Posts tagged optogenetics
Articles and news from the latest research reports.
Mice Give New Clues to Origins of OCD
Columbia Psychiatry researchers have identified what they think may be a mechanism underlying the development of compulsive behaviors. The finding suggests possible approaches to treating or preventing certain characteristics of OCD.
OCD consists of obsessions, which are recurrent intrusive thoughts, and compulsions, which are repetitive behaviors that patients perform to reduce the severe anxiety associated with the obsessions. The disorder affects 2–3 percent of people worldwide and is an important cause of illness-related disability, according to the World Health Organization.
Using a new technology in a mouse model, the researchers found that repeated stimulation of specific circuits linking the brain’s cortex and striatum produces progressive repetitive behavior. By targeting this region, it may be possible to stop abnormal circuit changes before they become pathological behaviors in people at risk for obsessive-compulsive disorder (OCD). The study, which was led by Susanne Ahmari, MD, PhD, assistant professor of clinical psychiatry at Columbia Psychiatry and the New York State Psychiatric Institute, was published in the June 7 issue of Science.
While the obsessions and compulsions that are the hallmarks of OCD are thought to be centered in the cortex, which controls thoughts, and the striatum, which controls movements, little is known about how abnormalities in these brain regions lead to compulsive behaviors in patients.
To simulate the increased activity that takes place in the brains of OCD patients, Dr. Ahmari and her colleagues used a new technology called optogenetics, in which light-activated ion channels are expressed in subsets of neurons in mice, and neural circuits are then selectively activated using light delivered through fiberoptic probes.
“What we found was really surprising,” said Dr. Ahmari. “That activation of cortico-striatal circuits did not lead directly to repetitive behaviors in the mice. But if we repeatedly stimulated for multiple days in a row for only five minutes a day, we saw a progressive development of repetitive behaviors—in this case, repetitive grooming behavior—that persisted up to two weeks after the stimulation was stopped.”
She added, “And not only that, when we treated the mice with fluoxetine, one of the most common medications used for OCD, their behavior went back to normal.” The current study, as well as others currently being performed by Dr. Ahmari and her team, may ultimately provide clues for new treatment targets in terms of both novel drug development and direct stimulation techniques, including deep brain stimulation (DBS).
MIT study sheds light on what causes compulsive behavior, could improve OCD treatments.
By activating a brain circuit that controls compulsive behavior, MIT neuroscientists have shown that they can block a compulsive behavior in mice — a result that could help researchers develop new treatments for diseases such as obsessive-compulsive disorder (OCD) and Tourette’s syndrome.
About 1 percent of U.S. adults suffer from OCD, and patients usually receive antianxiety drugs or antidepressants, behavioral therapy, or a combination of therapy and medication. For those who do not respond to those treatments, a new alternative is deep brain stimulation, which delivers electrical impulses via a pacemaker implanted in the brain.
For this study, the MIT team used optogenetics to control neuron activity with light. This technique is not yet ready for use in human patients, but studies such as this one could help researchers identify brain activity patterns that signal the onset of compulsive behavior, allowing them to more precisely time the delivery of deep brain stimulation.
“You don’t have to stimulate all the time. You can do it in a very nuanced way,” says Ann Graybiel, an Institute Professor at MIT, a member of MIT’s McGovern Institute for Brain Research and the senior author of a Science paper describing the study.
The paper’s lead author is Eric Burguière, a former postdoc in Graybiel’s lab who is now at the Brain and Spine Institute in Paris. Other authors are Patricia Monteiro, a research affiliate at the McGovern Institute, and Guoping Feng, the James W. and Patricia T. Poitras Professor of Brain and Cognitive Sciences and a member of the McGovern Institute.
Controlling compulsion
In earlier studies, Graybiel has focused on how to break normal habits; in the current work, she turned to a mouse model developed by Feng to try to block a compulsive behavior. The model mice lack a particular gene, known as Sapap3, that codes for a protein found in the synapses of neurons in the striatum — a part of the brain related to addiction and repetitive behavioral problems, as well as normal functions such as decision-making, planning and response to reward.
For this study, the researchers trained mice whose Sapap3 gene was knocked out to groom compulsively at a specific time, allowing the researchers to try to interrupt the compulsion. To do this, they used a Pavlovian conditioning strategy in which a neutral event (a tone) is paired with a stimulus that provokes the desired behavior — in this case, a drop of water on the mouse’s nose, which triggers the mouse to groom. This strategy was based on therapeutic work with OCD patients, which uses this kind of conditioning.
After several hundred trials, both normal and knockout mice became conditioned to groom upon hearing the tone, which always occurred just over a second before the water drop fell. However, after a certain point their behaviors diverged: The normal mice began waiting until just before the water drop fell to begin grooming. This type of behavior is known as optimization, because it prevents the mice from wasting unnecessary effort.
This behavior optimization never appeared in the knockout mice, which continued to groom as soon as they heard the tone, suggesting that their ability to suppress compulsive behavior was impaired.
The researchers suspected that failed communication between the striatum, which is related to habits, and the neocortex, the seat of higher functions that can override simpler behaviors, might be to blame for the mice’s compulsive behavior. To test this idea, they used optogenetics, which allows them to control cell activity with light by engineering cells to express light-sensitive proteins.
