Hypoalgesic effect of millimeter waves in mice: Dependence on the site of exposure

Based on a hypothesis of neural system involvement in the initial absorption and further processing of the millimeter electromagnetic waves (MW) signal, we reproduced, quantitatively assessed and compared the analgesic effect of a single MW treatment, exposing areas of skin possessing different innervation densities. The cold water tail flick test (cTFT) was used to assess experimental pain in mice. Three areas of exposure were used: the nose, the glabrous skin of the right footpad, and the hairy skin of the mid back at the level of T5–T10. The MW exposure characteristics were: frequency = 61.22 GHz; incident power density = 15 mW/cm2; and duration = 15 min. The maximum hypoalgesic effect was achieved by exposing to MW the more densely innervated skin areas — the nose and the footpad. The hypoalgesic effect in the cTFT after MW exposure to the murine back, which is less densely innervated, was not statistically significant. These results support the hypothesis of neural system involvement in the systemic response to MW.