Neuroscience  

Researchers have created models of neurons in the visual cortex of a mouse in order to better understand—and make predictions about—how neurons relay and code visual information.

Scientists at the Allen Institute for Brain Science have created models of neurons in the visual cortex of a mouse in order to better understand—and make predictions about—how neurons relay and code visual information.

This movie shows preliminary data of 10,000 neurons: 8,000 replicated pyramidal cells (an excitatory neuron, shown first) and 2,000 replicated interneurons (an inhibitory neuron, shown second).

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Copies of these two cells are displayed one after another in the movie until approximately 10% of the whole model is shown in the video.(More than that would be too cluttered to see what is happening.)

Toward the middle of the movie, the cells are colored according to their properties: excitatory in red and inhibitory in blue. The second half of the movie illustrates activity of the cells in a two second-long simulation. The cells that fire action potentials are intermittently highlighted, giving the viewer an impression of the simulated neuronal activity.

The results in themselves are amazing, but the scale compared with the 80 billion plus neurons in the human brain demonstrate the monumental task computational neuroscience projects like Europe's Human Brain Project and the US BRAIN Initiative have ahead of them.  Completing a connectome of a human brain in silico, will be some years away.



SOURCE  Allen Institute for Brain Science

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 Neuroscience  

Researchers have announced the discovery of a new neural circuit in the brain that directly links the site of fear memory with an area of the brainstem that controls behavior.

Fear is primal. In the wild, it serves as a protective mechanism, allowing animals to avoid predators or other perceived threats. For humans, fear is much more complex. A normal amount keeps us safe from danger. But in extreme cases, like post-traumatic stress disorder (PTSD), too much fear can prevent people from living healthy, productive lives. Researchers are actively working to understand how the brain translates fear into action. Scientists at Cold Spring Harbor Laboratory (CSHL) have announced the discovery of a new neural circuit in the brain that directly links the site of fear memory with an area of the brainstem that controls behavior. 

How does the brain convert an emotion into a behavioral response? For years, researchers have known that fear memories are learned and stored in a small structure in the brain known as the amygdala. Any disturbing event activates neurons in the lateral and then central portions of the amygdala. The signals are then communicated internally, passing from one group of neurons to the next. From there, they reach neurons in the brainstem, the action center for fear responses.

Last year, CSHL Associate Professor Bo Li and his colleagues were able to use new genetic techniques to determine the precise neurons in the central amygdala that control fear memory. His current research exploits new methods to understand how the central amygdala communicates fear memories to the areas of the brain that are responsible for action.

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In work published in The Journal of Neuroscience, Li and his team identify a group of long-range neurons that extend from the central amygdala. These neurons project to an area of the brainstem, known as the midbrain periaqueductal gray (PAG), that controls the fear response.

In the top image (via Bo Li), a new neural circuit in the brain that directly links the site of fear memory with an area of the brainstem that controls behavior is shown. Far-reaching neurons in the central amygdala, the location of fear memory in the brain seen here in red on the right, directly contact neurons in the brainstem, here in green on the left.

Li and his colleagues explored how these long-range neurons participate in fear conditioning. They trained animals to associate a particular sound with a shock, conditioning the animals to fear the sound. In these animals, the activity of the long-range projection neurons in the central amygdala became enhanced.

“This study not only establishes a novel pathway for fear learning, but also identifies neurons that actively participate in fear conditioning,” says Li. “This new pathway can mediate the effect of the central amygdala directly, rather than signaling through other neurons, as traditionally thought.”

The next step for these researchers is to apply this knowledge to models of PTSD. “We are working to find out how these circuits behave in anxiety disorders, so that we can hopefully learn to control fear in diseases such as PTSD,” says Li.



SOURCE  Cold Spring Harbor Laboratory

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Researchers have announced they are now able to 'film' a brain as it forms memories. The feat was accomplished by using mRNA molecules, which are crucial to forming memories, fluorescent "tags", so they could be watched more easily.

