SPREADING WAVES OF A REDUCED DIFFUSION-COEFFICIENT OF WATER IN NORMALAND ISCHEMIC RAT-BRAIN

Using echo planar diffusion-weighted magnetic resonance imaging, we me asured three-dimensional changes in the apparent diffusion coefficient (ADC) of water in eight contiguous coronal slices, encompassing the e ntire rat brain, before and after local cortical stimulation. We appli ed chemical (potassium chloride application; n = 6) and mechanical (ne edle stab; n = 4) stimulations to the right posterior parietal rat cor tex. In all animals in which potassium chloride or the needle stab was applied, a region of decreased ADC values to a mean of 0.45 +/- 0.03 x 10(-5) cm(2)/s occurred. These reduced ADC levels appeared in the po sterior parietal cortex within 1 min after cortical stimulation and th e change recovered within 1 min. Then a ripple-like movement of simila r changes developed across the unilateral cortex. This change was loca lized to the cortex and no significant ADC changes occurred in subcort ical structures. The propagating speed of this movement was 3.4 +/- 0. 5 mm/min. These findings are compatible with spreading depression as o bserved electrophysiologically. Similar ADC changes occurred in areas distinct from the ischemic lesion in 3 of 12 animals subjected to foca l cerebral ischemia. This magnetic resonance method could detect sprea ding ADC decline if it occurred in human diseases including brain isch emia.