Study type: Medical/biological study (experimental study)

IRIDIUM exposure increases c-fos expression in the mouse brain only at levels which likely result in tissue heating med./bio.

By: Morrissey JJ, Raney S, Heasley E, Rathinavelu P, Dauphinee M, Fallon JH
Published in: Neuroscience 1999; 92 (4): 1539-1546
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Aim of study (acc. to author)

To measure the expression of c-fos (a proto-oncogene) in sections of mouse brain tissue immediately following a 1h exposure to 1.6 GHz continuous wave (CW) and IRIDIUM RF (a ground-to-satellite-to-ground cellular communications web) up to SAR levels which exceed the maximal allowable FCC (Federal Communications Commission) limits.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 1.6 GHz
Modulation type: CW
Exposure duration: continuous for 1 h
  • power: 3.25 W (0.1; 0.2; 0.5; 1.25; 3.25 W)
  • SAR: 7.79 W/kg (0.23; 0.48; 1.19; 2.99; 7.79 W/kg at rostral forebrain (0 mm bregma))
  • SAR: 7.14 W/kg (0.22; 0.44; 1.10; 2.75; 7.14 W/kg at mid-caudal forebrain (-2 mm bregma))
  • SAR: 11.21 W/kg average over mass (brain) (0.35; 0.69; 1.73; 4.31; 11.21 W/kg)
  • SAR: 26.29 W/kg maximum (0.8; 1.62; 4.05; 10.11; 26.29 W/kg at the neck)
  • SAR: 6.42 W/kg average over mass (whole body) (0.19; 0.39; 0.99; 2.47; 6.42 W/kg)
Exposure 2: 1.6 GHz
Modulation type: pulsed
Exposure duration: continuous for 1 h
  • power: 3.25 W (0.1; 0.2; 0.5; 1.25; 3.25 W)
  • SAR: 7.79 W/kg (0.23; 0.48; 1.19; 2.99; 7.79 W/kg at rostral forebrain (0 mm bregma))
  • SAR: 7.14 W/kg (0.22; 0.44; 1.10; 2.75; 7.14 W/kg at mid-caudal forebrain (-2 mm bregma))
  • SAR: 11.21 W/kg average over mass (brain) (0.35; 0.69; 1.73; 4.31; 11.21 W/kg)
  • SAR: 26.29 W/kg maximum (0.8; 1.62; 4.05; 10.11; 26.29 W/kg at the neck)
  • SAR: 6.42 W/kg average over mass (whole body) (0.19; 0.39; 0.99; 2.47; 6.42 W/kg)

Exposure 1

Main characteristics
Frequency 1.6 GHz
Type
Charakteristic
Exposure duration continuous for 1 h
Modulation
Modulation type CW
Exposure setup
Exposure source
Distance between exposed object and exposure source 5 mm
Chamber The circular head-first and near-field Plexiglas carousel irradiator exposure system is described in the reference article.
Setup Five mice at a time were placed on a Plexiglas platform radially around (and with their noses 5 mm from the feedpoint of) a central resonant 0.5 λ dipole antenna and harnessed at the neck with a nylon tether.
Additional info Experiments also included untreated cage controls, sham-treated controls and Lindane positive controls for cortical c-fos expression.
Parameters
Measurand Value Type Method Mass Remarks
power 3.25 W - - - 0.1; 0.2; 0.5; 1.25; 3.25 W
SAR 7.79 W/kg - measured and calculated - 0.23; 0.48; 1.19; 2.99; 7.79 W/kg at rostral forebrain (0 mm bregma)
SAR 7.14 W/kg - measured and calculated - 0.22; 0.44; 1.10; 2.75; 7.14 W/kg at mid-caudal forebrain (-2 mm bregma)
SAR 11.21 W/kg average over mass measured and calculated brain 0.35; 0.69; 1.73; 4.31; 11.21 W/kg
SAR 26.29 W/kg maximum measured and calculated - 0.8; 1.62; 4.05; 10.11; 26.29 W/kg at the neck
SAR 6.42 W/kg average over mass measured and calculated whole body 0.19; 0.39; 0.99; 2.47; 6.42 W/kg
Additional parameter details

2.39 ± 0.74 W/kg/W in the caudate-putamen at the level of the rostral forebrain 2.21 ± 0.75 W/kg/W in the posterior thalamic nucleus at the level of the mid-caudal forebrain

Measurement and calculation details

Methods for determining SAR values for this study are described in the reference article. Briefly, temperature changes of mouse cadavers during a 1-min exposure at 25 W of input power were measured with a temperature probe inserted into the brain. The calculated SAR values were then used as reference points for the extrapolation of a thermographic infrared image of a sagittally sectioned mouse cadaver after a similar exposure.

Exposure 2

Main characteristics
Frequency 1.6 GHz
Type
Charakteristic
Exposure duration continuous for 1 h
Modulation
Modulation type pulsed
Pulse width 9.2 ms
Duty cycle 25 %
Repetition frequency 11 Hz
Additional info

IRIDIUM signal
Exposure setup
Exposure source
Distance between exposed object and exposure source 5 mm
Parameters
Measurand Value Type Method Mass Remarks
power 3.25 W - - - 0.1; 0.2; 0.5; 1.25; 3.25 W
SAR 7.79 W/kg - measured and calculated - 0.23; 0.48; 1.19; 2.99; 7.79 W/kg at rostral forebrain (0 mm bregma)
SAR 7.14 W/kg - measured and calculated - 0.22; 0.44; 1.10; 2.75; 7.14 W/kg at mid-caudal forebrain (-2 mm bregma)
SAR 11.21 W/kg average over mass measured and calculated brain 0.35; 0.69; 1.73; 4.31; 11.21 W/kg
SAR 26.29 W/kg maximum measured and calculated - 0.8; 1.62; 4.05; 10.11; 26.29 W/kg at the neck
SAR 6.42 W/kg average over mass measured and calculated whole body 0.19; 0.39; 0.99; 2.47; 6.42 W/kg

Reference articles

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 expression of c-fos was not significantly elevated in the brains of mice until exposure levels (SAR) exceeded 6 times the peak dose and 30 times the whole body average dose as maximal cellular telephone exposure limits in humans. Higher level exposure (continuos wave or IRIDIUM signal) elevated c-fos to a similar extent, what suggests no obvious pulsed modulation-specific effects. The pattern of c-fos elevation in limbic cortex and subcortex areas at higher exposure levels is most consistent with a stress response due to thermal perception. It is not consistent with any direct interaction of IRIDIUM energy with brain tissue.

Study character:

Study funded by

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