Scientists manipulate consciousness in rats

NIH-funded study may guide deep brain stimulation therapies used for neurological disorders

Scientists showed that they could alter brain activity of rats and either wake them up or put them in an unconscious state by changing the firing rates of neurons in the central thalamus, a region known to regulate arousal. The study, published ineLIFE, was partially funded by the National Institutes of Health.

"Our results suggest the central thalamus works like a radio dial that tunes the brain to different states of activity and arousal," said Jin Hyung Lee, Ph.D., assistant professor of neurology, neurosurgery and bioengineering at Stanford University, and a senior author of the study.

Located deep inside the brain the thalamus acts as a relay station sending neural signals from the body to the cortex. Damage to neurons in the central part of the thalamus may lead to problems with sleep, attention, and memory. Previous studies suggested that stimulation of thalamic neurons may awaken patients who have suffered a traumatic brain injury from minimally conscious states.

Dr. Lee's team flashed laser pulses onto light sensitive central thalamic neurons of sleeping rats, which caused the cells to fire. High frequency stimulation of 40 or 100 pulses per second woke the rats. In contrast, low frequency stimulation of 10 pulses per second sent the rats into a state reminiscent of absence seizures that caused them to stiffen and stare before returning to sleep.

"This study takes a big step towards understanding the brain circuitry that controls sleep and arousal," Yejun (Janet) He, Ph.D., program director at NIH's National Institute of Neurological Disorders and Stroke (NINDS).

When the scientists used functional magnetic resonance imaging (fMRI) to scan brain activity, they saw that high and low frequency stimulation put the rats in completely different states of activity.

Cortical brain areas where activity was elevated during high frequency stimulation became inhibited with low frequency stimulation. Electrical recordings confirmed the results. Neurons in the somatosensory cortex fired more during high frequency stimulation of the central thalamus and less during low frequency stimulation.

"Dr. Lee's innovative work demonstrates the power of using imaging technologies to study the brain at work," said Guoying Liu, Ph.D., a program director at the NIH's National Institute of Biomedical Imaging and Bioengineering (NIBIB).

How can changing the firing rate of the same neurons in one region lead to different effects on the rest of the brain?

Further experiments suggested the different effects may be due to a unique firing pattern by inhibitory neurons in a neighboring brain region, the zona incerta, during low frequency stimulation. Cells in this brain region have been shown to send inhibitory signals to cells in the sensory cortex.

Electrical recordings showed that during low frequency stimulation of the central thalamus, zona incerta neurons fired in a spindle pattern that often occurs during sleep. In contrast, sleep spindles did not occur during high frequency stimulation. Moreover, when the scientists blocked the firing of the zona incerta neurons during low frequency stimulation of the central thalamus, the average activity of sensory cortex cells increased.

Although deep brain stimulation of the thalamus has shown promise as a treatment for traumatic brain injury, patients who have decreased levels of consciousness show slow progress through these treatments.

"We showed how the circuits of the brain can regulate arousal states," said Dr. Lee. "We hope to use this knowledge to develop better treatments for brain injuries and other neurological disorders."

National Institute of Neurological Disorders and Stroke

Nanotechnology World Association

Tracking individual carbon atoms deep into the brain’s neurons

Using a geologist’s imaging tool, researchers have made unprecedented high-resolution images of how carbon atoms from glucose are integrated into brain cells, providing new insight and opening new doors into the fate of glucose in the brain.

Glucose – a form of sugar – fuels the brain. But how it goes from the blood to the brain cells and where it ultimately winds up are not yet well understood. Harnessing the power of a special kind of microscope that was used for the first time to image metabolism of the brain, researchers from EPFL, the Nestlé Health Institute, and the University of Lausanne have tracked the fate of individual carbon atoms deep into the brain’s neurons and astrocytes. Their work, published in the Journal of Chemical Neuroanatomy, paves the way for a better understanding of how healthy and diseased brains metabolize glucose, which in the future could contribute to the development of new methods to diagnose and treat neurological diseases.

“Half of the glucose we have in our blood is consumed by our brain; this we know. But what we don’t know, at least not in detail, is what this glucose is used for and where it winds up,” says Arnaud Comment, one of the study’s lead investigators. The reason for this is that existing experimental methods have been unable to conclusively resolve this question. But thanks to a microscope originally developed to study the isotopic composition of rock samples called a NanoSIMS, it looks like researchers may finally have a tool to help them find an answer.

“The NanoSIMS gives us a view of what goes on at the sub-cellular level that nobody has had access to before. It is an example of a geochemical technology that is being pushed into the realm of life sciences through a cross-campus collaboration,” says Meibom, whose EPFL research lab runs the NanoSIMS, the only one of its kind in Switzerland. Combining transmission electron microscopy (TEM) with secondary ion mass spectroscopy, the device lets researchers locate trace amounts of labeled atoms down to a resolution of only a few hundred nanometers.

