changes in fluorescence are usually much less than 10% per 100 mV. Conventional ratioing increases sensitivity to between 3 and 15% per 100 mV. Low sensitivity limits the value of these dyes, especially when imaged with low light systems like confocal scanners. Here we demonstrate the improvement afforded by shifted excitation and emission ratioing (SEER) as applied to imaging membrane potential in flexor digitorum brevis muscle fibers of adult mice. SEER—the ratioing of two images of fluorescence, obtained with different excitation wavelengths in different emission bands—was implemented in two commercial confocal systems. A conventional pinhole scanner, affording optimal setting of emission bands but less than ideal excitation wavelengths, achieved a sensitivity of up to 27% per 100 mV, nearly doubling the value found by conventional ratioing of the same data. A better pair of excitation lights should increase the sensitivity further, to 35% per 100 mV. The maximum acquisition rate with this system was 1 kHz. A fast “slit scanner” increased the effective rate to 8 kHz, but sensitivity was lower. In its high-sensitivity implementation, the technique demonstrated progressive deterioration of action potentials upon fatiguing tetani induced by stimulation patterns at >40 Hz, thereby identifying action potential decay as a contributor to fatigue onset. Using the fast implementation, we could image for the first time an action potential simultaneously at multiple locations along the t-tubule system. These images resolved the radially varying lag associated with propagation at a finite velocity.

Absolute spectroscopic determination of cross-membrane potential

Spectroscopic determination of the cross-membrane electric potential has been used for more than 20 years. This method, which usually employs absorption or fluorescence measurements, allows for a rapid and noninvasive study of the electrical properties of the membranes of cells and liposomes. However, the usual fluorescence techniques preferably allow monitoring changes in the potential on triggerable or excitable membranes, and not the absolute value of the potential. They also do not provide means for measuring the potential on single cells. This paper reviews three methods that solve these issues. Nernstian dyes which partition between intra-and extracompartmental volumes enable a fluorescence microscopic determination of a single cell and even a single organelle. Dual-wavelength ratiometric recording from membrane-staining dyes also provides means for measuring the field on a single cell. Resonance Raman probes provide a spectroscopic method with a natural internal standard for the absolute measurement of membrane potential.

Palette of fluorinated voltage-sensitive hemicyanine dyes

Optical recording of membrane potential permits spatially resolved measurement of electrical activity in subcellular regions of single cells, which would be inaccessible to electrodes, and imaging of spatiotemporal patterns of action potential propagation in excitable tissues, such as the brain or heart. However, the available voltage-sensitive dyes (VSDs) are not always spectrally compatible with newly available optical technologies for sensing or manipulating the physiological state of a system. Here, we describe a series of 19 fluorinated VSDs based on the hemicyanine class of chromophores. Strategic placement of the fluorine atoms on the chromophores can result in either blue or red shifts in the absorbance and emission spectra. The range of one-photon excitation wavelengths afforded by these new VSDs spans 440-670 nm; the two-photon excitation range is 900-1,340 nm. The emission of each VSD is shifted by at least 100 nm to the red of its one-photon excitation spectrum. The set of VSDs, thus, affords an extended toolkit for optical recording to match a broad range of experimental requirements. We show the sensitivity to voltage and the photostability of the new VSDs in a series of experimental preparations ranging in scale from single dendritic spines to whole heart. Among the advances shown in these applications are simultaneous recording of voltage and calcium in single dendritic spines and optical electrophysiology recordings using two-photon excitation above 1,100 nm.

The Na conductance in the sarcolemma and the transverse tubular system membranes of mammalian skeletal muscle fibers

Na (and Li) currents and fluorescence transients were recorded simultaneously under voltage-clamp conditions from mouse flexor digitorum brevis fibers stained with the potentiometric dye di-8-ANEPPS to investigate the distribution of Na channels between the surface and transverse tubular system (TTS) membranes. In fibers rendered electrically passive, voltage pulses resulted in step-like fluorescence changes that were used to calibrate the dye response. The effects of Na channel activation on the TTS voltage were investigated using Li, instead of Na, because di-8-ANEPPS transients show anomalies in the presence of the latter. Na and Li inward currents (I(Na), I(Li); using half of the physiological ion concentration) showed very steep voltage dependences, with no reversal for depolarizations beyond the calculated equilibrium potential, suggesting that most of the current originates from a noncontrolled membrane compartment. Maximum peak I(Li) was ∼ 30% smaller than for I(Na), suggesting a Li-blocking effect. I(Li) activation resulted in the appearance of overshoots in otherwise step-like di-8-ANEPPS transients. Overshoots had comparable durations and voltage dependence as those of I(Li). Simultaneously measured maximal overshoot and peak I(Li) were 54 ± 5% and 773 ± 53 µA/cm(2), respectively. Radial cable model simulations predicted the properties of I(Li) and di-8-ANEPPS transients when TTS access resistances of 10-20 Ω cm(2), and TTS-to-surface Na permeability density ratios in the range of 40:60 to 70:30, were used. Formamide-based osmotic shock resulted in incomplete detubulation. However, results from a subpopulation of treated fibers (low capacitance) provide confirmatory evidence that a significant proportion of I(Li), and the overshoot in the optical signals, arises from the TTS in normal fibers. The quantitative evaluation of the distribution of Na channels between the sarcolemma and the TTS membranes, as provided here, is crucial for the understanding of the radial and longitudinal propagation of the action potential, which ultimately govern the mechanical activation of muscle in normal and diseased conditions.

