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Glial cells come out of the shadows: researchers have discovered that keeping these important cells healthy is essential to proper brain function.

Scientists no longer consider glial cells--those underappreciated nonneuronal cells that make up an estimated 90 percent of brain tissue--the mere caretakers of neurons (nerve cells), or a sort of packing material that surrounds gray matter throughout the brain. New discoveries have added to a lengthening list of what experts now know about the critical functions of glia, the most recent being the revelation that glial cells may be responsible for a hitherto unknown system designed to remove debris and toxic waste products from the brain.

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Researchers used advanced imaging technology to discover in the brains of mice a "glymphatic system," which appears to eliminate debris--including toxic beta-amyloid proteins, a hallmark of Alzheimer's disease (AD)--from brain tissue. This system, which is similar to the lymphatic system, is overseen by glial cells and is far larger and more comprehensive than other processes that remove waste from the brain, according to a study published online Aug. 15, 2012 in Science Translational Medicine. Experts believe a similar system may exist in humans.

"This is an exciting and potentially important disovery," says Teresa Gomez-Isla, MD, a neurologist at Massachusetts General Hospital (MGH) and Associate Professor of Neurology at Harvard Medical School. "It opens new research avenues to understand how debris and toxic waste products are removed from the brain in normal conditions, and how alteration of these clearance mechanisms might contribute to neurodegenerative Alzheimer's disease."

The glymphatic system operates under a sort of hydraulic pressure, moving cerebrospinal fluid rapidly through the brain to force out debris and drain it away via channels adjacent to cerebral blood vessels. It had not been previously detected because it functions only in living brains and is not visible when a researcher's scalpel opens the system and breaks connections. Only recently has it become possible for researchers to view the system within the brains of living mice using newly developed two-photon microscopy technology.

"The finding that astrocytes may regulate the removal of brain beta-amyloid points to a novel molecular mechanism potentially relevant to the pathogenesis of AD," Dr. Gomez-Isla says. "It also highlights the importance of these frequently neglected brain cells. It is becoming clear that future therapies may need to be tailored for specific types of glial cells."

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Other advances in scientific understanding of the brain's glia have been achieved in the past few years. New findings suggest that glia may help neurons process information, ensure the brain's plasticity (its ability to adapt, learn, and store away new information), orchestrate the signaling between neurons, modulate levels of neuronal activity, supply nerve fibers with energy, and even help destroy neurons that excrete too much beta amyloid, among other functions.

KEEPING GLIA HEALTHY

Most experts agree that in order to keep your glial cells functioning optimally, you should adopt strategies designed to promote overall brain health. They suggest that you:

* Adopt a healthy lifestyle. Watch your weight and consume a nutritious, low-calorie diet with a minimum of processed foods, trans fats and saturated fats. Get regular exercise (at least 30 minutes or more a day, five days a week) and seven to eight hours of sleep at night. Avoid excessive alcohol consumption (more than a drink or two a day) and do not smoke.

* Stimulate your brain with challenging mental activities and frequent social interaction.

* Prevent and/or manage health problems that might negatively affect glia. Reduce stress, and get treatment for depression that lasts longer than two weeks or so, since both are linked with a decrease in glia. Work with your medical care provider to manage health conditions that might harm your brain, such as high blood pressure, cardiovascular disease, or diabetes.

* Control inflammation that can harm glial cells by treating infections such as gum disease promptly. See What You Can Do for a list of foods that help fight inflammation.

MANY TYPES, MANY TASKS

Glial cells come in many forms, including:

* Astrocytes: These star-shaped cells surround the communication points between neurons known as synapses, which they help build and strengthen. They are thought to provide neurons with nutrients and oxygen, help eliminate debris, soak up ions and excess neurotransmitters released by the neurons, and possibly repair neuronal connections.

Research suggests that astrocytes communicate with one another locally and in a vast network across the brain that uses calcium in the transmission of messages. The cells are thought to oversee the transfer of information between neurons, and affect how the brain processes information and learns. Studies suggest that when astrocytes are impaired, neuronal synapses do not function properly--an effect that may explain the memory problems experienced by people with depressive disorders or chronic stress, who suffer from a decrease in the number of glial cells. A deeper understanding of astrocyte functioning may one day lead to treatments for mood and memory disorders and dementia

* Microglia: These glia constitute the brain's immune defense, operating behind the blood-brain barrier to identify, hunt down, and destroy organisms that invade the brain. The cells also find and eliminate dead or damaged cells, plaques, and other debris, reshape neuronal connections in response to changing demands on the brain, and battle inflammation that can damage brain tissue. In some cases, microglia may become overactive and make inflammation more severe. Therapies that help block this overactivity may help in treating AD, which is associated with high levels of inflammation in the brain.

* Oligodendrocytes: This type of glial cell helps provide a fatty substance called myelin that insulates nerve fibers connecting neurons and speeds the passage of electrical impulses from neuron to neuron. Oligodendrocytes are thought to be involved in diseases such as multiple sclerosis and Parkinson's disease, which are characterized by deterioration of myelin, and it is hoped that discoveries involving these glial cells may one day lead to therapies.

* Oligodendrocyte precursor cells: These cells comprise up to eight percent of all the cells in the nervous system. Because they are multipotential stem cells capable of giving rise to astrocytes, oligodendrocytes, and neurons, they may be play a role in new therapies for neurodegenerative diseases. him

WHAT YOU CAN DO

Research suggests that the foods listed below help fight inflammation. Consuming them may protect glial cells from damage:

* Ginger

* Blueberries and other dark berries

* Green tea

* Fatty fish

* Soy products

RELATED ARTICLE: BRAIN BULLETIN: BREAKTHROUGH ENABLES DELIVERY OF DRUGS TO THE BRAIN

Researchers may have found a way to deliver medications through the blood-brain barrier (BBB), opening the way for future treatments for brain disorders such as Alzheimer's disease (AD), brain cancer, and Parkinson's disease. The BBB is a densely packed network of cells that separates circulating blood from the brain. It represents an obstacle to the delivery of larger-molecule therapeutic drugs via the bloodstream because it allows only very small essential molecules, such as glucose, oxygen, and water, to pass into the brain.

In animal research published in the Sept. 14, 2012 Journal of Neuroscience, researchers discovered that adenosine, a natural substance produced by the body, can be used to connect with receptors in the BBB and open a temporary pathway for large molecules. Working with a common adenosine-based drug, the scientists found that they could safely breach the BBB in mice, allowing entry of larger molecules such as antibodies to beta-amyloid (toxic proteins that are the hallmark of AD).

The researchers said that the gateway closed naturally after about three hours. Experts caution that additional research is required before the procedure is ready for clinical use in humans.
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Publication:Mind, Mood & Memory
Geographic Code:1USA
Date:Nov 1, 2012
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