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blood-brain barrier[¦bləd ¦brān ′bar·ē·ər]
a physiological mechanism that regulates the exchange of substances between the blood, the cerebrospinal fluid, and the brain.
The concept of the blood-brain barrier was introduced by the Soviet physiologist L. S. Shtern and the Swiss scientist R. Gauthier in 1921. Like other blood-tissue barriers,” the blood-brain barrier performs protective functions by preventing certain foreign substances introduced into the blood or the products of faulty metabolism formed in the body itself from penetrating the central nervous system. The state of the brain and spinal cells, which are particularly sensitive even to slight fluctuations in the composition and physicochemical properties of the environment, depends largely upon the permeability of the blood-brain barrier in the blood-to-brain and brain-to-blood directions. The idea of the blood-brain barrier as a single mechanism is being reexamined. A complex and varied system of specific formations has been found to function in the brain. The anatomical, physiological, physicochemical, and biological characteristics of these formations ensure their barrier properties. Various substances needed for the nutrition and activity of neural formations, which differ both in structure and in chemical composition, penetrate from the blood into the central nervous system through various sections of the blood-brain barrier. The walls of the brain capillaries and precapillaries and the vascular plexuses of the cerebral ventricles, neuroglia, and meninges constitute the anatomical elements of the blood-brain barrier. The so-called ground substance, which is found between the cells of the capillary walls and which consists of complexes of proteins and polysaccharides, plays an important part in the performance of the barrier functions. The condition of this substance largely determines the permeability of the blood-brain barrier.
Stains, salts, organic and inorganic compounds, and radioactive isotopes of phosphorus, iodine, and bromine are used to investigate the state of the blood-brain barrier.
The blood-brain barrier prevents not only injurious substances but also drugs, such as arsenic, mercury, bismuth compounds, and certain antibiotics, from penetrating the central nervous system, a fact that makes it difficult to treat certain brain diseases. Various methods are employed both in experiments and in the clinic to increase the permeability of the blood-brain barrier or to bypass it by injecting chemical substances into the cerebral ventricles or spinal canal.
REFERENCESShtern, L. S. “Neposredstvennaia pitatel’naia sreda organov i tkanei.… ” In Izbr. trudy. Moscow, 1960.
Kassil’, G. N. Gemato-entsefalicheskii bar’er. Moscow, 1963.
Fiziologiia i patologiia gisto-gematicheskikh bar’erov. Moscow, 1968. Pages 170-254.
Bakay, L. The Blood-Brain Barrier. Springfield, Ill., 1956.
Tschirgi, R. D., “The Blood-Brain Barrier.” In Biology of Neuroglia. Springfield, Ill., 1958.
G. N. KASSIL’