Millimeter-wave-induced hypoalgesia in mice: dependence on type of experimental pain

Millimeter-wave therapy (MWT) is based on the systemic biological effects resulting from local exposure of skin to low-power electromagnetic waves of millimeter wavelength. The aims of the present study are to quantitatively evaluate hypoalgesic effects of MWT in murine experimental models of acute and chronic neuropathic pain, and to compare them with the previously determined MWT-induced hypoalgesia in an experimental model of chronic nonneuropathic pain, and also to assess the ability of local heating with a Holmium YAG laser to produce hypoalgesia in mice. The cold and hot water tail-flick tests and the unilateral chronic constriction injury (CCI) to the sciatic nerve were used as pain models. The MWT characteristics were: frequency =61.22 GHz; average power density =13.3 mW/cm²; duration of exposure =15 min; and area of exposure-nose. This study demonstrated that a single MWT most effectively suppressed chronic nonneuropathic pain. Less effectively, a single MWT reduced pain sensitivity in the murine model of acute pain, and was ineffective in the model of chronic neuropathic pain. However, multiple MWT reduced the symptoms that developed following CCI. The local heating of the exposed area did not produce hypoalgesia. The findings support the use of MWT in chronic pain states.