SPONTANEOUS AND EVOKED ECTOPIC DISCHARGES RECORDED FROM SINGLE HUMAN AXONS

A quantitative assessment was made of the firing characteristics of re petitive axonal discharges encountered during microneurographic record ings from human peripheral nerves. Spontaneous activity was recorded f rom 16 single axons using tungsten microelectrodes inserted percutaneo usly into fascicles of the median or peroneal nerves in normal subject s. These discharges typically consisted of brief bursts of 2-5 spikes occurring at a frequency of 7-10 Hz. Peak instantaneous frequencies us ually exceeded 300 Hz. Based on their similarity with spontaneous high -frequency discharges recorded from single axons following nerve damag e, ischemia, prolonged electrical stimulation, or hyperventilation, it is concluded that they are generated ectopically at the site of a pre vious impalement of a nerve fiber. It is suggested that short-term dam age to the nerve fiber caused by the microelectrode may allow accumula tion of K+ underneath the myelin, triggering an inward flow of K+ and regenerative depolarizations. Alternatively, internodal channels may b e exposed following damage to the myelin, resulting in the generation of spontaneous pacemaker potentials and repetitive discharges. (C) 199 8 John Wiley & Sons, Inc.