In the gray matter of the adult central nervous system, a homogeneous positive periodic acid-Schiff reaction occurs in the spaces between the cells, dendrites, axon terminations, and neuroglia fibers. On the basis of histochemical tests, this reaction has been ascribed tentatively to the presence of a neutral mucopolysaccharide (Hess,10 1953) and has been regarded as demonstrating an intercellular ground substance of the adult central nervous system. The existence and finding of this reaction prompted the suggestion that "the presence of a ground substance of a carbohydrate-protein nature might well deserve attention when considering the problem of the penetration of substances into the central nervous system and the properties of the blood-brain barrier" (Hess10).
In an attempt to test this hypothesis, experiments were performed correlating the time of appearance of the ground substance of the central nervous system and the development of the blood-brain barrier.
The ground substance is
HESS A. Blood-Brain Barrier and Ground Substance of Central Nervous System: Similarities in Development. AMA Arch NeurPsych. 1955;73(4):380–386. doi:10.1001/archneurpsyc.1955.02330100012003
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