Adenosine A2A receptor contributes to ischemic brain damage in newborn piglet

Pharmacologic inactivation or genetic deletion of adenosine A_2A receptors protects ischemic neurons in adult animals, but studies in neonatal hypoxia-ischemia (H-I) are inconclusive. The present study in neonatal piglets examined the hypothesis that A_2A receptor signaling after reoxygenation from global H-I contributes to injury in highly vulnerable striatal neurons where A_2A receptors are enriched. A_2A receptor immunoreactivity was detected in striatopallidal neurons. In nonischemic piglets, direct infusion of the selective A_2A receptor agonist CGS 21680 through microdialysis probes into putamen increased phosphorylation of N-methyl-D-aspartic acid (NMDA) receptor NR1 subunit and Na⁺,K⁺-ATPase selectively at protein kinase A (PKA)-sensitive sites. In ischemic piglets, posttreatment with SCH 58261, a selective A_2A receptor antagonist, improved early neurologic recovery and preferentially protected striatopallidal neurons. SCH 58261 selectively inhibited the ischemia-induced phosphorylation of NR1, Na⁺,K⁺-ATPase, and cAMP-regulated phosphoprotein 32 KDa (DARPP32) at PKA-sensitive sites at 3 hours of recovery and improved Na⁺,K⁺-ATPase activity. SCH 58261 also suppressed ischemia-induced protein nitration and oxidation. Thus, A_2A receptor activation during reoxygenation contributes to the loss of a subpopulation of neonatal putamen neurons after H-I. Its toxic signaling may be related to DARPP32-dependent phosphorylation of PKA-sensitive sites on NR1 and Na⁺,K⁺-ATPase, thereby augmenting excitotoxicity-induced oxidative stress after reoxygenation.