 |
New technique offers a more detailed view of brain activity | ||
| March 1st, 2010 | ||
For neuroscientists, one of the best ways to study brain activity is with a scanning technique called functional magnetic resonance imaging (fMRI), which reveals blood flow in the brain. However, although fMRI is a powerful tool for identifying brain regions that are active during a particular task, it offers only an indirect view of what's happening. Measuring a more direct indicator of neural activity, such as concentrations of neurotransmitters (brain chemicals that carry messages between neurons) could be much more valuable.
"This new tool connects molecular phenomena in the nervous system with whole-brain imaging techniques, allowing us to probe very precise processes and relate them to the overall function of the brain and of the organism," says Alan Jasanoff, an associate professor of biological engineering at MIT and senior author of the paper. Dopamine holds particular interest for neuroscientists because of its role in motivation, reward, addiction and several neurodegenerative conditions, including Parkinson's disease. The new sensors could help scientists learn more about how dopamine acts in the brain and in other organs, says Andrew Alexander, co-director of the Brain Imaging Core at the University of Wisconsin at Madison. "Previously we really haven't had specific biomarkers for looking at things like dopamine or other chemical neurotransmitters" with MRI, says Alexander. Designing a new sensor Conventional fMRI measures blood flow in the brain by tracking hemoglobin, the molecule that carries oxygen. Hemoglobin has an iron atom at its core that binds to oxygen. When bound to oxygen, hemoglobin's magnetic properties change in a way that can be detected with MRI. "fMRI is an extremely powerful technique for studying how the brain functions, and it's the only way to obtain spatial information and information about when things are happening," says Jasanoff, who also has appointments in the Departments of Brain and Cognitive Sciences and Nuclear Science and Engineering, and in the McGovern Institute for Brain Research at MIT. However, the spatial and temporal information is imprecise. Researchers can detect increased activity in a certain area, but they can't see what the activity is, nor can they get a high-resolution picture of which neurons are involved. A more detailed picture of brain activity could emerge with MRI sensors specific to particular neurotransmitters. The MIT team designed sensors specifically for dopamine, but their technique could be used to create sensors for other neurotransmitters or even unrelated molecules of biological interest. To build the new sensors, the MIT team worked with chemical engineers at Caltech, using an approach called "directed evolution." They started with a protein called cytochrome P450, an enzyme found in most organisms that is paramagnetic (meaning it can become weakly magnetic when exposed to a magnetic field). Using a technique called error-prone PCR, which is a faulty version of the way cells naturally replicate their genes, they generated a large collection of different mutated forms of the gene. Each mutated gene was placed into an E. coli bacterium, which produced the mutated protein. The researchers then tested each protein for its ability to bind dopamine. At the end of each round, they took the best candidate and mutated it again for a new round of improvement. At the end of five rounds, they had two sensors that would bind strongly to dopamine but not to other neurotransmitters. "You want it to be specific to dopamine - you don't want it to bind to dopamine and half a dozen other things," says Jasanoff. In studies of rats, the researchers showed that the sensor can effectively detect dopamine in the brain. However, in its current form, the dopamine probe must be injected into the brain, and the imaging is limited to the site of injection. Bruce Jenkins, director of neurochemical imaging at the Martinos Center for Biomedical Imaging at MGH, says the new probe is "very cleverly designed," but points out that an important challenge is yet to come: getting the molecule to cross the layer of cells that separates the brain from circulating blood. "Trying to get a charged protein across the blood-brain barrier is very tricky," he says. The MIT team hopes to overcome that obstacle by applying barrier disruption techniques used historically to deliver chemotherapeutic agents to the brain. They will also try to genetically program brain cells to express the sensor, so it doesn't have to be injected. They plan to adapt the directed evolution strategy to look for sensors for other neurotransmitters as well. If successful, that could help researchers in Jasanoff's lab and elsewhere create a better wiring diagram of how different brain regions and neurotransmitters work together to yield behavior such as learning, memory, addiction and movement. "We hope to develop probes that target different parts of the mechanism, allowing us to piece these systems together in a way that's noninvasive," says Jasanoff. Contact: Anne Trafton gillooly@mit.edu MIT | ||
| This article is relevant to the following subject areas | ||
| •Medicine •Neurology •Biology | ||
| Copy & Share this link http://www.sciguru.com/newsitem/1719/New-technique-offers-a-more-detailed-view-of-brain-activity/ |
| SciGuru.com: "Science For All". Copyright Sciguru.com © All rights reserverd (2009-present). SciGuru.com is an online source for news and information in all areas of sciences. Copy and reproduction of the contents, in full or in part, may include citation to SciGuru.com or the relevant page in SciGuru.com. |
 |
 |
 |
 |
Related NewsLife's smallest motor, cargo carrier of the cells, moves like a seesaw Life's smallest motor, a protein that shuttles cargo within cells and hel... Nanodiamonds Produce "Game Changing Event" for MRI Imaging SensitivityA Northwestern University study shows that coupling a widely used magnetic ... NASA Unveils New Space-Weather Science Tool When NASA's satellite operators need accurate, real-time space-weather info... UC Davis researchers demonstrate link between brain chemical, cognitive decline in schizophreniaIn one of the first such studies involving human patients with schizophreni... |
 |
 |
 |
Recent Science News
Novel Antiviral: LJ-double-o-one is shown to be effective against more than 20 viruses
Researchers Find New Translocation; Weak Spots in DNA Cause Genetic Disease
Beware the smell of bitter almonds. Why do many food plants contain cyanide?
Study finds structural brain alterations in patients with irritable bowel syndrome
Excellence programs do not identify safest hospitals for bariatric surgery
Asteroid Impact in 2182?
Martian Dust Devil Whirls into Opportunity's View
Study: Weight issues move up need for walkers, canes, other devices
Two Catalysts Are Better Than One
More News