Clusters of human neurons have been successfully transplanted into the brains of newborn rats by scientists. This remarkable achievement of biological engineering may give more accurate models for neurological diseases such as autism and act as a tool to heal damaged brains.
Researchers from Stanford presented their findings in a paper that was published on Wednesday. They said that the clumps of human cells, which are referred to as “organoids,” developed into millions of new neurons and connected themselves into their new nervous systems on their own. When the organoids were successfully implanted into the brains of the rats, the rodents were able to create command signals and receive sensory cues from their whiskers. This enabled the rats to better control their movements.
Researchers were able to encourage the cells into developing into neurons by administering additional chemicals to the culture dish. After that, they were able to see as pulses of voltage travelled down the length of the neurons as they were laid out in a dish.
In a subsequent piece of research, he and his coworkers joined three organoids: one constructed of cortex, another built of spinal cord, and a third created of muscle cells. The contraction of the muscle cells was brought about by stimulation of the cortical organoid.
However, organoids are not the same thing as small brains in any way. One reason for this is because their neurons do not develop normally. In addition to this, the neurons in their brains do not have the same level of electrical activity as those in live brains.
In addition, Dr. Pasca and his group were working on organoid transplants; however, they opted to do their experiments on young mice rather than adults. A day or two after a rat was born, the researchers injected an organoid the size of a poppy seed into a section of the brain called the somatosensory cortex. This region of the brain is responsible for processing touch, pain, and other information from throughout the body. The area is extremely sensitive to impulses coming from the rats’ whiskers. Rats have this region.
Because of these connections, human neurons become sensitive to the sensations experienced by rats. The human organoid of the rat responded with a crackling sound when the researchers blew little puffs of air across the rat’s whiskers.
A water fountain was placed inside the cages of the rats that were used in the studies that Dr. Pasca and his colleagues conducted to determine how the organoids altered the behaviour of the rats.
After receiving instruction over a period of 15 days, the rats discovered that when their organoid was activated, they could get a drink from the fountain. It would seem that the human organoids were communicating with the parts of the rats’ brains responsible for seeking rewards.
Giorgia Quadrato, a neurobiologist at the University of Southern California who was not involved in the current work, made the observation that the rats did not become more human as a result of being exposed to human organoids. They did not do any better than other rats did, for instance, on tests of learning.
Instead, he is investigating neurological problems with the help of the organoids that have been transplanted. In one of the experiments, the group led by Dr. Pasca implanted an organoid from a patient suffering with Timothy syndrome on one side of the brain of a rat, and then implanted an organoid that did not have the mutation on the opposite side of the brain.
Both types of organoids developed within the rats. However, the neurons affected by Timothy syndrome grew twice as many dendrites, which are branches that are responsible for receiving incoming messages. In addition to this, the dendrites were much shorter.
Dr. Pasca has high expectations that he would be able to see variations in the behaviour of rats when they are carrying brain organoids from persons with neurological illnesses such as autism and other disorders. Experiments of this kind could provide light on how the functioning of the brain is affected by specific mutations.
Dr. Isaac Chen, a neurosurgeon and organoid researcher at the University of Pennsylvania who was not involved in the research, saw another potential in the new study: the healing of lesions to human brains. Dr. Isaac Chen was not involved in the research.
Dr. Chen envisioned a process in which brain organoids might be grown from the skin of a patient whose cortex had been injured. After being implanted into the patient’s brain, the organoid has the potential to mature and form connections with viable neurons.