Scientists create mice with a ‘hybrid brain’ that is part mouse, part rat (and that may offer interesting possibilities for us too)

During a recent study, scientists managed to get rat brain cells to work in a mouse.

You’re not reading it wrong: researchers have managed to get a ‘hybrid brain’ working for the first time. For the research, scientists successfully found a way to ‘replace’ the olfactory organ of a mouse with the olfactory organ of a rat. The research marks the first time ever that an animal can ‘borrow’ senses in this way. Scientist Kristin Baldwin contributed to the study. She says: “This research has shown us how we can use the flexibility of the brain, so that it can also use other stimuli. Consider, for example, transplanted stem cells, but also human-machine interfaces.” The research has been published in the journal Cell.

Cookies
For the study, the scientists injected stem cells from rats into blastocysts; egg cells from mice that have only just been fertilized. In this way, the stem cells of the different species could ‘move together’ and form the correct connections among themselves. The scientists landed on this solution following previous research that also focused on mice and rats. For this research, neurons from one species were transplanted into already formed brains of the other species. Baldwin adds: “These experiments have shown that we cannot simply add brain cells to brains that already exist. There is a turning point at which the transplanted cells can no longer make the right connections.”

After the successful transplant, it was time to put the ‘hybrid’ brain to work. For this purpose, an experiment was set up in which cookies were hidden in the mice’s cages. During this experiment, two ‘hybrid’ groups were tested. The mice in the first group were adapted so that they would mute their own olfactory cells during pregnancy. The second group of mice consisted of specimens that had been modified so that they had not developed their own olfactory cells – and therefore only had the olfactory cells of rats. The experiment showed that the second group had less difficulty finding the cookies than the mice from the first group. Baldwin says: “This suggests that you cannot simply replace neurons. If you want a good replacement, it is necessary to first remove the dysfunctional neurons.”

Epilepsy
The researchers find their results very significant. For example, the research indicates that the experiment could perhaps be repeated with primate stem cells. Baldwin explains: “This would help us understand human diseases even better. We are currently already transplanting stem cells and neurons into the brains of people with Parkinson’s and epilepsy. Unfortunately, we don’t yet know how well this solution will ultimately work. By using hybrid brains it becomes possible to finally find answers to this question, and even faster than is possible with a clinical trial.”