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Response of Cultured Neuronal Network Activity After High-Intensity Power Frequency Magnetic Field Exposure.

Published in: Front Physiol 2018; 9: 189

Aim of study (acc. to author)

To examine the threshold of the 50 Hz magnetic field-induced neuronal modulation in a rat brain-derived neuronal network.
Background/further details: Low frequency magnetic fields of high intensity stimulates the human body through excication of neuronal and muscle cells, for example resulting in phosphenes. Limit values are based on these effects including a safety margin. However, existing limit values are based on induced electric currents (see also information in the EMF-Portal about Low frequency (0.1 Hz–1 kHz)).
In this study, the threshold of the magnetic field-induced neuronal modulation should be elucidated.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 50 Hz
Exposure duration: 6 seconds
Exposure 2: 50 Hz
Exposure duration: 6 seconds
bursting activity blocking of inhibitory synapses
Exposure 3: 50 Hz
Exposure duration: 6 seconds
autonomuous activity of pacemaker-like neurons
Exposure 1
Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 6 seconds
Exposure setup
Exposure source
Chamber cell cultures were set on the multi-electrode array-based extracellular recording system that was attached to the thermostatic acrylic culture chamber system; temperature was stabilized around 37°C during the experiments; to exclude the influence of coil vibration, the culture chamber was set on a base designed not to contact the MF exposure coils, and all equipment was placed on an anti-vibration stand
Setup exposure system consisted of a custom-made saddle-type coil, a custom-made power supply, and a function generator; the coil included a hollow conductor (8.3 × 8.3 mm, ϕ 5.2 mm) for the water-based cooling system (circulation of water with 20°C) ; two saddletype coils were aligned in the vertical direction at a distance of 125 mm, and combined in a window frame-type iron core
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 50 mT effective value measured - -
magnetic flux density 100 mT effective value measured - -
magnetic flux density 200 mT effective value measured - -
magnetic flux density 400 mT effective value measured - -
Exposure 2
Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 6 seconds
Additional info bursting activity blocking of inhibitory synapses
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 400 mT effective value measured - -
Exposure 3
Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 6 seconds
Additional info autonomuous activity of pacemaker-like neurons
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 400 mT effective value measured - -
Reference articles
  • Takahashi M et al. (2017): Evaluation of the effects of power-frequency magnetic fields on the electrical activity of cardiomyocytes differentiated from human induced pluripotent stem cells.
  • Nakasono S et al. (2003): Effect of power-frequency magnetic fields on genome-scale gene expression in Saccharomyces cerevisiae.
Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated material:
Time of investigation:
  • before exposure
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

The number of spikes increased significantly only in the cells exposed to 400 mT when compared to control cells. However, the number of spikes in one synchronized burst firing did not increase. With bicuculline added, the exposure induced effect disappeared, which shows that magnetic field exposure was involved in the inhibition of inhibitory input through the GABA receptor. After application of D-AP5 and CNQX, autonomous spiking continued. However, during one minute after exposure to the 400 mT magnetic field, the spike frequency decreased gradually. The difference before and after exposure was statistically significant.
It was furthermore calculated that the magnetic field of 200-400 mT used in the experiments corresponds approximately to an electric field of 0.314 to 0.440 V/m in the culture medium and hence notably lower than the 8.7 V/m which is the estimated median threshold reported in the IEEE standard for 50 Hz and brain (IEEE Std C95.6 - 2002).
The authors conclude that the data indicate an increased synchronized bursting activity in neuronal networks from the rat's brain after 50 Hz magnetic field exposure with a magnetic flux density of 400 mT which was due to reduced inhibitory pacemaker-like neuronal activity.
Study character:

Study funded by

  • Japan Society for the Promotion of Science (JSPS), Japan

Related articles

  • Coskun O et al. (2011): Effects of 50 Hertz-1 mT magnetic field on action potential in isolated rat sciatic nerve.
  • Deans JK et al. (2007): Sensitivity of coherent oscillations in rat hippocampus to AC electric fields.
  • Marchionni I et al. (2006): Comparison between low-level 50 Hz and 900 MHz electromagnetic stimulation on single channel ionic currents and on firing frequency in dorsal root ganglion isolated neurons.
  • Francis JT et al. (2003): Sensitivity of neurons to weak electric fields.
  • Saunders RD (2003): Rapporteur report: weak field interactions in the central nervous system.
  • (2002): IEEE Standard for safety levels with respect to human exposure to electromagnetic fields, 0-3 kHz; IEEE Std C95.6:2002-10.
  • Bawin SM et al. (1986): Comparison between the effects of extracellular direct and sinusoidal currents on excitability in hippocampal slices.
  • Bawin SM et al. (1986): Long-term effects of sinusoidal extracellular electric fields in penicillin-treated rat hippocampal slices.
  • Bawin SM et al. (1984): Influences of sinusoidal electric fields on excitability in the rat hippocampal slice.