Magnetic stimulation and depression of mammalian networks in primary neuronal cell cultures

Optogenetics in cardiology: methodology and future applications

Optogenetics is an emerging biological approach with the unique capability of specific targeting due to the precise light control with high spatial and temporal resolution. It uses selected light wavelengths to control and modulate the biological functions of cells, tissues, and organ levels. Optogenetics has been instrumental in different biomedical applications, including neuroscience, diabetes, and mitochondria, based on distinctive optical biomedical effects with light modulation. Nowadays, optogenetics in cardiology is rapidly evolving for the understanding and treatment of cardiovascular diseases. Several in vitro and in vivo research for cardiac optogenetics demonstrated visible progress. The optogenetics technique can be applied to address critical cardiovascular problems such as heart failure and arrhythmia. To this end, this paper reviews cardiac electrophysiology and the technical progress about experimental and clinical cardiac optogenetics and provides the background and evolution of cardiac optogenetics. We reviewed the literature to demonstrate the servo type, transfection efficiency, signal recording, and heart disease targets in optogenetic applications. Such literature review would hopefully expedite the progress of optogenetics in cardiology and further expect to translate into the clinical terminal in the future.

Simultaneous electrophysiological and morphological assessment of functional damage to neural networks in vitro after 30-300 g impacts

An enigma of mild traumatic brain injury are observations of substantial behavior and performance deficits in the absence of bleeding or other observable structural damage. Altered behavior and performance reflect changes in action potential (AP) patterns within neuronal networks, which could result from subtle subcellular responses that affect synaptic efficacy and AP production. The aim of this study was to investigate and quantify network activity changes after simulated concussions in vitro and therewith develop a platform for simultaneous and direct observations of morphological and electrophysiological changes in neural networks. We used spontaneously active networks grown on microelectrode arrays (MEAs) to allow long-term multisite monitoring with simultaneous optical observations before and after impacts delivered by a ballistic pendulum (30 to 300 g accelerations). The monitoring of AP waveshape templates for long periods before and after impact provided an internal control for cell death or loss of cell-electrode coupling in the observed set of neurons. Network activity patterns were linked in real-time to high power phase contrast microscopy. There was no overt loss of glial or neuronal adhesion, even at high-g impacts. All recording experiments showed repeatable spike production responses: a loss of activity with recovery to near reference in 1 hr, followed by a slow activity decay to a stable, level plateau approximately 30–40% below reference. The initial recovery occurred in two steps: a rapid return of activity to an average 24% below reference, forming a level plateau lasting from 5 to 20 min, followed by a climb to within 10% of reference where a second plateau was established for 1 to 2 hrs. Cross correlation profiles revealed changes in firing hierarchy as well as in Phase 1 in spontaneous network oscillations that were reduced by as much as 20% 6–8 min post impact with only a partial recovery at 30 min. We also observed that normally stable nuclei developed irregular rotational motion after impact in 27 out of 30 networks. The evolution of network activity deficits and recovery can be linked with microscopically observable changes in the very cells that are generating the activity. The repeatable electrophysiological impact response profiles and oscillation changes can provide a quantitative basis for systematic evaluations of pharmacological intervention strategies. Future expansion to include fluorescent microscopy should allow detailed investigations of damage mechanisms on the subcellular level.

Influence of magnetic field on morphological structures and physiological characteristics of bEnd.3 cells cultured on polypyrrole substrates

This paper employs a spin-coated method to construct conductive polypyrrole (PPy) substrates which present superior properties for controlling the morphological structures and functions of bEnd.3 cells. The PPy substrates with a homogeneous particle size, uniform distribution and proper roughness show enhanced hydrophilic characteristics and improve cell adhesion to the substrates. The changes in the mechanical properties of cells and the responses to the designed substrates and magnetic field are also explored. Due to the synergistic effect between the magnetic field and the conductive PPy substrate, the cells cultured in such an environment exhibit applanate shapes with more branches and enhanced cell viability. In addition, the cells preferentially extend along the magnetic field direction. The mechanical characteristics of cells change significantly under varying magnetic intensity stimulations (5–16 mT). The satisfying effect on cells' morphology and outgrowth is acquired at the magnetic intensities of 9–10 mT and duration of 20 min, compared with other stimulated groups, while retaining cell viability. Moreover, the cells express higher adhesion up to 5.2 nN. The results suggest that the application of the PPy substrates and magnetic field is a promising candidate for the protection of neurovascular units and treatment of neurological diseases.

