Posts tagged science

February 21, 2012

There are a number of drugs and experimental conditions that can block cognitive function and impair learning and memory. However, scientists have recently shown that some drugs can actually improve cognitive function, which may have implications for our understanding of cognitive disorders such as Alzheimer’s disease. The new research is reported 21 February in the open-access journal PLoS Biology.

The study, led by Drs. Jose A. Esteban, Shira Knafo and Cesar Venero, is the result of collaboration between researchers from The Centro de Biología Molecular Severo Ochoa and UNED (Spain), the Brain Mind Institute (EPFL, Switzerland) and the Department of Neuroscience and Pharmacology (Faculty of Health Sciences, Denmark).

The human brain contains trillions of neuronal connections, called synapses, whose pattern of activity controls all our cognitive functions. These synaptic connections are dynamic and constantly changing in their strength and properties. This process, known as synaptic plasticity, has been proposed as the cellular basis for learning and memory. Indeed, alterations in synaptic plasticity mechanisms are thought to be responsible for multiple cognitive deficits, such as autism, Alzheimer’s disease and several forms of mental retardation.

The study by Knafo et al. provides new information on the molecular mechanisms of synaptic plasticity, and how this process may be manipulated to improve cognitive performance. They find that synapses can be made more plastic by using a small protein fragment (peptide) derived from a neuronal protein involved in cell-to-cell communication. This peptide (called FGL) initiates a cascade of events inside the neuron that results in the facilitation of synaptic plasticity. Specifically, the authors found that FGL triggers the insertion of new neurotransmitter receptors into synapses in a region of the brain called the hippocampus, which is known to be involved in multiple forms of learning and memory. Importantly, when this peptide was administered to rats, their ability to learn and retain spatial information was enhanced.

Dr. Esteban remarks: “We have known for three decades that synaptic connections are not fixed from birth, but they respond to neuronal activity modifying their strength. Thus, outside stimuli will lead to the potentiation of some synapses and the weakening of others. It is precisely this code of ups and downs what allows the brain to store information and form memories during learning”.

Within this framework, these new findings demonstrate that synaptic plasticity mechanisms mechanisms can be manipulated pharmacologically in adult animals, with the aim of enhancing cognitive ability. Dr. Knafo adds: “These are basic studies on the molecular and cellular processes that control our cognitive function. Nevertheless, they shed light into potential therapeutic avenues for mental disorders where these mechanisms go awry”.

Source: medicalxpress.com

ScienceDaily (Feb. 21, 2012) — The carnage evident in disasters like car wrecks or wartime battles is oftentimes mirrored within the bodies of the people involved. A severe wound can leave blood vessels and nerves severed, bones broken, and cellular wreckage strewn throughout the body — a debris field within the body itself.

Thriving DRG cells. (Credit: Image courtesy of University of Rochester Medical Center)

It’s scenes like this that neurosurgeon Jason Huang, M.D., confronts every day. Severe damage to nerves is one of the most challenging wounds to treat for Huang and colleagues. It’s a type of wound suffered by people who are the victims of gunshots or stabbings, by those who have been involved in car accidents — or by soldiers injured on the battlefield, like those whom Huang treated in Iraq.

Now, back in his university laboratory, Huang and his team have taken a step forward toward the goal of repairing nerves in such patients more effectively. In a paper published in the journal PLoS ONE, Huang and colleagues at the University of Rochester Medical Center report that a surprising set of cells may hold potential for nerve transplants.

In a study in rats, Huang’s group found that dorsal root ganglion neurons, or DRG cells, help create thick, healthy nerves, without provoking unwanted attention from the immune system.

The finding is one step toward better treatment for the more than 350,000 patients each year in the United States who have serious injuries to their peripheral nerves. Huang’s laboratory is one of a handful developing new technologies to treat such wounds.

"These are very serious injuries, and patients really suffer, many for a very long time," said Huang, associate professor of Neurosurgery and chief of Neurosurgery at Highland Hospital, an affiliate of the University of Rochester Medical Center. "There are a variety of options, but none of them is ideal.

"Our long-term goal is to grow living nerves in the laboratory, then transplant them into patients and cut down the amount of time it takes for those nerves to work," added Huang, whose project was funded by the National Institute of Neurological Disorders and Stroke and by the University of Rochester Medical Center.

For a damaged nerve to repair itself, the two disconnected but healthy portions of the nerve must somehow find each other through a maze of tissue and connect together. This happens naturally for a very small wound — much like our skin grows back over a small cut — but for some nerve injuries, the gap is simply too large, and the nerve won’t grow back without intervention.

