Evidence for Effects on Neurology and Behavior - BioInitiative Report

the brain. A similar but more pronounced effect was observed when the animals were exposed to
pulsed 1200-MHz RFR at an average power density of 0.2 mW/cm 2 . These data were interpreted
as an indication of an increase in permeability of the blood-brain barrier, since fluorescein
injected systemically does not normally permeate into the brain. On the other hand, Merritt et al.
[1978] did not observe a significant change in the permeability of fluorescein-albumin into the
brain of rats exposed to a similar dose-rate of RFR (1200 MHz, either continuous-wave or pulsed,
30 min, 2-75 mW/cm 2 ); however, an increase in permeability was observed, if the body
temperature of the animal was raised to 40 o C either by RFR or convective heating. In addition,
no significant change in permeability of mannitol and inulin to the brain was reported in this
experiment after RFR exposure.
Chang et al. [1982] studied in the dog the penetration of 131 I-labelled albumin into the
brain. The head of the dog was irradiated with 1000-MHz continuous-wave RFR at 2, 4, 10, 30,
50, or 200 mW/cm 2 and the tracer was injected intravenously. Radioactivity in the blood and
cerebrospinal fluid (CSF) was determined at regular time intervals postinjection. An increase in
the ratio of radioactivity in the CSF versus that in the blood was considered as an indication of
entry of the labelled albumin that normally does not cross the blood-brain barrier. At 30
mW/cm 2 , 4 of the 11 dogs studied showed a significant increase in the ratio compared to that of
sham-exposed animals, whereas no significant difference was seen at the other power densities.
The authors suggested a possible 'power window' effect.
Lin and Lin [1980] reported no significant change in the permeability of sodium
fluorescein and Evan's blue into the brain of rats with focal exposure at the head <strong>for</strong> 20 min to
pulsed 2450-MHz RFR at 0.5-1000 mW/cm 2 (local SARs 0.04-80 W/kg), but an increase was
reported after similar exposure of the head at an SAR of 240 W/kg [Lin and Lin, 1982]. The
brain temperature under the latter exposure condition was 43 o C. In a further study, by the same
laboratory, Goldman et al. [1984] used 86 Rb as the tracer to study the permeability of the bloodbrain
barrier after RFR exposure. The tracer was injected intravenously to rats after 5, 10, or 20
min of exposure to 2450-MHz pulsed RFR (10 s pulses, 500 pps) at an average power density
of 3 W/cm 2 (SAR 240 W/kg) on the left side of the head. Brain temperature was increased to 43
o C. The 86 Rb uptake in the left hemisphere of the brain was studied. Increase in uptake was
detected in the hypothalamus, striatum, midbrain, dorsal hippocampus, and occipital and parietal
cortex at 5 min postexposure. Increased uptake of the tracer in the cerebellum and superior
colliculus was also observed at 20 min after exposure. That increase in brain temperature played
a critical role in the effect of RFR on the permeability of the blood-brain barrier was further
supported in an experiment by Neilly and Lin [1986]. They showed that ethanol, infused into the
femoral vein, reduced the RFR-induced (3150 MHz, 30 W/cm 2 rms <strong>for</strong> 15 min on the left
hemisphere of the brain) increase in penetration of Evan's blue into the brain of rats. Ethanol
attenuated the RFR-induced increase in brain temperature.
Several studies used horseradish peroxidase as an indicator of blood-brain barrier
permeability. An increase in horseradish peroxidase in the brain after systemic administration
could be due to an increase in pinocytosis of the epithelial cells in the capillary of the brain, in
addition to or instead of an increase in the leakiness of the blood-brain barrier. Pinocytosis can
actively transport the peroxidase from the general blood circulation into the brain. An increase in
the concentration of horseradish peroxidase was found in the brain of the Chinese hamster after 2
h of irradiation to continuous-wave 2450-MHz RFR at 10 mW/cm 2 (SAR 2.5 W/kg) [Albert,
1977]. The increase was more concentrated in the thalamus, hypothalamus, medulla, and
cerebellum, and less in the cerebral cortex and hippocampus [Albert and Kerns, 1981]. Increases
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