Millimeter wave effects on electrical responses of the sural nerve in vivo

Millimeter wave (MMW, 42.25 GHz)‐induced changes in electrical activity of the murine sural nerve were studied in vivo using external electrode recordings. MMW were applied to the receptive field of the sural nerve in the hind paw. We found two types of responses of the sural nerve to MMW exposure. First, MMW exposure at the incident power density ≥45 mW/cm² inhibited the spontaneous electrical activity. Exposure with lower intensities (10–30 mW/cm²) produced no detectable changes in the firing rate. Second, the nerve responded to the cessation of MMW exposure with a transient increase in the firing rate. The effect lasted 20–40 s. The threshold intensity for this effect was 160 mW/cm². Radiant heat exposure reproduced only the inhibitory effect of MMW but not the transient excitatory response. 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 MMW and radiant heat exposures. However, the receptors and mechanisms involved in inducing the transient response to MMW exposure are not clear. The hypothesis of mast cell involvement was discussed. Bioelectromagnetics 31:180–190, 2010. © 2009 Wiley‐Liss, Inc.     

Reception of millimeter-band electromagnetic radiation by the ampullae of Lorenzini of skates

During recording of impulse activity from single nerve fibers of electroreceptors of the ampullae of Lorenzini of skates, we studied the responses to electromagnetic radiation (EMR) at a frequency of 37–55 GHz and an intensity of 1–100 mW/cm².Exposure of the ampullar canal pore to EMR at an intensity of 1–5 mW/cm² and a distance of 1–10 mm evoked a transient increase in the frequency of low-threshold receptor activity (current threshold was 0.04–0.2 µA). An increase in EMR intensity by more than 8–10 mW/cm² produced, together with elevation of receptor activity, an inhibition due to a rise in temperature of 1–3°C in the region exposed. The phase of increase in frequency of activity was absent in high current-threshold receptors (0.3–2.0 µA) when exposed to EMR. The receptors responded to irradiation of the ampullar canal pore at a distance of 15–20 mm by an increase in discharge frequency for 20 min. Direct irradiation of the ampullae of Lorenzini induced only inhibitory responses in receptor cells regardless of their excitability.The results obtained indicate that the sensory receptors of vertebrates are sensitive to EMR. It is concluded that the excitatory effects are due to direct reception of EMR by electroreceptors, and the inhibitory effects are related to local heating of the Lorenzini ampullar pore.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 325–329, September–October, 1993.     

The Non Thermal Effect of Weak Intensity Millimeter Waves on Physicochemical Properties of Water and Water Solutions

The comparative study of the effects of 5.8mW/cm² Millimeter Waves (MMW) and near Infrared (IR) irradiation on thermal properties, specific adsorption rate (SAR), specific electrical conductivity (SEC) and hydrogen peroxide (H₂O₂) content of distilled water (DW), and physiological solutions (PS) was performed. The thermal effect of MMW irradiation appeared only after the first minute of irradiation, while the IR heating started from the first minute of irradiation. The heat fusion of frozen MMW-treated DW and PS was significantly less than sham and IR-treated DW and PS. MMW irradiation had time-dependent elevation effect on water SEC and SAR, which was accompanied by the increase of H₂O₂ formation in it. We suggest that the MMW-induced vibration of water dipole molecules caused the non thermal changes of physicochemical properties of DW and PS, which promote the formation of H₂O₂ in water.     

