Researchers have discovered a new type of inhibitory neuron present in human, but not mouse, brains. So-called rosehip neurons, described yesterday (August 27) in Nature Neuroscience, have an unusually bushy appearance, express a particular set of human genes not found in mice, and could help provide insights into what distinguishes our brains from those of other animals.
“Finding cell types that are uniquely human . . . helps our understanding of the physiological differences that under[lie] our higher cognitive abilities and may better inform upon treatment strategies for brain-related disorders,” Blue Lake, an assistant project scientist in bioengineering at the University of California, San Diego, who was not part of the study, tells Live Science.
Two research groups—one in Hungary and the other in the USA—independently found the cells during studies of the human brain cortex. They then worked together to describe the new cell type using microscopy and genetic approaches. “It’s very bushy,” study coauthor Trygve Bakken of the Allen Institute for Brain Science in Seattle tells Live Science. The cell’s dendrites are “very compact with lots of branch points, so it kind of looks a little bit like a rosehip”—the bulbous fruit left behind when a rose’s petals fall.
Using transcriptomic analyses to probe the cells’ gene expression, the researchers found that rosehip neurons switch on a set of genes that have so far been found in humans but not in mice. “It’s too early to say that this is a completely unique cell type because [beyond humans and mice] we haven’t looked in other species yet,” study coauthor Ed Lein, also of the Allen Institute, tells Wired. “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.”
The team will now search for rosehip neurons in other human brain regions and investigate their potential roles in the organ’s function, according to a statement from the Allen Institute. “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,” Joshua Gordon, who was not involved in the study but directs the National Institutes of Mental Health, which helped fund the research, tells NPR.
Ongoing efforts to inventory all the cell types in the human brain may well turn up similar discoveries in future, Gordon adds. “I think it’s very, very likely that this is the tip of the iceberg.”