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.