I had no reason to believe that my brain did not have blood flowing in and around it. Paul Elrich a bacteriologist discovered this when he injected stains into animals and found that the stains did not travel to the brain. The reason eluded him and it was only in 1913 when another scientist Edwin Goldmann injected dye into the spine that it travelled to the brain. Your body has a highly selective permeable barrier that separates your blood from your brain. This barrier allows the passage of water, some gases, and lipid soluble molecules besides glucose and some amino acids. You have a discerning brain, you just didn’t know it.
The purpose for being picky is to protect the brain from pathogens. The blood-brain barrier therefore protects the brain from most of the pathogens that enter your blood stream. On the rare occasion that your brain does get infected it is hard to treat. This is because it is hard to use blood transmitted medication to treat the brain. Historically, it was believed that babies were born without a fully developed barrier but subsequent research on baby rabbits showed that you are born with it. Interestingly, to test this thesis, the researchers used materials like heroin, caffeine, ethanol among others which easily pass the barrier. Makes you want to rethink your drugs, coffee and rock and roll lifestyle doesn’t it?
Several diseases have developed the capacity to infect the brain despite the filter. Epilepsy is caused by a malfunctioning of the barrier which then triggers seizures. Sleeping sickness (no not your need to sleep all the time) is another disease where parasites are able to infect the brain. In Alzheimer’s it is blood plasma that enters the brain and then wrecks havoc. Even latent HIV has been known to cross the barrier and infect the brain. Your blood-brain barrier is weakened by high blood pressure, pollution, alcohol, drugs, environmental toxins including air fresheners and detergents and restricted blood flow among others. As if there wasn’t enough reason to live a healthy lifestyle already?