Variable response of the Mongolian gerbil to unilateral carotid occlusion: magnetic resonance imaging and neuropathological characterization

In the present investigation, we estimated both the evolution and the severity of ischemic damage following unilateral carotid occlusion (UCO) in Mongolian gerbils by using conventional magnetic resonance imaging (MRI, i.e. T2 weighted imaging) and histological techniques. Immediately after UCO, the animals showed different clinical effects. The mortality (46%) detected within the first 48h was considered an "stroke-sensitivity", the "stroke-resistant" animals showed wide variability in terms of both temporal evolution and the extent of ischemic damage. The signal hyperintensity and negative MRI observed during the first 30h after UCO did not always correlate with the cerebral damage presented after 14 days, although a close correlation was established between the T2 weighted images taken more than 30h after UCO and neuropathology: the gerbils negative to imaging showed no morphological changes, whereas an enhanced signal was always prognostic of ischemic injury. Moreover, late MRI documented ventricular dilatation. Histopathology showed that the ischemic damage differed among the stroke-resistant gerbils and was often bilateral. The present study confirms the differences in gerbil susceptibility to hemispheric infarction after permanent UCO and suggests that conventional MRI may be a useful non-invasive method for i) identifying the stroke-resistant animals prone to mature ischemic injury and ii) monitoring the evolution of therapeutic efficacy without sacrificing animals.