What makes us different from the rest of the mammals that inhabit the Earth? It is not an easy question to answer. Now, a team of scientists has discovered a new type of neuron, nicknamed the rosehip neuron or “rosehip” , which raises new clues with which to solve this riddle. The new neuron is compact, dense, and responsible for silencing other neurons.
“We really don’t understand what makes the human brain special,” says Ed Lein, a researcher at the Allen Institute for Brain Sciences. “Studying the differences at the cell and circuit level is a good place to start, and now we have new tools to do it.”
The study, which has been published in the journal Nature Neuroscience, has identified a new type of human brain cell that has never been seen before in mice and other humans.
Why do I know this name?
The rosehip is named after the extraordinary branching of its axons, which make it look like a rose: the dense bundle that the axon of each brain cell forms around the center of the cell looks like a rose after it has shed its petals, the authors state. The newly discovered cells belong to a class of neurons known as inhibitory neurons, which slow down the activity of other neurons in the brain.
The study has not shown that this special neuron is unique to humans, but the fact that the rosehip neuron does not exist in rodents is intriguing, adding these cells to a very small list of specialized neurons that may exist only in humans or only in primate brains.
Researchers don’t yet understand what these cells might be doing in the human brain, but their absence in rodents points to how difficult it is to model human brain diseases in laboratory animals.
One of the next steps the scientists will take is to look for rosehip neurons in post-mortem brain samples from people with neuropsychiatric disorders to see if these specialized cells can be altered into human disease.
In their study, the researchers used postmortem brain tissue samples from two 50-year-old men who had died and donated their bodies to science. They took sections of the upper layer of the cortex, the outermost region of the brain that is responsible for human consciousness and many other functions that we consider unique to our species. It is much larger, compared to our body size, than in other animals.
The Allen Institute group, in collaboration with researchers from the J. Craig Venter Institute, discovered that rosehip cells turn on a unique set of genes, a genetic signature not seen in any of the mouse brain cell types they have studied. . Researchers at the University of Szeged found that rosehip neurons synapse with other types of neurons in a different part of the human cortex, known as pyramidal neurons.
What appears to be unique about rosehip neurons is that they only bind to a specific part of their cell partner, indicating that they could be controlling the flow of information in a very specialized way.
“ This particular cell type can stop in places that other cell types cannot . The cells involved in the trafficking of a rodent brain cannot stop in these places,” says neuroscientist Gábor Tamás, co-author of the work.
“Many of our organs can be reasonably modeled on an animal model,” says Tamás. “But what sets us apart from the rest of the animal kingdom is the capacity and production of our brain. That makes us human. It turns out that humanity is very difficult to model in an animal system .”
Reference: Eszter Boldog et al, Transcriptomic and morphophysiological evidence for a specialized human cortical GABAergic cell type, Nature Neuroscience (2018). DOI: 10.1038 / s41593-018-0205-2
Image credit: Tamas Lab, University of Szeged
