Suppression of Analgesia in Rats Induced by Morphine or L-Name but not Both Drugs by Microtesla, Frequency-Modulated Magnetic Fields

Abstract

In Experiment I, the nociceptive threshold for a criterion response to thermal stimuli (hot plate) for rats was obtained following injections with one of various dosages of either morphine or the nitric oxide synthase inhibitor, L-NAME. On the bases of these results, rats in Experiment II were injected with either morphine (4mg/kg), L-NAME (50mg/kg), both morphine and L-NAME, or saline after baseline measurements for nociception and then exposed to either a 1 micro Tesla magnetic field or to a sham field for 30 min. The magnetic field, presented once every 4 sec, was a frequency-modulated pattern whose pixel durations, for each of the 837 successive values, were 1 msec. Nociceptive thresholds were measured immediately after the exposure and 30 min later. The results indicated that exposure to this magnetic field abolished the analgesic effects of morphine or L-NAME when injected separately but not when injected together relative to rats that had received these drugs and had been exposed to the sham field.

Key Words:

• Magnetic fields
• Morphine
• Analgesia
• Nitric oxide
• Micro Tesla
• Frequency-modulation
• Synergism
• Thermal stimuli