Orphanin FQ/nociceptin inhibits morphine withdrawal

The influence of orphanin FQ/nociceptin (OFQ/N) on the morphine-withdrawal symptom was investigated. Withdrawal syndrome was induced in the morphine-d ependent rats by an intraperitoneal tip) injection of 2 mg/kg naloxone hydr ochloride - an opioid receptors antagonist. Wet-dog shakes were used as a m easure of the abstinence syndrome. Intraventricular injections of OFQ/N (5- 20 mu g/animal) caused significant inhibition of the withdrawal signs at do ses between 15-20 mu g, in the morphine-dependent rats. OFQ/N alone did not change behavior of the morphine-dependent animals. The obtained results in dicate that OFQ/N can inhibit the morphine withdrawal symptoms induced by n aloxone. (C) 2000 Elsevier Science Inc.