Extracellular Brain Space Measured by S35 Sulfate

Abstract

Introduction Electron miscroscopic studies of the central nervous system have emphasized the virtual absence of detectable extracellular spaces. 1-4 These observations have provoked dissatisfaction with the chloride ion as an indicator of the extracellular space of brain. Calculations based on the assumption that chloride is entirely extracellular would indicate a compartment amounting to approximately 30% of brain weight. 5 Although an extracellular space of this order of magnitude is clearly untenable, it seems to us that it is equally unreasonable to interpret the electron photomicrographs too literally and thus conclude that there is essentially no fluid outside of cellular membranes. Resolution of these widely different findings is important to the understanding of the transfer of substances into brain as well as such neuropathologic phenomena as cerebral edema. A more satisfactory indicator of extracellular brain water is required and we have investigated the sulfate ion with this in view. S 35