For surgeons like Huang, the preferred option is to transplant nerve tissue from elsewhere in the patient’s own body — for instance, a section of a nerve in the leg — into the wounded area. The transplanted nerve serves as scaffolding, a guide of sorts for a new nerve to grow and bridge the gap. Since the tissue comes from the patient, the body accepts the new nerve and doesn’t attack it.

But for many patients, this treatment isn’t an option. They might have severe wounds to other parts of the body, so that extra nerve tissue isn’t available. Alternatives can include a nerve transplant from a cadaver or an animal, but those bring other challenges, such as the lifelong need for powerful immunosuppressant drugs, and are rarely used.

One technology used by Huang and other neurosurgeons is the NeuraGen Nerve Guide, a hollow, absorbable collagen tube through which nerve fibers can grow and find each other. The technology is often used to repair nerve damage over short distances less than half an inch long.

In the PLoS One study, Huang’s team compared several methods to try to bridge a nerve gap of about half an inch in rats. The team transplanted nerve cells from a different type of rat into the wound site and compared results when the NeuraGen technology was was used alone or when it was paired with DRG cells or with other cells known as Schwann cells.

After four months, the team found that the tubes equipped with either DRG or Schwann cells helped bring about healthier nerves. In addition, the DRG cells provoked less unwanted attention from the immune system than the Schwann cells, which attracted twice as many macrophages and more of the immune compound interferon gamma.

While both Schwann and DRG cells are known players in nerve regeneration, Schwann cells have been considered more often as potential partners in the nerve transplantation process, even though they pose considerable challenges because of the immune system’s response to them.

"The conventional wisdom has been that Schwann cells play a critical role in the regenerative process," said Huang, who is a scientist in the Center for Neural Development and Disease. "While we know this is true, we have shown that DRG cells can play an important role also. We think DRG cells could be a rich resource for nerve regeneration."

In a related line of research, Huang along with colleagues in the laboratory of Douglas H. Smith, M.D. , at the University of Pennsylvania are creating DRG cells in the laboratory by stretching them, which coaxes them to grow about one inch every three weeks. The idea is to grow nerves several inches long in the laboratory, then transplant them into the patient, instead of waiting months after surgery for the nerve endings to travel that distance within the patient to ultimately hook up.

Source: Science Daily

Article Date: 20 Feb 2012 - 2:00 PST

New connections between brain cells emerge in clusters in the brain as animals learn to perform a new task, according to a study published in Nature on February 19 (advance online publication). Led by researchers at the University of California, Santa Cruz, the study reveals details of how brain circuits are rewired during the formation of new motor memories.

The researchers studied mice as they learned new behaviors, such as reaching through a slot to get a seed. They observed changes in the motor cortex, the brain layer that controls muscle movements, during the learning process. Specifically, they followed the growth of new “dendritic spines,” structures that form the connections (synapses) between nerve cells.

“For the first time we are able to observe the spatial distribution of new synapses related to the encoding of memory,” said Yi Zuo, assistant professor of molecular, cell and developmental biology at UC Santa Cruz and corresponding author of the paper.

In a previous study, Zuo and others documented the rapid growth of new dendritic spines on pyramidal neurons in the motor cortex during the learning process. These spines form synapses where the pyramidal neurons receive input from other brain regions involved in motor memories and muscle movements. In the new study, first author Min Fu, a postdoctoral researcher in Zuo’s lab, analyzed the spatial distribution of the newly formed synapses.

Initial results of the spatial analysis showed that one third of the newly formed synapses were located next to another new synapse. These clustered synapses tended to form over the course of a few days during the learning period, when the mouse was repeatedly performing the new behavior. Compared to non-clustered counterparts, the clustered synapses were more likely to persist through the learning sessions and after training stopped.

In addition, the researchers found that after formation of the second spine in a cluster, the first spine grew larger. The size of the spine head correlates with the strength of the synapse. “We found that formation of a second connection is correlated with a strengthening of the first connection, which suggests that they are likely to be involved in the same circuitry,” Zuo said. “The clustering of synapses may serve to magnify the strength of the connections.”

Another part of the study also supported the idea that the clustered synapses are involved in neural circuits specific to the task being learned. The researchers studied mice trained first in one task and then in a different task. Instead of grabbing a seed, the mice had to learn how to handle a piece of capellini pasta. Both tasks induced the formation of clustered spines, but spines formed during the learning of different tasks did not cluster together.

