MAGNETIC-RESONANCE-IMAGING ASSESSMENT OF CEREBRAL HEMODYNAMICS DURINGSPREADING DEPRESSION IN RATS

High-speed magnetic resonance imaging was used to perform simultaneous measurements of relative cerebral blood volume (rCBV) and water diffu sion changes during spreading depression (SD) induced by cortical pota ssium chloride application. Rats were fitted epidurally with a rubber chamber. Potassium chloride was perfused through the cham ber until SD was indicated by a negative direct current (DC) potential shift. Magn etic resonance imaging scans used echo planar diffusion and T2-weighte d images. Iron dextran was injected as a blood pool contrast agent to make subsequent changes in T2 (or T2) directly proportional to change s in CBV. Multislice maps of apparent diffusion coefficient (ADC) and rCBV were generated with 6- to 16-second time resolution, which reveal ed transient ADC and rCBV changes propagating over the cortex after po tassium chloride application. Transient ADC declines appeared simultan eously with the DC shift, whereas rCBV increase followed with a delay of 16.4 +/- 14.9 seconds. Prolonged rCBV decrease was observed after t he initial increase during the SD in half of the animals. The delayed rCBV response after the ADC change supports the observation of increas ed energy demand because of repolarization. Simultaneous DC potential recording and ADC measurements in corresponding sites of the cortex in dicate that transient ADC decreases during SD reflect water shifts ass ociated with cell depolarization.