Mu-opioid receptor in the nucleus submedius: involvement in opioid-induced inhibition of mirror-image allodynia in a rat model of neuropathic pain.

Abstract	The current study investigated the roles of various subtypes of opioid receptors expressed in the thalamic nucleus submedius (Sm) in inhibition of mirror-image allodynia induced by L5/L6 spinal nerve ligation in rats. Morphine was microinjected into the Sm, which produced a dose-dependent inhibition of mirror-image allodynia; this effect was antagonized by pretreatment with non-selective opioid receptor antagonist naloxone. Microinjections of endomorphin-1 (mu-receptor agonist), or [D-Ala(2), D-Leu(5)]-enkephalin (DADLE, delta-/mu-receptor agonist), also inhibited mirror-image allodynia, and these effects were blocked by the selective mu-receptor antagonist, beta-funaltrexamine hydrochloride. The DADLE-induced inhibition, however, was not influenced by the delta-receptor antagonist naltrindole. The kappa-receptor agonist, spiradoline mesylate salt, failed to alter the mirror-image allodynia. These results suggest that Sm opioid receptor signaling is involved in inhibition of mirror-image allodynia; this effect is mediated by mu- (but not delta- and kappa-) opioid receptors in the rat model of neuropathic pain.
Authors	Jun-Yang Wang, Mei Zhao, Fen-Sheng Huang, Jing-Shi Tang, Yu-Kang Yuan
Journal	Neurochemical research (Neurochem Res) Vol. 33 Issue 10 Pg. 2134-41 (Oct 2008) ISSN: 1573-6903 [Electronic] United States
PMID	18473169 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Chemical References	Narcotic Antagonists Oligopeptides Receptors, Opioid, mu endomorphin 1 Naloxone Naltrexone Enkephalin, Leucine-2-Alanine beta-funaltrexamine Morphine naltrindole
Topics	Animals Behavior, Animal (drug effects) Disease Models, Animal Enkephalin, Leucine-2-Alanine (pharmacology) Hyperalgesia (drug therapy) Ligation Male Morphine (therapeutic use) Naloxone (pharmacology) Naltrexone (analogs & derivatives, pharmacology) Narcotic Antagonists (pharmacology) Neuralgia (drug therapy, metabolism) Oligopeptides (pharmacology) Pain Measurement Rats Rats, Sprague-Dawley Receptors, Opioid, mu (agonists, physiology) Spinal Nerves (physiology) Thalamic Nuclei (metabolism)

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