Dopamine D2 receptor mRNA is expressed in maturing neurons of the human hippocampal and subicular fields

Pyramidal neurons of the adult and fetal hippocampus and subicular fields were shown to express D2 mRNA using non-radioactive in situ hybridization histochemistry. At the earliest developmental stages examined (embryonic week (E) 13), cell packing within the CA1 region is dense and immature neuroblasts express D2 mRNA at high levels, as do more mature pyramid-like neurons in the deep aspect of the pyramidal cell layer. With development (E19 and E24), cell packing density is reduced, maturing neurons of the pyramidal layer are prominently D2 mRNA positive, while the majority of immature cells lining the superficial layer are D2 mRNA negative. In Layer II of the presubiculum there is a high density of immature D2 mRNA negative cells at E13 with D2 mRNA positive cells located on the periphery of the clusters. By E24, the cells in the layer II clusters are larger, express D2 mRNA, and D2 mRNA negative cells are rarely observed. Thus, expression of D2 mRNA in humans is an early and permanent feature of pyramidal neurons of these regions.