Abstract
After stroke, the brain has shown to be able to achieve spontaneous functional recovery despite severe cerebral damage. This phenomenon is poorly understood. To address this issue, focal transient ischemia was induced by 60 min middle cerebral artery occlusion in Wistar rats. The evolution of stroke was followed using two magnetic resonance imaging modalities: diffusion spectrum imaging (acquired before, one and four weeks after stroke) and functional magnetic resonance imaging (acquired before and five weeks after stroke). To confirm the imaging observations, immunohistochemical staining for myelin, astrocytes and macrophages/microglia was added. At four weeks after stroke, a focal alteration of the diffusion anisotropy was observed between the ipsilesional ventricle and the lesion area. Using tractography this perturbation was identified as reorganization of the ipsilesional internal capsule. Functional imaging at five weeks after ischemia demonstrated activation of the primary sensorimotor cortex in both hemispheres in all rats except one animal lacking a functional response in the ipsilesional cortex. Furthermore, fiber tracking showed a transhemispheric fiber connection through the corpus callosum, which-in the rat without functional recovery-was lost. Our study shows the influence of the internal capsule reorganization, combined with inter-hemispheric connections though the corpus callosum, on the functional activation of the brain from stroke. In conclusion, tractography opens a new door to non-invasively investigate the structural correlates of lack of functional recovery after stroke.
Highlights
In the Western civilization, stroke is a leading cause of mortality and significant morbidity, leaving many survivors permanently disabled
Value (ROIipsi) was observed in all ischemic animals except one rat that had a very small infarct in the caudate putamen. This area of high generalized fractional anisotropy (gFA) was localized between the ipsilesional lateral ventricle and the ischemic territory in the caudate putamen
Using generalized fractional anisotropy and fiber tracking, we have been able to follow the cerebral dynamics reflected by structural reorganizations during a month following stroke
Summary
In the Western civilization, stroke is a leading cause of mortality and significant morbidity, leaving many survivors permanently disabled. The brain appears to be able to compensate the tissue damage induced by stroke and to achieve partial or sometimes even complete functional recovery [1,2]. Functional and structural brain reorganization has been observed in human and animal studies [1,3]. During a chronic phase after stroke, changes in long-term potentiation (LTP), axonal regeneration as well as sprouting and synaptogenesis can induce cerebral reorganization [1]. This cerebral reorganization may well be the origin of the functional recovery. An adaptation of the neuronal networks, possibly combined with structural rearrangements, must be considered the basis of this functional recovery
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
