THE DISCOVERY OF THE BLOOD-BRAIN BARRIER A PRACTICAL EXERCISE FOR PHYSIOLOGY STUDENTS (Atena Editora)

Abstract

Brain tissue, basically irreparable after injury, is stored in a “strong box” built with several levels of protection: skull, meninges, extracellular fluids and, finally, the Blood-Brain Barrier (BBB). The BBB combines anatomical structures and physiological transport systems. The structures are the tight junctions between brain endothelial cells (CECs) that form the walls of most of the brain's approximately 400 kilometers of capillaries. Transport systems are selective processes that control substances and their rates of entry into the cerebral interstitial fluid. The formation of the BBB is influenced by paracrine signals originating from the microenvironment of CECs, involving pericytes, astrocytes and neurons. This neurovascular unit exhibits highly controlled cell-cell communication patterns, varying with factors such as age and pathologies. The concept of BHE dates back to the beginning of the 20th century, but the beginning of its history dates back to the 17th century with the work of Humphrey Ridley (1653 –1708). Ridley, by injecting mercury, or colored wax, into the cerebral veins of recently executed criminals, was the first to observe and document the complexity and low permeability of the cerebral vascular network. Two hundred years later, Paul Ehrlich resumed this research in rodents, concluding that the bright coloring he used did not stain either the brain or the cerebrospinal fluid. New research and discoveries followed, establishing the current understanding of the BBB and its role in maintaining brain homeostasis, and providing new clues for future research into possible points of pharmacological intervention.