Anesthesiology
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Increased descending pain facilitation accounts for opioid-induced hyperalgesia, but the underlying mechanisms remain elusive. Given the role of µ-opioid receptors in opioid-induced hyperalgesia in animals, the authors hypothesized that the dorsal reticular nucleus, a medullary pain facilitatory area, is involved in opioid-induced hyperalgesia through altered µ-opioid receptor signaling. ⋯ Chronic morphine shifted µ-opioid receptor signaling from inhibitory to excitatory at the dorsal reticular nucleus, likely enhancing descending facilitation during opioid-induced hyperalgesia in the rat.