Vol. 299, Issue 1, 213-219, October 2001

Pronociceptive Effects of Nociceptin/Orphanin FQ (13-17) at Peripheral and Spinal Level in Mice

Makoto Inoue, Shinobu Matsunaga, M. Harunor Rashid, Akira Yoshida, Kiyonobu Mizuno, Tsukasa Sakurada, Hiroshi Takeshima and Hiroshi Ueda

Department of Molecular Pharmacology and Neuroscience, Nagasaki University School of Pharmaceutical Sciences, Nagasaki, Japan (M.I., S.M., M.H.R., A.Y., K.M., H.U.); Department of Biochemistry, Daiichi College of Pharmaceutical Sciences, Fukuoka, Japan (T.S.); and Division of Cell Biology, Institute of Life Science, Kurume University, Fukuoka, Japan (H.T.)

The heptadecapeptide nociceptin/orphanin FQ (N/OFQ) is reported to be metabolized by aminopeptidase N and endopeptidase 24.15. In the present study, N/OFQ C-terminal fragments elicited nociceptive responses in the peripheral nociceptors and in the spinal cord, whereas N-terminal fragments had no significant nociception. The nociceptive effect of N/OFQ (13-17) was most potent and remained unchanged in N/OFQ peptide receptor (NOPR) gene knockout mice, indicating that N/OFQ (13-17)-induced nociception is mediated through a novel mechanism independent of the activation of NOPR. This finding was further confirmed by in vitro guanosine 5'-O-(3-[³⁵S]thio)triphosphate binding experiments, in which N/OFQ (13-17) showed no significant binding activity in baculovirus/sf21 cells expressing NOPR together with G protein _i1-, ₁-, and ₂-subunits, whereas N/OFQ showed stimulation in a concentration-dependent manner. On the other hand, although a typical bell-shaped dose-response relationship was observed with a wide range of N/OFQ doses in both peripheral and central nociception tests, N/OFQ (13-17) did not show bell-shaped dose-response relationship in the central nociception test. This finding indicates that N/OFQ (13-17), in contrast to N/OFQ, lacks the postsynaptic antinociceptive actions modulating substance P signaling in the spinal cord. Together, our results suggest that C-terminal fragments of N/OFQ have potent nociceptive actions, and N/OFQ (13-17) could have the potential to mediate its actions through a novel mechanism independent of the activation of NOPR in the nociceptors and in spinal synapses.