1. ¹Department of Preclinical and Clinical Pharmacology, University of Florence, Florence, Italy
2. ²Santa Lucia Foundation, and Department of Neuroscience, University of Rome Tor Vergata, Rome, Italy
3. ³Department of Preclinical and Clinical Pharmacology, University of Florence, Florence, Italy
4. ⁴Department of Histology, University of Florence, Florence, Italy
5. ⁵Institute of Neurobiology and Molecular Medicine – CNR, and Santa Lucia Foundation, Rome, Italy
6. ⁶Department of Neuroscience, University of Rome Tor Vergata, and Santa Lucia Foundation, Rome, Italy
7. ⁷Department of Preclinical and Clinical Pharmacology, University of Florence, Florence, Italy
8. ⁸Department of Neuroscience, University of Rome Tor Vergata, and Santa Lucia Foundation, Rome, Italy

Correspondence: Professor G Sancesario, Department of Neuroscience, University of Rome Tor Vergata, Via Montpellier 1, 00133 Rome, Italy. E-mail: sancesario@med.uniroma2.it

Received 22 July 2005; Revised 2 October 2005; Accepted 23 October 2005; Published online 4 January 2006.

Abstract

Adenosine 5'-triphosphate outflow increases after an ischemic insult in the brain and may induce the expression of P2X₇ receptors in resting microglia, determining its modification into an activated state. To assess the effects of P2X₇ receptor blockade in preventing microglia activation and ameliorating brain damage and neurological impairment, we delivered the P2 unselective antagonist Reactive Blue 2 to rats after middle cerebral artery occlusion. In sham-operated animals, devoid of brain damage, double immunofluorescence verified the absence of P2X₇ immunoreactivity on resting microglia, astrocytes, and neurons, identified, respectively, by OX-42, glial fibrillary acid protein, and neuronal nuclei (NeuN) immunoreactivity. After ischemia, vehicle-treated rats showed monolateral sensorimotor deficit and tissue damage in striatum and frontoparietal cortex. Moreover, P2X₇ immunoreactivity was de novo expressed on activated microglia in infarcted and surrounding areas, as well as on a reactive form of microglia, resting in shape but P2X₇ immunoreactive, present in ipsi- and contralateral cingulate and medial frontal cortex. Reactive Blue 2 improved sensorimotor deficit and restricted the volume of infarction, without preventing the expression of P2X₇, but inducing it in the microglia of contralateral frontal and parietal cortex and striatum, which had lost reciprocal connections with the remote infarct area. De novo expression of P2X₇ occurred in both activated and reactive microglia, suggesting their differentiated roles in the area of infarct and in remote regions. Reactive Blue 2 reduced ischemic brain damage, likely blocking the function of activated microglia in the infarct area, but in the remote brain regions promoted the expression of P2X₇ on reactive microglia, developing defense and reparative processes.