Chimeric Mice With Implanted Human Brain Cells Much Smarter Than Average

 Neuroscience  

Mice have been created whose brains are made up of half human cells. These animals are much smarter than their siblings. The idea is not to create a science fiction scenario, but to advance our understanding of human brain diseases by studying them in whole mouse brains rather than in dishes.

By injecting human cells into baby mice, scientists have created mice whose brains are essentially part human. These hybrid, or chimeric mice grew to be much more intelligent than other mice, especially in tests for memory and cognition.

With this work, researchers hope to glean a lot of data. For example, by studying brain diseases in whole organisms rather than in cells in a dish, researchers should gain a better understanding of how the conditions develop and progress.

Uplift, a concept from science fiction author David Brinis the process of actively upgrading the capacities of a species, perhaps most recently played out in the Planet of the Apes movies, but according to the researchers, this is not their intention.

"This does not provide the animals with additional capabilities that could in any way be ascribed or perceived as specifically human," lead researcher Steven A. Goldman told New Scientist. "Rather, the human cells are simply improving the efficiency of the mouse's own neural networks. It's still a mouse."

"It's still a mouse brain, not a human brain, but all the non-neuronal cells are human." he says.

However, the team decided not to try putting human cells into monkeys. "We briefly considered it but decided not to because of all the potential ethical issues," Goldman says.

In the study, which has been published in The Journal of Neuroscience, researchers from the University of Rochester Medical Center started off by isolating immature glial cells from donated human fetuses. Glial cells are one of the two main cell types that build the nervous system, the other being neurons. Glia perform a variety of roles in the nervous system, such as providing support and protection for neurons, but unlike nerve cells they do not participate directly in electrical signaling, which is a form of communication used to transmit information between cells.

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The researchers then injected these cells into the brains of newborn mice, where they were found to change into star-shaped glial cells called astrocytes. These larger cells, which are the most common type of glial cell, wrap their tendrils around synapses, the active junctions between neurons through which chemical or electrical signals flow. In doing so, astrocytes provide support to neighboring neurons and also strengthen their synaptic connections.  It widely regarded that this support is essential for conscious thought.

"These were whopping effects. We can say they were statistically and significantly smarter than control mice."

Human astrocytes are 10 to 20 times the size of mouse astrocytes and carry 100 times as many tendrils. This means they can coordinate all the neural signals in an area far more adeptly than mouse astrocytes can. "It's like ramping up the power of your computer," says Goldman.

Within just one year, the astrocytes had proliferated so much that they displaced the native cells, resulting in populations of cells in some brain areas that were largely, and sometimes entirely, of human origin. The cells eventually reached 12 million, but they only stopped replicating because they reached the physical limits of the space.

“We could see the human cells taking over the whole space,” Goldman says. “It seemed like the mouse counterparts were fleeing to the margins.”

With the human astrocytes being dramatically larger than mouse astrocytes and possessing so many more many projections, the transplanted cells could coordinate the signaling in neural networks much more efficiently than native cells. This essentially gave their brains an upgrade, but it didn’t make the animals more human, say the researchers.

The researchers then performed various memory and cognitive tests on the mice and compared them with control mice, which revealed that they were significantly smarter than their peers. One test even suggested that their memory was four times better than the controls. “These were whopping effects,” Goldman remarked.

In one test that measures ability to remember a sound associated with a mild electric shock, for example, the chimeric mice froze for four times as long as other mice when they heard the sound, suggesting their memory was about four times better. "These were whopping effects," says Goldman. "We can say they were statistically and significantly smarter than control mice."

To explore further how the human astrocytes affect intelligence, memory and learning, Goldman is already grafting the cells into rats, which are more intelligent than mice. "We've done the first grafts, and are mapping distributions of the cells," he says.

Whether they proceed up the hierarchy of mammals with this work is a very serious ethical matter.


SOURCE  New Scientist

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