The Blood-Brain Barrier: Nature’s Security System
Published February 8, 2016 | Health, Immune & Brain Disorders
Story Highlights- The blood-brain barrier is a “dynamic interface” that allows nutrients and other essential molecules into the brain to support it and the central nervous system.
- The character of the blood-brain barrier makes medical intervention difficult: Many drugs are unable to penetrate the barrier.
- The potential for toxins to cross the prenatal and infant blood-brain barrier suggests that any treatment of infants or pregnant women deserves careful consideration.
The BBB is one of the most studied and complex of the body’s systems. At Johns Hopkins University, the Blood-Brain Barrier workgroup describes it this way: “The blood-brain barrier (BBB) is a dynamic interface that separates the brain from the circulatory system and protects the central nervous system from potentially harmful chemicals while regulating transport of essential molecules and maintaining a stable environment.”1
As described by that physician workgroup, highly specialized cells line the capillaries of the brain and facilitate a “complex interplay between the different cell types (such as the endothelial cells, astrocytes, and pericytes), and the extracellular matrix of the brain and blood flow in the capillaries.”
The Society for Neuroscience calls it “the brain’s security system,” and explains that, as is the case in all blood vessels of the body, “the brain’s blood vessels are lined with endothelial cells, which serve as an interface between circulating blood and the vessel wall. However, unlike other blood vessels in the body, the endothelial cells in the brain are tightly wedged together, creating a nearly impermeable boundary between the brain and bloodstream.”2 Dense stuff.
Discovery of the BBB
As so often happens in science, the BBB was discovered essentially by accident during the course of research into something else. In 1885, German scientist Paul Ehrlich (ultimately famed for discovering a cure for syphilis) was trying to figure out why different body tissues absorbed chemical dyes in different ways. He found that when mice were injected intravenously with a blue dye, all of their organs were stained blue except for the brain and the central nervous system.Ehrlich’s original conclusion was that the dye had a lesser affinity for nerve cells than for other tissues. Later, in 1913, Edwin Goldman, a colleague of Ehrlich’s, found similarly that, when the dye was injected directly into the cerebrospinal fluid of study animals, the brain and only the brain was stained blue. Although that led to an awareness that there was an actual physical barrier between the brain and the rest of the circulatory system, it was not until the 1960s and with the aid of the electron-microscope—approximately 5,000 times more powerful than Ehrlich’s—that scientists could confirm and detail the structure of the brain’s defensive system that became known as the blood-brain barrier.3
The BBB Blocks Many Medical Interventions
Since that time, much of the research into the BBB has focused on trying to bypass the barrier in order to medicate or manipulate the brain chemistry in some way… very difficult because the BBB does its job incredibly well. Like security guards at any vitally important facility, cells within and on either side of the BBB are hyper-vigilant and in constant communication with each other, monitoring and either allowing or blocking the transport of circulating molecules.Water, gases, and molecules that are either very small or lipid (fat)-soluble seem able to pass through the barrier fairly easily (antidepressants, anti-anxiety medications, alcohol, cocaine, and many hormones for example), while others molecules that are larger (like glucose and insulin) need to be “ferried across,” piggy-backed onto “transporter proteins.”4 5
Finding ways to “trick” the barrier into allowing life-saving drugs to cross into the brain is only one of the hurdles facing medical researchers. The other is the opposite problem: Finding ways to heal leaks in the barrier or repair damage that may occur with certain brain injuries or infections.
Fetal Development of the BBB
The infant BBB is often referred to as “immature,” an adjective that has commonly been interpreted as “leaky,” “nonfunctional,” or even “absent” by many researchers.6 More recently, though, studies have shown that the barrier is in fact fully functional starting early in the developmental process but several of its characteristics differ from those of an adult. For example, some transporters are more active in the developing brain and fetal cerebral vessels are more fragile compared to the mature neurological system.7For these reasons, mechanisms affecting the fetal BBB, “while functionally effective in the developing brain, may nonetheless be more susceptible than in the adult to adverse circumstances and that damage to brain barrier mechanisms during development may lead to neurological and neuropsychological dysfunction in later life.”8
Challenging the BBB With Vaccines
Any toxin capable of crossing the BBB, and there are many, may cause damage to neurons and glia in the brain, mainly through an oxidative process that may compromise “the functions of the central nervous system expressed as motor, sensory and cognitive deficits and psychological alterations.”9Given the rise in the types of toxic exposures the developing fetus encounters in utero, including the alarming trend toward administering influenza, diphtheria, tetanus and pertussis vaccines to pregnant women starting in the first trimester, the impact of any treatment on the preterm or infant BBB deserves careful consideration. As Joseph Mercola, MD put it, “Today, children are vaccinated at birth for HiB and begin their long vaccination-journey at 2 months of age, before the blood brain barrier is fully developed. A review of the medical literature around the world will turn up many articles linking vaccinations with many neurological disorders.”10
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