Pain relief caused by millimeter waves in mice: results of cold water tail flick tests

Purpose : To find out if millimeter waves can decrease experimental pain response in mice using cold water tail flick test. Materials and methods : Male Swiss albino mice (15 mice per group) were exposed to continuous millimeter waves at a frequency of 61.22 GHz with incident power densities (IPD) ranging from 0.15 to 5.0 mW/cm 2 for 15 min or sham exposed. Latency of tail withdrawal in a cold water (1 +/- 0.5°C) tail flick test was measured before the exposure (baseline) and then four times after the exposure with 15 min breaks. Results : The mean latency of the tail flick response in mice exposed to millimeter waves was more than twice that of sham-exposed controls (p < 0.05). This effect was proportional to the power of millimeter waves and completely disappeared at an IPD level of 0.5 mW/cm 2. Pretreatment of mice with the opioid antagonist naloxone (1 mg/kg i.p.) blocked the effect of millimeter waves. Conclusions : Results suggest that the antinociceptive effect of millimeter waves is mediated through endogenous opioids.