この研究は、ラットを用いた実験で、出生前の低レベル磁界ばく露による出生後の仔ラットの脳の発達への影響を調べた。妊娠中のWistarラットに、妊娠期間中（21日間）、24時間連続で磁界ばく露を与えた。ばく露レベルは、4レベルのうちのいずれか一つのレベル（参照：5 - 20 nT、低：30 - 50 nT、中：90 - 580 nT、高：590 - 1200 nT ）とし、磁界は様々なシーケンスの4つのパターン（複合パターン、LTPパターン、パルス化50 Hzパターンなど）を用いた。すべてのパターンは10秒間繰り返され、その後40秒間は磁界なしの構成で反復された。一つのパターンで24時間ばく露を行い、４日間で4つのパターンが繰り返された。その結果、低ばく露群から出生した仔ラットは、文脈的恐怖学習の障害を示した；また、海馬の細胞学的および形態学的発達の異常として、特に、海馬全体のサイズ縮小、CA1およびCA3領域の微かな発育不全が見られた；対照的に、これより弱いまたはより強いばく露レベルでは、海馬の発達または恐怖行動への影響は見られなかった；著者は、これらの知見は磁界レベルの狭い窓効果の可能性を示唆する、と報告している。
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To investigate the effect of weak intensity magnetic fields on the prenatal brain development.
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
ばく露時間: 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
|ばく露装置の詳細||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|
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.