The effect of a 94 GHz electromagnetic field on neuronal microtubules

Hardware that generates electromagnetic waves with wavelengths from 1 to 10 mm (millimeter waves, “MMW”) is being used in a variety of applications, including high‐speed data communication and medical devices. This raises both practical and fundamental issues concerning the interaction of MMW electromagnetic fields (EMF) with biological tissues. A 94 GHz EMF is of particular interest because a number of applications, such as active denial systems, rely on this specific frequency. Most of the energy associated with MMW radiation is absorbed in the skin and, for a 94 GHz field, the power penetration depth is shallow (≈0.4 mm). At sufficiently high energies, skin heating is expected to activate thermal pain receptors, leading to the perception of pain. In addition to this “thermal” mechanism of action, a number of “non‐thermal” effects of MMW fields have been previously reported. Here, we investigated the influence of a 94 GHz EMF on the assembly/disassembly of neuronal microtubules in Xenopus spinal cord neurons. We reasoned that since microtubule array is regulated by a large number of intracellular signaling cascades, it may serve as an exquisitely sensitive reporter for the biochemical status of neuronal cytoplasm. We found that exposure to 94 GHz radiation increases the rate of microtubule assembly and that this effect can be entirely accounted for by the rapid EMF‐elicited temperature jump. Our data are consistent with the notion that the cellular effects of a 94 GHz EMF are mediated entirely by cell heating. Bioelectromagnetics 34:133–144, 2013. © 2012 Wiley Periodicals, Inc.     

Current state and implications of research on biological effects of millimeter waves: A review of the literature

In recent years, research into biological and medical effects of millimeter waves (MMW) has expanded greatly. This paper analyzes general trends in the area and briefly reviews the most significant publications, proceeding from cell-free systems, dosimetry, and spectroscopy issues through cultured cells and isolated organs to animals and humans. The studies reviewed demonstrate effects of low-intensity MMW (10 mW/cm² and less) on cell growth and proliferation, activity of enzymes, state of cell genetic apparatus, function of excitable membranes, peripheral receptors, and other biological systems. In animals and humans, local MMW exposure stimulated tissue repair and regeneration, alleviated stress reactions, and facilitated recovery in a wide range of diseases (MMW therapy). Many reported MMW effects could not be readily explained by temperature changes during irradiation. The paper outlines some problems and uncertainties in the MMW research area, identifies tasks for future studies, and discusses possible implications for development of exposure safety criteria and guidelines. Bioelectromagnetics 19:393–413, 1998. © 1998 Wiley-Liss, Inc.     

Thermal Mechanisms of Millimeter Wave Stimulation of Excitable Cells

Interactions between millimeter waves (MMWs) and biological systems have received increasing attention due to the growing use of MMW radiation in technologies ranging from experimental medical devices to telecommunications and airport security. Studies have shown that MMW exposure alters cellular function, especially in neurons and muscles. However, the biophysical mechanisms underlying such effects are still poorly understood. Due to the high aqueous absorbance of MMW, thermal mechanisms are likely. However, nonthermal mechanisms based on resonance effects have also been postulated. We studied MMW stimulation in a simplified preparation comprising Xenopus laevis oocytes expressing proteins that underlie membrane excitability. Using electrophysiological recordings simultaneously with 60 GHz stimulation, we observed changes in the kinetics and activity levels of voltage-gated potassium and sodium channels and a sodium-potassium pump that are consistent with a thermal mechanism. Furthermore, we showed that MMW stimulation significantly increased the action potential firing rate in oocytes coexpressing voltage-gated sodium and potassium channels, as predicted by thermal terms in the Hodgkin-Huxley model of neurons. Our results suggest that MMW stimulation produces significant thermally mediated effects on excitable cells via basic thermodynamic mechanisms that must be taken into account in the study and use of MMW radiation in biological systems.     

Thermal Mechanisms of Millimeter Wave Stimulation of Excitable Cells

Interactions between millimeter waves (MMWs) and biological systems have received increasing attention due to the growing use of MMW radiation in technologies ranging from experimental medical devices to telecommunications and airport security. Studies have shown that MMW exposure alters cellular function, especially in neurons and muscles. However, the biophysical mechanisms underlying such effects are still poorly understood. Due to the high aqueous absorbance of MMW, thermal mechanisms are likely. However, nonthermal mechanisms based on resonance effects have also been postulated. We studied MMW stimulation in a simplified preparation comprising Xenopus laevis oocytes expressing proteins that underlie membrane excitability. Using electrophysiological recordings simultaneously with 60 GHz stimulation, we observed changes in the kinetics and activity levels of voltage-gated potassium and sodium channels and a sodium-potassium pump that are consistent with a thermal mechanism. Furthermore, we showed that MMW stimulation significantly increased the action potential firing rate in oocytes coexpressing voltage-gated sodium and potassium channels, as predicted by thermal terms in the Hodgkin-Huxley model of neurons. Our results suggest that MMW stimulation produces significant thermally mediated effects on excitable cells via basic thermodynamic mechanisms that must be taken into account in the study and use of MMW radiation in biological systems.     

