GEMATO-ENTSEFALICHESKIY BARRIER

From Big Medical Encyclopedia

GEMATO-ENTSEFALICHESKIY BARRIER (grech, haima, haimat[os] blood + lat. encephalon, from grech, enkephalos a brain) — the physiological mechanism which is selectively regulating a metabolism between blood and the central nervous system. - e. carries out also protective function, interfering with penetration into cerebrospinal liquid and a brain (head and back) some alien substances getting to blood and the intermediate products of a metabolism which are formed in an organism at some patol, states. Therefore conditionally distinguish the protective and regulating functions G. closely connected among themselves - e., providing a relative invariance of structure, physical. - chemical and biol, properties of cerebrospinal liquid and adequacy of a microenvironment of separate nervous elements.

On existence of the mechanism limiting transition of some chemical connections, generally dyes from blood in a brain, specified P. Earl them (1885), M. Lewandowski, (1900), Goldmann (E. Goldmann, 1913), etc. The term «blood-brain barrier» is offered L. S. Stern and R. Gauthier in 1921 Stern, based on the analysis of big experimental material, for the first time formulated fiziol, bases of the doctrine about G. - e. also defined value G. - e. for activity of c. N

of the village of Morfol, substrate G. - e. the anatomic elements located between blood and neurons are: endothelium of capillaries, basal membrane of a cell, glia, vascular textures, covers of a brain. Great value in G.'s structures - e. has so-called main substance, complexes of protein and polysaccharides — mucopolysaccharides are a part to-rogo. Many authors a special role in implementation of function G. - e. attribute to cells of a neuroglia. The final perivascular (prisoskovy) legs of astrocytes adjacent to an outer surface of capillaries can selectively extract from a blood-groove of substance, necessary for food of neurons and return in blood products of their exchange [Brayerli (J. Century of Brierley), 1957]. At the same time in all structures of G. - e. there can be enzymatic reactions promoting reorganization, oxidation, neutralization and destruction of the substances arriving from blood (A. Labori, 1964).

Assessment of the regulating function is made by definition of a permeability coefficient (more precisely, a distribution coefficient), i.e. the relations of concentration of this or that substance in cerebrospinal liquid to its concentration in blood serum. For the majority of the studied elements of blood the permeability coefficient is less than unit and only for ions of magnesium and chlorine it more unit. The size of coefficient depends on composition of blood and cerebrospinal liquid.

Use of radio isotope indication (see. Radio isotope diagnosis ) led to nek-rum to review of idea of G. - e. It is established that G.'s permeability - e. it is not identical in various departments of a brain and in turn can change differently. The theory of plurality of barrier educations (system of the brain barriers) functioning depending on chemism and the changing requirements of these or those nervous structures was widely adopted. It is established that in a brain there are «barrier-free» zones (area postrema, a neurohypophysis, a leg of a hypophysis, an epiphysis, a gray hillock) where the substances entered into blood arrive almost freely. In some departments of a brain (e.g., in a hypothalamus) G.'s permeability - e. in relation to biogenic amines, electrolytes, a nek-eye to alien substances above, than in other departments of a brain that provides timely receipt of humoral information in the highest vegetative centers; emergence of some patol, processes (disturbance of mechanisms of regulation of functions, vegetative frustration, diencephalic syndromes, etc.) it can be connected with increase or decrease in permeability of G. - e.

The protective and regulating functions G. - e. are studied at the person and animals in onto-and phylogenesis, and also at various conditions of an organism — during periods and pregnancy, at changes of body temperature and the environment, in the conditions of the broken food, starvation and avitaminosis, at exhaustion, sleeplessness, endocrine and vegetative dysfunctions, asphyxia, nervous breakdowns and disorders of internals, infections, an anesthesia, a craniocereberal injury, shock, introduction various pharmakol, drugs, impact of ionizing radiation etc. So, in particular, it is established that in the course of phylogenesis nervous cells become more sensitive to changes of structure and properties of the environment surrounding them. It leads to improvement of barrier mechanisms of c. N of page. So, e.g., some substances easily get from blood into a brain at low-organized, but G. - e are late. at more high-organized organisms. Besides, G. - e. differs in high-permeability at embryos and newborns in comparison with an adult organism. There is an assumption that high lability of a nervous system at children to a certain extent depends on a hyperpermeability of their G. - e.

