Abstract

Radiofrequency electromagnetic field (RF-EMF) is used globally in conjunction with mobile communications. There are public concerns of the perceived deleterious biological consequences of RF-EMF exposure. This study assessed neuronal effects of RF-EMF on the cerebral cortex of the mouse brain as a proxy for cranial exposure during mobile phone use. C57BL/6 mice were exposed to 835 MHz RF-EMF at a specific absorption rate (SAR) of 4.0 W/kg for 5 hours/day during 12 weeks. The aim was to examine activation of autophagy pathway in the cerebral cortex, a brain region that is located relatively externally. Induction of autophagy genes and production of proteins including LC3B-II and Beclin1 were increased and accumulation of autolysosome was observed in neuronal cell bodies. However, proapoptotic factor Bax was down-regulted in the cerebral cortex. Importantly, we found that RF-EMF exposure led to myelin sheath damage and mice displayed hyperactivity-like behaviour. The data suggest that autophagy may act as a protective pathway for the neuronal cell bodies in the cerebral cortex during radiofrequency exposure. The observations that neuronal cell bodies remained structurally stable but demyelination was induced in cortical neurons following prolonged RF-EMF suggests a potential cause of neurological or neurobehavioural disorders.

Wireless mobile phone communication is globally ubiquitous and popular. There have long been concerns regarding possible adverse biologically-related health effects of exposure to radiofrequency electromagnetic field (RF-EMF). The central nervous system (CNS) is a main concern with regards to the effects of RF-EMF, since mobile phone use involves close exposure or immediate contact with the head¹. The biological effects of RF-EMF exposure on human health remain unclear because of conflicting findings of various studies^2,3.

A number of studies have reported that RF-EMF exposure of animal models increases blood-brain barrier permeability, impairs intracellular calcium homeostasis, alters neurotransmitters, and increases neuronal loss and damage in brain tissue^4,5,6,7,8. Epidemiologic studies have linked RF-EMF exposure from mobile phones with neurological and cognitive dysfunctions^9,10,11.

Cellular effects of RF-EMF exposure reportedly involve the apoptotic pathway, extracellular signal pathway, DNA damage response, cell proliferation, and cell cycle^{3,12,13,14,15}. The effect of EMF exposure on autophagy in mammalian cells has been documented^16,17. Autophagy is catabolic cellular degradation process responsible for degrading damaged organelles or unusual protein aggregates, which is activated in the presence of a variety of stimuli¹⁸. Suppression of autophagy may have a role in progression of cancers, neurodegenerative diseases, and infections, and is a common feature of aging^19,20. Therefore, autophagy plays an important role in maintaining cellular homeostasis and further functions protecting cells from various stressors²¹.

The cerebral cortex is a thin layer of neural tissue²² that surrounds brain tissues such as hippocampus, striatum, basal ganglia, and thalamus. In addition, the mouse cortex has a smooth surface, while that of humans is folder rather like a walnut²³. It is a highly-developed region of the human brain that processes most of the actual information, including sensory functions, such as hearing, touch, vision, smell, and movement, as well as cognitive functions, such as thought, perception, memory-related problem solving, and understanding language^24,25. Abnormalities of the human cerebral cortical region could be associated with various neurodegenerative diseases including Alzheimer’s disease, Lafora disease, and various cognitive disorders^26,27,28. RF-EMF exposure of the human cerebral cortex reportedly causes physiological alterations in blood flow and increases glucose metabolism^29,30. Exposure of cultured neurons to RF-EMF results in neurotoxicity, with oxidative damage caused to mitochondrial DNA³¹. Thus, RF-EMF exposure could induce various neurological changes. Information of phenotypes or symptoms following EMF exposure is still lacking even though some of studies have been reported with respect to electromagnetic hypersensitivity following EMF exposure^32,33.

The present study hypothesized that the cerebral cortex of brain can be appreciably affected by RF-EMF exposure. The focus was cerebral cortical neurons, which are involved in the autophagy intracellular pathway that could function in adaptation to continuous RF-EMF stress or for neuronal protection by generating autophagosome in their neuronal cell bodies. Previously, we showed that RF-EMF exposure induces autophagy in specific interior regions of mice brain¹⁶. In this study, we have focused on the cerebral cortex of mice. Although the whole body of mice were exposed by RF-EMF system but the cerebral cortex of mice brain is more directly exposed than the interior regions of mice brain because the horn antenna was located top of the exposure cage.

Results

Long-term exposure to 835 MHz RF-EMF induces hyperactivity

The rota rod test was done to determine the impact of chronic RF-EMF exposure on behavioural changes. This test is widely used to evaluate motor dysfunctions, especially coordination and balance. There was no significant difference between the control and RM-EMF groups (Fig. 1a). The latency to fall for control group was 141.0 ± 30.55 and the RF-EMF group 155.7 ± 8.78. Mice were also evaluated using an open field test. This test is usually used to evaluate fear in response to novelty and locomotory motivation³⁴. Rearing frequency, total distance moved, and total duration movement were monitored for 30 minutes, with data presented as cumulative total values of each parameter. The total moving distance was significantly increased in the RF-EMF exposed group (4274 ± 280.8) compared to the control group (3265 ± 116.8) (Fig. 1c). Total duration movement in the RF-EMF exposed group was significantly increased compared with the control group (Fig. 1d). However, there is no significant difference in rearing frequencies between the groups (Fig. 1b). Overall, the mice exposed to RF-EMF were hyperactive.

Behavioural tests of RF-EMF exposed mice.

Basic motor activity (rota-rod, a) and general locomotor activity (rearing frequency, total distance moved, and total duration movement) in the open field (b–d) were measured after RF-EMF exposure. Each bar illuminates the mean ± SEM of value of 6 mice. *P < 0.05.