News-Medical Life Sciences speaks to Dr. Quentin Barraud about his work on spinal cord repair and how he uses the CLARITY technique in his research.
Spinal cord repair and rehabilitation is a difficult but important topic to research, can you please give a brief overview of research in this field?
There are many grades of spinal cord injuries, in terms of range of movement, from small disabilities to becoming wheelchair bound for the rest of your life, the range is very broad.
There are many different approaches to try to overcome these disabilities, with key areas of research being focussed on developing stem cell therapies and using growth factors to promote regrowth of the nerve tissue after the injury.
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Can you please give a brief overview of your area of research?
In our lab our strategy is a bit different. We focus on utilizing what is left following an injury, what is spared by the lesion. In most of the cases, in humans, only a small part of the tissue is spared.
We want to take advantage of this spared tissue and allow the brain to access the spinal cord again after the lesion. For this, we have developed a method of electrical stimulation of the spinal cord combined with pharmacological stimulation.
To summarize briefly, by applying electrical stimulation below the injury we will take over the excitatory drive that initially originated from the brain which is now separated from the lower spinal region.
By applying electrical stimulation, we give the command to the motor system to move the leg. In combination with this we also apply a cocktail of pharmacological agents to modulate the neurones and act like a fuel making them active.
By combining electrical and chemical stimulation of the spinal cord we have demonstrated in animal models that we were able to restore voluntary control of motion of serious spinal cord injury.
The first development was using very simple electrodes to stimulate the spinal cord. This was done in the lab about ten years ago. Now, we have improved the stimulation protocol. Now we are able to stimulate the spinal cord more precisely and stimulate the extension muscle when it's needed, stimulate the flexion muscle when it's needed.
We can finely control the movement of the leg after an injury in space and time. This is something we've improved. Now, we are translating our technology that we developed on the Holden's Model to human beings.
For that we launched pre-clinical studies in higher mammals. When using non-human primates, we had positive outcomes and now a clinical trial has started in a hospital, where the first patients were in play a few weeks ago, which is really promising.
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What models are used in pre-clinical research? What techniques do you use?
We use many different kinds of models for studying the spinal cords. We have projects that look at the mechanism of locomotion and how to restore this mechanism after an injury.
This is the model we are working with, we have different kinds of spinal cord injuries ranging from simple cut of the spinal cord to contusion model, which mimics the human condition of having a contusion on the spinal cord.
Depending on the research question we have in the lab we simply choose a different kind of model. Then using these models, we can train the animal to regain a certain ability to walk after an injury using a robotic interface.
We use a lot of anatomical techniques trying to understand the underlying mechanism and for that we use an immunochemistry technique, in particular the new clarity technique that was developed to visualize the neurons in 3-dimensions.
This is extremely useful for our work, to see how a system gets reorganized after an injury. Whether the cut axon can grow within or across the lesion when using our approach, and whether we can promote a better outcome for the cut fibers.
We use e-dura electrodes, developed to be stretchable and mimic the properties of the dura matter to have close interactions with the biological tissue. We have shown by using this kind of technology we can deliver electrical and chemical stimulation to neural tissue. Helping the neural system to reorganize. It's important to develop these kind of strategies.
How has the Wyss Center helped support your research?
The Wyss Center helps researchers to bring concepts that were demonstrated pre-clinically to humans, they provide all the tools in order to do this. The Wyss Center has a strong focus on the neural prosthetic devices that will closely interact with the biological tissue.
For example they are developing an implantable brain radio that can read the thoughts of people with paralysis and wirelessly transmit the intention to move outside the body. They were also involved in the development of the e-dura electrodes, which are flexible and stretchable electrodes and have the same properties as the dura mater.
Advanced technology like this is developed at the Wyss Center. We are working with them to bring our concept to humans, using the technology they are helping to develop our models.
What role has the X-CLARITY tissue clearing system played within your research? What do you do with this tissue clearing system?
Before the X-CLARITY system came up on the market, a few years ago, we were using passive clearing to clear out samples, which took us weeks or months. With this new system, this process can be done within six or seven hours, you can even clear an entire brain in this time.
