In the brains of mice grow the cells of man

Researchers in San Diego have designed mice containing fully functional human nerve cells as a novel way to study and potentially treat neurodegenerative diseases such as Parkinson's and Alzheimer's.

The neurons were formed in the brains of mice that had been injected with human embryonic stem cells as 2-week-old embryos.

Studies at the Salk Institute for Biological Sciences in La Jolla showed that the human cells migrated throughout the mouse brain and took on the traits of their mouse-cell neighbors. The results present direct evidence that primitive human stem cells can be cultured in the lab, be injected into an animal, and then develop into a particular type of desired cell.

The report appears in this week's Proceedings of the National Academy of Sciences.

Scientists said it was the first time cultured human embryonic stem cells have been shown to develop into a particular type of cell in the body of another living species.

Creation of a so-called "mouse-human chimeric nervous system" stops well short of spawning a mouse with a human-like cerebral cortex. In fact, all the brain structures...