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Scientists identify a new kind of human brain cell, not found in lab mice
Neuroscientists have discovered a new type of brain cell in a region of the human brain thought to be responsible for human consciousness. The researchers are speculating that the brain cell may be unique to humans as it has never been seen in lab rodents. Researchers think that the intriguing cells may comprise one of the characteristics that set humans apart from animals. While the study, published Aug. 27 in the journal Nature Neuroscience, has not confirmed that the newly discovered cell, dubbed the “rosehip cell”, exists only in humans, the fact that the cell has “features never described in rodents” reinforces the idea that studies on laboratory mice cannot stand as adequate models for human disease, especially human brain diseases, the researchers explained in a press release. “It’s too early to say that this is a completely unique cell type because we haven’t looked in other species yet,” researcher Ed Lein from the Allen Institute for Brain Science told Wired.com. “But it really highlights the fact that we need to be careful about assuming that the human brain is just a scaled-up version of a mouse.” "Many of our organs can be reasonably modeled in an animal model," Gabor Tamas, a neuroscientist at the University of Szeged, Hungary, said in the press release. "But what sets us apart from the rest of the animal kingdom is the capacity and the output of our brain. That makes us human. So it turns out humanity is very difficult to model in an animal system." Rosehip Neurons in the Neocortex Researchers examined tissue samples from the brains of two men who had died in their 50s and donated their bodies to research. The tissues were taken from the top layer of the cortex—known as the neocortex, thought to be responsible for human consciousness and other characteristics considered to be unique to humans. "It's the most complex part of the brain, and generally accepted to be the most complex structure in nature," Lein said. In a stroke of serendipity, two different groups of researchers—one from the Allen Institute in Seattle and another from the University of Szeged in Hungary—found that they had been studying the same type of cell from the tissues of the neocortex, albeit via different methods and while focusing on different characteristics of the cell. And so they decided to collaborate and consolidate their findings. That's when they realized that such a cell had never been found in the brains of laboratory mice. Defining the Cell and Future Steps The newly-discovered cell is being dubbed by researchers as a “rosehip neuron,” owing to its shape which looks like a rose that had shed its petals. Neurons, or nerve cells, are classified into excitatory cells or inhibitory cells. Excitatory cells carry information while inhibitory cells slow down or stop excitatory cells from acting. Researchers found that the rosehip neuron cells belong to the inhibitory category. “We all have inhibitory neurons and excitatory neurons,” Trygve Bakken, co-author of the paper and a neuroscientist at the Allen Institute for Brain Science, told Forbes. “But this particular type of inhibitory neuron is what’s new in this study. It's special based on its shape and its connections, and also the genes that it expresses.” Rosehip neurons turn on a unique set of genes, which is what enabled the scientists to distinguish it from other types of cells. Researchers also found that rosehip cells link with another type of brain cell—the pyramidal neurons—in a different part of the human cortex and appear to attach to only one specific part of that cell. This suggests that the rosehip neurons may be controlling information flow in a unique manner. Researchers plan to see whether rosehip neurons can be found in other regions of the brain, or in the brains of people with neuropsychiatric disorders, to see whether these cells may be different in those with brain or neurological diseases.