Light Treatment Reduces Pain Sensitivity In Mice

Today's post from news.stanford.edu (see link below) is a strange sounding one that looks at the effect of using gene therapy to alter the responses of mice to light being shone on their paws. The result is that pain responses can be toned up or down. Stanford scientists believe this can have far-reaching consequences for controlling human pain responses. It's called optogenetics and seems to me to require external genetic manipulation in order to be effective. Whether humans will respond positively to that idea remains to be seen but for those living with stubborn chronic pain, it may well be a price worth paying. This fascinating article is definitely worth a read.

Technique developed by Stanford scientists could lead to new treatments for pain
By Amy Adams, Shrivats Iyer, Kate Montgomery Stanford Report, February 19, 2014 

 A team of Bio-X researchers at Stanford has developed mice whose sensitivity to pain can be dialed up or down by shining light on their paws. The research could help scientists understand and eventually treat chronic pain in humans.

Light-sensitive proteins, or opsins, are used in a Stanford study on pain control through optogenetics.

The mice in Scott Delp's lab, unlike their human counterparts, can get pain relief from the glow of a yellow light.

Right now these mice are helping scientists to study pain – how and why it occurs and why some people feel it so intensely without any obvious injury. But Delp, a professor of bioengineering and mechanical engineering, hopes one day the work he does with these mice could also help people who are in chronic, debilitating pain.

"This is an entirely new approach to study a huge public health issue," Delp said. "It's a completely new tool that is now available to neuroscientists everywhere." He is the senior author of a research paper published Feb. 16 in Nature Biotechnology.
 
A switch for pain

The mice are modified with gene therapy to have pain-sensing nerves that can be controlled by light. One color of light makes the mice more sensitive to pain. Another reduces pain. The scientists shone a light on the paws of mice through the Plexiglas bottom of the cage.

Graduate students Shrivats Iyer and Kate Montgomery, who led the study, say it opens the door to future experiments to understand the nature of pain and also touch and other sensations that are part of our daily lives but little understood.

"The fact that we can give a mouse an injection and two weeks later shine a light on its paw to change the way it senses pain is very powerful," Iyer said.

For example, increasing or decreasing the sensation of pain in these mice could help scientists understand why pain seems to continue in people after an injury has healed. Does persistent pain change those nerves in some way? And if so, how can they be changed back to a state where, in the absence of an injury, they stop sending searing messages of pain to the brain?

Leaders at the National Institutes of Health agree the work could have important implications for treating pain. "This powerful approach shows great potential for helping the millions who suffer pain from nerve damage," said Linda Porter, the pain policy adviser at the National Institute of Neurological Disorders and Stroke and a leader of the NIH's Pain Consortium.

"Now, with a flick of a switch, scientists may be able to rapidly test new pain relieving medications and, one day, doctors may be able to use light to relieve pain," she said. 

Accidental discovery

The researchers took advantage of a technique called optogenetics, which involves light-sensitive proteins called opsins that are inserted into the nerves. Optogenetics was developed by a colleague of Delp, Karl Deisseroth, a co-author of the journal article. He has used the technique as a way of activating precise regions of the brain to better understand how the brain functions. Deisseroth is a professor of bioengineering, psychiatry and behavioral sciences.

Delp, who has an interest in muscles and movement, saw the potential for using optogenetics not just for studying the brain – interesting though those studies may be – but also for studying the many nerves outside the brain. These are the nerves that control movement, pain, touch and other sensations throughout our body and that are involved in diseases like amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's Disease.

A few years ago Stanford Bio-X, which encourages interdisciplinary projects like this one, supported Delp and Deisseroth in their efforts to use optogenetics to control the nerves that excite muscles. In the process of doing that work, Delp said, his student at the time, Michael Llewellyn, would occasionally find that he'd placed the opsins into nerves that signal pain rather than the ones that control muscle.

That accident sparked a new line of research. Delp said, "We thought 'wow, we're getting pain neurons, that could be really important.'" He suggested that Montgomery and Iyer focus on those pain nerves that had been a byproduct of the muscle work. 

A faster approach

A key component of the work was a new approach to quickly incorporate opsins into the nerves of mice. The team started with a virus that had been engineered to contain the DNA that produces the opsin. Then they injected those modified viruses directly into mouse nerves. Weeks later, only the nerves that control pain had incorporated the opsin proteins and would fire, or be less likely to fire, in response to different colors of light.

The speed of the viral approach makes it very flexible, both for this pain work and for future studies. Researchers are developing newer forms of opsins with different properties, such as responding to different colors of light. "Because we used a viral approach we could, in the future, quickly turn around and use newer opsins," said Montgomery, who is a Stanford Bio-X fellow.

This entire project, which spans bioengineering, neuroscience and psychiatry, is one Delp says could never have happened without the environment at Stanford that supports collaboration across departments. The pain portion of the research came out of support from NeuroVentures, which was a project incubated within Bio-X to support the intersection of neuroscience and engineering or other disciplines. That project was so successful it has spun off into the Stanford Neurosciences Institute, of which Delp is now a deputy director.

Delp said there are many challenges to meet before results of these experiments – either new drugs based on what they learn, or optogenetics directly – could become available to people, but that he always has that as a goal.

"Developing a new therapy from the ground up would be incredibly rewarding," he said. "Most people don't get to do that in their careers."

