Study type: Medical/biological study (experimental study)

Effects of high power microwave pulses on synaptic transmission and long term potentiation in hippocampus med./bio.

By: Pakhomov AG, Doyle J, Stuck BE, Murphy MR
Published in: Bioelectromagnetics 2003; 24 (3): 174-181
Download citation in RIS format

Aim of study (acc. to author)

To explore the effects of short, extremly high power microwave pulses on neuronal network function by electrophysiological techniques in the isolated rat hippocampal slice model.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 9.3 GHz
Modulation type: pulsed
Exposure duration: continuous for 2 min
  • SAR: 330 kW/g peak value
  • SAR: 0.33 kW/kg average over time
Exposure 2: 9.3 GHz
Modulation type: pulsed
Exposure duration: continuous for 2 min
  • SAR: 360 kW/g peak value
  • SAR: 0.7 kW/kg average over time (at 2 Hz)
  • SAR: 1.8 kW/kg average over time (at 5 Hz)
  • SAR: 3.6 kW/kg average over time (at 10 Hz)
Exposure 3: 9.3 GHz
Modulation type: pulsed
Exposure duration: continuous for 7 min
  • SAR: 500 kW/g peak value
  • SAR: 0.25 kW/kg average over time (at 0.5 µs)
  • SAR: 1 kW/kg average over time (at 2 µs)
Exposure 4: 9.3 GHz
Modulation type: CW
Exposure duration: continuous for 7 min
  • SAR: 0.25 kW/kg average over time
  • SAR: 1 kW/kg average over time

Exposure 1

Main characteristics
Frequency 9.3 GHz
Type
Charakteristic
  • guided field
Exposure duration continuous for 2 min
Modulation
Modulation type pulsed
Pulse type rectangular
Additional info

pulses of 2 µs width at 0.5 Hz and 0.5 µs width at 2 Hz
Exposure setup
Exposure source
Chamber The exposure chamber design was principally the same as described before [Pakhomov et al., 2000]. The chamber, provided with a continuous but laminar flow of fresh artificial cerebrospinal fluid (ACSF) of about 20 mm depth, was mounted on top of a waveguide opening sealed with a sapphire matching plate covered with 0.5 mm Plexiglas, which served as a chamber bottom.
Setup A brain slice was centered in a small frame (also made of 0.5 mm Plexiglas), which was fixed to the chamber bottom and aligned with the waveguide axis. MW exposures were performed essentially the same way as described before [Pakhomov et al., 2002].
Sham exposure A sham exposure was conducted.
Additional info It is important to note that the temperature stabilization system did not (and was not intended to) compensate for MW heating.
Parameters
Measurand Value Type Method Mass Remarks
SAR 330 kW/g peak value measured and calculated - -
SAR 0.33 kW/kg average over time measured and calculated - -
Additional parameter details

The peak E field in the waveguide reached 1.57 MV/m.

Measurement and calculation details

Incident and reflected powers in the waveguide were measured via directional couplers by a power meter with power sensors. Reflection from the exposure chamber into the waveguide was less than 3%. Local SAR values were measured in the ACSF using a microthermocouple technique [Pakhomov et al., 2000, 2002]. For field mapping, the MTC was driven in three orthogonal directions by means of a micromanipulator. An analytical approach proposed by Alekseev and Ziskin [2000] was employed to account for differences in dielectric properties of the brain tissue and ACSF. The presence of the plastic bottom cover and the brain slice holding frame in the exposure chamber decreased local SAR by 50-60%, and at the same time, reduced variations at the brain slice location to ±20%.

Exposure 2

Main characteristics
Frequency 9.3 GHz
Type
Charakteristic
  • guided field
Exposure duration continuous for 2 min
Modulation
Modulation type pulsed
Pulse width 1 µs
Pulse type rectangular
Additional info

pulse rates of 2, 5, and 10 Hz
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
SAR 360 kW/g peak value measured and calculated - -
SAR 0.7 kW/kg average over time measured and calculated - at 2 Hz
SAR 1.8 kW/kg average over time measured and calculated - at 5 Hz
SAR 3.6 kW/kg average over time measured and calculated - at 10 Hz

Exposure 3

Main characteristics
Frequency 9.3 GHz
Type
Charakteristic
  • guided field
Exposure duration continuous for 7 min
Modulation
Modulation type pulsed
Repetition frequency 1 Hz
Pulse type rectangular
Additional info

pulse widths of 0.5 or 2 µs
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
SAR 500 kW/g peak value measured and calculated - -
SAR 0.25 kW/kg average over time measured and calculated - at 0.5 µs
SAR 1 kW/kg average over time measured and calculated - at 2 µs

Exposure 4

Main characteristics
Frequency 9.3 GHz
Type
Charakteristic
  • guided field
Exposure duration continuous for 7 min
Modulation
Modulation type CW
Exposure setup
Exposure source
  • same setup as exposure 1
  • but sweep oscillator and amplifier instead of magnetron
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
SAR 0.25 kW/kg average over time measured and calculated - -
SAR 1 kW/kg average over time measured and calculated - -

Reference articles

  • Pakhomov AG et al. (2002): Comparison of dose dependences for bioeffects of continuous-wave and high-peak power microwave emissions using gel-suspended cell cultures
  • Pakhomov AG et al. (2000): Comparative effects of extremely high power microwave pulses and a brief CW irradiation on pacemaker function in isolated frog heart slices
  • Alekseev SI et al. (2000): Reflection and absorption of millimeter waves by thin absorbing films

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

Irradiation did not affect the ability of neurons to develop long term potentiation (LTP) in response to tetanus or to retain the potentiated state that was induced before irradiation. No lasting or delayed effects of extremly high power microwave pulses were observed.

Study character:

Study funded by

Related articles