A rat with a human brain

Human brain organoids implanted in the brain of a live rat

Anatoly Alizar, Geektimes

Questions of ethics and morality do not keep up with scientific and technological progress - and they should not be a deterrent. Especially if ethics and morality constrain scientific research in important areas that can help develop new drugs and save millions of human lives. This is the opinion of scientists who refuse to stop research on the integration of human and rat brains.

Four years ago, a group of Austrian scientists published a scientific article describing the technology of growing tiny human brain organoids ("mini-brain" of a human) from stem cells inside rat brain cells in a test tube. Scientists have proved that fragments of the human brain integrate with the carrier. In 2016, another group proved that the human brain continues to grow in these conditions, that is, new neurons appear. More recently, scientists have managed to grow six layers of the human cerebral cortex in a test tube – the area that is responsible for thinking, speech, judgment and other advanced cognitive functions (September 2017).

The fact is that such a unique "mini-brain" of a person in a test tube reacts to many stimuli exactly like a real full-fledged human brain, up to a reaction to psychedelic drugs. In other words, scientists receive a unique and universal material for testing various drugs, studying the development of diseases and other studies that are difficult to conduct on living beings. Not to mention the study of the development of the human brain: you can study in detail how neural connections are formed in it, how the development of various areas differs in the initial stage. This is a real breakthrough in neurobiology and pharmacology.

Brain organoid cultivation scheme

Unfortunately, with the latest achievements in this field, science has entered the field where disputes about the ethics of such research begin. Of course, it is clear to all scientists that the organoid of the human brain in a test tube is not capable of mental activity, but the trend is obvious – this organoid is becoming more complex. Many believe that research in this area should be suspended, and the problem should be discussed with the involvement of the public. However, formally, such studies are still allowed. For example, the US National Institutes of Health (NIH) has announced a moratorium on funding research that involves the cultivation of human stem cells in vertebrate embryos at an early stage of development, but this moratorium does not apply to the implantation of human organoids.

Now the discussions can flare up with renewed vigor, because the annual meeting of the American Society for Neuroscience (Society for Neuroscience) will be held on November 11, 2017. Two scientific groups are scheduled to speak there, which are going to present new results on the integration of human brain organoids into the brains of living rats. For the first time, such experiments are conducted not in a test tube, but on real living beings.

According to preliminary information, the results of the experiments are really amazing. It is said that the 2-millimeter organoids survived in the brains of living rats for a long period of time, in one case – two months, and even connected to the vascular and nervous systems of the rat, transferring blood through the vessels, receiving and sending nerve impulses to the brain of the animal! Some axons of the human brain penetrated into the rat brain to a depth of 1.5 mm and connected with the corpus callosum, which connects the left and right hemispheres. When the light was shining in the rat's eye, human neurons reacted to the light, indicating functional integration with the rat's brain. These are truly unprecedented results, because scientists have not done anything like this yet.

"We're entering a whole new territory here," says Christof Koch, president of the Allen Institute for Brain Science in Seattle. "Science is developing so fast that ethics cannot keep up with it."

If earlier scientists argued that the embryo of the human brain in a test tube could realize its existence in the future, then with the implantation of this embryo into the brain of a rat, ethical disputes reach a new level. Here we are already talking about creating real chimeras. In biology, chimeras are organisms consisting of genetically heterogeneous cells.

There is an opinion that human organoids can develop faster inside the living brain of a vertebrate animal (rat) than in a test tube, so the ethical problem with the possible emergence of consciousness should be solved as quickly as possible. Although there is no problem now, but this does not mean that it will never arise, say supporters of the ethical approach. The point is to discuss the consequences before the actual occurrence of the problem, so that there is a chance to stop the research at some stage.

In recent experiments, human brain organoids were implanted into the brains of adult rats whose development had already stopped. Scientists say it's hard to even imagine what level of integration can be achieved if organoids are implanted into the brain of a rat embryo.

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