Neuroscientists Roll Out First Comprehensive Atlas of Brain Cells

A slew of 17 studies reveals the first comprehensive list of all cell types in the primary motor complex, offering "a starting point for tracing cellular networks to understand how they control our body and mind and how they are disrupted in mental and physical disorders," reports ScienceDaily. From the report: The 17 studies, appearing online Oct. 6 in the journal Nature, are the result of five years of work by a huge consortium of researchers supported by the National Institutes of Health's Brain Research Through Advancing Innovative Neurotechnologies (BRAIN) Initiative to identify the myriad of different cell types in one portion of the brain. It is the first step in a long-term project to generate an atlas of the entire brain to help understand how the neural networks in our head control our body and mind and how they are disrupted in cases of mental and physical problems. [...] Individual researchers have previously identified dozens of cell types based on their shape, size, electrical properties and which genes are expressed in them. The new studies identify about five times more cell types, though many are subtypes of well-known cell types. For example, cells that release specific neurotransmitters, like gamma-aminobutyric acid (GABA) or glutamate, each have more than a dozen subtypes distinguishable from one another by their gene expression and electrical firing patterns. While the current papers address only the motor cortex, the BRAIN Initiative Cell Census Network (BICCN) -- created in 2017 -- endeavors to map all the different cell types throughout the brain, which consists of more than 160 billion individual cells, both neurons and support cells called glia. The BRAIN Initiative was launched in 2013 by then-President Barack Obama. [Researchers] have already used CRISPR-Cas9 to create mice in which a specific cell type is labeled with a fluorescent marker, allowing them to track the connections these cells make throughout the brain. For the flagship journal paper, the Berkeley team created two strains of "knock-in" reporter mice that provided novel tools for illuminating the connections of the newly identified cell types. "The big advance by the BICCN is that we combined many different ways of defining a cell type and integrated them to come up with a consensus taxonomy that's not just based on gene expression or on physiology or morphology, but takes all of those properties into account," [UC Berkeley colleague Dirk Hockemeyer] said. "So, now we can say this particular cell type expresses these genes, has this morphology, has these physiological properties, and is located in this particular region of the cortex. So, you have a much deeper, granular understanding of what that cell type is and its basic properties." [F]uture studies could show that the number of cell types identified in the motor cortex is an overestimate, but the current studies are a good start in assembling a cell atlas of the whole brain.

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