In two studies in the January 24 issue of Science, researchers at Albert Einstein College of Medicine of Yeshiva University used advanced imaging techniques to provide a window into how the brain makes memories.

These insights into the molecular basis of memory were made possible by a technological tour de force never before achieved in animals: a mouse model developed at Einstein in which molecules crucial to making memories were given fluorescent "tags" so they could be observed traveling in real time in living brain cells.

The research has been published in two articles, "Visualization of Dynamics of Single Endogenous mRNA as Labeled in Live Mouse," and "Single Beta-actin mRNA Detection in Neurons Reveals a Mechanism for Regulating Its Translatability," in the journal Science.

Efforts to discover how neurons make memories have long confronted a major roadblock: Neurons are extremely sensitive to any kind of disruption, yet only by probing their innermost workings can scientists view the molecular processes that culminate in memories. To peer deep into neurons without harming them, Einstein researchers developed a mouse model in which they fluorescently tagged all molecules of messenger RNA (mRNA) that code for beta-actin protein – an essential structural protein found in large amounts in brain neurons and considered a key player in making memories. mRNA is a family of RNA molecules that copy DNA's genetic information and translate it into the proteins that make life possible.

Robert Singer, Ph.D. Image Source: Albert Einstein College of Medicine

Robert Singer, Ph.D., is the senior author of both papers and professor and co-chair of Einstein's department of anatomy & structural biology and co-director of the Gruss Lipper Biophotonics Center at Einstein.

In the research described in the two Science papers, the Einstein researchers stimulated neurons from the mouse's hippocampus, where memories are made and stored, and then watched fluorescently glowing beta-actin mRNA molecules form in the nuclei of neurons and travel within dendrites, the neuron's branched projections. They discovered that mRNA in neurons is regulated through a novel process described as "masking" and "unmasking," which allows beta-actin protein to be synthesized at specific times and places and in specific amounts.

Singer states, "we know the beta-actin mRNA we observed in these two papers was ‘normal' RNA, transcribed from the mouse's naturally occurring beta-actin gene and attaching green fluorescent protein to mRNA molecules did not affect the mice, which were healthy and able to reproduce."

Neurons come together at synapses, where slender dendritic "spines" of neurons grasp each other, much as the fingers of one hand bind those of the other. Evidence indicates that repeated neural stimulation increases the strength of synaptic connections by changing the shape of these interlocking dendrite "fingers." Beta-actin protein appears to strengthen these synaptic connections by altering the shape of dendritic spines.

Memories are thought to be encoded when stable, long-lasting synaptic connections form between neurons in contact with each other.

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The first paper describes the work of Hye Yoon Park, Ph.D., a postdoctoral student in Dr. Singer's lab. Her research was instrumental in developing the mice containing fluorescent beta-actin mRNA—a process that took about three years.

Dr. Park stimulated individual hippocampal neurons of the mouse and observed newly formed beta-actin mRNA molecules within 10 to 15 minutes, indicating that nerve stimulation had caused rapid transcription of the beta-actin gene. Further observations suggested that these beta-actin mRNA molecules continuously assemble and disassemble into large and small particles, respectively. These mRNA particles were seen traveling to their destinations in dendrites where beta-actin protein would be synthesized.

In the second paper, lead author and graduate student Adina Buxbaum of Dr. Singer's lab showed that neurons may be unique among cells in how they control the synthesis of beta-actin protein.

These findings suggest that neurons have developed an ingenious strategy for controlling how memory-making proteins do their job. "This observation that neurons selectively activate protein synthesis and then shut it off fits perfectly with how we think memories are made," said Dr. Singer. "Frequent stimulation of the neuron would make mRNA available in frequent, controlled bursts, causing beta-actin protein to accumulate precisely where it's needed to strengthen the synapse."

To gain further insight into memory's molecular basis, the Singer lab is developing technologies for imaging neurons in the intact brains of living mice. Since the hippocampus resides deep in the brain, they hope to develop infrared fluorescent proteins that emit light that can pass through tissue. Another possibility is a fiberoptic device that can be inserted into the brain to observe memory-making hippocampal neurons.