When the researchers stimulated light-sensitive cortical cells that send messages to the striatum at the same time that the tone went off, the knockout mice stopped their compulsive grooming almost totally, yet they could still groom when the water drop came. The researchers suggest that this cure resulted from signals sent from the cortical neurons to a very small group of inhibitory neurons in the striatum, which silence the activity of neighboring striatal cells and cut off the compulsive behavior.
“Through the activation of this pathway, we could elicit behavior inhibition, which appears to be dysfunctional in our animals,” Burguière says.
The researchers also tested the optogenetic intervention in mice as they groomed in their cages, with no conditioning cues. During three-minute periods of light stimulation, the knockout mice groomed much less than they did without the stimulation.
Scott Rauch, president and psychiatrist-in-chief of McLean Hospital in Belmont, Mass., says the MIT study “opens the door to a universe of new possibilities by identifying a cellular and circuitry target for future interventions.”
“This represents a major leap forward, both in terms of delineating the brain basis of pathological compulsive behavior and in offering potential avenues for new treatment approaches,” adds Rauch, who was not involved in this study.
Graybiel and Burguière are now seeking markers of brain activity that could reveal when a compulsive behavior is about to start, to help guide the further development of deep brain stimulation treatments for OCD patients.
Physicist’s tool has potential for brain mapping
A new tool being developed by UT Arlington assistant professor of physics could help scientists map and track the interactions between neurons inside different areas of the brain.
The journal Optics Letters recently published a paper by Samarendra Mohanty on the development of a fiber-optic, two-photon, optogenetic stimulator and its use on human cells in a laboratory. The tiny tool builds on Mohanty’s previous discovery that near-infrared light can be used to stimulate a light-sensitive protein introduced into living cells and neurons in the brain. This new method could show how different parts of the brain react when a linked area is stimulated.
The technology would be useful in the BRAIN mapping initiative recently championed by President Barack Obama, Mohanty said. BRAIN stands for Brain Research Through Advancing Innovative Neurotechnologies and will include $100 million in government investments in research.
“Scientists have spent a lot of time looking at the physical connections between different regions of the brain. But that information is not sufficient unless we examine how those connections function,” Mohanty said. “That’s where two-photon optogenetics comes into play. This is a tool not only to control the neuronal activity but to understand how the brain works.”
The two-photon optogenetic stimulation described in the Optics Letter paper involves introducing the gene for ChR2, a protein that responds to light, into a sample of excitable cells. A fiber-optic infrared beam of light can then be used to precisely excite the neurons in a tissue circuit.
In the brain, researchers would then observe responses in the excited area as well as other parts of the neural circuit. In living subjects, scientists would also observe the behavioral outcome, Mohanty said.
Optogenetic stimulation avoids damage to living tissue by using light to stimulate neurons instead of electric pulses used in past research. Mohanty’s method of using low-energy near-infrared light also enables more precision and a deeper focus than the blue or green light beams often used in optogenetic stimulation, the paper said.
Using fiber optics to deliver the two-photon optogenetic beam is another advance. Previous methods required bulky microscopes or complex scanning beams. Mohanty’s group is collaborating with UT Arlington Department of Psychology assistant professor Linda Perrotti to apply this technology in living animals.
“Dr. Mohanty’s innovations continue to be recognized because of the great potential they hold,” said Pamela Jansma, dean of the UT Arlington College of Science. “Hopefully, his work will one day provide researchers in other fields the tools they need to examine how the human body works and why normal processes sometimes fail.”
(Image: Shutterstock)
Mapping The Brain Onto The Mind
BRAIN initiative aims to improve tools for studying neurons to answer questions about human thought and behavior
The images appearing on the computer screen were almost too detailed and fast-moving to take in, Misha B. Ahrens remembers. He and colleague Philipp J. Keller were recording the activity of about 80,000 neurons in a live zebrafish brain, the first time something on this scale had been done. Cross-sectional pictures of the young fish’s head flew by, dotted with splotches of light.
The Howard Hughes Medical Institute (HHMI) neuroscientists were using a zebrafish larva with a fluorescent protein inserted in its neurons, and the protein was lighting up every time the cells fired. Their custom-built microscope imaged and recorded the resulting lightning storm in the fish’s brain in real time.
Ahrens commemorated the milestone experiment—which took place nearly seven months ago in a lab at the institute’s Janelia Farm Research Campus outside Washington, D.C.—by filming it with his iPhone. “It was mind-blowing to see the entire brain flash past our eyes,” he remembers.
Keller sat in awe at the computer, repeatedly pulling up and admiring slices of data the high-speed apparatus was collecting. The translucent zebrafish, immobilized in a glass tube filled with gel and nestled among the microscope’s optics, was completely unaware that its neural processing was causing such a stir.
Up until that point, scientists had been able to record simultaneous activity from only about 2 to 3% of the 100,000 neurons in a young zebrafish’s head, Keller says. He and Ahrens managed to capture 80%—a giant leap for fishkind.
