Effect of a 0.5-T static magnetic field on conduction in guinea pig spinal cord

Compound-evoked potentials were recorded from excised adult guinea pig spinal cords before, during, and following exposure to a 0.5-T static magnetic field (SMF). There was no change in response latency during exposure but there was a small, statistically significant, decrease in amplitude. Maximum effect was evident 1 to 2 min after the field was turned on with return to baseline within 1 min after the field was turned off. These results may be explained by a conduction block in the small axon subpopulation due to the effect of static magnetic fields on voltage-activated sodium channels. The relative selectivity of the field is believed to occur because of the relatively greater number of sodium channels present in smaller axons. (C) 2004 Elsevier B.V. All rights reserved.