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- •Opioid-specific effects were seen on cold-pressor pain ratings.
- •Opioid-specific spinal effect was evidenced as reduced spinal nociceptive withdrawal reflexes size.
- •Opioid-specific supra-spinal effects were evidenced as changes in tonic pain electroencephalography.
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This work is funded by the Lundbeck Foundation under reference number R209-2015-2416. The authors declare no conflict of interest regarding the work presented in this article.