A review on the consequences of molecular and genomic alterations following exposure to electromagnetic fields: Remodeling of neuronal network and cognitive changes

The use of electromagnetic fields (EMFs) is essential in daily life. Since 1970, concerns have grown about potential health hazards from EMF. Exposure to EMF can stimulate nerves and affect the central nervous system, leading to neurological and cognitive changes. However, current research results are often vague and contradictory. These effects include changes in memory and learning through changes in neuronal plasticity in the hippocampus, synapses and hippocampal neuritis, and changes in metabolism and neurotransmitter levels. Prenatal exposure to EMFs has negative effects on memory and learning, as well as changes in hippocampal neuron density and histomorphology of hippocampus. EMF exposure also affects the structure and function of glial cells, affecting gate dynamics, ion conduction, membrane concentration, and protein expression. EMF exposure affects gene expression and may change epigenetic regulation through effects on DNA methylation, histone modification, and microRNA biogenesis, and potentially leading to biological changes. Therefore, exposure to EMFs possibly leads to changes in cellular and molecular mechanisms in central nervous system and alter cognitive function.

Effect of music rhythm magnetic field on long-term potentiation of hippocampal Schaffer-CA1 synapse plasticity

Music and magnetic fields both play important regulatory roles in brain learning and memory. The present study aimed to investigate the effects of music rhythmic magnetic fields at different frequencies on long-term potentiation (LTP) in the Schaffer-CA1 region of the hippocampus, with the goal of elucidating the molecular mechanisms underlying the impact of music rhythmic magnetic fields on brain learning and memory. Three different frequency music tracks were selected, including soothing track 1: Courante from the Baroque Suite, medium-frequency track 2: saxophone version of Liang Zhu, and high-frequency track 3: Johann Pachelbel's music track Canon (trumpet version). Using an external sound card, power amplifier, and homemade coils, a time-varying magnetic field with a 2-mT music rhythm was produced to assess the effects of this magnetic field on LTP in the Schaffer-CA1 synapses of isolated rat hippocampal brain slices. The experimental results demonstrated that as the music frequency increased, the enhancing effect of the music rhythmic magnetic field on hippocampal synaptic plasticity LTP gradually intensified. Thus, high-frequency music rhythmic magnetic fields may offer a more effective means of enhancing LTP.

Modulatory effects of real-time electromagnetic stimulation on epileptiform activity in juvenile rat hippocampus based on multi-electrode array recordings

Electromagnetic stimulation (EMS) has proven to be useful for the focal suppression of epileptiform activity (EFA) in the hippocampus. There is a critical period during EFA for achieving the transition from brief interictal discharges (IIDs) to prolonged ictal discharges (IDs), and it is unknown whether EMS can modulate this transition. Therefore, this study aimed to evaluate the intensity- and time-dependent effect of EMS on the transition of EFA. A juvenile rat EFA model was constructed by perfusing magnesium-free artificial cerebrospinal fluid (aCSF) on brain slices, and the induced EFA was recorded using a micro-electrode array (MEA) platform. After a stable EFA event was recorded for some time, real-time pulsed magnetic stimulation with low and high peak-to-peak input magnetic field intensities was carried out. A 5-min intervention with real-time magnetic fields with low intensity was found to reduce the amplitude of IDs (ID events still existed), whereas a 5-min intervention with real-time magnetic fields with high input voltages completely suppressed IDs. Short-time magnetic fields (9s and 1min) with high or low input intensity had no effect on EFA. Real-time magnetic fields can block the normal EFA process from IIDs to IDs (i.e., a complete EFA cycle) and this suppression effect is dependent on input intensities and intervention duration. The experimental findings further indicate that magnetic stimulation may be chosen as an alternative antiepileptic therapy.

A Review of Aspects of Synaptic Plasticity in Hippocampus via mT Extremely Low-Frequency Magnetic Fields

The subthreshold magnetic modulation technique stimulates cells with mT extremely low-frequency magnetic fields (ELF-MFs), which are insufficient to induce neuronal action potentials. Although they cannot directly induce resting neurons to discharge, mT magnetic stimulation can regulate the excitability of the nervous system, which regulates learning and memory by some unknown mechanisms. Herein, we describe the regulation of mT ELF-MFs with different parameters on synaptic plasticity in hippocampal neurons. Additionally, we summarize the latest research on the possible mechanism of the effect of ELF-MFs on synaptic plasticity. Some studies have shown that ELF-MFs are able to inhibit long-term potentiation (LTP) by increasing concentration of intracellular Ca²⁺ concentration ([Ca²⁺ ]_i ), as well as concentration of reactive oxygen species. The research in this paper has significance for the comprehensive understanding of relevant neurological mechanisms of learning and memory by mT ELF-MFs stimulation. However, more high-quality research is necessary to determine the regulatory mechanism of mT ELF-MFs on synaptic plasticity in order to optimize this technique as a treatment for neurological diseases. © 2023 Bioelectromagnetics Society.

