LOW STRINGENCY HYBRIDIZATION STUDY OF THE DOPAMINE D4 RECEPTOR REVEALED D4-LIKE MESSENGER-RNA DISTRIBUTION OF THE ORPHAN 7-TRANSMEMBRANE RECEPTOR, APJ, IN HUMAN BRAIN

We recently reported that the density of mRNA for the dopamine D4 rece ptor was extremely low in human cerebral cortex but unexpectedly highe r in the corpus callosum and spinal cord both of which contain substan tial white-matter area. Under low stringency conditions, Northern blot analysis using the D4 probe detected cross-hybridized mRNAs having a similar distributional profile to the D4 mRNA in human brain regions, suggesting the mRNA distributional profile is not peculiar to the D4 r eceptor. Homology screening revealed one of the mRNAs to be an orphan seven-transmembrane receptor, APJ, abundantly expressed in the corpus callosum and spinal cord. in porcine spinal cord the APJ mRNA was dete cted at a higher level in white-matter rather than in gray-matter area . These data suggest that a group of seven-transmembrane receptors, in cluding the D4 and APJ receptor, is preferentially expressed in the wh ite-matter area probably in non-neuronal glial cells.