Ontogeny of the dopamine D2 receptor mRNA expressing cells in the human hippocampal formation and temporal neocortex

The study details the cellular expression of the dopamine D-2 receptor mRNA in the human temporal lobe during prenatal development. At 13 embryonic weeks (E13) D-2 mRNA was widely expressed in the temporal lobe. At this time point in the dentate gyrus D-2 mRNA positive cells first appeared at the outer border of the granular layer and their number increased with development. The CA1 exhibited the highest level of D-2 mRNA expression. By E19-25 the hippocampal formation underwent rapid morphological maturation. D-2 mRNA expression became more uniform and dense in the ammonic subfield. At all ages the subiculum appeared more mature morphologically but less intensely stained for D-2 mRNA than the ammonic fields. In the entorhinal cortex D-2 mRNA expression was most conspicuous in the future layer II at all ages. In the temporal neocortex D-2 mRNA-positive cells were detected in the subplate and cortical plate. Differentiation of the cortical plate was accompanied by concentration of D-2 mRNA-positive cells in layer V. The most conspicuous cells expressing D-2 mRNA were found in the marginal zone of all regions and resembled Cajal-Retzius cells in morphology and location. Density of putative Cajal-Retzius cells expressing D-2 mRNA decreased with development. They all but disappeared from the hippocampal areas by mid gestation, but in the temporal neocortex occasional cells were seen even at term. Early and widespread but region and cell type specific expression of D-2 receptor mRNA suggests an important role of this DA receptor subtype in prenatal development of the human temporal lobe. (C) 2000 Elsevier Science B.V. All rights reserved.