Regulation of LTP at rat hippocampal Schaffer-CA1 in vitro by musical rhythmic magnetic fields generated by red-pink (soothing) music tracks

PURPOSE

Music therapy, like red-pink (soothing) music, is an important treatment for neurological disorders associated with learning and memory. Magnetic fields have been proved to have a similar regulating effect. However, the effect of magnetic fields with musical rhythm generated by the combination of the two has not been confirmed. This study aimed to investigate the regulation of magnetic stimulation with music rhythm on LTP (long-term potentiation) of Schaffer-CA1.

MATERIALS AND METHODS

This article selected three sorts of music tracks in different frequencies (music track (1) Turkish March, music track (2) Moonlight Sonata, music track (3) Funeral March) and four sorts of pure sinusoidal tracks of four different harmonic frequency (music track (4) the frequency is 3500 Hz; music track (5) the frequency is 2500 Hz; music track (6) the frequency is 1500 Hz; music track (7) the frequency is 500 Hz). These music tracks are converted into analog signals by the external sound card and power amplifier and fed into a homemade coil that meets the demand for this frequency bandwidth. The coil can generate seven sorts of time-varying magnetic fields with musical rhythm with a mean intensity of about 2 mT. We used multi-electrode array (MEA) to record the LTP signals of Schaffer-CA1 synaptic induced by seven sorts of musical rhythmic magnetic fields and analyze the regulation of them.

RESULTS

The musical rhythmic magnetic fields generated by track 1 and track 2 have a remarkable enhancing effect on the amplitude of fEPSPs (field excitatory postsynaptic potentials) (p < .05), and these effects intensify with the increase of frequency. Nevertheless, there is no significant enhancing effect on LTP of the rhythmic magnetic field generated by track 3 (p > .05). The sinusoidal magnetic fields generated by track 4 and track 5 have an enhancing effect on the amplitude of fEPSPs (p < .05), and the enhancement is better than track 1 and track 2. The sinusoidal magnetic fields generated by track 6 and track 7 have an inhibiting effect (p < .05).

CONCLUSION

We found that the enhancing effect of musical rhythmic magnetic fields generated by track 1 was the most significant. The frequency of 1500 Hz could be a turning-point frequency in the regulation of magnetic field on LTP.

Short-Term Extremely Low-Frequency Electromagnetic Field Inhibits Synaptic Plasticity of Schaffer Collateral-CA1 Synapses in Rat Hippocampus via the Ca2+/Calcineurin Pathway

In this study, we investigate the intrinsic mechanism by which an extremely low-frequency electromagnetic field (ELF-EMF) influences neurons in the Schaffer collateral-CA1 (SC-CA1) region of rat hippocampus using electrophysiological techniques. ELF-EMF has an interesting effect on synaptic plasticity: it weakens long-term potentiation and enhances long-term depression. Here, the magnetic field effect disappeared after a blockade of voltage-gated calcium channels and calcineurin, which are key components in the Ca²⁺/calcineurin pathway, with two blockers, cadmium chloride and cyclosporin A. This fully establishes that the effect of ELF-EMF on synaptic plasticity is mediated by the Ca²⁺/calcineurin pathway and represents a novel technique for studying the specific mechanisms of action of ELF-EMF on learning and memory.

The Time-Dependence of Three Different Modes of ELF-EMF Stimulation on LTP at Schaffer Collateral-CA1 Synapses

