The distribution of exogenous
45Ca in the focal ischemia rat model (middle cerebral artery occlusion) was studied using
45Ca autoradiography. High
45Ca accumulations were observed in the frontal cortex and caudate-putamen corresponding with morphological damage shown by HE staining. Regional
45Ca concentrations were calculated from the optical density on the
45Ca autoradiograms. Rapid uptake of
45Ca in the ischemic brain occurred during the first 5 hours, and continued more slowly between 5 and 24 hours after ischemia. The area of
45Ca accumulation was also expanded between 5 and 24 hours. An area of low
45Ca concentration around the area of high accumulation developed 5 hours after ischemia, which presumably accumulated
45Ca between 5 and 24 hours after ischemia. The lower concentration of
45Ca in the periphery of ischemia may result from: 1) a decrease in the total amount of calcium due to narrowing of extracellular space accompanied by cytotoxic edema, and 2) delayed accumulation of exogenous
45Ca due to reduced clearance of extracellular fluid.
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