WEAK ELF MAGNETIC-FIELD EFFECTS ON HIPPOCAMPAL RHYTHMIC SLOW ACTIVITY

Several investigations have revealed that electrical activity within t he central nervous system (CNS) can be affected by exposure to weak ex tremely-low-frequency (ELF) magnetic fields, Many of these studies hav e implicated CNS structures exhibiting endogenous oscillation and sync hrony as optimal sites for held coupling. A particularly well characte rized structure in this regard is the rat hippocampus. Under urethane anesthesia, synchronous bursting among hippocampal pyramidal neurons p roduces a large-amplitude quasi-sinusoidal field potential oscillation , termed ''rhythmic slow activity'' (RSA) or ''theta.'' Using this in vivo model, we investigated the effect of exposure to an externally ap plied sinusoidal magnetic field (16.0 Hz; 28.9 mu T-rms) on RSA During a 60-min exposure interval, the probability of RSA decaying to a less coherent mode of oscillation, termed ''large irregular-amplitude acti vity'' (LIA), was increased significantly. Moreover, this instability persisted for up to 90 min postexposure. These results are consistent with the hypothesis that endogenous CNS oscillators are uniquely susce ptible to held-mediated perturbation and suggest that the sensitivity of these networks to such fields may be far greater than had previousl y been assumed. This sensitivity may reflect nonlinearities inherent t o these networks which permit amplification of endogenous fields media ting the initiation and propagation of neuronal synchrony. (C) 1998 Ac ademic Press.