Thresholds of microwave-evoked warmth sensations in human skin

We measured thresholds for microwave-evoked skin sensations of warmth at frequencies of 2.45, 7.5, 10, 35, and 94 GHz. In the same subjects, thresholds of warmth evoked by infrared radiation (IR) were also measured for comparison. Detection thresholds were measured on the skin in the middle of the back in 15 adult male human subjects at all microwave (MW) frequencies and with IR. Long duration (10-s), large area (327-cm²) stimuli were used to minimize any differential effects of temporal or spatial summation. Sensitivity increased monotonically with frequency throughout the range of microwave frequencies tested. The threshold at 94 GHz (4.5 ± 0.6 mW/cm²) was more than an order of magnitude less than at 2.45 GHz (63.1 ± 6.7 mW/cm²), and it was comparable to the threshold for IR (5.34 ± 1.07 mW/cm²). Bioelectromagnetics 18:403–409, 1997. © 1997 Wiley-Liss, Inc.     

Cooperative Response of Escherichia Coli Cells to the Resonance Effect of Millimeter Waves at Super Low Intensity

Cells of Escherichia coli K12 AB1157 were irradiated with millimeter waves (MMW) within the power density (PD) range of 10^?20 to 10 ⁴ W/cm². MMW were applied for 0.5–70 min at 51.76 GHz or 41.32 GHz at which, as had been shown earlier, MMW resonantly changes the genome conformational state (GCS) of E. coli K12 AB1157 cells. The changes in the GCS were tested with the method of anomalous viscosity time dependence (AVTD). It was demonstrated that the resonance effect of MMW manifests itself at PD up to 10^?19 W/cm². Dependences of MMW effect on power density and time of exposure proved to have distinct characteristics when cells are irradiated during the logarithmic or stationary phases of the culture's growth. It was found that the resonance effect of MMW on the GCS of E. coli cells at the early stationary phase changes the developmental dynamics of the irradiated culture. It was established for the first time that the magnitude of the resonance MMW effect depends on the concentration of irradiated cells. An analysis of the results indicates an electromagnetic rather than diffusion nature of the cells' cooperative responses to millimeter waves.     

Search for frequency-specific effects of millimeter-wave radiation on isolated nerve function

Effects of a short-term exposure to millimeter waves (CW, 40–52 GHz, 0.24–3.0 mW/cm²) on the compound action potential (CAP) conduction were studied in an isolated frog sciatic nerve preparation. CAPs were evoked by either a low-rate or a high-rate electrical stimulation of the nerve (4 and 20 paired pulses/s, respectively). The low-rate stimulation did not alter the functional state of the nerve, and the amplitude, latency, and peak latency of CAPs could stay virtually stable for hours. Microwave irradiation for 10–60 min at 0.24–1.5 mW/cm², either at various constant frequencies or with a stepwise frequency change (0.1 or 0.01 GHz/min), did not cause any detectable changes in CAP conduction or nerve refractoriness. The effect observed under irradiation at a higher field intensity of 2–3 mW/cm² was a subtle and transient reduction of CAP latency and peak latency along with a rise of the test CAP amplitude. These changes could be evoked by any tested frequency of the radiation; they reversed shortly after cessation of exposure and were both qualitatively and quantitatively similar to the effect of conventional heating of 0.3–0.4°C. The high-rate electrical stimulation caused gradual and reversible decrease of the amplitude of conditioning and test CAPs and increased their latencies and peak latencies. These changes were essentially the same with and without irradiation (2.0–2.7 or 0.24–0.28 mW/cm²), except for attenuation of the decrease of the test CAP amplitude. This effect was observed at both field intensities, but was statistically significant only for certain frequencies of the radiation. Within the studied limits, this effect appeared to be dependent on the frequency rather than on the intensity of the radiation, but this observation requires additional experimental confirmation. Bioelectromagnetics 18:324–334, 1997. © 1997 Wiley-Liss, Inc.     

