µ-opioid receptor activation at the dorsal reticular nucleus shifts diffuse noxious inhibitory controls to hyperalgesia in chronic joint pain in male rats.
Journal
Anesthesiology
ISSN: 1528-1175
Titre abrégé: Anesthesiology
Pays: United States
ID NLM: 1300217
Informations de publication
Date de publication:
21 Feb 2024
21 Feb 2024
Historique:
medline:
21
2
2024
pubmed:
21
2
2024
entrez:
21
2
2024
Statut:
aheadofprint
Résumé
The dorsal reticular nucleus is a pain facilitatory area involved in the diffuse noxious inhibitory controls (DNIC), through opioidergic mechanisms that are poorly understood. We hypothesized that signaling of µ-opioid receptors is altered in this area at prolonged chronic inflammatory pain and that this accounts for the loss of DNIC occurring in this condition. Monoarthritis was induced in male Wistar rats (n=5-9/group) by tibiotarsal injection of complete Freund's adjuvant. We quantified the immunolabeling of µ-opioid receptors and the phosphorylated forms of µ-opioid receptors and cAMP response element-binding protein. Pharmacological manipulation of µ-opioid receptors at the dorsal reticular nucleus was assessed in DNIC, through the Randall-Selitto test. At 42 days of monoarthritis, µ-opioid receptor labeling decreased at the dorsal reticular nucleus, while its phosphorylated form and the phosphorylated cAMP response element-binding protein increased. D-ALA2,N-ME-PHE4,GLY5-OL)-enkephalin acetate (DAMGO) enhanced DNIC analgesia in normal animals ([Mean ± SD]: pre-DNIC: 126.9 ± 7.0g; DNIC - DAMGO: 147.5 ± 8.0g vs. DNIC + DAMGO: 198.1 ± 19.3g, p < 0.001), whereas it produced hyperalgesia in monoarthritis (pre-DNIC: 67.8 ± 7.5g; DNIC - DAMGO: 70.6 ± 7.7g vs. DNIC + DAMGO: 32.2 ± 2.6g, p < 0.001). An ultra-low dose of naloxone, which prevents the excitatory signaling of the µ-opioid receptor, restored DNIC analgesia in monoarthritis (DNIC - Naloxone: 60.0 ± 6.1g vs. DNIC + Naloxone: 98.0 ± 13.5g, p < 0.001), compared to saline (DNIC - Saline: 62.5 ± 5.2g vs. DNIC + Saline: 64.2 ± 3.8g). When injected prior to DAMGO, it restored DNIC analgesia and decreased the phosphorylated cAMP response element-binding protein in monoarthritis. The dorsal reticular nucleus is likely involved in a facilitatory pathway responsible for DNIC hyperalgesia. The shift of µ-opioid receptor signaling to excitatory in this pathway likely accounts for the loss of DNIC analgesia in monoarthritis.
Sections du résumé
BACKGROUND
BACKGROUND
The dorsal reticular nucleus is a pain facilitatory area involved in the diffuse noxious inhibitory controls (DNIC), through opioidergic mechanisms that are poorly understood. We hypothesized that signaling of µ-opioid receptors is altered in this area at prolonged chronic inflammatory pain and that this accounts for the loss of DNIC occurring in this condition.
METHODS
METHODS
Monoarthritis was induced in male Wistar rats (n=5-9/group) by tibiotarsal injection of complete Freund's adjuvant. We quantified the immunolabeling of µ-opioid receptors and the phosphorylated forms of µ-opioid receptors and cAMP response element-binding protein. Pharmacological manipulation of µ-opioid receptors at the dorsal reticular nucleus was assessed in DNIC, through the Randall-Selitto test.
RESULTS
RESULTS
At 42 days of monoarthritis, µ-opioid receptor labeling decreased at the dorsal reticular nucleus, while its phosphorylated form and the phosphorylated cAMP response element-binding protein increased. D-ALA2,N-ME-PHE4,GLY5-OL)-enkephalin acetate (DAMGO) enhanced DNIC analgesia in normal animals ([Mean ± SD]: pre-DNIC: 126.9 ± 7.0g; DNIC - DAMGO: 147.5 ± 8.0g vs. DNIC + DAMGO: 198.1 ± 19.3g, p < 0.001), whereas it produced hyperalgesia in monoarthritis (pre-DNIC: 67.8 ± 7.5g; DNIC - DAMGO: 70.6 ± 7.7g vs. DNIC + DAMGO: 32.2 ± 2.6g, p < 0.001). An ultra-low dose of naloxone, which prevents the excitatory signaling of the µ-opioid receptor, restored DNIC analgesia in monoarthritis (DNIC - Naloxone: 60.0 ± 6.1g vs. DNIC + Naloxone: 98.0 ± 13.5g, p < 0.001), compared to saline (DNIC - Saline: 62.5 ± 5.2g vs. DNIC + Saline: 64.2 ± 3.8g). When injected prior to DAMGO, it restored DNIC analgesia and decreased the phosphorylated cAMP response element-binding protein in monoarthritis.
CONCLUSIONS
CONCLUSIONS
The dorsal reticular nucleus is likely involved in a facilitatory pathway responsible for DNIC hyperalgesia. The shift of µ-opioid receptor signaling to excitatory in this pathway likely accounts for the loss of DNIC analgesia in monoarthritis.
Identifiants
pubmed: 38381969
pii: 139850
doi: 10.1097/ALN.0000000000004956
doi:
Types de publication
Journal Article
Langues
eng
Sous-ensembles de citation
IM
Informations de copyright
Copyright © 2024 American Society of Anesthesiologists. All Rights Reserved.
Déclaration de conflit d'intérêts
Conflicts of Interest: The authors declare no conflict of interests.