Long-term potentiation (LTP) is considered the cellular basis of learning and memory. Extremely low-frequency electromagnetic fields (ELF-EMFs) are neuromodulation tools for regulating LTP. However, the temporal effects of short-term ELF-EMF stimulation on LTP are not yet known. In this study, we evaluated the time-dependent effects of 15 Hz/2 mT ELF-EMF stimulation on LTP at the Schaffer collateral-CA1 (SC-CA1) synapses in Sprague-Dawley rats. Hippocampal slices were exposed to three different modes of ELF-EMFs (sinusoidal, single-frequency pulse, and rhythm pulse) and durations (10, 20, 40, and 60 s). The baseline was recorded for 20 min and field excitatory postsynaptic potential (fEPSP) was recorded for 60 min using multi-electrode arrays (MEA) after plasticity induction using 100 Hz electrical high-frequency stimulation (HFS). Compared to the control group, the LTP decreased under three different magnetic fields and was proportional to time; that is, the longer the time, the greater the inhibition. We also compared the three magnetic fields and showed that the continuous sinusoidal magnetic field had the largest inhibitory rate of LTP, while pulsed and rhythm pulsed magnetic fields were similar. We showed that different modes of ELF-EMF stimulation had a time-dependent effect on LTP at Schaffer collateral-CA1 synapses, which provides experimental evidence for the treatment of related neurological diseases. © 2021 Bioelectromagnetics Society.

Comparison of ELF-EMFs stimulation with current stimulation on the regulation of LTP of SC-CA1 synapses in young rat hippocampus

BACKGROUND

Long-term potentiation (LTP) is an important functional indicator for synaptic plasticity. Extremely low frequency electromagnetic fields (ELF-EMFs) are a physical means to regulate LTP, which induce induced currents. It is unknown whether induced current is the key factor when LTP is regulated by ELF-EMFs.New Method: A method is proposed for calculating the current value induced by ELF-EMFs. Then, a comparison of ELF-EMFs with current on the regulation of theta-burst or high-frequency stimulation (TBS/HFS)-LTP was performed.

RESULTS

The LTP after ELF-EMFs and μA current regulation was significantly reduced. The regulatory effect of 0.1 μA current on LTP was similar with 100 Hz/2 mT ELF-EMFs, while 0.2 μA had a stronger regulatory effect than 200 Hz/2 mT on HFS-LTP.Comparison with Existing Methods: Most of the existing methods were used to calculate the induced current in human models, while we present a more accurate model for calculating the induced current induced by ELF-EMFs in the rat brain slices.

CONCLUSIONS

This work indicated that μA current and ELF-EMFs stimulation reduced LTP. Also, we demonstrated that the regulatory effect of ELF-EMFs on LTP is not entirely deriving from the induced current, since its magnetic mechanism might have played a certain role.

Exploring the Inhibitory Effect of Low-frequency Magnetic Fields on Epileptiform Discharges in Juvenile Rat Hippocampus

Stimulation with a low frequency electromagnetic field (LF-EMF) has proven to represent a powerful method for the suppression of seizures, as demonstrated in select clinical and laboratory studies. However, the mechanism by which LF-EMF suppresses seizures remains unclear. The purpose of the present study was to explore the modulatory effect of LF-EMF on epileptiform discharges (EDs) using rat hippocampal slices and investigate the underlying mechanisms that mediate these effects. EDs in hippocampal slices was induced by magnesium-free (zero-Mg²⁺) artificial cerebrospinal fluid (ACSF) and recorded using an in vitro micro-electrode array (MEA). A small sub-decimeter coil was designed and incorporated in a flexible magnetic stimulation device that allowed electromagnetic fields with different parameters to be delivered to slices. After a stable ED event was recorded, magnetic fields of 0.5 Hz (30 min) with a magnetic intensity of 0.13 mT (5 V_pp voltage input) and 0.25 mT (20 V_pp voltage input) were applied. The results indicated that a high-amplitude 0.5 Hz magnetic field could lead to persistent suppression of ictal discharges (IDs), while low-amplitude magnetic fields did not influence IDs. The persistent suppression of complex ED was prevented if the magnetic fields were applied in the presence of 10 μmol/L bicuculline (BIC), a γ-aminobutyric acid type A (GABA_A) receptor antagonist, while the application of BIC subsequent to a magnetic field application led to the reappearance of ID. The addition of BIC resulted in EDs that had previously been inhibited by magnetic fields, reappearing. Low-frequency magnetic stimulation was able to inhibit the conversion from interictal discharges (IIDs) or preictal discharges (PIDs) to IDs. This suppression was attributed to the modulation of GABA_A receptor activity.

Electromagnetic activity: a possible player in epilepsy

Epilepsy is a common disease with frequent occurrences. Many precipitating factors contribute to epileptic seizures, such as hyperventilation and alcohol consumption. An increasing number of studies have also found that electromagnetic activity in the environment can also affect epileptic seizures. However, many neuromodulatory devices that produce electromagnetic fields have been applied in the diagnosis and treatment of epilepsy. In this paper, we performed literature search in the PubMed, Medline and EMBASE databases and reviewed retrospective, prospective, or cross-sectional studies and case reports on the effects of electromagnetic activity on epilepsy. The application of electromagnetic activity in the diagnosis and treatment of epilepsy is also reviewed.