Modification of the repeated acquisition of response sequences in rats by low-level microwave exposure

The acute effects of microwave exposure on a repeated acquisition baseline were investigated in three rats. Each session the animals acquired a different four-member response sequence. Each of the first three correct responses advanced the sequence to the next member, and the fourth correct response produced food reinforcement. Incorrect responses produced a three-second timeout. Baseline and control sessions were characterized by a decrease in errors within each session. The animals were acutely exposed to a 2.8 GHz pulsed-microwave field prior to test sessions, with average power densities ranging from 0.25 to 10 mW/cm². In comparison to control sessions, 1/2 hour of exposure to microwave radiation at power densities of 5 and 10 mW/cm² increased errors and altered the pattern of within-session acquisition. Exposure to the 10 mW/cm² power density decreased the rate of sequence completion in all animals. The results of exposures at 0.25, 0.5, and 1 mW/cm² power densities were generally within the control range. The results are interpreted as indicating a disruption in the discriminative stimulus control of the repeated acquisition behavior.     

Effects of Microwave Exposure at Various Power Densities on Mitochondrial Marker Enzymes in Mouse Brains

Four groups of C₅₇BL mice were irradiated with 3 GHz pulse (PW) microwaves for 3 hours at incident power densities of 0.1, 0.5, 1 and 5 mW/cm² respectively. The amount of mitochondria1 marker enzymes succinate dehydrogenase (SDH) and monoamine oxidase (MAO) in the hypothalamus and hippocampus were determined by microspectrophotometry. SDH and MA0 in the irradiated groups (except 0.1 mW/cm²) were significantly lower compared to the control group (p < 0.01). The lowest level occurred in the 5 mW/cm² group. The threshold level was 0.5 mW/cm². To compare the effects of PW with continuous wave (CW) exposure, two experimental groups were exosed to 2.45 GHz, using CW; the enzymes were decreased only in the 5 mW/cm² group. The results show that PW radiation is more effective then CW radiation in decreasing SDH and MA0 levels.     

Effects of Salicylic Acid and Its Salts on Electrical Activity of Neurons of <Emphasis Type="Italic">Helix albescens</Emphasis>

We studied changes in the parameters of electrical activity of identified neurons of the parietal ganglion, PPa1 and PPa2, and of non-identified cells of the visceral ganglion (VG) of the snail Helix albescens; these changes were caused by application of salicylic acid and its salts (cobalt and zinc salicylates, CS and ZS, respectively). The above substances began to modify significantly the functional state of the neurons under study when applied in concentrations of 10⁻⁴ to 10⁻³ M. Salicylic acid suppressed the activity of all studied neurons. Application of salicylic acid in the concentration of 10⁻³ M led to a decrease in the impulsation frequency of VG neurons by factors of 1.2 to 1.5 and to an increase in the duration of AP (on average, by 2.8 ± ± 0.6 msec). In PPa1 and PPa2 cells, we observed increases in both the AP duration (by 2.4 ± 0.8 and 3.6 ± ± 1.3 msec, respectively) and that of postactivation hyperpolarization (by 29.8 ± 11 0 and 39.6 ± 9.4 msec). In the concentration of 10⁻² M, salicylic acid completely but relatively reversibly suppressed the impulse activity of all the neurons under study, causing deep hyperpolarization of their membranes. Salts of this acid, CS and ZS, demonstrated significant modulatory effects on the activity of the studied neurons; these substances initiated or enhanced the grouping of APs in bursts and also increased the AP duration. Application of 10⁻³ M CS resulted in an increase in the AP duration by, on average, 2.75 ± 0.4 msec (only in the PPa2 neuron), whereas 10⁻³ M ZS exerted analogous effects on both above neurons (in PPa1, by 2.7 ± 0.4, while in PPa2, by 3.1 ± 0.6 msec). In the case where the tested salicylates were applied in the concentration of 10⁻² M, the AP duration increased in all the cells under study (on average, by 11.8 ± 2.46 msec in VG neurons, and by 7.0 ± ± 0.4 and 7.8 ± 1.2 msec in PPa1 and PPa2 cells, respectively). With application of CS, analogous values determined by application of ZS were 14.6 ± 4.6, 6.8 ± 0.54, and 9.0 ± 0.89 msec. We assume that the modulatory effects of salicylates are mediated by their influence on the intracellular system of cyclic nucleotides. Neirofiziologiya/Neurophysiology, Vol. 37, No. 2, pp. 142–150, March–April, 2005.     

