A companion paper (Seegal et al., 1989) reported the effects of twice-weekly-evoked potentials during the daily 6-hr field-off period. No effects of field exposure were detected on the auditory-, visual-, or somatosensory-evoked potentials of the early or mid-latency components of the response. A significant decrease in the amplitude of the late components of the somatosensory-evoked potentials was detected during two high-strength field exposures. The discussion of the results suggested that these changes might be due to opiate antagonistic effects of exposure to electric and magnetic fields. The metabolites serotonin and dopamine were changed in the monkeys exposed to electric and magnetic fields. Substantial data relates the endogenous serotonin system with analgesia; however, the mechanism is not clear through which electric and magnetic fields have an influence on serotonin and its effect on somatosensory-evoked potentials.

In a related study in rats, Ossenkopp and Cain (1988) showed that 1-hr exposures to 60-Hz magnetic fields at 100 µT (1 G) resulted in a shorter duration of fully developed seizures. These investigators also linked their results to the substantial evidence that magnetic fields inhibit the nocturnal analgesic effects of morphine in a field-strength-dependent manner (Ossenkopp and Kavaliers 1987). The mechanism of this effect is not known; however, studies using calcium-channel agonists and antagonists administered with morphine demonstrate that calcium channel antagonists inhibit and agonists enhance the analgesic effects of morphine in the presence of magnetic fields. The authors of those studies proposed that the effect of magnetic fields on analgesia is mediated through the calcium channels and cited the in vitro results of magnetic fields on calcium channels as evidence. However, direct evidence for the mechanisms of action remains undetermined.

Several studies examined the effects of magnetic fields on learning and performance in simple and complex behavioral tasks. Examples from even the best studies show mixed results. Hong et al. (1988) exposed infant rats to a static magnetic field at 0.5 T for 14 postnatal days. After a 1-month rest period, exposed and sham-exposed rats were trained to reverse a position habit in an enclosed T-maze four times. Although exposed and unexposed male and female rats differed, no differences were detected for total errors committed over the four reversal problems.

In contrast to this static-field report, Salzinger et al. (1990) reported results from rats exposed perinatally to 60-Hz electric fields at 30 kV/m and 100-µT magnetic fields for 22 days in utero and for 20 hr per day during the first 8 days postpartum. As adult rats, they were trained to emit responses for food on a random-interval schedule. When the rats were tested as adults, the exposed rats consistently responded at lower rates than the sham-exposed rats. In addition, the decrease in response was not eliminated by extinction procedures or by an additional month of testing. These results do not necessarily imply a deleterious effect of perinatal exposure to magnetic fields, but they do appear to indicate an effect was produced.

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