On March 18, the duo reported their brain-imaging feat online at Nature Methods. Just 15 days later, President Barack Obama announced a large-scale neuroscience initiative to study the dynamics of brain circuits (C&EN, April 8, page 9).
Unlike the Human Connectome Project—a federal program that strives to uncover a static map of the brain’s circuits—this new initiative aims to uncover those circuits’ activity and interplay. BRAIN (Brain Research through Advancing Innovative Neurotechnologies), as the project is called, will get $100 million in federal support if Obama’s request is granted (see page 25), and it will get a similar amount from private foundations such as HHMI in 2014.
“It was a coincidence,” Keller says of the timing of the proposal. He and Ahrens weren’t involved in developing BRAIN, but their goal—to record all the activity from all the neurons in a simple organism’s brain at once—falls directly in line with the initiative.
Eighty-thousand neurons is a lot. But it’s nothing compared with the 85 billion nerve cells that humans have in their brains, or even the 75 million that mice have. To make the leap to measuring large swaths of the brain circuits of rodents or even humans, BRAIN researchers will need to develop new methods of measuring neuronal activity. They are already working on molecular tags to more accurately indicate nerve cell firing in real time. And scientists are developing miniaturized probes to monitor brain cells without disturbing the organ itself, as well as faster techniques for analyzing the flood of data generated by such a huge number of neurons.
Some imaging methods that monitor multitudes of neurons, like that of Ahrens and Keller, already exist. As do techniques for probing scads of nerve cells with tiny electrodes. BRAIN will likely build on these technologies, experts say. But it will also shoot to build “dream” technologies such as implantable nanomaterials that transmit the activity of individual neurons from inside the head.
At the moment, however, no one knows the exact scope of BRAIN. The National Institutes of Health has already appointed a team of neuroscientists to draw up a blueprint for what should be a multiyear initiative. Other federal agencies involved—the National Science Foundation and the Defense Advanced Research Projects Agency—have yet to announce their strategies.
“Neuroscience is getting to the point where researchers cannot take the next big step to understand neural circuits armed with traditional technology,” says Rafael Yuste, a neuron-imaging expert at Columbia University.
And taking that step, he argues, is vital to understanding human thought. “We have a suspicion that the brain is an emerging system,” Yuste says. In other words, how the brain produces memories or actions involves the interactions of all its neurons, rather than just one or even 1,000. It’s like watching television, Yuste adds. “You need to see all the pixels, or at least most of them, to figure out what’s playing.”
Along with five other scientists, Yuste made the original pitch for a public-private project to map the brain’s dynamics in a 2012 article in Neuron. The group argued that not only could this approach help reveal how the human mind works, but it might also offer some insight into what happens when the brain malfunctions. Knowing how the brain’s circuits are supposed to function, Yuste says, could help pinpoint what’s going wrong in conditions such as schizophrenia, which likely involve faulty circuitry.
BRAIN proponents also say areas outside of science and medicine could profit from the initiative. If successful, they claim, BRAIN could yield economic benefits similar to the Human Genome Project, a program launched in 1990 to sequence all the base pairs in a person’s DNA. “Every dollar we spent to map the human genome has returned $140 to our economy,” President Obama noted when he announced BRAIN.
As was the case for the Human Genome Project, BRAIN has been criticized by many scientists. In an already-tight fiscal climate, some researchers have voiced worries that paying for the initiative will mean losing their own funds. And others have expressed reservations that the project is going after too many neurons to yield interpretable, useful results.
But no one seems to dispute that better tools to record activity from nerve cells is a worthwhile goal. “There’s definitely room to grow in many of the techniques we use to record brain activity,” says Mark J. Schnitzer, a neuroscientist at Stanford University. So far, he says, progress has been made mainly by individual labs doing their own thing. But to get to the next level more rapidly, a coordinated effort like BRAIN—centers and labs of neuroscientists, chemists, and researchers in other disciplines working together—might be the ticket.
Until recently, the number of neurons being recorded simultaneously in experiments was doubling every seven years, according to a 2011 review in Nature Neuroscience. But the Janelia team blew this trend out of the water with its high-speed camera and microscope, which rapidly illuminates and images slices of the brain.
The Janelia experiment worked primarily because zebrafish larvae are transparent to light and can be easily immobilized without negative consequences to their brain activity. But moving to mice, which have more neurons and a light-impenetrable skull, will require some more serious innovation, Keller adds.
Some researchers have designed implantable prisms and fiber-optic probes to direct light into the depths of the mouse brain. But those optical tricks are still limited to measuring a few hundred neurons at once. Plus, the mouse has to be tethered to the fibers or prevented from moving altogether.
Stanford’s Schnitzer has overcome the mobility issue with a miniaturized microscope that he and his team designed to fit onto a mouse’s head. Standing three-quarters of an inch tall, the lightweight device, which contains its own light source and camera, gets implanted into the rodent’s brain, enabling researchers to track the freely moving animal’s nerve cell activity.
Early this year, Schnitzer’s group used the setup to follow the dynamics of roughly 1,000 neurons in a mouse’s brain for more than a month (Nat. Neurosci., DOI: 10.1038/nn.3329). The team learned that neurons in one part of the mouse’s brain fired in similar patterns whenever the mouse returned to a familiar spot in its enclosure.
