Adenosine receptors are G-protein
coupled P1 purinergic receptors that are broadly expressed in the peripheral
immune system, vasculature, and the central nervous system (CNS). Within the
immune system, adenosine 2A (A2A) receptor-mediated signaling

exerts a suppressive effect on ongoing
inflammation. In healthy CNS, A2A receptors are expressed mainly within the neurons of

the basal ganglia. Alterations in A2A receptor
function and expression have been noted in movement disorders, and in
Parkinson’s

disease pharmacologicalA2A receptor
antagonism leads to diminishedmotor symptoms. AlthoughA2A receptors are expressed only at a low
level in the healthy CNS outside striatum, pathological challenge or
inflammation has been shown to lead to upregulation of A2A receptors in
extrastriatal CNS tissue, and this has been successfully quantitated using in vivo positron emission tomography (PET)
imaging and A2A receptor-binding radioligands. Several radioligands for PET imaging of A2A receptors
have been developed in recent years, and A2A receptor-targeting PET imaging may thus
provide a potential additional tool to evaluate various aspects of neuroinflammation in vivo. This review
article provides a brief overview of A2A receptors in healthy brain and in a selection of most important
neurological diseases and describes the recent advances in A2A receptor-targeting
PET imaging studies.