Absence of corneal endothelium injury in non‐human primates treated with and without ophthalmologic drugs and exposed to 2.8 GHz pulsed microwaves

Microwave‐induced corneal endothelial damage was reported to have a low threshold (2.6 W/kg), and vasoactive ophthalmologic medications lowered the threshold by a factor of 10–0.26 W/kg. In an attempt to confirm these observations, four adult male Rhesus monkeys (Macaca mulatta) under propofol anesthesia were exposed to pulsed microwaves in the far field of a 2.8 GHz signal (1.43 ± 0.06 µs pulse width, 34 Hz pulse repetition frequency, 13.0 mW/cm² spatial and temporal average, and 464 W/cm² spatial and temporal peak (291 W/cm² square wave equivalent) power densities). Corneal‐specific absorption rate was 5.07 W/kg (0.39 W/kg/mW/cm²). The exposure resulted in a 1.0–1.2 °C increase in eyelid temperature. In Experiment I, exposures were 4 h/day, 3 days/week for 3 weeks (nine exposures and 36 h total). In Experiment II, these subjects were pretreated with 0.5% Timolol maleate and 0.005% Xalatan® followed by 3 or 7 4‐h pulsed microwave exposures. Under ketamine–xylazine anesthesia, a non‐contact specular microscope was used to obtain corneal endothelium images, corneal endothelial cell density, and pachymetry at the center and four peripheral areas of the cornea. Ophthalmologic measurements were done before and 7, 30, 90, and 180 days after exposures. Pulsed microwave exposure did not cause alterations in corneal endothelial cell density and corneal thickness with or without ophthalmologic drugs. Therefore, previously reported changes in the cornea exposed to pulsed microwaves were not confirmed at exposure levels that are more than an order of magnitude higher. Bioelectromagnetics 31:324–333, 2010. Published 2010 Wiley‐Liss, Inc.     

The in vivo effects of 2.45 GHz microwave radiation on rabbit serum components and sleeping times

Summary An investigation was conducted to determine the effects of relatively low power density microwave exposures on various serum components of the Dutch rabbit. Both continuous wave and pulsed mode exposures at 2.45 GHz were used at power densities of 25, 10 and 5 mW/cm². Studies of 10 serum components were performed. Additional studies were conducted on changes in sleeping times of pentobarbital-sedated rabbits at various power densities. Gross and histopathological examinations were performed on representative samples of animals.Changes in the blood chemistry of irradiated animals were consistent with a dose-dependent response to a non-specific thermal stress at all power densities used. Observed physiological response, as well as rectal temperature measurements, indicated that the thermoregulatory capability of the rabbits was sufficient to compensate for the thermal burden at 5 and 10 mW/cm², but could be overridden by a 2 h exposure at 25 mW/cm². Pathology findings included a mild, repairable nephrosis in animals exposed at a power density of 25 mW/cm².A further investigation of analeptic effects at power densities varying from 5 mW/cm² to 50 mW/cm² resulted in a statistically significant decrease in sleeping times, apparently proportional to power density below 15 mW/cm².This research was partially supported by the US Army Medical Research and Development Command, Contract No. DADA17-72-C-2144. (The views expressed are those of the authors and do not necessarily reflect those of the Department of the Army)     

Pulse flows of populations of cortical neurons under microwave irradiation: Burst activity

The pulse flows of populations of sensomotor cortical neurons are studied in unanesthetized non-immobilized rabbits before, during, and after 1-min exposure to microwave electromagnetic irradiation (wavelength 37.5 cm, power density 0.2–0.3, 0.4, 0.5, and 40 mW/cm²) by analyzing the burst activity detected at time thresholds of 5, 10, and 20 ms. These exposures change the number of spike bursts. The changes in pulse flows are recorded both during irradiation and during the first minute after its cessation. The directions of shifts and their dynamics are determined by both the irradiation intensity and the types of bursts themselves.