Human Brain Cells Are Grown In Mice

Human Brain Cells Are Grown In Mice: "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."

The finding that the human cells are working in their new environment provides encouragement for those who hope to develop stem-cell-based therapies for neurodegenerative diseases such as Parkinson's.