Suppression of analgesia in rats induced by morphine or L-name but not both drugs by microtesla, frequency-modulated magnetic fields

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 If were injected with either morphine (4 mg/kg), L-NAME (50 mg/kg), both morphine and L-NAME, or saline after baseline measurements for nociception and then exposed to either a I microTesla 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 I 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.