この研究は、SW雄マウスの後足の腓腹神経の受容野にミリ波（MMW, 42.25 GHz）ばく露を与え、腓腹神経の電気活動の変化を外部電極記録法により調べた。その結果、2つのタイプの反応が見られたと報告している。第一は、入射電力密度45 mW/cm2のMMWばく露で自発的電気活動が阻害されたことである（ただし、低レベル(10-30 mW/cm2)では発火頻度の変化は見られなかった）。第二は、MMWばく露の停止に反応して発火頻度の一過性上昇が起きることで、この効果は20-40秒継続し、この効果の閾値は160 mW/cm2であった。補完的に以下の実験を行った結果、輻射熱ばく露では、MMWの阻害効果のみが再現され、一過性の興奮反応は再現されなかった；コンパウンド48/80投与により肥満細胞を破壊すると、この一過性反応は消失した、ことなどを報告している。
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To study the effects of millimeter waves (42.25 GHz) on electrical activity of the murine sural nerve (one of the main branches of the sciatic nerve). The aim of the study was to find out whether millimeter wave exposure was able to activate cutaneous sensory receptors in the murine hind paw.
Millimeter waves are almost totally absorbed within the superficial layers of the skin. Therefore, the initial effect of millimeter waves is limited to structures located in the outer layers of the skin (there is no scientific theory based on a known physiology that would explain how local millimeter wave exposure of the skin produces a systemic effect).
All experiments were conducted under anesthesia. The paw temperature was 35.8°C (n=17). In some experiments the paw skin temperature was lowered to examine different temperature influences on nerve responses.
Different branches of the sciatic nerve were dissected. The nerve was cut 3-5 mm from the spinal cord.
To reproduce the thermal effects of millimeter waves, a radiant heat source was used (the same mice were used).
Capsaicin (a TRPV1 (transient receptor potential ion channel) agonist used for activation of polymodal nociceptor fibers) was used to examine the role of capsaicin-sensitive receptors. Compound 48/80 was used for depletion of mast cells.
| 周波数 | 42.25 GHz |
|---|---|
| タイプ |
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| ばく露時間 | continuous for 20 s to 10 min |
| Modulation type | CW |
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| 周波数 | 42.25 GHz |
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| タイプ |
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| ばく露時間 | continuous for 20 s to 10 min |
| Additional information | This exposure was applied in 5 experiments to study whether pulse intensity or temporal-average intensity is the critical paramter for eliciting the transient response. |
| Modulation type | pulsed |
|---|---|
| Repetition frequency | 1 kHz |
| Pulse type | rectangular |
| ばく露の発生源／構造 |
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Two types of responses of the sural nerve to millimeter wave exposure were found. First, millimeter wave exposure at the incident power density >/= 45 mW/cm² inhibited the spontaneous electrical activity of the sural nerve. Exposure with lower intensities (10-30 mW/cm²) produced no detectable changes in the firing rate. Second, the nerve responded to the cessation of exposure with a transient increase in the firing rate (this effect lasted 20-40 s). The threshold intensity for this effect was 160 mW/cm².
Radiant heat exposure reproduced only the inhibitory effect of millimeter wave exposure, but not the transient excitatory response after the cessation of the heat exposure.
Depletion of mast cells by compound 48/80 eliminated the transient response of the nerve. It was suggested that the cold sensitive fibers were responsible for the inhibitory effect of millimeter wave and radiant heat exposures. However, the receptors and mechanisms involved in inducing the transient response to millimeter wave exposure are not clear. The hypothesis of mast cell involvement was discussed.
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