Repetitive electrical stimulation of peripheral nerve and spinal cord activity

Spinal cord neuron and dorsal column fiber responses to electrical stimulation of the sciatic nerve in anesthetized cats were recorded before, during, and after periods of repetitive electrical stimulation of the sciatic nerve through an implantable nerve cuff stimulator device of the type and method used in human patients for pain relief. In previous publications from this laboratory using similar experimental conditions, we reported that repetitive electrical stimulation of the peripheral nerve suppressed all components of the compound action potential of nerves. The present study confirms that 5 percent of the spinal cord units studied showed facilitated discharge, 46 percent showed inhibited or depressed discharge, 36 percent underwent no change, and 13 percent showed equivocal responses to repetitive electrical stimulation. Inhibition of dorsal column fiber activity following repetitive electrical stimulation of peripheral nerve is not consistent with the Melzack-Wall gate hypothesis in which suppression of small fiber nociceptive input is mediated by large fiber activity. Our work suggests that the most commonly observed effect of electroanalgesia is to cause a more diffuse depression of nociceptive as well as nonnociceptive spinal cord activity.