LIGHT-DEPENDENT AND LIGHT-INDEPENDENT BEHAVIORAL-EFFECTS OF EXTREMELY-LOW-FREQUENCY MAGNETIC-FIELDS IN A LAND SNAIL ARE CONSISTENT WITH A PARAMETRIC RESONANCE MECHANISM

Exposure to extremely low frequency (ELF) magnetic fields has been sho wn to attenuate endogenous opioid peptide mediated antinociception or ''analgaesia'' in the terrestrial pulmonate snail, Cepaea nemoralis. H ere we examine the roles of light in determining this effect and addre ss the mechanisms associated with mediating the effects of the ELF mag netic fields in both the presence and absence of light. Specifically, we consider whether the magnetic field effects involve an indirect ind uced electric current mechanism or a direct effect such as a parametri c resonance mechanism (PRM). We exposed snails in both the presence an d absence of light at three different frequencies (30, 60, and 120 Hz) with static field values (B-DC) and ELF magnetic held amplitude (peak ) and direction (BAG) set according to the predictions of the PRM for Ca2+. Analgaesia was induced in snails by injecting them with an enkep halinase inhibitor, which augments endogenous opioid (enkephalin) acti vity. We found that the magnetic field exposure reduced this opioid-in duced analgaesia significantly more if the exposure occurred in the pr esence rather than the absence of light. However, the percentage reduc tion in analgaesia in both the presence and absence of light was not d ependent on the ELF frequency. This finding suggests that in both the presence and the absence of light the effect of the ELF magnetic field was mediated by a direct magnetic field detection mechanism such as t he PRM rather than an induced current mechanism. (C) 1997 Wiley-Liss, Inc.