Perhaps nowhere else in the body are cells attached as firmly and closely as they are in the 00-mile network of capillaries in the brain. The walls of these microscopic blood vessels are but a single cell thick. They form sheets that fold into minute tubules. Studies in 1969 using the electron microscope revealed that the cell membranes overlap to form a barrier of tight junctions. Unlike the cells forming capillary walls elsewhere in the body, which are pocked with vesicles and window-like portals called clefts, the cells comprising the blood-brain barrier have few vesicles, and no clefts.

Why do the capillaries in the brain form such an impenetrable barrier? This anatomical arrangement shields delicate brain tissue from toxins in the bloodstream and from biochemical fluctuations that could be overwhelming if the brain had to continually respond to them. But all this protection has a downside--the brain is strictly off-limits to many therapeutic drugs. By studying the types of molecules embedded in the membranes of the cells forming the barrier, researchers are developing clever ways to sneak drugs into the brain. they can tag drugs to substances that can cross the barrier, design drugs to fit natural receptors in the barrier, or inject substances that temporarily relax the tight junctions forming the barrier.

The need to control the blood-brain barrier for drug delivery is compelling, for there are several increasing sources of brain disease in our population: pocked with vesicles and window-like portals called clefts, the cells comprising the blood-brain barrier have few vesicles, and no clefts.

Why do the capillaries in the brain form such an impenetrable barrier? This anatomical arrangement shields delicate brain tissue from toxins in the bloodstream and from biochemical fluctuations that could be overwhelming if the brain had to continually respond to them. But all this protection has a downside--the brain is strictly off-limits to many therapeutic drugs. By studying the types of molecules embedded in the membranes of the cells forming the barrier, researchers are developing clever ways to sneak drugs into the brain. they can tag drugs to substances that can cross the barrier, design drugs to fit natural receptors in the barrier, or inject substances that temporarily relax the tight junctions forming the barrier.

The need to control the blood-brain barrier for drug delivery is compelling, for there are several increasing sources of brain disease in our population: Neurodegenerative diseases such as stroke, Alzheimer's disease, and Parkinson's disease increase in prevalence as the population ages.

Brain tumors are more common as people survive other cancers because of improved treatments and earlier detection. Each year 15,000 people develop cancer in the brain as the primary site, but 150,000 develop brain tumors due to spread of a cancer that began elsewhere.

AIDS has introduced several brain infections, such as Cryptococcal meningitis, caused by a fungus, and toxoplasmosis encephalitis, caused by a protozoan.

Genetic research has identified the genes behind several disorders affecting the brain, leading the way to more targeted therapies.