Still, such optical techniques are invasive. “The most elegant experiment would be done from the outside, without mechanical disturbance to the brain,” Columbia’s Yuste says. He’d like to see BRAIN help develop new light sources that can penetrate farther into brain tissue than a few millimeters.
Also on Yuste’s neuron-imaging wish list is a better way to indicate cell firing. As in the Janelia experiment and Schnitzer’s microscope study, the imaging of neuronal activity is typically carried out with calcium indicators. These are molecules that move to the insides of neurons or are proteins engineered to reside there, both designed to fluoresce when they bind to calcium ions.
As a nerve cell fires, its ion channels open, allowing calcium ions to trickle inside and trigger the indicators.
However, “calcium imaging is flawed,” Yuste says. “It’s an indirect method of tracking neuronal firing.” The indicators can’t tell scientists whether a nerve cell fired a little or a lot, he argues. And they don’t track the cells’ electrical activity in real time because calcium diffusion and binding are comparatively slow.
So Yuste and others are working to develop dyes or nanomaterials, called voltage indicators, that bind within a neuron’s membrane and optically signal the cell’s electrical status. Progress is slow-going, however, because a cell’s membrane can hold only so many indicators on its surface and the resulting signal is low.
Another way neuroscientists are more directly measuring nerve cells’ electrical activity is with miniaturized electrodes and nanowires. These probes measure, at submillisecond speeds, the electrical current emitted by a neuron when it fires.
“But anytime you plunge anything into the brain, you have to worry about tissue damage,” says Sotiris Masmanidis, a neurobiologist at the University of California, Los Angeles. “The concern is, how much are you perturbing the system you’re studying?”
To minimize tissue disturbance, Masmanidis and others are lithographically fabricating arrays of microelectrodes that can record nerve cells’ electrical signals from 50 to 100 µm away. So far, the UCLA researcher says, electrode arrays are capable of measuring, at most, 100 to 1,000 neurons at a time.
Determining what types of nerve cells an arrayed microelectrode is measuring, however, is not exactly straightforward, given that it blindly measures any neuron in its vicinity, Masmanidis says. To figure it out, scientists have to take extra steps and monitor the cells’ reaction to drugs or other modulators.
But what good is measuring the dynamics of a slew of nerve cells without having any idea why they’re firing? BRAIN supporters think one way of getting an answer to which environmental cues or perceptions trigger certain neuronal activity patterns is a technique called optogenetics.
Hailed by Nature Methods as the “method of the year” in 2010, optogenetics enables scientists to activate particular nerve cells in the brains of animals with light. The researchers first engineer light-activated proteins into a mouse’s neurons and then trigger the macromolecules via fiber-optic arrays implanted in the rodent’s brain.
Once researchers have measured a firing pattern from an animal’s nerve cells, they can later play it back to see what happens, says Edward S. Boyden, an optogenetics pioneer and neurobiologist at Massachusetts Institute of Technology. “Once we ‘dial’ an activity pattern into the brain,” he says, “if we see that it’s enough to drive some behavior, that could be quite powerful for understanding which parts of the brain drive specific functions.”
Researchers have already been optogenetically stimulating clusters of a few hundred cells in mice, investigating the rodents’ decision-making abilities and aggressive tendencies.
But a brain is more than just electrical activity, says Anne M. Andrews, a psychiatry professor at UCLA. It also uses at least 100 types of neurotransmitters that are involved in triggering neuronal activity at cell junctions, or synapses. “If we want to understand how information is encoded in neuronal signaling, we have to study chemical neurotransmission at the level of synapses,” Andrews says.
And what better way to do that than with nanotechnology? asks Paul S. Weiss, a chemist and nanoscience expert, also at UCLA. After all, the junctions between neurons are just 10 nm wide, he adds.
Andrews and Weiss are hoping BRAIN will support the development of nanoscale sensors to measure the chemical activity at synapses. And they’re already in talks with UCLA’s Masmanidis to functionalize channels on his microelectrodes with molecules that could sense neurotransmitters.
No matter what BRAIN ends up encompassing, one thing is clear: Advances in the numbers of neurons monitored will necessitate improvements in data analysis and storage.
Take, for instance, the experiment done at Janelia. That single session of recording from a zebrafish brain generated 1 terabyte of data. “So you can fit two or three experiments on a computer hard drive,” Ahrens says. “It’s not a bottleneck yet, but when we start creating faster microscopes, computational power might become a problem.”
He and Keller also have just scratched the surface when it comes to analyzing the data they obtained from their initial experiments. As they reported in their Nature Methods paper, the pair found a circuit in the fish’s hindbrain functionally coupled to a specific part of its spinal cord. But determining what that means and what the rest of the brain is doing will require more study and help from computational neuroscientists.
Scientists probe the source of a pulsing signal in the sleeping brain
New findings clarify where and how the brain’s “slow waves” originate. These rhythmic signal pulses, which sweep through the brain during deep sleep at the rate of about one cycle per second, are assumed to play a role in processes such as consolidation of memory. For the first time, researchers have shown conclusively that slow waves start in the cerebral cortex, the part of the brain responsible for cognitive functions. They also found that such a wave can be set in motion by a tiny cluster of neurons.
