Scientists create first hybrid rat brain with functional human neurons

Scientists at USA successfully transplanted for first time human brain tissue in rat brains, opening a new field of biomedical and pharmaceutical research especially in the field of neuropsychiatry, e.g. with the aim of testing new drugs and other treatments for human diseases in hybrid organisms.

Living human neurons were integrated into rodent brains in the laboratory, creating hybrid brain circuits, which are activated by the animals’ sensory stimuli. At the same time, human brain tissue created two-way connections within the animal’s brain, receiving stimuli as well as sending commands. In other words, the rats perceive their environment by now also having human nerve cells, which – as experiments have shown – can change the behavior of the animals.

This development has a positive side (it turns the brain of rats into a living biological laboratory where, for example, human neurological-mental disorders such as schizophrenia can be studied, as well as new drugs under development), but also a negative side, as raises concerns about where such experiments to create hybrid life forms could end up.

The researchers, led by professor of psychiatry and behavioral sciences Sergio Paska of the Stanford University School of Medicine in California, who made the relevant publication in the journal “Nature”, implanted human brain organoids (lab cell cultures that create mini-brains) in the somatosensory cortex of 100 two- to three-day-old newborn rats.

The animals’ brains smoothly incorporated the graft, supporting it with new blood vessels and protecting it with immune cells. Thus the human neurons proliferated and eventually covered about a third of one hemisphere of the animal’s brain. As Paska said, “it was like adding another transistor to an electronic circuit.” Eventually the human neurons formed connections (synapses) with the brain circuits of the rats and ended up influencing their behavior, while no side effects were seen in the animals.

Inevitably, the bioethical question arises as to whether it is appropriate to conduct such highly invasive experiments on large rodents such as rats, but also where such research might lead down the road. The prospect of creating animals with (more or less) human brains raises reasonable concerns, especially if these animals acquire human consciousness and intelligence.

Supporters of such controversial experiments argue that what should primarily count is how such hybrid organisms will significantly advance research into neurological and mental diseases (epilepsy, bipolar disorder, schizophrenia, etc.), neurodegeneration (dementia-Alzheimer), neurodevelopmental disorders (e.g. autism) etc.

“Psychiatric disorders are a huge burden on society and it’s very, very clear that we need better models to study them. We see patients and their families in a state of despair. There is absolutely no time to waste,” Paska said.

But Hank Greeley, director of Stanford University’s Center for Law and Life Sciences, pointed out: “What if this organelle has some kind of (human) consciousness and suffers as a consequence of its transplant? Or what if the animal after the transplant ( of the organoid) acquire human characteristics?”

Tammy Bryant, a professor of animal law at the University of California, Los Angeles (UCLA), said: “It seems to me that the consciousness of rats as it is, without any human manipulation, is rather remarkable, and that damaging a rat’s brain it is an emblematic act of an attitude toward nature that endangers the prospects of both humans and nonhuman animals for continued life on Earth.”

Read the scientific publication here

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