Human Neurons Transplanted into Rat Brains ! 

No, this is not some realistic sci-fi story you scare your kids with before bedtime. Much like the weirdly maginificent experiments done with “robotic” cockroaches (cockroaches with “built-in” solar panels on their backs), this scientific breakthrough could mean a new era for the study of the human brain. Mainly, research work like this could help us better understand the mystery behind some neurodegenerative diseases such as autism or schizophrenia. However, it also poses some important ethical questions on the subject of conciousness. 

So, what is all the fuss about? 

In a recent study, published in Nature, scientists from Stanford University have revealed the astonishing result of their work. They have successfully managed to implant a human organoid into a rat! An organoid is essentially a small lump of cells of a certain organ – a cluster of cells performing, more or less, the job of the organ, but in a much smaller capacity. The organoid in question is a part of our brain, called the cerebral cortex. This particular structure is very important, since it constitutes the outmost layer of the brain and has a key role in many different functions, such as memory, learning, emotions and much more. What scientists have done, is they have managed to form those organoids from stem cells and then transplant them into a 2-3 year old rat. 

How exactly have Dr. Sergiu Pasca  and his colleagues managed to conduct their experiment? 

Firstly, they extracted skin cells from two types of patients – one from the controlled group (an individual without any genetic conditions predisposing to a neurodegenerative disease) and a patient carrying genetic mutations responsable for the Timothy syndrome. The latter being a rare genetic condition which can cause heart problems and is classified as an autism spectrum disorder. To be able to see clearer results, they implanted the two clusters of neurons in different regions of the same rat brain. After waiting for over 6 months, they managed to establish a clear influence of the genetic condition on the rat’s brain and, more specifically, on the way the implanted human neurons behaved. 

The transplantation of the neurons themselves is not really news-worthy information, since research like this has been conducted for quite some time now, particularly in rodents such as mice. However, these experiments have historically failed to deliver important breakthrough information, since mice live a lot shorter than rats. So, the time needed for the human nerve cells to be able to grow and integrate themselves into the biological structure of their host is a lot longer. In addition, neurons on their own have also been grown in labs. Yet their counterparts, the rat-transplanted cells, have shown to be significantly bigger and more capable of executing more complex tasks. Finally, the last reason why the transplantation is seen as a solutionis simply because lab grown neurons are virtually incapable of surviving. They cannot reach a state in which they can grow blood vessels, which means that they are uncapable of getting nutrients and that is essential to any neuron activity. We all know how drouzy we feel if we skip breakfast. That is because our brain is consuming more than 30 percent of our daily energy consumption to fuel its own machinery. If a brain doesn’t get its food, it gets grumpy, meaning it does not work properly. Even though we are very far away from even thinking about transplantingt a fully developed brain, in the context of this experiment, it becomes more evident why those neurons needed to be placed in a host.

After the six months required for the success of the experiment, scientists observed a severly lowered electrical activity in the two sides of the brain of the rodent. Specifically, the region where the cells from the patient with Timothy’s syndrome were implanted, showed a significantly smaller activity and, more importantly, were unable to pick up as many extension from neighbour neurons nearby. This is essential because it shows the way neurodegenerative diseases impact the structures of the brain. 

What about ethical concerns?

Namely, although Prof. Pasca and his team members are very cognisant of the rats’ well being, he does not believe that such experiments should be conducted with primates. He is certain that the moment the scientific research starts to pose problems in regards to the behaviour of the subject, such study should be terminated. In addition, a lot of ethicists have began to hypothesize about the possibility of a human brain organoid (HBO) to develop a consciousness. Even though such suggestions are very unlikely to be realised in the near future, it is still worth considering the possibility. 

In conclusion, we still don’t have an exact guideline on consciousness. Scientists have expressed the need for some regulations in the field. These could include a range of different options, such as limiting the number of human brain cells that are being created, using HBOs only in scenarios where it is impossible to reach the result without their participation, and others. Having such restrictions and rules would be an extremely important topic going forward, since it could help scientists weigh the costs and benefits to creating a conscious entity in a lab. Until then, just remember, the next time you see a rat, don’t be immediately grossed out – after all, it might have something human in itself, too.

Trayana Hrisrova

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Couverture : ©Image par Gerd Altmann de Pixabay

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