Distribution of dopamine D1, D2, and D5 receptor mRNAs in the monkey brain: ribonuclease protection assay analysis

The distribution of the mRNAs encoding the dopamine D1, D2 and D5 receptors was determined in brain tissues obtained from intact female rhesus monkeys, using a ribonuclease protection assay. Tissue blocks from the frontal cortex, striatum, thalamus, hippocampus and substantia nigra were dissected and total RNA was extracted. Dopamine D2 and D5 receptor DNA fragments were generated from rhesus monkey genomic DNA using polymerase chain reaction. To generate dopamine receptor subtype-specific cRNA probes, DNA fragments corresponding to the carboxy terminus of the rhesus monkey D1 and D2 receptor genes and to the putative transmembrane domain regions (IV-VI) of the D5 receptor gene, were subcloned into the pGEM3Z/4Z vectors. Expression of D1 receptor mRNA exhibited significant regional differences: striatum > > > cerebral cortex ≥ hippocampus ≥ lateral thalamus. D1 receptor mRNA was found in low quantities in the medial thalamus, but was not consistently expressed in the substantia nigra area. In contrast, D2 receptor mRNA was detected in all regions that were studied: striatum > > > substantia nigra > > hippocampus ≥ cerebral cortex ≥ medial thalamus ≥ lateral thalamus. D5 receptor mRNA was also expressed in all regions, with highest levels in the cerebral cortex, striatum and lateral thalamus, and moderate levels in the substantia nigra, medial thalamus and the hippocampus. The D5 receptor mRNA appears to be widely distributed in the monkey brain. Most interesting is the expression of D5 receptor mRNA in tissues of the substantia nigra area.