Delp and Deisseroth have started a company called Circuit Therapeutics to develop therapies based on optogenetics.
Media Contact

Amy Adams, Stanford News Service: (650) 796-3695, amyadams@stanford.edu

http://news.stanford.edu/news/2014/february/biox-numb-pain-021914.html

MANIPULATING MEMORY WITH LIGHT

Just look into the light: not quite, but researchers at the UC Davis Center for Neuroscience and Department of Psychology have used light to erase specific memories in mice, and proved a basic theory of how different parts of the brain work together to retrieve episodic memories

Optogenetics, pioneered by Karl Diesseroth at Stanford University, is a new technique for manipulating and studying nerve cells using light. The techniques of optogenetics are rapidly becoming the standard method for investigating brain function.

Kazumasa Tanaka, Brian Wiltgen and colleagues at UC Davis applied the technique to test a long-standing idea about memory retrieval. For about 40 years, Wiltgen said, neuroscientists have theorized that retrieving episodic memories -- memories about specific places and events -- involves coordinated activity between the cerebral cortex and the hippocampus, a small structure deep in the brain.

"The theory is that learning involves processing in the cortex, and the hippocampus reproduces this pattern of activity during retrieval, allowing you to re-experience the event," Wiltgen said. If the hippocampus is damaged, patients can lose decades of memories.

But this model has been difficult to test directly, until the arrival of optogenetics.

Wiltgen and Tanaka used mice genetically modified so that when nerve cells are activated, they both fluoresce green and express a protein that allows the cells to be switched off by light. They were therefore able both to follow exactly which nerve cells in the cortex and hippocampus were activated in learning and memory retrieval, and switch them off with light directed through a fiber-optic cable.

They trained the mice by placing them in a cage where they got a mild electric shock. Normally, mice placed in a new environment will nose around and explore. But when placed in a cage where they have previously received a shock, they freeze in place in a "fear response."

Tanaka and Wiltgen first showed that they could label the cells involved in learning and demonstrate that they were reactivated during memory recall. Then they were able to switch off the specific nerve cells in the hippocampus, and show that the mice lost their memories of the unpleasant event. They were also able to show that turning off other cells in the hippocampus did not affect retrieval of that memory, and to follow fibers from the hippocampus to specific cells in the cortex.

"The cortex can't do it alone, it needs input from the hippocampus," Wiltgen said. "This has been a fundamental assumption in our field for a long time and Kazu’s data provides the first direct evidence that it is true."

They could also see how the specific cells in the cortex were connected to the amygdala, a structure in the brain that is involved in emotion and in generating the freezing response.

Co-authors are Aleksandr Pevzner, Anahita B. Hamidi, Yuki Nakazawa and Jalina Graham, all at the Center for Neuroscience. The work was funded by grants from the Whitehall Foundation, McKnight Foundation, Nakajima Foundation and the National Science Foundation.

SENSING NEURONAL ACTIVITY WITH LIGHT

For years, neuroscientists have been trying to develop tools that would allow them to clearly view the brain's circuitry in action -- from the first moment a neuron fires to the resulting behavior in a whole organism. To get this complete picture, neuroscientists are working to develop a range of new tools to study the brain. Researchers at Caltech have developed one such tool that provides a new way of mapping neural networks in a living organism.

Hunt Morgan Professor of Biology, to test Archer1 as a sensor in a living organism -- the tiny nematode worm C. elegans. "There are a few reasons why we used the worms here: they are powerful organisms for quick genetic engineering and their tissues are nearly transparent, making it easy to see the fluorescent protein in a living animal," she says.

After incorporating Archer1 into neurons that were a part of the worm's olfactory system -- a primary source of sensory information for C. elegans -- the researchers exposed the worm to an odorant. When the odorant was present, a baseline fluorescent signal was seen, and when the odorant was removed, the researchers could see the circuit of neurons light up, meaning that these particular neurons are repressed in the presence of the stimulus and active in the absence of the stimulus. The experiment was the first time that an Arch variant had been used to observe an active circuit in a living organism.

Gradinaru next hopes to use tools like Archer1 to better understand the complex neuronal networks of mammals, using microbial opsins as sensing and actuating tools in optogenetically modified rodents.

"For the future work it's useful that this tool is bifunctional. Although Archer1 acts as a voltage sensor under red light, with green light, it's an inhibitor," she says. "And so now a long-term goal for our optogenetics experiments is to combine the tools with behavior-controlling properties and the tools with voltage-sensing properties. This would allow us to obtain all-optical access to neuronal circuits. But I think there is still a lot of work ahead."

One goal for the future, Gradinaru says, is to make Archer1 even brighter. Although the protein's fluorescence can be seen through the nearly transparent tissues of the nematode worm, opaque organs such as the mammalian brain are still a challenge. More work, she says, will need to be done before Archer1 could be used to detect voltage changes in the neurons of living, behaving mammals.

And that will require further collaborations with protein engineers and biochemists like Arnold.

"As neuroscientists we often encounter experimental barriers, which open the potential for new methods. We then collaborate to generate tools through chemistry or instrumentation, then we validate them and suggest optimizations, and it just keeps going," she says. "There are a few things that we'd like to be better, and through these many iterations and hard work it can happen."

The work published in both papers was supported with grants from the National Institutes of Health (NIH), including an NIH/National Institute of Neurological Disorders and Stroke New Innovator Award to Gradinaru; Beckman Institute funding for the BIONIC center; grants from the U.S. Army Research Office as well as a Caltech Biology Division Training Grant and startup funds from Caltech's President and Provost, and the Division of Biology and Biological Engineering; and other financial support from the Shurl and Kay Curci Foundation and the Life Sciences Research Foundation.