Background and Purpose Parkinson's disease (PD) involves an initial loss of striatal dopamine terminals evolving into degeneration of dopamine neurons in substantia nigra (SN), which can be modelled by 6‐hydroxydopamine (6‐OHDA) administration. Adenosine A2A receptor blockade attenuates PD features in animal models, but the source of the adenosine causing A2A receptor over‐activation is unknown. As ATP is a stress signal, we have tested if extracellular catabolism of adenine nucleotides into adenosine (through ecto‐5′‐nucleotidase or CD73) leads to A2A receptor over‐activation in PD. Experimental Approach Effects of blocking CD73 with α,β‐methylene ADP (AOPCP) were assayed in 6‐OHDA‐treated rats and dopamine‐differentiated neuroblastoma SH‐SY5Y cells. Key Results 6‐OHDA increased ATP release and extracellular conversion into adenosine through CD73 up‐regulation in SH‐SY5Y cells. Removing extracellular adenosine with adenosine deaminase, blocking CD73 with AOPCP, or blocking A2A receptors with SCH58261 were equi‐effective in preventing 6‐OHDA‐induced damage in SH‐SY5Y cells. In vivo striatal exposure to 6‐OHDA increased ATP release and extracellular formation of adenosine from adenosine nucleotides and up‐regulated CD73 and A2A receptors in striatal synaptosomes. Intracerebroventricular administration of AOPCP phenocopied effects of SCH58261, attenuating 6‐OHDA‐induced (a) increase of contralateral rotations after apomorphine, (b) reduction of dopamine content in striatum and SN, (c) loss of TH staining in striatum and SN, (d) motor dysfunction in the cylinder test, and (e) short‐term memory impairment in the object recognition test. Conclusion and Implications Our data indicate that increased ATP‐derived adenosine formation is responsible for A2A receptor over‐activation in PD, suggesting CD73 as a new target to manage PD.

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Brain ischemia pathophysiology involves a complex cascade of events such as inflammation and oxidative stress that lead to neuronal loss and cognitive deficits. Caffeic acid (CA) is a natural phenolic compound with antioxidant and anti-inflammatory properties. To evaluate the neuroprotective efficacy of this compound in mice subjected to a permanent middle cerebral artery occlusion, animals were pretreated and post-treated with CA, 2, 20, and 60 mg/kg/day, intraperitoneally, at 24, 48, 72, 96, or 120 h after ischemia. Animals were evaluated at 24 h after the permanent middle cerebral artery occlusion for brain infarction and neurological deficit score. At 72 h after the occlusion, animals were evaluated for locomotor activity, working memory, and short-term aversive memory; long-term aversive memory was evaluated 24 h after the evaluation of short-term aversive memory. Finally, at 120 h after the event, spatial memory and the expression levels of synaptophysin (SYP), SNAP-25, and caspase 3 were evaluated. The treatment with CA reduced the infarcted area and improved neurological deficit scores. There was no difference in locomotor activity between groups. The working, spatial, and long-term aversive memory deficits improved with CA. Furthermore, western blotting data showed that the expression of SYP, which correlates with synaptic formation and function, decreased after ischemic insult, and CA inhibited the reduction of SYP expression. Ischemia also increased, and CA treatment decreased, caspase 3 expression. These results suggest that CA exerts neuroprotective and antidementia effects, at least in part, by preventing the loss of neural cells and synapses in ischemic brain injury.