الفهرس 
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Abstract
T
he aim of the present work was to compare the histological alterations in the thyroid gland resulting from exposure to 2G versus 4G mobile phones using the adult male albino rat as an experimental model.
Forty-five adult male albino rats weighing 180-220 gms were used in the present study. They were obtained from the animal household of medical research center, Faculty of Medicine, Ain Sham University. They were divided into 4 groups:
group I (Control group) consisted of nine adult male rats that were kept away from any source of EMR including mobile phones. group II (Sham exposed group) consisted of twelve adult male rats that were exposed to switched off cell phones 24 hrs. per day for eight weeks. This group was divided into 2 subgroups; subgroup IIA consisted of six adult male rats and were exposed to switched off Nokia Asha 501 phones. Subgroup IIB consisted of six adult male rats and were exposed to switched off Lenovo B phones. group III consisted of twelve adult male rats that were exposed to Nokia Asha 501 phones as sources of 2G radiation (900 MHz) emitted by ringing for one hour per day for eight weeks and group IV consisted of twelve adult male rats that were exposed to Lenovo B phones as sources of 4G-LTE radiation (2100-2400 MHz) emitted by ringing for one hour per day for eight weeks.
At the end of the experiment, animals were sacrificed; thyroid gland specimens were removed from all groups, processed and examined using light microscope (Hematoxylin and Eosin, Masson’s trichrome and toluidine blue stains) and electron microscope. Morphometric analysis was done on H&E-stained slides with statistical analysis using IPM SPSS Statistics Data Editor.
The results revealed that all the control groups (I, IIA& IIB) showed the same histological and ultrastructural features.
Examination of H&E-stained thyroid sections from the control groups showed that the gland was formed of multiple lobules separated by thin connective tissue septa. The thyroid lobule consisted of variable sized follicles with connective tissue in between. The large follicles were found at the periphery of the gland while the smaller ones were found mostly at the center of each lobule. Each follicle was lined with a single layer of cuboidal or columnar thyrocytes that had vesicular rounded nuclei. The lumen of each thyroid follicle had acidophilic homogenous colloid.
Regarding Masson’s trichrome-stained thyroid sections, thin collagen fibers were observed in between the thyroid follicles and in the septa between the thyroid lobules.
Examination of semithin sections stained with toluidine blue showed that each follicle was lined with a single layer of follicular thyrocytes that was resting on a basal lamina and had convex apical membranes. The follicular cells or thyrocytes were either cuboidal or columnar in shape with large oval or rounded vesicular nuclei and had prominent nucleoli. The lumen of each follicle contained a homogenous colloidal material. Large polyhedral parafollicular cells were also observed and characterized by their large oval nuclei, pale cytoplasm, and small granules. They were not reaching the lumen of the follicles. Capillaries were seen in between the follicles.
Electron microscopic examination of the ultrathin thyroid gland sections from rats in the control groups showed that the thyrocytes were large cells contained large rounded or oval vesicular nuclei with prominent nucleoli and their apical border showed numerous microvilli that project into the lumen that contains homogeneous colloid. Junctional complexes between the lateral walls of the adjacent thyrocytes were found near the cellular apices. Their cytoplasm showed cisternae of well-developed rough endoplasmic reticulum that were arranged in parallel cisternae around the nucleus. Few mitochondria and electron dense lysosomal granules of variable sizes were also encountered. The parafollicular cells were also noticed between the thyroid follicular cells and the basement membrane. They were relatively larger and stained less intensely than the thyrocytes. Each cell had large oval euchromatic nucleus and presented mitochondria, and small amount of rough endoplasmic reticulum. The most striking feature of these cells was the presence of numerous small electron dense secretory granules.
H&E-stained thyroid sections from group III showed that the general histological architecture of the gland was preserved, however, in some sites the lobulation of the gland was hardly detected. The follicles were variable in shape and size. Multiple follicles were large and irregular, and some small sized follicles was also noticed. Most of the follicles were completely filled with colloid, however, follicles with vacuolated colloid, peripheral scalloping or even depleted colloid were also encountered. Follicular cells varied from flattened to high cuboidal with flat or rounded darkly stained nuclei and many of them had vacuolated cytoplasm. Some thyroid follicles were lined by more than one layer of follicular thyrocytes. Congested and dilated blood vessels were also noticed between the follicles.
