Effects of orphanin FQ on endomorphin-1 induced analgesia

• Published in: Brain research Vol. 835; no. 2; pp. 241 - 246
• Main Authors: Wang, Yan-Qing, Zhu, Chong-Bin, Wu, Gen-Cheng, Cao, Xiao-Ding, Wang, Yan, Cui, Da-Fu
• Format: Journal Article
• Language: English
• Published: London Elsevier B.V 24.07.1999; Amsterdam Elsevier; New York, NY
• Subjects: Analgesia; Analgesics, Opioid - pharmacology; Animals; Biological and medical sciences; Endomorphin-1; Fundamental and applied biological sciences. Psychology; Hyperalgesia; Injections, Intraventricular; Injections, Spinal; Nociceptin; Oligopeptides - pharmacology; Opioid Peptides - pharmacology; ORL1 receptor; Orphanin FQ; Pain - drug therapy; Pain Measurement; Rats; Rats, Sprague-Dawley; Reaction Time - drug effects; Receptors, Opioid - agonists; Somesthesis and somesthetic pathways (proprioception, exteroception, nociception); interoception; electrolocation. Sensory receptors; Vertebrates: nervous system and sense organs; μ-opiate receptor; Orphanin FQ; Analgesia; ORL1 receptor; Endomorphin-1; μ-opiate receptor; Hyperalgesia; Nociception; Noxious stimulus; Vertebrata; Mammalia; Rat; Rodentia; μ Opioid receptor
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/S0006-8993(99)01589-9

Orphanin FQ (also known as nociceptin) is a 17-amino-acid peptide which acts as a potent endogenous agonist of the orphan opioid receptor-like (ORL1) receptor. Endomorphin-1, a 4-amino-acid peptide discovered recently, is a potent and selective endogenous agonist for the μ-opiate receptor. In the present study, the effect of OFQ or/and endomorphin-1 on the response to noxious thermal stimuli was observed using the tail-flick test in rats. Intracerebroventricular (i.c.v.) administration of OFQ (1, 5 μg) could shorten tail-flick latency; In contrast, intrathecal (i.t.) administration of OFQ (1, 2 or 10 μg) could increase the latency; i.c.v. (1, 2, 5 μg) or i.t. (0.2, 2, 5 μg) administration of endomorphin-1 dose-dependently increased the latency, indicating an analgesic effect. Furthermore, OFQ (0.1–5 μg) when intraventricularly injected together with endomorphin-1 (5 μg), could dose-dependently reverse the analgesia induced by the latter. On the contrary, OFQ (1 μg) intrathecally injected together with endomorphin-1 (0.2 μg) could further increase the tail-flick latency. The results showed that OFQ at the supraspinal level produces hyperalgesia and is antagonistic to endomorphin-1, while at the spinal level it produces analgesia and is synergic with endomorphin-1. Different interaction mechanism between OFQ and endomorphin-1 in the brain and the spinal cord is thus suggested.