From MSNBC:
Add another creation to the strange scientific menagerie where animal species are being mixed together in ever more exotic combinations. Scientists announced Monday that they had created mice with small amounts of human brain cells in an effort to make realistic models of neurological disorders such as Parkinson’s disease. Led by Fred Gage of the Salk Institute in San Diego, the researchers created the mice by injecting about 100,000 human embryonic stem cells per mouse into the brains of 14-day-old rodent embryos. Those mice were each born with about 0.1 percent of human cells in each of their heads, a trace amount that doesn’t remotely come close to “humanizing” the rodents.
More here.