Magnetic resonance imaging of temporal changes of neurotoxic lesion in the rat

Destruction of striatal neurons in the rat brain, induced by intracerebral injection of N-methyl D-aspartic acid (NMDA), has been visualized noninvasively by magnetic resonance imaging (MRI). The changes in images were monitored from 12 h to one month after the stereotaxic microinfusion of NMDA (10 μg in 0.4 μl) into the striatum, using a T₂- weighted rapid acquisition by relaxation enhancement (RARE) sequence. A localised hyperintense (bright) area was visible after 12 h at the site of the injection, and it persisted for the next three days. The size of the hyperintense area decreased thereafter and, after one week, the increased brightness was restricted to the lateral ventricle. Post-mortem histological examination, done after one month, showed a dilated lateral ventricle. The size and location of the lesioned area, identified in histological sections, corresponded to the hyperintense area observed during these initial days after NMDA lesion. The present study demonstrates that noninvasive MRI techniques, using a typical RARE sequence, offer a powerful tool for the early detection of neurotoxic lesion of the brain area, although some caution is required in its use for estimating the size of the lesioned area three days after its formation. The present findings indicate that, in long-term studies, alterations of the neighbouring structures, such as enlargement of the ventricular system, may confound the MRI evaluation of neurotoxic lesions in vive.