Newly discovered rosehip neurons may be unique to humans

10/09/2018 12:25:00​​​​​​​
​​​​​​​WPHC

Using transcriptomic, morphophysiological and bioinformatics tools, an international team of neuroscientists from the United States and Hungary has uncovered a new type of human brain cell that has never been seen in mice and other well-studied lab animals.

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Dubbed ‘rosehip neurons,’ the newly-discovered brain cells belong to a class of neurons known as inhibitory neurons, which put the brakes on the activity of other neurons in the brain.

“We don’t yet understand what these cells might be doing in the human brain, but their absence in the mouse points to how difficult it is to model human brain diseases in laboratory animals,” said co-lead author Dr. Gábor Tamás, a neuroscientist at the University of Szeged in Hungary.

In their study, Dr. Tamás and colleagues analyzed tissue samples from brains of two men. They took sections of the top layer of the cortex, the outermost region of the brain that is responsible for human consciousness and many other functions that we think of as unique to our species. It’s much larger, compared to our body size, than in other animals.

Digital reconstruction of a rosehip neuron in the human brain showing bundle of nerve fibers around central cell body (Tamas Lab, University of Szeged)
 

“It’s the most complex part of the brain, and generally accepted to be the most complex structure in nature,” said co-lead author Dr. Ed Lein, investigator at the Allen Institute for Brain Science.


The researchers found that the rosehip cells turn on a unique set of genes, a genetic signature not seen in any of the mouse brain cell types they’ve studied.


They also found that the rosehip neurons form synapses with another type of neuron in a different part of the human cortex, known as pyramidal neurons.​​​​​​​
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“This is one of the first studies of the human cortex to combine these different techniques to study cell types,” said co-author Dr. Rebecca Hodge, senior scientist at the Allen Institute for Brain Science.


What appears to be unique about rosehip neurons is that they only attach to one specific part of their cellular partner, indicating that they might be controlling information flow in a very specialized way.


“If you think of all inhibitory neurons like brakes on a car, the rosehip neurons would let your car stop in very particular spots on your drive,” Dr. Tamás said.


“They’d be like brakes that only work at the grocery store, for example, and not all cars (or animal brains) have them.”


“This particular cell type — or car type — can stop at places other cell types cannot stop. The car or cell types participating in the traffic of a rodent brain cannot stop in these places.”


The team now plans to look for rosehip neurons in other parts of the brain, and to explore their potential role in brain disorders.


“Our brains are not just enlarged mouse brains,” said co-author Dr. Trygve Bakken, senior scientist at the Allen Institute for Brain Science.


“People have commented on this for many years, but this study gets at the issue from several angles.”


The study​​​​​​​ was published in the journal Nature Neuroscience.


​​​​​​​Eszter Boldog et al. Transcriptomic and morphophysiological evidence for a specialized human cortical GABAergic cell type. Nature Neuroscience, published online August 27, 2018; doi: 10.1038/s41593-018-0205-2