New patterns of intracortical projections after focal cortical stroke

Cortical strokes alter functional maps but associated changes in connection s have not been documented. The neuroanatomical tracer biotinylated dextran amine (BDA) was injected into cortex bordering infarcts 3 weeks after foca l strokes in rat whisker barrel (somatosensory) cortex. The mirror locus in the opposite hemisphere was injected as a control. After 1 week of surviva l, brains were processed for cytochrome oxidase (CO)-, Nissi-, and BDA-labe led neurons. Cortex bordering the infarct (peri-infarct cortex) had abnorma l CO and Nissl structure. BDA-labeled neurons were plotted and projections were analyzed quantitatively. Animals with small strokes had intracortical projections, arising from peri-infarct cortex, not seen in normal hemispher es: the overall orientation was statistically significantly different from and rotated 157 degrees relative to the controls. Compared to the controls, significantly fewer cells were labeled in the thalamus. Thus, after focal cortical stroke, the peri-infarct cortex is structurally abnormal, loses th alamic connections, and develops new horizontal cortical connections by axo nal sprouting. (C) 2001 Academic Press.