Supraspinal melatonin MT receptor agonism alleviates pain via a neural circuit that recruits mu opioid receptors.
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Date publication
novembre 2022
Journal
Journal of pineal research
Auteurs
Membres identifiés du Cancéropôle Est :
Dr DARCQ Emmanuel
Tous les auteurs :
Posa L, De Gregorio D, Lopez-Canul M, He Q, Darcq E, Rullo L, Pearl-Dowler L, Luongo L, Candeletti S, Romualdi P, Kieffer BL, Gobbi G
Lien Pubmed
Résumé
Melatonin, through its G protein-coupled receptor (GPCR) (MTNR1B gene) MT , is implicated in analgesia, but the relationship between MT receptors and the opioid system remains elusive. In a model of rodent neuropathic pain (spared nerve injured [SNI]), the selective melatonin MT agonist UCM924 reversed the allodynia (a pain response to a non-noxious stimulus), and this effect was nullified by the pharmacological blockade or genetic inactivation of the mu opioid receptor (MOR), but not the delta opioid receptor (DOR). Indeed, SNI MOR, but not DOR knockout mice, did not respond to the antiallodynic effects of the UCM924. Similarly, the nonselective opioid antagonist naloxone and the selective MOR antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP) blocked the effects of UCM924 in SNI rats, but not the DOR antagonist naltrindole (NTI). Electrophysiological recordings in the rostral-ventromedial medulla (RVM) revealed that the typical reduction of the firing activity of pronociceptive ON-cells, and the enhancement of the firing of the antinociceptive OFF-cells, induced by the microinjection of the MT agonist UCM924 into the ventrolateral periaqueductal gray (vlPAG) were blocked by MOR, but not DOR, antagonism. Immunohistochemistry studies showed that MT receptors are expressed in both excitatory (CaMKIIα ) and inhibitory (GAD65 ) neuronal cell bodies in the vlPAG (~2.16% total), but not RVM. Only 0.20% of vlPAG neurons coexpressed MOR and MT receptors. Finally, UCM924 treatment induced an increase in the enkephalin precursor gene (PENK) in the PAG of SNI mice. Collectively, the melatonin MT receptor agonism requires MORs to exert its antiallodynic effects, mostly through an interneuronal circuit involving MOR and MT receptors.
Mots clés
MOR, MT2 receptor, melatonin, neuropathic pain, opioid
Référence
J Pineal Res. 2022 11;73(4):e12825