Effects of millimeter wave irradiation and equivalent thermal heating on the activity of individual neurons in the leech ganglion

Abstract

Many of today's radiofrequency-emitting devices in telecommunication, telemedicine, transportation safety, and security/military applications use the millimeter wave (MMW) band (30–300 GHz). To evaluate the biological safety and possible applications of this radiofrequency band for neuroscience and neurology, we have investigated the physiological effects of low-intensity 60-GHz electromagnetic irradiation on individual neurons in the leech midbody ganglia. We applied incident power densities of 1, 2, and 4 mW/cm2 to the whole ganglion for a period of 1 min while recording the action potential with a standard sharp electrode electrophysiology setup. For comparison, the recognized U.S. safe exposure limit is 1 mW/cm2 for 6 min. During the exposure to MMWs and gradual bath heating at a rate of 0.04°C/s (2.4°C/min), the ganglionic neurons exhibited similar dose-dependent hyperpolarization of the plasma membrane and decrease in the action potential amplitude. However, narrowing of the action potential half-width during MMW irradiation at 4 mW/cm2 was 5 times more pronounced compared with that during equivalent bath heating of 0.6°C. Even more dramatic difference in the effects of MMW irradiation and bath heating was noted in the firing rate, which was suppressed at all applied MMW power densities and increased in a dose-dependent manner during gradual bath heating. The mechanism of enhanced narrowing of action potentials and suppressed firing by MMW irradiation, compared with that by gradual bath heating, is hypothesized to involve specific coupling of MMW energy with the neuronal plasma membrane.

Effects of 60-GHz millimeter waves on neurite outgrowth in PC12 cells using high-content screening

“…In this study, a 60 GHz exposure with a maximum power density of 600 mW/cm² altered activity levels of voltage-gated channels and ionic pumps, and increased the action potential firing rate of exposed oocytes [26]. Eventually, another team observed that a 60 GHz MMW exposure at 4 mW/cm² of individual neurons in the leech midbody ganglia could dramatically increase the narrowing of the neurons action potential half-width, while transiently reducing their firing rate [27]. Those observations could not be fully reproduced by equivalent bath heating.…”

Exposure to 50 Hz electric fields reduces stress‐induced glucocorticoid levels in BALB/c mice in a kV/m‐ and duration‐dependent manner

“…In addition, in vitro studies have suggested that exogenous EFs can induce changes in intracellular calcium ion concentrations and protein synthesis [McLeod et al, 1987;Cho et al, 1999]. Although in vitro and in vivo effects of high-frequency EFs and magnetic fields have been investigated [Kim et al, 2014;Romanenko et al, 2014], analyses of in vivo effects of power-line frequency EFs have not been analyzed. To conduct such analyses, it is first necessary to establish experimental methods to assess quantitative and qualitative effects of exogenous EFs.…”

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“…Using 60 GHz low-density short time (5 s) radiation power (~4 mW/cm 2 ) incident on the object, it was shown that the real-time effects in isolated leech ganglions could not mimicked by equivalent bath heating [65]. Therefore, it seems that the needs of THz radiation effects researches on living organisms for determination of THz and mm waves ultimate dosage and exposure time are important for evaluation of the transient effects on the health and for elaboration of safety standards.…”

“…The fact that THz radiation has a shorter wavelength than microwave radiation and thus has the capability of having a higher spatial resolution, and at low levels of radiation power does not pose any known harm to living organisms, makes THz imaging a powerful and presumably safe imaging technology [12,45,65].…”