Dopamine D2-like receptors labeled by [3H]YM-09151-2 in the rat hippocampus: characterization and autoradiographic distribution.

Dopamine D2-like receptor labeled by [3H]YM-09151-2 in the rat hippocampus proper was examined by in vitro receptor autoradiography. In the dorsal hippocampus, [3H]YM-09151-2 bindings were high in the whole layers of CA1, the stratum pyramidale of CA4 and the stratum molecular of gyrus dentatus, moderate in the stratum oriens of CA3 and hilus of the gyrus dentatus, and low in remaining CA3 and the subiculum. In the 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 stratum lacnosum moleculare of CA1 and the hilus of the gyrus dentatus. Saturation analysis using hippocampal sections demonstrated that the Kd value was about five times higher than that using striatal sections. The rank order potency of competition on [3H]YM-09151-2 binding by dopaminergic ligands in the hippocampus was YM-09151-2 > (+)-butaclamol > dopamine > sulpiride > SCH-23390; which shows the appropriate dopamine D2-like receptor profile. The hippocampal [3H]YM-09151-2 binding did not represent serotonergic receptors (5-HT1A and 5-HT2) and sigma receptor, since Ki values of ketanserine, serotonin, 8-OH-DPAT and DTG were much lower than D2-like receptor antagonists. These findings suggest tha [3H]YM-09151-2 binds hippocampal D2-like receptor site with different association kinetics of striatal D2-like receptor site, and demonstrates widespread distribution of D2-like receptor in the hippocampus with distinct region-specific profile.