Brain's Connective Cells Are Much More Than Glue

Glia cells also regulate learning and memory, new Tel Aviv University (TAU) research finds. Glia cells, named for the Greek word for "glue," hold the brain's neurons together and protect the cells that determine our thoughts and behaviors, but scientists have long puzzled over their prominence in the activities of the brain dedicated to learning and memory. Now Tel Aviv University researchers say that glia cells are central to the brain's plasticity — how the brain adapts, learns, and stores information.

A network of neurons (in red) and glia cells (in green) grown in a petri dish. Blue dots are the cells' nuclei.

Photo: Pablo Blinder.

According to Ph.D. student Maurizio De Pittà of TAU's Schools of Physics and Astronomy andElectrical Engineering, glia cells do much more than hold the brain together. A mechanism within the glia cells also sorts information for learning purposes, De Pittà says. "Glia cells are like the brain's supervisors. By regulating the synapses, they control the transfer of information between neurons, affecting how the brain processes information and learns."

De Pittà's research, led by his TAU supervisor Prof. Eshel Ben-Jacob, along with Vladislav Volman of The Salk Institute and the University of California at San Diego and Hugues Berry of the Université de Lyon in France, has developed the first computer model that incorporates the influence of glia cells on synaptic information transfer. Detailed in the journal PLoS Computational Biology, the model can also be implemented in technologies based on brain networks such as microchips and computer software, Prof. Ben-Jacob says, and aid in research on brain disorders such as Alzheimer's disease and epilepsy.

Regulating the brain's "social network"

The brain is constituted of two main types of cells: neurons and glia. Neurons fire off signals that dictate how we think and behave, using synapses to pass along the message from one neuron to another, explains De Pittà. Scientists theorize that memory and learning are dictated by synaptic activity because they are "plastic," with the ability to adapt to different stimuli.

But Ben-Jacob and colleagues suspected that glia cells were even more central to how the brain works. Glia cells are abundant in the brain's hippocampus and the cortex, the two parts of the brain that have the most control over the brain's ability to process information, learn and memorize. In fact, for every neuron cell, there are two to five glia cells. Taking into account previous experimental data, the researchers were able to build a model that could resolve the puzzle.

The brain is like a social network, says Prof. Ben-Jacob. Messages may originate with the neurons, which use the synapses as their delivery system, but the glia serve as an overall moderator, regulating which messages are sent on and when. These cells can either prompt the transfer of information, or slow activity if the synapses are becoming overactive. This makes the glia cells the guardians of our learning and memory processes, he notes, orchestrating the transmission of information for optimal brain function.

New brain-inspired technologies and therapies

The team's findings could have important implications for a number of brain disorders. Almost all neurodegenerative diseases are glia-related pathologies, Prof. Ben-Jacob notes. In epileptic seizures, for example, the neurons' activity at one brain location propagates and overtakes the normal activity at other locations. This can happen when the glia cells fail to properly regulate synaptic transmission. Alternatively, when brain activity is low, glia cells boost transmissions of information, keeping the connections between neurons "alive."

The model provides a "new view" of how the brain functions. While the study was in press, two experimental works appeared that supported the model's predictions. "A growing number of scientists are starting to recognize the fact that you need the glia to perform tasks that neurons alone can't accomplish in an efficient way," says De Pittà. The model will provide a new tool to begin revising the theories of computational neuroscience and lead to more realistic brain-inspired algorithms and microchips, which are designed to mimic neuronal networks.

To read the article, see:
http://www.ploscompbiol.org/article/info%3Adoi%2F10.1371%2Fjournal.pcbi.1002293

Contacts and sources: 

George Hunka
American Friends of Tel Aviv University

Don't Put All Your Eggs In 1 Basket -- Or All Your Horses On 1 Pasture

Winters in the Gobi desert are usually long and very cold but the winter of 2009/2010 was particularly severe, a condition Mongolians refer to as “dzud”. Millions of livestock died in Mongolia and the re-introduced wild Przewalski’s horse population crashed dramatically. Petra Kaczensky and Chris Walzer from the Research Institute of Wildlife Ecology (FIWI) of the University of Veterinary Medicine, Vienna have used spatially explicit loss statistics, ranger survey data and GPS telemetry to provide insights into the effect of a catastrophic climate event on wild horses, wild asses and livestock that share the same habitat but show different patterns of spatial use. Their results are now published online in the international Journal PLoS ONE.

Przewalski horses in the snow 

Credit: Chris Walzer

In Mongolia, extreme weather conditions – droughts followed by cold and snowy winters – occur at irregular intervals. However, the dzud of 2009/10 was the most extreme winter Mongolia had experienced in the past 50 years. Fifteen out of Mongolia’s twenty-one provinces were declared disaster zones and over 7.8 million livestock, 17% of the national stock, are believed to have perished.

Przewalski’s horses have been re-introduced intto Mongolia since 1992 and there are now free-ranging populations in Hustai National Park in central Mongolia and in the Great Gobi B Strictly Protected Area (SPA) in south-western Mongolia. Due to its special location at the fringe of the Dzungarian basin, flanked by high mountains, the Great Gobi B SPA received particularly high amounts of snowfall in the winter of 2009/2010. Most snow came with weather from the west and when the snow clouds hit the Altai Mountains on the eastern edge of the Great Gobi B SPA they discharged large amounts of snow, resulting in a strong east-west gradient in snow depth. The high, tightly packed snow made it hard for animals to gain access to the vegetation under the snow.

