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

Purpose: To find out if millimeter waves can decrease experimental pain res ponse in mice using cold water tail flick test. Materials and methods: Male Swiss albino mice (15 mice per group) were expo sed to continuous millimeter waves at a frequency of 61.22 GHz with inciden t power densities (IPD) ranging from 0.15 to 5.0 mW/cm(2) for 15 min or sha m exposed. Latency of tail withdrawal in a cold water (1 +/- 0.5 degrees 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 mil limeter waves was more than twice that of sham-exposed controls (p < 0.05). This effect was proportional to the power of millimeter waves and complete ly disappeared at an IPD level of less than or equal to 0.5 mW/cm(2). Pretr eatment 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.