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Muscle movement is enabled by signals sent from the brain to motor neurons; However, these impulses often transit through spinal interneurons before reaching their targets. How the brain and this highly diverse group of “switchboard operator” cells are connected is less understood. Read this also Brain cells play a game: are they ‘conscious’?
To address this, researchers at St. Jude Children’s Research Hospital have developed a whole-brain atlas that shows the brain regions that deliver direct input to V1 interneurons, a type of cell essential for movement. The resulting atlas and associated three-dimensional interactive website provide a foundation for learning more about the physical landscape of the nervous system and how the brain communicates with the spine. The results were reported today in Neuron
“We have known for decades that the motor system is a distributed network, but the final output is through the spinal cord,” said corresponding author Jay Bikoff, PhD, St. Jude Department of Developmental Neurobiology. “There, you have motor neurons that cause muscle contraction, but motor neurons do not function in isolation. Their activity is orchestrated by networks of molecularly and functionally diverse interneurons.”
While great leaps have been made in understanding how different areas of the brain relate to different aspects of motor control, exactly how these areas connect to specific neurons in the spinal cord has been a blind spot in the field. Interneurons are difficult to study, primarily because they come in hundreds of different, intermingled varieties. Read this also How does the brain clear waste products? Study takes a look inside
Study findings:
“It’s similar to untangling a ball of Christmas lights, except it’s more challenging because what we’re trying to untangle is the result of more than 3 billion years of evolution,” said co-first author Anand Kulkarni, PhD. Is.”
Recent advances have demonstrated the existence of molecularly and evolutionarily distinct interneuron subclasses, but much is still unknown about their location within neural communication. “Defining the cellular targets of descending motor systems is fundamental to understanding the neural control of movement and behavior,” Bikoff said. “We need to know how the brain is communicating these signals.”
To dissect the circuits connecting the brain to the spinal cord, the researchers used a genetically modified version of the rabies virus that is missing a key protein, the glycoprotein, from its surface. This hindered the ability of the virus to spread between neurons.
This essentially trapped the virus at its point of origin. By reintroducing this glycoprotein to a specific population of interneurons, the virus can make a jump to the synapse before being trapped again. The researchers used a fluorescent tag to track the virus. By finding where the virus ends up, researchers could figure out which areas of the brain were connected to these interneurons. Read this also Your heart has its own ‘little brain’: Study reveals how the heart works surprisingly like the brain
3D map allows researchers to see connections: The researchers applied this approach to a class of interneurons called V1 interneurons, which were previously shown to play a key role in shaping motor output. This work allowed them to precisely trace the origin of many of the signals received by these interneurons to the brain.
“We’re only targeting V1 interneurons, but these are actually a highly heterogeneous group of neurons, so we thought, ‘Let’s target as many V1s as possible and see what’s projecting to them,'” Bikoff said.
The researchers turned to serial two-photon tomography to visualize these neurons and generate a three-dimensional reference atlas. This technique renders the brain as it creates hundreds of micron-thick sections to reveal fluorescently labeled neurons. The atlas allowed researchers to make precise predictions about the network that connects various brain structures to the spinal cord and the intrinsic neurons with which they interact.
Identifying how these structures connect to the spinal cord will allow researchers to further investigate the neural circuits that control movement, and together the web atlas will ensure that the data is freely accessible to all. is capable. Bikoff explained, “We understand what some of the identified brain regions do from a behavioral perspective, but we can now hypothesize about how these effects are mediated and what the role of V1 interneurons might be. It will be very useful for the field as a hypothesis generating engine.
Disclaimer: This article is for informational purposes only and is not a substitute for professional medical advice. Always seek the advice of your doctor with any questions you may have about a medical condition.
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