SOURCE  Albert Einstein College of Medicine

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 Neuroscience  

Researchers at Princeton University have created “souped up” versions of the calcium-sensitive proteins that for the past decade or so have given scientists an unparalleled view and understanding of brain-cell communication.

Researchers at Princeton University have created “souped up” versions of the calcium-sensitive proteins that for the past decade or so have given scientists an unparalleled view and understanding of brain-cell communication.

Reported in the journal Nature Communications, the enhanced proteins developed at Princeton respond more quickly to changes in neuron activity, and can be customized to react to different, faster rates of neuron activity. Together, these characteristics would give scientists a more precise and comprehensive view of neuron activity.

The researchers sought to improve the function of proteins known as green fluorescent protein/calmodulin protein (GCaMP) sensors, an amalgam of various natural proteins that are a popular form of sensor proteins known as genetically encoded calcium indicators, or GECIs. Once introduced into the brain via the bloodstream, GCaMPs react to the various calcium ions involved in cell activity by glowing fluorescent green. Scientists use this fluorescence to trace the path of neural signals throughout the brain as they happen.

GCaMPs and other GECIs have been invaluable to neuroscience, said corresponding author Samuel Wang, a Princeton associate professor of molecular biology and the Princeton Neuroscience Institute.

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Scientists have used the sensors to observe brain signals in real time, and to delve into previously obscure neural networks such as those in the cerebellum. GECIs are necessary for the BRAIN Initiative President Barack Obama announced in April, Wang said. The estimated $3 billion project to map the activity of every neuron in the human brain cannot be done with traditional methods, such as probes that attach to the surface of the brain. “There is no possible way to complete that project with electrodes, so you have to do it with other tools — GECIs are those tools,” he said.

Despite their value, however, the proteins are still limited when it comes to keeping up with the fast-paced, high-voltage ways of brain cells, and various research groups have attempted to address these limitations over the years, Wang said.

“GCaMPs have made significant contributions to neuroscience so far, but there have been some limits and researchers are running up against those limits,” Wang said.

One shortcoming is that GCaMPs are about one-tenth of a second slower than neurons, which can fire hundreds of times per second, Wang said. The proteins activate after neural signals begin, and mark the end of a signal when brain cells have (by neuronal terms) long since moved on to something else, Wang said. A second current limitation is that GCaMPs can only bind to four calcium ions at a time. Higher rates of cell activity cannot be fully explored because GCaMPs fill up quickly on the accompanying rush of calcium.

The Princeton GCaMPs respond more quickly to changes in calcium so that changes in neural activity are seen more immediately, Wang said. By making the sensors a bit more sensitive and fragile — the proteins bond more quickly with calcium and come apart more readily to stop glowing when calcium is removed — the researchers whittled down the roughly 20 millisecond response time of existing GCaMPs to about 10 milliseconds, Wang said.

The researchers also tweaked certain GCaMPs to be sensitive to different types of calcium ion concentrations, meaning that high rates of neural activity can be better explored. “Each probe is sensitive to one range or another, but when we put them together they make a nice choir,” Wang said.

The Princeton researchers will soon introduce their sensor into fly and mammalian brains.

“At some level, what we’ve done is like taking apart an engine, lubing up the parts and putting it back together. We took what was the best version of the protein at the time and made changes to the letter code of the protein,” Wang said. “We want to watch the whole symphony of thousands of neurons do their thing, and we think this variant of GCaMPs will help us do that better than anyone else has.”



SOURCE  Princeton University

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 Nanotech Neuroscience  

Neuroscientists may soon be modern-day harpooners, snaring individual brain-cell signals instead of whales with tiny spears made of carbon nanotubes. The new brain cell spear is a millimeter long, only a few nanometers wide and harnesses the superior electromechanical properties of carbon nanotubes to capture electrical signals from individual neurons.

Neuroscientists may soon be modern-day harpooners, snaring individual brain-cell signals instead of whales with tiny spears made of carbon nanotubes.

