BLOOD-BRAIN BARRIER AS AN INTERFACE

Abstract

The blood brain barrier (BBB) is the interface between peripheral tissues and the brain. The morphological substrate of the BBB is made up of endothelial cells of the brain capillaries, connected by tight junctions. Functionally the BBB also includes: (a) substances secreted by the processes of astrocytes, and (b) enzymes located in the tissues between the blood and brain neurons. The ability of substances to penetrate the BBB is determined by their lipophilicity. There are active transport systems in the BBB for hydrophilic substances necessary for the brain, e. g. glucose and amino acids. Regulatory connections between the periphery and the brain can be carried out without penetration of substances through the BBB: on its outer side and vagal afferents, there are specific receptors for many hydrophilic humoral agents. The BBB transport systems selectively carry regulatory peptides from the blood to the brain and/or from the brain to the blood. No physiological basis for designing peptide drugs to penetrate the BBB has been found yet. The same problem is with the hypothetical nose brain pathway: intranasally administered peptides bind to specific receptors in the submucosa and cause central effects without penetrating the central nervous system (CNS). The methods used in experiments to increase the BBB permeability are not suitable for clinical use. Studying the mechanism of CNS dependant effects of some substance should include finding out whether this substance passes through the BBB or affects the brain without penetrating it. This review continues and completes the paper by A.T. Maryanovich & M.V. Andreevskaya. The Blood Brain Barrier: The Protective Function // Rus Biomed Res. 2020. Vol. 5, No. 2. P. 42-48.