THE NOVEL ALPHA(2)-ADRENOCEPTOR AGONIST [H-3] MIVAZEROL BINDS TO NONADRENERGIC BINDING-SITES IN HUMAN STRIATUM MEMBRANES THAT ARE DISTINCT FROM IMIDAZOLINE RECEPTORS

The alpha(2) adrenergic agonist [H-3]mivazerol labelled two population s of binding sites in membranes from the human striatum. Forty per cen t of the sites labelled by 3 nM [H-3]mivazerol corresponded to alpha, adrenergic receptors as they displayed a high affinity for (-)-adrenal ine and for rauwolscine. The remaining binding was displaced by mivaze rol with a pIC(50) of 6.5+/-0.1. These sites displayed higher affinity for dexmedetomidine (pIC(50)=7.1+/-0.1), but much lower affinity for clonidine (pIC(50)<5.0) and for idazoxan (pIC(50)=5.1+/-0.1). Mivazero l also showed low affinity for the [H-3]clonidine-labelled I-1 imidazo line receptors and for the [H-3]idazoxan-labelled I-2 receptors (pIC(5 0)=5.1 and 3.9, respectively). These results suggest that the non-adre nergic [H-3]mivazerol binding sites are distinct from the imidazoline receptors in the human striatum. (C) 1997 Elsevier Science Ltd.