Adenosine A2A receptors and brain injury:: Broad spectrum of neuroprotection, multifaceted actions and "fine tuning" modulation

This review summarizes recent developments that have contributed to understand how adenosine receptors, particularly A(2A) receptors, modulate brain injury in various animal models of neurological disorders, including Parkinson's disease (PD), stroke, Huntington's disease (HD), multiple sclerosis, Alzheimer's disease (AD) and HIV-associated dementia. It is clear that extracellular adenosine acting at adenosine receptors influences the functional outcome in a broad spectrum of brain injuries, indicating that A(2A)Rs may modulate some general cellular processes to affect neuronal cells death. Pharmacological, neurochemical and molecular/genetic approaches to the complex actions of A(2A) receptors in different cellular elements suggest that A(2A) receptor activation can be detrimental or protective after brain insults, depending on the nature of brain injury and associated pathological conditions. An interesting concept that emerges from these studies is A(2A)R's ability to fine tune neuronal and glial functions to produce neuroprotective effects. While the data presented here clearly highlight the complexity of using adenosinergic agents therapeutically in PD and other neurodegenerative disorders and point out many areas for further inquiry, they also confirm that adenosine receptor ligands, particularly A(2A) receptor ligands, have many promising characteristics that encourage the pursuit of their therapeutic potential. (C) 2007 Published by Elsevier Ltd.