Just a decade ago, some scientists were calling optogenetics
a long shot, a crazy idea. Then it turned out to be not so crazy.
This relatively new technology allows neuroscientists to use
light to probe the inner workings of the brain to study—and even
control—pinpointed regions believed to be implicated in disorders like
addiction, epilepsy, and autism.
The formula involves light-sensitive algae proteins, a
detoxified virus (which acts as the rocketship that delivers the payload
protein into the brain), and LED light (sometimes in multiple colors)
administered via superfine fiber optic cables.
With support from MnDRIVE—an infusion of research dollars by
the Minnesota Legislature into brain sciences, among other areas, at the
University of Minnesota—and the federal BRAIN Initiative, a group of University
neuroscientists is now all in on this groundbreaking work.
“One of the most exciting things about optogenetics,” says
Patrick Rothwell, Ph.D., assistant professor in the Department of
Neuroscience,“is that it may, in and of itself, one day be used as a treatment
strategy, but it may also be used to identify other interventions … based on
our discovery of what is actually going wrong in the brain.”
Targeting relapse
There’s a lot scientists still don’t know about the brain
and its billions of neural connections. Over time, though, they have identified
areas that seem to hold the key for disorders like addiction.
“If you think of the brain as a powerful computer, it has
specific circuits dedicated to controlling particular functions,” explains Mark
Thomas, Ph.D., associate professor in the Department of Neuroscience. “Studying
morphine addiction in mice over time, we’ve identified brain circuits that are
involved in a relapse-like phenomenon.”
Using optogenetics, Thomas has recently shown that he can
retool those circuits, returning them to what he calls a “drug naïve state”—a
discovery that could ultimately lead to treatments that would help people
struggling with addiction avoid relapse.
“The challenge with addiction is to identify which circuits
are really producing the addiction-like pattern of behavior so that, ultimately,
we can target them with therapeutic intervention,” he says. “That’s what
optogenetics, which is so exquisitely precise, allows us to do.”
Precise seizure control
Every day in the United States, doctors diagnose 500 people
with epilepsy, a condition that causes recurrent seizures. Current treatments,
says assistant professor of neuroscience Esther Krook-Magnuson, Ph.D., tend
toward a “hammer” approach: drugs, surgical removal of brain tissue, and deep
brain stimulation surgery, all of which can have unwelcome side effects because
they can’t be focused intently on only the disordered circuits.
Using optogenetics, however, Krook-Magnuson can target the
circuits with great specificity. In her
lab, she monitors mice using brain electrodes and software that detects
epileptic seizures. As soon as the seizure begins, the investigators shine LED
light directly on to the targeted circuits, stopping the seizure.
“That specificity—seizure control without negative side
effects—is what attracted me to optogenetics,” Krook-Magnuson says. “It’s like
a classroom full of kids where only one is misbehaving. It doesn’t make sense
to discipline the whole class.”
Zeroing in on autism
Rothwell, new to the U’s faculty this year, uses a different
metaphor to describe his optogenetics work involving autism and addiction.
“Imagine the brain as an orchestra, with all of the cells
working together. You might hear a problem in, say, the strings section. But
then you have to break it down further, to the cellos, the violas, the violins,
to find out which is out of tune.”
Rothwell has pinpointed a particular group of malfunctioning
synaptic connections—say, the violins—in the brain’s striatum that he believes
plays a role in autism; now he wants to pluck each string to find the
discordant notes.
“My previous work got us to the violins,” he explains. “Now,
using optogenetics, we’re looking closer in hopes of being able to ‘tune’ those
cells, to restore healthy function.”
Rothwell keeps a foot in two camps—both autism and addiction
research—because the same area of the striatum appears to be problematic in
both disorders, he says. Addiction research in general is further along, he
says, so he can learn from that and apply it, where indicated, to his autism
investigations. He now has philanthropic backing for this work, too.
On a roll
The MnDRIVE and BRAIN Initiative funding were critical to
producing this body of optogenetics knowledge, says Thomas, which is being
shared with multiple labs across campus.
Now scientists are focused on the next steps: developing
improved viruses to deliver the optogenetics proteins into the brain and using
functional magnetic resonance imaging to actually watch what happens as the
photosensitive neurons are activated.
“There’s so much promise here,” Thomas says. “Optogenetics
has been a transformative tool, allowing us to work in the brain in a whole new
way, to tackle the unknowns. And is it possible that it could be used as a
therapeutic tool for humans? Yes, I think that’s on the horizon.”
How optogenetics works
The roots of optogenetics can be traced back to the 1970s, when scientists discovered that certain types of algae contained photosensitive proteins.
Jump forward several decades, when neuroscientists wondered whether, if they somehow put that algae protein into specific neurons in the brain, they could become light-sensitive. And could the scientists then control those neurons with light? Vastly simplified, the answers were yes and yes.
To deliver the protein, scientists use a benign virus (one that won’t replicate or cause sickness), injecting it into the target cells of interest in the brain of a mouse. Those brain cells take up the virus—and thereby, the protein—while other neurons nearby remain unaffected.
Then, with a superfine fiber optic probe, the scientist shines LED light on to the target area and essentially turns on a particular set of neurons. Or they can use another protein that, once lit, inhibits the neurons from firing.
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