Basal μ-opioid receptor availability in the amygdala predicts the inhibition of pain-related brain activity during heterotopic noxious counter-stimulation.

Abstract

The aim of this study was to investigate the association between the magnitude of anti-nociceptive effects induced by heterotopic noxious counter-stimulation (HNCS) and the basal μ-opioid receptor availability in the amygdala. In 8 healthy volunteers (4 females and 4 males), transcutaneous electrical stimulation was applied to the right sural nerve to produce the nociceptive flexion reflex (RIII-reflex), moderate pain, and scalp somatosensory evoked potentials (SEPs). Immersion of the left hand in cold water for 20min was used as HNCS. In a separate session, basal μ-opioid receptor availability was measured using positron emission tomography with the radiotracer [(11)C]carfentanil. HNCS produced a reduction of the P260 amplitude (p<0.05), a late component of SEP that reflects activity in the anterior cingulate cortex. This reduction was associated with higher basal μ-opioid receptor availability in the amygdala on the right (R(2)=0.55, p=0.03) with a similar trend on the left (R(2)=0.24, p=0.22). Besides, HNCS did not induce significant changes in pain and RIII-reflex amplitude (p>0.05). These results suggest that activation of μ-opioid receptors in the amygdala may contribute to the anti-nociceptive effects of HNCS. The lack of RIII-reflex modulation further suggests that μ-opioid receptor activation in the amygdala contributes to decrease pain-related brain activity through a cerebral mechanism independent of descending modulation.

• Authors: Mathieu Piché, Nobuhiro Watanabe, Muneyuki Sakata, Keiichi Oda, Jun Toyohara, Kenji Ishii, Kiichi Ishiwata, Harumi Hotta
• Journal: Neuroscience research (Neurosci Res) 2014 Apr-May Vol. 81-82 Pg. 78-84 ISSN: 1872-8111 [Electronic] Ireland
• PMID: 24583336 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2014 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.

Chemical References

• Receptors, Opioid, mu

Topics

• Amygdala (metabolism)
• Analgesia
• Brain (physiology)
• Cold Temperature
• Electric Stimulation
• Evoked Potentials, Somatosensory
• Female
• Humans
• Male
• Neural Inhibition
• Pain (metabolism, physiopathology)
• Pain Measurement
• Receptors, Opioid, mu (metabolism)
• Reflex (physiology)