Chronic exposure to a 60‐Hz electric field: Effects on synaptic transmission and peripheral nerve function in the rat

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Abstract
Several reports have suggested that the nervous system can be affected by exposure to electric fields and that these effects may have detrimental health consequences for the exposed organism. The purpose of this study was to investigate the effects of chronic (30‐day) exposure of rats to a 60‐Hz, 100‐kV/m electric field on synaptic transmission and peripheral‐nerve function. One hundred forty‐four rats, housed in individual polycarbonate cages were exposed to uniform, vertical, 60‐Hz electric fields in a system free of corona discharge and ozone formation and in which the animals did not receive spark discharges or other shocks during exposure. Following 30 days of exposure to the electric field, superior cervical sympathetic ganglia, vagus and sciatic nerves were removed from rats anesthetized with urethan, placed in a temperature‐controlled chamber, and superfused with a modified mammalian Ringer's solution equilibrated with 95% O2 and 5% CO2. Several measures and tests were used to characterize synaptic transmission and peripheral‐nerve function. These included amplitude, area, and configuration of the postsynaptic or whole‐nerve compound‐action potential; conduction velocity; accommodation; refractory period; strength‐duration curves; conditioning‐test (C‐T) response, frequency response; post‐tetanic response; and high‐frequency‐induced fatigue. The results of a series of neurophysiologic tests and measurements indicate that only synaptic transmission is significantly and consistently affected by chronic (30‐day) exposure to a 60‐Hz, 100‐kV/m electric field. Specifically, an increase in synaptic excitability was detected in replicated measurements of the C‐T response ratio. In addition, there are trends in other data that can be interpreted to suggest a generalized increase in neuronal excitability in exposed animals.