The antagonistic effects of naloxone on acupuncture inhibition of the vibration-induced grasp reflex in man.

It is known that the vibration-induced grasp reflex (VGR) is inhibited by the insertion of needles into the acupuncture points. Effects of intravenous administration of naloxone on acupuncture inhibition of the VGR were studied in human subjects to determine if acupuncture inhibition of the VGR might be mediated by endogenous opioids. Acupuncture inhibition of the VGR was partly reversed by the administration of naloxone. The VGR is mediated by a polysynaptic pathway through which the acupuncture inhibition that is reversed by naloxone is considered to occur. We conclude that the facilitatory influence of interneurons on motoneurons in the VGR was reduced by endogenous opioids to inhibit the VGR.