The X-CLARITY therefore brings obvious advantages. It saves a lot of time, we were able to image an entire set of brain and spinal cords in a relatively short amount of time. This allowed us to clearly see the benefit of the approaches were having on spinal cord networks following an injury. It's a great device to save time for your research.
Another benefit of the X-CLARITY system is that it allows you to better standardize your methodology, otherwise it's difficult to have quantitative measures. Previously, all we could do was produce qualitative data, as it was difficult to quantify the amount of fibers in a sample.
Using the X-CLARITY system gives us clarity with standardizing the clearing process. Being able to have quantitative data enables all the brain samples to be compared with each other because they will all follow the same protocol, in different conditions. It will be a huge advantage in having quantitative analysis.
In summary, the X-CLARITY system benefits researchers by saving a lot of time and helping to standardize protocols in the lab.
How do you foresee the X-CLARITY tissue clearing system helping your research? What would you share with others about it?
The X-CLARITY system will help us to understand how the network reorganizes after the injury. This system allows you to visualize and follow the course of an axon coming from the motor cortex, coming down to the lumbar spinal cord. You can visualize, in 3D, the course of single or several axons when they go around the lesion for example.
This is something that is unique to the X-CLARITY system at the moment. That's why this technique is very exciting. Compared to classical storage techniques, when working on brain and spinal cord in very thin slices they are all in 2D images and this makes it difficult to get the whole picture of what's going on.
Using the clarity we get from the X-CLARITY system, recently in a few sample we have been able to see fiber tracks that we were not able to visualize in 2D sections. We were surprised to see how the axons were actually organizing into different, segregating bundles. This is something we could not see when using classic techniques.
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What successes have there been with biomaterials that can create a long-term interface between the neural tissues and spinal implants?
It was very challenging to find something that would match the properties and last a long time as well, they have tried different kinds of materials with different stiffness for example. What they found is the appropriate combination to match the properties of the dura matter.
They also tested the materials for biocompatibility of the device and they showed that there was near normal level of immune reaction. It's something that works in symbiosis with the biological systems.
How do the spinal implants work?
The neural implant that we use is replacing the lost function that was initially coming from the brain and that got cut following a lesion.
Simply put, by delivering electrical stimulation, we replace the excitatory drive coming from the brain, and because the spinal circuits below the injury are still functioning but are just dormant. By delivering stimulation we ‘awaken’ them and allow the system to be functional again. That's the idea behind the new implant, to mimic the inputs coming from the brain and replace them.
What technique do you use to measure how well implants have connected to the spinal tissues?
We have a lot of measurements that are carried out over an extended period of time to measure the incidence of the electrodes and see how they interact with the tissue. If we see that the threshold of activation is increasing it's a sign that something is going wrong.
The idea is always to develop implants that are stable over a long period of time and retain stable properties when in close interaction with the tissue.
What does the future hold for spinal cord repair research? What challenges are there to overcome?
As labs are working on stem cell approaches, other labs are developing neural devices, others are trying to connect using spinal interface from the brain to the spinal cord.
The idea in the future is to have combinatory research. Combining all the fields together in the same patient to have a combination of stem cell graphs for example and cross factors which are steered by the application of a brain spinal interface, where actually the brain can control the electrical stimulation below the injury.
The next big challenge in the field of imaging for clear sampling and for huge samples is the data processing. This is the next hurdle that people will have to overcome. Now we have been using this kind of system, the clearing process is standardized but now we need to have proper microscopes for imaging that will allow us to have the ability to visualize large samples.
Of course you need power for computers to process and analyze this sort of data. That's the next challenge, in terms of technical development for this clearing technique. I know for example that at the Wyss Center they are developing technology that will help us overcome these challenges. This is the beginning of huge wave in the field to start using these procedures.
Where can readers find more information?
About Quentin Barraud
Quentin Barraud has a PhD in Neuroscience where he studied at the University of Bordeaux and graduated in 2010.
Currently he has a post-doctoral position in the EPFL (École Polytechnique Fédérale de Lausanne) laboratory where he works on spinal cord injury models to try to find new strategies to improve quality of life of patients with spinal cord injuries.