“In this study, we imaged the fate of glucose, the brain’s main energy source, at the cellular level,” says Meibom, who is also the study’s second lead investigator. “Our question was: where is the brain putting its money? We do not have an answer quite yet, but we do have data showing that after a few hours, neurons have accumulated more carbon from the glucose in their structure than astrocytes. We can find high concentrations of carbon atoms from the glucose in the neurons’ nuclei and other cellular compartments – a sign of increased metabolic activity.”

While their findings neither refute nor validate current theory holding that astrocytes extract glucose from the blood stream and deliver some of it to neurons, they provide an unprecedented and very accurate snapshot into exactly where the carbon from the glucose is going in the brain.

But, the researchers hope, their method could help determine the early metabolic signature of certain types of disease, which could be a boon to research and the development of treatment strategies. Catching the onset of Alzheimer’s, for example, is complicated by the fact that, by the time the structure of the brain’s cells is visibly affected, it is already too late. Instead, more subtle cues would have to be picked up, such as changes to the cells’ metabolism – the chemical reactions that sustain them, providing them with energy and matter. Changes in glucose metabolism of specific parts of the brain could, for example, provide an early warning for the onset of Alzheimer’s.

Today, the NanoSIMS lets researchers study the incorporation of labeled atoms into solid structures, but Meibom wants to take it one step further. “We are working on extending the capabilities of the NanoSIMS to be able to work with frozen samples, giving us a means of visualizing soluble compounds as well. Using such a CryoNanoSIMS, we will not only be able to see where specific compounds have been integrated into the proteins that make up the cell, but we will also be able to trace their dissolved metabolite precursors,” he says.

Reference: Yuhei Takado et al. Imaging the time-integrated cerebral metabolic activity with subcellular resolution through nanometer-scale detection of biosynthetic products deriving from 13C-glucose, Journal of Chemical Neuroanatomy, Available online 25 September 2015,

EPFL

UNC neuroscientists discover new 'mini-neural computer' in the brain

This is a dendrite, the branch-like structure of a single
neuron in the brain. The bright object from the top is a
pipette attached to a dendrite in the brain...

Dendrites, the branch-like projections of neurons, were once thought to be passive wiring in the brain. But now researchers at the University of North Carolina at Chapel Hill have shown that these dendrites do more than relay information from one neuron to the next. They actively process information, multiplying the brain's computing power.
"Suddenly, it's as if the processing power of the brain is much greater than we had originally thought," said Spencer Smith, PhD, an assistant professor in the UNC School of Medicine.

His team's findings, published October 27 in the journal Nature, could change the way scientists think about long-standing scientific models of how neural circuitry functions in the brain, while also helping researchers better understand neurological disorders.

"Imagine you're reverse engineering a piece of alien technology, and what you thought was simple wiring turns out to be transistors that compute information," Smith said. "That's what this finding is like. The implications are exciting to think about."

Axons are where neurons conventionally generate electrical spikes, but many of the same molecules that support axonal spikes are also present in the dendrites. Previous research using dissected brain tissue had demonstrated that dendrites can use those molecules to generate electrical spikes themselves, but it was unclear whether normal brain activity involved those dendritic spikes. For example, could dendritic spikes be involved in how we see?

The answer, Smith's team found, is yes. Dendrites effectively act as mini-neural computers, actively processing neuronal input signals themselves.

Directly demonstrating this required a series of intricate experiments that took years and spanned two continents, beginning in senior author Michael Hausser's lab at University College London, and being completed after Smith and Ikuko Smith, PhD, DVM, set up their own lab at the University of North Carolina. They used patch-clamp electrophysiology to attach a microscopic glass pipette electrode, filled with a physiological solution, to a neuronal dendrite in the brain of a mouse. The idea was to directly "listen" in on the electrical signaling process.

"Attaching the pipette to a dendrite is tremendously technically challenging," Smith said. "You can't approach the dendrite from any direction. And you can't see the dendrite. So you have to do this blind. It's like fishing if all you can see is the electrical trace of a fish." And you can't use bait. "You just go for it and see if you can hit a dendrite," he said. "Most of the time you can't."

But Smith built his own two-photon microscope system to make things easier.

Once the pipette was attached to a dendrite, Smith's team took electrical recordings from individual dendrites within the brains of anesthetized and awake mice. As the mice viewed visual stimuli on a computer screen, the researchers saw an unusual pattern of electrical signals – bursts of spikes – in the dendrite.

