Evaluation of whole-animal data using the ion parametric resonance model

Effects on rats of low intensity and frequency electromagnetic field stimulation on thoracic spinal neurons receiving noxious cardiac and esophageal inputs

Objective  Low intensity and low frequency electromagnetic field stimulation (EMFs) provides substantial pain relief in patients with various chronic pains. The aim of this study was to examine the effects of EMFs on the activity of thoracic spinal neurons responding to noxious visceral stimuli. Materials and Methods  Extracellular potentials of single T(3) -T(4) spinal neurons were recorded in pentobarbital anesthetized male rats. A catheter was placed in the pericardial sac to administer a mixture of algogenic chemicals for noxious cardiac stimulation (0.2 mL, 1 min). Noxious esophageal distension was produced by water inflation (0.4 mL, 20 sec) of a latex balloon. EMFs (0.839-0.952 Hz, 0.030-0.034 µG, 30-40 min) was applied with a pair of Helmholtz coils placed on both sides of the chest. Results  After the onset of EMFs, excitatory neuronal responses to intrapericardial chemicals were reduced in 24/32 (75%) spinal neurons, increased in three neurons and were not affected in five neurons. The inhibitory effect on spinal neurons occurred 10-20 min after the onset of EMFs. Even after termination of EMFs, the suppression of spinal neuronal activity lasted for 1-2 hr. In contrast, excitatory responses of 7/18 (39%) neurons to esophageal distension were inhibited, five (28%) were excited and six (33%) were not affected by EMFs. Conclusions  Results showed that EMFs generally reduced nociceptive responses of spinal neurons to noxious cardiac chemical stimuli, whereas it was not effective for nociceptive responses to esophageal mechanical stimulation.

Extremely low frequency magnetic fields can either increase or decrease analgaesia in the land snail depending on field and light conditions

Results of prior investigations with opioid peptide mediated antinociception or analgaesia have suggested that these extremely low frequency (ELF) magnetic field effects are described by a resonance mechanism rather than mechanisms based on either induced currents or magnetite. Here we show that ELF magnetic fields (141-414 microT peak) can, in a manner consistent with the predictions of Lednev's parametric resonance model (PRM) for the calcium ion, either (i) reduce, (ii) have no effect on, or (iii) increase endogenous opioid mediated analgaesia in the land snail, Cepaea nemoralis. When the magnetic fields were set to parameters for the predictions of the PRM for the potassium ion, opioid-peptide mediated analgaesia increased and there was evidence of antagonism by the K(+) channel blocker, glibenclamide. Furthermore, these effects were dependent on the presence of light; the effects were absent in the absence of light. These observed increases and decreases in opioid analgaesia are largely consistent with the predictions of Lednev's PRM.