The researchers also looked at mice that were challenged with new motor tasks every day, but did not repeat the same task over and over like the ones trained in seed-grabbing or capellini-handling. These mice also grew lots of new dendritic spines, but few of the new spines were clustered.

“Repetitive activation of the same cortical circuit is really important in learning a new task,” Zuo said. “But what is the optimal frequency of repetition? Ultimately, by studying the relationship between synapse formation and learning, we want to find out the best way to induce new memories.”

The study used mice that had been genetically altered to make a fluorescent protein within certain neurons in the motor cortex. The researchers used a special microscopy technique (two-photon microscopy) to obtain images of those neurons near the surface of the brain. The noninvasive imaging technique enabled them to view changes in individual brain cells of the mice before, during, and after learning a new behavior.  

Source: Medical News Today

ScienceDaily (Feb. 19, 2012) — New connections between brain cells emerge in clusters in the brain as animals learn to perform a new task, according to a study published in Nature on February 19 (advance online publication). Led by researchers at the University of California, Santa Cruz, the study reveals details of how brain circuits are rewired during the formation of new motor memories.

Rendering of neural network. New connections between brain cells emerge in clusters in the brain as animals learn to perform a new task, according to a study. (Credit: © nobeastsofierce / Fotolia)

The researchers studied mice as they learned new behaviors, such as reaching through a slot to get a seed. They observed changes in the motor cortex, the brain layer that controls muscle movements, during the learning process. Specifically, they followed the growth of new “dendritic spines,” structures that form the connections (synapses) between nerve cells.

"For the first time we are able to observe the spatial distribution of new synapses related to the encoding of memory," said Yi Zuo, assistant professor of molecular, cell and developmental biology at UC Santa Cruz and corresponding author of the paper.

In a previous study, Zuo and others documented the rapid growth of new dendritic spines on pyramidal neurons in the motor cortex during the learning process. These spines form synapses where the pyramidal neurons receive input from other brain regions involved in motor memories and muscle movements. In the new study, first author Min Fu, a postdoctoral researcher in Zuo’s lab, analyzed the spatial distribution of the newly formed synapses.

Initial results of the spatial analysis showed that one third of the newly formed synapses were located next to another new synapse. These clustered synapses tended to form over the course of a few days during the learning period, when the mouse was repeatedly performing the new behavior. Compared to non-clustered counterparts, the clustered synapses were more likely to persist through the learning sessions and after training stopped.

In addition, the researchers found that after formation of the second spine in a cluster, the first spine grew larger. The size of the spine head correlates with the strength of the synapse. “We found that formation of a second connection is correlated with a strengthening of the first connection, which suggests that they are likely to be involved in the same circuitry,” Zuo said. “The clustering of synapses may serve to magnify the strength of the connections.”

Another part of the study also supported the idea that the clustered synapses are involved in neural circuits specific to the task being learned. The researchers studied mice trained first in one task and then in a different task. Instead of grabbing a seed, the mice had to learn how to handle a piece of capellini pasta. Both tasks induced the formation of clustered spines, but spines formed during the learning of different tasks did not cluster together.

The researchers also looked at mice that were challenged with new motor tasks every day, but did not repeat the same task over and over like the ones trained in seed-grabbing or capellini-handling. These mice also grew lots of new dendritic spines, but few of the new spines were clustered.

"Repetitive activation of the same cortical circuit is really important in learning a new task," Zuo said. "But what is the optimal frequency of repetition? Ultimately, by studying the relationship between synapse formation and learning, we want to find out the best way to induce new memories."

The study used mice that had been genetically altered to make a fluorescent protein within certain neurons in the motor cortex. The researchers used a special microscopy technique (two-photon microscopy) to obtain images of those neurons near the surface of the brain. The noninvasive imaging technique enabled them to view changes in individual brain cells of the mice before, during, and after learning a new behavior.

Source: Science Daily

February 19, 2012 

In two landmark papers in the journal Nature this week, scientists at The Scripps Research Institute report that they have identified a class of proteins that detect “painful touch.”

Scientists have known that sensory nerves in our skin detect pressure, pain, heat, cold, and other stimuli using specialized “ion channel” proteins in their outer membranes. They have only just begun, however, to identify and characterize the specific proteins involved in each of these sensory pathways. The new work provides evidence that a family of sensory nerve proteins known as piezo proteins are ion channel proteins essential to the sensation of painful touch.

