この研究は、大脳皮質組織の切片を用いて、ミリ波（MMW）電磁界が個々の錐体ニューロンに与える影響を調べた。実験に用いたMMW電力のレベルは、既存の人体ばく露の安全限度値1 mW/ cm2を3桁下回るレベルとした。その結果、驚くべきことに、このように低い電力レベルでも、MMWはニューロンの発火率および原形質膜の特性にかなりの変化をもたらすことが示された；電力密度が1 μW/ cm2付近、1分間のMMWばく露により、検査した8つのニューロンのうち4つで、発火率がばく露前のレベルの3分の1に減少した；すべてのニューロンにおいて、活動電位の幅はベースライン値の17 %に狭められ、膜入力抵抗はベースライン値の54 %に減少した。これらの影響は短期間（2分以下）持続した；組織切片を入れた水溶液の温度はMMWにより3 %高くなった、と報告している。
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Slices of cortical tissue were used to evaluate the effects of millimeter wave exposure on individual pyramidal cells under conditions mimicking their in vivo environment.
The brains were isolated from three neonatal rats. A total of eight neurons were patched in eight slices from three rats. Several millimeter wave power flux densities were applied to the slice in randomized order to remove any possible effects of cumulative exposure.
For evaluation of the neuronal activity in the absence of intracellular calcium signaling, the intracellular calcium stores were buffered by adding 10 mM EGTA.
Several millimeter wave power flux densities were applied to the slice in randomized order to remove any possible effects of cumulative exposure.
| 周波数 | 60.125 GHz |
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| タイプ |
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| 偏波 |
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| ばく露時間 | continuous for 60 s |
| Modulation type | CW |
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| ばく露の発生源／構造 | |
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| ばく露装置の詳細 | open-ended rectangular waveguide with a 3.8 mm x 1.9 mm aperture positioned above the tissue chamber; microwave power perpendicular to the chamber's plane; tip of the waveguide placed with an air gap of 4.8 mm to the surface of the aCSF (artifical cerebrospinal fluid) solution and 7 mm on top of the brain slice; the microwave beam expands at the aCSF surface forming a half-power ellipse of 5.5 mm² (major and minor axis 14.2 mm and 4.9 mm respectively); it is refracted upon entering the solution and forms a half-power ellipse of 6.5 mm² (major and minor axis 15.2 mm and 5.4 mm respectively) at the top of the 300 µm thick brain slice |
Even at these low power levels (three orders of magnitude below the existing limit value for human exposure of 1 mW/cm²), millimeter waves were able to produce considerable changes in neuronal firing rate and plasma membrane properties. At the power flux density approaching 1 µW/cm², 1 minute of exposure reduced the firing rate to one third of the pre-exposure level in four out of eight examined neurons. The width of the action potential amplitudes was narrowed by millimeter wave exposure to 17 % of the baseline value and the membrane input resistance decreased to 54 % of the baseline value across all neurons. These effects were short lasting (2 min or less) and were accompanied by millimeter wave-induced heating of the bath solution at 3°C.
Comparison of these data with previously published data* on the effects of bath heating of 10°C indicated that millimeter wave-induced effects cannot be fully attributed to heating and may involve specific millimeter wave absorption by the tissue.
Blocking of the intracellular Ca2+-mediated signaling did not significantly alter the millimeter wave-induced neuronal responses suggesting that millimeter waves interacted directly with the neuronal plasma membrane.
*Lee JCF et al. (2005): Effects of temperature on calcium transients and Ca2+-dependent after hyperpolarizations in neocortical pyramidal neurons. J. Neurophysiol. (93) 2012-20.
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