Human brain organelles implanted into the brain of a living rat

Questions of ethics and morality do not keep pace with scientific and technological progress - and they should not be a deterrent. Especially if ethics and morality constrain research in important areas that can help develop new medicines and save millions of lives. So say scientists who refuse to stop research on the integration of the brain of humans and rats .

Four years ago, a group of Austrian scientists published a scientific article describing the technology of growing tiny human brain organelles (human “mini-brain”) from stem cells inside rat brain cells in a test tube. Scientists have proven that fragments of the human brain are integrated with the carrier. In 2016, another group proved that the human brain continues to grow under these conditions , that is, new neurons appear. More recently, scientists have managed to grow in vitro six layers of the human cerebral cortex - an 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 responds to many stimuli exactly as a real full-fledged human brain, up to a reaction to psychedelic drugs. In other words, scientists get a unique and versatile 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: it is possible to study in detail how neural connections are formed in it, how different areas develop at the initial stage. This is a real breakthrough in neuroscience and pharmacology.

Schematic description of the cultivation system of cerebral organelles

Unfortunately, with the latest achievements in this area, science has entered the area where the debate about the ethical nature of such studies begins. Of course, all scientists understand that the organoid of the human brain in a test tube is not capable of thinking, but the trend is obvious - this organoid is becoming more complex. Many believe that research in this area should be stopped, and the problem 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 research funding that involves growing human stem cells in vertebrate embryos at an early stage of development, but this moratorium does not apply to the implantation of human organelles.

Now the discussions can flare up with a new force, because on November 11, 2017, the annual meeting of the American Society of Neuroscience will be held. There will be a presentation of two scientific groups that are going to present new results on the integration of organoids of the human brain into the brain of living rats . For the first time such experiments are carried out 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 2-millimeter organoids survived in the brain of living rats for a long period of time, in one case two months, and even connected to the rat vascular and nervous systems , transferring blood through the vessels, receiving and sending nerve impulses to the animal's brain! Some axons of the human brain penetrated the rat's brain to a depth of 1.5 mm and connected to the corpus callosum, which connects the left and right hemispheres. When the eyes of the rat were illuminated, human neurons reacted to light, which indicates functional integration with the rat brain. These are truly unprecedented results, because scientists have not done anything like this yet.

“Here we are entering completely new territory,” said 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 an embryo of a human brain in a test tube may eventually recognize its existence, then with the implantation of this embryo in a rat's brain, ethical debates go to a new level. Here we are talking about the creation of these chimeras. In biology, chimeras call organisms consisting of genetically heterogeneous cells.

It is believed that within the living brain of a vertebrate animal (rat), human organelles can develop faster than in vitro, so the ethical problem with the possible emergence of consciousness must be solved as quickly as possible. Although now there is no problem, but this does not mean that it will never arise, supporters of an ethical approach say. 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, organelles of the human brain were implanted into the brain of adult rats, whose development has already stopped. Scientists say that it is difficult to even imagine what level of integration can be achieved if organoids are implanted into the brain of the rat embryo.


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