DETERMINATION OF NOCICEPTIN-LIKE IMMUNOREACTIVITY IN THE RAT DORSAL SPINAL-CORD

An endogenous ligand for the opioid receptor-like (ORL(1)) receptor ha s been characterized recently. This 17 amino acid peptide, nociceptin, has potent effects on pain processing in experimental animals. In the present study, we describe the development of a radioimmunoassay for nociceptin, suitable for quantification of immunoreactivity in the rat spinal cord. In the dorsal spinal cord me found 641 fmol nociceptin-l ike immunoreactivity (IR)/mg protein, while in the ventral spinal cord the amount was below the detection limit of the assay (11 fmol/mg pro tein). High pressure liquid chromatography (HPLC) showed that the immu noreactive material was heterogeneous with the major part eluting at t he position of synthetic nociceptin. The presence of nociceptin in the dorsal spinal cord is compatible with its proposed involvement in mod ulating afferent transmission. (C) 1997 Elsevier Science Ireland Ltd.