THE HUMAN DELTA-OPIOID RECEPTOR - GENOMIC ORGANIZATION, CDNA CLONING,FUNCTIONAL EXPRESSION, AND DISTRIBUTION IN HUMAN BRAIN

We have used the mouse delta-opioid receptor (mDOR) cDNA to isolate th e mDOR gene and its human homologue. In both species the coding region is interrupted by two introns with conserved exon-intron boundaries l ocated after transmembrane domains 1 and 4. Using the polymerase chain reaction and primers based on the sequence of the cloned human delta- opioid receptor (hDOR) gene, we have obtained a full length cDNA encod ing the hDOR from SH-SY5Y neuroblastoma cells. The cDNA sequence is 10 0% identical to the cloned human genomic sequence and 94% identical to the mouse sequence at the protein level. When expressed in COS cells, hDOR displays nanomolar affinities for delta-selective ligands, where as the affinities far mu- and kappa-selective ligands are in the micro molar range. The delta agonists [D-Ala(2), D-Leu(5)]enkephalin, cyclic [D-penicillamine(2),D-penicillamine(5)]enkephalin, and BW373U86 effic iently decrease forskolin-induced cAMP levels in hDOR-expressing COS c ells, indicating functional coupling of the receptor. The distribution of hDOR mRNA in human brain was investigated using delta-selective re verse transcription-polymerase chain reaction amplification, followed by Southern hybridization with a delta-specific probe. The transcript is found in cortical areas, including olfactory bulb, hippocampus, and amygdala, as well as in basal ganglia and hypothalamus. No expression is detected in internal globus pallidus, thalamus, any investigated b rainstem structure, or pituitary gland. Taken together, our results in dicate similar structural, pharmacological, functional, and anatomical properties for the hDOR and the mDOR and therefore support the use of rodent models for the study of these receptors in opioid function.