Regarding Masson’s trichrome-stained thyroid sections, excessive amount of collagen fibers was found in the septa between the lobules and also in between the follicles.
Examination of semithin sections stained with toluidine blue from group III showed more histological changes; Some follicles appeared relatively larger than that of the control groups. Those were lined mostly with flattened or low cuboidal thyrocytes and resting on a thickened basal lamina. Perifollicular collagen deposition was obvious in some sites. As regards the nuclei of the thyrocytes, they were flat or oval in shape. Moreover, darkly stained rounded or irregular nuclei were also observed. The cytoplasm of some thyrocytes showed vacuolation, while in other cells presented darkly stained small granules. The colloid in most of the follicles was homogenous, however cellular debris was observed in the lumina of some follicles. In addition, there was apparent increase in the parafollicular cells and the mast cells. Congested and dilated blood vessels were noticed in between the follicles.
Ultra-structurally, the most notable feature of the thyroid follicular cells was the presence of variable degrees of dilated rough endoplasmic reticulum with loss of their lamellar arrangement in their cytoplasm. Moreover, multiple electron dense lysosomes were distributed in the cytoplasm of most of the thyrocytes. Areas of rarified cytoplasm were noticed in some cells. Marked nuclear atypia was a prominent finding in the form of bizarre shaped hyperchromatic nuclei. Shrunken and vesicular nuclei were also noticed. The apical border of the thyrocytes showed either sparse or completely lost microvilli, however some cells showed condensed microvilli. Cell junctions between the thyrocytes were hardly observed in some areas. Perifollicular deposition of collagen was a striking finding.
Examination of H&E-stained thyroid sections from group IV showed wider septa between the thyroid lobules. There were apparent histological changes of the thyroid follicles. Many follicles were irregular in shape and large. Multiple follicles had interrupted follicular walls with desquamated epithelial cells in their lumina. Others were coalesced together. The colloid in some follicles showed peripheral scalloping. Moreover, follicles with retracted and depleted colloid were also observed. Follicular cells varied from flattened to low cuboidal and most of them had flat, darkly stained nuclei and vacuolated cytoplasm. Some thyroid follicles were lined by more than one layer of follicular thyrocytes. Congested and dilated blood vessels were also noticed between the follicles.
Regarding Masson’s trichrome-stained thyroid sections, excessive amount of collagen fibers was found in the septa between the lobules and also in between the follicles.
Examination of semithin sections stained with toluidine blue from group IV clarified disintegration and disorganization of most of the thyroid follicles; most of the follicles were disfigured and disrupted and few follicles showed proliferation of their lining epithelium. Cellular debris and detached desquamated cells were frequently noticed in the lumina of the follicles. The thyrocytes were low cuboidal or flattened and few of them were swollen. The cytoplasm was mostly degenerated in some areas, and it was vacuolated and granulated in other areas. As regards the nuclei of the thyrocytes, they were flat, rounded, darkly stained, irregular or pyknotic. In addition, extruded colloid, congested and dilated blood vessels were noticed in between the thyroid follicles and there was apparent increase in the parafollicular cells, and the mast cells were frequently noticed in many semithin sections of this group.
Ultra-structurally, some thyrocytes showed mild to markedly dilated cisternae of rough endoplasmic reticulum with loss of their lamellar arrangement. Fragmented rough endoplasmic reticulum was also noticed. In addition, small to large sized electron dense lysosomes were observed in the cytoplasm of most cells. Swollen mitochondria with disrupted cristae, along with vacuoles and rarified cytoplasm were further encountered. As regards the nuclei of the thyrocytes, they showed marked nuclear atypia in the form of irregular, shrunken, hyperchromatic and pyknotic nuclei. An interesting finding was the presence of cytoplasmic blebs arising from the apical surface of some thyrocytes. Moreover, the apical pole of most cells showed partial or complete loss of the microvilli and became flattened. Cell junctions between the thyrocytes were hardly observed in some areas. The parafollicular cells were frequently noticed in this group. Dilated and congested blood vessels were noticed in between the thyroid follicles. In addition, bundles of collagen fibers invading some thyrocytes were also observed.
Conclusion
These results were discussed with the previous literature, and it could be concluded that exposing the adult male rats’ thyroid glands to the radiofrequency radiation of 2G and 4G cell phones caused structural alterations at the light and electron microscopic levels. Degenerative changes were observed in both exposed groups and it was more exaggerated among rats exposed to 4G mobile phones.