Identification of a high-affinity orphanin FQ/nociceptin(1–11) binding site in mouse brain

✍ Scribed by John P. Mathis; Ira E. Goldberg; Sharon R. Letchworth; Jennifer P. Ryan-Moro; Gavril W. Pasternak

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 153 KB
• Volume: 34
• Category: Article
• ISSN: 0887-4476
• DOI: 10.1002/(sici)1098-2396(19991201)34:3<181::aid-syn2>3.0.co;2-v

✦ Synopsis

The presence of pairs of basic amino acids within the orphanin FQ/Nociceptin (OFQ/N) sequence has raised the possibility that truncated versions of the peptide might be physiologically important. OFQ/N(1-11) is pharmacologically active in mice, despite its poor affinity in binding assays (K i Ͼ 250 nM) for the OFQ/N receptor. Using an analog of OFQ/N(1-11), [ 125 I][Tyr 10 ]OFQ/N(1-11), we identified a high-affinity binding site (K D 234 pM; B max 43 fmol/mg protein) with a selectivity profile distinct from the OFQ/N receptor and all the traditional opioid receptors. This site had very high affinity for OFQ/N and its related peptides. The most striking differences between the new site and the OFQ/N receptor previously observed in brain were seen with traditional opioids. Dynorphin A analogs and ␣-neoendorphin competed with [ 125 I][Tyr 10 ]OFQ/N(1-11) binding in mouse brain with K i values below 10 nM, while naloxone benzoylhydrazone (K i 3.9 nM) labeled the [ 125 I][Tyr 10 ]OFQ/N(1-11) binding site as potently as many traditional opioid receptors. Several other opioids, including fentanyl, (Ϫ)cyclazocine, levallorphan, naltrindole, and diprenorphine, also displayed moderate affinities for this site. Finally, the [ 125 I][Tyr 10 ]OFQ/N(1-11) site had a unique regional distribution consistent with a distinct receptor. Thus, [ 125 I][Tyr 10 ]OFQ/N(1-11) labels a novel site in brain with a selectivity profile intermediate between that of either opioid or OFQ/N receptors.