The experiments in the new study were conducted in fruit flies, a model system for the sensory nervous system of mammals, where piezo proteins are also expressed, as well as in certain cell types in the ear, kidney, heart, and other tissues. Future studies will focus on the roles of piezo proteins in sensing sound, blood pressure, and related stimuli that press and/or stretch cell membranes.

"Researchers in this field have been trying for decades to identify pressure-transducing ion channel proteins that exist in mammals, and these piezo proteins are exceptionally strong candidates," said Ardem Patapoutian, a professor in the Department of Cell Biology and the Dorris Neuroscience Center at Scripps Research, and a senior investigator for both papers. "We now have solid clues that we can follow up to learn how the mechanotransduction pathway works and how it is disrupted in diseases."

The two papers appear online in Nature on February 19, 2012.

Following the Path of Clues

Patapoutian’s laboratory specializes in the study of sensory ion-channel proteins. When hit by a stimulus to which it is sensitive, one of these proteins typically will open its structure to allow charged calcium, sodium, or potassium molecules (“ions”) to flow from the fluid outside the cell into the cell’s interior. Ion channels that sense mechanical pressure are thought to open when the membrane in which they are embedded is distorted past a certain threshold. The resulting flow of charge can trigger other signals inside the cell, for example a nerve impulse within sensory neurons—and in a human, a sufficient number of these nerve impulses would be interpreted by the brain as a touch- or pressure-related feeling.

 In a highly cited paper published in Science in late 2010, Patapoutian and his colleagues reported that two mouse proteins of previously unknown function exhibited properties of mechanotransducers. Cells to which these proteins were added drew in positively charged ions when subjected to mechanical pressure. Bertrand Coste, the first author of the paper, named the two closely related proteins piezo1 and piezo2—the prefix “piezo-” being derived from the ancient Greek word for pressure or squeezing.

"Since these proteins bore little resemblance to known ion channel proteins, the next step for us was to confirm that they are indeed ion channel proteins," Patapoutian said. The new studies take this step and more.

In the first of the new studies, lead authors Bertrand Coste, Bailong Xiao, and their colleagues confirmed that piezo proteins are indeed ion channel proteins, and very large ones. “It assembles into a ‘tetramer’ complex of four piezo proteins, which appears to be the biggest plasma membrane ion channel yet discovered,” said Coste, a research associate in the Patapoutian lab. The protein sequences within piezo also suggest that its ion channel structure weaves through the cell membrane more than 100 times.

Collaborating researchers in the laboratory of Mauricio Montal, a Distinguished Professor of Neurobiology at the University of California, San Diego, found that even in the absence of other proteins, piezo proteins could self-assemble into this tetramer complex, forming ion channels in artificial membranes known as lipid bilayers.

The second of the new studies involved experiments with the fruit fly Drosophila. Sung Eun Kim, first author of the study, genetically engineered a line of Drosophila that does not express the Drosophila piezo (dpiezo) gene. “We found that their larvae showed a severe loss of responsiveness to mechanical stimuli that would be expected to generate pain-related signals, though they responded normally to other kinds of stimuli such as heat and mild pressure,” she said. Kim is a graduate student who divides her time between the Patapoutian lab and the lab of Scripps Research Assistant Professor Boaz Cook, who was co-principal investigator of this study.

Kim also used genetic “knockdown” techniques in Drosophila to show that interrupting dpiezo expression in certain sensory neurons could reproduce this loss of sensitivity. Finally, when she artificially reinstated dpiezo expression in larvae that had been born without the gene, they displayed normal sensitivity to strong pressure. “It’s the first demonstration of a specific physiological function of a piezo family protein,” said Cook.

The Patapoutian lab now is now conducting detailed follow-up studies of piezo and other possible mechanotransduction proteins. “In the next several years, we’ll be trying to determine all the biological processes and diseases in which these pressure-sensing proteins play a role,” he said.

More information: “Piezos Are Pore-Forming Subunits of Mechanically Activated Channels,” Nature (2012).

Provided by The Scripps Research Institute

Source: medicalxpress.com

February 16, 2012

(Medical Xpress) — Gene therapy not only helps injured brain cells to live longer and regenerate, but also changes the shape of the cells, according to researchers The University of Western Australia. 

The study, published in the international science and medicine journal PLoS One, was led by Winthrop Professor Alan Harvey from UWA’s School of Anatomy, Physiology and Human Biology, and Associate Professor Jennifer Rodger, NHMRC Research Fellow in Experimental and Regenerative Neurosciences at UWA’s School of Animal Biology.  The research was funded primarily by the WA Neurotrauma Research Program.

Professor Harvey said gene therapy was a relatively new strategy that attempted to help injured brain cells survive and regrow.

