Human Brain Organoids Integrated Into Rats to Repair Injuries in Their Visual Processing Systems

For many decades, research has shown that it is possible for human and rodent neurons to be transplanted into rat brains. But more recently, researchers have advanced into making lab-grown brains for rodents.

In the new study, titled "Structural and Functional Integration of Human Forebrain Organoids With the Injured Adult Rat Visual System" published in the journal Cell Stem Cell, researchers have shown that human brain organoids may integrate with developing rat brains and respond to visual processing systems.

First Step to Repairing Brain Injuries

The new study shows that miniature lab-grown models of the wrinkled surface of the human brain can be used to patch injuries in the brains of living rats, which means it can repair broken connections in the rodents' sensory processing systems. The researchers believe that such mini-brains, known as brain organoids, could one day be used to repair the brains of human patients.

Neurosurgery assistant professor Dr. Han-Chiao Isaac Chen from the University of Pennsylvania Perelman School of Medicine said that this could be the first step toward developing a new strategy to repair the brain.

He told Live Science that organoids might eventually be utilized to restore brain function following a catastrophic accident, invasive surgery, or stroke, and even to help counteract the effects of neurodegenerative illnesses such as Parkinson's disease. However, he believes that there is more to do that take many more years before the technology could be applied to humans.

Transporting Brain Organoids to Older Rats

The researchers cultured neurons from human stem cells that could grow into different kinds of cells in the lab for around 80 days before transplanting them into the brains of adult rats with visual cortex lesions, Science Daily reported.

The grafted organoids had become vascularized, increased in size and number, sent out neuronal projections, and formed synapses with the host's neurons just after three months.

Researchers used fluorescent-tagged viruses that hop along synapses from one neuron to another to track physical connections between the organoid and the host rat's brain cells. They successfully traced the neuronal connections downstream from the retina by injecting one of the viral traces into the rat's eye because the tracer reached the organoid.

Then they used electrode probes to measure each neuron's activity within the organoid while the animals were subjected to flashing lights and alternating white and black bars. They found a significant number of neurons in the organoid reacted to the light, which shows that the neurons of the brain organoid integrated with the visual system of the rat's brain and assumed a highly specialized visual cortex.

The team was astounded by the extent to which the organoids integrated in such a short time. Chen said they were not expecting to see this level of functional integration so soon since previous studies of cell transplantation took nine to 10 months for the neurons to mature. He noted that this is yet the first step in treating the injured brain and more studies are needed.