Characterizing the binding of dopamine D1-D2 receptors in vitro and in temporal and frontal lobe tissue total protein.

Dysfunction of the dopaminergic pathway is linked to numerous diseases of the nervous system. The D1-D2 receptor heteromer is known to play a role in certain neuropsychiatric disorders, such as depression. Here, we synthesized an eight amino acid residue peptide, EAARRAQE, derived from the third intracellular loop of the D2 receptor and show that the peptide binds to the D1 receptor with comparable efficiency as that of the full-length D2 receptor protein. Moreover, immunoprecipitation studies show the existence of a heteromeric complex formed both in vitro and in total protein derived from temporal and frontal lobe tissue from normal and depressed subjects. The efficiency of the peptide to block the D1-D2 heteromeric complex was comparable in all the samples tested.