Neurons on the run
A device for studying the brain activity of mobile mice
Russian and American physicists have created a device based on specialized optical fiber, which can be used to observe the work of single neurons in the brains of mice and other animals during movement. The results of the work are presented in the Journal of Biophotonics (Pochechuev et al., Implantable graded-index fibers for neural-dynamics-resolving brain imaging in awake mice on an air-lifted platform).
"We have demonstrated that our system allows us to observe the brain work of mice that move freely inside a cell adapted to study their cognitive abilities. This will allow biologists to study interactions between individual nerve cells in key brain regions of free—moving experimental rodents," the researchers write in their paper.
To date, there are several systems for visualizing the activity of brain cells that allow you to observe the work of groups of neurons in a living organism. As a rule, their work requires modifications of the animal genome, causing nerve cells to fluoresce during the manifestation of any forms of electrical activity.
Such technologies have significantly enriched the arsenal of neurophysiologists, but their use is complicated by the fact that complex optical systems are needed to monitor the work of brain cells, allowing them to focus the image coming from the brain. This imposes serious restrictions on the use of these neuroimaging systems during experiments that allow animals to move freely.
A group of physicists from NUST MISIS, the University of Texas, MSU and The Russian Quantum Center under the leadership of Alexey Zheltikov, Professor at Texas A&M University in College Station (USA), has developed a system that allows such experiments to be carried out. Scientists have achieved this through the use of specialized optical fiber and a platform-an aviary on an air cushion.
The developed optical fiber, as scientists explain, is arranged in such a way that its refractive power smoothly changes from the center to the edges of the light-conducting material. This feature makes it possible to significantly increase the information capacity of the fluorescent signal received from the brain.
Although the head of a mouse with an optical fiber implanted in the brain is rigidly fixed under a microscope, an air cushion platform allows mice to walk while exploring space. The device is somewhat similar to a "squirrel wheel": when a mouse fixed under a microscope moves its paws, the floor suspended on an air cushion moves under them, but the mouse, in theory, should have the impression that it is moving on the floor.
A mouse with an optical fiber embedded in the brain is fixed under a microscope, under it is a light platform on an air cushion. On the right side of the inset is an image of a fluorescent neuron.
The physicists tested the operation of this system on several GM mice with neurons that fluoresce during activity. Experiments have confirmed that the new system can actually track the activity of nerve cells in the body of moving mice and get clear pictures of individual neurons. Scientists hope that the complex they have created will accelerate the study of the work of animal brain cells during movement.
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