"The brain is a rhythm machine, producing all kinds of rhythms all the time," says Prof. Arthur Konnerth of the Technische Universitaet Muenchen (TUM). "These are clocks that help to keep many parts of the brain on the same page." One such timekeeper produces the so-called slow waves of deep sleep, which are thought to be involved in transmuting fragments of a day’s experience and learning into lasting memory. They can be observed in very early stages of development, and they may be disrupted in diseases such as Alzheimer’s.
Previous studies, relying mainly on electrical measurements, have lacked the spatial resolution to map the initiation and propagation of slow waves precisely. But using light, Konnerth’s Munich-based team – in collaboration with researchers at Stanford and the University of Mainz – could both stimulate slow waves and observe them in unprecedented detail. One key result confirmed that the slow waves originate only in the cortex, ruling out other long-standing hypotheses. “The second major finding,” Konnerth says, “was that out of the billions of cells in the brain, it takes not more than a local cluster of fifty to one hundred neurons in a deep layer of the cortex, called layer 5, to make a wave that extends over the entire brain.”
New light on a fundamental neural mechanism
Despite considerable investigation of the brain’s slow waves, definitive answers about the underlying circuit mechanism have remained elusive. Where is the pacemaker for this rhythm? Where do the waves start, and where do they stop? This study – based on optical probing of intact brains of live mice under anesthesia – now provides the basis for a detailed, comprehensive view.
"We implemented an optogenetic approach combined with optical detection of neuronal activity to explore causal features of these slow oscillations, or Up-Down state transitions, that represent the dominating network rhythm in sleep," explains Prof. Albrecht Stroh of the Johannes Gutenberg University Mainz. Optogenetics is a novel technique that enabled the researchers to insert light-sensitive channels into specific kinds of neurons, to make them responsive to light stimulation. This allowed for selective and spatially defined stimulation of small numbers of cortical and thalamic neurons.
Access to the brain via optical fibers allowed for both microscopic recording and direct stimulation of neurons. Flashes of light near the mouse’s eyes were also used to stimulate neurons in the visual cortex. By recording the flux of calcium ions, a chemical signal that can serve as a more spatially precise readout of the electric activity, the researchers made the slow waves visible. They also correlated optical recordings with more conventional electrical measurements. As a result, it was possible to watch individual wave fronts spread – like ripples from a rock thrown into a quiet lake – first through the cortex and then through other brain structures.
A new picture begins to emerge: Not only is it possible for a tiny local cluster of neurons to initiate a slow wave that will spread far and wide, recruiting multiple regions of the brain into a single event – this appears to be typical. “In spontaneous conditions,” Konnerth says, “as it happens with you and me and everyone else every night in deep sleep, every part of the cortex can be an initiation site.” Furthermore, a surprisingly simple communication protocol can be seen in the slow wave rhythm. During each one-second cycle a single neuron cluster sends its signal and all others are silenced, as if they are taking turns bathing the brain in fragments of experience or learning, building blocks of memory. The researchers view these findings as a step toward a better understanding of learning and memory formation, a topic Konnerth’s group is investigating with funding from the European Research Council. They also are testing how the slow waves behave during disease.
Tiny Wireless Device Shines Light on Mouse Brain, Generating Reward
Using a miniature electronic device implanted in the brain, scientists have tapped into the internal reward system of mice, prodding neurons to release dopamine, a chemical associated with pleasure.
The researchers, at Washington University School of Medicine in St. Louis and the University of Illinois at Urbana-Champaign, developed tiny devices, containing light emitting diodes (LEDs) the size of individual neurons. The devices activate brain cells with light. The scientists report their findings April 12 in the journal Science.
“This strategy should allow us to identify and map brain circuits involved in complex behaviors related to sleep, depression, addiction and anxiety,” says co-principal investigator Michael R. Bruchas, PhD, assistant professor of anesthesiology at Washington University. “Understanding which populations of neurons are involved in these complex behaviors may allow us to target specific brain cells that malfunction in depression, pain, addiction and other disorders.”
For the study, Washington University neuroscientists teamed with engineers at the University of Illinois to design microscale (LED) devices thinner than a human hair. This was the first application of the devices in optogenetics, an area of neuroscience that uses light to stimulate targeted pathways in the brain. The scientists implanted them into the brains of mice that had been genetically engineered so that some of their brain cells could be activated and controlled with light.
Although a number of important pathways in the brain can be studied with optogenetics, many neuroscientists have struggled with the engineering challenge of delivering light to precise locations deep in the brain. Most methods have tethered animals to lasers with fiber optic cables, limiting their movement and altering natural behaviors.
But with the new devices, the mice freely moved about and were able to explore a maze or scamper on a wheel. The electronic LEDs are housed in a tiny fiber implanted deep in the brain. That’s important to the device’s ability to activate the proper neurons, according to John A. Rogers, PhD, professor of materials science and engineering at the University of Illinois.
“You want to be able to deliver the light down into the depth of the brain,” Rogers says. “We think we’ve come up with some powerful strategies that involve ultra-miniaturized devices that can deliver light signals deep into the brain and into other organs in the future.”
