Human “Mini-Brains” Transplantation Shows a Way to Cure Blindness

by Nai Ye Yeat
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Researchers from the University of Pennsylvania have tried integrating human neurons into the brains of adult rats with damaged visual cortices, and surprisingly, some of the functions of the organs’ visual system are restored. 

The finding is reported in the journal Cell Stem Cell. It revealed the potential of lab-grown brain tissue to reverse blindness in people.

Related article: Scientists Make Rat-Human Hybrid Brain for Neuropsychiatric Research Purposes 

Neuronal Response to Flashing Lights After Transplantation

The team first cultured human stem cells, which are able to develop into various types of cells, for 80 days so that they formed a three-dimensional tissue culture of brain cortex cells. The cortex cells make up the outer layer of the brain and play a key role in vision.   

They then grafted the clumps of cells into the brains of 46 rats that had sustained injuries to their visual cortices.  After three months, about 82% of the grafts had successfully integrated into the rats’ brains, in terms of growing size and number of lab-grown neurons, while also forming synapses with the rats’ own neurons, and developing healthy vasculatures.

In order to observe neuronal response, an electrode was put into a transplanted organoid while the rat watched a series of images on a screen. One set of images consisted of flashing lights, while another had alternating black and white lines in various orientations, such as horizontal and diagonal.

The organoids’ neuronal response is altered alongside the flashing lights and depending on the orientation of the black and white lines. The result suggests that the neurons were integrating into the rats’ brains and taking over some of their visual system’s function.

Novel Technique to Reverse Brain Injuries

However, about 75% of the neurons in the rats’ own visual cortices responded to the light stimulation, while only 20% of those in the grafted human mini-brains did. The number of  neurons that responded to light is fewer than expected; thus, how to improve the response rate would be the next goal of scientists.

Next, the team planned to repeat this experiment by removing other cortices in a rat’s brain, such as its motor cortex to confirm the role of organoids in restoring brain function. Eventually, scientists hope to implement the technique of transplanting organoids into chronic neurodegenerative diseases patients such as Parkinson’s or those who have suffered physical damage to their brains. 

Although it is still too early to apply the same technology to humans as more detailed mechanisms and animal studies are needed before moving into human trials, it provides a new insight to reverse brain injuries.

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