AUTORADIOGRAPHY OF DOPAMINE-D2 RECEPTORS USING [H-3] YM-09151-2

Rat brain dopamine D2 receptors were labeled autoradiographically using the potent and selective benzamide, [H-3]YM-09151-2. Saturation binding data, quantified from autoradiograms, showed specific binding of [H-3]YM-09151-2 to striatal D2 receptors with a K(D) of 82 pM and B(max) of 0.696 pmol/mg protein. Binding equilibrium occurred within 3 h, and a dissociation constant of 15 pM was obtained in kinetic studies. Antagonist competition curves were monophasic and displayed an order of potency expected for D2 receptors: (+)-butaclamol > (-)-sulpiride > SCH 23390 > mianserin. Competition by dopamine resulted in a shallow, biphasic displacement curve. The distribution of [H-3]YM-09151-2 binding sites matched the known pattern for D2 receptors, with dense labeling in striatum, olfactory tubercles and nucleus accumbens, and moderate levels in substantia nigra pars compacta and mamillary nuclei. Much lower levels of non-specific binding were observed than are typically obtained when using [H-3]spiperone as the ligand. The coincident high affinity and selectivity of [H-3]YM-09151-2 for D2 sites should make this compound a preferred choice for tritium-based D2 autoradiography.