Dopamine D2 receptors are unevenly distributed in the rat hippocampus and are modulated differently than in striatum

The characteristics of dopamine (DA) D2 receptors were studied in rat hippocampus and for comparison in striatum using the [3H]spiperone radioreceptor assay in vitro. D2 receptors exhibit a bimodal distribution along the length of the hippocampus. Heterogeneity also exists in the transverse axis with high densities in the molecular layers of the subiculum and CA1 plus CA2. As in the striatum, D2 receptors in both dorsal and ventral hippocampus display high and low affinity states for agonists, but all three regions differ with regard to the percentage of receptors in these states. The modulation of these affinity states by GTP, Mg2+ and the iron-chelator, 1,1-O-phenanthroline, differs markedly between dorsal and ventral hippocampus, and between these regions and the striatum. A new model for the modulation of the affinity of D2 receptors for agonists is presented. These data suggest the presence of regional differences in the composition of the D2 receptor-regulatory protein complex.