Eric Hopton for redOrbit.com – Your Universe Online

“Are you a man or a mouse?” In the future, the answer may not be quite so easy.

Scientists from the University of Rochester Medical Center in New York have blurred the distinction by implanting human brain cells to create a part-human “supermouse.” The modified mouse is said to be four times as smart as a normal mouse.

The purpose of this work is to aid understanding of human brain diseases by studying them in living mouse brains. These hybrid brains retain the mouse’s own neurons which constitute about half of their brain cells. But almost all the glial cells, which support the neurons, are human.

“It’s still a mouse brain, not a human brain, but all the non-neuronal cells are human” Rochester’s Steve Goldman told Andy Coghlan of New Scientist.

The immature glial cells were taken from donated human fetuses and were then injected into mouse pups. The cells developed into star-shaped glial cells known as astrocytes. 300,000 human cells were injected into each mouse, but 12 months later that number had increased to 12 million. The mouse’s own glial cells had been driven out by human astrocytes which are up to 20 times larger than those in mice.

“It’s like ramping up the power of your computer,” said Goldman.

After carrying out a series of standard memory and cognition tests on the mice, Goldman’s team found that the modified mice were a lot smarter. There was a fourfold improvement in memory – Goldman described these findings, a little unscientifically, as “whopping effects.”

Goldman carried out similar research last year using mature human brain cells but the cells did not “take over” the mouse brain in the way that the fetal, or “progenitor glial cells” did in the latest experiments. He discovered that the progenitor cells were able to divide and multiply.

As Wolfgang Enard of Ludwig-Maximilians University Munich in Germany, told Coghlan, “That the cells work at all in a different species is amazing, and poses the question of which properties are being driven by the cell itself and which by the new environment.”

In another experiment, Goldman’s team found that when immature human glial cells were introduced into mouse pups that were defective in producing myelin, some of the human glial cells developed into oligodendrocytes. These are brain cells that play a role in the formation of myelin. Somehow, the human cells detected the defect and found a way to repair it.

This has implications for the treatment of diseases like multiple sclerosis where damage to the myelin sheath is implicated. “These human glial chimeric mice should permit us to define the specific contributions of glia to a broad variety of neurological disorders, using human cells in vivo” says Goldman’s report. He is hoping to get permission to treat MS patients using glial progenitor cells. Further studies are already under way grafting the cells into rats.

Goldman is clearly aware of the ethical challenges posed by the research and is keen to head off any accusations of creating a kind of “Frankenmouse.” He stressed that the subject should not be perceived as human in any way. “It’s still a mouse” he told the New Scientist reporter. Nevertheless, the team stopped short of extending the study to include monkeys because of the ethical implications.

“We briefly considered it buy decided not to because of all the potential ethical issues,” Goldman told Sarah Knapton of The Telegraph.

Results of the new research have been published in the Journal of Neuroscience.

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