One of the earliest finding in medical science was that some of the medicines that entered the rest of the body freely were barred from entry into the brain.
While that was definitely a disadvantage, the consolation was that the barrier impartially applied that “ban” to some harmful chemicals too.
But those days science lacked the wherewithal to explain it or to embark on a fact finding trip.
So, much of the explanation of the mysterious blood brain barrier eluded the world and remained theoretical.
The lack of a visible physical blood-brain barrier (BBB) meant that its nature was more functional than anatomical. That, in turn, suggested the “fortress” was more of a biochemical nature.
Later as the resolution of electron microscopes and micro-endoscopes increased, the scientists could tell us the physical extent of the barrier. But still the exact biochemical processes remained in hypothetical territories.
Now the scientists at Sweden’s Karolinska Institute and Sahlgrenska Academy has found is that at least one histological entity is involved in the operation of the blood-brain barrier.
They are the “pericytes” that form a layer outside the innermost layer (endothelium) of small blood vessels. Small blood vessels comprise the capillaries, arterioles that come before them and venules that come after them.
By their histological appearance, “pericytes” are connective tissue cells that perform supportive functions. Being “undifferentiated” cells, they can be transformed (“differentiated”in scientific parlance) by the body into some other connective tissue cells if the local situation demanded so at various parts of the body.
That also explains why these cells were given different names by different investigators at different times: Rouget cells, adventitial cells, perivascular cells, Marchand cells, mural cells, deep cells and so on. It took some time to realize that they all are modifications of the same cell but one that has adapted itself to different functions at different anatomical location in the body.
Yes, there are “pericytes” in every small blood vessel in the body. In the brain, until now, pericytes were just objects of interests as far as the barrier was concerned, suspected to have a hand in its smooth but highly organized operation.
The Swedish study elevates that possibility to the realm of probability. The “pericytes” in the brain appear to have been endowed with special responsibilities as required by their location in the brain.
While the scientists are still far away from a full-fledged scientific explanation of the blood-brain barrier (BBB), the discovery or confirmation of an anatomical entity in its regulation is a big step forward from the realm of theoretical possibilities.
Further studies will be required to find out how these regulator cells allow preferential treatment to some chemical molecules of varied sizes while not to others.
Once that complex “biochemical” mystery is unraveled, study should naturally lead to how that can be beneficially “manipulated” to allow critical medicines in through the blood-brain barrier (BBB) for curing some brain diseases.
Of course, that will take time and much effort.
Hats off to scientists who are relentlessly in hot pursuit of cures for our maladies despite all that.