If they exist there can they go back and forth across BBB when needed or required?
 

Whether this is a good thing or bad isn't yet clear. "Currently, the biological significance of harbouring male DNA and male cells in the human brain requires further investigation," lead author Dr. William Chan, of the department of biochemistry at the University of Alberta, said in a statement.

Nevertheless, "this is the first evidence that microchimerism can cross the blood-brain barrier to establish male fetal cells in the human female brain," he said.

http://www.vancouversun.com/health/M...309/story.html