'Frankenstein' mice with brain cells from rats raised in the lab

In an experiment reminiscent of "Frankenstein," scientists found that rat brain cells can fill in for lost neurons in mice, even allowing the host rodents to sniff out sweets. 

While splicing rat and mouse brains together may sound odd, this work aims to build a basis for understanding how maMMAl brains develop, said Kristin Baldwin, a neuroscientist at Columbia University and the lead author of a new study describing the experiment. 

Baldwin and her team's study, which was published in the journal Cell alongside a second study from collaborators at the University of Texas (UT) Southwestern, shows that the rat brain cells introduced into a mouse brain pick up cues from their new environment. These cells develop in the same time frame as nearby mouse brain cells, communicating with them and even adjusting their size to match.  

"The host is controlling at least two aspects: the size and also the developmental speed," said Jun Wu, a molecular biologist at the UT Southwestern Medical Center and the lead author of the second study. "That's very interesting and suggests the microenvironment has iNFLuence on the pace, as well as the size, of the donor cell." 

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The study led by Baldwin focuses on how networks form in a hybrid mouse-rat brain, while the study led by Wu focuses more on replacing an entire brain region with transplanted cells. The research could lead to other cross-species brain tissue, helping scientists study brain development and disease and potentially develop new treatments for people. 

Baldwin's team first used bacterial toxins to either kill or silence brain cells in developing mouse embryos. They started when the developing embryo was just a hollow ball of 100 to 200 cells, called a blastocyst, and targeted cells involved in sensing scents. Into these blastocysts, they also injected stem cells from rats, using a type of cell capable of developing into many cell types.