Smith's team then found that the dendritic spikes occurred selectively, depending on the visual stimulus, indicating that the dendrites processed information about what the animal was seeing.
To provide visual evidence of their finding, Smith's team filled neurons with calcium dye, which provided an optical readout of spiking. This revealed that dendrites fired spikes while other parts of the neuron did not, meaning that the spikes were the result of local processing within the dendrites.
Study co-author Tiago Branco, PhD, created a biophysical, mathematical model of neurons and found that known mechanisms could support the dendritic spiking recorded electrically, further validating the interpretation of the data.

"All the data pointed to the same conclusion," Smith said. "The dendrites are not passive integrators of sensory-driven input; they seem to be a computational unit as well."
His team plans to explore what this newly discovered dendritic role may play in brain circuitry and particularly in conditions like Timothy syndrome, in which the integration of dendritic signals may go awry.

Source: http://news.unchealthcare.org/news/2013/october/unc-neuroscientists-discover-new-2018mini-neural-computer2019-in-the-brain

Capturing brain activity with sculpted light

Researchers in Vienna develop new imaging technique to study the function of entire nervous systems   Scientists at the Campus Vienna Biocenter (Austria) have found a way to overcome some of the limitations of light microscopy. Applying the new technique, they can record the activity of a worm’s brain with high temporal and spatial resolution, ultimately linking brain anatomy to brain function. The journal Nature Methods publishes the details in its current issue.

A major aim of today’s neuroscience is to understand how an organism’s nervous system processes sensory input and generates behavior. To achieve this goal, scientists must obtain detailed maps of how the nerve cells are wired up in the brain, as well as information on how these networks interact in real time.

The organism many neuroscientists turn to in order to study brain function is a tiny, transparent worm found in rotting soil. The simple nematode C. elegans is equipped with just 302 neurons that are connected by roughly 8000 synapses. It is the only animal for which a complete nervous system has been anatomically mapped.

Researchers have so far focused on studying the activity of single neurons and small networks in the worm, but have not been able to establish a functional map of the entire nervous system. This is mainly due to limitations in the imaging-techniques they employ: the activity of single cells can be resolved with high precision, but simultaneously looking at the function of all neurons that comprise entire brains has been a major challenge. Thus, there was always a trade-off between spatial or temporal accuracy and the size of brain regions that could be studied.

Scientists at Vienna’s Research Institute of Molecular Pathology (IMP), the Max Perutz Laboratories (MFPL), and the Research Platform Quantum Phenomena & Nanoscale Biological Systems (QuNaBioS) of the University of Vienna have now closed this gap and developed a high speed imaging technique with single neuron resolution that bypasses these limitations. In a paper published online in Nature Methods, the teams of Alipasha Vaziri and Manuel Zimmer describe the technique which is based on their ability to “sculpt” the three-dimensional distribution of light in the sample. With this new kind of microscopy, they are able to record the activity of 70% of the nerve cells in a worm’s head with high spatial and temporal resolution.  

“Previously, we would have to scan the focused light by the microscope in all three dimensions”, says quantum physicist Robert Prevedel. “That takes far too long to record the activity of all neurons at the same time. The trick we invented tinkers with the light waves in a way that allows us to generate “discs” of light in the sample. Therefore, we only have to scan in one dimension to get the information we need. We end up with three-dimensional videos that show the simultaneous activities of a large number of neurons and how they change over time.” Robert Prevedel is a Senior Postdoc in the lab of Alipasha Vaziri, who is an IMP-MFPL Group Leader and is heading the Research Platform Quantum Phenomena & Nanoscale Biological Systems (QuNaBioS) of the University of Vienna, where the new technique was developed. 

However, the new microscopic method is only half the story. Visualising the neurons requires tagging them with a fluorescent protein that lights up when it binds to calcium, signaling the nerve cells’ activity. “The neurons in a worm’s head are so densely packed that we could not distinguish them on our first images”, explains neurobiologist Tina Schrödel, co-first author of the study. “Our solution was to insert the calcium sensor into the nuclei rather than the entire cells, thereby sharpening the image so we could identify single neurons.” Tina Schrödel is a Doctoral Student in the lab of the IMP Group Leader Manuel Zimmer.

The new technique that came about by a close collaboration of physicists and neurobiologists has great potentials beyond studies in worms, according to the researchers. It will open up the way for experiments that were not possible before. One of the questions that will be addressed is how the brain processes sensory information to “plan” specific movements and then executes them. This ambitious project will require further refinement of both the microscopy methods and computational methods in order to study freely moving animals. The team in Vienna is set to achieve this goal in the coming two years.  

Source: http://medienportal.univie.ac.at/presse/aktuelle-pressemeldungen/detailansicht/artikel/capturing-brain-activity-with-sculpted-light/