Dopamine receptor gene expression in the human medial temporal lobe.

The distributions of the messenger RNA molecules encoding the five known dopamine receptors have been determined in the medial temporal lobe of postmortem human brain. All five receptor mRNAs are present in temporal lobe structures, although their distributions are heterogeneous. The D1-like receptors, D1 and D5, have strikingly dissimilar distributions. D1 receptor mRNA is abundant in temporal neocortex but is rare elsewhere. D5 receptor message, however, is seen in the hippocampus, subicular complex, and in temporal cortex. The D2-like receptors have similar distributions: D2, D3, and D4 receptor mRNAs are all identifiable in the hippocampal formation and in the cortical regions of the medial temporal lobe. Distinct patterns of relative regional concentrations for each message are observed, however, suggesting a neuroanatomical substrate for potential differences in dopaminergic regulation within discrete regions of the medial temporal lobe. These results provide a description of the distribution of these receptor mRNAs in normal humans and suggest multiple levels of complexity as well as regulation of the medial temporal lobe dopamine projection.