A lot remains hidden within the tissues stuffed inside our craniums. As Yasemin Saplakoglu at LiveScience reports this week, researchers recently discovered an entirely new type of neuron that may only exists in the human brain.
The new cell type is called the “rosehip neuron” since the cells are shaped like the fruit of rose bushes. According to a press release, several years ago two different labs, one at the University of Szeged in Hungary and another at the Allen Institute for Brain Science in Seattle both identified what appeared to be a new type of brain cell. When they learned they were both investigating the same neuron they decided to collaborate on a study. Using two brains donated to science from deceased men in their mid-fifties, the labs used different techniques to investigate the neurons—with the Hungarian team examining the neuron’s shape and electrical properties while the Allen team looked at the genetics of the neurons. The results appear in the journal Nature Neuroscience.
Molecular neuroscientist Trygve Bakken of the Allen Institute, a lead author of the paper, tells Saplakoglu that most neurons have long dendrites, branches that carry electrical signals. The new neuron, however, is a little different. “It’s very bushy,” he says. “[The dendrites are] very compact with lots of branch points, so it kind of looks a little bit like a rosehip.”
This type of neuron exists in humans, but not in rodents that are frequently used as model species in neuroscience. Therefore, the existence of the rosehip neuron may explain why so many treatments for brain disorders seem to work in mouse models, but fail when applied to humans. “It may be that in order to fully understand psychiatric disorders, we need to get access to these special types of neurons that exist only in humans,” neuroscientist Joshua Gordon, director of the National Institute of Mental Health, tells Jon Hamilton at NPR.
“Our brains are not just enlarged mouse brains,” Bakken says in the release. “People have commented on this for many years, but this study gets at the issue from several angles.”
“Many of our organs can be reasonably modeled in an animal model,” co-author Gábor Tamás, a neuroscientist the University of Szeged, says. “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.”
So what, exactly does the rosehip neuron do? That’s not quite clear. The cells make up about 10 percent of the neocortex, the last part of our brain to evolve which is associated with sight and hearing. Rosehip appears to be an inhibitory neuron, which regulates the flow of information to certain parts of the brain. Saplakoglu reports the rosehips seem to connect to pyramidal neurons, an “excitatory” neuron that makes up about two-thirds of the neuron cells in the neocortex.
“It has these really discrete connections with [pyramidal] neurons,” says Bakken. “It has the potential to sort of manipulate the circuit in a really targeted way, but how that influences behavior will have to come in later work,” Bakken tells Andrea Morris at Forbes.
Looking forward, the teams hope to look at brain samples from people suffering neuropsychiatric disorders to see if they have altered rosehip neurons.