Long-term effects of sequential cortical infarcts on scar size, brain volume and cognitive function

Focal ischemia induces long-term pathophysiological consequences in widespread brain areas. Here we analyzed long-term effects of sequential cortical lesions on brain volume and cognitive function. Rats received either single photothrombotic lesions in the forelimb sensorimotor cortex (SL) or two lesions in sequence either immediately (DL0), 2 days (DL2), 7 days (DL7), or 10 days (DL10) after the first surgery in the homotopic contralateral area. Infarct and global brain volume were measured 7 days (SL and DL2 groups) and one month (all groups) after the last period of ischemia. In the weeks following a stroke, the single lesion shrank considerably. This shrinkage was accentuated by a further lesion received either earlier or later. Thirty-one days after obtaining the second lesion, the lesion scars on both sides had a mean volume of 5.8 +/- 2.3 mm3 in DL2 as compared to 8.5 +/- 3.5 mm3 in SL-animals. In addition, there was a super-additive loss of residual brain volume by 2.2-8.0% in each hemisphere in animals with sequential lesions. In the watermaze, this loss of brain volume corresponded to a slight but significant impairment in performance. The present study revealed a complex interaction of lesions in animals with sequential strokes associated with global reduction of brain volume and cognitive impairment indicating degenerative processes beyond the lesions itself.