Friday, 26 July 2013

Protecting your brain's 'borders'

With all the current discussion in Federal politics about 'protecting our borders' it's an opportune time to talk about a less controversial border - the one in our brain. It's called the blood-brain barrier (BBB). Our brain houses up to 650 kilometres of blood vessels! These vessels are lined by a structure, the BBB, which regulates the passage of nutrients, proteins, chemical substances and microscopic organisms between the bloodstream and the brain tissue. Basically, it controls what is, and what isn't, allowed to leave the blood supply and enter the brain.

Blood vessels supply our organs with the nutrients that they need, and help to remove waste products. It has long been known that the blood vessels in the brain and spinal cord are particularly good at protecting the brain from harmful substances, through the BBB, but until recently it hasn't been completely understood how this occurs.

Emerging research using imaging techniques has revealed that the blood vessels in the brain

and spinal cord are lined with specialised cells. These cells have molecular passageways embedded in the cell membrane. These passageways will actively block some chemicals, which are likely to be dangerous to the brain, and play a role in pushing other chemicals across into the brain. The entry and exit of these chemicals are controlled by cells called astrocytes and pericytes.

In mouse models, a deficiency in pericytes has been shown to increase the permeability of the BBB to chemicals. And a deficiency in astrocytes has been shown to result in small haemorrhages at the BBB/brain junction.

Using a 'two photon' microscope to probe inside the living brain, researchers have seen these astrocytes and pericytes doing their job, as well as witnessed white blood cells move across from blood vessels into the brain, and back again.

In addition immune system cells, 'microglia', search the brain for harmful substances that have found their way into the brain, and look for damaged or cancerous cells, and remove them.

The practical application of this knowledge is that neuroscientists are now discovering that many neurodegenerative conditions such as Alzhemier's dementia and Parkinson's disease involve defective BBB and related cells.

For example, it is thought that Alzheimer's dementia involves having too much of a chemical called beta-amyloid in the brain. The BBB has a protein that brings the beta-amyloid out of the bloodstream into the brain, and another protein does the opposite. Perhaps keeping the beta amyloid out of the brain might be a prevention, or even a cure, for Alzheimer's dementia.

We look forward to more research in this area, helping us to better understand, and hopefully formulate better treatments for these neurodegenerative diseases.

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