Electromagnetic millimeter waves increase the duration of anaesthesia caused by ketamine and chloral hydrate in mice

BALB/c mice were injected i.p. with either ketamine 80 mg/kg or chloral hydrate 450 mg/kg. Anaesthetized mice were exposed to unmodulated electromagnetic millimeter waves at the frequency of 61.22 GHz with a peak specific absorption rate of 420 W/kg and corresponding incident power density of 15 mW/cm2 for 15 min or sham-exposed. In combination with either of the anaesthetics used, mm waves increased the duration of anaesthesia by approximately 50% (p < 0.05) in a dose (power)-dependent manner. Sham exposure to mm waves did not affect the sleeping time of mice. Pretreatment of mice with naloxone, an opioid antagonist, did not change the duration of anaesthesia caused by the corresponding chemical agent, but completely blocked or decreased the additional effect of mm waves. The data in this study indicates that exposure of mice to mm waves in vivo releases endogenous opioids or enhances the activity of opioid signalling pathway.