"Our previous work has shown that when growth-promoting genes are introduced into injured brain cells for long periods of time (up to nine months), the cells’ capacity for survival and regeneration is significantly increased," he said.

"We have now shown that these same neurons have also changed shape in response to persistent over-expression of the growth factors.  Importantly, it is not just neurons containing the introduced growth-promoting gene that are affected, but neighbouring "bystander" neurons."

Professor Harvey said neural morphology was very important in determining how a cell communicated with other cells and formed the circuits that allowed the brain to function.

"Any changes in morphology are therefore likely to alter the way neurons receive and transmit information.  These changes may be beneficial but could also interfere with normal brain circuits, reducing the benefits of improved survival and regeneration."

Professor Harvey said the results were significant for those involved in designing gene therapy-based protocols to treat brain and spinal cord injury and degeneration.

"These new results suggest that we may need to be careful about the types of genes we use in neurotherapy and how long we continue the therapy.  While it may be beneficial for these genes to move around and cause changes in other cells, we need to be able to switch them off once the change has taken place."

Provided by University of Western Australia

Source: medicalxpress.com

February 16th, 2012

Researchers have created a living 3-D model of a brain tumor and its surrounding blood vessels. In experiments, the scientists report that iron-oxide nanoparticles carrying the agent tumstatin were taken by blood vessels, meaning they should block blood vessel growth. The living-tissue model could be used to test the effectiveness of nanoparticles in fighting other diseases. Results appear in Theranostics.

Brown University scientists have created the first three-dimensional living tissue model, complete with surrounding blood vessels, to analyze the effectiveness of therapeutics to combat brain tumors. The 3-D model gives medical researchers more and better information than Petri dish tissue cultures.

The researchers created a glioma, or brain tumor, and the network of blood vessels that surrounds it. In a series of experiments, the team showed that iron-oxide nanoparticles ferrying the chemical tumstatin penetrated the blood vessels that sustain the tumor with oxygen and nutrients. The iron-oxide nanoparticles are important, because they are readily taken up by endothelial cells and can be tracked by magnetic resonance imaging.

Previous experiments have shown that tumstatin was effective at blocking endothelial cell growth in gliomas. The tests by the Brown researchers took it to another level by confirming, in a 3-D, living environment, the iron-oxide nanoparticles’ ability to reach blood vessels surrounding a glioma as well as tumstatin’s ability to penetrate endothelial cells.

“The 3-D glioma model that we have developed offers a facile process to test diffusion and penetration into a glioma that is covered by a blood vessel-like coating of endothelial cells,” said Don Ho, a graduate student in the lab of chemistry professor Shouheng Sun and the lead author of the paper in the journal Theranostics. “This assay would save time and money, while reducing tests in living organisms, to examine an agent’s 3-D characteristics such as the ability for targeting and diffusion.”

The tissue model concept comes from Jeffrey Morgan, a bioengineer at Brown and a corresponding author on the paper. Building on that work, Ho and others created an agarose hydrogel mold in which rat RG2-cell gliomas roughly 200 microns in diameter formed. The team used endothelial cells derived from cow respiratory vessels, which congregated around the tumor and created the blood vessel architecture. The advantage of a 3-D model rather than Petri-dish-type analyses is that the endothelial cells attach to the tumor, rather than being separated from the substrate. This means the researchers can study their formation and growth, as well as the action of anti-therapeutic agents, just as they would in a living organism.

“You want to see nanoparticles that diffuse through the endothelial cells, which is lost in 2-D because you just have diffusion into media,” Ho said.

Other 3-D tissue models have been “forced cell arrangements,” Ho said. The 3-D glioma model, in contrast, allowed the glioma and the endothelial cells to assemble naturally, just as they would in real life. “It more clearly mimics what would actually happen,” Ho explained.

The group then attached tumstatin, part of a naturally occurring protein found in collagen, to iron-oxide nanoparticles and dosed the mold. True to form, the nanoparticles were gobbled up by the endothelial cells. In a series of in vitro experiments, the team reported the tumstatin iron-oxide nanoparticles decreased vasculature growth 2.7 times more than under normal conditions over eight days. “The growth is pretty much flat,” Ho said. “There’s no new growth of endothelial cells.” The next step is to test the tumstatin nanoparticles’ performance in the 3-D environment.

“This model has significant potential to help in the testing and optimization of the design of therapeutic/diagnostic nanocarriers and determine their therapeutic capabilities,” the researchers write.

Source: Neuroscience News