http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1241519/pdf/ehp0111-000881.pdf

Research Article Research Article

Nerve Cell Damage in Mammalian Brain after Exposure to Microwaves from

GSM Mobile Phones

Leif G. Salford,1 Arne E. Brun,2 Jacob L. Eberhardt,3 Lars Malmgren,4 and Bertil R. R. Persson3

1Department of Neurosurgery, 2Department of Neuropathology, 3Department of Medical Radiation Physics, and 4Department of Applied

Electronics, Lund University, The Rausing Laboratory and Lund University Hospital, Lund, Sweden

The possible risks of radio-frequency electromagnetic fields for the human body is a growing concern

for our society. We have previously shown that weak pulsed microwaves give rise to a significant

leakage of albumin through the blood–brain barrier. In this study we investigated whether a

pathologic leakage across the blood–brain barrier might be combined with damage to the neurons.

Three groups each of eight rats were exposed for 2 hr to Global System for Mobile

Communications (GSM) mobile phone electromagnetic fields of different strengths. We found

highly significant (p < 0.002) evidence for neuronal damage in the cortex, hippocampus, and basal

ganglia in the brains of exposed rats. Key words: blood–brain barrier, central nervous system,

microwaves, mobile phones, neuronal damage, rats. Environ Health Perspect 111:881–883 (2003).

doi:10.1289/ehp.6039 available via http://dx.doi.org/ [Online 29 January 2003]

The voluntary exposure of the brain to

microwaves from hand-held mobile phones

by one-fourth of the world’s population has

been called the largest human biologic experiment

ever (Salford et al. 2001). In the near

future, microwaves will also be emitted by an

abundance of other appliances in the cordless

office and also in the home. The possible risks

of radio-frequency electromagnetic fields (RF

EMFs) for the human body is a growing concern

for our society (for a review, see Hyland

2000). Most researchers in the field have

dwelled on the question of whether RF EMFs

may induce or promote cancer growth.

Although some have indicated increased risk

(Hardell et al. 2002; Repacholi et al. 1997),

most studies, including our own, have shown

no effects (Salford et al. 1997a) or even a

decreased risk (Adey et al. 1999).

The possible risks of microwaves for the

human body has attracted interest since the

1960s (i.e., before the advent of mobile

phones), when radar and microwave ovens

posed a possible health problem. Oscar and

Hawkins (1977) performed early studies on

effects of RF EMFs on the blood–brain barrier.

They demonstrated that at very low

energy levels (< 10 W/m2), the fields in a

restricted exposure window caused a significant

leakage of 14C-mannitol, inulin, and also

dextran (same molecular weight as albumin)

from the capillaries into the surrounding

cerebellar brain tissue. These findings, however,

were not repeated in a study using 14Csucrose

(Gruenau et al. 1982). A recent in

vitro study has shown that EMF at 1.8 GHz

increase the permeability of the blood–brain

barrier to sucrose (Schirmacher et al. 2000).

Shivers and colleagues (Shivers et al. 1987;

Prato et al. 1990) examined the effect of magnetic

resonance imaging upon the rat brain.

They showed that the combined exposure to

RF EMFs and pulsed and static magnetic

fields gave rise to a significant pinocytotic

transport of albumin from the capillaries into

the brain.

Inspired by this work, since 1988 our

group has studied the effects of different intensities

and modulations of 915 MHz RF EMFs

in a rat model where the exposure takes place

in a transverse electromagnetic transmission

line chamber (TEM-cell) during various time

periods. In series of more than 1,600 animals,

we have proven that subthermal power densities

from both pulse-modulated and continuous

RF EMFs—including those from GSM

(Global System for Mobile Communications)

mobile phones—have the potency to significantly

open the blood–brain barrier such that

the animals’ own albumin (but not fibrinogen)

passes out of the bloodstream into the brain

tissue and accumulates in the neurons and glial

cells surrounding the capillaries (Malmgren

1998; Persson et al. 1997; Persson and Salford

1996; Salford et al. 1992, 1993, 1994, 1997b,

2001) (Figure 1). These results have been

duplicated recently in another laboratory (Töre

et al. 2001). Similar results have been reported

by others (Fritze et al. 1997).

We and others (Oscar and Hawkins

1977; Persson et al. 1997) have pointed out

that when such a relatively large molecule as

albumin can pass the blood–brain barrier, so

too can many other smaller molecules,

including toxic ones, which may escape into

the brain because of exposure to RF EMFs.

We have hitherto not concluded that such

leakage is harmful for the brain. However,

Hassel et al. (1994) have shown that autologous

albumin injected into the brain tissue of

rats leads to damage to neurons at the injection

site when the concentration of albumin

in the injected solution is at least 25% of that

in blood. In the present study, we investigated

whether leakage across the blood–brain

barrier might cause damage to the neurons.

