Possible involvement of P2X7 receptor activation in microglial neuroprotection against focal cerebral ischemia in rats

Microglia play important roles in the pathogenic cascade following cerebral ischemia, since they express growth factors, chemokines and regulatory cytokines as well as free radicals and other toxic mediators. P2X(7) receptor, a subtype of a family of P2 purinoceptors, is primarily expressed in microglia and macrophages, suggesting that it regulates immune function and inflammatory responses. However, the involvement of ATP in such microglial responses after cerebral ischemia is not yet understood. In this study, we investigated the possible involvement of ATP, especially through the P2X(7) receptors, in a rat model of focal cerebral ischemia. In immunohistochemical analysis, P2X(7) receptor-like immunoreactivity was predominantly detected in microglia, and then activated microglia accumulated in the ischemic region, in rats subjected to middle cerebral artery occlusion (MCAO) and reperfusion. Intracerebroventricular injection with P2X(7) receptor agonist 2'-3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP) improved behavioral dysfunction accessed by rota-rod test and ischemic neural injury induced by MCAO. In contrast, P2X(7) receptor antagonist adenosine 5'-triphosphate-2',3'-dialdehyde (OxATP) exacerbated ischemic brain damage. These results suggest that microglia play an important role in neuroprotection against rat cerebral ischemia, which is regulated by a P2X(7) receptor-mediated ATP signal.