Pregnant rats were continuously exposed to one of four intensities during the pregnancy: 1.) 5-20 nT, 2.) 30-50 nT, 3.) 90-580 nT und 4.) 90-1200 nT (n=2 per group). After one year, the male offspring (n=6-7 per group) were used in the open field test and the contextual fear conditioning was examined. Additionally, the number and the structure of hippocampal neurons were analyzed (n=4 per group).
Previous studies showed that there were no differences between rats exposed to a weak magnetic field of 5-20 nT and a control group without any magnetic field. Therefore, in this study, the reference group (5-20 nT) was used as a control.
The experiment was performed twice.
Modulation type: pulsed
Exposure duration: continuous to different field patterns for 24 h/day during gestation (21 days)
composite pattern: composed of 40 sequential 250 ms signatures of specific frequency-modulated patterns as well as of those derived from mathematical relationships; LTP-pattern: repeated sequences of a primer pulse followed 170 ms later by four working pulses; 50 Hz pattern: rise time and fall time of 1 ms and a plateau and trough of 20 ms; all patterns were presented in a repeating cycle for 10 s, followed by 40 s of no field for 24 h before the next pattern was initiated; each pattern repeated every fourth day throughout gestation
|magnetic flux density||20 nT||maximum||measured||-||B = 5 - 20 nT reference group|
|magnetic flux density||50 nT||maximum||measured||-||B = 30 - 50 nT low-intensity group|
|magnetic flux density||580 nT||maximum||measured||-||B = 90 - 580 nT medium-intensity group|
|magnetic flux density||1,200 nT||maximum||measured||-||B = 590 - 1200 nT high-intensity group|
Individual analyses of open field related behaviors revealed no significant differences between any of the exposure conditions. In the fear conditioning, it was found that exposure to the low-intensity (30-50 nT) complex magnetic field during prenatal development resulted in a significant reduction of freezing time compared to the reference group (5-20 nT). Additionally, rats exposed to the low-intensity (30-50 nT) complex magnetic field showed anomalies in the cytological and morphological development of the hippocampus (reduction in overall hippocampal size and promoted subtle malformation of some regions) as compared to the reference group (5-20 nT). In contrast, exposure to weaker or stronger intensities of the same complex magnetic field did not interfere with hippocampal development or anxiety behavior.
These findings suggest that prenatal exposure to complex magnetic fields of a narrow intensity window during development could result in subtle but permanent alterations in hippocampal structure and function.