Scientists now know that the purpose of the blood–brain barrier is to protect against circulating toxins or pathogens that could cause brain infections, while at the same time allowing vital nutrients to reach the brain and maintaining levels of hormones, nutrients and water in the brain. But it wasn’t until the 1960s that researchers could use microscopes powerful enough to see the physical layer of the blood–brain barrier. The dye infiltrated all tissues except the brain and spinal cord showing that a barrier did indeed exist between brain and blood. The German physician Paul Ehrlich discovered the blood-brain barrier when he injected a dye into the bloodstream of a mouse in the late 19 th century. Whereas the skull, meninges and cerebrospinal fluid protect against physical damage, the blood–brain barrier provides a defense against disease-causing pathogens and toxins that may be present in our blood.” As the name suggests, this is a barrier between the brain’s blood vessels (capillaries) and the cells and other components that make up brain tissue. “Another protective element is the blood–brain barrier. Both provide further defense against physical injury,” writes Jürgen Götz, director of Clem Jones Centre for Ageing Dementia Research at The University of Queensland. The most obvious is our 7mm thick skull, but the brain is also surrounded by protective fluid (cerebrospinal – of the brain and spine) and a protective membrane called the meninges.
“The brain is precious, and evolution has gone to great lengths to protect it from damage.
As a result, they say, it is estimated that only two percent of therapies actually enter the organ. Scientists have discovered these limitations in their efforts to use antibodies to treat the buildup of amyloid beta plaques that accumulate in the brains of people with Alzheimer’s, Nedergaard said. Researchers at URMC believe that because antibodies are typically administered intravenously, the entry of these large proteins into the brain is stopped by the blood-brain barrier. “This is because the brain maintains its own closed environment that is protected by a complex system of molecular gateways – called the blood-brain barrier – that tightly control what can enter and exit the brain,” According to Nedergaard, many promising therapies for diseases of the central nervous system have failed in clinical trials because of the difficulty in getting enough of the drugs into the brain to be effective.
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