First published online August 17, 2006
Journal of Experimental Biology 209, 3322-3328 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02375
Light and electron microscopic study of the thyroid gland in rats exposed to power-frequency electromagnetic fields
Vesna Rajkovic1,2,*,
Milica Matavulj1 and
Olle Johansson2
1 Department of Biology and Ecology, Faculty of Sciences, Trg Dositeja
Obradovica 2, 21000 Novi Sad, Serbia and Montenegro
2 Experimental Dermatology Unit, Department of Neuroscience, Karolinska
Institute, 171 77 Stockholm, Sweden

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Fig. 1. Photomicrographs of frozen sections of the thyroid gland stained with
Haematoxylin-Eosin in a control animal (a) and an animal exposed to 50 Hz EMF
(b). Thyroid parenchyma is composed mainly of macrofollicles rich in colloid
content in a. Follicles of different diameter are present in b with a
preponderance of smaller (microfollicles) over larger follicles.
Microfollicles have low to very low colloid content in b. The lobular
structure is more prominent in b with each lobule completely divided by
connective tissue (compared with a). Both photomicrographs are of the same
magnification. Scale bar, 200 µm.
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Fig. 2. Photomicrographs of frozen sections of the thyroid gland stained with
Haematoxylin-Eosin from a control animal (a) and animals exposed to 50 Hz EMF
(b,c). Note the difference in follicle size in a compared to b and c.
Occasional follicles with a squamous cell lining, probably due to a low
activity state can be seen in a-c. There is a prominent increase in connective
tissue content in b and c compared to a. All photomicrographs are of the same
magnification. Scale bar, 50 µm.
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Fig. 3. Photomicrographs of semithin sections of the thyroid gland stained with
Toluidine Blue-Cresyl Violet in a control animal (a) and an animal exposed to
50 Hz EMF (b). There is a more extensive capillary bed (carets) in b compared
with a. Both photomicrographs are of the same magnification. Scale bar, 25
µm.
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Fig. 4. Electron micrographs of a part of the follicle wall showing the
ultrastructure of follicular cells in control animals (a,b) and animals
exposed to 50 Hz EMF (c,d). In a and b the follicular epithelial cells have
euchromatic nuclei (n) and prominent excentrically positioned nucleoli (no).
In the treated cells the nuclei are placed basally in the cell (carets in c)
and the euchromatin is darker in appearance. The rough endoplasmic reticulum
(er) is relatively well developed in both cisternal and vesicular form in a-c.
The baso-lateral compartments (bl) of some cells in a, c and d have distended
cisternae (er). There are more pleomorphic electron-dense lysosomes (ly) under
the apical membrane (am) of thyrocytes in a and b compared with c. Lysosomes
of different electron density are seen in c. Note two large colloid droplets
(cd) in the apical cytoplasm of the same thyrocyte in c and a large group of
droplets of various diameter occupying nearly the entire apical region of one
follicular cell (carets in d). c, colloid; bm, basement membrane; pf,
parafollicular cell. All photomicrographs are of the same magnification. Scale
bar, 1 µm.
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Fig. 5. (a-c) Electron micrographs of follicular cells in animals exposed to 50 Hz
EMF. The significant features are: a giant colloid droplet (carets) in a; a
large colloid droplet (carets) surrounded by lysosomes in the central part of
a thyrocyte in b and near the basal membrane (carets) in c; pleomorphic
lysosomes (ly) in the apical cytoplasm in b; rough endoplasmic reticulum (er)
with amorphous contents of different density and dilated cisternae in a, b and
c. c, colloid; am, apical membrane; bm, basement membrane; pf, parafollicular
cell. All photomicrographs are of the same magnification. Scale bar, 1
µm.
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© The Company of Biologists Ltd 2006