In vivo dopamine receptor binding studies with a non-radioactively labeled agonist, dipropyl-5,6-ADTN

Evidence is presented that a low dose of peripherally administered N,N-dipropylamino-5,6-dihydroxytetralin (DiPr-5,6-ADTN) specifically labels dopamine (DA) receptors in rat brain. Concentrations of this potent DA receptor agonist were determined by a highly selective method using reversed phase liquid chromatography and amperometric detection. The binding characteristics satisfy all criteria regarding saturability, stereospecificity, regional distribution and relation with pharmacological effects that are associated with DA receptor interactions. A rough estimation of the density of binding sites in the striatum resulted in values of 60-70 pmol/g. Lesioning the nigrostriatal pathway does not significantly alter the amount of ligand bound, nor do pretreatments with serotonergic, alpha-adrenergic or beta-adrenergic antagonists. DiPr-5,6-ADTN has thus been shown to be a useful ligand for labeling central DA receptors and a powerful tool in the study of DA-ergic mechanisms.