In a previous study, the authors reported that an immobilization stress-induced increase in glucocorticoid level in mice was suppressed by exposure to a 50 Hz electric field (Hori et al. 2015). In the present study, the effects of different configurations of the exposure setup should be investigated. The electric field strength was always 10 kV/m.
To investigate the influence of the factors immobilization stress, field strength, distance between electrodes and contact of mice to lower (grounded) electrode, male mice were divided into the following groups: 1) immobilization and exposure to the electric field with 50 mm distance between electrodes (n=8), 2) immobilization and exposure to the electric field with 100 mm distance between electrodes (n=8), 3) immobilization and exposure to the electric field with 200 mm distance between electrodes (n=8), 4) immobilization and exposure to the electric field with 100 mm distance between electrodes and contact to lower electrode (n=6), immobilization and exposure to the electric field with 100 mm distance between electrodes and polypropylene sheet of 5) 0.1 mm, 6) 1 mm and 7) 5 mm thickness between mouse and lower electrode (n=6 each). Moreover, control groups with and without immobilization were used (n=6 each).
Exposure duration: continuous for 60 minutes
|Exposure duration||continuous for 60 minutes|
|Chamber||cylindrical acrylic cage (diameter: 200 mm; height: 50, 100 or 200 mm depending on group); mice were immobilized within a 50 ml centrifuge tube placed on the lower electrode|
|Setup||two stainless steel electrodes (1,000 x 600 mm) that were placed over and under the cage and 6 polypropylene pillar spacers (height: 50, 100 or 200 mm); the cage had slits (100 x 5 mm) all around at 5 mm intervals to remove smudges; the center of the lower electrode was also covered with a parallel cross-pattern mesh (280 x 280 mm); to generate the electric field, 0.5, 1 or 2 kV (depending on the group or distance of electrodes, respectively) was applied to the upper electrode and the lower electrode was grounded; a separate cage and immobilization tube were used for each animal; the temperature within the cage was constant at 25 ± 3°C during exposure and sham expossure; the humidity was kept between 45% and 55%|
|Sham exposure||A sham exposure was conducted.|
|Additional info||immobilization was applied 30 min after the beginning of exposure (for 30 minutes)|
|electric field strength||10 kV/m||-||measured||-||error of ± 1%|
Immobilization alone significantly increased plasma glucocorticoid levels compared to non-immobilized control mice. However, plasma glucocorticoid levels were significantly decreased in mice exposed to an electric field with 100 mm electrode distance (group 2) compared to immobilized mice in the control group but not in mice exposed to a electric field with 50 mm or 200 mm electrode distance (groups 1 and 3). Furthermore, the suppressive effect of the 100 mm electrode distance electric field was canceled when a polypropylene sheet of 0.1 or 1 mm thickness was placed between the animal and lower electrode (groups 5 and 6).
The authors conclude that the suppressive effect of an exposure of mice to a 50 Hz electric field of 10 kV/m on the immobilization stress-induced increase in blood glucocorticoid level is dependent on the configuration of the exposure setup even if the field strength remains the same.