The combination of magnetic stimulation and polypyrrole (PPy) substrates regulate the bEnd.3 cells mechanical and physical characterizations.

Non-conductive and miniature fiber-optic imaging system for real-time detection of neuronal activity in time-varying electromagnetic fields

Establishing an appropriate threshold value for neuronal modulation by time-varying electromagnetic field (EMF) exposure is important for developing international guidelines to protect against the potential health effects, and to design a variety of medical devices. However, it is technically difficult to achieve real-time detection of neuronal activity under repetitive and long-term exposure to EMF. For this purpose, we developed a non-conductive, miniature, and flexible fiber-optic imaging system that does not affect the electromagnetic noise, induction heating, or vibration in a high-intensity and repetitive time-varying EMF exposure. Using the proposed system, we succeeded at real-time detection of spontaneous Ca²⁺ oscillations in single neuronal and glial cells, as well as synchronized bursting activities of multiple neuronal networks at a micrometer-scale and millisecond-order spatiotemporal resolution during long-term EMF exposure (sinusoidal wave, 20kHz, 8.6mT, >30min). The results indicated that short-term (<5min) exposure-related neuronal modulation was not detectable; however, long-term (15-30min) exposure was observed to depress neuronal activities. In addition, the simultaneous and real-time recording of neuronal activity and the environmental temperature revealed that the neuronal modulation was accompanied by a 0.5-1°C rise in the temperature of the culture medium induced by the heat generation of exposure coils. These findings suggest that our real-time imaging system can be used for precise evaluation of the threshold values and clarification of the mechanisms of neuronal modulation induced by time-varying EMF exposure.

In vitro Magnetic Stimulation: A Simple Stimulation Device to Deliver Defined Low Intensity Electromagnetic Fields

Non-invasive brain stimulation (NIBS) by electromagnetic fields appears to benefit human neurological and psychiatric conditions, although the optimal stimulation parameters and underlying mechanisms remain unclear. Although, in vitro studies have begun to elucidate cellular mechanisms, stimulation is delivered by a range of coils (from commercially available human stimulation coils to laboratory-built circuits) so that the electromagnetic fields induced within the tissue to produce the reported effects are ill-defined. Here, we develop a simple in vitro stimulation device with plug-and-play features that allow delivery of a range of stimulation parameters. We chose to test low intensity repetitive magnetic stimulation (LI-rMS) delivered at three frequencies to hindbrain explant cultures containing the olivocerebellar pathway. We used computational modeling to define the parameters of a stimulation circuit and coil that deliver a unidirectional homogeneous magnetic field of known intensity and direction, and therefore a predictable electric field, to the target. We built the coil to be compatible with culture requirements: stimulation within an incubator; a flat surface allowing consistent position and magnetic field direction; location outside the culture plate to maintain sterility and no heating or vibration. Measurements at the explant confirmed the induced magnetic field was homogenous and matched the simulation results. To validate our system we investigated biological effects following LI-rMS at 1 Hz, 10 Hz and biomimetic high frequency, which we have previously shown induces neural circuit reorganization. We found that gene expression was modified by LI-rMS in a frequency-related manner. Four hours after a single 10-min stimulation session, the number of c-fos positive cells increased, indicating that our stimulation activated the tissue. Also, after 14 days of LI-rMS, the expression of genes normally present in the tissue was differentially modified according to the stimulation delivered. Thus we describe a simple magnetic stimulation device that delivers defined stimulation parameters to different neural systems in vitro. Such devices are essential to further understanding of the fundamental effects of magnetic stimulation on biological tissue and optimize therapeutic application of human NIBS.

