Abbreviated Title: Millimeter wave irradiation of leech ganglion neurons

37 Many of today’s radiofrequency-emitting devices in telecommunication, telemedicine, 38 transportation safety, and security/military applications use the millimeter-wave (MMW) band 39 (30-300 GHz). To evaluate the biological safety and possible applications of this radiofrequency 40 band for neuroscience and neurology, we have investigated the physiological effects of low41 intensity 60 GHz electromagnetic irradiation on individual neurons in the leech midbody ganglia. 42 We applied incident power densities of 1, 2, and 4 mW/cm to the whole ganglion for a period of 43 1 minute, while recording the action potential with a standard sharp-electrode electrophysiology 44 setup. For comparison, the recognized U.S. safe exposure limit is 1 mW/cm for 6 minutes. 45 During the exposure to MMWs and gradual bath heating at a rate of 0.04 oC/sec (2.4 oC/min), the 46 ganglionic neurons exhibited similar dose-dependent hyperpolarization of the plasma membrane 47 and decrease in the action potential amplitude. However, narrowing of the action potential half48 width during MMW irradiation at 4 mW/cm was 5 times more pronounced, as compared to 49 equivalent bath heating of 0.6 oC. Even more dramatic difference in the effects of MMW 50 irradiation and bath heating was on the firing rate, which was suppressed at all applied MMW 51 power densities and was increased in a dose-dependent manner during gradual bath heating. The 52 mechanism of enhanced narrowing of action potentials and suppressed firing by MMW 53 irradiation, as compared to gradual bath heating, is hypothesized to involve specific coupling of 54 MMW energy with the neuronal plasma membrane. 55 56