Cloning of nocistatin receptor and development of new aanalgesics

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We previously isolated a peptide termed as nociceptin/orphanin FQ (Noc/OFQ) from bovine brain as an endogenous ligand for the orphan opioid-like receptor ROR-C.We demonstrated that intrathecal (i.t.) administration of Noc/OFQ into conscious mice induced hyperalgesia and tactile pain (allodynia). We found a novel heptadecapeptide which blocks the Noc/OFQ-evoked pain responses, on the same precursor as Noc/OFQ and named it nocistatin. Nocistatin exerts actions through the postulated nocistatin receptor. To develop novel analgesics, we tried to characterize pain transmission involving Noc/OFQ and nocistatin and clone cDNA of nocistatin receptor and obtained following results.1) Based on the results obtained by a Noc/OFQ antagonist developed recently, nocistatin only blocked the responses mediated by the Noc/OFQ receptor. 2) Nocistatin has a broad spectrum of analgesics ; it alleviated the pain induced by i.t. PGE2, i.t. PGF2α and intraplantar formalin in addition to i.t. Noc/OFQ.3) Nocistatin activated adenylate cyclase in the membrane prepared from mouse brain and spinal cord in a GTP-dependent manner and increased cAMP.4) In order to develop a new analgesic, we synthesized various peptides on the basis of amino acid sequence of nocistatin and evaluated them by analgesic effects and capability of cAMP increase. 5) We have tried to clone a nocistatin receptor cDNA from a cDNA library prepared from mouse brain with expression-cloning methods by use of mammalian cell lines and Xenopus oocytes. Since the cloning of nocistatin receptor is a requisite for the development of nocistatin antagonists as new analgesics, purification of the nocistatin receptor has been also tried by photoaffinity labeling, in parallel with the cloning of the nocistatin receptor cDNA.