A second molecular form of D2 dopamine receptor in rat and bovine caudate nucleus

OVEREXPRESSION of the D2dopamine receptor has been proposed to be part of the pathology of schizophrenia1.The isolation of a D2dopamine receptor clone has assisted the molecular characterization of D2 receptors2. We have now isolated an identical rat clone along with two other clones — a second related rat clone (RD-2in) and a homologous bovine clone (BD-2in), both of which contain an insert encoding an additional 29 amino acids relative to the original rat clone (RD-20). All three clones encode D2 receptor binding sites when expressed in COS-7 cells. The a mi no-acid insert encoded by D-2in lies in the domain of the receptor believed to interact with the GTP-binding proteins (G proteins) of various signal transduction pathways3. By using oligonucleotide probes specific for either D-20 or D-2in RNA transcripts, we have found that the level of expression of the D-2in-encoded form of the receptor is seven times that of the D-20 form in the caudate nucleus, the richest brain source of D2receptors4.