In Situ Hybridization of Adenosine Receptors in Brain

Abstract

Recent progress in molecular biology of receptors has led to the cloning of the different adenosine receptors subtypes. Indeed, the A1 and A2a receptors, and more recently the A2b and A3 receptors, have been cloned in several species [1]. In the late 1980s, the technique of receptors cloning using the polymerase chain reaction (PCR) and degenerated oligonucleotides led to the identification of some already known receptors and to the discovery of new but orphan receptors, in quest for their ligands [2]. Since study of their distribution may help in their identification, it was taken advantage of by using the in situ hybridization technique to localize in the brain [3–5] the mRNAs encoding two orphan receptors, RDC7 and RDC8, which belong to the G-protein–coupled receptor superfamily. Based on these established distributions [3–5], RDC7 and RDC8 were definitively identified and pharmacologically characterized as the canine A1 [6] and A2a [6,7] adenosine receptors, respectively. The cloning of these canine A1 and A2a receptors, identified using in situ hybridization as a key technique, further allowed their cloning in different species and the cloning of the other adenosine receptors subtypes [1].