BLOOD-BRAIN BARRIER

Abstract

This barrier is localized in the capillaries of the C-N-S which are endowed with a selective permeability. The choroid plexus, meningeal vessels and C-S-F (cerebro-spinal fluid) are not concerned with the exchange of substances between blood and C-N-S. The permeability of the capillaries of the C-N-S has now been detd. for a considerable number of aniline dyes, toxins, viruses, antibodies and drugs. The cerebral capillaries are permeable to substances carrying a positive or no qharge at the pH of the blood while they are impermeable to those carrying a negative charge. The permeability of the capillary system as a whole may be more correctly correlated to the potential than to the sign of the electrical charge. The capillaries in the. majority of organs are permeable to electronegative substances but they are more readily passed by the electropositive ones. The choroid plexus, ciliary plexus and the capillaries of the peritoneum are permeable to acid (electronegative) and impermeable to basic (electropositive) dyes. The higher permeability of the capillary system as a whole to electropositive substances explains the greater toxicity of basic drugs and the rapid action of cobra venom and lamb dysentery toxin in contradistinction to the slow action of tetanus, diphtheria and botulinus toxins. These investigations have shown that toxins, viruses and antibodies can be used for the study of physiological problems, while, on the other hand, the physiological approach to bacteriological and immunological problems has led to some important results. The distribution of toxins between blood and C-N-S and differences in the lengths of incubation periods have been explained from the point of view of permeability and on an electrochemical basis.