Breakthrough Brain Cell Discovery Shocks Neuroscientists

Scientists have discovered a new type of brain cell that promises to shake up the field of neuroscience.

The discovery brings an end to a decades-old controversy and may pave the way for new targeted treatments for a range of health conditions.

The results, from neuroscientists at the University of Lausanne in Switzerland and the Wyss Center for Bio and Neuroengineering in Geneva, were published on September 6 in the journal Nature.

To understand the relevance of the study, let's first establish what we already know about brain cells.

The Body's Cellular Electricians

In the past, it was believed that the mammalian nervous system was made up of two types of cells: neurons and glia. Neurons are the specialized cells that receive and transmit electrical and chemical signals throughout the body, like the wires in a circuit. Neurons send signals between each other using special signaling molecules called neurotransmitters, such as one called glutamate—which was central to the latest study.

Glia do not conduct nerve impulses but instead support and protect the neurons and clean debris from the environment that they are in. They are almost like cellular electricians, making sure that the body's wires are maintained and going to the right place.

Within these broad groups are sub-populations of specialized cells. Perhaps the most abundant sub-population of glia in the human brain is a star-shaped cell called an astrocyte. One of the many roles of these special cells is to surround the points of contact between neuron cells, called synapses, and facilitate the transmission of neurotransmitters between neurons.

End to a Decades-Old Debate

But can astrocytes themselves produce neurotransmitters? That is the question at the heart of this new study.

"Based on experimental observations, some of the authors of this study proposed almost 20 years ago that cells classified as astrocytes could release glutamate," Andrea Volterra, co-director of the study, told Newsweek. "However, many other scientists in the field could not reproduce these observations and the topic became one of the most controversial in neuroscience."

Using cutting edge genomic tools to analyse which genes were switched on in different brain cells, the team were able to finally set the record straight. "We identified a subpopulation of cells classified as astrocytes—the main family of glial cells in the central nervous system—that also possessed the typical machinery used by neurons to secrete glutamate, the main neurotransmitter assuring neuron-to-neuron communication at brain synapses," Volterra said.

In other words, they had discovered a sort of hybrid cells with properties of both neurons and glia. "The hybrid 'transcriptome' [signature of gene expression] of this cell sub-population does not correspond to any of the known cell types described so far," Volterra said. "Ours was then the feeling that we achieved a major step forward."

Further analysis showed that these cells were not evenly distributed around the brain—rather, they were clustered in specific areas. Clearly, the cells have a specific role in certain areas of the brain. But what?

The Promise of New Treatments

To find out what these hybrid cells actually do, the team tampered with the cells so that they no longer produced the machinery required to release the glutamate neurotransmitter. When these tampered cells were present in mice, the animals had a reduced capacity to memorize and retrieve stored memories, exacerbated seizures, and changes to the hormonal circuitry controlling movement that becomes damaged in Parkinson's disease.

"Therefore, these cells are important for cognitive function, correct movement control and help prevent insurgence of epileptic seizures," Volterra said. "To note, we have not mapped these cells throughout the brain yet, so new roles in other regions than those studied so far will likely emerge from future studies."

This discovery highlights a new level of complexity and specificity in the function of different areas and cells in the brain, which may help develop more targeted treatments for brain disease. "These new levels of complexity and specificity need now to be incorporated in our understanding of brain function and dysfunction," Volterra said.

The team are currently studying how this newly discovered cell population might play a role in the development of Alzheimer's disease. "New and much more specific medical strategies can be envisaged based on our findings," Volterra said.

The next steps for the team are to explore where else these new hybrid cells can be found and what other roles they might play in healthy brain function. "We would like to extend the mapping of 'our cells' throughout the brain and thereby possibly discover other roles in brain function and dysfunction," Volterra said. "We also want to better understand how these hybrid cells have merged, why they are needed and the exact modalities by which they contribute to the function of specific brain circuits."

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