Human Neurons in Mouse Brains

I've blogged about the ethical and philosophical controversy over this before(here and here), and now scientists appear to have successfuly grown human brain cells in fetal mouse brains.

By injecting human embryonic stem cells into the brains of fetal mice inside the womb, scientists in California have created living mice with working human brain cells inside their skulls.

The research offers the first proof that human embryonic stem cells -- vaunted for their potential to turn into every kind of human cell, at least in laboratory dishes -- can become functional human brain cells inside a living animal, reaching out to make connections with surrounding brain cells.

The human cells had no apparent impact on the animals' behavior. About 100,000 cells were injected into each animal and just a fraction survived in their new hosts. That means the animals' brains were still more than 99 percent mouse -- a precaution that helped avoid ethical objections to creating animals that were "too human."

There's no denying the benefits of research like this could be tremendous:

More immediately, mice with humanized brains could be a boon for research, providing a living laboratory where scientists can study human brain diseases and drug companies can test the safety of experimental medicines.

"Let's say you're in the last stages of research before testing a new drug in humans," said lead researcher Fred Gage of the Salk Institute for Biological Sciences in La Jolla, Calif. "This could help tell you what effect it will have on human neurons inside a brain."

Researchers estimate as few as 100 of the injected cells survived in the mice. Obviously 100 cells of of the billions that comprise a mouse brain, are not much of threat to turn the mouse into a creature that has any semblence of human consciosness. And yet as I talked about before, it's hard to know where exactly the line should be drawn on this kind of research. Some think it shouldn't be done at all, while others think there should be even less limitations on it then there are. I'm somewhat closer to the former then the latter, but when you compare the potential incredible benefits against the highly troubling possibilities for mis-use, it's hard to know exacxtly which course we should take.