Decreased cerebral blood flow, hence decreased oxygen and glucose, leads to ischemic brain injury via complex pathophysiological events, including excitotoxicity, mitochondrial dysfunction, increased intracellular Ca 2+ , and reactive oxygen species (ROS) generation. Each of these could also contribute to cerebral edema, which is the primary cause of patient mortality after stroke. In vitro brain slices are widely used to study ischemia. Here we introduce a slice model to investigate ischemia-induced edema. Significant water gain was induced in coronal slices of rat brain by 5 min of oxygen and glucose deprivation (OGD) at 35°C, with progressive edema formation after return to normoxic, normoglycemic medium. Edema increased with increasing injury severity, determined by OGD duration (5-30 min). Underlying factors were assessed using glutamate-receptor antagonists (AP5/CNQX), blockade of mitochondrial permeability transition [cyclosporin A (CsA) versus FK506], inhibition of Na + /Ca 2+ exchange (KB-R7943), and ROS scavengers (ascorbate, Trolox Ò , dimethylthiourea, Tempol Ò ). All agents except KB-R7943 and FK506 significantly attenuated edema when applied after OGD; KB-R7943 was effective when applied before OGD. Significantly, complete prevention of ischemia-induced edema was achieved with a cocktail of AP5/CNQX, CsA and Tempol Ò applied after OGD, which demonstrates the involvement of multiple, additive mechanisms. The efficacy of this cocktail further shows the potential value of combination therapies for the treatment of cerebral ischemia.

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Increasing evidence implicates reactive oxygen species, particularly hydrogen peroxide (H(2)O(2)), as intracellular and intercellular messengers in the brain. This raises the question of how the antioxidant network in the brain can be sufficiently permissive to allow messages to be conveyed yet, at the same time, provide adequate protection against oxidative damage. Here we present evidence that this is accomplished in part by differential antioxidant compartmentalization between glia and neurons. Based on the rationale that the glia-to-neuron ratio is higher in guinea-pig brain than in rat brain, we examined the neuroprotective role of the glial antioxidant network by comparing the consequences of elevated H(2)O(2) in guinea-pig and rat brain slices. The effects of exogenously applied H(2)O(2) on evoked population spikes in hippocampal slices and on edema formation in forebrain slices were assessed. In contrast to the epileptiform activity observed in rat hippocampal slices after H(2)O(2) exposure, no pathophysiology was seen in guinea-pig hippocampal slices. Similarly, elevated H(2)O(2) caused edema in rat brain slices, whereas this did not occur in guinea-pig brain tissue. The resistance of guinea-pig brain tissue to H(2)O(2) challenge was lost, however, when glutathione (GSH) synthesis was inhibited (by buthionine sulfoximine), GSH peroxidase activity was inhibited (by mercaptosuccinate), or catalase was inhibited (by 3-amino-1,2,4,-triazole). Strikingly, exogenously applied ascorbate, a predominantly neuronal antioxidant, was able to compensate for loss of any other single component of the antioxidant network. Together, these data imply significant roles for glial antioxidants and neuronal ascorbate in the prevention of pathophysiological consequences of the endogenous neuromodulator, H(2)O(2).

Binding of the peripheral benzodiazepine receptor ligand, [3H]‐PK 11195, to rat hippocampal membranes has been used to quantify the reactive gliosis resulting from neuronal death induced by intraperitoneally administered kainic acid. Intraperitoneal administration of kainic acid (10 mg kg−1) caused a 350–500% increase in [3H]‐PK 11195 binding measured in rat hippocampal P2 membranes 7 days later. Co‐treatment with the adenosine derivative R‐phenylisopropyladenosine (R‐PIA) (100, 25 or 10 μg kg−1, i.p.) abolished this elevation. The protective action of R‐PIA could itself be abolished by co‐treatment with 8‐phenyltheophylline (1 mg kg−1). Body temperatures were recorded in the antagonist experiments and no significant changes were recorded, suggesting that the protective action of R‐PIA was not mediated by hypothermia. Since systemic kainic acid‐induced neurotoxicity has been claimed as a good model of neuronal death in temporal lobe epilepsy, the results suggest that the systemic administration of purines in low doses may provide protection against certain neurodegenerative insults.