Bihemispheric ischemic tolerance induced by a unilateral focal cortical lesion

The purpose of the present study was to determine whether a unilateral photothrombotic brain lesion induces bilateral ischemic tolerance towards a subsequent severe ischemia performed 5 days later. Severe ischemia was induced by transient (1h; t) or permanent (p) occlusion of the middle cerebral artery (MCAO). Rats were sacrificed 24h later. Preconditioning reduced the size of subsequent infarcts in both hemispheres. This effect was most prominent with tMCAO, and ipsilateral preconditioning was more effective than contralateral preconditioning (% of hemispheric volume, mean ± SD: 31.9 ± 3.7 to 19.0 ± 10.3 with ipsilateral tMCAO; 31.9 ± 3.7 to 22.9 ± 4.9 with contralateral tMCAO; 64.7 ± 4.3% to 47.2 ± 12.5% with ipsilateral pMCAO; 64.7 ± 4.3% to 53.1 ± 8.9% with contralateral pMCAO). Ischemic preconditioning was associated with a successive bilateral up-regulation of superoxide dismutases which may be involved in the development of ischemic tolerance. Our data suggest that a focal ischemic brain lesion induces neuroprotective mechanisms in extensive brain areas and thus cause bilateral ischemic tolerance within a certain time window.