Biological Effects - RF/Microwave Interaction with Biological Tissues - page 98

levels that do not increase brain temperature, thus suggesting a direct inhi-
bition of metabolic processes by RF exposure. The authors of the study pro-
posed the following speculative mechanism, which is consistent with the results
obtained. Radio-frequency exposure at 200 and 591 MHz inhibits specific
enzymes or electron transport proteins important in maintaining the cell's ATP
pool. Such inhibition can be the result of RF-radiation-induced dipole oscilla-
tion involving the divalent metal ion in the active site during catalytic or trans-
port activity. During such oscillations, the ability of the enzyme to perform its
function could be decreased. For a given molecular species, the induction of
dipole oscillation and change in catalytic or transport activity would be fre-
quency dependent and should be responsive to the local electric field, that is,
the field in the tissue. The frequency dependence would be determined by the
detailed structure of the segment of the molecule and its freedom of move-
ment in relation to the other parts of the active site. This proposed mechanism
is consistent with Pethig's observation that RF-induced dipole oscillations in
proteins in solution are found precisely in the 30-1000-MHz frequency range
[38]. It is also consistent with the delta dispersion of the dielectric constant for
proteins in solution, which exists between 10 and 1000 MHz [39].
To measure the relationship between pain and the release of neurotrans-
mitters , a push-pull cannula has been inserted into the center of pain re-
ception in the brain of rabbits [40]. Artificial cerebrospinal fluid (CSF) was
injected at a very low and very constant speed. The CW microwave stimula-
tion at 2.45 GHz was applied by a coaxial cable in an adequate acupuncture
point. The sample of fluid was collected from the pull cannula. The pain thresh-
old was measured three times per stimulation, before, during, and after, using
an especially designed dolormeter. The radioenzymatic assay was used to
measure the levels of norepinephrine release in the sample perfusates. It was
found that the respective variations in pain threshold and neurotransmitter
release were proportional [35].
In an in vivo experiment set up to compare evoked potentials in both the
presence and absence of microwaves illuminating directly the spinal cord, an
electrical stimulus was applied on the peripheral nervous system of rabbits
while the impulse response (evoked potential) was measured by an electrode
in the cortex. The spinal cord was exposed to 4.2-GHz pulses by a micro-
antenna implanted in the spinal cord within the dorsal column. The purpose
of the experiment was to distinguish between thermal and possible nonther-
mal effects. A statistical analysis of the recorded data clearly illustrated a
microwave effect. Power deposition was calculated and used in the bioheat
equation, which showed that the microwave effect resulted in an increased
temperature within the spinal cord. No nonthermal effect was observed in this
experiment [8].

3.2.3 Blood-Brain Barrier

A series of investigations on BBB permeability changes at a very low level of
microwave exposure has captured increasing attention. The BBB protects the