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Scientists have grown a miniature brain in a dish with the spinal cord and attached muscles, an advance that promises to accelerate the study of diseases such as motor neuron disease.
It was found that gray cells the size of a gray lens of human brain cells spontaneously sent connections resembling tendrils connecting to the spinal cord and muscle tissue, which had been taken from a mouse. It was then observed that the muscles contracted visibly under the control of the so-called cerebral organoid.
This research is the latest in a series of increasingly sophisticated approximations of the human brain developed in the laboratory – this time with a system close to the central nervous system.
Madeline Lancaster, who led the work of the molecular biology lab at the Medical Research Council in Cambridge, said, "We like to think of them as moving mini-brains."
Scientists used a new method to grow the miniature brain from human stem cells, which allowed the organoid to reach a more sophisticated stage of development than previous experiments. The last blob shows similarities, in terms of variety of neurons and their organization, with the human fetal brain at 12-16 weeks of pregnancy.
However, the scientists said the structure was still too small and too primitive for thoughts, feelings or consciousness to approach.
"It's always a good idea to have this discussion every time we take a step forward," Lancaster said. "But we generally agree that we are still very far from that."
While a fully developed human brain has between 80 and 90 billion neurons, the organoid has a few million, placing it somewhere between the badroach and the zebrafish in terms of gray matter volume.
Previously, the sophistication of organoids that scientists had been able to achieve was limited by the lack of nutrients in the center of the drop. Once reached a certain size, the neurons of the center would be cut off from their nutrient intake and would begin to die, and the structure would stop growing.
In the latest research, scientists cultivated the organoid and then used a tiny vibrating blade to cut it into half-millimeter thick slices that were placed on a membrane, floating on a nutrient-rich liquid . This meant that the entire slice had access to energy and oxygen and continued to grow and create new connections when it was kept in cultivation for one year.
Next to the organoid, scientists added a 1 mm long spinal cord taken from a mouse embryo and the surrounding dorsal muscle. Brain cells automatically started sending neuronal connections, connected to the spinal cord, and started sending electrical impulses, which caused muscle contraction.
The ambition is to use systems like this one to study the evolution of the brain and the nervous system as well as the causes of the problems related to diseases such as the motor neuron, epilepsy and schizophrenia.
"Obviously, we're not just trying to create something for fun," Lancaster said. "We want to use that to model diseases and understand how these networks are put in place."
Gray Camp, a geneticist at the Institute of Molecular Ophthalmology and Clinic in Basel, Switzerland, who did not participate in the latest work, called the move "a big step forward." "It's extremely exciting to see evidence of the formation of functional nerve pathways from developing human brain tissue and the innervation of other tissues," he said.
The results are published in the journal Nature Neuroscience.
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