Study type: Medical/biological study (experimental study)

Low-level microwave irradiation and central cholinergic activity: a dose-response study med./bio.

By: Lai H, Carino MA, Horita A, Guy AW
Published in: Bioelectromagnetics 1989; 10 (2): 203-208
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Aim of study (acc. to author)

To measure sodium-dependent high-affinity choline uptake in the brain of rats after acute exposure to pulsed 2450 MHz microwaves in a cylindrical waveguide system.

Background/further details

Since the dosimetry of this irradiation system is well documented, and the power density of exposure can be adjusted to give different whole-body averaged SARs in the exposed animals, the system provides a reliable means to investigate the dose (SAR)-response relationship of microwave irradiation. This preliminary report describes the effect of varying the power density of microwave exposure on choline uptake in different regions of the brain.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 2,450 MHz
Modulation type: pulsed
Exposure duration: continuous for 45 min
  • power density: 2 mW/cm² mean (0.5, 0.75, 1.0, 1.5, 1.75, and 2.0 mW/cm²)
  • SAR: 1.2 W/kg average over mass (whole body) (0.3, 0.45, 0.6, 0.75, 0.9, and 1.2 W/kg)

Exposure 1

Main characteristics
Frequency 2,450 MHz
Type
Charakteristic
  • guided field
Polarization
  • circular
Exposure duration continuous for 45 min
Modulation
Modulation type pulsed
Pulse width 2 µs
Repetition frequency 500 Hz
Exposure setup
Exposure source
Chamber The cylindrical waveguide system [Guy et al., 1979] consisted of eight individual exposure tubes consisting of a section of circular waveguide made of galvanized wire screen. The circularly polarised field in TE11 mode propagated from one end of the waveguide to the other end. The rat was housed in a plastic chamber with a floor of glass rods.
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
power density 2 mW/cm² mean - - 0.5, 0.75, 1.0, 1.5, 1.75, and 2.0 mW/cm²
SAR 1.2 W/kg average over mass - whole body 0.3, 0.45, 0.6, 0.75, 0.9, and 1.2 W/kg
Additional parameter details

The power densities were averaged over the cross section of the waveguide at the position of exposure.

Measurement and calculation details

The dosimetry of this irradiation system was well documented [Guy et al., 1979 and Chou et al., 1985].

Reference articles

  • Chou CK et al. (1985): Specific absorption rate in rats exposed to 2,450-MHz microwaves under seven exposure conditions
  • Guy AW et al. (1979): Circularly polarized 2450 MHz waveguide system for chronic exposure of small animals to microwaves

Exposed system:

Methods Endpoint/measurement parameters/methodology

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

Main outcome of study (acc. to author)

The results show a dose-response relationship of central choline uptake with microwave irradiation. However, different brain areas have different sensitivities to the exposure. Decrease in choline uptake was observed in the striatum at a SAR of 0.75 W/kg and above. For the frontal cortex and hippocampus, decreases in choline uptake were observed at a SAR of 0.45 W/kg and above. No significant effect was observed in the hypothalamus at the irradiation power densities studied. The probit analysis was used to determine the SAR50 in each brain area (i.e. the SAR at which 50% of maximum response was elicited). SAR50 for the striatum, frontal cortex, and hippocampus were 0.65, 0.38, and 0.44 W/kg, respectively.

Study character:

Study funded by

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