Astrocytes: Keeping Your Brain Healthy

Astrocytes are powerful cells in the brain that support the health of the brain, in part via their involvement at the blood-brain-barrier. The blood-brain-barrier is the boundary between the blood running through vessels that pass through the brain, and the brain tissue itself. Among many functions, astrocytes project “end-feet”, which act almost like hands holding the blood vessel, and keeping the boundary between the vessel and the brain very tight. The boundary is so tight, that dye injected into the blood of an animal, will not enter the animal’s brain. Also, dye injected into the spinal fluid (fluid that flows around the brain), will not pass into the blood stream.


Astrocytes are also connected to neuronal signaling. Here is a diagram of an astrocyte connected to eight neurons. When a neuron fires, neurotransmitter released into the synaptic cleft signals a calcium wave in the astrocyte. The astrocyte may thus be involved in coordinating synaptic transmission.

However, when astrocytes are infected, they can lose their ability to perform their protective function well. A study done in June 2011 found that astrocytes infected with HIV were more likely to allow the a simulated barrier between brain and blood to be permeable, so more able for elements from the blood, including viral elements, to get into the brain. The significance of this research is in identifying a way in which HIV can enter the brain, and so a possible target of treatment. Also, permeability of the blood-brain-barrier is involved in other illnesses, including mental illness.

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For more on the study showing the HIV-infected astrocytes, see the post on NIMH that briefly describes the study published by E. A. Eugenin and colleagues in the Journal of Neuroscience.

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An illness involving the blood-brain-barrier, and gaining increasing appreciation for its effect, although it is still rare, is limbic encephalitis. Limbic encephalitis is a disease in which a person presents with memory problems, often with short-term memory problems that fluctuate in terms of their severity. Accompanying symptoms can include seizures, psychiatric problems such as personality change or depression or anxiety or even hallucinations, changes to blood pressure, and to sodium content in the blood. The illness progresses over time. The different disease processes that can cause fluctuating confusion include a long list of possibilities, so many illnesses must be ruled out by a physician before limbic encephalitis is considered. However, if suspected, auto-antibodies can be detected in the blood, that are antibodies that attach to neurons in the brain, particularly the hippocampus, where the majority of new neuron cell growth in adults is thought to take place. If diagnosed early, the limbic encephalitis may also be connected to a type of cancer, and early detection of that cancer can lead to better treatment.

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Could astrocytes be involved in limbic encephalitis? Possibly.

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Join us in January for a talk on astrocyte transmission, by a fascinating researcher, Dr. Brian MacVicar.

 

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Post by M. Love