NOCICEPTIN ORPHANIN FQ BINDING INCREASES IN SUPERFICIAL LAMINAE OF THE RAT SPINAL-CORD DURING PERSISTENT PERIPHERAL INFLAMMATION/

Regulation of nociceptin/orphanin FQ neurotransmission in conjunction with peripheral inflammation and hyperalgesia was explored, using rece ptor autoradiography. Binding of [H-3]nociceptin was quantified in spi nal segment L4 of rats at 2, 4 and 8 days following injection of compl ete Freund's adjuvant (CFA) into one hind-paw. Densitometric analysis of autoradiograms showed that [H-3]nociceptin binding increased in med ial and lateral laminae I-II bilaterally 4 days following injection of CFA compared to untreated rats; no change in binding occurred in lami na X at the times examined. Biochemical studies confirmed that the spe cific binding of [H-3]nociceptin to sections of rat brain was consiste nt with the binding characteristics of the nociceptin receptor. These results suggest that spinal nociceptin receptors are upregulated durin g hyperalgesia. This response may enhance endogenous mechanisms of ant inociception to attenuate the hyperalgesia induced by CFA. (C) 1998 El sevier Science Ireland Ltd. All rights reserved.