The new brain cell spear is a millimeter long, only a few nanometers wide and harnesses the superior electromechanical properties of carbon nanotubes to capture electrical signals from individual neurons.

"To our knowledge, this is the first time scientists have used carbon nanotubes to record signals from individual neurons, what we call intracellular recordings, in brain slices or intact brains of vertebrates," said Bruce Donald, a professor of computer science and biochemistry at Duke University who helped developed the probe.

He and his collaborators describe the carbon nanotube probes in the journal PLOS ONE.

"The results are a good proof of principle that carbon nanotubes could be used for studying signals from individual nerve cells," said Duke neurobiologist Richard Mooney, a study co-author. "If the technology continues to develop, it could be quite helpful for studying the brain."

 SEM images of CNT probes -(A) Low magnification view of a CNT probe. Tungsten wire extends from lower left to the white arrow; CNT probe extends from the arrow for 1.5 mm to upper right. (B) Tip of a CNT probe after dielectrophoresis. The tip tapers down to a single CNT (white arrow). (C) CNTs in the probe show a clearly self-entangled morphology. (D) A CNT probe tip after coating with 300 nm Parylene-C, which homogeneously covers the entire probe. (E) An exposed CNT probe tip after FIB cutting. Two FIB cutting planes are perpendicular to the picture, crossing at the end of the probe. (F) An angled view (at 40° with respect to the electron beam in the SEM) of exposed CNT probe tip shows the two cut planes. The FIB cutting did not damage nearby insulation coating, which is clearly visible (white arrow). Scale bars in (B)- (F): 1 µm Image Source: doi:10.1371/journal.pone.0065715.g003

Scientists want to study signals from individual neurons and their interactions with other brain cells to better understand the computational complexity of the brain.

Currently, they use two main types of electrodes, metal and glass, to record signals from brain cells. Metal electrodes record spikes from a population of brain cells and work well in live animals. Glass electrodes also measure spikes, as well as the computations individual cells perform, but are delicate and break easily.

"The new carbon nanotubes combine the best features of both metal and glass electrodes. They record well both inside and outside brain cells, and they are quite flexible. Because they won't shatter, scientists could use them to record signals from individual brain cells of live animals," said Duke neurobiologist Michael Platt, who was not involved in the study.

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In the past, other scientists have experimented with carbon nanotube probes. But the electrodes were thick, causing tissue damage, or they were short, limiting how far they could penetrate into brain tissue. They could not probe inside individual neurons.

To change this, Donald began working on a harpoon-like carbon-nanotube probe with Duke neurobiologist Richard Mooney five years ago. The two met during their first year at Yale in the 1976, kept in touch throughout graduate school and began meeting to talk about their research after they both came to Duke.

Mooney told Donald about his work recording brain signals from live zebra finches and mice. The work was challenging, he said, because the probes and machinery to do the studies were large and bulky on the small head of a mouse or bird.

With Donald's expertise in nanotechnology and robotics and Mooney's in neurobiology, the two thought they could work together to shrink the machinery and improve the probes with nano-materials.

To make the probe, graduate student Inho Yoon and Duke physicist Gleb Finkelstein used the tip of an electrochemically sharpened tungsten wire as the base and extended it with self-entangled multi-wall carbon nanotubes to create a millimeter-long rod. The scientists then sharpened the nanotubes into a tiny harpoon using a focused ion beam at North Carolina State University.

Yoon then took the nano-harpoon to Mooney's lab and jabbed it into slices of mouse brain tissue and then into the brains of anesthetized mice. The results show that the probe transmits brain signals as well as, and sometimes better than, conventional glass electrodes and is less likely to break off in the tissue. The new probe also penetrates individual neurons, recording the signals of a single cell rather than the nearest population of them.

Based on the results, the team has applied for a patent on the nano-harpoon. Platt said scientists might use the probes in a range of applications, from basic science to human brain-computer interfaces and brain prostheses.

SOURCE  Duke University

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