DOPAMINE D-2-LIKE RECEPTORS LABELED BY [H-3] YM-09151-2 IN THE RAT HIPPOCAMPUS - CHARACTERIZATION AND AUTORADIOGRAPHIC DISTRIBUTION

Dopamine D-2-like receptor labeled by [H-3]YM-09151-2 in the rat hippo campus proper was examined by in vitro receptor autoradiography. In th e dorsal hippocampus, [H-3]YM-09151-2 bindings were high in the whole layers of CA1, the stratum pyramidale of CA4 and the stratum molecular e of gyrus dentatus, moderate in the stratum oriens of CA3 and hilus o f the gyrus dentatus, and low in remaining CA3 and the subiculum. In t he ventral hippocampus, the binding densities were high in the stratum oriens and the stratum radiatum of CA1, the stratum pyramidale of CA4 , and the stratum moleculare of gyrus dentatus, moderate in the stratu m lacnosum moleculare of CA1 and the hilus of the gyrus dentatus. Satu ration analysis using hippocampal sections demonstrated that the K-d v alue was about five times higher than that using striatal sections. Th e rank order potency of competition on [H-3]YM-09151-2 binding by dopa minergic ligands in the hippocampus was YM-09151-2 > (+)-butaclamol > dopamine > sulpiride > SCK-23390; which shows the appropriate dopamine D-2-like receptor profile. The hippocampal [H-3]YM-09151-2 binding di d not represent serotonergic receptors (5-HT1A and 5-HT2) and sigma re ceptor, since K-i values of ketanserine, serotonin, 8-OH-DPAT and DTG were much lower than D-2-like receptor antagonists. These findings sug gest that [H-3]YM-09151-2 binds hippocampal D-2-like receptor site wit h different association kinetics of striatal D-2-like receptor site, a nd demonstrates widespread distribution of D-2-like receptor in the hi ppocampus with distinct region-specific profile.