FOR MORE than a decade, an unexplained disparity has existed between the values for extracellular space in the cerebral cortex obtained by different methods. Electron microscopy of thin sections has revealed, with rare exceptions, a space between cells or cell processes measuring only 150 to 200 Angstrom wide.1-5 More recently, localized obliterations of even this small gap by the formation of so-called tight junctions6-8 has been described. Calculations based on measurement of the cortical extracellular space in electron micrographs9 yield a maximum value of 5% for this compartment as a fraction of total cortical volume. Not only has a consistent average value of 200 A for the width of the intercellular gap been measured in electron micrographs of normal cerebral cortex fixed and embedded in various ways, but brain slices incubated in vitro10,11show astrocytic swelling without change in the dimensions of the extracellular space. A
HARTMANN JF. High Sodium Content of Cortical Astrocytes: Electron Microscopic Evidence. Arch Neurol. 1966;15(6):633–642. doi:10.1001/archneur.1966.00470180073008
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