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Effects of supraspinal orphanin FQ/nociceptin
1Department of Psychology, Furman University, 29613, Greenville, SC, USA.
Abstract:
The first reported behavioral action of the endogenous ligand for the "orphan" opioid receptor was a seemingly paradoxical increased sensitivity to nociception (i.e. hyperalgesia) after supraspinal injection into the cerebral ventricles of mice. In the continuing absence of an appropriate in vivo receptor antagonist, studies attempting to define the role of orphanin FQ/nociceptin (OFQ/N) in pain modulation and other behaviors have also featured central injection of peptide. This article reviews the findings of such studies. There appears to be concordance around the observation of anti-opioid actions of supraspinally injected OFQ/N, whereas the observations of hyperalgesia and/or analgesia are much less clear. A portion of the discrepant data may be explained in terms of methodological issues, stress-induced analgesia accompanying experimental protocols, and genotypic variation among subjects. Clarification of OFQ/N's role in nociception, as with other putative biologic functions, will probably depend upon the availability of a selective receptor antagonist.
Insights
Orphanin FQ/nociceptin (OFQ/N) shows anti-opioid effects when injected centrally, but its role in pain modulation remains unclear due to conflicting research and lack of specific antagonists.
Area of Science:
- Neuroscience
- Pharmacology
- Pain Research
Background:
- The endogenous ligand for the orphan opioid receptor, orphanin FQ/nociceptin (OFQ/N), was initially linked to hyperalgesia.
- Research into OFQ/N's function is hampered by the absence of a specific in vivo receptor antagonist.
Purpose of the Study:
- To review studies investigating the role of OFQ/N in pain modulation and other behaviors.
- To analyze the discrepancies in findings regarding OFQ/N's effects on nociception.
Main Methods:
- Central (intracerebroventricular) injection of OFQ/N peptide in animal models.
- Review and synthesis of existing research findings on OFQ/N's behavioral effects.
Main Results:
- Concordance exists regarding the anti-opioid actions of supraspinally administered OFQ/N.
- Observations of hyperalgesia or analgesia are inconsistent, with potential explanations including methodological variations, stress-induced analgesia, and genetic differences.
Conclusions:
- The precise role of OFQ/N in nociception requires further investigation.
- Development of a selective OFQ/N receptor antagonist is crucial for clarifying its biological functions.