Most people have at least heard of the blood brain barrier (BBB). This barrier isn’t exactly a wall but a physiological system of substance control that is allowing some things in and preventing the movement of others into the brain.
This was first observed in people with jaundice (from bilirubin) or a yellow color throughout the body affecting the skin and the eyes from liver disease. Doctors in the 1800’s noticed that all tissues had a yellow tint, except for the brain and spinal cord.
Researchers decided to test this further and injected lab animals with a blue dye. Through this they were able to duplicate the observations that the CNS was able to protect itself somehow from the dyes as well as the bilirubin that caused jaundice in other tissues including the eyes.
The BBB has been under intense scrutiny these last 30 years and we have learned much since then. The key component of the BBB is the layer of capillary endothelial cells that are very tightly bound to each other creating a seal of sorts (tight junctions). The developing brain has a BBB structure somewhat different than the adult brain. We have good evidence that many mechanisms in the adult BBB are also present in the fetus, including those tight junctions between the capillary endothelial cells. Some substances are actively transported across the BBB in the adult and developing brain, but some plasma proteins are more easily transported across the BBB of fetal and infant brain. Also some of the cerebral capillaries seem to be more fragile. Therefore the developing brain is subject to damage from drugs, toxins and pathological conditions at a greater rate than that of the adult brain.
This brings up a couple of questions. How do we know the condition of our BBB and what we can do to improve it if something is amiss.
We now have a couple of ways to more directly assess the BBB. Some of this research comes out of studies done on repeated head trauma in athletes. The brain protein S100B has been found to be in higher levels in the serum of athletes who also have objective signs of brain damage than their non-brain damaged counterparts. Maybe you saw the move Concussion. In the early stages of the study of traumatic brain damage we could only find the evidence in microscopic examination of the brain post mortem. BBB disruption can appear with trauma below the level of diagnosable concussion. Repeated blows to the head as might occur in soccer, hockey, boxing and football can cause damage and these players should be monitored even the absence of clear concussion signs.
Coaches, players and especially concerned loved ones obviously want a better way of determining brain damage than waiting for a person to die and then examine samples under a microscope. The S100B protein has been really helpful.
Another way to assess this is called dynamic contrast-enhanced MRI (DCE-MRI). This technique is well established for some conditions but the quality of the data derived from DEC-MRI for BBB problems is dependent on the experience of the doctor and technicians performing the tests. Plus, as good as this might turn out to be, an MRI will probably never be very cheap and convenient for routine use. It should be a great tool for research to evaluate other methods like various blood tests and clinical evaluation.