Materials and Methods

TEM-cells used for the RF EMF exposure of

rats were designed by dimensional scaling from

previously constructed cells at the National

Bureau of Standards (Crawford 1974). TEM-

cells are known to generate uniform electromagnetic

fields for standard measurements. A

genuine GSM mobile phone with a programmable

power output was connected via a coaxial

cable to the TEM-cell; no voice modulation

was applied.

The TEM-cell is enclosed in a wooden

box (15 × 15 × 15 cm) that supports the outer

conductor and central plate. The outer conductor

is made of brass net and is attached to

the inner walls of the box. The center plate, or

septum, is constructed of aluminum.

The TEM-cells were placed in a temperature-

controlled room, and the temperature in

the TEM-cells was kept constant by circulating

room air through holes in the wooden box.

The specific absorption rate (SAR) distribution

in the rat brain has been simulated with

the finite-difference time-domain method

(Martens et al. 1993) and found to vary < 6 dB

in the rat brain.

The rats were placed in plastic trays (12 ×

12 × 7 cm) to avoid contact with the central

plate and outer conductor. The bottom of the

tray was covered with absorbing paper to collect

urine and feces.

Thirty-two male and female Fischer 344

rats 12–26 weeks of age and weighing 282 ±

91 g were divided into four groups of eight

rats each. The peak output power of 10 mW,

100 mW, and 1,000 mW per cell from the

GSM mobile telephone was fed into two

TEM-cells simultaneously for 2 hr. This

exposed the rats to peak power densities of

0.24. 2.4, and 24 W/m2, respectively. This

exposure resulted in average whole-body

SARs of 2 mW/kg, 20 mW/kg, and 200

mW/kg, respectively. For further details about

exposure conditions and SAR calculations, see

Martens et al. (1993) and Malmgren (1998).

The fourth group of rats was simultaneously

Address correspondence to L.G. Salford, Dept. of

Neurosurgery, Lund University Hospital, S-221 85

Lund, Sweden. Telephone: 46-46-171270. Fax: 4646-

188150. E-mail: Leif.Salford@neurokir.lu.se

We thank S. Strömblad and C. Blennow at the

Rausing Laboratory for excellent technical assistance.

The work was supported by a grant from the

Swedish Council for Work Life Research.

The authors declare they have no conflict of interest.

Received 4 October 2002; accepted 28 January 2003.

Environmental Health Perspectives • VOLUME 111 | NUMBER 7 | June 2003

Article | Salford et al.

kept for 2 hr in nonactivated TEM-cells. The

animals were awake during the exposure and

could move and turn within the exposure

chamber.

The animals in each exposure group were

allowed to survive for about 50 days after

exposure. They were carefully observed daily

for neurologic and behavioral abnormalities

during this period, at the end of which they

were anesthetized and sacrificed by perfusion

fixation with 4% formaldehyde.

The brains were removed from the skull

by nontraumatic technique (resection of bone

structures at the skull base, followed by a

midline incision from the foramen magnum

to the nose) after an extended in situ postmortem

fixation time of 30 min. Each brain

was sectioned coronally in 1–2-mm-thick

slices, which all were embedded in paraffin,

cut in 5-µm sections, and stained for

RNA/DNA with cresyl violet to show dark

neurons. Applying albumin antibodies

(Dakocytomation Norden AB, Älvsjö,

Sweden) reveals albumin as brownish spotty

or more diffuse discolorations (Salford et al.

1994).

The occurrence of “dark neurons” was

judged semiquantitatively by the neuropathologist

as 0 (no or occasional dark neurons), 1

(moderate occurrence of dark neurons), or 2

(abundant occurrence). The microscopic

analysis was performed blind to the test situation.

The Kruskal-Wallis one-way analysis of

variance by ranks was used for a simultaneous

statistical test of the score distributions for the

four exposure conditions. When the null

hypothesis could be rejected, comparisons

between controls and each of the exposure

conditions was made with the Mann-Whitney

nonparametric test for independent samples.

Results and Discussion

Controls and test animals alike showed the

normal diffuse positive immunostaining for

albumin in hypothalamus, a kind of built-in

method control.

Control animals showed either no positivity

or an occasional and often questionable

positivity for albumin outside the hypothalamus

(Figure 1A). In one control animal we

observed a moderate number of dark neurons,

but no such change was observed in all the

other controls.

Exposed animals usually showed several

albumin-positive foci around the finer blood

vessels in white and gray matter (Figure 1B).

Here the albumin had spread in the tissue

between the cell bodies and surrounded neurons,

which either contained no albumin or

contained albumin in some foci. Scattered

neurons, not associated with albumin leakage

between the neurons, were also positive.

The cresyl violet staining revealed scattered

and grouped dark neurons, which were

often shrunken and darkly stained, homogenized

with loss of discernible internal cell

structures. Some of these dark neurons were

also albumin positive or showed cytoplasmic

microvacuoles indicating an active pathologic

process. There were no hemorrhages

and no discernible glial reaction, astrocytic

or microglial, adjacent to changed neurons.

