Thermal analgesic effects from weak, complex magnetic fields and pharmacological interactions med./bio.

To study thermal analgesic effects from weak, complex magnetic fields and pharmacological interactions in rats.

Rats were placed on a thermal plate that was maintained at 55°C. Once the rat was observed to lick one hind feet twice, the rat was removed from the apparatus.
Several experiments were performed: 1) electrical versus thermal analgesia; 2) intensity dependence of analgesia (exposure to 3 µT (the usual), 0.3 µT, or about 30 nT); 3) spatial parameters of field (usual field parameters or the same field condition within a Helmholtz coil); 4) comparison of two complex patterns (the efficacy of a frequency modulated pattern was compared with the typical burst-firing pattern); 5) verifying the specifity of experiment 4; 6) interactions between two types of magnetic fields (burst-firing magnetic field and frequency modulated magnetic field) and morphine (4 mg/kg) or agmatine (10 mg/kg); 7) naloxone (1 mg/kg) blocking of morphine and burst-firing magnetic field analgesia.

• animal
• rat/Wistar albino
• whole body

In several experiments, robust analgesia (equivalent to about 4 mg/kg of morphine) in rats to thermal stimuli following exposures to weak complex magnetic fields was explored. The analgesia occurred when patterns of magnetic fields with burst-firing-like configurations were presented once every approximately 4 s (for 30 min). The effects were intensity dependent. A different frequency modulated pattern produced analgesic effects more quickly. Analgesia following exposure to the burst-firing magnetic fields were augmented conspicuously by preinjections of morphine or agmatine, but blocked by naloxone.
The data of these experiments indicate that rational design of the temporal structure of weak magnetic fields may be a novel, inexpensive, and reliable technique for elevating thresholds to some classes of painful stimuli.