Herders in and around the Great Gobi B Strictly Protected Area were severely affected by the dzud and lost on average 67% of their livestock. Although herders are semi-nomadic, it was hard for them to escape the worst of the weather as competition for the available winter camps was high. Przewalski’s horses were found to use three different winter ranges, two in the east and one in the west. Losses averaged 60% but mainly affected the groups wintering in the east, with the group in the west suffering almost no mortalities. 

As spatial use of Przewalski’s horses is extremely conservative, groups did not attempt to venture beyond their known home ranges. In contrast, Asiatic wild asses seem to have suffered few losses. These animals roam over much larger areas than Przewalski’s horses and are not restricted to any particular wintering areas. 

Petra Kaczensky, the first author on the PLoS paper, says that “wild asses were obviously able to outrun the worst of the dzud by moving west. The long-distance movements and shifts in range highlight how important it is to manage migratory or nomadic species on a landscape level, including multi-use areas outside of protected areas. Fragmentation of their range will reduce their flexibility and can easily result in local population crashes such as the one seen for the Przewalski’s horses.”

The severe effect of this localized catastrophic event was largely due to the small size and limited range of the present-day Przewalski’s horse population. A large and continuous population would be much more robust as it could counteract local population lows or extinctions via re-colonization. The dzud winter of 2009/2010 is a textbook example of how vulnerable small and spatially confined populations are in an environment prone to fluctuations and catastrophes. Losses of this magnitude are difficult to model or predict. 

As long as populations remain small and spatially confined, their survival cannot be guaranteed, necessitating a long term conservation commitment to ensure the species’ future. "The winter disaster really highlighted how dangerous it is to have all our eggs in one basket or in this case all the horses on a single pasture,” says Petra Kaczensky. “The national strategy for Przewalski’s horse conservation in Mongolia should continue to aim at multiple re-introduction sites with spatially dispersed populations. Ideally the sites should cooperate closely and if necessary also exchange animals on a national as well as international scale. 

 Such steps have already been initiated in Mongolia and the recent downlisting of the Przewalski's horse in the IUCN Red List from ‘critically endangered’ to ‘endangered’ shows that this strategy is paying off." Generally, it is not feasible, either technically or financially, to breed and re-introduce all endangered species, as has been done for the Przewalski´s horse. Chris Walzer explains, “More promising strategies involve timely science-based measures to reduce threats to fauna and flora. These may include the establishment of protected areas but it is also important to maintain natural spaces and structures that make multi-purpose landscapes ‘permeable’ for wildlife, so that wide-ranging species can roam, as Asiatic wild asses tend to do”.


Contacts and sources:
Petra Kaczensky
University of Veterinary Medicine -- Vienna

Turn Down The iPod To Save Your Hearing, Risk Of Hearing Loss Before Middle Age

Today's ubiquitous MP3 players permit users to listen to crystal-clear tunes at high volume for hours on end — a marked improvement on the days of the Walkman. But according toTel Aviv University (TAU) research, these advances have also turned personal listening devices into a serious health hazard, with teenagers as the most at-risk group.

Using MP3 players at high volume puts teens at risk for early hearing loss, say TAU researchers

Credit: TAU

One in four teens is in danger of early hearing loss as a direct result of these listening habits, says Prof. Chava Muchnik of TAU'sDepartment of Communication Disorders in the Stanley Steyer School of Health Professions at the Sackler Faculty of Medicine and the Sheba Medical Center. With her colleagues Dr. Ricky Kaplan-Neeman, Dr. Noam Amir, and Ester Shabtai, Prof. Muchnik studied teens' music listening habits and took acoustic measurements of preferred listening levels.

The results, published in the International Journal of Audiology, demonstrate clearly that teens have harmful music-listening habits when it comes to iPods and other MP3 devices. "In 10 or 20 years it will be too late to realize that an entire generation of young people is suffering from hearing problems much earlier than expected from natural aging," says Prof. Muchnik.

Hearing loss before middle age

Hearing loss caused by continuous exposure to loud noise is a slow and progressive process. People may not notice the harm they are causing until years of accumulated damage begin to take hold, warns Prof. Muchnik. Those who are misusing MP3 players today might find that their hearing begins to deteriorate as early as their 30's and 40's — much earlier than past generations.

The first stage of the study included 289 participants aged 13 to 17. They were asked to answer questions about their habits on personal listening devices (PLDs) — specifically, their preferred listening levels and the duration of their listening. In the second stage, measurements of these listening levels were performed on 74 teens in both quiet and noisy environments. The measured volume levels were used to calculate the potential risk to hearing according to damage risk criteria laid out by industrial health and safety regulations.

The study's findings are worrisome, says Prof. Muchnik. Eighty percent of teens use their PLDs regularly, with 21 percent listening from one to four hours daily, and eight percent listening more than four hours consecutively. Taken together with the acoustic measurement results, the data indicate that a quarter of the participants are at severe risk for hearing loss.

Dangerous decibels

Currently, industry-related health and safety regulations are the only benchmark for measuring the harm caused by continuous exposure to high volume noise. But there is a real need for additional music risk criteria in order to prevent music-induced hearing loss, Prof. Muchnik says. In the meantime, she recommends that manufacturers adopt the European standards that limit the output of PLDs to 100 decibels. Currently, maximum decibel levels can differ from model to model, but some can go up to 129 decibels.

Steps can also be taken by schools and parents, she says. Some school boards are developing programs to increase awareness of hearing health, such as the "Dangerous Decibels" program in Oregon schools, which provides early education on the subject. Teens could also choose over-the-ear headphones instead of the ear buds that commonly come with an iPod.

In the near future, the researchers will focus on the music listening habits of younger children, including pre-teens, and the development of advanced technological solutions to enable the safe use of PLDs.

Contacts and sources:
George Hunka
American Friends of Tel Aviv University