Thinning, movement, and volume loss of residual cortical tissue occurs after stroke in the adult rat as identified by histological and magnetic resonance imaging analysis

Plasticity of residual cortical tissue has been identified as an important mediator of functional post-stroke recovery. Many studies have been directed toward describing biochemical, electrophysiological, and cytoarchitectural changes in residual cortex and correlating them with functional changes. Additionally, after neonatal stroke the thickness of residual tissue can change, the tissue can move, and tissue can fill in the stroke core. The purpose of the present study was to systematically investigate and document possible gross morphological changes in peri-infarct tissue after forelimb motor cortex stroke in the adult rat. Rats received a unilateral forelimb motor cortex stroke of equivalent size by pial strip devascularization or photothrombotic occlusion and were then examined using histology or magnetic resonance imaging (MRI) at 1 h, 1, 3, 7, 14, or 31 days post-stroke. Middle cerebral artery occlusion was used as a control stroke procedure. Decreases in cortical thickness, volume, and neural density were found to extend far beyond the stroke infarct and included most of the sensorimotor regions of the stroke and intact hemispheres. Movement of residual tissue towards the infarct was observed and confirmed using anatomical markers placed in intact cortical tissue at the time of stroke induction. The results are discussed in relation to the idea that extensive time-dependent morphological changes that occur in residual tissue must be considered when evaluating plasticity-related cortical changes associated with post-stroke recovery of function.