Chronic lesion development
Monitoring stroke over several months
The knowledge base of MRI characterization of the cerebral ischemic lesion evolution has been critically analyzed. Up to now, the chronic phase of lesion development during weeks following stroke onset had received rather little attention and has therefore been unsufficiently characterized. We have followed stroke now over several months. Characterization of the chronic lesion evolution is important as regeneration is expected to unfold as a longterm process.
Two types of ischemic lesion
For induction of stroke, occlusion of the middle cerebral artery (MCAO) for 60 min using the the intraluminal filament technique was used in male Wistar rats. Two basically different types of lesion were noted:
Type I consisted of exclusively subcortical damage, while type II, encompassed a cortico-subcortical lesion territory.
Following the lesion over 10 weeks, a primary hyperintensity on T2-weighted MR images was consistently observed during the first week, followed by a T2 normalization in both lesion types.
Distinct patterns in behavior testing
Combination with sensorimotoric behavior tests demonstrated that animals with type I lesions showed no behavior deficit. Animals with type II lesions, on the other hand, resulted in profound behavioral deficits.
Using histological analysis we could demonstrate that the fiber tracts through the striatum characterized by selective neuronal death and gliosis remained intact. This may account for the significantly better prognosis regarding functional deficits.
Ring model: ischemic core and penumbra
In collaboration with Per Wester from Umea, Sweden, we have established the photothrombotic ring model in the rat. This model produces a well defined ischemic core and a distinct peripheral region (penumbra) by virtue of this ring-wise illumination. Hereby, the penumbra is represented by the “donut hole” of the lesion. The core is formed by the ring-shaped torus of the illuminated tissue.
The lesion evolution has been characterized with multiple MRI parameters and histological, biochemical and autoradiographic imaging techniques. Thus, we could, on the one hand, describe the acute time window of the first 6 hours following the lesion induction, and, on the other hand, the window of the chronic evolution phase during the following two weeks.
Understanding the potential for functional recovery
These studies above are the basis for further investigations for the specific behavior of ischemic penumbra and core region and for the postulated spontaneous cortical neurogenesis. Both aspects are essential for the understanding of the potential for functional recovery. Therefore, we are planning combined fMRI and behavior studies for this specific stroke model.