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April 18, 2012

In Research

Once considered mainly ‘brain glue,’ astrocytes’ power revealed

astrocyte
A human astrocyte.

A type of cell plentiful in the brain, long considered mainly the stuff that holds the brain together and oft-overlooked by scientists more interested in flashier cells known as neurons, wields more power in the brain than has been realized, according to new research published in Science Signaling.

Neuroscientists at the Medical Center report that astrocytes are crucial for creating the proper environment for our brains to work. The team found that the cells play a key role in reducing or stopping the electrical signals that are considered brain activity, playing an active role in determining when cells called neurons fire and when they don’t.

That is a big step forward from what scientists have long considered the role of astrocytes—to nurture neurons and keep them healthy.

“Astrocytes have long been called housekeeping cells—tending to neurons, nurturing them, and cleaning up after them,” says Maiken Nedergaard, professor of neurosurgery and leader of the study. “It turns out that they can influence the actions of neurons in ways that have not been realized.”

Proper brain function relies on billions of electrical signals—tiny molecular explosions, really—happening remarkably in sync. Recalling the face of a loved one, swinging a baseball bat, walking down the street— all those actions rely on electrical signals passed instantly along our nerves like a molecular hot potato from one brain cell to another.

For that to happen, the molecular brew of chemicals like sodium, calcium, and potassium that brain cells reside in must be just right—and astrocytes help to maintain that balanced environment.

In the paper in Science Signaling, Nedergaard’s team discovered an expanded role for astrocytes. The team learned that in addition to simply absorbing excess potassium, astrocytes themselves can cause potassium levels around the neuron to drop, putting neuronal signaling to a stop.

“Far from only playing a passive role, astrocytes can initiate the uptake of potassium in a way that affects neuronal activity,” says Nedergaard. “It’s a simple, yet powerful mechanism for astrocytes to rapidly modulate neuronal activity.”

In the latest research Nedergaard’s team found that by sucking up potassium, astrocytes quell the firing of neurons, increasing what scientists call “synaptic fidelity.” Important brain signals are crisper and clearer because there is less unwanted activity or “chatter” among neurons that should not be firing. Such errant neuronal activity is linked to a plethora of disorders, including epilepsy, schizophrenia, and attention-deficit disorder.

“This gives us a new target for a disease like epilepsy, where signaling among brain cells is not as controlled as it should be,” says Nedergaard. Read more at www.urmc.rochester.edu/news/story/index.cfm?id=3452.

Sprinkle of ‘pixie dust’ reduces post-surgical spine infection

Scattering a gram of powdered antibiotic (vancomycin) directly into a spinal surgery wound appears to be a safe, cost-effective way to achieve low post-operative infection rates, according to a Medical Center study.

The team retrospectively reviewed the medical records of more than 1,500 patients who received this novel treatment at Strong Memorial Hospital and reported the results at the American Academy of Orthopaedic Surgeons 2012 Annual Meeting in March. The findings also have been presented at a Scoliosis Research Society meeting and recently published in European Spine Journal.

Robert Molinari, associate professor in the Department of Orthopaedics, began using this method in the 1990s while deployed as a U.S. Army surgeon and working in less-than-sterile environments.

“My theory was that sprinkling powdered antibiotics directly into the wound might provide the highest concentration of medicine where it was needed most,” Molinari says. “And what I noticed was that my infections rates from that time period were low.”

After his deployment ended in 2003, Molinari began using the same technique at the Medical Center in his most complex cases, with patients most prone to infection due to severe spinal trauma or cancer. A dusting of vancomycin was used in addition to intravenous antibiotics prior to surgery, the latter of which is called for in evidence-based guidelines set by the North American Spine Society.

“Our surgical residents said it looked like I was sprinkling pixie, dust and they observed that it seemed to work like magic,” Molinari said.

Thus, the surgical residents—William Molinari III (Molinari’s nephew), and Oner A. Khera—agreed to review the data from Molinari’s 1,512 consecutive cases from 2005 through 2010. They found a general infection rate of only 0.99 percent, equal to 15 patients or one in 100. That compared to a national, general infection average of approximately 2.1 percent among 108,419 patients in the national database of the Scoliosis Research Society.

Infection after spinal surgery is a complication that can occur in up to 20 percent of all cases. It is associated with significant long-term illness or death.

“We think we’re on to something, and our study has been well received by the orthopaedics community,” Molinari says. “The next step would be a large, case-controlled trial—and already several institutions across the country have expressed interest.” Read more at www.urmc.rochester.edu/news/story/index.cfm?id=3459.

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