permeability, but that, depending on the particular pulse characteristics, pulsed energy could be either
more or less effective than continuous-wave energy. Effects were observed at average powers as low as
30 ,µW/cm2. Preston et al., on the other hand, failed to find an effect on the permeability of the blood-
brain barrier even at thermal-level EMFs (21). Frey concluded that Preston's failure resulted from an
inappropriate choice of statistical procedures (11).
Biochemical studies of EMF-induced changes in brain tissue have yielded remarkably similar
results at widely different frequencies. Fischer et al. (22) found that 50Hz, 5300 v/m, resulted in an
initial rise of norepinephrine in rat brain, and a subsequent decline below the control level (Fig. 5.4 A).
Grin (23 ) observed the same sequence of changes at 2.4 GHz, 500 µW/cm2 Fig. 5.4 B); at 50
µW/cm2, however, the norepinephrine level in Grin's study rose continuously throughout the exposure
period.
Noval et al. (24) found that the activity of choline acetyltransferase (ChAC)-a neuronal enzyme
which catalyses the synthesis of acetylcholine-was significantly reduced in the brainstem portion of
brains from rats exposed to 10-100 v/m, 45 Hz, for 30-40 days; ChAC activity in the cerebral
hemispheres was not affected by the field. Cytochrome oxidase activity in rat-brain mitochondria was
significantly reduced after 1 month's exposure at 1000 and 1000 ,µW/cm2, 2.4 GHz; no effect was
found at 10 µW/cm2 (25).
Cholinesterase is the neuronal enzyme that destroys acetylcholine, thereby permitting re-
establishment of the membrane potential; alteration in blood cholinesterase levels reflects changes in
the functional state of the nervous system. Chronic exposure to both low-frequency (22 ) and
highfrequency (32) EMFs have produced lowered blood cholinesterase levels.
Fig.5.4. Norepinephrine levels in rat brain following exposure to EMFs:A, 5300 v/m, 50 Hz; B,500
µW/cm2, 2.4 GHz.
Microscopic studies of brain tissue of EMF-exposed animals have disclosed several kinds of
functional histopathological effects. Kholodov (2 ) reported changes in brain tissue of rabbits and cats
exposed to 200-300 gauss for up to 70 hours. In the sensorimotor cortex he found hyperplasia,
hypertrophy, atrophy. and dystrophic nerve lesions. In an attempt to confirm11-210 gauss DC and 5-11
gauss at 0.1-0.2 Hz for up to 60 hours. Four of the 12. exposed rabbits and 2 of the 13 controls
exhibited some histopathological change consisting principally of scattered granulomata in the
meninges and the cortex, often associated with vascular proliferation, leukocyte infiltration, and small
Gram-positive organisms. They concluded that their results could not be reconciled with those of
Kholodov, but rather were consistent with a sub-clinical encephalitozoonosis which was exacerbated
ELECTROMAGNETISM & LIFE - 74