Using light from the cellular-scale LEDs to stimulate dopamine-producing cells in the brain, the investigators taught the mice to poke their noses through a specific hole in a maze. Each time a mouse would poke its nose through the hole, that would trigger the system to wirelessly activate the LEDs in the implanted device, which then would emit light, causing neurons to release dopamine, a chemical related to the brain’s natural reward system.
“We used the LED devices to activate networks of brain cells that are influenced by the things you would find rewarding in life, like sex or chocolate,” says co-first author Jordan G. McCall, a neuroscience graduate student in Washington University’s Division of Biology and Biomedical Sciences. “When the brain cells were activated to release dopamine, the mice quickly learned to poke their noses through the hole even though they didn’t receive any food as a reward. They also developed an associated preference for the area near the hole, and they tended to hang around that part of the maze.”
The researchers believe the LED implants may be useful in other types of neuroscience studies or may even be applied to different organs. Related devices already are being used to stimulate peripheral nerves for pain management. Other devices with LEDs of multiple colors may be able to activate and control several neural circuits at once. In addition to the tiny LEDs, the devices also carry miniaturized sensors for detecting temperature and electrical activity within the brain.
Bruchas and his colleagues already have begun other studies of mice, using the LED devices to manipulate neural circuits that are involved in social behaviors. This could help scientists better understand what goes on in the brain in disorders such as depression and anxiety.
“We believe these devices will allow us to study complex stress and social interaction behaviors,” Bruchas explains. “This technology enables us to map neural circuits with respect to things like stress and pain much more effectively.”
The wireless, microLED implant devices represent the combined efforts of Bruchas and Rogers. Last year, along with Robert W. Gereau IV, PhD, professor of anesthesiology, they were awarded an NIH Director’s Transformative Research Project award to develop and conduct studies using novel device development and optogenetics, which involves activating or inhibiting brain cells with light.
(Source: newswise.com)
Lights, Chemistry, Action: New Method for Mapping Brain Activity
Building on their history of innovative brain-imaging techniques, scientists at the U.S. Department of Energy’s Brookhaven National Laboratory and collaborators have developed a new way to use light and chemistry to map brain activity in fully-awake, moving animals. The technique employs light-activated proteins to stimulate particular brain cells and positron emission tomography (PET) scans to trace the effects of that site-specific stimulation throughout the entire brain. As described in a paper published online today in the Journal of Neuroscience, the method will allow researchers to map exactly which downstream neurological pathways are activated or deactivated by stimulation of targeted brain regions, and how that brain activity correlates with particular behaviors and/or disease conditions.
"This technique gives us a new way to look at the function of specific brain cells and map which brain circuits are active in a wide range of neuropsychiatric diseases — from depression to Parkinson’s disease, neurodegenerative disorders, and drug addiction — and also to monitor the effects of various treatments," said the paper’s lead author, Panayotis (Peter) Thanos, a neuroscientist and director of the Behavioral Neuropharmacology and Neuroimaging Section — part of the National Institute on Alcohol Abuse and Alcoholism (NIAAA) Laboratory of Neuroimaging at Brookhaven Lab — and a professor at Stony Brook University. "Because the animals are awake and able to move during stimulation, we can also directly study how their behavior correlates with brain activity," he said.
The new brain-mapping method combines very recent advances in a field known as “optogenetics” — the use of optics (light activation) and genetics (genetically coded light-sensitive proteins) to control the activity of individual neurons, or nerve cells — and Brookhaven’s historical development of radioactively labeled chemical tracers to track biological activity with PET scanners.
The scientists used a modified virus to deliver a light-sensitive protein to particular brain cells in rats. Genetic coding can deliver the protein to specifically targeted brain-cell receptors. Then, after stimulating those proteins with light shone through an optical fiber inserted through a tiny tube called a cannula, they monitored overall brain activity using a radiotracer known as 18FDG, which serves as a stand-in for glucose, the body’s (and brain’s) main source of energy.
The unique chemistry of 18FDG causes it to be temporarily “trapped” inside cells that are hungry for glucose — those activated by the brain stimulation — and remain there long enough for the detectors of a PET scanner to pick up the radioactive signal, even after the animals are anesthetized to ensure they stay still for scanning. But because the animals were awake and moving when the tracer was injected and the brain cells were being stimulated, the scans reveal what parts of the brain were activated (or deactivated) under those conditions, giving scientists important information about how those brain circuits function and correlate with the animals’ behaviors.
"In this paper, we wanted to stimulate the nucleus accumbens, a key part of the brain involved in reward that is very important to understanding drug addiction," Thanos said. "We wanted to activate the cells in that area and see which brain circuits were activated and deactivated in response."
The scientists used the technique to trace activation and deactivation in number of key pathways, and confirmed their results with other analysis techniques.
The method can reveal even more precise effects.
"If we want to know more about the role played by specific types of receptors — say the dopamine D1 or D2 receptors involved in processing reward — we could tailor the light-sensitive protein probe to specifically stimulate one or the other to tease out those effects," he said.
Another important aspect is that the technique does not require the scientists to identify in advance the regions of the brain they want to investigate, but instead provides candidate brain regions involved anywhere in the brain – even regions not well understood.
