Modifications in the contralateral “healthy” hemisphere in a population of rats bearing cortical infarction were studied in vivo by magnetic resonance imaging (MRI) with the aim to investigate whether cerebral areas not directly involved in the lesion react at the presence of an ischemic lesion. The study was performed in rats in which a transtemporal approach was adopted to occlude the right middle cerebral artery (MCA). For MRI, the animals were examined at 4.7 Tesla and quantitative T2 parametric images were obtained by a multiecho sequence. Healthy rats and sham-operated animals were used as control groups. The quantitative T2 parametric images showed that in the first week after the ischemia a significant increase in the mean T2 was seen in the lesioned parietal cortex, compared to the corresponding region of healthy rats (106 msec vs. 68 msec, P < 0.001). The contralateral “healthy” hemisphere showed T2 mean values not significantly different from the corresponding hemisphere of healthy rats (71 msec vs. 70 msec). However, a statistically significant increase in the T2 values was evident in the hypothalamic region (74 msec vs. 66 msec, P < 0.001). In rats examined 1 month after the ischemia, the T2 values of the hypothalamus were lower than those observed one week after ischemia (69 msec) but remained higher than in controls. The present study demonstrates that after a cerebral ischemia areas of secondary involvement distant from the lesion are present and can be studied in vivo by quantitative MRI.
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