Biological Effects - RF/Microwave Interaction with Biological Tissues - page 97

thermal effects, when the power absorbed is of the same order of magnitude
as the basic metabolic rate.

3.2.2 Effects on Brain and Spinal Cord

Molecular processes involved with the brain energy metabolism of the rat may
be affected by radiation in the RF range. It has been indicated that there are
27-29 divalent iron atoms and two divalent copper atoms in molecules of the
respiratory chain [36]. Each of these is essential to the function of the respi-
ratory chain at the molecular level. Charged particles in an electric field
undergo translational motion if not otherwise constrained. Therefore, some of
the divalent metal ions in these key chains could be affected by the oscillat-
ing electric field of the RF exposure, at least until the critical relaxation fre-
quency for each structure is exceeded. This concept has been tested by
examining brain metabolism of rats during exposure at CW frequencies of 200,
591, and 2450 MHz and by developing dose-response relationships for the
effects [37]. The presence of specific molecular interaction(s) would indeed be
supported by a frequency specificity based on the macroscopic dielectric
properties of biological systems. The measurement techniques included
time-sharing fluorescence at the brain surface to determine relative levels of
reduced nicotinamide adenine dinucleotide (NADH) and biochemical assays
for adenosine triphosphate (ATP) and creatine phosphate (CP). The NADH,
ATP, and CP are key compounds in brain energy metabolism. The ATP is a
key compound in energy metabolism because it is the carrier of energy to the
processes in living cells. The NADH is oxidized to produce ATP in the mito-
chondria, while brain ATP concentration is maintained at the expense of CP.
When demand for ATP is higher than the mitochondrial production capacity,
CP is rapidly converted to ATP to sustain ATP levels, and significant decreases
in CP levels are observed prior to any decrease in ATP.
Frequency-dependent changes have been found for all three key com-
pounds. The measured temperature in the brain of the rat was essentially con-
stant for all exposures. At 200 and 591 MHz, NADH fluorescence increased in
a dose-dependent manner between approximately 1 and 10 mW cm -2 and then
became constant at higher exposures, up to at least 40 mW cm -2 . There was no
effect at 2450 MHz. Levels of ATP and CP were measured in the whole brain
after exposure. The CP levels decreased only at 591 MHz. The effect was inves-
tigated for all compounds at 200 and 2450 MHz exposure up to 5 min and at
591 MHz up to 20 min.
Microwave exposure at 591 MHz resulted in a decrease in ATP levels to
75% of controls, while CP levels are no lower than 60% of controls. During the
200-MHz exposures, brain ATP levels decreased to 80-90% of controls even
though CP levels were not significantly decreased. These results are not con-
sistent with normal energy metabolism where ATP levels are maintained at the
expense of CP and suggest that at 200 MHz there is RF inhibition of the reac-
tion converting CP to ATP. Furthermore, these results occur at RF exposure