Great theoretical and practical value has a question of selectivity (selective permeability) of G. - e. in relation to substances, quite often close to each other on a chemical structure and biol, to properties. So, e.g., L-dofa in c. the N of page gets easily, and D-dofa and dopamine are late. G.'s selectivity - e. upon transition of substances from blood in cerebrospinal fluid and c. to N of page it is considerably more expressed, than upon transition from cerebrospinal fluid to blood. - e. in this case it is similar to the selection filter in the direction blood — c. N to page or safety valve in the opposite direction (L. S. Stern and Gaultier, 1918).

According to modern representations, G. - e. is self-regulating system, the state a cut depends on the needs of nervous cells and level of metabolic processes not only for the brain, but also for other bodies and body tissues. G.'s permeability - e. it is regulated by nervous and humoral mechanisms. At the same time yet there is no theory which is completely explaining pattern of transition of various substances from blood in cerebrospinal liquid and tissues of a brain.

Studying of protective function G. - e. has special value for identification of a pathogeny and in therapy of diseases of c. N of page. Decrease in permeability of a barrier promotes penetration into c. N of page not only alien substances, but also products of the broken metabolism; at the same time increase in resilience of G. - e. closes (partially or completely) a way to zazashchitny bodies, hormones, metabolites, mediators. Extremely finite permeability of G. - e. in relation to a nek-eye to the chemotherapeutic drugs used in a wedge, practice (to compounds of arsenic, bismuth, mercury, etc.), to antibiotics (e.g., to penicillin, streptomycin), to antibodies (antitoxins, agglutinins, hemolysins) quite often is an obstacle at treatment of diseases of c. N of page. Various methods of increase in permeability of G. - e are offered. (overheating or overcooling of an organism, influence by X-ray, an inoculation of malaria etc.), however they are not always effective. In these cases introduction pharmakol is possible. drugs to lay down. serums, biologically active agents directly in cerebrospinal liquid (a lumbar or suboccipital prick on Stern).

For studying of function G. - e. the substances getting into cerebrospinal liquid and a brain in insignificant quantities are applied usually. For this purpose in experiments on animals most often enter into blood acid (first of all tripanovy blue) or the main dyes, salts monohydroiodide, picric or salicylic to - t and determine their content (quantitative or qualitative test) in cerebrospinal liquid and tissue of a brain. Broad application was found by methods autoradiography (see), gistol., chemistry, submicroscopy.; In a wedge, also other methods of a research G. - e are offered practice bromic, iodic, salicylic, nitrate, uraninovy, gemolizinovy, glucosic. According to Walter (F. Walter, 1929), the substances applied for this purpose shall meet the following requirements: to be distributed in blood and cerebrospinal liquid before there comes their allocation, not to be split in an organism and not to contact proteins; they shall not change G.'s condition - e. and to do harm to an organism. It is necessary to choose the indicator which is giving in to exact quantitative definition.

With the known precautions for a research of a condition of G. - e. the tracer technique can be used also at the person.

See also Barrier functions , Cerebrospinal liquid .


Bibliography: Kassil G. N. Blood-brain barrier, M., 1963; Stern L. S. A direct medium of bodies and fabrics, the Physiological mechanisms defining its structure and properties, M., 1960; In a k and at L. The blood-brain barrier, with special regard to the use of radioactive isotopes, Springfield, 1956; Brain-barrier systems ed. by A. Lajtha, Amsterdam, 1968; Dob-b i n g J. The blood-brain barrier, Physiol. Rev., v. 41, p. 130, 1961; Handbook of physiology, sec. 1 — Neurophysiology, ed. by J. Field a. o., v. 3, Washington, 1960.

Of H. Kassil.

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