ANTINOCICEPTION MEDIATED BY THE PERIAQUEDUCTAL GRAY IS ATTENUATED BY ORPHANIN FQ

ORPHANIN FQ or nociceptin (OFQ/N1-17) is a recently discovered peptide which, upon intracerebroventricular administration, reverses opioid-m ediated analgesias. OFQ/N1-17 terminals are located in the periaqueduc tal gray (PAG), a structure known to be involved in pain modulation, s uggesting that the functional anti-opioid effects of OFQ/N1-17 are med iated by PAG neurons. To test this, subsequent microinjections of morp hine or kainic acid and OFQ/N1-17 were made into the PAG of awake rats . Administration of OFQ/N1-17 attenuated the tail flick inhibition pro duced by both morphine and kainic acid microinjection. OFQ/N1-17 atten uation of antinociception produced by a neuroexcitant indicates that O FQ/N1-17 reverses opioid antinociception by inhibiting PAG output neur ons.