Effect of static magnetic fields on the amplitude of action potential in the lateral giant neuron of crayfish

Purpose: To investigate whether exposure to static magnetic field (SMF) affects the passive properties Of neurons that mediate tail-flip escape behavior in crayfish. Materials and methods: A permanent magnet was placed under the isolated nerve cord of crayfish to experience SMF at 4.74 to 43.45 mT intensity for various period of time (20 seconds to 3 hours). An intracellular electrode was impaled on the axon of the lateral giant neuron (LG) of the last abdominal ganglion of crayfish to record the evoked action potential (AP) and excitatory postsynaptic potential (EPSP). The amplitudes of evoked AP and EPSPs before and after SMF exposure were measured to study the effect of SMF exposure. Results: The exposure to SMF increased the amplitude of AP in the LG depending upon both the intensity of field and duration of field exposure. The changes in AP by field exposure arc likely to be mediated by the increasing level of intracellular Ca2+ in the LG because the chelating of intracellular Ca2+ would block the effects by SMF exposure, while the injection of Ca2+ into the LG could mimic the effects of SMF exposure. SMF exposure also increases the input resistance of the LG membrane. Therefore, the magnitude of the EPSP in LG evoked by electrical shock on the sensory nerves was found to be enhanced after SMF exposure. Conclusion: SMF is usually considered to be safe for the biological issues since no electrical current is induced via the Faraday effect. Our results showed that some passive membrane properties of neurons are affected by SMF exposure. The increase in magnitude of evoked AP and EPSP suggests an increase in the sensitivity of the LG neuron. These changes by SMF exposure may not necessarily to be harmful to animals; however, further study is needed to address the biological effects from SMF exposure, especially in nervous systems.