Time-dependent changes in the suppressive effect of electric field exposure on immobilization-induced plasma glucocorticoid increase in mice

Anxiolytic-like effects of extremely low frequency electric field in stressed rats: involvement of 5-HT2C receptors

BACKGROUND

Possible modulatory effects of noninvasive brain stimulation have gained interest recently. In our study, the effect of low frequency electric fields (LF-EF) on stress-induced electrophysiological, behavioral changes and the possible involvement of serotonergic 5-HT2C receptors were investigated.

MATERIALS AND METHODS

A total of eight groups including the control groups were formed by applying LF-EF with or without a 5-HT2C receptor agonist to naïve or acute stress exposed rats to demonstrate the effects of LF-EF. LF-EF administration at 10 kV/m was started 30 min before acute stress application and lasted for 1 h in total. Anxiety levels and social interaction were evaluated using the elevated plus maze test and social interaction test, respectively. Auditory evoked potentials (AEP) were recorded by using ascending loudness paradigms. Loudness dependence AEP (LDAEP) was calculated by using amplitude values to analyze serotonergic transmission. Serotonin and glucocorticoid levels were measured in the frontal cortex and hippocampus.

RESULTS

It was observed that the applied LF-EF reduced the anxiety behavior, and attenuated the LDAEP responses in stress and/or 5-HT2C receptor agonist applied groups. In parallel, an increase in serotonin levels and a decrease in glucocorticoid levels were observed. However, LF-EF exposure was ineffective in impaired social interaction.

CONCLUSIONS

Our findings show that 10 kV/m LF-EF administration may modulate the neural network and physiological responses associated with mild acute stress. 5-HT2C receptor dependent functions are thought to play a role in the anxiolytic effect of LF-EF.

Extremely low-frequency electric field suppresses not only induced stress response but also stress-related tissue damage in mice

Although extremely low-frequency electric fields (ELF-EF) have been utilised for therapeutic purposes, the biological effect and the underlying mechanism of ELF-EF have not been elucidated. Here, we developed a mouse model of immobilisation-induced increase in glucocorticoid (GC) to evaluate the effect of ELF-EF. Mice were exposed to 50-Hz 10 kV/m EF via a parallel plate electrode and immobilised as needed. The ELF-EF suppressed the immobilisation-induced increase in blood GC level. Here, the results of 32 tests using the model were pooled and analysed. The suppressive effect of ELF-EF on immobilisation-induced increase in GC was reproduced, and the GC level was slightly higher in the ELF-EF-treated mice than in the sham-controlled mice, a novel observation. The immobilisation-induced increase in lactate dehydrogenase, glutamic oxaloacetic transaminase, and glutamic pyruvic transaminase, markers of tissue damage, was suppressed by co-treatment with EF in the biochemical tests using the same plasma sample. In the metabolome analysis, the changes in corticosterones, leukotrienes, and hydroxyeicosatetraenoic acids, markers of inflammation, showed a pattern similar to that of the plasma GC level. Thus, ELF-EF suppresses the stress response that causes an increase in the GC level and slightly promotes GC production in the absence of stress. Moreover, the suppressive effect of ELF-EF on induced stress response might be involved in stress-induced tissue damage or inflammation in immobilised mice. Overall, the model and the data help explore the biological effect of ELF-EF and explain the stress-relieving effect of EF. They would be useful in determining the medical applications of EF in humans and animals.

Gender and Age Differences in the Suppressive Effect of a 50 Hz Electric Field on the Immobilization-Induced Increase of Plasma Glucocorticoid in Mice

We developed an experimental system to characterize the suppressive effect of extremely low-frequency (ELF) electric fields (EFs) on the stress response. We assessed differences in the EF effects by age and gender. Control, EF-alone, immobilization-alone, and co-treated groups were subjected to an EF (50 Hz, 10 kV/m). Co-treated mice were exposed to the EF for 60 min, with immobilization during the latter half. Our results indicate that the suppressive effects of ELF EFs on the stress response in immobilized mice occur regardless of gender or age. As stress plays an important role in the onset and progression of various diseases, these findings may have broad implications for understanding the efficacy of EFs in animal, and perhaps human, health. Bioelectromagnetics. 2020;41:156-163. © 2019 Bioelectromagnetics Society.

Characterization of the suppressive effects of extremely-low-frequency electric fields on a stress-induced increase in the plasma glucocorticoid level in mice

We recently suggested that an increase in the plasma glucocorticoid (GC) level in immobilized mice is suppressed by a 50-Hz electric field (EF) in an EF strength-dependent manner. The present study aimed to assess the anti-stress effect of EFs in three scenarios: exposure to an EF of either 50 or 60 Hz, which are the standard power frequencies in most regions; varying levels of environmental brightness during EF exposure; complete or partial shielding of the mouse from the EF. We compared the GC levels and blood parameters among control, EF-alone, immobilization-alone, and co-treatment groups. There was no difference between EFs of 50 and 60 Hz in terms of the suppression of the immobilization-induced increase in GC, that is, the anti-stress effect upon EF exposure. Examination of the effects of three environmental illuminance levels, 0, 200, and 490 lux, revealed that the effect of the EF was influenced by environmental illuminance. Shielding of the mice from the EF by wrapping the animals with an electrically conductive sheet inhibited the EF effect, which showed a negative correlation with the area shielded. Hence, environmental illuminance and the body area exposed to the EF might influence the effects of an EF on stress-induced increases in plasma GC levels in mice. Because stress plays an important role in the onset and progression of various diseases, these findings may have broad implications for understanding the efficacy of EFs in health. Bioelectromagnetics. 39:516-528, 2018 © 2018 Wiley Periodicals, Inc.