INTRACEREBROVENTRICULAR INJECTION OF MU-OPIATE AND DELTA-OPIATE RECEPTOR ANTAGONISTS BLOCK 60 HZ MAGNETIC-FIELD-INDUCED DECREASES IN CHOLINERGIC ACTIVITY IN THE FRONTAL-CORTEX AND HIPPOCAMPUS OF THE RAT

In previous research, we have found that acute exposure to a 60 Hz mag netic field decreased cholinergic activity in the frontal cortex and h ippocampus of the rat as measured by sodium-dependent high-affinity ch oline uptake activity. We concluded that the effect was mediated by en dogenous opioids inside the brain because it could be blocked by pretr eatment of rats before magnetic field exposure with the opiate antagon ist naltrexone, but not by the peripheral antagonist naloxone methiodi de. In the present study, the involvement of opiate receptor subtypes was investigated. Rats were pretreated by intracerebroventricular inje ction of the mu-opiate receptor antagonist, beta-funaltrexamine, or th e delta-opiate receptor antagonist, naltrindole, before exposure to a 60 Hz magnetic held (2 mT, 1 hour). It was found that the effects of m agnetic field on high-affinity choline uptake in the frontal cortex an d hippocampus were blocked by the drug treatments. These data indicate that both mu- and delta-opiate receptors in the brain are involved in the magnetic field-induced decreases in cholinergic activity in the f rontal cortex and hippocampus of the rat. Bioelectromagnetics 19:432-4 37, 1998. (C) 1998 Wiley-Liss, Inc.