Morphine-induced analgesia and exposure to low-intensity 60-Hz magnetic fields: inhibition of nocturnal analgesia in mice is a function of magnetic field intensity.

In 2 experiments male CF-1 mice were exposed for 60 min, during the mid-dark period of the day-night cycle, to low-intensity (0.5-1.5 gauss, rms) 60-Hz magnetic fields and then tested for levels of analgesia induced by morphine (10 mg/kg) injections. The magnetic field exposures inhibited the degree of morphine-induced analgesia in a field intensity-dependent manner in both experiments (P less than 0.01) with the largest inhibitory effect after exposure to the 1.5-gauss field. Analysis of the combined data from the two experiments revealed a significant (P less than 0.001) linear relationship between level of analgesia and magnetic field intensity. Thus, these data demonstrated a functional relationship between the behavioral effects of morphine in mice and the strength of the 60-Hz magnetic field. Possible mechanisms underlying these effects are discussed.