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The mechanism of coupling between neurons and the microvasculature continues to remain unclear. This was examined during potassium-induced spreading depression (SD), since SD is thought to be a phenomenon of local neuronal depolarization in association with flow changes. In α-chloralose-urethane anesthetized rats, a new optical method was employed by which both the light transparency (LT) changes of the somatosensory cortex as well as its associated capillary-level flow were measured simultaneously in a region of interest (ROI; 2×2 mm) of the sensorimotor cortex. Microinjection of concentrated potassium chloride solution into the cortex produced spreading depression which was observed as a function of time and space, with attention given to the increase and decrease in wave-rings marked by cortical LT variance. The wave-ring was observed to enlarge at a speed of ca. 2.2 mm/min and approximately 1–2 min later, a new wave-ring appeared. This cycle continued repeatedly for more than 30 min. The study was performed on seven rats, with ring propagation in three, an abortive form in another three, and no rings in one rat. In a 3-D microflow map produced by intracarotid injection of diluted carbon black (CB) (Pelikan Werke, Germany) in Ringer solution, a low-flow ring was approximately collocated at the wave-front ΔLT ring, followed by a flow increase. A close correlation between topographical microflow changes and LT changes indicates that local depolarization of the neurons induces an immediate decrease followed rapidly by an increase in microflow, suggesting that the depolarized neurons induced changes in adjacent microvascular (capillary) flow. |
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