Study type: Medical/biological study (experimental study)

Neurodevelopmental anomalies of the hippocampus in rats exposed to weak intensity complex magnetic fields throughout gestation. med./bio.

Published in: Int J Dev Neurosci 2012; 30 (6): 427-433

Aim of study (acc. to author)

To investigate the effect of weak intensity magnetic fields on the prenatal brain development.

Background/further details

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.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 50 Hz
Modulation type: pulsed
Exposure duration: continuous to different field patterns for 24 h/day during gestation (21 days)

Exposure 1

Main characteristics
Frequency 50 Hz
Type
Exposure duration continuous to different field patterns for 24 h/day during gestation (21 days)
Additional info temporal structures of a complex magnetic field (composite, LTP-like, and non-sinusoidal 50 Hz field)
Modulation
Modulation type pulsed
Additional info

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

Exposure setup
Exposure source
Setup rats kept in one of four identical compartments of a 140 cm x 33 cm x 33 cm plastic cage; identical Herlmholtz coils positioned at each end of the cage; coils created by wrapping 38 cm x 33 cm x 27 cm cartons with 305 m of 30 AWG wire
Parameters
Measurand Value Type Method Mass Remarks
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

Reference articles

  • Whissell PD et al. (2009): Prenatal exposures to LTP-patterned magnetic fields: quantitative effects on specific limbic structures and acquisition of contextually conditioned fear.
  • St-Pierre LS et al. (2008): Altered blood chemistry and hippocampal histomorphology in adult rats following prenatal exposure to physiologically-patterned, weak (50-500 nanoTesla range) magnetic fields.
  • St-Pierre LS et al. (2003): Conspicuous histomorphological anomalies in the hippocampal formation of rats exposed prenatally to a complex sequenced magnetic field within the nanoTesla range.

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

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.

Study character:

Study funded by

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