Mice from NIMH

Ok, this is creepy:

Transplanting human brain cells into mice makes the mice smarter, a new study shows.

In the new study, researchers led by stem cell biologist Steven Goldman and neurobiologist Maiken Nedergaard of the University of Rochester Medical Center in New York implanted human cells called glial progenitor cells into the brains of newborn mice. Glial progenitor cells are a type of stem cell that is poised to make several varieties of glia, including astrocytes. . . .

By the time the mice were 6 months old, the human cells had pushed out the mouse progenitor cells and replaced many of the mouse astrocytes with human astrocytes. Some mice got a transplant of mouse glial progenitors instead of human cells to make sure any effect was due to the action of human cells and not to having extra brain cells.

The researchers put the mice through a battery of tests, probing the animals’ ability to learn mazes, distinguish new objects from old ones, and learn that a certain sound portends a mild electric shock. It took normal mice and mice with mouse cell transplants several tries to pick up on the association between the sound and the shock. Mice with human astrocytes “pretty much picked up the association immediately and got more fearful,” Goldman says.

In these scientists' defense, they started this research to find a cure for MS, not to create super mice. But transplanting human cells into the brains of other mammals strikes me as inherently dubious.