Study of intracranial pressure in human brain during transcranial magnetic stimulation

This paper presents the results of cranial force in human brain due to electromagnetic pulse during transcranial magnetic stimulation. To model the force in a realistic brain, we used three dimensional magnetic resonance image of the 26 years old female subject. Simulation results show that during TMS procedure, there is a small force generated within the cranial tissue layers along with a torque value in different layers of brain tissues. The force depends on the magnitude of the magnetic field generated by the TMS coil.

Modulation of neuronal network activity using magnetic nanoparticle-based astrocytic network integration

Investigating the mechanisms of the neuron-glia interaction is important in the basic research of neuroscience and neural transplantation. Synaptic transmission is modulated by astrocyte activation in the pre- and post-synaptic terminals, and this phenomenon is spread to the surrounding astrocytes through gap junctions. However, the modulation of network-wide neuronal activity dependent on extensive astrocyte activation is not well understood. In this study, we show network-wide neuronal modulation associated with a newly developed three-dimensional neuronal and astrocytic network co-culture method. To establish widespread neuronal and astrocytic network interactions in vitro, we performed integration of magnetic nanoparticle-injected astrocytes (Mag-AS) onto the matured monolayer of neuronal networks using an external magnetic force. The neuronal electrical activity was dynamically synchronized at 24 h after integration of the Mag-AS network. In addition, Mag-AS network activation using a caged calcium compound rapidly induced suppression and subsequent synchronization of neuronal electrical activity. These results indicate that the high-density astrocytic network integration onto the neuronal network can induce widespread neuronal modulation, and our in vitro co-culture method contributes to the advancement of neuronal and astrocytic transplantation research.

Neurostimulation in Alzheimer's disease: from basic research to clinical applications

The development of different methods of brain stimulation provides a promising therapeutic tool with potentially beneficial effects on subjects with impaired cognitive functions. We performed a systematic review of the studies published in the field of neurostimulation in Alzheimer's disease (AD), from basic research to clinical applications. The main methods of non-invasive brain stimulation are repetitive transcranial magnetic stimulation and transcranial direct current stimulation. Preliminary findings have suggested that both techniques can enhance performances on several cognitive functions impaired in AD. Another non-invasive emerging neuromodulatory approach, the transcranial electromagnetic treatment, was found to reverse cognitive impairment in AD transgenic mice and even improves cognitive performance in normal mice. Experimental studies suggest that high-frequency electromagnetic fields may be critically important in AD prevention and treatment through their action at mitochondrial level. Finally, the application of a widely known invasive technique, the deep brain stimulation (DBS), has increasingly been considered as a therapeutic option also for patients with AD; it has been demonstrated that DBS of fornix/hypothalamus and nucleus basalis of Meynert might improve or at least stabilize cognitive functioning in AD. Initial encouraging results provide support for continuing to investigate non-invasive and invasive brain stimulation approaches as an adjuvant treatment for AD patients.

Dynamic steering of in vitro cortical neurons using field stimulation

Neurological disorders are often characterized by abnormal neuronal activity. In the case of epilepsy, this can manifest itself in the form of uncontrolled synchronous activity often in the form of bursting. Pattern steering is the ability to apply stimulation to a network that effectively changes its dynamical firing pattern. In an epileptic network, the stimulation would be used to move the seizing network from its abnormal state to a normal state. This idea is explored here in cultured networks of cortical neurons plated on microelectrode arrays. Stimulation was applied to the bath resulting in an electric field generated throughout the network. This field was verified as sub-threshold in strength using a finite element model simulation. Stimulated networks showed a significant suppression in the number of bursts and increase in the interburst interval as compared to control networks. This observed burst suppression suggests that the sub-threshold stimulating field moved networks from a state of high frequency bursting to a state of low frequency bursting.

