Supplementary Material for: New view on the impact of the low-frequency electromagnetic field (50 Hz) on stress responses – hormesis effect

Introduction: Low-frequency electromagnetic field (50 Hz) (EMF) can modify crucial neuronal processes. Existing data indicate that exposure to EMF may represent a mild stressor and contribute to disturbances of hypothalamic-pituitary-adrenal (HPA) axis. The important regulatory pathways controlling HPA axis activity include two types of corticosteroid receptors: mineralocorticoid (MR) and glucocorticoid (GR) receptors. There are particularly abundant in the hippocampus, a key locus of HPA axis feedback control. The research aimed at determining whether 1) EMF exhibits hormesis, it means bidirectional action depending on EMF intensity (1 or 7 mT), and 2) repeated EMF exposure changes stress response to subsequent stress factors. Methods: The exposure (7-day, 1h/day) of adult rats to EMF (1 mT and 7 mT) was repeated 3 times. HPA axis hormones and their receptors were analysed after each following exposure. Moreover, the impact of EMF exposure on hormonal and behavioural responses to subsequent stress factor - open-field test was evaluated. Results/Discussion: Our data suggest that exposure to EMF can establish a new “set-point” for HPA axis activity. The direction and dynamics of this process depend on the intensity of EMF and the number of exposures. EMF of 1 mT induced an adaptive stress response, but 7 mT EMF caused sensitization. Consequently, EMF changed the vulnerability of the organism to a subsequent stress factor. We have also shown the increase of MR mRNA abundance in hippocampus of 1 mT EMF exposed rats, which can represent the possible neuroprotective response and suggest therapeutic properties of electromagnetic fields.