"We look at the whole brain," Thanos said. "We take the PET images and co-register them with anatomical maps produced with magnetic resonance imaging (MRI), and use statistical techniques to do comparisons voxel by voxel. That allows us to identify which areas are more or less activated under the conditions we are exploring without any prior bias about what regions should be showing effects.”
After they see a statistically significant effect, they use the MRI maps to identify the locations of those particular voxels to see what brain regions they are in.
"This opens it up to seeing an effect in any region in the brain — even parts where you would not expect or think to look — which could be a key to new discoveries," he said.
![Researchers shine light on how stress circuits learn
Researchers at the University of Calgary’s Hotchkiss Brain Institute have discovered that stress circuits in the brain undergo profound learning early in life. Using a number of cutting edge approaches, including optogenetics, Jaideep Bains, PhD, and colleagues have shown stress circuits are capable of self-tuning following a single stress. These findings demonstrate that the brain uses stress experience during early life to prepare and optimize for subsequent challenges.
The team was able to show the existence of unique time windows following brief stress challenges during which learning is either increased or decreased. By manipulating specific cellular pathways, they uncovered the key players responsible for learning in stress circuits in an animal model. These discoveries culminated in the publication of two back-to-back studies in the April 7 online edition of Nature Neuroscience [1, 2], one of the world’s top neuroscience journals.
"These new findings demonstrate that systems thought to be ‘hardwired’ in the brain, are in fact flexible, particularly early in life," says Bains, a professor in the Department of Physiology and Pharmacology. "Using this information, researchers can now ask questions about the precise cellular and molecular links between early life stress and stress vulnerability or resilience later in life."
Stress vulnerability, or increased sensitivity to stress, has been implicated in numerous health conditions including cardiovascular disease, obesity, diabetes and depression. Although these studies used animal models, similar mechanisms mediate disease progression in humans.
"Our observations provide an important foundation for designing more effective preventative and therapeutic strategies that mitigate the effects of stress and meet society’s health challenges," he says.](http://40.media.tumblr.com/f83bb6a8164f8684439d2d63343d84d0/tumblr_mkwno9M5HF1rog5d1o1_500.jpg)
Researchers shine light on how stress circuits learn
Researchers at the University of Calgary’s Hotchkiss Brain Institute have discovered that stress circuits in the brain undergo profound learning early in life. Using a number of cutting edge approaches, including optogenetics, Jaideep Bains, PhD, and colleagues have shown stress circuits are capable of self-tuning following a single stress. These findings demonstrate that the brain uses stress experience during early life to prepare and optimize for subsequent challenges.
The team was able to show the existence of unique time windows following brief stress challenges during which learning is either increased or decreased. By manipulating specific cellular pathways, they uncovered the key players responsible for learning in stress circuits in an animal model. These discoveries culminated in the publication of two back-to-back studies in the April 7 online edition of Nature Neuroscience [1, 2], one of the world’s top neuroscience journals.
"These new findings demonstrate that systems thought to be ‘hardwired’ in the brain, are in fact flexible, particularly early in life," says Bains, a professor in the Department of Physiology and Pharmacology. "Using this information, researchers can now ask questions about the precise cellular and molecular links between early life stress and stress vulnerability or resilience later in life."
Stress vulnerability, or increased sensitivity to stress, has been implicated in numerous health conditions including cardiovascular disease, obesity, diabetes and depression. Although these studies used animal models, similar mechanisms mediate disease progression in humans.
"Our observations provide an important foundation for designing more effective preventative and therapeutic strategies that mitigate the effects of stress and meet society’s health challenges," he says.
Laser Light Zaps Away Cocaine Addiction
By stimulating one part of the brain with laser light, researchers at the National Institutes of Health (NIH) and the Ernest Gallo Clinic and Research Center at UC San Francisco (UCSF) have shown that they can wipe away addictive behavior in rats – or conversely turn non-addicted rats into compulsive cocaine seekers.
“When we turn on a laser light in the prelimbic region of the prefrontal cortex, the compulsive cocaine seeking is gone,” said Antonello Bonci, MD, scientific director of the intramural research program at the NIH’s National Institute on Drug Abuse (NIDA), where the work was done. Bonci is also an adjunct professor of neurology at UCSF and an adjunct professor at Johns Hopkins University.
Described this week in the journal Nature, the new study demonstrates the central role the prefrontal cortex plays in compulsive cocaine addiction. It also suggests a new therapy that could be tested immediately in humans, said Billy Chen of NIDA, the lead author of the study.
Any new human therapy would not be based on using lasers, but would most likely rely on electromagnetic stimulation outside the scalp, in particular a technique called transcranial magnetic stimulation (TMS). Clinical trials are now being designed to test whether this approach works, Chen added.
The High Cost of Cocaine Abuse
Cocaine abuse is a major public health problem in the United States today, and it places a heavy toll on society in terms of lost job productivity, lost earnings, cocaine-related crime, incarcerations, investigations, and treatment and prevention programs.
The human toll is even greater, with an estimated 1.4 million Americans addicted to the drug. It is frequently the cause of emergency room visits – 482,188 in 2008 alone – and it is a top cause of heart attacks and strokes for people under 35.
