The influence of naloxone on analgesia produced by peripheral conditioning stimulation

Abstract

Conditioning electrical stimulation of peripheral nerves is presently routinely employed for alleviation of chronic pain in humans. Most commonly, high frequency stimulation of probably mainly coarse myelinated afferents from the skin is used as proposed in the gate theory of Melzack and Wall 25. However, only a limited number of patients benefit from such stimulation. To improve the results of such treatment we have developed a kind of acupuncture-like electrical stimulation where mixed nerves are stimulated with short trains of stimuli given at a slow repetition rate via surface electrodes to elicit muscle contractions. The compiled results of conditioning stimulation for analgesia were then markedly improved. To see whether the analgesia experienced by the chronic pain patients is mediated via links utilizing endorphins, the opiate antagonist naloxone was administered to these patients under double-blind conditions, saline being used as a placebo. We then found that 6 out of 10 patients receiving acupuncture-like stimulation but none out of 10 patients receiving high frequency stimulation of skin nerves, reported an inhibition of the stimulation-produced analgesia by naloxone. This indicates that the analgesia produced by acupuncture-like stimulation is mediated via mechanisms utilizing endorphins whereas the analgesia produced from high frequency stimulation of coarse cutaneous afferents is mediated via some other mechanism.