Stimulation of adenosine A1 receptors decreases in vivo dopamine D1 receptor binding of [11C]SCH23390 in the cat striatum revealed by positron emission tomography.

It has been previously suggested that activation of adenosine A1 receptor modulates dopamine D1 receptor binding in vitro, although the direct mechanism of this interaction in vivo has not yet been demonstrated. Here, we conducted a positron emission tomography (PET) study to demonstrate in vivo the interaction between these receptors. The specific adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) was acutely administered to cats under anesthetized condition. Cats underwent repeated measurement of striatal and cerebellar radioactivity following intravenous injection of dopamine D1 receptor-specific [11C]SCH23390. The pretreatment with CPA decreased the striatum/cerebellum ratio of the uptake of [11C]SCH23390. Using the cerebellar radioactivity as an input function, kinetic analysis was performed and demonstrated that CPA caused about 40% decrease in the association rate constant. These results suggest that stimulation of adenosine A1 receptors modulates dopamine D1 receptor binding in vivo.