Effects of the adenosine A2A receptor antagonist SCH 58621 on cyclooxygenase-2 expression, glial activation, and brain-derived neurotrophic factor availability in a rat model of striatal neurodegeneration

Inhibition of adenosine A(2A) receptors (A(2A)Rs) is neuroprotective in several experimental models of striatal diseases. However, the mechanisms elicited by A(2A)R blockade are only partially known, and critical aspects about the potential beneficial effects of A(2A)R antagonism in models of neurodegeneration still await elucidation. In the present study, we analyzed the influence of the selective A(2A)R antagonist SCH 58261 in a rat model of striatal excitotoxicity obtained by unilateral intrastriatal injection of quinolinic acid (QA). We found that SCH 58261 differently affected the expression of cyclooxygenase-2 (COX-2) induced by QA in cortex and striatum. The antagonist enhanced COX-2 expression in cortical neurons and prevented it in striatal microglia-like cells. Similarly, SCH 58261 differently regulated astrogliosis and microglial activation in the 2 brain regions. In addition, the A(2A)R antagonist prevented the QA-induced increase in striatal brain-derived neurotrophic factor levels. Because COX-2 activity has been linked to excitotoxic processes and because brain-derived neurotrophic factor depletion has been observed in mouse models as well as in patients with Huntington disease, we suggest that the final outcome of A(2A)R blockade (namely neuroprotection vs neurodegeneration) is likely to depend on the balance among its various and region-specific effects.