Changed neurons were seen in all locations,

but especially the cortex, hippocampus, and

basal ganglia, mixed in among normal neurons

(Figure 2). The percentage abnormal

neurons is roughly appreciated to be maximally

around 2%, but in some restricted areas

they dominated the picture.

The occurrence of dark neurons under the

different exposure conditions is presented in

Figure 3, which shows a significant positive

relation between EMF dosage (SAR) and

number of dark neurons.

A combined nonparametric test for the

four exposure situations simultaneously

revealed that the distributions of scores differed

significantly between the groups (p < 0.002).

We present here for the first time evidence

for neuronal damage caused by nonthermal

microwave exposure. The cortex as well as the

hippocampus and the basal ganglia in the

brains of exposed rats contained damaged neurons.

We realize that our study comprises few

animals, but the combined results are highly

significant and exhibit a clear dose–response

relation.

We considered the observed dark neurons

not to be artifacts for the following reasons:

first, the brains were removed atraumatically

and perfusion fixed in situ; second, the dark

Figure 1. Cross-section of central parts of the brain of (A) an unexposed control rat and (B) an RF EMF-

exposed rat, both stained for albumin, which appears brown. In (A), albumin is visible in the central inferior

parts of the brain (the hypothalamus), which is a normal feature. In (B), albumin is visible in multiple small

foci representing leakage from many vessels. Magnification, about ×3.

Score for occurrence of dark neurons

2 24 5

0 2 20 200

SAR (mW/kg)

1 1 2 42

.

.

0 74 1

Figure 2. Photomicrograph of sections of brain from an RF EMF-exposed rat stained with cresyl violet. (A)

Row of nerve cells in a section of the pyramidal cell band of the hippocampus; among the normal nerve

cells (large cells) are interspersed black and shrunken nerve cells, so-called dark neurons. (B) The cortex,

top left, of an RF EMF-exposed rat showing normal nerve cells (pale blue) intermingled with abnormal,

black and shrunken “dark neurons” at all depths of the cortex, but least in the superficial upper layers.

Magnification, ×160.

Figure 3. Distribution of scores for the occurrence

of “dark neurons” as a function of exposure condition.

The dashed line connects mean values for

each condition. Numbers in the figure indicate the

number of animals in the treatment group with that

score. A simultaneous nonparametric comparison

of all four conditions revealed significant differences

(p < 0.002). As compared to control, p < 0.2

for 2 mW/kg; p = 0.01 for 20 mW/kg; and p = 0.03 for

200 mW/kg.

VOLUME 111 | NUMBER 7 | June 2003 • Environmental Health Perspectives

Article | Nerve cell damage from GSM mobile phones

neurons were intermingled with normal-

appearing neurons (see Figure 2). Also, the

presence of vacuoles in several of the dark

neurons is a clear sign that damage occurred

in the living animal. We cannot exclude that

the neuronal change described may represent

apoptotic cell death.

The neuronal albumin uptake and other

changes described would seem to indicate serious

neuronal damage, which may be mediated

through organelle damage with release of not

only hydrolytic lysosomal enzymes but also, for

example, sequestered harmful material, such as

heavy metals, stored away in cytoplasmic

organelles (lysosomes).

The time between last exposure and sacrifice

is of great importance for the detection of

foci of leakage because extravasated albumin

rapidly diffuses down to, and beyond, concentrations

possible to demonstrate accurately

immunohistologically. However, the initial

albumin leakage into the brain tissue (seen

within hours in ~40% of exposed animals in

our previous studies) may start a secondary

blood–brain barrier opening, leading to a

vicious circle—because we demonstrate albumin

leakage even 8 weeks after the exposure.

We chose 12–26-week-old rats because

they are comparable with human teenagers—

notably frequent users of mobile phones—with

respect to age. The situation of the growing

brain might deserve special concern from society

because biologic and maturational

processes are particularly vulnerable during the

growth process. The intense use of mobile

phones by youngsters is a serious consideration.

A neuronal damage of the kind described

here may not have immediately demonstrable

consequences, even if repeated. In the long

run, however, it may result in reduced brain

reserve capacity that might be unveiled by

other later neuronal disease or even the wear

and tear of aging. We cannot exclude that

after some decades of (often) daily use, a

whole generation of users may suffer negative

effects, perhaps as early as in middle age.

Correction

Figure 1 in the original manuscript was

cited in “Materials and Methods” and

illustrated albumin leakage that we had

reported earlier. The figure showed

examples of cross-sections of the brains

of rats sacrificed immediately after exposure

to microwaves. Because this could

be misunderstood, in the interest of

clarity and with the permission of the

editor, we have replaced that figure.

The new Figure 1 is now cited in

“Results” and shows animals from the

present study. Figure 1A illustrates the

brain of a sham-exposed control animal,

and Figure 1B illustrates an animal

exposed to 2 mW/kg for 2 hr.

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