Sustained Decrease and Remarkable Increase in Red Blood Cell Velocity in Intraparenchymal Capillaries Associated With Potassium-Induced Cortical Spreading Depression

Objectives: To examine changes in red blood cell (RBC) velocity in intraparenchymal capillaries of rat cerebral cortex in response to KCl-induced cortical spreading depression (CSD). Methods: In isoflurane-anesthetized rats, the velocity of fluorescently labeled RBCs flowing in capillaries in layer I was measured with a high-speed camera laser-scanning confocal fluorescence microscope, with simultaneous monitoring of DC potential, the electroencephalogram (EEG), partial pressure of oxygen (PO ₂), and cerebral blood flow (CBF). Results: After KCl application, a transient deflection of DC potential (i.e., CSD) repeatedly appeared concomitantly with depression of EEG, and was propagated in the distal direction. PO ₂ transiently decreased and CBF was slowly elevated. The frequency distribution of RBC velocity was shifted downward during CSD and was still low after the passage of CSD. When we observed RBC velocity in 38 individual capillaries, 10 capillaries exhibited slowed-down RBC during CSD and RBC velocity remained low in 2 even after the passage of CSD. On the other hand, RBCs with moderately (<3mm/sec) or remarkably (>3mm/sec) increased velocities were seen in 10 and 5 capillaries, respectively. Conclusion: CSD-induced excitation of neurons may sustainably decrease or greatly increase RBC velocity in capillaries.