One of the hallmarks of cocaine addiction is compulsive drug taking – the loss of ability to refrain from taking the drug even if it’s destroying one’s life.
What makes the new work so promising, said Bonci, is that Chen and his colleagues were working with an animal model that mimics this sort of compulsive cocaine addiction. The animals, like human addicts, are more likely to make bad decisions and take cocaine even when they are conditioned to expect self-harm associated with it.
Electrophysiological studies involving these rats have shown that they have extremely low activity in the prefrontal cortex – a brain region fundamental for impulse control, decision making and behavioral flexibility. Similar studies that imaged the brains of humans have shown the same pattern of low activity in this region in people who are compulsively addicted to cocaine.
Altering Brain Activity with a Laser
To test whether altering the activity in this brain region could impact addiction, Chen and his colleagues employed a technique called optogenetics to shut the activity on and off using a laser.
First they took light-sensitive proteins called rhodopsins and used genetic engineering to insert them into neurons in the rat’s prefrontal cortex. Activating this region with a laser tuned to the rhodopsins turned the nerve cells on and off.
Turning on these cells wiped out the compulsive behavior, while switching them off turned the non-addicted ones into addicted, researchers found.
What’s exciting, said Bonci, is that there is a way to induce a similar activation of the prelimbic cortex in people through a technique called transcranial magnetic stimulation (TMS), which applies an external electromagnetic field to the brain and has been used as a treatment for symptoms of depression.
Bonci and his colleagues plan to begin clinical trials at NIH in which they will use this technique a few sessions a week to stimulate the prefrontal cortex in people who are addicted to cocaine and see if they can restore activity to that part of the brain and help them avoid taking the drug.
Portion of Hippocampus Found to Play Role in Modulating Anxiety
Columbia University Medical Center (CUMC) researchers have found the first evidence that selective activation of the dentate gyrus, a portion of the hippocampus, can reduce anxiety without affecting learning. The findings suggest that therapies that target this brain region could be used to treat certain anxiety disorders, such as panic disorder and post-traumatic stress syndrome (PTSD), with minimal cognitive side effects. The study, conducted in mice, was published in the online edition of the journal Neuron.
The dentate gyrus is known to play a key role in learning. Some evidence suggests that the structure also contributes to anxiety. “But until now no one has been able to figure out how the hippocampus could be involved in both processes,” said senior author Rene Hen, PhD, professor of neuroscience and pharmacology (in psychiatry) at CUMC.
“It turns out that different parts of the dentate gyrus have somewhat different functions, with the dorsal portion largely dedicated to learning and the ventral portion dedicated to anxiety,” said lead author Mazen A. Kheirbek, PhD, a postdoctoral fellow in neuroscience at CUMC.
To examine the role of the dentate gyrus in learning and anxiety, the investigators used a state-of-the-art technique called optogenetics, in which light-sensitive proteins, or opsins, are genetically inserted into neurons in the brains of mice. Neurons with these genes can then be selectively activated or silenced through the application of light (via a fiber-optic strand), allowing researchers to study the function of the cells in real time. Previously, the only way to study the dentate gyrus was to silence portions of it using such long-term manipulations as drugs or lesions, techniques that yielded conflicting results.
In the current study, opsins were inserted into dentate gyrus granule cells (the principal cells of the dentate gyrus). The researchers then activated or silenced the ventral or dorsal portions of the dentate gyrus for three minutes at a time, while the mice were subjected to two well-validated anxiety tests (the elevated plus maze and the open field test).
“Our main findings were that elevating cell activity in the dorsal dentate gyrus increased the animals’ desire to explore their environment. But this also disrupted their ability to learn. Elevating activity in the ventral dentate gyrus lowered their anxiety, but had no effect on learning,” said Dr. Kheirbek. The effects were completely reversible — that is, when the stimulation was turned off, the animals returned to their previous anxiety levels.
“The therapeutic implication is that it may be possible to relieve anxiety in people with anxiety disorders by targeting the ventral dentate gyrus, perhaps with medications or deep-brain stimulation, without affecting learning,” said Dr. Hen, who is also director of the Division of Integrative Neuroscience, the New York State Psychiatric Institute, and a member of The Kavli Institute for Brain Science. “Given the immediate behavioral impact of such manipulations, these strategies are likely to work faster than current treatments, such as serotonin reuptake inhibitors.”
According to Dr. Hen, such an intervention would probably work best in people with panic disorder or PTSD. “There is evidence that people with these anxiety disorders tend to have a problem with pattern separation — the ability to distinguish between similar experiences,” he said. “In other words, they overgeneralize, perceiving minor threats to be the same as major ones, leading to a heightened state of anxiety. Such patients could conceivably benefit from therapies that fine-tune hippocampal activity.”
Dr. Hen and his team are currently exploring strategies aimed at modulating the activity of the ventral dentate gyrus by stimulating neurogenesis in the ventral dentate gyrus. “Indeed the dentate gyrus is one of the few areas in the adult brain where neurons are continuously produced, a phenomenon termed adult hippocampal neurogenesis,” added Dr. Hen.
(Image: Catherine E. Myers, Memory Loss and the Brain)