Unraveling the cellular and molecular mechanisms of repetitive magnetic stimulation

Despite numerous clinical studies, which have investigated the therapeutic potential of repetitive transcranial magnetic stimulation (rTMS) in various brain diseases, our knowledge of the cellular and molecular mechanisms underlying rTMS-based therapies remains limited. Thus, a deeper understanding of rTMS-induced neural plasticity is required to optimize current treatment protocols. Studies in small animals or appropriate in vitro preparations (including models of brain diseases) provide highly useful experimental approaches in this context. State-of-the-art electrophysiological and live-cell imaging techniques that are well established in basic neuroscience can help answering some of the major questions in the field, such as (i) which neural structures are activated during TMS, (ii) how does rTMS induce Hebbian plasticity, and (iii) are other forms of plasticity (e.g., metaplasticity, structural plasticity) induced by rTMS? We argue that data gained from these studies will support the development of more effective and specific applications of rTMS in clinical practice.

Induced current pharmacological split stimulation system for neuronal networks

Magnetic stimulation noninvasively modulates neuronal activity through a magnetically induced current. However, despite the usefulness and popularity of this method, the effects of neuronal activity in the nonstimulated regions on the stimulus responses are unknown. Here, we report that the induced current-evoked responses were affected by neuronal activities in the nonstimulated regions. Our experiment used a Mu-metal-based localized induced current stimulation (LICS) system combined with the microfabricated cell culture chamber system and a microelectrode array (MEA). The cell culture chamber system has radiating microtunnels connecting one central and eight outer chambers, which were fabricated using soft lithography and a replica modeling technique with SU-8 photoresist and polydimethylsiloxane (PDMS). Rat cortical neurons were separately cultured in the chambers and formed functional synaptic connections through the microtunnels. By applying a biphasic alternating pulsed magnetic field to the Mu-metal located in the central chamber, induced currents were mainly generated near the cultured neurons and modified the neuronal activities, which were recorded through MEA. Furthermore, we confirmed that the evoked responses were modified by localized pharmacological stimulation (LPS) in the outer chambers. These results suggest that our system would be promising tool for analyzing the effect of magnetic stimulation on interacting neuronal activity.

Effect of magnetic stimulation on the gene expression profile of in vitro cultured neural cells

Transcranial magnetic stimulation is a non-invasive tool in clinical diagnostics and therapy for physiological and psychological diseases and has an increased application in experimental neurophysiology. Despite this, the mechanisms of magnetic stimulation of the central nervous system remain still unclear. We applied sinus-shaped high frequency magnetic fields in different stimulation patterns and repeated treatments to cell cultures derived from frontal cortex of murine embryos (BALB/cOlaHsd mice) to elucidate the effects of repetitive magnetic stimulation on the gene expression of in vitro cultured neural cells. Gene expression profiling was performed by using qRT-PCR array and single qRT-PCR analyses. Our methodological approach using microelectrode arrays data recording and analysis minimizes variations in transcriptome analysis arising from cell differentiation status and tissue complexity. With 10 significant changes in gene expression out of 171 genes using Alzheimer disease and neurodegeneration related qRT-PCR arrays we demonstrate significant impact of repetitive magnetic stimulation on the mRNA transcript of neural cell cultures. Sixteen candidate genes were analyzed using single qRT-PCR in a replicated statistical design, which provided more precise estimates of differences in expression profiles. We discussed the utility of the experimental methods used for cell culture selection and the changes in gene expression considering physiological aspects.

Spinal cord stimulation for complex regional pain syndrome

The therapy of spinal cord stimulation (SCS) is based on producing an electrical field on the dorsal surface of the spinal cord that blocks only neuropathic pain (ie, pain from damage to the nervous system). Most SCS devices deliver a biphasic pulse consisting of a pair of equal amplitude pulses with opposite polarity. SCS therapy is based on the gate control theory of pain and has been used for the treatment of diverse conditions of neuropathic pain, including complex regional pain syndromes (CRPS). In addition to CRPS, SCS is helpful in patients with failed back surgery syndrome, degenerative disk disease, and in patients with peripheral neuropathies. When used in the right patient, SCS provides significant pain relief in a majority of patients with CRPS. This review focuses on the effects of SCS on CRPS. In addition, an overview of the state of the art technologies used for implantable SCS medical devices is also provided.