Mechanism of detection of acute cerebral ischemia in rats by diffusion-weighted magnetic resonance microscopy.
OBJECTIVE
The aim of this study was to measure apparent diffusion coefficients in rat brain tissue exposed to ouabain, glutamate, and N-methyl-D-aspartate and to compare them with apparent diffusion coefficients found in acute cerebral ischemia.


METHODS
The apparent diffusion coefficient was measured using magnetic resonance microscopy in four groups of Sprague-Dawley rats after occlusion of the right middle cerebral artery and ipsilateral common carotid artery (n = 7), after ouabain exposure (n = 6), during glutamate exposure (n = 7), or during N-methyl-D-aspartate exposure (n = 3). Ouabain, glutamate, and N-methyl-D-aspartate were applied via an intracerebrally implanted microdialysis membrane.


RESULTS
Three hours after the induction of focal cerebral ischemia, a 33% reduction in the apparent diffusion coefficient was observed in the right dorsolateral corpus striatum and olfactory cortex. After ouabain exposure, reductions in the apparent diffusion coefficient were observed within a 1,500-microns radius of the microdialysis membrane. Quantitative analysis revealed that apparent diffusion coefficient values in ischemic and ouabain-exposed tissue fell within the same range. Glutamate and N-methyl-D-aspartate reduced the brain tissue apparent diffusion coefficient by 35% and 40%, respectively.


CONCLUSIONS
On the basis of these findings, we conclude that ischemia-induced apparent diffusion coefficient reductions are likely caused by a shift of extracellular to intracellular water.
Benveniste
H
H
Department of Radiology, Duke University Medical Center, Durham, N.C. 27710.
Hedlund
L W
LW
Johnson
G A
GA
D000208:Acute Disease; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D002545:Brain Ischemia / Q000175:diagnosis* / Q000378:metabolism; D004058:Diffusion; D005260:Female; D005971:Glutamates / Q000494:pharmacology; D018698:Glutamic Acid; D008279:Magnetic Resonance Imaging / Q000379:methods*; D016202:N-Methylaspartate / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013194:Staining and Labeling
D005971:Glutamates; D018698:Glutamic Acid; D010042:Ouabain; D016202:N-Methylaspartate