Stanford researchers have developed a device to activate neurons of the brain, spinal cord or limbs in mice and, is powered wirelessly using the mouse’s own body to transfer energy. The device is the first to deliver optogenetic nerve stimulation in a fully implantable format.
It has the size of a peppercorn can, with the blue glowing light.
The miniature device that combines optogenetics – using light to control the activity of the brain – with a newly developed technique for wirelessly powering implanted devices is the first fully internal method of delivering optogenetics.
The device dramatically expands the scope of research that can be carried out through optogenetics to include experiments involving mice in enclosed spaces or interacting freely with other animals.
The work is published in the Aug. 17 edition of Nature Methods.
Traditionally, optogenetics has required a fiber optic cable attached to a mouse’s head to deliver light and control nerves. With this somewhat restrictive headgear, mice can move in an open cage but can’t navigate an enclosed space or burrow into a pile of sleeping cage-mates the way an unencumbered mouse could. Also, before an experiment a scientist has to handle the mouse to attach the cable, stressing the mouse and possibly altering the outcome of the experiment.
These restrictions limit what can be learned through optogenetics. People have successfully investigated a range of scientific questions including how to relieve tremors in Parkinson’s disease, the function of neurons that convey pain and possible treatments for stroke. However, addressing issues with a social component like depression or anxiety or that involve mazes and other types of complex movement is more challenging when the mouse is tethered.
Optogenetics only works on nerves that have been carefully prepared to contain the proteins that respond to light. In the lab, scientists either breed mice to contain those proteins in select groups of nerves or they carefully and painstakingly inject viruses carrying the protein DNA into nerves the size of dental floss. Shining a light – whether through a fiber optic cable or a wireless device – on neurons that haven’t been prepared has no effect.
In behavioral experiments, the mouse would be moving all around, and the researchers needed a way of tracking that movement to provide localized power. In other labs, they were tackling the same problem using bulky devices that affix to the skull and complex arrays of coils paired with sensors to locate the mouse and deliver localized power.
But in this research, they use the mouse’s own body to transfer radio frequency energy that was just the right wavelength to resonate in a mouse. This result is published on Aug. 4 in Physical Review Applied.
“The key is that there’s a bit of wiggle room at the grid. So if something like, say, a mouse paw were present, it would come in contact with the boundary of all that stored energy. And remember how the wavelength is the exact wavelength that resonates in mice? The mouse essentially becomes a conduit, releasing the energy from the chamber into its body, where it is captured by a 2 mm coil in the device.”
Wherever the mouse moves, its body comes in contact with the energy, drawing it in and powering the device. Elsewhere, the energy stays tidily contained. In this way, the mouse becomes its own localizing device for power delivery.
This novel way of delivering power is what allowed the team to create such a small device. And in this case, size is critical. The device is the first attempt at wireless optogenetics that is small enough to be implanted under the skin and may even be able to trigger a signal in muscles or some organs, which were previously not accessible to optogenetics.
The team says the device and the novel powering mechanism open the door to a range of new experiments to better understand and treat mental health disorders, movement disorders and diseases of the internal organs. They have possibly developed new treatments for chronic pain.
