Disturbances of neural conduction in isolated frog nerves following exposure to strong electric fields.

Frog sciatic nerves were isolated and the middle portion of each exposed to condenser discharges (field strength up to 1000 V/cm; time constants 0.2-8.0 ms) through the bathing fluid. The ability of the nerve to propagate action potentials (AP) was examined by stimulating the proximal end and recording the AP from the distal end of the exposed section. The fraction of the nerve fibers remaining propagative was estimated from the amplitude (or the area) of the compound AP. Strong discharges brought about a total block of propagation lasting for up to 30 minutes, followed by slow, but almost complete, restitution. The restitution was exponential against time and depended on the field strength and duration of the discharge. Discharges equal in energy but different in their voltage--condenser combinations had markedly different actions, with stronger effects being found at higher voltages and vice versa. Hence, the described effects are unlikely to be caused by dissipation of thermal energy only. Other mechanisms (ionic imbalance, dielectric breakdown, punch through) are discussed.