Altered development in rodent brain cells after 900 MHz radiofrequency exposure.

The ICNIRP has established exposure guidelines for radiofrequency (RF) radiation: 0.08 W/kg for the general population and 0.4 W/kg for occupationally exposed persons. However, it is unclear whether these guidelines provide adequate protection. Previous studies have shown that exposure to comparable levels can cause oxidative stress and altered growth in rodents. These biological effects may occur at these thresholds, especially during sensitive developmental stages. Thus, this study examined the impact of 2G radiofrequency (RF) exposure on the developing brain by using in vivo and in vitro rat models. The ICNIRP limits were adhered to. Most synapses in rats form between postnatal days (PND) 0 and 21, with synaptogenesis (the formation of synapses) peaking during PND 14. In human children, this peak occurs between the ages of 1 and 2. This study focused on proteomic changes and cellular parameters, including proliferation, synaptogenesis, and differentiation of neural cells.

The male Sprague Dawley rats were examined after being exposed in utero from the eighth day of gestation until the seventh postnatal day at most. The rats were exposed to 900 MHz radiation at either the public exposure limit (30.2 V/m; whole-body SAR 0.08 W/kg) or the occupational exposure limit (67.5 V/m; whole-body SAR 0.4 W/kg). The controls were sham-exposed. A total of 9 control animals (n = 9) and 8 exposed animals (n = 8) were exposed. Examined endpoints included proteomic analyses of the hippocampus and cortex immediately after birth; quantification of brain-derived neurotrophic factor (BDNF), which is essential for maintaining and developing neurons and synapses, as well as memory processes; cell proliferation; the number of synapses and the balance between excitatory and inhibitory synapses; and oxidative stress markers in the hippocampus and cortex on the postnatal days (PND) 8 and 17. (Due to the different time points, the number of animals available for respective endpoint analyses varied from n = 3 to n = 9; editor's note.) These in vivo studies were supplemented by in vitro analyses of neural stem cells. The cells were exposed to 900 MHz radiation and 0.08 W/kg for 3 or 7 days. The scientists evaluated cell differentiation, cell proliferation, and DNA damage.

Proteomic analysis on postnatal day (PND) 0 revealed different expression levels of 10 proteins in the exposed groups compared to the sham-exposed control group. These changes primarily affected proteins associated with synapse formation and cell growth. A significant decrease in the number of synapses was observed in the hippocampus of young animals exposed on PND 8. The balance between excitatory and inhibitory synapses shifted significantly toward inhibitory synapses in both exposed groups. Both effects leveled off by PND 17. There were no significant differences in the number of synapses in the cortex. However, the balance shifted significantly in the more heavily exposed group on PND 17. In the cortex, but not the hippocampus, there were significantly fewer proliferating cells on PND 8. A significant decrease in BDNF levels was also observed on PND 17. Examination of oxidative stress markers showed no significant changes. In vitro, there were significantly more apoptotic and proliferating cells, as well as DNA double-strand breaks. In addition, there was a statistically significant change in the differentiation pattern of neural stem cells.

The study data suggest that exposure within regulatory limits for the general population may adversely impact brain development. These changes include reduced cell proliferation, BDNF levels, and synapse formation in vivo, as well as changes in neural stem cell differentiation in vitro. The authors hypothesize that the increase in inhibitory synapses may result from increased neuronal excitability of the organism. Changes in this balance have been linked to developmental disorders of the nervous system, such as autism spectrum disorder. In summary, the scientists' hypothesis that developing organisms are susceptible to RF radiation is confirmed. They recommend exercising caution when using mobile devices, especially around pregnant women and young children.

Editor's note:

The study design is impressive thanks to its combination of in vivo and in vitro experiments and a multimodal approach that includes proteomics, immunohistochemistry, and functional analyses. The study's significance is also enhanced by its use of low field strengths that fall within regulatory limits for the general population. However, there are areas for improvement. For example, the total number of experimental animals is small, and the number varies depending on the endpoints investigated. While the chosen study times are well-selected in terms of neural development, an additional study including adult animals would have been desirable to analyze functional consequences that may persist into adulthood. As with any animal model, the question of transferability to humans arises. Nevertheless, the data suggest that regulatory limits may not be safe at all stages of development. (RH)