THE ELECTROPHYSIOLOGICAL CONSEQUENCES OF ELECTRODE IMPALEMENT OF PERIPHERAL-NERVES IN THE RAT

Peripheral nerve fascicles are deliberately impaled during microneurog raphy experiments. We have assessed conduction block under these circu mstances. First we recorded compound action potentials (CAP) in the su ral nerve following stimulation of the sciatic nerve. The insertion of injection and microneurography electrodes between stimulation and rec ording sites produced a 20% decrease in the size of the CAP, which was maintained for the 10 min duration of impalement. After withdrawal, t he conduction block partially resolved. In other experiments, single-u nit action potentials were recorded from L(4) and L(5) dorsal roots fo llowing peripheral nerve stimulation. Microneurography electrodes inse rted into the sciatic nerve produced conduction block in 50% of these axons. When axons were blocked, anodal stimulation through the tungste n electrode became more effective than cathodal stimulation. These res ults suggest that a temporary conduction block occurs in a significant number of myelinated fibers near the site df an inserted electrode.