Faculty Collaboration Database

Contribution of endogenous enkephalins to the enhanced analgesic effects of supraspinal mu opioid receptor agonists after inflammatory injury. J Neurosci 2001 Apr 01;21(7):2536-45

Date

03/27/2001

Pubmed ID

11264327

Pubmed Central ID

PMC6762402

DOI

10.1523/JNEUROSCI.21-07-02536.2001

Scopus ID

2-s2.0-0035313099 (requires institutional sign-in at Scopus site)   86 Citations

Abstract

This study examined a mechanism responsible for the enhanced antihyperalgesic and antinociceptive effects of the mu opioid receptor agonist (ORA) [D-Ala(2), NMePhe(4), Gly(5)-ol]enkephalin (DAMGO) microinjected in the rostroventromedial medulla (RVM) of rats with inflammatory injury induced by injection of complete Freund's adjuvant (CFA) in one hindpaw. In rats injected with CFA 4 hr earlier, microinjection of the mu opioid receptor antagonist D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP) in the RVM antagonized both the marginal enhancement of the potency of DAMGO and its antinociceptive effect. The delta opioid receptor antagonist naltriben (NTB) was without effect. In rats injected with CFA 2 weeks earlier, CTAP antagonized the effects of DAMGO to a lesser extent. However, NTB completely prevented the enhancement of the potency of DAMGO, whereas it did not antagonize DAMGO's antinociceptive effects. Microinjection of NTB alone, but not CTAP in the RVM of CFA-treated rats, enhanced the hyperalgesia present in the ipsilateral hindpaw and induced hyperalgesia in the contralateral, uninjured hindpaw. These results suggest that persistent inflammatory injury increased the release in the RVM of opioid peptides with preferential affinity for the delta opioid receptor, which can interact in a synergistic or additive manner with an exogenously administered mu opioid receptor agonist. Indeed, the levels of [Met(5)]enkephalin and [Leu(5)]enkephalin were increased in the RVM and in other brainstem nuclei in CFA-treated rats. This increase most likely presents a compensatory neuronal response of the CNS of the injured animal to mitigate the full expression of inflammatory pain and to enhance the antinociceptive and antihyperalgesic effects of exogenously administered mu opioid receptor analgesics.

Author List

Hurley RW, Hammond DL

Author

Robert W. Hurley MD, PhD Adjunct Professor of Anesthesiology and CTSI in the Anesthesiology department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Animals
Brain
Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
Enkephalins
Inflammation
Male
Microinjections
Naltrexone
Pain
Peptide Fragments
Peptides
Rats
Rats, Sprague-Dawley
Receptors, Opioid, mu
Somatostatin