[I-125] [TYR(14)]ORPHANIN BINDING TO RAT-BRAIN - EVIDENCE FOR LABELING THE OPIOID-RECEPTOR-LIKE-1 (ORL1)

[I-125][Tyr(14)]Orphanin binds to a number of saturable non-interactin g binding sites in rat brain cortical membrane preparations, with a de nsity of 510 fmol/mg protein and affinity 0.9 nM. This high affinity, saturable [I-125[Tyr(14)]orphanin binding was not inhibited by leuenke phalin and by other ligands for opiate and neurotransmitter receptors both in membrane preparations and brain sections. In rat brain section s, the highest density of binding was found in the outer and medial co rtical layers, subiculum, hippocampus and nucleus accumbens; intermedi ate binding densities were found in the inner cortical layer, pontine nuclei, thalamus and hypothalamus. Very low specific binding was seen in the cerebellum and striatum, according to the described distributio n of ORL1 transcripts. These results suggest that [I-125][Tyr(14)] orp hanin binding in rat brain occurs to the described ORL1 receptor. (C) 1997 Elsevier Science Ireland Ltd.