Measurements and implications of the membrane dipole potential

There are three kinds of membrane potentials: the surface potentials, resulting from the accumulation of charges at the membrane surfaces; the transmembrane potential, determined by imbalance of charge in the aqueous solutions; and the dipole potential, a membrane-internal potential from the dipolar components of the phospholipids and interface water. The absolute value of the dipole potential has been very difficult to measure, although its value has been estimated to be in the range of 200-1,000 mV from ion translocation rates (determined by the planar lipid bilayer method), the surface potential of lipid monolayers (determined by the lipid monolayer method), molecular-dynamics calculations, and electron scattering using cryoelectron microscopy (cryo-EM). Spectroscopy methods have also been used to monitor the dipole potential changes on the basis of the observed fluorescence changes of voltage-sensitive probes. The dipole potential accounts for the much larger permeability of a bare phospholipid membrane to anions than cations and affects the conformation and function of membrane proteins.

Mechanism of acetylcholine receptor cluster formation induced by DC electric field

Background

The formation of acetylcholine receptor (AChR) cluster is a key event during the development of the neuromuscular junction. It is induced through the activation of muscle-specific kinase (MuSK) by the heparan-sulfate proteoglycan agrin released from the motor axon. On the other hand, DC electric field, a non-neuronal stimulus, is also highly effective in causing AChRs to cluster along the cathode-facing edge of muscle cells.

Methodology/Principal Findings

To understand its molecular mechanism, quantum dots (QDs) were used to follow the movement of AChRs as they became clustered under the influence of electric field. From analyses of trajectories of AChR movement in the membrane, it was concluded that diffuse receptors underwent Brownian motion until they were immobilized at sites of cluster formation. This supports the diffusion-mediated trapping model in explaining AChR clustering under the influence of this stimulus. Disrupting F-actin cytoskeleton assembly and interfering with rapsyn-AChR interaction suppressed this phenomenon, suggesting that these are integral components of the trapping mechanism induced by the electric field. Consistent with the idea that signaling pathways are activated by this stimulus, the localization of tyrosine-phosphorylated forms of AChR β-subunit and Src was observed at cathodal AChR clusters. Furthermore, disrupting MuSK activity through the expression of a kinase-dead form of this enzyme abolished electric field-induced AChR clustering.

Conclusions

These results suggest that DC electric field as a physical stimulus elicits molecular reactions in muscle cells in the form of cathodal MuSK activation in a ligand-free manner to trigger a signaling pathway that leads to cytoskeletal assembly and AChR clustering.

Current status of the use of modalities in wound care: electrical stimulation and ultrasound therapy

Wound healing is a complex pathway that requires cells, an appropriate biochemical environment (i.e., cytokines, chemokines), an extracellular matrix, perfusion, and the application of both macrostrain and microstrain. The process is both biochemically complex and energy dependent. Healing can be assisted in difficult cases through the use of physical modalities. In the current literature, there is much debate over which treatment modality, dosage level, and timing is optimal. The mechanism of action for both electrical stimulation and ultrasound are reviewed along with possible clinical applications for the plastic surgeon.

Recordings from human myenteric neurons using voltage-sensitive dyes

Voltage-sensitive dye (VSD) imaging became a powerful tool to detect neural activity in the enteric nervous system, including its routine use in submucous neurons in freshly dissected human tissue. However, VSD imaging of human myenteric neurons remained a challenge because of limited visibility of the ganglia and dye accessibility. We describe a protocol to apply VSD for recordings of human myenteric neurons in freshly dissected tissue and myenteric neurons in primary cultures. VSD imaging of guinea-pig myenteric neurons was used for reference. Electrical stimulation of interganglionic fiber tracts and exogenous application of nicotine or elevated KCl solution was used to evoke action potentials. Bath application of the VSDs Annine-6Plus, Di-4-ANEPPS, Di-8-ANEPPQ, Di-4-ANEPPDHQ or Di-8-ANEPPS revealed no neural signals in human tissue although most of these VSD worked in guinea-pig tissue. Unlike methylene blue and FM1-43, 4-Di-2-ASP did not influence spike discharge and was used in human tissue to visualize myenteric ganglia as a prerequisite for targeted intraganglionic VSD application. Of all VSDs, only intraganglionic injection of Di-8-ANEPPS by a volume controlled injector revealed neuronal signals in human tissue. Signal-to-noise ratio increased by addition of dipicrylamine to Di-8-ANEPPS (0.98±0.16 vs. 2.4±0.62). Establishing VSD imaging in primary cultures of human myenteric neurons led to a further improvement of signal-to-noise ratio. This allowed us to routinely record spike discharge after nicotine application. The described protocol enabled reliable VSD recordings from human myenteric neurons but may also be relevant for the use of other fluorescent dyes in human tissues.