Exploring the form- And time-dependent effect of low-frequency electromagnetic fields on maintenance of hippocampal long-term potentiation

Low-frequency electromagnetic field (LF-EMF) stimulation is an emerging neuromodulation tool that is attracting more attention because of its non-invasive and well-controlled characteristics. However, the effect of different LF-EMF features including the forms and the time of addition on neuronal activity has not been completely understood. In this study, we used multi-electrode array (MEA) systems to develop a flexible in vitro magnetic stimulation device with plug-and-play features that allows for real-time delivery of LF-EMFs to biological tissues. Crucially, the method enables different forms of LF-EMF to be added at any time to a long-term potentiation (LTP) experiment without interrupting the process of LTP induction. We demonstrated that the slope of field excitatory postsynaptic potentials (fEPSPs) decreased significantly under post or priming uninterrupted sine LF-EMFs. The fEPSPs slope would continue to decline significantly when LF-EMFs were added two times with a 20-min interval. Paired-pulse ratio (PPR) was analyzed and the results reflected that LF-EMFs induced LTP was expressed postsynaptically. The results of pharmacological experiments indicated that AMPA receptor activity was involved in the process of LTP loss caused by post-LF-EMFs. Moreover, the effect of priming sine or Quadripulse stimulation (QPS)-patterned LF-EMFs depended on the time interval between the end of LF-EMF and the beginning of baseline recording. Interestingly, the effect of sine LF-EMFs on LTP would not disappear within 120 min, while the impact of QPS-patterned LF-EMFs on LTP might disappear after 90 min. These results indicated that LF-EMF might have a form- and time-dependent effect on LTP.

Focal Suppression of Epileptiform Activity in the Hippocampus by a High-frequency Magnetic Field

Electric current has been used for epilepsy treatment by targeting specific neural circuitries. Despite its success, direct contact between the electrode and tissue could cause side effects including pain, inflammation, and adverse biological reactions. Magnetic stimulation overcomes these limitations by offering advantages over biocompatibility and operational feasibility. However, the underlying neurological mechanisms of its action are largely unknown. In this work, a magnetic generating system was assembled that included a miniature coil. The coil was positioned above the CA3 area of mouse hippocampal slices. Epileptiform activity (EFA) was induced with low Mg²⁺/high K⁺ perfusion or with 100 µM 4-aminopyridine (4-AP). The miniature coil generated a sizable electric field that suppressed the local EFA in the hippocampus in the low-Mg²⁺/high-K⁺ model. The inhibition effect was dependent on the frequency and duration of the magnetic stimulus, with high frequency being more effective in suppressing EFA. EFA suppression by the magnetic field was also observed in the 4-AP model, in a frequency and duration - dependent manner. The study provides a platform for further investigation of cellular and molecular mechanisms underlying epilepsy treatment with time varying magnetic fields.

Effects of Exercise on Long-Term Potentiation in Neuropsychiatric Disorders

Various neuropsychiatric conditions, such as depression, Alzheimer's disease, and Parkinson's disease, demonstrate evidence of impaired long-term potentiation, a cellular correlate of episodic memory function. This chapter discusses the mechanistic effects of these neuropsychiatric conditions on long-term potentiation and how exercise may help to attenuate these detrimental effects.

Neuromodulation with electromagnetic stimulation for seizure suppression: From electrode to magnetic coil

Non-invasive brain tissue stimulation with a magnetic coil provides several irreplaceable advantages over that with an implanted electrode, in altering neural activities under pathological situations. We reviewed clinical cases that utilized time-varying magnetic fields for the treatment of epilepsy, and the safety issues related to this practice. Animal models have been developed to foster understanding of the cellular/molecular mechanisms underlying magnetic control of epileptic activity. These mechanisms include (but are not limited to) (1) direct membrane polarization by the magnetic field, (2) depolarization blockade by the deactivation of ion channels, (3) alteration in synaptic transmission, and (4) interruption of ephaptic interaction and cellular synchronization. Clinical translation of this technology could be improved through the advancement of magnetic design, optimization of stimulation protocols, and evaluation of the long-term safety. Cellular and molecular studies focusing on the mechanisms of magnetic stimulation are of great value in facilitating this translation.