Effects of millimeter wave irradiation and equivalent thermal heating on the activity of individual neurons in the leech ganglion.
Bottom Line: 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).For comparison, the recognized U.S. safe exposure limit is 1 mW/cm(2) 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.
Affiliation: Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California; Neural Engineering Program, Huntington Medical Research Institutes, Pasadena, California; and.Show MeSH
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Mentions: The MMW irradiation system consisted of a synthesized microwave source for 17–23 GHz (HP 83650L; Agilent Technologies, Santa Clara, CA), a 4× frequency-multiplying stage (HP 83557A; Agilent Technologies) or an active quadrupler (AMC15; Millitech, Deerfield, MA), followed by a 20-dB amplifier (AMP-15; Millitech, Northampton, MA) to generate continuous wave power between 4 and 64 mW at 60 GHz (for the reported experiments, the powers of 4, 8, and 16 mW were used). Power levels could be controlled using internal or external attenuators and were continuously monitored with both a 60-GHz waveguide square-law detector (47344H-1200; Hughes Electronics) and a calibrated absolute thermoelectric power meter (ML83A; Anritsu, Atsugi-shi, Japan). Coupling to the ganglion was accomplished through a single-mode open-ended rectangular waveguide (WR15; 50–75 GHz band, 3.8 × 1.9-mm aperture) placed 1 mm below the petri dish bottom. The path of the MMW radiation after exiting the waveguide was through a central opening in the microscope stage, the polystyrene petri dish bottom (1 mm thick), the low-radiofrequency (RF)-loss paraffin holding the ganglion pins (3.2 mm thick), and then directly into the pinned-out ganglion (0.2 mm thick) (Fig. 1A). The petri dish was filled with leech saline to a level ∼1.5 mm above the top of the ganglion. The waveguide was aligned with the microscope optical axis so that the peak of the irradiating MMW beam was directed at the ganglion (the beam was much wider than the ganglion diameter; Fig. 1, B–F). The duration of MMW irradiation was 1 min in these experiments, and a minimal between-exposure interval of 5 min was chosen to avoid possible cumulative exposure effects.
Affiliation: Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California; Neural Engineering Program, Huntington Medical Research Institutes, Pasadena, California; and.