Proteins of the Brain Extracellular Fluid: Evidence for Release of S‐100 Protein

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Abstract
Extracellular protein fractions were obtained by mild, isotonic irrigation of freshly perfused brain tissue; by collection of proteins released into superfusing medium by physiologically viable slices of rat hippocampus; and by sampling the CSF of anesthetized rats. Analysis of the S-100 protein content of these fractions gave values of 2.8, 4.2, and 1.8 .mu.g S-100/mg protein, respectively. These values were 3- to 6-fold higher than the S-100 content of the soluble cytoplasmic protein fractions from the same tissue. S-100 is selectively released into the extracellular spaces of the brain. Apparently, the biological function of this CNS protein may involve intercellular transfer.