Structure of the Blood-Brain Barrier

Hawkins RA, et al. Structure of the blood-brain barrier and its role in the transport of amino acids. J Nutr. 2006 136(1 Suppl) 218S-26. 

The blood-brain barrier forms the interface between the bloodstream and the brain parenchyma and thus controls the passage of endogenous substances and xenobiotics into and out of the central nervous system. Brain microvessels exhibit a variety of unique structural features, such as an extremely tight endothelium without fenestration, a very low rate of pinocytosis, tight junctions between endothelial cells excluding paracellular permeability, and a series of polarized transport proteins. The following chapter describes the structural and functional characteristics of the blood-brain barrier with emphasis on transport proteins, as well as in vitro techniques, which allow studying this complex barrier in the brain. 

Biochemically lead binds to sulfhydryl (-SH) groups in proteins, that is, it can inhibit enzymes and affect the structures and functions of structural proteins. Some of the effects of this binding include increased permeability of the blood-brain-barrier, breakdown of vascular tissue, destruction of the ground substance in cells leading to conditions of anemia and kidney damage. 

Chapter 27 Structure and Function of the Blood-Brain Barrier.575... 

Because the blood-brain barrier is less well developed in immature brains, children are more susceptible to CNS toxicity from certain toxic substances, such as lead salts, than are adults. The patency of the blood-brain barrier may also become increased under conditions of disease and dehydration. Although the CNS is generally well protected from certain drugs by the blood-brain barrier, the PNS does not have a comparable structure. Therefore, it is possible to have drug effects restricted to peripheral structures only, if their entry into the CNS is excluded. 

A passage of the blood-brain barrier has, however, not to be expected due to their polarity and molecular size. Due to the particular structure of the brain capillaries only lipoid-soluble low molecular substances are able to enter the brain vessels from the blood. This fact is called the blood-brain or blood-liquor barrier which indeed cannot be overcome by polymers but by free low-molecular active substances like mezcalin or aminoantipyrine. 

Describe the structure and function of the blood-brain barrier... 

Its action has been postulated to be intraneuronal on the oxidation cycle at a phase above the cytochrome b level of the cytochrome oxidase system though its precise mechanism has not been elucidated. It is primarily a neurotoxin with a chemical structure that allows for easy penetration of the blood-brain barrier. 

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