Nociceptin attenuates opioid and gamma-aminobutyric acid(B) receptor-mediated analgesia in the mouse tail-flick assay

Nociceptin (NC) and the opioid receptor like-1 receptors are widely distrib uted in areas of the neuraxis that are part of the descending modulatory pa in system. We used the tail-flick assay in mice to assess the interaction b etween NC and other analgesic compounds acting on different areas of the de scending pathway. Given by intracerebroventricular injection, NC induced hy peralgesia at 10 nmol (39% of reduction vs. control group). The same dose o f NC reversed analgesia induced by distinct classes of analgesia-producing compounds such as morphine, dynorphin A or baclofen. NC caused a reduction of their antinociceptive effects: 61, 41 and 27%, respectively. Thus, NC at the supraspinal level appears to interact with both opioid and gamma-amino butyric acid(B) systems producing anti-analgesic effects probably through t he descending pathway for pain control, (C) 2000 Elsevier Science Ireland L td. All rights reserved.