The Ying and Yang of Adenosine A 1 and A 2A Receptors on ERK1/2 Activation in a Rat Model of Global Cerebral Ischemia Reperfusion Injury.

Adenosine impacts cerebral ischemia reperfusion (IR) through the inhibitory A1 and the excitatory A2 receptors. The present study aimed at investigating the contrasting role of pERK1/2 in mediating adenosine A1 R (protective) versus A2A R (deleterious) effects in IR. Male Wistar rats subjected to bilateral carotid occlusion (45 min) followed by reperfusion (24 h) exhibited increased pERK1/2 activity, downstream from DAG pathway, along with increases in hippocampal glutamate, c-Fos, NF-κB, TNF-α, iNOS, TBARS, cytochrome c, caspase-3, BDNF, Nrf2, and IL-10 contents. Further, hippocampal microglial reactivity, glial TNF-α, and BDNF expression were observed. Although unilateral intrahippocampal injection of either the A1 R agonist CHA or the A2A R agonist CGS21680 increased pERK1/2, only CHA mitigated histopathological and behavioral deficits along with reducing glutamate, microglial activation, c-Fos, TNF-α, iNOS, TBARS, cytochrome c and caspase-3 and elevating Nrf2 and IL-10 levels in IR rats. These results yield insight into the double-faceted nature of pERK1/2 in mediating protective and deleterious effects of A1 R and A2A R signaling, respectively, against IR injury.