MOLECULAR-CLONING OF THE RAT ADENOSINE-A2 RECEPTOR - SELECTIVE COEXPRESSION WITH D2-DOPAMINE RECEPTORS IN RAT STRIATUM

A cDNA fragment homologous to other G protein-coupled receptors was isolated from rat brain using the PCR method and demonstrated to be abundantly expressed in striatum. Using this fragment as a probe, a 2.1 kb full-length cDNA was isolated from a rat striatal cDNA library. This cDNA encodes a protein of 410 amino acids and is highly homologous to previously isolated adenosine receptor cDNAs. Expression of this cDNA in COS cells revealed high affinity (K(d) = 38.6 nM) and saturable binding of the A2 adenosine receptor-selective ligand [H-3]CGS 21680. Agonist displacement profile of [H-3]CGS 21680 binding was consistent with an adenosine receptor of the A2 subtype (NECA > (R)-PIA > CPA > (S)-PIA). In situ hybridization demonstrated that rat A2 adenosine receptor mRNA was co-expressed in the same striatal neurons as D2 dopamine receptor mRNA, and never co-expressed with striatal D1 dopamine receptor mRNA. Several lines of evidence have previously suggested that dopamine-induced changes in motor behavior can be modulated by adenosine analogs acting at the A2 subtype of adenosine receptor in the forebrain. The co-expression of D2 dopamine and A2 adenosine receptors in a subset of striatal cells provides an anatomical basis for dopaminergic-adenosinergic interactions on motor behavior.